INSTITUTE OF TECHNOLOGY UNIVERSITY OF MORATUWA
REPORT ON INDUSTRIAL TRAINING At
CEYLON ELECTRICITY BOARD Sri Devananda RD, Piliyandala.
NAME
:
K.B GONAGALA
REGISTRATION N0
:
10/IT/EE/114
COURSE
:
NATIONAL DIPLOMA IN TECHNOLOGY
FIELD
:
ELECTRICAL ENGINEERING TECHNOLOGY
PERIOD
:
11 MARCH 2013 – 2013 – 16 MAY 2013
0
INDEX
1. CEYLON ELECTRICITY BOARD
-
02
2. CENTRAL WORKSHOP
-
03 – 03 – 05
3. POWER PLANT
-
06 – 06 – 10
4. LIFT BRANCH
-
11 – 11 – 15
5. AC BRANCH
-
16 - 18
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CEYLON ELECTRICITY BOARD The Ceylon Electricity Board (CEB), the largest electricity company in Sri Lanka. It is the major institute in charge of electricity power in sir lanka.power generation, transmission; distribution and retailing are the major functions coming under its authority. CEB being its vision to enrich life through power was opened in 1969. To develop and maintain an efficient, coordinated and economical system of electricity supply to the whole of Sri Lanka is the mission of CEB enhancing its generating capacity to 2,684 MW, of which 846 MW is from thermal energy, and 1,357 MW is from hydroelectricity. Due to Low wind resource, rough terrain and poor road conditions in Sri Lanka, CEB owns only one 3 MW Wind farm in Hambantota, known as the Hambantota Wind Farm. The farm consists of five fiv e Turbines, measuring 600 KW each. CEB manages numerous hydro power plants under Mahaweli Mahaweli and Laxapana complexes. It has ongoing main power plant projects such as Broadlands, Trincomalee and Puttalam power plant . Its latest projects are upper Kotmale and Lakvijaya coal power plants.
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CENTRAL WORKSHOP In first two weeks we were assigned to be trained in Aniyakanda Central Workshop. In addition to main services carried out by CEB it has its own workshop. For the yielding of its needs n eeds the work shop has been carried out. The manufacturing metal accessories need for electrical repairs and installation, electrical motor repairing and automobile repairs are carried out in the central workshop. It’s under the administration of a chief engineer, a mechanical and an electrical engineer and mechanical and electrical superintends. There are two main workshops. One is the electrical workshop and the other one being the metal workshop. Under the metal workshop there is a forging forgin g workshop. Duty of the electrical workshop is rewinding, repairing and maintaining AC and DC motors.
FAULTS AVAILABLE IN MOTORS A/C or D/C motors may not work due to the following faults.
Damages or faults on the electricity power supply.
Damages on the electrical insulation coating on the cables such as cuts, removal of insulation coating and bruises on it.
Thermal damages on the winding. Such as burns of burn coils.
Loose connections of the winding connections.
Wrong winding connections or terminal box.
During the time we spent in the central workshop we learnt how to carry c arry out the rewinding of A/C motors.
Fan motor
In a fan motor there are three windings.
Stator winding
Regulator winding
Running winding
Normally the starting and the regulator winding are in the same winding. Number of turns in the regulator winding is 1/3 of the turns available in the (starting + regulator) winding. LOW SPEED -N
MEDIUM SPPED -N
HIGH SPEED -N
3
3 phase motor
In a 3 phase motor the windings must be connected such that the windings are in a balanced position. That is to say if there are 12 windings each phase must have 4 windings.
A 3 phase motor can be power in a star and delta connected system.
Star connection
delta connection
Armature winding
Armatures are used in high speed motors where higher torque is applied. Normally the speed is over 7000 rpm. In an armature there are commutator segments as well as the slots. In some armatures the number of slots = number of commutator segments while the other is (2*number of slots) = number of commutator segments The coil pitch = number of slots/ poles Number of coils per winding = number of commutator segments/ number of slots In motor rewinding several types of insulating papers are used.
Plebian
Milliner
Luminex
Nomex
Combined paper
Letharoid
Mica
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Winding tapes are also available to tight the winding
Empire cloth
Cotton tape
Glasuoal
During three training the winding of an armature was carried out. The size of the coils was measured by a micrometer after the coil was burnt such that the insulated coating was removed. To rewind the armature can be carried out manually. But the process was hard and it takes a long time to rewind. Removing of the previous winding was done using a chip. We had to care while winding the armature so that not to break the coil due to the high tension applied on it.when such thing happed we combined two coils by soldering after the coating was removed. In the mechanical workshop the forging process was studied. The forging molding mixture consists of silica sand (92%) and phentonite (8%). Phentonite is used to make the mixture strong. Cu (60-65 %) and Zn (40-35%) are used to make the brass from which the electrical accessories are made of. The mixture is melted until it reaches 9000C. If higher strength is needed then the Zn is added 35%.the mixture is put to the crossable cold which is made of graphite.deoxidising crystals are used to remove the air inside the mixture to make sure no hoes are available in the final product. The cupric powder is also added to remove the impurities in the melted mixture. If they are available they come to the surface and then they are removed.
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POWER PLANT After that period we were trained two weeks at Power plant section – section – Kolonnawa. The power plant branch is providing generator supplies where it is required. In CEB standby diesel power generator supplies for some government institutes and various occasions they carry out maintain of the installed generators as well. Some of them are available in temple trees, presidents house, parliament and hospitals .installing the generators as well as the maintenance is carried out by the power plant branch. Especially during the presidents meetings and during three cricket matches CEB supplies standby diesel generators. There we studied about large diesel power plants and its controlling system. They own 2KW smallest generators up to 1MW huge Generators. Type of appliance
generator capacity
Homes, small shops and offices
8 to 30 kVA
Large industires,large office complexes
up to 2,000 kVA
Small power plants
up to about 5 MW
A 2,000 kVA set can be housed in a 40ft ISO container and fully packaged and portable. Sometimes when the generator is larger than the engine and the generator are brought to the site and then assembled. Generators are used not only for emergency power but also for secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators. Sometimes the generator supply becomes the main supply while the CEB supply becomes secondary. Most of the time the domestic power supply is single phase requirement while in the commercial and industrial requires it is a three phase supply.
Types of Diesel Engines Two types of diesel engines are available 1. two-stroke 2. four-stroke Most of the diesel engines are generally operated on the four-stroke cycle, with some larger engines operating on the two-stroke cycle.
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Four Stroke Diesel Engines
Four-stroke cycle
Intake stroke On the intake stroke of the piston, the piston moves from the Top of the cylinder to the bottom of the cylinder, decreasing the pressure inside the cylinder. A mixture of fuel (diesel) and air is forced. The intake valve then closes.
Compression stroke When the both intake and exhaust valves are closed, the piston moves upwards of the cylinder compressing the fuel and air mixture.
Power stroke While the piston is closed to Top Dead Center, the compressed air –fuel –fuel mixture is ignited, usually due to the heat and pressure of compression. Large amount of energy is released released and it drives the piston upward. Due to the movement of the piston the crankshaft is rotates. The rotation of the crankshaft rotates the flywheel attached to the generator. 7
Exhaust stroke During the exhaust stroke, the piston once again moves to TDC (top dead center) making the exhaust valve is opened. The smoke due to the brunt of the fuel is released in this stroke and the other remains as well.
Generator
R
N AVR
Y B MAIN STATOR
EXCITOR STATOR
MAIN ROTOR
EXCITOR
SHAFT ROTOR
P
DIODE
M
PALTEE
G
EXCITOR STATOR
MAIN STATOR
There we learnt how a generator generates power... when the shaft rotates due to the rotation of the flywheel. When the shaft rotates the main stator rotates and generates a voltage due to the rate change of flux of the main stator. Then the generated voltage is fed to AVR and the then the regulated voltage is applied to the exciter stator. The exciter rotary then subjected to the rate of change of flux and an ace voltage is applied. The ac supply is then applied tom the diode plate and rectified to dc. The dc supply is applied to the rotor. But this method takes a little time to generate the required voltage. But if we used a PMG we can generate the required voltage rapidly. R, Y and B wires are connected to the AVR to get signal from it to check whether they are working properly. There we learnt about the changeover. A changeover is used to change the power supply source, CEB or GENSET. The manual change over and automatic tracking tracking system can work as the changeover.
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Generator Control Panel Features
AUTOMATIC MAINS FAILURE FAILURE
ENGINE CONTROL
GENERATOR PROTECTION
3 PHASE MAIN VOLTAGE INPUTS
3 PHASE GENSET VOLTAGE INPUTS
ENGINE OIL PRESSURE MEASUREMENT
ENGINE COOLANT TEMP MEASUREMENT MEASUREMENT
BUILT IN ALARMS AND WARNING
GENSET ACTIVE POWER MEASUREMENT
GENSET POWER FACTOR MEASUREMENT
PERIODIC MAINTENANCE REQUEST INDICATOR I NDICATOR
LED DISPLAY
There we learnt about bypass unit. A bypass unit is attached when we need to maintain or repair the ATS. What a bypass unit does is to isolate the ATS. So we can carry out the maintains or repairs when the ATS is attached to GENSET.
ATS BYPASS UNIT TO GENERATOR LOAD CHANGE
ATS
OVER
BREAKER
CEB MAIN 9
Before the generator is installed it is tested under various loads. It is done using a load bank.
LOAD BANK
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LIFT BRANCH Then we were assigned to the lift branch . CEB has several Lift branches in the island. A major depo is located in General Hospital, Colombo. The function of the Lift barh is to install the new lifts and to maintain them. There are several kinds of lifts
Passenger lifts
Dummy lifts
Home lifts
Bed lifts
PARTS OF A LIFT
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Three phas einduction motor, main sheave,auxiliary rope are called as trction machine. On the basis of the traction machine and roping over itthere are two types of methods are available.
LIFT CAR
WEIGHT =
COUNTER WEIGHT
W
WEIGHT =W + LOAD/2
1:1 System
2:1 System
Since a lift is a suspended installment over several meters away from the ground necessary safety precautions have to be taken. The aim of these safety features is to avoid and minimize the damages on passengers, goods and the lift.
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SAFETY FEATURES
Governor
Governor can detect over speed of a lift and it gives signal to motor and also mechanical break. break . There are two main break system of a lift. One is electrical breaking, another is mechanical breaking. There is a maximum speed recommended for a lift, if that speed exceeds, (If ropes Breaks, motor failures….) governor detects the problem and car comes immediately stop. Modern lifts has an electronic sensors to detect the speed of the lift.
Limit switches (slow down switches)
Upper limit switches
Lower limit switches
These switches are used in the upper and lower limits of the hoist way. A device to slowdown and stop the elevator at or near a terminal landing independently of the operating device. Type S3 switches are used as slowdown switches. Normally called as 29 circuits.
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BUFFERS
Buffers are fixed at the bottom of the hoist way such that to minimize the damaged happen to the lift and the inside resource in case of a sudden crash. There are oil buffers, hydraulic buffers are available.it absorbers the mechanical vibrations of the defensing car or counter weight if moves beyond their limits.
Door interlocks
Land door as well as the car door is interlocked electrically and mechanically in away away that the lift doesn’t move in case of any door being open. Modern doors are fully automatic and driven by electric motor. The door unit is again controlled by a separate processing unit. The door mechanism is also prevented from closing the door when passengers are entering or exiting the lift. This is done by a number of sensing devices which monitor entrance area of the car. Also electrical interlocks prevent the lift from moving when the car door is opened.
14
CAR OPERTAING ANDFLOOR OPERATING PANEL Car operating panel is inside the lift car while the floor operating panel is on the floor where the car is landing.
CAR OPERATING PANEL
DOOR OPERATING PANEL
15
AC BRANCH After lift branch training we had the training in the AC branch at national hospital. The AC branch is with the function of installing new plants, maintaining and repairing the plants. There we studied about various types of AC plants.
Window type AC plants
Split type window AC plants
Centralized AC plants (chill plants)
Centralized AC plant During the two weeks training I got lot knowledge on the operating of an AC plant. Each AC plant has a compressor. Inside the compressor a refrigerant gas is filled. It may be R22, R12and R134.on the operation of the compressor it has 4 types of compressors.
Rotary type
Piston type
Screw type
squirrel type
When the refrigerant gas is compressed by a piston or any other method out of the above it becomes hot gas. Then the hot gas flows through the discharge tube. The discharge tube has a small diameter. Then the gas is sent to the condenser. Fan inside the condenser makes the gas cool and it becomes a cold liquid. The cold liquid is then going through the filter dryer that makes the liquid dry. That is due to incase of any water drops are available then they become ice and act as barriers to the flow of the cycle. Then the liquid is the flow to the evaporator through separate two tubes. In the evaporator the th e liquid absorbs the hot temperature of the room air which blows to the evaporator by a blower. Then the cold liquid becomes hot gas and the air inside the room becomes cold and dry. After that the cold liquid is flows through the suction pipe toward the compressor.
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There is a thermostat which helps to keep the room temperature at a constant level. When the room temperature temp erature comes to the set temperature the gas inside the thermostat stop the function of the compressor. When the temperature is high again it makes the compressor work. All the tube available in an AC plant is made of copper. In a window type AC plant the compressor c ompressor and the condenser are outside the room while the evaporator is inside the room at the same position where the condenser and the compressor is fixed. In a split type AC plant the same is inside and outside. But the compressor and the condenser can be placed several floors away from the floor where the evaporator is placed. The centralized system the water is cooled and it is done at a point and then it is transferred to the air handle unit. The air is intakes and it goes through bag and free filters. Then the air is releases making contact with the tubes where the cold water flows. This is used in large scale compartments.
AC PLANT MAINTAINCE During the training we could engaged in a practical on how to check the leaks occurs in AC plants. N2 gas is filled to the plant in the low pressure side under 150 psi. Then the soap water is applied on the tubes to check whether there is a leak. Then it is kept 24 hours to check whether there is a decree in the N2 pressure. If need we can check it by sinking it in ate water. If there are no leakage then the N2 is vacuumed unit the manifold shows -30 psi. After that the R22 gas is pressurized to the low pressure side and run the plant. When the plant runs the pressure on the low pressure side should be 55-65 psi. During the training of maintenance and a nd repair of AC plants they are cleaned c leaned by water and a blower. The cap c ap of the evaporator is removed and then the filters inside were washed and cleaned by a blower to remove the dust particles which makes the function of the plant weaker.
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MEASUREMENT OF PRESSURE Measurement of pressure is done by manifold. The left side if for low pressure and the right side is for high pressure side. The pressure is read in psi generally, while it can be read in bar also. Pressures for various refrigerant gases are displayed on it with the temperature
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