L. Lab Manual - PSPD (2180903)

8TH SEM. – B.E. ELECTRICAL

PARUL INSTITUTE OF TECHNOLOGY Electrical Engineering Department

Parul Institute of Technology

CERTIFICATE

This is to certify that Mr. / Ms. ______________________________of B.E. 8th Semester Electrical branch, Enrollment No. ____________has satisfactorily completed his/her term work for the subject Power System Planning and Design (2180903) during the academic year 2016-17 and submitted on Date: ____________.

Staff in Charge

Head of Department

INDEX Exp. No.

Aim

Pg. No.

01.

To design Transmission Line.

1.1

02.

To study about transmission line tower.

2.1

03.

To design electrical substation.

3.1

04.

To study about insulation coordination and different types of insulators used in transmission line and substation.

4.1

05.

To study about different aspects of earthing system.

5.1

06.

To study about pipe earthing and plate earthing.

6.1

07.

To study about Indian standards related to transmission line.

7.1

08.

To study about Indian standards related to electrical substation.

8.1

09.

To study about rural electrification.

9.1

10.

To study about power system planning.

10.1

11.

Industrial Visit Report

11.1

Date

Sign.

PARUL INSTITUTE OF TECHNOLOGY Subject:- Power System Planning and Design (2180903) Specialization : Electrical (B.E. 8th )

Department:- ELECTRICAL ENGINEERING Experiment No. : 1

Aim: To design Transmission Line. Electrical Transmission Line Transmission lines are sets of wires, called conductors that carry electric power from generating plants to the substations that deliver power to customers or it is an arrangement of conductors through which power is transmitted. It is a link between generating station to consumer or substation to substation or link between two large systems. Requirements of transmission line are:  It should transmit power over the required distance economically.  It should satisfy the electrical and mechanical requirements.  Power should be transmitted with within the limit of the given regulation, efficiency and losses.  Transmission lines should stand the weather conditions of the locality in which they are laid.  It is used for interconnecting power systems having number of power stations. Economic choices of conductor size and transmission voltage are points which influence the design of transmission line. Types of transmission line are:  According to Distance - Short Transmission Line - Medium Transmission Line - Long Transmission Line  According to Number of Circuits - Single Circuit - Double Circuit - Multi Circuit  According to Voltage Level - Low Voltage - Medium Voltage - High Voltage - Extra High Voltage - Ultra High Voltage Points which need to be taken care of in electrical design of transmission lines are:  Transmission line current capacity and Transmission line voltage  Conductor types and Conductor spacing  Insulation  Transmission line losses  Voltage regulation and Voltage drop  Corona loss In this experiment, students will do detail electrical design of transmission line based on design problems given to them. Following tables may be used for electrical design of transmission line: Prepared by: Ishan Desai

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Department:- ELECTRICAL ENGINEERING Experiment No. : 1 Table-1

Table-2

Length of Line in km

Line to Line Voltage (kV)

Minimum

Maximum

66

40

120

110

50

140

132

50

160

166

80

180

230

100

300

Table-3

Table-4

Prepared by: Ishan Desai

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Table-6


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Design Problem: Design a transmission line to transmit three-phase, 85,000 kW at 0.9 power factor lagging, over a distance of 160 km. The regulation should be within 12.5 per cent of the receiving end voltage, efficiency 95 per cent and corona loss not to exceed 0.6 kW/km. - Choose voltage, size of conductor spacing between conductors. - Calculate the constants of the line and determine the regulation. - Find the efficiency on full load. - Predict corona loss per kilometre of the line and the total corona loss. - Find the charging current on the line on no load. - Choose the number of insulator units. Find the voltage distribution on insulator units. Determine string efficiency. - Find surge impedance loading of transmission line. - Find reactive power of transmission line.


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Calculation:


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Conclusion:


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Aim: To study about transmission line tower. Electrical Transmission Line Transmission lines are sets of wires, called conductors that carry electric power from generating plants to the substations that deliver power to customers or it is an arrangement of conductors through which power is transmitted. It is a link between generating station to consumer or substation to substation or link between two large systems. Requirements of transmission line are:  It should transmit power over the required distance economically.  It should satisfy the electrical and mechanical requirements.  Power should be transmitted with within the limit of the given regulation, efficiency and losses.  Transmission lines should stand the weather conditions of the locality in which they are laid.  It is used for interconnecting power systems having number of power stations. Economic choices of conductor size and transmission voltage are points which influence the design of transmission line. Points which need to be taken care of in mechanical design of transmission lines are:  Loading of transmission line  Span and clearance of transmission line  Effect of wind loading, ice loading, tower height etc. Transmission Line Towers The tower of various shapes had been used in the past without considering detrimental influence on the environment. Factors responsible for changes in shapes of towers are the need for use of higher transmission voltages, limitation of right of way availability, audible noise level, radio and TV interference, electrostatic field aspects etc. The types of towers based on their constructional features, which are in use on the power transmission lines are: - Self-Supporting Towers - Conventional Guyed Towers - Chainette Guyed Towers Self-Supporting Towers Self-Supporting broad-based/narrow-based latticed steel towers are used in India. These are fabricated, using tested quality mild steel structurals or a combination of tested quality mild steel and high tensile steel structurals confirming to IS:2062 and IS:8500 respectively. Self-Supporting towers usually have square/rectangular base and four separate footings. For lower voltage, narrow based towers having combined monoblock footings may be used depending upon overall economy. Self-Supporting Towers as compared to guyed towers have higher steel consumption. Self-Supporting towers are also used for compact line design. Compact tower may comprise fabricated steel body, cage and groundwire peak, fitted with insulated cross arms. Compaction is also achieved by arrangement of phases, using V insulator strings etc. Prepared by: Ishan Desai

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Single Circuit Towers

Double Circuit Towers


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B-Delta/CAT Head Tower

Multi Circuit Tower


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Conventional Guyed Towers These towers comprises portal structures fabricated in ‘Y’ and ‘V’ shapes and have been used in some of the countries for Extra High Voltage transmission lines. The guys may be internal or external. The guyed tower including guy anchor occupy much larger land as compared to self-supporting towers and as such this type of construction finds applications in long unoccupied, waste land.

Chainette Guyed Towers Chainette guyed towers is also known as cross rope suspension tower, and consists of two masts each of which is supported by two guys and a cross rope which is connected to the tops of two masts and supports the insulator strings and conductor bundles in horizontal formation. For angle towers, the practice is to use three separate narrow based masts each for carrying one set of bundled conductors or use self supporting towers. Each narrow based mast is supported with the help of two main guys.


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Tower Shapes Tower shapes in use are as follows: i) Vertical/Barrel type ii) Horizontal/Wasp waist type iii) Delta/Cat head iv) H-Structure type In India, tower shapes at (i) and (ii) are used for single circuit lines whereas tower shapes at (i) has been used for double circuit and multi-circuit lines. In other countries, all the above shapes have been used. Tower shape at (i) structurally more stable and ideally suitable for multi-circuit lines whereas tower shape at (ii) offers better performance from the consideration of audible noise and radio and television interference and electrostatic potential gradient at ground level and at the edge of the right-of-way. Tower Designation Towers are designated as, - Suspension Tower - Tension Tower - Transposition Tower - Special Tower Suspension Towers These towers are used on the lines for straight run or for small angle of deviation up to 2° or 5°. Conductor on suspension tower may be supported by means of I-strings, V-strings or a combination of I & V strings. Tension Towers Tension towers also known as angle towers are used at locations where the angle of deviation exceeds that permissible on suspension towers and/or where the towers are subjected to uplift loads. These towers are used and classified according to the angle of deviation of the line. One of the classes of angle towers depending on the site conditions is also designated as section tower. The section tower is introduced in the line after 15 suspension towers to avoid cascade failure. The design of such towers is checked for adequacy both for angle location requirements as well as for arresting cascade failure. Transposition Towers Transposition towers used to transpose the phase conductors in three sections in such a way that each phase by rotation occupies each of the three phase positions in a circuit. A typical transposition tower is shown in figure below.


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Special Towers These towers are used at locations such as those involving long span river and valley crossing, creek crossing, power line crossing etc. falling on the line routes. Tower Anatomy A tower is constituted of the following components as shown in figures below: - Peak

- Tower Body

- Cross Arm

- Body Extension

- Boom

- Leg Extension

- Cage

- Stub/Anchor bolts and Base plate assembly


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Single Circuit Tower


Double Circuit Tower

Horizontal/Wasp waist type tower Prepared by: Ishan Desai

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Tower Outline Tower outline is fixed from the requirement of minimum ground clearance, terrain type, right of way limitation, electrical clearance etc. Tower outline is defined in terms of the following parameters:  Tower Width - Minimum Ground Clearance - Maximum sag including creep effect of conductor - Length of suspension insulator string assembly - Vertical spacing between power conductors - Location of ground wires - Angle of shield - Minimum mid span clearance - Tension insulator drop  Tower Height - At base or ground level - At waist level - At cross arm/boom level  Cross Arm Spread - Type of insulator string assembly - Swing angle - Phase to phase horizontal spacing Conclusion:


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Aim: To design electrical substation. Electrical Substation The assembly of apparatus used to change some characteristic (e.g. voltage, a.c. to d.c., frequency, p.f. etc.) of electric supply is called a sub-station. Sub-stations are important part of power system. The continuity of supply depends to a considerable extent upon the successful operation of sub-stations. It is, therefore, essential to exercise utmost care while designing and building a sub-station. The following are the important points which must be kept in view while laying out a sub-station: (i) It should be located at a proper site. As far as possible, it should be located at the centre of gravity of load. (ii) It should provide safe and reliable arrangement. For safety, consideration must be given to the maintenance of regulation clearances, facilities for carrying out repairs and maintenance, abnormal occurrences such as possibility of explosion or fire etc. For reliability, consideration must be given for good design and construction, the provision of suitable protective gear etc. (iii) It should be easily operated and maintained. (iv) It should involve minimum capital cost. Preparation of Single Line Diagram, Plan Layout and Side View are important primary steps for designing a substation. After deciding ratings of various equipments in substation and before their locations in the substations are finalized, it is necessary to draw a single line diagram, also called key diagram. This diagram indicates the proposed busbar arrangement and relative positions, undimensioned, of various equipments of substation. After the bus arrangement is decided and Single Line Diagram is prepared, Layout drawing is prepared to show the actual position of each equipment. General Layout shows the area acquired by switchyards of different voltage level. The electrical layout would reveal,  Physical position of each equipment and Gantry structure  Distance between various equipment  Phase to Phase distance  Location of buildings like control room, Storage yard, Fire pump house, D.G. set room, etc. The Layout plan has to be prepared keeping in mind the cost, reliability, ease of maintenance and safety clearances. After preparation of layout plan, sectional elevation is prepared which shows,  Phase to Ground Clearance  Gantry structure height  Actual view of substation equipment connection. In this experiment, student will study design of electrical substation as per CBIP publication no.: 299. In this experiment, student will learn how to prepare layout plan and side view through AutoCAD software. Also, they will do basic calculation like bill of quantity related to it. Prepared by: Ishan Desai

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Single Line Diagram

Layout Plan


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Sectional Elevation


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Single Line Diagram (132 kV):


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Layout Plan (132 kV):


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Sectional Elevation (132 kV):


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Calculation:


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Conclusion:


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Aim: To study about insulation coordination and different types of insulators used in transmission line and substation. Insulation Coordination It is the correlation of the insulation of electrical equipment and lines with the characteristics of protective devices such that the insulation of the whole power system is protected from excessive overvoltages. Insulation strength of various equipments should be higher than that of the lightning arresters and other surge protecting devices. Insulation coordination is thus the matching of the volt-time flashover and breakdown characteristics of equipment and protecting devices, in order to obtain maximum protective margin at a reasonable cost. Insulation coordination involves three basic steps: (i) Selection of standard insulation level. (ii) Making sure that every equipment has breakdown strength equal to or higher than insulation level. (iii) Application of protective devices which will provide as good protection as can be justified economically.

Basic Insulation Level In order to protect the equipment of the power system from overvoltages of excessive magnitude, it is necessary to fix an insulation level for the system to see that insulation in the system does not breakdown or flashover below this level. Best method of providing coordination between insulation levels in the station and on the line leading to the station is to establish a definite common level for all insulation in the station and bring all insulation to or above this level. The common insulation level for all the insulation in the station is known as Basic Impulse Insulation Level (BIL). Basic Impulse Insulation Level can be define as reference level expressed in impulse crest voltage with a standard wave not longer than a 1.2/50 μs wave, according to IS. Prepared by: Ishan Desai

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Rated Insulation as per different voltage level (As per IEC-60071)

Insulation coordination between lines and substations Either the line or the substation is over insulated with normal insulation for the other. (a) Lines normally insulated, substation over insulated: This scheme is used for earthed overhead lines. It ensures that flashover occurs at or near the position of strike. Precautions are taken to prevent damage to line insulation. If adequate shielding against direct stroke is provided at substation, the substation will be subjected only to chopped wave. These chopped waves are limited to safe values. (b) Lines over insulated, substation normally insulated: This scheme, applicable to wooden pole lines possibly with wooden cross-arms and large conductor spacings aims at reducing to a minimum, the risk of flashover and damage to the overhead line. The substation is, then, likely to be subjected to high surges and adequate protection at substation is necessary. This is provided through selection of proper rating and location of surge arresters. Insulation coordination within a substation The coordination of insulation within a substation is very important. The following points must be kept in this regard: (i) The provision of surge protective devices must be based on the weakest component in the substation equipment under impulse conditions. The weakest component is not necessarily the costliest component i.e., transformer. If a current transformer breaks down, the subsequent power current may damage a large part of the stations. (ii) The dispersion of volt-time curves of individual components must be taken into account. Thus if a solid piece of insulation is to be protected, its withstand voltage must be higher than the highest sparkover voltage of the arrester (over the whole range of volt-time characteristics) by a suitable margin. Prepared by: Ishan Desai

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(iii) The flashover voltage of an insulator under bad weather conditions may be about 20% less than that under fair weather conditions. However, the impulse flashover voltage of an airgap varies very little under different weather conditions. Therefore, for the outdoor equipments the insulation coordination should be based on worst probable atmosphere conditions. (iv) The protective device must safeguard the equipment over the whole range of volt-time characteristics and for both positive and negative waves. Insulators Insulator provides necessary insulation between line conductors and supports and thus prevents any leakage current from conductors to earth. The insulators should have the following desirable properties: - High mechanical strength in order to withstand conductor load, wind load etc. - High electrical resistance of insulator material in order to avoid leakage currents to earth. - High relative permittivity of insulator material in order that dielectric strength is high. - The insulator material should be non-porous; free from impurities and cracks otherwise the permittivity will be lowered. - High ratio of puncture strength to flashover. Types of insulators used in transmission and distribution system are: - Pin type - Strain type - Shackle type - String type Pin type insulator

Pin type insulator is secured to the cross-arm on the pole. There is a groove on the upper end of the insulator for housing the conductor. The conductor passes through this groove and is bound by the annealed wire of the same material as the conductor. Pin type insulators are used for transmission and distribution of electric power at voltages up to 33 kV. Beyond operating voltage of 33 kV, the pin type insulators become too bulky and hence uneconomical. Prepared by: Ishan Desai

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Strain type insulator

When there is a dead end of the line or there is corner or sharp curve, the line is subjected to greater tension. In order to relieve the line of excessive tension, strain insulators are used. For low voltage lines (< 11 kV), shackle insulators are used as strain insulators. However, for high voltage transmission lines, strain insulator consists of an assembly of suspension insulators as shown in figure. The discs of strain insulators are used in the vertical plane. When the tension in lines is exceedingly high at long river spans, two or more strings are used in parallel. Shackle type insulator

In early days, the shackle insulators were used as strain insulators. But now a day, they are frequently used for low voltage distribution lines. Such insulators can be used either in a horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt or to the cross arm. Figure shows a shackle insulator fixed to the pole. The conductor in the groove is fixed with a soft binding wire. Prepared by: Ishan Desai

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String type insulator The cost of pin type insulator increases rapidly as the working voltage is increased. Therefore, this type of insulator is not economical beyond 33 kV. For high voltages (>33 kV), it is a usual practice to use string type insulators shown in figure.

They consist of a number of porcelain discs connected in series by metal links in the form of a string. The conductor is suspended at the bottom end of this string or connected in series with the string while the other end of the string is secured to the cross-arm of the tower. Each unit or disc is designed for low voltage, say 11 kV. The number of discs in series would obviously depend upon the working voltage. Types of string type insulator are: - Suspension type insulator - Tension type insulator


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Advantages of string type insulator are: (i) Cheaper than pin type insulators for voltages beyond 33 kV. (ii) Depending upon the working voltage, the desired number of discs can be connected in series. (iii) If anyone disc is damaged, the whole string does not become useless because the damaged disc can be replaced by the sound one. (iv) Provides greater flexibility to the line. (v) Connection at the cross arm is such that insulator string is free to swing in any direction and can take up the position where mechanical stresses are minimum. (vi) As the conductors run below the earthed cross-arm of the tower, therefore, this arrangement provides partial protection from lightning. Conclusion:


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Aim: To study about different aspects of earthing system. Earthing or Grounding Earthing is important part in Electrical Power System. It is also important from the point of view of protection and safety to the equipments and human beings. In substation, it is important for, neutral point of transformers and generators to ground and for connecting non-current carrying metal part such as structures, overhead shielding wire, tanks, frames etc., to earth. In transmission line, it is important for connecting noncurrent carrying metal part such as structures, overhead shielding wire to earth. The process of connecting the metallic frame (i.e. non-current carrying part) of electrical equipment or some electrical part of the system (e.g. neutral point in a star-connected system, one conductor of the secondary of a transformer etc.) to earth (i.e. soil) is called Grounding or Earthing. Objectives of earthing are: • To save human life from danger of shock in case it comes in contact with charged frame due to any fault, leakage current • To maintain the line voltage constant • To protect large buildings from atmospheric lightning • To protect all machines fed from O/H lines exposed to lightning • To protect all substation equipments against lightning • Safety compliance Grounding or earthing may be classified as: (i) Equipment grounding (ii) System grounding. Equipment grounding deals with earthing the non-current-carrying metal parts of the electrical equipment. On the other hand, system grounding means earthing some part of the electrical system e.g. earthing of neutral point of star-connected system in generating stations and sub-stations. Equipment Grounding The process of connecting non-current-carrying metal parts (i.e. metallic enclosure) of the electrical equipment to earth (i.e. soil) in such a way that in case of insulation failure, the enclosure effectively remains at earth potential is called equipment grounding. In the interest of easy understanding, we can divide the discussion into three heads viz. (i) Ungrounded enclosure (ii) enclosure connected to neutral wire (iii) ground wire connected to enclosure. System Grounding The process of connecting some electrical part of the power system (e.g. neutral point of a star connected system, one conductor of the secondary of a transformer etc.) to earth (i.e. soil) is called system grounding. The system grounding has assumed considerable importance in the fast expanding power system. By adopting proper schemes of system grounding, we can achieve many advantages including protection, Prepared by: Ishan Desai

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reliability and safety to the power system network. Neutral grounding is also known as system grounding. The process of connecting neutral point of 3-phase system to earth (i.e. soil) either directly or through some circuit element (e.g. resistance, reactance etc.) is called neutral grounding. The following are the advantages of neutral grounding:  Voltages of the healthy phases do not exceed line to ground voltages  The high voltages due to arcing grounds are eliminated  The overvoltages due to lightning are discharged to earth  Provides greater safety to personnel and equipment  Provides improved service reliability  Reduced operating and maintenance expenditures Types of neutral earthing are:  Solid Earthing  Resistance Earthing  Reactance Earthing  Resonant Earthing  Voltage Transformer Earthing Permissible body current limits The duration, magnitude, and frequency of the current affect the human body as the current passes through it. The most dangerous impact on the body is a heart condition known as ventricular fibrillation, a stoppage of the heart resulting in immediate loss of blood circulation. Humans are very susceptible to the effects of electric currents at 50 and 60 Hz. The let-go current, the ability to control the muscles and release the source of current, is recognized as between 1 and 6 mA. The loss of muscular control may be caused by 9–25 mA, making it impossible to release the source of current. At slightly higher currents, breathing may become very difficult, caused by the muscular contractions of the chest muscles. Although very painful, these levels of current do not cause permanent damage to the body. In a range of 60–100 mA, ventricular fibrillation occurs. The substation grounding system design should limit the electric current flow through the body to a value below the fibrillation current. Equation which determines the allowable body current:

Where, IB rms magnitude of the current through the body, A

ts duration of the current exposure, sec Prepared by: Ishan Desai

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Value of k is k = 0.116 for persons weighing approximately 50 kg or k = 0.157 for a body weight of 70 kg. Based on a 50-kg weight, the tolerable body current is

The equation is based on tests limited to values of time in the range of 0.03–3.0 sec. It is not valid for other values of time. Reasons for substation grounding system The substation grounding system is an essential part of the overall electrical system. The proper grounding of a substation is important for the following two reasons:  It provides a means of dissipating electric current into the earth without exceeding the operating limits of the equipment.  It provides a safe environment to protect personnel in the vicinity of grounded facilities from the dangers of electric shock under fault conditions. The grounding system includes all of the interconnected grounding facilities in the substation area, including the ground grid, overhead ground wires, neutral conductors, underground cables, foundations, deep well, etc. The ground grid consists of horizontal interconnected bare conductors (mat) and ground rods. The design of the ground grid to control voltage levels to safe values should consider the total grounding system to provide a safe system at an economical cost. There are many parameters that have an effect on the voltages in and around the substation area. Since voltages are site-dependent, it is impossible to design one grounding system that is acceptable for all locations. The grid current, fault duration, soil resistivity, surface material, and the size and shape of the grid all have a substantial effect on the voltages in and around the substation area. During typical ground fault conditions, unless proper precautions are taken in design, the maximum potential gradients along the earth surface may be of sufficient magnitude to endanger a person in the area. Moreover, hazardous voltages may develop between grounded structures or equipment frames and the nearby earth. The circumstances that make human electric shock accidents possible are:  Relatively high fault current to ground in relation to the area of the grounding system and its resistance to remote earth.  Soil resistivity and distribution of ground currents such that high potential gradients may occur at points at the earth surface.  Presence of a person at such a point, time, and position that the body is bridging two points of high potential difference.  Absence of sufficient contact resistance or other series resistance to limit current through the bod to a safe value under the above circumstances.  Duration of the fault and body contact and, hence, of the flow of current through a human bod for a sufficient time to cause harm at the given current intensity. Prepared by: Ishan Desai

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Definitions related to Earthing  Touch voltage: The potential difference between the GPR and the surface potential at the point where a person is standing while at the same time having a hand in contact with a grounded structure.

 Step voltage: The difference in surface potential experienced by a person bridging a distance of 1 m with the feet without contacting any other grounded object.


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 Mesh voltage: The maximum touch voltage within a mesh of a ground grid.  Metal-to-metal touch voltage: The difference in potential between metallic objects or structures within the substation site that can be bridged by direct hand-to-hand or hand-to-feet contact.  Transfer red voltage: A special case of the touch voltage where a voltage is transferred into or out of the substation, from or to a remote point external to the substation site. The maximum voltage of any accidental circuit must not exceed the limit that would produce a current flow through the body that could cause fibrillation.

To provide a safe condition for personnel within and around the substation area, the grounding system design limits the potential difference a person can come in contact with to safe levels. IEEE Std. 80, IEEE Guide for Safety in AC Substation Grounding, provides general information about substation grounding and the specific design equations necessary to design a safe substation grounding system. The guide’s design is based on the permissible body current when a person becomes part of an accidental ground circuit. Permissible body current will not cause ventricular fibrillation, i.e., stoppage of the heart. The design methodology limits the voltages that produce the permissible body current to a safe level. Prepared by: Ishan Desai

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Steps for designing substation grounding grid  Input data required for earthing grid design: - Symmetrical Fault Current (kA) - Duration of shock for determining allowable body current (Sec) - Duration of Fault Current for sizing ground conductor (Sec) - Soil Resistivity (Ω∙m) - Depth of ground grid conductor (m) - Grid reference depth (m) - Surface layer resistivity (Ω∙m) - Surface layer thickness (m) - Length of ground rod (m) - Number of rod placed - Decrement factor for determining Ig - Spacing between parallel conductor (m) - Total earth mat area (m2)  Standard values for earth mat conductor of Zinc Coated Steel (as per IEEE 80-2000): - Reference Temperature for Material Constant (°C) = 20 - Ambient Temperature (°C): 50 - Fusing Temperature (°C): 419 - Thermal Coefficient for Resistivity at 0°C (1/°C): 0.00341 - Thermal Coefficient for Resistivity at 20°C ( 1/°C): 0.0032 - Resistivity of the Ground Conductor at 20°C (μΩ·cm): 20.1 - Ko at 0°C (1/°C): 293 - Thermal Capacity TCAP (J/cm2·°C): 3.93  Step-1: Determine size of earthing conductor Equation for determining size (minimum required area) of earthing conductor:

Where, I = Symmetrical grid current in kA Amm2 = Conductor cross section Tm = Maximum allowable temperature in °C Ta = Ambient temperature in °C Tr = Reference temperature for material constants in °C Prepared by: Ishan Desai

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αo = Thermal coefficient of resistivity at 0°C αr = Thermal coefficient of resistivity at reference temperature Tr ρr = Resistivity of ground conductor at reference temperature Ko = (1/ αo) tc = Duration of current in S TCAP = Thermal capacity per unit volume From CBIP Publication No 223, the following values of Corrosion factor has been considered for different types of soil resistivity: - In case of conductors to be laid in soils having resistivity greater than 100 Ohm-metre-- No allowance. - In case of conductors to be laid in soils having resistivity from 25 to 100 Ohm-metre - 15 percent allowance - In case of conductors to be laid in soils having resistivity lower than 25 Ohm-metre or where treatment of soil around electrodes is carried out -- 30 percent allowance. Calculate provided area as per standard size conductor. Condition for safe earthing grid: Provided area > Minimum required area  Step-2: Tolerable Touch and Step potential criteria Reflection Factor,

Where, Cs = Surface layer derating factor

ρ = Resistivity of the earth beneath the surface material ρS = Surface material resistivity hs = Thickness of the surface material ts = Duration of shock for determining allowable body current Considering personnel weight of 50kg, tolerable touch voltage,

Tolerable step voltage,


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 Step-3: Determine grid resistance

Where, Rg = Grid Resistance, resistance of ground grid to remote earth without other metallic conductors connected, Ω

ρ = Soil resistivity, Ω∙m A = Area occupied by ground grid, m2 h = Depth of ground grid L = Total buried length of conductor, m  Step-4: Maximum grid current Maximum current that will flow through grid,

Where, Df = Decrement factor for the entire duration of fault Fault Duration (S) 0.008 0.1 0.25 0.5 or more

Decrement Factor (Df) 1.65 1.25 1.10 1.0

Sf = Split factor = Fault current division factor

Ig = Symmetrical grid current  Step-5: Ground Potential Rise

IG = Maximum grid current Rg = Grid resistance Prepared by: Ishan Desai

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 Step-6: Mesh Voltage Effective number of parallel conductors,

Where,

nb = 1 for square grid else, Lc = Total length of the conductor in horizontal grid Lp = Peripheral length of grid

A = Area of grid

nc = 1 for square and rectangular grid nd = 1 for rectangular, square and L-shaped grid

hₒ = 1 (Grid reference depth) Kii = 1 for grids with rods along perimeter or for grids with rods in grid corner or for grid with no ground rods or grids with only few ground rods Kii is

Geometric factor,

Correction factor,


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Mesh Voltage (calculated touch voltage),

Where, Lx = Maximum length in X direction Ly = Maximum length in Y direction D = Spacing between parallel conductors h = Depth of ground grid d = Diameter of grid conductor LM = Effective buried length = LC + LR – for grids with no rods or rods spreads all over LR = Total length of all ground rods  Step-7: Step Voltage (calculated) Geometrical factor (for usual buried depth of 0.25 < h < 2.5 m),

Step Voltage,

Where, Ls = Effective burial conductor length = 0.75LC + 0.85LR  Step-8: Comparison of Calculated and Tolerable Touch & Step Voltages Tolerable

Calculated

Touch Voltage (V)

>

Touch Voltage (V)

Step Voltage (V)

>

Step Voltage (V)

Earthing design is SAFE.


P a g e | 5.10



Calculation:


P a g e | 5.11




P a g e | 5.12




P a g e | 5.13



Conclusion:


P a g e | 5.14



Aim: To study about pipe earthing and plate earthing. Earthing or Grounding Earthing is important part in Electrical Power System. It is also important from the point of view of protection and safety to the equipments and human beings. In substation important for, neutral point of transformers and generators to ground and for connecting non-current carrying metal part such as structures, overhead shielding wire, tanks, frames etc., to earth. The process of connecting the metallic frame (i.e. noncurrent carrying part) of electrical equipment or some electrical part of the system (e.g. neutral point in a star-connected system, one conductor of the secondary of a transformer etc.) to earth (i.e. soil) is called Grounding or Earthing. Basic earthing types are pipe earthing and plate earthing. Pipe Earthing Pipe earthing is the most commonly adopted method and is the best system of earthing, compared to other systems. In this method of earthing, a galvanized iron and perforated pipe of approved length and diameter is used as earth electrode.


P a g e | 6.1



The size of pipe depends upon the current to be carried and the type of soil. Usually pipe used for this purpose is of diameter 40 mm and 2.5 m in length for ordinary soil or of greater length in case of dry and rocky soil. The depth at which pipe must be buried depends upon the moisture of the ground. According to Indian Standards, the pipe should be at a depth of 4.75 m if the moisture content in the soil is moderate. If there is sufficient moisture in the soil, the depth of the pipe can be reduced up to 3.75 meters (minimum). The pipe is provided with a tapered casting at the lower end in order to facilitate the driving. Pipe earthing is shown in figure. The bottom layer of the pipe should be surrounded by coke and charcoal for a distance of 15 cm around the pipe. Generally alternate layers of coke and salt are used to increase the effective area of the earth and to decrease the earth resistance respectively. In summer season, soil becomes dry, in such case, salt water is poured through the funnel connected to the main G.I. pipe through 19 mm diameter pipe of minimum length 1.25 m. This keeps the soil wet. The pipe has 12 mm diameter hole drilled in it so that water poured is made to spread in charcoal layers to decrease the earth resistance. The earth wire (either GI wire or GI strip of sufficient cross-section to carry fault current safely) is carried in a GI pipe of diameter 12 mm at a depth of about 60 cm from the ground. Care must be taken that earth wire is well protected from mechanical injury when it is carried over from one machine to another. At the top, a cement concrete work is made for the protection of the earth pipe from mechanical damage and to facilitate water pouring arrangement. A funnel with wire mesh is provided in the concrete work. The pipe to which funnel is connected is further connected to main earthing pipe. The only disadvantage of pipe earthing is that the embedded pipe length has to be increased sufficiently in case soil resistively is high enough. This increases the excavation work and hence increased cost. In ordinary soil condition, the range of earth resistance should be 2 to 5 ohms. In the places where rocky soil earth bed exists, horizontal strip earthing is used. This is suitable as soil excavation required is difficult in such places. For such soils, earth resistance is between 5 to 8 ohms. Plate Earthing This is another common system of earthing. In plate earthing, the earth connection is provided with the help of copper plate or galvanized iron (G.I.) plate. According to standards, the dimensions of G.I. plate should not be less than 60 cm * 60 cm * 6.3 mm and that of the copper plate should not be less than 60 cm * 60cm * 3.18 mm. The G.I. plates are commonly used now-a-days. The plate is embedded 3 meters (10 feet) into the ground. The plate is kept with its face vertical. Plate earthing method is shown in figure. The plate is surrounded by the alternate layers of coke and salt up to a distance of 15 cm surrounding the plate. The funnel is provided for wetting the soil, whenever required. The earth wire is drawn through G.I. pipe and is securely bolted to the earth plate with the help of nuts, bolts and washers. These nuts and bolts must be copper if copper plate is used and of galvanized iron if G.I. plate is used.


P a g e | 6.2



The earth lead used must be G.I. wire or G.I. strip of sufficient cross-sectional area to carry the fault current safely. The earth wire is drawn through G.I. pipe of 19 mm diameter at about 60 cm below the ground. If the resistively of soil is high, then it is necessary to embed the plate vertically at a greater depth into the ground.

The only disadvantage of this method is that method the discontinuity of the earth wire from the earthing plate below the earth cannot be observed physically. This may cause misleading and my result into heavy losses under fault conditions. A small masonry brick wall enclosure with a cast iron cover on the top or an RCC pipe round the earth plate is provided to facilitate its identification and for carrying out periodical inspection and tests. Conclusion:


P a g e | 6.3



Aim: To study about Indian standards related to transmission line. Indian Standards for Transmission Line IS 802 – Use of structural steel in overhead transmission line towers IS 802 is divided in four parts. Part-1/Section-1 of this standard stipulates materials and loads to be adopted in the design of self supporting steel lattice towers for overhead transmission lines. Permissible stresses and other design parameters are covered in Part-1/Section-2. Part-2 of this standard covers the provisions relating to the fabrication, galvanizing, inspection and packing requirements of self-supporting steel lattice towers for overhead transmission lines. Part-3 of this standard covers the provisions relating to the testing requirements of prototype self supporting steel lattice towers for overhead transmission lines. This code does not cover guyed towers and special towers for river crossing or other long spans. IS 2165 – Insulation Coordination This standard covers the principles of insulation coordination and applies to equipments for three phase ac systems, having a highest voltage for equipment above 1 kV. Standard voltage for insulation coordination is divided in to three parts as below: Range-A

1 kV < Um < 52 kV

Range-B

52 kV < Um < 300 kV

Range-C

Um > 300 kV

Insulation level according to IS 2165:


P a g e | 7.1




P a g e | 7.2



IS 398 – Aluminium conductors for overhead transmission purpose – specification IS 398 is divided in four parts. Part-1 of this standard covers the requirements and tests for aluminium stranded conductors used for overhead transmission purposes. Part-2 of this standard covers the requirements and tests for aluminium conductors, galvanized steel-reinforced used for overhead power transmission purposes. Part-3 of this standard covers the requirements and tests for aluminium conductors, aluminized-steel reinforced used for overhead power transmission purposes. Part-4 of this standard covers the requirements and tests for aluminium alloy stranded conductors of the aluminium magnesium-silicon type for overhead power transmission purposes. Part-4 of this standard covers the requirements and tests for aluminium conductors, galvanized steel-reinforced used for extra high voltage overhead power lines (400 kV and above). Types of ACSR conductor as per IS 802:

Types of earth wire used in transmission system:


P a g e | 7.3



Conclusion:


P a g e | 7.4



Aim: To study about Indian standards related to electrical substation. Indian Standard for Substation IS 2165 – Insulation Coordination This standard covers the principles of insulation coordination and applies to equipments for three phase ac systems, having a highest voltage for equipment above 1 kV. Standard voltage for insulation coordination is divided in to three parts as Range-A (1 kV < Um < 52 kV), Range-B (52 kV < Um < 300 kV), Range-C (Um > 300 kV). Insulation level according to IS 2165:


P a g e | 8.1



IS 398 – Aluminium conductors for overhead transmission purpose – specification IS 398 is divided in four parts. Part-1 of this standard covers the requirements and tests for aluminium stranded conductors used for overhead transmission purposes. Part-2 of this standard covers the requirements and tests for aluminium conductors, galvanized steel-reinforced used for overhead power transmission purposes. Part-3 of this standard covers the requirements and tests for aluminium conductors, aluminized-steel reinforced used for overhead power transmission purposes. Part-4 of this standard covers the requirements and tests for aluminium alloy stranded conductors of the aluminium magnesium-silicon type for overhead power transmission purposes. Part-4 of this standard covers the requirements and tests for aluminium conductors, galvanized steel-reinforced used for extra high voltage overhead power lines (400 kV and above). Types of ACSR conductor as per IS 802: Prepared by: Ishan Desai

P a g e | 8.2



Types of earth wire used in transmission system:


P a g e | 8.3



IS 731 – Porcelain insulators for overhead power line with a normal voltage greater than 1000 V This standard applies to the porcelain insulators for ac overhead power lines suitable for normal system voltage greater than 1000 V and a frequency not greater than 100 Hz. IS 1180 – Three Phase Distribution Transformers up to and including 100 kVA, 11 kV outdoor type Part-I of this standard specifies the requirements and tests for oil-immersed, naturally air-cooled, threephase, double-wound non-sealed type outdoor distribution transformers of ratings up to and including 100 kVA, for use on systems with nominal system voltages up to and including 11 kV. Part-2 of this standard specifies the requirements and tests for oil immersed, naturally air-cooled, three-phase, doublewound outdoor distribution transformers of sealed tank construction up to and including 100 kVA, for use on nominal system voltages up to and including 11 kV. IS 2026 – Power Transformer This standard covers points related to design of power transformers used in transmission as well as distribution system. IS 2099 – Bushings for Alternating Voltages above 1000 V This standard covers rated values, performance requirements and tests for bushings for three phase alternating current systems, having rated voltage above 1000 volts and frequencies between 15 to 60 Hz. It also applies to bushings which are supplied separately, intended for use in electrical apparatus and installation for three phase alternating current systems, having rated voltage above 1000 volts and frequencies between 15 to 60 Hz. IS 2705 – Current Transformer This standard covers points related to specifications of current transformers used in transmission as well as distribution system. IS 3151 – Earthing Transformer This standard specifies the requirements and tests for oil immersed and dry type earthing transformers. IS 3156 – Voltage Transformer This standard covers points related to specifications of different types of voltage transformers used in transmission as well as distribution system.


P a g e | 8.4



IS 5547 – Application guide for Capacitive Voltage Transformer This guide covers the application of capacitive voltage transformers for use with electrical measurement and protecting devices. IS 5553 – Shunt Reactors This standard covers points related to specifications of shunt reactors used in transmission system. IS 3043 – Code of practice for Earthing This code of practice gives guidance on the methods that may be adopted to earth an electrical system for the purpose of limiting the potential (with respect to general mass of earth) of current carrying conductors forming part of the system, that is, system earthing and non-current carrying metal work association with equipment, apparatus and appliance connected to the system (that is, equipment earthing). IS 9921 – Alternating Current Disconnectors for voltage above 1000 V This standard covers points related to specifications of alternating current disconnectors (Isolators) and earthing switches for voltages above 1000 Volts used in transmission as well as distribution system. IS 10136 – Code of practice for selection of disc insulator fittings for highest system voltages of 72.5 kV and above This code of practice provides guidance for selection of disc insulator fitting for overhead power lines with highest system voltages of 72.5 kV and above. IS 13118 – Specification for high voltage ac circuit breakers This standard covers points related to specifications of high voltage ac circuit breakers used in transmission as well as distribution system. Ratings for Power Transformers, Current Transformer, Voltage Transformer, Isolator, Circuit Breakers for different voltage level as per Indian Standards are as below:


P a g e | 8.5



Ratings of Power Transformer (For 765 kV and 400 kV)


P a g e | 8.6



Ratings of Current Transformer

Current Transformer Accuracy Classes


P a g e | 8.7



Ratings of Voltage Transformer


P a g e | 8.8



Ratings of Isolators


P a g e | 8.9



Ratings of Circuit Breakers


P a g e | 8.10



Conclusion:


P a g e | 8.11



Aim: To study about rural electrification. Rural Electrification Rural electrification is the process of bringing electrical power to rural and remote areas. Electricity is used not only for lighting and household purposes, but it also allows for mechanization of many farming operations, such as threshing, milking, and hoisting grain for storage. In areas facing labor shortages, this allows for greater productivity at reduced cost. Social and economic benefits of rural electrification are:  Allow activities to occur after daylight hours, including education. In impoverished and undeveloped areas, small amounts of electricity can free large amounts of human time and labor. In the poorest areas, people carry water and fuel by hand, their food storage may be limited, and their activity is limited to daylight hours.  Reduce isolation through telecoms.  Improve safety with the implementation of street lighting, lit road signs.  Improve healthcare by electrifying remote rural clinics.  Reduces the need for candles and kerosene lamps with their inherent fire safety risks and improves indoor air quality.  Improve productivity, through the use of electricity for irrigation, crop processing, and other activities. In this experiment student will learn rural electrification considering load of Parul Institute of Technology. They will calculate total load of the institute and based on it, they will calculate capacity of transformer which supplies power to the institute. Load distribution will also be covered in this experiment. Calculation:


P a g e | 9.1




P a g e | 9.2




P a g e | 9.3



Conclusion:


P a g e | 9.4



Aim: To study about power system planning. Electricity plays a key-role in the modem society because of its versatility with respect to input energy form. The annual per capita consumption in India was about 335 kWh (1996). A rise in this consumption to hundred times the value is likely to substantially raise the standard of living of the people in the country with respect to education, health, transport, communication, media, productivity etc. Electricity can be produced with coal, nuclear fuels, oil, gas, hydro power, diesel, geothermal energy, biomass, wind -energy, solar energy or fuel cells. Electrical supply also offers the opportunity of total environmental enhancement compared to other energy use patterns. For increasing the supply of electricity, new power projects will have to be installed. Expansion, modernization, and maintenance of the electricity utility industry will require increased capital costs, financial and environmental restraints, increasing fuel costs and regulatory delays. All these factors lead to the necessity for a more comprehensive understanding and analysis of electric power systems. Recent developments in system analysis and synthesis as well as in related. Digital, analog, and hybrid computer techniques provide important tools which will aid the planning engineer in meeting these challenges. It is very challenging process as power system has to be planned considering points like economy and reliability. Methods of Power System Planning When planning for the future, the main characteristics of the present system should be studied and data collected, e.g. electrical energy demand and peak load demand, rate of growth of energy consumption in the last 20 years, energy production, type of generation plant and its size, transmission, interconnection and subtransmission systems. Accurate calculations can be done on various alternatives in system planning quickly with the help of digital programs. The steps are: - Forecast of annual energy and power demand - Load modelling - Generation and choice of mixing the various types of generating stations such as thermal, hydro, nuclear plants, etc. in suitable proportion for economic operation - Optimization of power plant characteristics - New substation, their capacity and their location - New power plants and their subdivision in the main areas - Network expansion - Optimization of equipment characteristics Planning should take into account: uncertainty about the future, many alternative action choices and many goals and constraints. Planning can be seen as consisting of three cyclical components: 1) Learning about the environment, the relevant issues and possible future scenarios in order to identify: (i) Strategically goals, (ii) The decision criteria and constraints and (iii).Technological needs and opportunities 2) Action that involves choosing preferred plans or strategies on the basis of supporting analysis Prepared by: Ishan Desai

P a g e | 10.1



3) Thinking about available strategic options, the associated costs and risks and their implications. This involves: - Investment of resources - Possible unforeseen factors - Reliability of outcome The steps taken in medium and long term planning are shown in figure below.


P a g e | 10.2



Load Forecasting Load forecasting is very important procedure in power system planning. Demand forecasts are used to determine the capacity of generation, transmission and distribution. System and energy forecast to determine the type of generation facilities required. There are five broad categories of loads-domestic, commercial, industrial, agricultural and residential. Commercial and agricultural loads are characterized by seasonal variations. Industrial loads are considered base loads that contain little weather dependent variation. Forecasting of electric load basically consists of, - Long-term forecasting which is connected with load growth and supply/demand side resource management adjustments. - Mid / short-term forecasting which is connected with seasonal or weather variations in a year, weekly or daily load forecast etc. The planning for the addition of new generation, transmission and distribution facilities is based on longterm load forecasts and must begin 2-25 years in advance of the actual in service. In India, electricity load forecasts at the national, the Annual Power Survey committee under Central Electricity Authority prepares regional and state levels. Load forecasting is required in all three facets of power system operation, viz., long-range system planning, operational planning and operational control, generally in the following time frames, - Long-term forecasting (periods ranging more than 2 years) - Medium-term forecasting (periods from one month to two years) for operational planning - Short term forecasting (periods from one day to a few weeks) for operational planning - Very short term forecasting (a few minutes to 24 hours) for operational control. Long Term Forecasts Long-range forecasts involve Identification of both energy and demand forecasts for a utility over a period exceeding two years. Whereas the energy requirements decide the type of generating units (i.e., peaking or intermediate or base-load units), expansion and the demand of peak power requirements decide the utility’s investment in generation and the resultant transmission capacity additions. Long-term forecasts are used for, - Exploration of natural fuel and water resource - Development of trained human power - Reinforcement planning of generation transmission and distribution equipment - Establishing future fuel requirement Forecasts based on either past trends on or very broad based factors do not provide sufficient confidence level for long-range planning. Forecasting in today's environment has increased in complexity due to rapid and random changes in the factors that influence load consumption. The following factors are relevant for their impact on utility's growth, - The country's economic policy, developmental plans, technological development in production of products and services Prepared by: Ishan Desai

P a g e | 10.3



- Growth pattern in domestic, commercial, industrial and agricultural loads - Population growth and electrification plan (urban and rural) - Political, developmental and environmental decisions. Statistical methods with adaptive techniques are employed to forecast long-range load requirements, as the method chosen shall have to use past data, growth patterns and human judgment. Mid Term Forecasts These forecasts are aimed to determine yearly or monthly peak, minimum load and energy requirements for one to few years for the purpose of: - Deciding structure for billing of different consumer categories - Power exchange contract with neighboring utilities and interchange schedules - Annual planning and budgeting for fuel requirements and other operational requirements - Maintenance scheduling of generation and transmission equipment - Scheduling of captive plants - Scheduling of multi-purpose hydro plans for irrigation, flood control, cooling water requirements etc., apart from generation Short Term Forecasts Short-term load forecasting is required for operational planning for, - Unit commitment and economic dispatch calculations - Maintenance scheduling updates - On-line load flows - Spinning reserve calculations - Short-term interchange schedules with neighbouring system - System security analysis - Scheduling of pumped storage units - Load management scheduling - Optimization of fuel stocking Utilities use past normalized data, weather data, and information on known random phenomena for short-term forecasting of, - Peak load conditions for system in a day - System load at various intervals of time (half hour /hour) in a day - Hourly or half-hourly energy requirements - Individual bus load prediction - A few minutes to several hours ahead forecast and is useful in utility's systems operations to deal with economic load dispatching & security assessment


P a g e | 10.4



Generation Planning When the load requirements have been determined, the next problem is to determine the type and size of generating stations that will be required to supply power and energy. The selection of a site for the location of the generating stations depends on many factors including the cost of transmitting the energy to the consumers, of transporting fuel to the stations, the availability of sound foundations, the cost of land, the availability of cooling water and avoidance of atmospheric pollution. Steam station should be located at the coal pits or as near the coal pits as possible to avoid transport cost and time of transport. For most economical distribution and the lowest cost of power and energy, the power station should be located at the center of gravity of load, if a suitable site is available. There is trend for increase in the size of generator units to be used in large power system. This reduces the cost per kW and improves the efficiency of the stations. Hydro plants have transmission liability as they would be located far from the load centers, at sites where water is availability in enough quantity at enough head. Nuclear power stations are designed to operate on base load with as high a load factor as possible, preferably 90% and above. Steam stations with high efficiency units can be used on the next slab of load duration curve of the power system at high load factor. Most of the hydro plants in large power systems are designed for low power factor operation, e.g. 25% to 30%. Some hydro plants with ample storage are designed for 60% load factor. The choice of the type of plant used on a portion of the load curve of a particular power system would be decided by the local economic conditions. The problem is to find the optimum mix of generating plants from among those available, to meet the load with adequate reliability. This will depend in the quality, type and size of various types of plants such as conventional steam stations, nuclear stations, rearrangement of the existing hydro stations for modulation and gas turbine plants and pumped storage plants for peak duty and energy transfer. The available national resources of energy should be studied to decide which type of generating stations can be considered for expansion of the system. Knowing the availability of generation, characteristics of turbines, hydraulic inflows, uncertainty of load forecasts etc. calculation are done using computers and the operation of the production system is examined for a long period of 20 years. This is done by quantitative evaluation in each year (week by week) of the reliability indexes (risk of power energy shortages) and of capital and energy cost. The function to be optimized is the sum of the present worthed costs relevant to capital, operation and risk of shortage. Careful choice should be made of the composition and characteristics of the generation plant and it should be possible to continue studies quickly every time a new event occurs such as energy crisis which may affect the conclusions reached. The choice of sitting new thermal and nuclear plants is studied as optimization problem using linear programming. The points considered are costs of production, transport and interaction with the environment down to the minimum.


P a g e | 10.5



Transmission System Planning The major transmission requirements of a power system and their associated costs are much influenced by the location of future generation capacity. The object of transmission planning is to select the most desirable transmission network for each of the generation expansion patterns under consideration. Both economics and reliability are considered in the problem. The application of a digital computer in automated transmission planning allows the system planner to consider and investigate many alternatives quickly. The ultimate selection of generation expansion plan is then done by considering transmission as an integral part of the total costs. A basic problem in transmission line planning is the determination of transmission adequacy under the forced outage of various system components. A more consistent approach to transmission planning would be to consider the reliability. The investment in transmission improvement is made at the most desired locations in the system, in terms of an acceptable risk level at the various loading points. The adequacy of transmission network is examined using conventional ac load flow methods. The network is first tested for adequacy under normal operating conditions without considering any forced outages. New transmission facilities are added to alleviate any unacceptable bus voltages and line or transformer overloads by separate low voltage logic and overload logic. The economic generation schedule should be included in the examination of transmission system adequacy under both the peak load and off load conditions. Reliability evaluation is done by a selected approach and new facilities are added to alleviate any unacceptable bus risk levels. The transmission system is planned to satisfy the bus voltages and line loadings under normal operating conditions may be adequate only if high risk levels are acceptable. The costs of transmission improvements increases as higher reliability levels are expected. The use of quantitative reliability criterion facilitates optimum utilization of the investments in transmission improvements. A fixed contingency criterion without using probability values can result in higher investment than required at some locations, if a lower reliability can be tolerated at these points. The planner should decide the acceptable risk level at each load point in the system. The utilization of individual load point reliability indices permits the planning engineer to include the cost of maintaining these levels in alternative planning schemes. Distribution System Planning Since the system variables are quite complex, it is necessary to make a thorough analysis while planning distribution systems. The problems to be studied in the total system environment for the purpose are (i) selection of most economical combination of subtransmission and distribution voltage levels, (ii) determination of economical sizes of substations and (iii) comparison of different methods of regulating voltage. Some of the important factors that should be considered are the actual geographical distribution of loads, configuration of the existing system, step by step expansion of the distribution system with time and load growth and comparative reliability of the various arrangements.


P a g e | 10.6



The design of one portion of the distribution system is closely related to the design of other parts of the system e.g. if the change in the primary distribution voltage level is to be studied, it is necessary to study the effects of subtransmission levels, substation arrangements, their capacities and locations, short circuit duties and the reliability of the resulting system. If the methods of regulating voltages are being considered, methods of supplying reactive power, effect of reactive power flow on loads as well as voltages, layout of primary distribution feeders and the design of distribution transformer - secondary combination should be studied. Conclusion:


P a g e | 10.7



Aim: Industrial Visit Report Students will prepare industrial visit report for the industry they have visited. They will prepare detail report and submit it to the lab faculty.


P a g e | 11.1

L. Lab Manual - PSPD (2180903)

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