MPEB Summer Training report

PREFACE This report comprises of all the sessions of training, I have been through in the duration of four weeks during vacations. I visited MPMKVV Co. ltd.(Madhya Pradesh Madhya Kshetra Vidyut Vitran), a govt. undertaking company dedicated to distribution of Power and Tariffing .The City Circle is divided in four zones and its one of the premier company of MPSEB (Madhya Pradesh State Electricity Board ), which focuses ob providing the best services to the consumers that include quality and reliable supply of power, quicker attention to fuse-off calls and billing related problems. There are one 220/132KV substation, three 132/33KV substations, twelve 33/11KV substations in City circle (west zone). Substations of each category were visited where I was made aware of all the equipments installed there, their controlling and the distribution system functioning. I also had one week visit of Transformer repairement unit, Energy meter testing lab of MPMKVV Co. ltd. were informative knowledge about the devices was given. We also were made familiar with the general way of conduct with the consumers of the company, how to handle their problems and entertain up to the possible satisfactory level.

The overall experience was very informative.

ACKNOWLEDGEMENTS Practical training is an important aspect of an engineering curriculum as it enables to understand the practical application of the theoretical concepts that were learned during academics. It acquainted the student with the latest advancement in the field of technology & engineering. To get this training completed we are thankful to Mr. K.K. Dubey (EE,Training cell) ,Mr. Amrit Tiwari (AEE) ,Mr. Manoj Kelkar (AEE), Mr. Shivram Solanki (Supervisor,Transformer repairment unit) and all the employees if MPMKVV Co. Ltd. who shared their knowledge zealously. We are thankful to Prof. K.S. Sandhu (H.O.D.,Electrical Dept.) for providing us opportunity to undergo this training session during vacations at MPMKVV Co. Ltd. I want to convey my sincere note of thanks to all Professors and lecturers of Electrical Dept. NIT Kurukshetra , for being a key guide and kind support.

CONTENTS Forwarding letter Preface Acknowledgements 1. Electrical Energy Meters Introduction  Types of meters o Electromechanical meters o Mechanism of electromechanical meters o Solid state electronic meters  Testing and calibration  Domestic and Industrial energy meters 2. Electrical Substations Introduction  Transmission substations  Distribution Substations  Switching Function  Equipments installed  Capacitor bank Charging unit  Tasks performed by substation staff

3. Transformer testing and repairment         

Introduction Basic Principle Induction law Practical considerations Effect of frequency Energy losses calculations General faults Transformer oil testing Instrument transformers Accessories of transformers

4. Functions and tasks performed by MPMKVV Co. Ltd. Introduction  Electrification of new localities  Load surveys  Tariffs  Action against electricity theft  Minimization in transmission losses

ELECTRICAL ENERGY METERS INTRODUCTION An electric meter or energy meter is a device that measures the amount of electrical energy consumed by a residence, business or an electrically powered device. Electric meters are typically calibrated in billing units, the most common one being the kilowatt hour. A periodic reading of electric meters establishes billing cycles and energy used during a cycle. In settings when energy savings during certain periods are desired, meters may measure demand, the maximum use of power in some interval. In some areas, the electric rates are higher during certain times of day, to encourage reduction in use. Also, in some areas meters have relays to turn off nonessential equipment. The most common unit of measurement on the electricity meter is the kilowatt hour, which is equal to the amount of energy used by a load of one kilowatt over a period of one hour, or 3,600,000 joules. Some electricity companies use the SI mega joule instead. Demand is normally measured in watts, but averaged over a period, most often a quarter or half hour. Reactive power is measured in "Volt-amperes reactive", (varh) in kilovar-hours. By convention, a "lagging" or inductive load, such as a motor, will have positive reactive power. A "leading", or capacitive load, will have negative reactive power.

TYPES OF METERS Electricity meters operate by continuously measuring the instantaneous voltage (volts) and current (amperes) and finding the product of these to give instantaneous electrical power (watts) which is then integrated against time to give energy used (joules, kilowatt-hours etc.). Meters for smaller services ( such as small residential customers) can be connected directly in-line between source and customer. For larger loads, more than about 200 amps of load, current transformers are used, so that the meter can be located other than in line with the service conductors. The meters fall into two basic categories, electromechanical and electronic.

Current transformers being used with meters

ELECTROMECHANICAL METERS The most common type of electricity meter is the Thomson or electromechanical induction watt-hour meter, invented by Elihu Thomson in 1888. The electromechanical induction meter operates by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power. The number of revolutions is thus proportional to the energy usage. It consumes a small amount of power, typically around 2 watts. The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees using a lag coil. This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power being used. The disc drives a register mechanism

which integrates the speed of the disc over time by counting revolutions, much like the odometer in a car, in order to render a measurement of the total energyused over a period of time. The type of meter described above is used on a single-phase AC supply. Different phase configurations use additional voltage and current coils. The aluminum disc is supported by a spindle which has a worm gear which drives the register. The register is a series of dials which record the amount of energy used. The dials may be of the cyclometer type, an odometer-like display that is easy to read where for each dial a single digit is shown through a window in the face of the meter, or of the pointer type where a pointer indicates each digit. With the dial pointer type, adjacent pointers generally rotate in opposite directions due to the gearing mechanism. The amount of energy represented by one revolution of the disc is denoted by the symbol Kh which is given in units of watt-hours per revolution. The value 7.2 is commonly seen. Using the value of Kh, one can determine their power consumption at any given time by timing the disc with a stopwatch. If the time in seconds taken by the disc to complete one revolution is t, then the power in watts is . For example, if Kh = 7.2, as above, and one revolution took place in 14.4 seconds, the power is 1800 watts. This method can be used to determine the power consumption of household devices by switching them on one by one. Most domestic electricity meters must be read manually, whether by a representative of the power company . Where the meter reader reads the meter, the reading may be supplied to the power company by records, post or over the internet. The electricity company will normally require a visit by a company representative at least monthly in order to verify customer-supplied readings and to make a basic safety check of the meter. In an induction type meter, creep is a phenomenon that can adversely affect accuracy, that occurs when the meter disc rotates continuously with potentialapplied and the load terminals open circuited. A test for error due to creep is called a creep test.

.. energy meters

MECHANISM OF ELECTROMECHANICAL ENERGY METERS The key point: metering is based on the product of two electrical entities, current I and voltage V; power is the product of these two entities, V and I. Energy is calculated integrating over time (that is adding together time after time) the V*I products. It is energy what we are paying for. Within electromechanical meters V and I feed two coils: the voltage coil (which is in parallel to the line) requiring low power and a current coil (in series with the line) made of thick copper wire. Metering can be stopped or started interrupting the connection to the voltage coil.

Internal assembly of a electromechanical energy meter

The meter has two coils in it, one responsive to voltage, the other to current. They are arranged so that the torque they apply to the disc is proportional to the voltage times the current times the cosine of the phase angle so that the disc only responds to active power (kWh) and not to reactive power (kVAR). The device works upon induction principle with current coils and the torque is produced in the aluminium disc and the dials records the energy consumed.

SOLID STATE OR ELECTRONIC ENERGY METERS Electronic meters display the energy used on an LCD or LED display, and can also transmit readings to remote places. In addition to measuring energy used, electronic meters can also record other parameters of the load and supply such as maximum demand, power factor and reactive power used etc. They can also support time-of-day billing, for example, recording the amount of energy used during on-peak and off-peak hours. As in the block diagram, the meter has a power supply, a metering engine, A processing and communication engine (i.e. a microcontroller), and other add-on modules such as RTC, LCD display, communication ports/modules and so on.The metering engine is given the voltage and current inputs and has a voltage reference, samplers and quantisers followed by an ADC section to yield the digitalised equivalents of all the inputs. These inputs are then processed using a Digital Signal Processor to calculate the various metering parameters such as powers, energies etc.The largest source of long-term errors in the meter is drift in the preamp, followed by the precision of the voltage reference. Both of these vary with temperature as well, and vary wildly because most meters are outdoors. Characterizing and compensating for these is a major part of meter design.The processing and communication section has the responsibility of calculating the various derived quantities from the digital values generated by the metering engine. This also has the responsibility of communication using various protocols and interface with other addon modules connected as slaves to it.RTC and other add-on modules are attached as slaves to the processing and communication section for various input/output functions. On a modern meter most if not all of this will be implemented inside the microprocessor, such as the Real Time Clock (RTC), LCD controller, temperature sensor, memory and analog to digital converters. Electronic meter possess a microprocessor and interfaced by a Programmable Periphral Device which receives its Input from Two CT's, one is on the phase & the other is on the neutral,the PPI recieves signals from both CT,s but it reads whichever the current is greater & a V.T. is positioned in the casing of Energy meter of which outputs is fed to PPI so the proceessor reads V from V.T.,I(depends on Power Factor) from C.T. so their product is seen on the

digital screen of the Meter.

TESTING AND CALIBRATION Sometimes due to excessive load on the meter the current becomes very and crosses its upper limits which may burn the current coil which leads to meter jammed and sometimes due to sudden change in load partial damage is done to the meter which leads to loss in calibration due to which meter runs slower and sometimes when we have heavy load on meters the calibration is disturbed and meter runs fasted even on less load. So inorder to overcome such problems of the customers the meters are tested and calibrated on complaint of the customers by the MPMKVV staff members. General and traditional method of meter testing is by putting only 1Kw load across the meter and the pulses are counted and if the supervisor finds an error then the meter is replaced and if the error is still unnoticeable then the meter is sent to meter testing lab of MPMKVV (CPRI, Bhopal ). General methods of testing and calibration includes calibration test bench, where every meter is tested before installation. The bench accords with the standards of “IEC 60736:1982”. The bench can do warm up test, starting test, no load test(creep test), error test, dial test, test of influence quantities (negative phase, voltage unbalance,harmonic wave and so on)and test of repeatability of measurements. The bench uses the PWM( Pulse Width Modulation) to amplify voltage/current output, the high efficiency >85% and lowers the heat. The bench is using the HY5303C-22 reference standard energy meter with comparision technology to offer test for error determination and calibration. Load tests are done at starting meter reading is taken ,meters are calibrated at unbalanced phase voltages, tests are done at negative power factors ,temperature and vibration tests are also done on energy meters to provide good service to the consumers.

Meter testing lab

Temperature testing lab

DOMESTIC AND COMMERCIAL ENERGY METERS Domestic energy meters generally record active energy consumed by the consumer and they are charged accordingly. The domestic meters are generally electromechanical and electronics meters are also installed in new connections with rating 10-40 Amps. They have simple construction and give basic information with LED indicators 3 indicators for three phases, 1 for earth if any short circuit occurs in wiring this indicator blinks, 1 for reverse this indicator blinks when there is leakage due to improper wiring. The meter reader takes monthly meter reading on its billing machine and gives the bill on the spot. The bill is then billed by consumers at MPMKVV zonal offices or through automatic billing machine installed at various places in city. Commercial and Industrial energy meters are sophisticated their rating is 100500 Amps. They have CTs installed with the meter setup, these energy meters are digital meters where Kw, Kwh, KVAR, PF, MD, CMD, DATE, TIME, Voltages of 3 phases, current in three phases are recorded. These energy meters automatically detect and correct the phase reversal eliminating the need to be concerned with CT load orientation.They have push buttons, hwen they are pressed various quantities mentioned above can be seen and are thus recorded by representative of MPMKVV. The bill is processed at the regional level on the basis of Kwh and KVAR of power consumed at authenticated limit of pf. The bill is mailed to the commercial units and they are collected monthly at regional office.

Industrial energy meter

Domestic energy meter

ELECTRICAL SUBSTATIONS INTRODUCTION An electrical substation is a subsidiary station of an electricity generation, transmission and distribution system where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between generating plant and consumer, and may be changed in voltage in several steps. A substation that has a step-up transformer increases the voltage while decreasing the current, while a step-down transformer decreases the voltage while increasing the current for domestic and commercial distribution.

Sukhi Sewaiya Substation

TRANSMISSION SUBSTATION - EHV 220KV SUBSTATION EHV Substation forms an important transmission network and distribution network. It has a vital influence of reliability of service. Apart from ensuring efficient transmission and distribution of power the substation configuration should me such that it enables easy maintenance of equipment and minimum interruption in power supply. Flexibility in future expansion in terms of number of circuits and transformer MVA capacity also needs to be considered while choosing the actual configuration of the substation. EHV substations are constructed as near as possible to the load centre. The voltage level of the power transmission is decided on the quantum of power to be transmitted to the load centre. Generally, the relation between EHV voltage level and the power to be transmitted is as follows: Sno. 1. 2. 3.

Power to be transmitted Upto 150MVA From 150MVA to 300MVA 300MVA to 1000MVA

Voltage level 132KV 220KV 400KV

Substations visited The 220KV/33KV substation at Sukhi Sewaiya, Bhopal (2x100 MVA +50 MVA) and 132KV/33KV substation at MACT, Bhopal (2x40 MVA + 40 MVA) were visited the distribution 33KV/11KV substations under these substations are also visited : Sno. 1 2 3 4 5 6 7 8 9 10 11 12

Substation Name Chambal E-8 Rohitas Rachna Nagar Saket Nagar Vidhya Nagar Rajat Nagar Amramad Baag Mugalia Vallabh Nagar Misrod Habibganj

Single line diagram :

Sukhi sewaiya 220KV/33KV substation

Capacity 2x5 MVA 2X5 MVA 2X5 MVA 2X5 MVA 2X5 MVA 2X5 MVA 1x3.15 MVA 1x3.15 MVA 2X5 MVA 2X5 MVA 1x5 MVA 1x5 MVA

Chambal 33/11 KV substation

Various equipments installed at substation : The instruments are named below according to the single line diagram as follows: 1. Lightening arrestors, 2. C V T 3. Wave trap 4. Current transformer 5. Isolators with earth switch 6. Circuit breaker 7. Line isolator 8. BUS 9. Potential transformer in the bus with a bus isolator 10. Isolator 11. Current transformer 12. Circuit breaker 13. Lightening arrestors

14. Transformer 15. Lightening arrestors with earth switch 16. Circuit breaker 17. Current transformer 18. Isolator 19. Bus 20. Potential transformer with a bus isolator 21. A capacitor bank attached to the bus. 22. AB switch 23. Measuring Equipments (ME) 24. DC supply 25. Control system and measuring instruments 26. Outgoing feeders

Brief descriptions of the instruments in the line diagram are1. Lightening arrestors : Lightening arrestors are the instrument that are used in the incoming feeders so that to prevent the high voltage entering the main station. This high voltage is very dangerous to the instruments used in the substation. Even the instruments are very costly, so to prevent any damage lightening arrestors are used. The lightening arrestors do not let the lightening to fall on the station. If some lightening occurs the arrestors pull the lightening and ground it to the earth. In any substation the main important is of protection which is firstly done by these lightening arrestors. The lightening arrestors are grounded to the earth so that it can pull the lightening to the ground. The lightening arrestor works with an angle of 30° to 45° making a cone.

Lightening arrester

2. C V T : A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra high voltage signals and provide low voltage signals either for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitors across which the voltage signal is split, an inductive element used to tune the device to the supply frequency and a transformer used to isolate and further step-down the voltage for the instrumentation or protective relay. The device has at least four terminals, a high-voltage terminal for connection to the high voltage signal, a ground terminal and at least one set of secondary terminals for connection to the instrumentation or protective relay. CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the

use of voltage transformers would be uneconomical. In practice the first capacitor, C1, is often replaced by a stack of capacitors connected in series. This results in a large voltage drop across the stack of capacitors that replaced the first capacitor and a comparatively small voltage drop across the second capacitor, C2, and hence the secondary terminals.

C.V.T.

WAVE-TRAP

3. Wave trap: Wave trap is an instrument using for tripping of the wave. The function of this trap is that it traps the unwanted waves. Its function is of trapping wave. Its shape is like a drum. It is connected to the main incoming feeder so that it can trap the waves which may be dangerous to the instruments here in the substation. 4. Current transformer: Current transformers are basically used to take the readings of the currents entering the substation. This transformer steps down the current from 800 amps to 1 amp. This is done because we have no instrument for measuring of such a large current. The main use of this transformer is (a) distance protection; (b) backup protection; (c) measurement.

CT in 33KV/11KV S/S

CT INTERNAL DAIGRAM

CT in 220KV/132KV S/S

The working of CT can be understood by the diagram J1 is the current in the conductor and CT core is around the conductor J2 is the current induced in CT winding which is proportional to current in the conductor and thus current and voltage of the line can be measured using CT. 5. Lightening arrestors with earth switch: Lightening arrestors after the current transformer are used so as to protect it from lightening i.e. from high voltage entering into it. This lightening arrestor has an earth switch, which can directly earth the lightening. The arrestor works at 30° to 45° angel of the lightening making a cone. The earth switch can be operated manually, by pulling the switch towards ground. This also helps in breaking the line

entering the station. By doing so maintenance and repair of any instrument can b performed. 6. Circuit breaker: The circuit breakers are used to break the circuit if any fault occurs in any of the instrument. These circuit breaker breaks for a fault which can damage other instrument in the station. For any unwanted fault over the station we need to break the line current. This is only done automatically by the circuit breaker. There are mainly two types of circuit breakers used for any substations. They are (a) SF6 circuit breakers; (b) vacuum circuit breakers. The use of SF6 circuit breaker is mainly in the substations which are having high input kv input, say above 220kv and more. The gas is put inside the circuit breaker by force i.e. under high-pressure. When if the gas gets decreases there is a motor connected to the circuit breaker. The motor starts operating if the gas went lower than 20.8 bar. There is a meter connected to the breaker so that it can be manually seen if the gas goes low. The circuit breaker uses the SF6 gas to reduce the torque produce in it due to any fault in the line. The circuit breaker has a direct link with the instruments in the station, when any fault occur alarm bell rings. During the arching period SF6 gas is blown axially along the arc. The gas removes the head from the arc by axial convection and radial dissipation as a result the arc diameter reduces during the decreasing mode of the current wave. The diameter becomes very small during current zero period and arc is extinguished. Due to its electro negativity and low arc time constant, the SF6 regains its dielectric strength rapidly after the current zero the rate of rise of dielectric strength is very high and time constant is very low. The vacuum circuit breakers is used for small kv stations. The spring here reduces the torque produced so that the breaker can function again. The spring type is used for step down side of 132kv to 33kv also in 33kv to 11kv and so on. They are only used in low distribution side. With rated current upto 3000 Amps., these breakers interrupt the current by creating and extinguishing the arc in a vacuum container.

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Power VCB

7. Line isolator :The line isolators are used to isolate the high voltage from flow through the line into the bus. This isolator prevents the instruments to get damaged. It also allows the only needed voltage and rest is earthed by itself.It is used to isolate the system from other incoming feeders and this is done using a handle connected through a pipe (can be viewed in picture in red colour)

Line isolators

220KV BUS

Pot. transformer

8. BUS :The bus is a line in which the incoming feeders come into and get into the instruments for further step up or step down. The first bus is used for putting the incoming feeders in la single line. There may be double line in the bus so that if any fault occurs in the one the other can still have the current and the supply will not stop. The two lines in the bus are separated by a little distanceby a conductor having a connector between them. This is so that one can work at a time and the other works only if the first is having any fault. 9. Potential transformers with bus isolators :There are two potential transformers used in the bus connected both side of the bus. The potential transformer uses a bus isolator to protect itself. The main use of this transformer is to measure the voltage through the bus. This is done so as to get the detail information of the voltage passing through the bus to the instrument. There are two main parts in it (a) measurement; (b) protection. 10. Isolators :The use of this isolator is to protect the transformer and the other instrument in the line. The isolator isolates the extra voltage to the ground and thus any extra voltage cannot enter the line. Thus an isolator is used after the bus also for protection.

Isolator handle

isolator bars at feeder bus

11. Current transformer :Current transformers are used after the bus for measurement of the current going out through the feeder and also for protection of the instruments. 12. Circuit breaker :The circuit breakers are used to break the circuit if any fault occurs in the circuit of the any feeders. 13. Lightening arrestors : The use of lightening arrestors after the bus is to protect the instrument in the station so that lightening would not affect the instruments in the station. 14. Transformer :There are three transformers (100MVA each) in the incoming feeders of 220KV substation so that the three lines are step down at the same time. In case of a 400kv or more kv line station auto transformers are used. While in case of lower kv line such as less than 220kv line double winding transformers are used. In 33KV substation two transformers( 5MVA each) are installed in incoming feeders.

15. Lightening arrestors with earth switch : The lightening arrestors are used with earth switch so that lightening would not pass through the Instruments in the station. 16. Circuit breaker :The bus is a line in which the incoming feeders come into and get into the instruments for further step up or step down. The first bus is used for putting the incoming feeders in la single line. There may be double line in the bus so that if any fault occurs in the one the other can still have the current and the supply will not stop. The two lines in the bus are separated by a little distance by a conductor having a connector between them. This is so that one can work at a time and the other works only if the first is having any fault.

17. Current transformer :Current transformers are used to measure the current passing through the transformer. Its main use is of protection and measurement. 18. Isolator : These are used to ground the extra voltage to the ground. 19. Bus :This bus is to carry the output stepped down voltage to the required place.

20. Potential transformer with a bus isolator : Two PT are always connected across the bus so that the voltage across the bus could be measured.