Gandhi Institute for Education and Technology Baniatangi, Bhubaneswar Bhubaneswar
LABORATORY MANUAL Electrical Power Transmission & Distribution Lab DEPT. OF _______________________
NAME: .......................................................................... REGD. NO: .......................... ....................................... .......................... .......................... ............. BRANCH: ........................ ..................................... ........................... .......................... ................ .... SEMESTER: ...................... ...........................YEAR.... .....YEAR................. .......................... ............. ACADEMIC YEARS:................. YEARS:.............................. .......................... ........................ ...........
GANDHI INSTITUTE FOR EDUCATION & TECHNOLOGY Baniatangi,Bhubaneswar-752060 1
Introduction:
For economical generation of power large generating stations are used. Capacities of individual generating sets have gone up recently. Generating sets in the range of 10 MW, 210 MW and 500 MW are being manufactured in many countries. Generating station are now not necessarily located at load centers. In fact other factors like availability of fuel and water play more dominating role in the selection of sites for thermal stations. Hydro stations are obviously located only at the sites where water is available at sufficient head. A vast network of transmission system has been created so that power generated at one station may be fed to grid system and may be distributed over large areas and number of states. The transmission and distribution system comprises a network of three-phase circuits with transforming and or switching substations at the various junctions. The parts of a transmission and distribution network maybe grouped as given below. Alternating Current is used for electric power distribution because it can easily be transformed to a higher or lower voltage. Electrical energy losses are dependent on current flow. By using transformers, the voltage can be stepped up so that the same amount of power may be distributed over long distances at lower currents and hence lower losses due to the resistance of the conductors. The voltage can also be stepped down again so it is safe for domestic supply. Three-phase electrical generation and transmission is common and is an efficient use of conductors as the current-rating of each conductor can be fully utilized in transporting power from generation through transmission and distribution to final use. Three-phase el ectricity is supplied only in industrial premises and many industrial electric motors are designed for it. Three voltage waveforms are generated that are 120 degrees out of phase with each other. At the load end of the circuit the return legs of the three phase circuits can be coupled together at a 'neutral point', where the three currents sum to zero if supplied to a balanced load. This means that all the current can be carried using only three cables, rather than the six that would otherwise be needed. Three phase power is a type of polyphase system. In most situations only a single phase is needed to supply street lights or residential consumers. When distributing three-phase electric power, a fourth or neutral cable is run in the street distribution to provide one complete circuit to each house. Different houses in the street are placed on different phases of the supply so that the load is balanced, or spread evenly, across the three phases when consumers are connected. Thus the supply cable to each house can consist of a live and neutral conductor with possibly an earthed armoured sheath. In North America, the most common technique is to use a transformer to convert one distribution phase to a center-tapped 'split-phase' 240V winding; the connection to the consumer is typically two 120-volt power lines out of phase with each other, and a grounded 'neutral' wire, which also acts as the physical support wire.
2
Contents
Sl.No
Name of The Experiment
Page Start
Page End
1
To measure the Earth Resistance.
4
7
2
To determine the string efficiency
8
10
3
study of various lightning arrester
11
16
4
Series and shunt Capacitance Computation in Transmission line
17
21
5
Study of Ferranti Effect
22
24
6
Determination of ABCD parameter of a transmission line
25
27
7
To measure the dielectric (Breakdown) strength of transformer oil.
28
29
8
To Study corona discharge
30
32
Sign
3
Experiment no-1
Date:
AIM OF THE EXPERIMENT: To measure the Earth Resistance. APPARATUS REQUIRED:
1.
Earth Tester-1 no.
2. Spikes --3 No. THEORY:Construction of Megger
Circuit Construction features:•
Deflecting and Control coil : Connected parallel to the generator, mounted at right angle to each other
and maintain polarities in such a way to produced torque in o pposite direction. •
Permanent Magnets : Produce magnetic field to deflect pointer with North-South pole magnet.
•
Pointer : One end of the pointer connected with coil another end deflects on scale from infinity to zero.
•
Scale : A scale is provided in front-top of the megger from range ‘zero’ to ‘infinity’, enable us to read
the value. •
D.C generator or Battery connection : Testing voltage is produced by hand operated DC generator for
manual operated Megger. Battery / electronic voltage charger is provided for automatic type Megger for same purpose. •
Pressure coil resistance and Current coil resistance : Protect instrument from any damage because of
low external electrical resistance under test. Working Principle of Megger:•
Voltage for testing produced by hand operated megger by rotation of crank in case of hand operated
type, a battery is used for electronic tester. •
500 Volt DC is sufficient for performing test on equipment range up to 440 Volts.
•
1000 V to 5000 V is used for testing for high voltage electrical systems.
•
Deflecting coil or current coil connected in series and allows flowing the electric current taken by the
circuit being tested. •
The control coil also known as pressure coil is connected across the circuit.
•
Current limiting resistor (CCR and PCR) connected in series with control and deflecting coil to protect
damage in case of very low resistance in external circuit. •
In hand operated megger electromagnetic induction effect is used to produce the test voltage i.e.
armature arranges to move in permanent magnetic field or vice versa. 4
•
Where as in electronic type megger battery are used to produce the testing voltage.
•
As the voltage increases in external circuit the deflection of pointer increases and deflection of pointer
decreases with a increases of current. •
Hence, resultant torque is directly proportional to voltage and inversely proportional to current.
•
When electrical circuit being tested is open, torque due to voltage coil will be maximum and pointer
shows ‘infinity’ means no shorting throughout the circuit and has maximum resistance within the circuit under test. •
If there is short circuit pointer shows ‘zero’, which means ‘NO’ resistance w ithin circuit being tested.
•
Work philosophy based on ohm-meter or ratio-meter. The deflection torque is produced with Megger
tester due to the magnetic field produced by voltage and curre nt, similarly like ‘Ohm's Law’. Torque of the Megger varies in ration with V/I , (Ohm's Law: - V = IR or R = V/I). Electrical resistance to be measured is connected across the generator and in series with deflecting coil. Produced torque shall be in opposite direction if current supplied to the coil. •
High resistance = No current: - No current shall flow through deflecting coil, if resistance is very high i.e.
infinity position of pointer. •
Small resistance = High current :- If circuit measures small resistance allows a high electric current to
pass through deflecting coil, i.e. produced torque make the pointer to set at ‘ZERO’. •
Intermediate resistance = varied current: - If measured resistance is intermediate, produced torque
align or set the pointer between the range of ‘ZERO to INIFINITY’. Connection Diagram of Megger for Testing:-
5
PROCEDURE:-
1) Put the two spikes acting as current & potential electrode in to the ground at a distance of 15 cm & 7.5 cm from earth electrode under test. 1) Connect the two spikes to C2 & P2 terminals respectively. 2) Short the P1 & C1 terminals of motor & connect it to the earth electrode under test. 3) Place the megger on horizontal firm stud. 4) Turn the handle of megger to speed slightly higher then rated speed & note down the deflection of the needle. 5) Take down the 3 to 4 readings by keeping the distance same and placing the electrodes at the other positions. 6) Take the average of these readings which is equal to earth resistance.
6
Tabulation:-
Sl.No
D1 Distance reference
in
cm
from
D2 Distance reference
in
cm
from
Earth Ohms
Resistance in
Mean Value
CONCLUSION:-
The value of earth resistance by direct method is ------------- Ω
Name of the student Registration Number Signature of Faculty Date
7
Experiment no-2
Date:
Aim of the experiment: To determine the string efficiency Apparatus Required:
1. Matlab Software Theory:
From equivalent circuit, applying Kirchoff's current law to node A, I2 = I1 + i1 V2ωC = V1ωC + V1ωkC V2 = V1 + V1k V2 = (1 + k)V1
...... eq.(i)
applying Kirchoff's current law to node B, I3 = I2 + i2 V3ωC = V2ωC + (V2 + V1)ωkC V3 = V2 + (V1 + V2)k V3 = kV1 + (1 + k) V2 V3 = kV1 + (1 + k)2 V1
...... from eq.(i)
V3 = V1 [k + (1 + k)2] V3 = V1 [k + 1 + 2k + k2] V3 = V1 (1 + 3k + k2)
...... eq.(ii)
Now, voltage between the conductor and the earther tower is, V = V1 + V2 + V3 V = V1 + (1 + k)V1 + V1 (1 + 3k + k2) V = V1 (3 + 4k + k2)
...... eq.(iii)
from the above equations (i), (ii) & (iii), it is clear that the voltage across the top disc is minimum while voltage across the disc nearest to the conductor is maximum, i.e. V3 = V1 (1 + 3k + k2). As we move towards the cross arm, voltage across the disc goes on decreasing. Due to this non-uniform voltage distribution across the string, the unit nearest to the conductor is under maximum electrical stress and is likely to be punctured. String Efficiency
8
As explained above, voltage is not uniformly distributed over a suspension insulator string. The disc nearest to the conductor has maximum voltage across it and, hence, it will be under maximum electrical stress. Due to this, the disc nearest to the conductor is likely to be punctured and subsequently, other discs may puncture successively. Therefore, this unequal voltage distribution is undesirable and usually expressed in terms of string efficiency. The ratio of voltage across the whole string to the product of number of discs and the voltage across the disc nearest to the conductor is called as string efficiency String efficiency = Voltage across t he string / (number of discs X voltage across the disc nearest to the conductor). Circuit Diagram:
Program Body:
clear all; r =33*1e3; v=r/sqrt(3) k =0.11; ins=3; v1=v/(3+4*k+k^2); v2=v1*(1+k); v3=v1*(1+3*k+k^2); 9
d=v*100/ins/v3; fprintf('( i ) Voltage across top unit =%.2fkV \n\n',v1/1000) ; fprintf('Voltage across middle unit = %.2fkV \n\n',v2/1000) ; fprintf('Voltage across bottom unit = %.2fkV \n\n',v3/1000) ; fprintf('( i i ) String efficiency = %.2f \n\n',d); Output:
v= ( i ) Voltage across top unit =
kV
Voltage across middle unit =
kV
Voltage across bottom unit =
kV
( i i ) String efficiency =
Conclusion: The String Efficiency is studied and is found out to be ______________ %
Name of the student Registration Number Signature of Faculty Date
10
Experiment no-3
Date:
Aim of the Experiment:- study of various lightning arrester Apparatus Required:-
1. Thyrite type lightning 2. Pellet type lightning Theory
Lightning Arrester -Over voltages may c ause burning of insulation of sub station equipment if not well protected. Lightning is one of the most serious causes of over voltages. Lightning arrestors/ surge arrestors are connected to protect the equipments from lightning and switching surges. Various types of lightning arrestor construction are Rod gap, Expulsion type, Valve type, Horn gap, Pellet type, Thyrite type etc. An ideal LA should posses the following characteristics. 1. It must not take any current at normal system voltage 2. Any transient wave with voltage pe ak exceeding the spark over voltage must cause it to break down. 3. After break down it must be capable of carrying the resulting discharge c urrent without any damage to itself and without voltage across it excee ding the breakdown voltage. 4. The power frequency current following the breakdown must be interrupted as soon as the tr ansient voltage has fallen below the breakdown value. Location of Lightning Arrestor •Lightning Arrestor should be located close to the e quipment that it is expected to protect. • In large sub stations arrestors should be installed at take off points of the lines and of ter minal apparatus. •Many factors like system voltages, basic impulse insulation level, arrestor rating, station lay out, number and arrangement of lines, position of isolators, distance between e quipments etc. have to be taken into account in fixing the location of the arrestors. •The length of the arrestor lead should be as low as possible and should not exceed 10M. Arrestors are installed both on HV and LV side of t he transformers. • Junction of an OH line and the cable should be protected by LA. •Separate earth should be provided for each LAs. LA ground leads should not be connected to the station earth bus. Lightning Arrestor Ratings The Rating of lightning arrestor are given below, 11
Normal or rated voltage: It is de signated by the maximum permissible value of power frequency voltage which it can support across its line and e arth terminal while still carrying effectively and without the automatic extinction of the follow up current. The voltage rating of the arrestors should be greate r than the maximum sound phase to ground voltage. Normal Discharge current: It is the surge current which flows through the LA after the spark over, expressed in crest value (peak value) for a spec ified wave shape. Example 10, 5, 2.5, 1.5, 1 kA rating. Power frequency spark over voltage: It is the RMS value of the power frequency voltage applied between the line and earth terminals of the arrestor and earth which causes spark over of the series gap. As per IS 3070, the recommended spark over voltage is 1.5 t imes the rated voltage. There are also other ratings like maximum impulse spark over voltage, residual or discharge voltage, maximum discharge current etc Selection of Lightning Arrestor For the protection of substation above 66KV an arrestor of 10kA rating is used. Voltage rating of LA = Line to line voltage × 1.1 × coefficient of earthing. Power frequency spark over voltage = 1.5 ×Voltage rating of LA (Assuming coefficient of earthing equals 0.8 for effectively earthed system) For 220KV side: Voltage rating = 1.1 × 220 × 0.8 = 193.6KV Power frequency spark over voltage = 1 .5 ×193.6 = 290.4KV Rated discharge current = 10 kA For 110KV side: Voltage rating = 1.1 × 110×0.8 = 96.8KV Power frequency spark over voltage = 1.5 × 96.8 = 145.2KV Rated discharge current
= 10kA
For 66kV Side Voltage rating = 1.1 × 66×0.8 = 58.08kV Power frequency spark over voltage = 1.5 × 58.08 = 87.12kV Rated discharge current = 10kA For 11 KV side: Voltage rating = 1.1× 11×0.8 = 9.68KV 12
Power frequency spark over voltage = 1.5×9.68 = 14.52KV Nominal discharge current = 5kA
Rod Gap Type Lightning Arrester
Pellet type lightning
Thyrite type lightning
Horngap type lightning arrester 13
Rod gap arrester
It is a very simple type of diverter and consists of two 1.5 cm rods, which are bent at right angles with a gap in between as shown in Fig. One rod is connected to the line circuit and the other rod is connected t o earth. The distance between gap and insulator (i.e. distance P) must not be less than one third of the gap length so that the arc may not reach the insulator and damage it. Generally, the gap length is so adjusted that breakdown should occur at 80% of spark-voltage in order to avoid cascading of very steep wave fronts across the insulators. The string of insulators for an overhead line o n the bushing of transformer has frequently a rod gap across it. Fig 8 shows the rod gap across the bushing of a transformer. Under normal operating conditions, the gap remains non-conducting. On the occurrence of a high voltage surge on the line, the gap sparks over and the surge current is conducted to earth. In this way excess charge on the line due to the surge is harmlessly conducted to earth Limitations •After the surge is over, the arc in the gap is maintained by the normal supply voltage, leading to short-circuit on the system. •The rods may melt or get damaged due to excessive heat produced by the arc.T •he climatic conditions (e.g. rain, humidity, temperature etc.) affect the performance of rod gap arrester. •The polarity of the f the surge also affects the performance of this arrester. •Due to the above limitations, the rod gap arrester is only used as a back-up protection in case of main arresters. Horn gap arrester
Fig shows the horn gap arrester. It consists of a horn shaped metal rods A and B separated by a small air gap. The horns are so constructed that distance between them gradually increases towards the top as shown. The horns are mounted on porcelain insulators. One end of horn is connected to the line through a resistance and choke coil L while the other end is effectively grounded. The resistance R helps in limiting the follow curre nt to a small value. The choke coil is so designed that it offers small reactance at normal power fre quency but a very high reactance at transient frequency. Thus the choke does not allow the transients to enter the apparatus to be protected. The gap between the horns is so adjusted that normal supply voltage is not enough to cause an arc across the gap. Under normal conditions, the gap is non-conducting i.e. normal supply voltage is insufficient to initiate the arc between the gap. On the occurrence of an over voltage, spark-over takes place across the small gap G. The heated air around the arc and the magnetic effect of the arc cause the arc to travel up the gap. The arc moves progressively into positions 1, 2 and 3.
14
At some position of the arc (position 3), the distance may be too gre at for the voltage to maintain the ar c; consequently, the arc is extinguished. The excess charge on the line is thus conducted t hrough the arrester to the ground.
Expulsion type arrester
This type of arrester is also called ‘protector tube’ and is commonly used on system operat ing at voltages up to 33kV. Fig shows the essential parts of an expulsion type lightning arrester. It essentially consists of a rod gap AA’ in serie s with a second gap enclosed within the fiber tube. The gap in the fiber tube is formed by two ele ctrodes. The upper electrode is connected to rod gap and the lower electrode to the earth. One expulsion arrester is placed under each line conductor. On the occurrence of an over voltage on the line, the series gap AA’ spanned and an arc is stuck between the electrodes in the tube. The heat of the arc vaporizes some of the fiber of tube walls resulting in the production of neutral gas. In an extremely short time, the gas builds up high pressure and is expelled through the lower electrode, which is hollow. As the gas leaves the tube violently it carries away ionized air around the arc. This deionizing effect is generally so strong that the arc goes out at a current zero and will not be reestablished. Advantages •They are not very expensive. •They are improved form of rod gap arresters as they block the flow o f power frequency follow currents •They can be easily installed. Limitations •An expulsion type arrester can perform only limited number of operations as during each operation some of the fiber material is used up. •This type of arrester cannot be mo unted on enclosed equipment due to discharge of gases during operation. •Due to the poor volt/am characteristic of the arrester, it is not suitable for protection of expensive equipment Valve type arrester
Valve type arresters incorporate non linear resistors and are extensively used on systems, operating at high voltages. Fig shows the various parts of a valve type arrester. It consists of two assemblies (i) series spark gaps and (ii) non-linear resistor discs in series. The non-linear elements are connected in series with the spark g aps. Both the assemblies are accommodated in tight porcelain container. The spark gap is a multiple assembly consisting of a number of identical spark gaps in series. Each gap consists of two electrodes with fixed gap spacing. The voltage distribution across the gap is line raised by m eans of additional resistance elements called grading resistors across the gap. The spacing of the series gaps is such 15
that it will withstand the normal circuit voltage. However an over voltage will cause the gap t o break down causing the surge current to ground via the non-linear resistors.
The non-linear resistor discs are made of inorganic compound such as thyrite or metrosil. These discs are connected in series. The non-linear resistors have the property of offering a high resistance to current flow when normal system voltage is applied, but a low resistance to the flow of high surge curre nts. In other words, the resistance of these non-linear elements decreases with the increase in current through them and viceversa. Under normal conditions, the normal system voltage is insufficient to cause the break down of air gap assembly. On the occurrence of an o ver voltage, the breakdown of the se ries spark gap takes place and the surge current is conducted to earth via the non-linear resistors. Since the magnitude of surge current is very large, the non-linear elements will offer a very low resistance to the passage of surge. The result is that the surge will rapidly go to earth instead of being sent back over the line. When the surge is over, the non-linear resistors assume high resistance to stop the flow of current. Thyrite Lightning Arrester
Such type of arrester is most commonly used for the protection against dangerous high voltage. I t consists the thyrite which is an inorganic compound of ceramic mater ial. The resistance of such material decreases rapidly from high value to low value and for c urrent from a low value to high value. It consists a disc whose both the side is sprayed so as to give the electric contact between the consecutive disc. The disc is assembled inside the glazed porcelain container. It is used in conjunction with the container. When the lightning takes place, the voltage is raised, and breakdowns of the gaps oc cur, the resistance falls to a very low value, and the wave is discharged to earth. After the surge has passed the thyrite again come back to its original position. Pellet type lightning arrester
Pellet Type Oxide Film Arrester Competing head to head with the first ex pulsion arrester was the new Pellet Type Oxide Film Arrester. This new design was a product of arrester t itan, GE. From the patents and other literature, it is clear that GE had numerous engineers designing arresters in t his era. This new pellet type arrester had the excellent voltage current characteristics of the Aluminum Cell arrester, but without a liquid dielectric. Conclusion:-The various types of lightning arresters are studied and their properties were noted.
Name of the student Registration Number Signature of Faculty Date 16
Experiment-4
Date:
Aim of the Experiment: - Series and shunt Capacitance Computation in Transmission line Apparatus Required
1. Matlab Software Theory:Inductance of Transmission Line
In the medium and long transmission lines inductance (reactance) is more effective than resistance. The current flow in the transmission line interacts w ith the other parameter, i.e the Inductance. We know that when current flow within a conductor, magnetic flux is set up. With the variation of c urrent in the conductor, the number of lines of flux also changes, and an emf is induced in it (Faraday’s Law). This induced emf is represented by the parameter known as inductance. The flux linking with the conductor consist of two parts, namely, the internal flux and the ext ernal flux. The internal flux is induced due to the curre nt flow in the conductor. The external flux produced around the conductor is due to its own c urrent and the current of the other conductors place around it. The total inductance of the conductor is determined by the calculation of the internal and exter nal flux.
Capacitance of Transmission Line
Transmission line conductors constitute a capacitor between them. The conductors of the transmission line act as a parallel plate of the capacitor and the air is just like a dielectric medium between them. The capacitance of a line gives rise to the leading current between the conductors. It depends on the length of the conductor.
17
Program Body:-
1. %3 phase double circuit %3 phase single circuit D12=input('enter the distance between D12in cm: '); D23=input('enter the distance between D23in cm: '); D31=input('enter the distance between D31in cm: '); d=input('enter the value of d: '); r=d/2; Ds=0.7788*r; x=D12*D23*D31; Deq=nthroot(x,3); Y=log(Deq/Ds); inductance=0.2*Y capacitance=0.0556/(log(Deq/r)) fprintf('\n The inductance per phase per km is %f mH/ph/km \n',inductance); fprintf('\n The capacitance per phase per km is %f mf/ph/km \n',capacitance); enter the distance between D12in cm: 350 enter the distance between D23in cm: 350 enter the distance between D31in cm: 350 enter the value of d: 20 inductance = capacitance = The inductance per phase per km is
mH/ph/km
The capacitance per phase per km is
mf/ph/km
18
2. %3 phase double circuit %3 phase single circuit D12=input('enter the distance between D12in cm: '); D23=input('enter the distance between D23in cm: '); D31=input('enter the distance between D31in cm: '); d=input('enter the value of d: '); r=d/2; Ds=0.7788*r; x=D12*D23*D31; Deq=nthroot(x,3); Y=log(Deq/Ds); inductance=0.2*Y capacitance=0.0556/(log(Deq/r)) fprintf('\n The inductance per phase per km is %f mH/ph/km \n',inductance); fprintf('\n The capacitance per phase per km is %f mf/ph/km \n',capacitance); enter the distance between D12in cm: 236 enter the distance between D23in cm: 245 enter the distance between D31in cm: 700 enter the value of d: 20 inductance =
capacitance = The inductance per phase per km is
mH/ph/km
The capacitance per phase per km is
mf/ph/km
3. %3 phase double circuit S = input('Enter row vector [S11, S22, S33] = '); H = input('Enter row vector [H12, H23 ] = '); 19
d = input('Bundle spacing in inch = '); dia = input('Conductor diameter in inch = '); r=dia/2; Ds = input('Geometric Mean Radius in inch = '); S11 = S(1); S22 = S(2); S33 = S(3); H12 = H(1); H23 = H(2); a1 = -S11/2 + j*H12; b1 = -S22/2 + j*0; c1 = -S33/2 - j*H23; a2 = S11/2 + j*H12; b2 = S22/2 + j*0; c2 = S33/2 - j*H23; Da1b1 = abs(a1 - b1); Da1b2 = abs(a1 - b2); Da1c1 = abs(a1 - c1); Da1c2 = abs(a1 - c2); Db1c1 = abs(b1 - c1); Db1c2 = abs(b1 - c2); Da2b1 = abs(a2 - b1); Da2b2 = abs(a2 - b2); Da2c1 = abs(a2 - c1); Da2c2 = abs(a2 - c2); Db2c1 = abs(b2 - c1); Db2c2 = abs(b2 - c2); Da1a2 = abs(a1 - a2); Db1b2 = abs(b1 - b2); Dc1c2 = abs(c1 - c2); DAB=(Da1b1*Da1b2* Da2b1*Da2b2)^0.25; DBC=(Db1c1*Db1c2*Db2c1*Db2c2)^.25; DCA=(Da1c1*Da1c2*Da2c1*Da2c2)^.25; GMD=(DAB*DBC*DCA)^(1/3) Ds = 2.54*Ds/100; r = 2.54*r/100; d = 2.54*d/100; Dsb = (d*Ds)^(1/2); rb = (d*r)^(1/2); DSA=sqrt(Dsb*Da1a2); rA = sqrt(rb*Da1a2); DSB=sqrt(Dsb*Db1b2); rB = sqrt(rb*Db1b2); 20
DSC=sqrt(Dsb*Dc1c2); rC = sqrt(rb*Dc1c2); GMRL=(DSA*DSB*DSC)^(1/3) GMRC = (rA*rB*rC)^(1/3) L=0.2*log(GMD/GMRL) % mH/km C = 0.0556/log(GMD/GMRC) % micro F/km Enter row vector [S11, S22, S33] = [ Enter row vector [H12, H23] = [
] ]
Bundle spacing in inch = Conductor diameter in inch = Geometric Mean Radius in inch = GMD = GMRL = GMRC = L= C= Conclusion:- The series and and shunt Capacitance Computation in Transmission line is studied.
Name of the student Registration Number Signature of Faculty Date 21
Experiment -5
Date
Aim of the Experiment:- Study of Ferranti Effect Apparatus Required:-
1. Matlab Software 2. Voltmeter 3. Ammeter 4. Single Phase Load 5. Variac 6. Transformers Theory:- Transmission line model consists of four sections and each section represents 50 kmlong 400 KV
transmission line. Parameters of 50 km long 400 KV Transmission line are taken as:Series Inductance = 80 mH Series Resistance = 2 ohm (In addition to resistance of inductance coil) Shunt Capacitance = 0.47 microF Leakage resistance or Shunt Conductance = 470 kohm For actual 400 KV transmission lines range of parameter is :l = Series Inductance = 1.0 to 2.0 mH/Km r = Series Resistance = 0.5 to 1.5 ohm /Km c = Shunt Capacitance = 0.008 to 0.010 microF/Km g = Leakage resistance (Shunt Conductance) = 3 x 10 –8 to 5 x 10 –8 mho/Km
A long transmission line draws a substantial quantity of charging current. If such a line is open circuited for a very lightly loaded at the receiving end, the voltage at the receiving end may become higher then the voltage at the sending end. This is known as ‘FERRANTI EFFECT’ and is due to the voltage drop across the line inductance (due to the charging current) being in phase the sending end voltage. The both capacitance and inductance are 22
necessary to produce this phenomenon. The capacitance and charging curre nt is negligible in short line but significant in medium length lines and appreciable in long lines. Therefore, phenomenon occures in medium and long lines. In the phasor diagram, Fer ranti effect is illustrated. The line may be re presented by a nominal pi circuit so that half of the total line capacitance is assumed to be concentrated at the receiving end. OM represents the receiving end voltage. OC represents the current drawn by the capacitance assumed to be consetrated at the receiving end. MN is the resistance drop and NP is inductive react ance drop. OP is the sending end voltage under no load condition and is less than receiving end voltage. Procedure:
(i) Apply the voltage (200 V max.) to the sending end and connect power factor meter. Also connect 1 ammeter and voltmeter to each end (receiving and sending). (ii) Connect the load comprising of R, L and C at the receiving end and note down the value of rece iving end voltage. (iii) Now remove the load from the rece iving end and note down the voltage on rec eiving end. This voltage at the receiving end is quite large as compared to sending end voltage. Observation Table:-
Sl.No.
Sending Voltage
Sending Current
Receiving Voltage
ReceivingCurrent
Load
Comment
Program Body:-
clc clear all vr=220e3/sqrt(3); alpha=0.163e-3; beta=1.0683e-3; L=5000; K=1; for i=0:10:L, vs=(vr/2)*exp(alpha*i)*exp(j*beta*i)+(vr/2)*exp(-alpha*i)*exp(-j*beta*i); X(K)=real(vs); Y(K)=imag(vs); 23
K=K+1; p(K)=vs; q(K)=i; end figure(1); plot(p,q); figure(2); plot(X,Y); Sample Graph:-
a-Ferranti Effect if the length of transmission line is varied
Conclusion:- The details of Ferranti Effect is studied and its simulation conducted gave the study report for
variation of voltage in respect to distance and type of load.
Name of the student Registration Number Signature of Faculty Date
24
Experiment-6
Date:-
Aim of the Experiment:-Determination of ABCD parameter of a transmission line Apparatus required:-
1. MAtlab Software 2. Voltmeter 3. Ammeter 4. Single Phase Load 5. Variac 6. Transformers Theory:-
ABCD Parameter are widely used in analysis of power transmission engineering where they will be turned as “Generalized circuit parameter” ABCD parameters are also called as Transmission parameter. It is conventional to designate the input port as sending end and the output port as rece iving end while representing ABCD parameter Vs = A Vr + B Ir Is = C Vr + Dir [Vs/Is] = [A B/C D] [Vr / Ir] Assuming the receiving end open Circuit i.e. A =Vs / Vr Where Ir = 0 B = Vs / Ir Where Vr = 0 C = Is / Vr Where Ir = 0 D = Is / Ir Where Vr = 0
Fig:- Model of Transmission Line Tabulation
Sl.No. 1 2 3
VS
VR
IS
IR
A
B
C
D
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Program Body:clc clear all f=50;L=300;z=40+i*125;y=i*1e-3; PR=50e6/3;VR=220e3/(sqrt(3));Pfload=0.8;IRR=PR/(VR*Pfload);IR=IRR*(0.8-i*0.6); z=z/L;y=y/L;k=1; for i=10:10:600, %short line aproximation VS_shortline(k)=VR+((z*i*IR)); IS_shortline(k)=IR; spf_shortline(k)=cos(angle(VS_shortline(k))-angle(IS_shortline(k))); spower_shortline(k)=3*abs(VS_shortline(k))*abs(IS_shortline(k))*spf_shortline(k); %nominal pi method A=1+(y*i)*(z*i)/2; B=z*i; C=y*i*(1+(y*i)*(z*i)/4); D=A; VS_nominalpi(k)=A*VR+B*IR; IS_nominalpi(k)=C*VR+D*IR; spf_nominalpi(k)=cos(angle(VS_nominalpi(k))-angle(IS_nominalpi(k))); spower_nominalpi(k)=3*abs(VS_nominalpi(k))*abs(IS_nominalpi(k))*spf_nominalpi(k); point(k)=i; k=k+1; end%plots of short line in red and nominal pi in red figure(1); plot(point,abs(VS_shortline),'r',point,abs(VS_nominalpi),'g') figure(2); plot(point,abs(IS_shortline),'r',point,abs(IS_nominalpi),'g') figure(3); plot(point,abs(spf_shortline),'r',point,abs(spf_nominalpi),'g') figure(4);
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plot(point,abs(spower_shortline),'r',point,abs(spower_nominalpi),'g')
Sample Graph:-
Graph-1- Sending End power variation
Graph-2-Pf variation using shortline
using shortline and nominal pi method
and nominal Pi method
Graph-3-VS variation using shortline and nominal Pi
Graph-4-IS variation using shortline and
method
nominal Pi method
Conclusion:- ABCD parameter of a transmission line is studied and its was observed.
Name of the student Registration Number Signature of Faculty Date
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Experiment-7
Date:-
Aim of the Experiment:-To measure the dielectric (Breakdown) strength of transformer oil. Equipment Required:
1. Portable oil testing set-220/250 V 2. HV transformer-50 kV/250 V 3. Gap setting gauges -0.15711 width Theory:-
The two unit portable testing set is designed for the periodical testing of samples of insulating oils drawn from plant on site and for checking the dielectric strength of new samples of oil. The equipment is designed to operate from 200/250V, 50Hz, Single phase AC supply. Test gap voltage up to 5 0kV, it consists of two units, one is containing the testing transformer and other is control and metering equipments. These equipments are kept in a metal box to provide full protection to the apparatus during transport and storage. The gap is adjusted between electrodes in accordance with I Standard Specification (BSS) no. 148. The gap between the spheres is adjusted to 4 mm with the help of a gauge and the spheres are immersed in oil to a depth as mentioned earlier. The voltage is increased gradually and continuously till a flash over of t he gap is seen or the MCB operates. Note down this voltage. This voltage is known as rapidly-applied voltage. The breakdown of the gap has taken place mainly due to field effect. The thermal effect is minimal as the time of application is short. Next bring the voltage back to zero and start with 40% of the rapidly applied voltage and wait for one minute. See if the gap has broken. If not increase the voltage every time by 2.1/2% of the rapidly applied voltage and wait for one minute till the flash over is seen or the MCB Mm. Note down this voltage. Start again with zero voltage and increase the voltage to a value just obtained in the previous step and wait for a minute. It is expected that the breakdown will take place
Procedure:
1. Place the High Voltage transformer unit about 7 away from the control unit. 2. The control unit is connected to supply voltage taking care that the ear th connections are effective. 3. The multiple point control switch is set at its lowest tapping.
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4. The push button on control unit is pressed firmly for at least 5 seconds. Note that no Breakdown to occurs, in which case button should be released at once without delay. Break down is indicated by a continuous discharge across the gap, bubbling of oil in the c ell and meter indicating a sudden voltage drop. Tabulation:
Sl.No.
Break Down Voltage
Mean
1 2 3 4 5 6 7 8 9 10
Conclusion:-The measurement of the dielectric (Breakdown) strength of transformer oil is studied and it’s
mean was found out to be _________ KV
Name of the student Registration Number Signature of Faculty Date 29
Experiment-8
Date:-
Aim of the Experiment:-To Study corona discharge. Apparatus Required:
1. Matlab Software Theory:-
A corona discharge is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. Spontaneous corona discharges occur naturally in high-voltage systems unless care is taken to limit the electric field strength. A co rona will occur when the strength (potential gradient) of the electric field around a conductor is high enough to form a conductive region, but not high enough to cause electrical breakdown or arcing to nearby objects. It is often seen as a bluish (or other c olor) glow in the air adjacent to pointed metal conductors carrying high voltages, and emits light by the same property as a gas discharge lamp. Factors Affecting Corona
Atmosphere: As it is already explained that the corona forms due to ionization of the air. There are always some free electrons in the air (which means air is pre-ionized to a little extent). However, in stormy weather, the number of free electrons is more than that in normal conditions. In such case, corona occurs at much lesser voltage.
Conductor size: Corona discharge also depends on the shape and size of the conductors. Irregularities on the conductor surface concentrate the electric field at locations, resulting in corona at these spots. Thus, a stranded conductor gives rise to mor e corona than a solid conductor with a smooth surface. Also, conductors having large diameter have lower electr ic field gradient at the surface. Hence, conductors having large diameter produce lower corona than small-diameter c onductors.
Spacing between the conductors: Larger distance between the conductors reduces the electric stresses between them. And, hence, larger the distance between conductors, lesser the corona formation.
Line voltage: As it is already explained, lesser the line voltage, lesser the ionization of surrounding air. Corona discharge starts to occur whe n the voltage becomes greater than a minimum critical voltage called as critical disruptive voltage.
How To Reduce The Corona Discharge?
Corona discharge is always accompanied by power loss (which is dissipated in the form of sound, light, heat and chemical action). Corona discharge can be reduced by the following methods:
By increasing the conductor size: As ex plained above, larger the diameter of the co nductor, lesser the corona discharge.
By increasing the distance between conductors: Larger the conductor spacing, lesser the corona.
Using bundled conductors: Using a bundled conductor increases the effective diameter of the conductor. This results in reduction of the corona discharge..
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Program Body
clc clear all E=zeros(3,50); E_0=8.85e-21; ii=1; for i=2:0.1:7 tmp_mat=zeros(3,1); tmp_mat=cal(i)./(2*pi*E_0*i); E(1:3,ii)=tmp_mat; ii=ii+1; end axes1 = axes('YGrid','on',... 'XTick',[2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2 .8 2.9 3 3.1 3.2 3.3 3.4 3 .5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.99999999999999 6.09999999999999 6.19999999999999 6.29999999999999 6.39999999999999 6.49999999999999 6.59999999999999 6.69999999999999 6.79999999999999 6.89999999999999 6.99999999999999 7],... 'XGrid','on'); hold(axes1,'all'); plot(2:0.1:7,E(1,:),'Marker','*','Color',[1 0 0]); xlabel('Variation of radius [cm]'); ylabel('GRADIENT- [kv/cm]'); title('Figure One'); figure axes1 = axes('YGrid','on',... 'XTick',[2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2 .8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4 .8 4.9 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.99999999999999 6.09999999999999 6.19999999999999 6.29999999999999 6.39999999999999 6.49999999999999 6.59999999999999 6.69999999999999 6.79999999999999 6.89999999999999 6.99999999999999 7],... 'XGrid','on'); hold(axes1,'all'); plot(2:0.1:7,E(2,:),'Marker','*','Color',[0 1 0]); 31
