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SUMMER TRAINING REPORT
AND
PROJECT REPORT ON
GENERATOR PROTECTION
AT
SUBMITTED BY:-
JANARDAN KUMAR
ELECTRICAL & ELECTRONICS ENGINEERING
143/07, 6th SEMESTER
NATIONAL INSTITUTE OF TECHNOLOGY, JAMSHEDPUR
Plant training report Completed Project on Generator Protection
Under the guidance of completed under the guidance of
Mr. Cosmos D. Lakra Mr. Sanjay Kumar
Sr. Manager, HR Sr. Manager, Electrical
Tata Power Jojobera Plant Tata Power Jojobera Plant
JAMSHEDPUR JAMSHEDPUR
Acknowledgement
I would like to express my gratitude and thanks to all those who gave me this great opportunity to compare my report .Firstly I want to thank Mr. Cosmos D. Lakra , Sr. Manager H.R. ,Tata Power , Jamshedpur and the Department of Electrical for giving me permission to commence this report in the first instance, to do the necessary field work and to use departmental data.
I would like to extend my gratitude to Mr. Sanjay Kumar Sr.Manager, Electrical for his immense support, encouraged and all technical help without which the completion of this project would have been impossible.
I am also deeply indebted to Mr. S. K. Sahoo and Mr. Saket Kumar whose technical input, stimulating suggestions and encouragement helped me in the completion of report and provided me with practical on- field knowledge of the subject.
Moreover, I would like to give my special thanks to
Mr. G.P. Shastri
Mrs. Archana Sharma
Miss. Neha Kumari
Mr. B.C. Majhi
Who all helped to get knowledge about working and maintenance of the plant and the vital role they play in the performance of the plant.
My co-trainees from various colleges supported me in my work. I want to thank them for all their help, support, interest and valuable hints. Their presence made my stay at TATA Power a pleasant and learning experience in all aspects of life.
CONTENT
Plant overview
Environmental Management
Coal Handling Plant
Operation
Control and Instrumentation
Electrical System
Protective Relays
Generator Protection
Trip Classes
Protective Relay Form generators and Generator-transformer units
Protection Application
REG
SPAJ
Reference
TATA POWER- OVERVIEW
The Tata Power Company Limited is one of the oldest power sector utilities in India. The Tata Power group (TEC) comprised three companies:-
Tata Power - set up in 1919
Andhra Valley - set up in 1916
Tata Hydro - set up in 1910
These companies were merged in the year 2000 to form Tata power.
Now The Tata Power manages around 3200 mw of generation, transmission and distribution business at present and has set goals to take this level to 5000 MW by the year 2008.
Tata Power started its operations in Jharkhand with the acquisition of 67.5 MW of coal based captive power unit of Tata steel in April 1996. Tata power added three units of three units of 120 MW capacities each at Jamshedpur .The first unit began commercial operation in February 2001 followed by the second unit in February 2002 while the third became operational by 2005.A 120MW plant is going to be operational from July 2010.
UNIT COMMISSIONING:
Unit #1: 67.5 MW (commissioned in 1996)
Unit #4: 120 MW (commissioned in 2000)
Unit #3: 120 MW (commissioned in 2001)
Unit #4: 120 MW (commissioned in 2005)
NET GENERATION: 427.5 MW AT Jojobera Plant, Jamshedpur
FUEL: - The materials used for power generation are coal, LDO (light diesel oil) and water
The primary fuel is coal,60% of which is procured from Tata steel .The balance quality is supplied by Mahanadi Coalfields Limited (MCL) . The specific consumption of the division is 0.76 kg/KWh.
The secondary fuel used in the plant is Light Diesel oil (LDO). It is sourced from Indian Oil Corporation or HPCL or BPCL. Specific LDO consumption of the division is 2.46 Liter/KWh.
WASTE DISPOSAL:-
In the Power generation process coal ash is generated in two forms- fly ash and Bottom Ash .Fly ash is conveyed pneumatically to M/S Lafarge and through baulker to ACC and Grasim for Cement making. Bottom Ash is disposed to ash pond for setting and water is recovered, recycled and reused.
PROCESS:-
Steam is generated, is tangentially fired, pulverized coal generator (Boiler).In the process coal is fired in the Boiler to convert water into superheated steam . Then the thermal energy stored in steam is utilized in the turbine- generator set to generate electrical power .after passing through the turbine, steam comes into condenser where it is condensed where it is condensed into the water. The condensate water is reutilized in the steam generator for producing further steam and the system runs in a closed cycle.
A small percentage of make-up water is required to compensate the losses in the process .To convert Turbine exhaust steam into condensate water in the condenser ,circulating water system is provided .Coal is used as primary fuel and LDO firing system is provided for starting up/Shut down/ low-load operations .coal is received in the coal yard and after primary and secondary crushing; coal is fed to coal bunkers through conveyors .From coal bunkers ,it is fed into coal mills where pulverization takes place and coal-primary air mixture is pneumatically fed into boiler furnace through coal burners .
The product of coal/LDO consumption i.e. flue gas comes out through boiler stack after passing through air pre heater and economize .Fly –ash thus generated is collected in
bottom ash hopper beneath steam generator . To evacuate the Fly –ash and Bottom ash, a mechanized ash evacuation system is provided. All three units are provided through Electrostatic precipitator (ESP) to bring down the suspended particulate matter (SPM) level in conformity with the pollution control norms.
Important parameters are monitored on continuous basis through DCS. VISTA and other systems all the important control loops run in auto mode with self –correcting characteristics. The power is generated at 11KV level and then stepped up to 132 KV level by generators transformers. Electrical power is supplied to Tata Steel at two voltage levels 132 KV and 32 KV.
The power at 132 KV level is fed directly to the main grid of Tata Steel at Golmuri Substation. The division feds the 33KV power to local industries through a 33KV substation directly as per guidelines given by Tata Steel. Power generation, in –house consumption and power supply to customer is monitored on – line through VISTA system.
DEMINERALIZING PLANT:
The high pressure boiler at the Jojobera thermal power station unit requires high purity water for their smooth and safety operation. This insures that the boiler water will always have limited salinity and the problem of scaling and corrosion of boiler internals is prevented. Further in the event of high salinity in the boiler water there is always the danger of salts being carried over with steam, to be ultimately deposited on lower pressure side of the turbine blades. This salt laden water may also damage the turbine blades as it is emitted at a very high velocity.
To produce this high quality water for the boiler feed purposes, DM plant is installed to remove all the salts to maximum extent from the available normal incoming raw water.
ELECTROSTATIC PRECIPITATORS (E.S.P.):-
Exhaust gases contain large quantity dust particles which are emitted into the atmosphere. This poses threat to mankind as devastating health hazard.
E.S.P. Advantages :
Ability to treat volume of gases at high temperature.
Ability to cope up with corrosive atmosphere.
Offer low resistance path to gas flow
E.S.P. uses intense electric forces to separate suspended particles from the flue gases. Process involves :
Electric charging of suspended particles
Collection of charged particles on collecting diodes
Removal of particles from collecting diodes
Five fields to keep emission within limits.
Electromagnetic control system is used.
Ammonia dosing for better result.
COOLING TOWERS:-
Cooling tower is very large and is divided in smaller parts as the size of droplets. These water droplets drops fall from a height of 8 to 10 meters to the bottom of cooling tower. The splitting of water into small droplets, the draught provided by the tower and the large evaporating surface helps to cool water very quickly practically during the time when it is descending. Water from the base of the cooling is pumped into the condenser and the cycle is repeated. Some water about 2% to 5% is lost due to evaporation and has to be added from the tank. Cooling tower are classified as atmospheric (or natural draught) and mechanical draught.
Counter flow cooling tower with PVC fills.
Chemical treatment, to avoid scaling and corrosion in condenser tubes.
Fig. Cooling Tower structure
ENVIRONMENTAL MANAGEMENT
(D M PLANT)Environment stricture are to be strictly abided by governing authority of any industry with pollutants as effluent .So the Electrostatic Precipitator has been installed to extrude 99% of ash and prevent it from moving out into the atmosphere air.
As DM water is required in many of power plant operation , a DM plant is invariably required .It is basically an Unit for producing clarified drinking , make-up and mostly DM water .Apart from drinking ,water is mostly used as coolant in Heat exchanger & Boiler. Some salt like Sulphate, Chloride, Silicate not having retrograde solubility comes out of solution for exceeding solubility limit due to concentration .Ultimately the salt which comes out of solution settle on the heat exchanger surface restricting heat transfer, thus reducing the heat transformer efficiency.
The water supply source is river Subarnrekha which is treated with Na2SO3 to drive away C12, which would otherwise oxidize and damage resin permanently and then with iron-ammonium alum to precipitate suspended impurity materials.
CONTACT TANK
Takes care of suspended matter and filter them out .Alum solution dosed to incoming raw water facilitate proper reaction. To place in the contact tank with sufficient retention capacity for the alum, to form a filterable flock.
PRESSURE SAND FILTER:
It minimizes the carry over of suspended matter to the subsequent vessels.
DEGASSER:
It removes the carbonic acid at the SAC outlet .At SAC inlet, soluble carbonates are there .They are converted in SAC to carbonic acid .An intimate contact between solution and air enable CO2 stripping. As the bicarbonate content is nearly half of total anion load of
the influent water to plant, degasser educe the load on anion resin and regenerate significantly.
MIXED BED EXCHANGER:
The anion and cation not absorbed earlier are absorbed her.
COAL HANDLING PLANT (CHP)
Coal handling plant is the most essential plant of any thermal plant .The CHP is responsible for the procurement and supply of the coal to the coal mill bunkers so that the supply of pulverized coal, required for filling of generation of power is maintained without interruption.
Function of the coal handling plant :-
1. Procurement of coal.
2. Unloading ,sizing and storing of coal
3. Feeding of coal.
PROCESS FLOW CHART :-
Railway rakes Wagon tippler Hopper Apron Feeder Primary crusher Eccentric Disc Screen Secondary crusher Conveyor Bunker
ASH PLANT :-
Dry collection of Ash in Hoppers.
Pneumatic conveying system to silos.
Provision of four types of ash evacuation from silos.
Wet ash disposal system.
Ash conditioning for unloading into dumpers.
OPERATION
The steam cycle is working on a non heat regeneration cycle. Feed water is supplied to the drum through the economizer outer limbs. Water in the boiler tubes absorbs heat from the furnaces. The mixture of water and steam is discharged into the boiler drums. The separated saturated steam is led to the super heater where it is heated to about 810 k.
Super heated steam from the boiler is fed to the turbine via the turbine top valve, emergency stop and governing valve. Steam first enters the HP turbine, gets expanded here and then it is directed to the inlet of the LP turbine for further expansion. In the process the turbine starts rotating which in turn rotates the prime mover of the generator, thus producing electricity.
Steam undergoing expansion in the turbine is allowed to flow through the condenser where the steam is condensed by cooling water supplied by C.W. pumps. The condensate collected in the hot wells and pumped by vertical condensate extraction pumps to the de aerator through air ejector, gland steam condenser, drain cooler and LP heater. From the De aerator feed water storage tank, feed water is pumped to the economizer inlet header through two HP heater. During this process, the condensate steam collected steam collected in different
system. Heat is recovered at various points and is fed to the main feed water system.
BOILER AND ITS AUXILIARIES :-
Steam generation is done in a radiant reheat, wet circulation, single drum, direct corner fired fitting burners and top supported type boiler.
Super heater section
Re-heater section
Draught system
Fuel firing system.
TURBINE AND ITS AUXILIARIES:-
A stem turbine is a prime mover in which rotary motion is obtained by the gradual change of momentum of the steam.
In a steam turbine following are the main parts:-
1. The nozzle in which energy of high pressure is converted into kinetic energy, so that steam issues from nozzle at high velocity.
2. The blade which change the direction of motion of steam issuing from the nozzle that force acts on the blades to change momentum and propel them.
The turbine mainly consists of nozzle or set of nozzle and rotary blade wheel. The steam expanded from high pressure to low pressure either in the nozzle or in the blades and kinetic energy thus obtained is supplied to the blades where the it is transformed into mechanical work. The power is made available at a turbine shaft directly or with the help of reduction gear.
Condensate extraction pump.
Hotwell make up pump.
Gland steam condenser.
Surface condenser.
Extraction steam system
- LP heater
- HP heater
- De aerator
CONTROL AND INSTRUMENTATION
Thermal power plant have a number of equipments performing number of complex processes for the ultimate aim , the conversion of mechanical energy into electrical energy. In order to have stable generating condition in power plant, always a balance is obtained. This balance is distributed due to
Grid troubles
Trouble in process
Trouble in equipment.
When this balance is disturbed, all the process variables deviate from the normal value. Thus, they create a necessity for the deviation .
Instruments – to measure and indicate the amount of deviation.
Automatic control – to correct the deviation and bring back to normalcy.
Protection – to isolate the equipments from dangerous operating conditions caused due to such excessive deviation.
TYPE OF INSTRUMENTS:-
The instruments that are being used in the process instrumentation for measuring the physical qualities can classified as
1. Indicators : They are of two categories local and remote local indicators are self controlled and self operative and are mounted on the site .the remote indicators are used for telemeter purpose and are mounted in the centralized control panel.
2. Recorders : Recorders are necessary wherever operating history is required for analyzing the trend and for future case and efficiency purpose.
POWER PLANT INSTRUMENTS:-
1. Temperature Measuring Instruments :- Accurate measurement of temperature is required to assess the material fatigue ,heat transfer etc. measurement of bearing babbets , turbine top, bottom generator and core super heater, tube metal temperature filled system thermometer such as mercury in steel , vapors filled or gas filled is used for local indicators of
temperature depending upon the range. Resistance thermometer or thermocouples are used as sensor in remote measurement of temperature depending upon the range.
2. Pressure Measuring Instruments : - For local indication of pressure and differential pressure , Border type and diaphragm type gauge or liquid manometer are used . Transmitter does remote measurement of pressure either electronic or pneumatic coupled with secondary instrument indicator/recorder.
3. Level Measurement :- In power plant ,level measurement in open tank s such as DM water storage tank and oil tanks and close tanks such as de-aerator , hotwell ,HP heaters ,LP heaters ,boiler drums are to be made . Gauge glass is used for local indication and transmitters are used for remote indication.
4. Flow Measurement :- In power plant , flow measurements are based on differential pressure principles . Diffrential pressure is created by placing suitable restriction in the flow path of the Fluids in pipe. The restriction devices are suitably selected depending on the media, flow etc. The devices are orifice, venture, flow nozzle, pilot tube.
Electrical System
Electrical System is one of the most important components of a power plant. With the help of this system the mechanical energy is converted to electrical energy and is distributed to various consumers according to their requirements.
Air cooled generators.
Digital voltage Regulator.
Numerical protection relays for fastest response
Fault data recorder
SF-6 Circuit breaker for high voltage applications
Energy management System
Real time display of generation, dispatch and Aux. consumption.
SCADA for remote switchyard operation and data transfer to Load Dispatch
Centre.
Centralized monitoring of HT motor protection relays.
Turbo –Generators:-
The turbo –generator is designed for continuous operation with voltage variations of +- 1% in general. The machines are designed for the air temperature of 45 degree Celsius maximum, with cooling water temperature of 38 degree Celsius maximum at the inlet. The 2- pole generator uses direct cooling for the rotor winding and indirect air cooling for stator winding. The entire losses are dissipated through the air.
Stator:-
The stator consists of two parts viz. the outer casing and inner frame supporting the core and the winding .Outer casing is of welded construction .Welded tubes and ducts provide flow paths for cooling. Inner stator consists of stator and core windings. Stator core stacked with insulated electrical sheet steel laminations clamping fingers ensures uniform pressure and intensive cooling of stator core ends. Stator winding fractional pitched, two layers consisting of individual bars. To minimize the losses, the bars are separately brazed together and insulated from each other.
Generator name plating of unit 1:-
KW: - 67500
PF: - 0.8
KVA: - 84375
Stator: - 10500 volts
4639 amps
RPM: - 3000
Frequency: - 50 Hz
Phase: - 3
Connection: - Y
Coolant: - Air
Insulation Class: - B
Generator Cooling System:-
The heat generated inside the stator and rotor due to the copper losses, iron losses, friction and windage losses are dissipated through the secondary coolant air. Direct cooling of rotor essentially eliminates hot spot and different temperature between adjacent components, which could result in mechanical stress, particularly to the copper conductor. Indirect cooling is used for stator winding.
The cooling air is circulated in generator interior in closed circuitry to axial flow fans arrange on the rotor shaft journals. The cooling air has three flow paths. The air flow mixes in the air gap. The cooling air then flows radially outward through ventilating slots in the core within the range of hot air compartments for cooling further portion of the stator core and stator winding. The hot air returns to the air cooler. The air cooler shell and tube type heat exchanger, which cools the air in the generator. From hot air heat is dissipated through cooling water which is regulated through the valve. In the stator cooling medium is circular which has copper fins to obtain a large heat transfer area. It is designed on principal of cross counter flow system.
Transformer:-
According to uses and types, transformer can be divided into different category. Power transformer, Control transformer, Rectifier transformer, Auto transformer.
According to windings configuration it can be Core type or Shell type. According to cooling it can be classified as AN, ON, ONAN, ONAF, OFAF, OFWF type. It can be Liquid filled (OIL), Air cooled or Resin Cast type. It can be Delta, Star, Zig- Zag , single phase to poly phase
Transformer core:-
Transformer provides continuous path for electromagnetic flux and are made of cold rolled grain oriented alloy steel (CRGO), which reduced Hysteresis loss and enable the core to operate at higher flux density. Generally it has limbs which mitered with top and bottom yokes. CRGO steel has a feature that has specific loss in Watt/Kg is lowest in the direction of rolling.
Cores are laminated and each lamination is coated with phosphorous glass type coating to reduce the Eddy Current losses in the core. Laminations built to from a stepped Limb (cross section) having as near as possible a circular section and mitered at 45 degree with top and bottom yoke.
Radiators and Cooling:-
Radiators are provided to enlarge the cooling surface area of the oil filled transformer. It is made of mild steel but not designed for vacuum. For ONAF and OFAF type, electrically driven cooling fans are provided to cool the radiators. They are mounted either below or at side of the radiator. For OFAF type of cooling, OIL pumps are also provided to circulate the oil between Main Tank and Radiator to improve the cooling. Hot oil comes from top of the Main tank in the Radiator and cold pushed from bottom in the Main Tank.
Transformer Oil:-
Transformer oil protects the core and coil assembly from chemical attack. It provides dielectric strength of the transformer insulation system. It provides efficient cooling system of transformer. Transformer oil is a pure hydrocarbon mineral oil and generally paraffin base.
Oil temperature indicator:-
It indicates the top oil temperature and operates on the principle expansion of liquid with temperature. The indicator is fitted with a maximum pointer and two mercury switches to provide alarm and trip signals.
Relief Vent:-
In case of severe fault inside HVR, terminal pressure may be built up to a very high value, which may result in the explosion of tank .To avoid such a contingency, a relief vent of diaphragm type is fitted. The diaphragm breaks open and relieves the pressure if the pressure is more than 35 KN/m2.
Buchholz Relay:-
A double float relay is fitted with a mercury switch. The switch contacts are brought to thermometer box for alarm and tripping.
Conservator:-
Oil conservator is connected to HVR tank to account for any change in the volume of the oil due to variation in the oil temperature. A prismatic oil gauge is provided to indicate the oil level. In some of the cases conservator is provided with magnetic type oil level gauge with low oil level alarm as per the contact requirement.
Dehydrating Breather:-
The conservator is connected to the atmosphere through a dehydrating breather to make sure that air entering the conservator is dry. Silica gel in the breather is blue when dry and it turns pink as the crystals absorb moisture.
Circuit-Breakers:-
The circuit breakers are the device, which is capable of making and breaking of an electrical circuit under normal and abnormal conditions. During Normal operating
Condition the CB can be opened or closed by a station operator for the purpose of switching and maintenance. During the abnormal or faulty conditions the relays senses the fault and closes the trip circuit of the circuit breaker. Thereafter the circuit breaker opens .The circuit breaker has two working positions, open & closed .These correspond to open circuit breaker contact and closed circuit breaker contact respectively. The operation of automatic opening and closing the contact is achieved by means of operating of the circuit breaker. As the relay
contact closes the trip circuit is closed and the operating mechanism. In Tata power , the 132 KV breakers for GT #1,2,3 are all ABB and are SF6 circuit breaker in which closing and tripping is through charged spring .
Lightning Arrestor:-
Lightning Arrestor are usually connected between phases and ground in the distribution system to protect apparatus insulation from lightning surges. The resistor blocks in the arrestor offers low resistance to the full impulse wave. Here zinc oxide arrestors are used. Zinc oxide arrestors have higher energy absorption level.
DC System:-
Total power failure of a thermal power station is a most critical situation for the station .Since the turbo –generators sets takes about 20-25 minutes for coasting down to barring speed; it is essential to provide emergency oil supply to the turbine and generated journal bearings.
In the event of total power failure any delay in coming up emergency DG sets, DC supply system takes over the oil supply to scanners in steam generators in addition to catering power to entire protection system.
Float charger:-
The Float Charger is meant for supplying the continuous dc load and at the same trickle charging the battery to keep it in fully charged condition. The float charger may either be operated in auto or manual mode. In the automatic mode, the output voltage is held constant at present value (around 2.15 V/cell) whereas in manual mode the output voltage may be varied within the limits by potentiometer.
Boost Charger :-
The boost charger is basically meant for quick charging the battery (cc mode) after a heavy discharge so as to restore the capacity of the battery within minimum time. The charger may be operated in auto mode or manual mode. In the manual mode the output current may be varied within the limits by adjusting a potentiometer.
PROTECTIVE RELAYS
Protective relaying is one of several features of system design concerned with minimizing damage to equipment and interruptions to service when electrical failuresOccur. When we say that relays “protect” we mean that, together with other equipment, the relays help to minimize damage and improve service. It will be evident that all the mitigation features are dependent on one another for successfully minimizing the effects of failure.
THE FUNCTION OF PROTECTIVE RELAYING
The function of protective relaying is to cause the prompt removal from service of anyelement of a power system when it suffers a short circuit, or when it starts to operate in any abnormal manner that might cause damage or otherwise interfere with the effective operation of the rest of the system. The relaying equipment is aided in this task by circuit breakers that are capable of disconnecting the faulty element when they are called upon to do so by the relaying equipment.
FUNDAMENTAL PRINCIPLES OF PROTECTIVE RELAYING
There are two groups of such equipments one which we shall call “primary” relayingand the other “back-up” relaying. Primary relaying is the first line of defense, whereas back-up relaying functions only when primary relaying fails.
PRIMARY RELAYING
Fig. 1. One-line diagram of a portion of an electric power system illustrating Primary relaying .
BACK-UP RELAYING
Back-up relaying is employed only for protection against short circuits. Because shortcircuits are the preponderant type of power failure, there are more opportunities for failurein short primary relaying. When we say that primary relaying may fail, we mean that any of several things may happen to prevent primary relaying from causing the disconnection of a power-system fault. Primary relaying may fail because of failure in any of the following:A. Current or voltage supply to the relays.B. D-C tripping-voltage supply.C. Protective relays.D. Tripping circuit or breaker mechanism.E. Circuit breaker.
THE EVALUATION OF PROTECTIVE RELAYING
Although a modern power system could not operate without protective relaying, this does not make it priceless. As in all good engineering, economics plays a large part. Although the protection engineer can usually justify expenditures for protective relaying on the basis of standard practice, circumstances may alter such concepts, and it often becomes necessary to evaluate the benefits to be gained. It is generally not a question of whether protective relaying can be justified, but of how far one should go toward investing in the best relaying available.
Like all other parts of a power system, protective relaying should be evaluated on the basis of its contribution to the best economically possible service to the customers.
1. The contribution of protective relaying is to help the rest of the power system to function as efficiently and as effectively as possible in the face of trouble.
2. How protective relaying does this is as follows. By minimizing damage when failures occur, protective relaying minimizes:
A. The cost of repairing the damage.B. The likelihood that the trouble may spread and involve other equipment.C. The time that the equipment is out of service.D. The loss in revenue and the strained public relations while the equipment is out of service.
3. By expediting the equipment’s return to service, protective relaying helps to minimize the amount of equipment reserve required, since there is less likelihood of another failure before the first failure can be repair. The ability of protective relaying to permit fuller use of the system capacity is forcefully
illustrated by system stability. Figure 4 shows how the speed of protective relaying influences the amount of power that can be transmitted without loss of synchronism when short circuits occur.
4. More loads can be carried over an existing system by speeding up the protective relaying. This has been shown to be a relatively inexpensive way to increase the transient stability limit.
5. Where stability is a problem, protective relaying can often be evaluated against the cost of constructing additional transmission lines or switching stations.
Other circumstances will be shown later in which certain types of protective-relayingEquipment can permit savings in circuit breakers and transmission lines. The quality of the protective-relaying equipment can affect engineering expense in applying the relaying equipment itself. Equipment that can still operate properly when future changes are made in a system or its operation will save much future engineering and other related expense.
One should not conclude that the justifiable expense for a given protective-relayingequipment is necessarily proportional to the value or importance of the system element to be directly protected. A failure in that system element may affect the ability of the entire system to render service, and therefore that relaying equipment is actually protecting the service of the entire system. Some of the most serious shutdowns have been caused by consequential effects growing out of an original failure in relatively unimportant equipment that was not properly protected.
HOW DO PROTECTIVE RELAYS OPERATE?
Thus far, we have treated the relays themselves in a most impersonal manner, telling what they do without any regard to how they do it. This fascinating part of the story of protective relaying will be told in much more detail later. But, in order to round out this general consideration of relaying and to prepare for what is yet to come, some explanation is in order here.
All relays used for short-circuit protection, and many other types also, operate by virtue of the current and/or voltage supplied to them by current and voltage transformers connected in various combinations to the system element that is to be protected. Through individual or relative changes in these two quantities, failures signal their presence, type, and location to the protective relays. For every type and location of failure, there is some distinctive difference in these quantities, and there are various types of protective-relaying equipments
available, each of which is designed to recognize a particular difference and to operate in response to it.
More possible differences exist in these quantities than one might suspect. Differences in each quantity are possible in one or more of the following:
A. Magnitude.
B. Frequency.
C. Phase angle.
D. Duration.
E. Rate of change.
F. Direction or order of change.
G. Harmonics or wave shape
GENERATOR PROTECTION
Introduction
Generators are designed to run at a high load factor at a high load factor for a large number of Years and permit certain incidences of abnormal working conditions .The machine and its auxiliaries are supervised by monitoring devices to keep the incidences of abnormal working conditions down to a minimum. Despite the monitoring , electrical and mechanical faults may occur , and the generators may be provided with protective relays which in case of faults ,quickly initiate a disconnection of the machine from the system and , if necessary , initiate a complete shutdown of the machine.
Problem faced in the generators
a. Stator electrical faults
b. Overload
c. Over Voltage
d. Unbalanced Loading
e. Over fluxing
f. Inadvertent Energisation
g. Rotor Electrical faults
h. Loss of excitation
i. Loss of Synchronization
j. Failure of prime mover
k. Lubrication Oil failure
l. Over-speeding
m.Rotor Distortion
n. Difference in expansion between rotating and stationary parts
o. Excessive Vibration
p. Core Lamination faults
Class-A Tripping
This is adopted for those electrical faults of Generator and Generator transformer and unit auxiliary transformer for which tripping cannot be delayed.
This leads to simultaneous tripping of
- Generator Transformer HV side CB
- Field Circuit Breaker
- LV side incomer breakers of UAT
- Auto changeover from unit to station for unit auxiliaries and tripping of turbine
Class-B Tripping
This is adopted for all turbine Faults (Mechanical) and for some electrical faults of generator, Generator transformer and unit auxiliary transformer for which it is safe the turbine
Subsequently the generator is tripped through reverse power interlock
Ensures that unit does not over speed due to trapped steam in the turbine during the shut down and also the loss of power to the grid from the Generator is not sudden.
Class-C Tripping
This is adopted for all faults beyond the generator system which can be cleared by tripping of generator Transformer HV side CB alone.
In this case the TG set run with HP-LP bypass system in operation and the generator continues to feed the unit auxiliary transformers
Protective relays for generators and generator transformer units
CT, PT Inputs to relays
Sl.No. Power System Element Type of Relay CT PT1 132 kV feeders Earth leakage -2 ,, Over Load -3 ,, Distance Relay 4 ,, Directional OL 5 ,, Directional EL Open delta
6 400 kV, 220 kV feeders
Main 1 Distance relay
7 ,, Main 2 Distance relay 8 ,, Over Voltage - 9 ,, LBB Protection -10 ,, Power relays 11 ,, Check synchronizing
relay-
12 ,, Bus bar Protection -13 Power Tr. Transformer differential -14 ,, Non directional OL -15 ,, HV – directional EL Open delta16 ,, LV Non directional OL -17 ,, LV Non directional EL -18 ,, LV Directional EL Open delta19 ,, Over fluxing (V/F) -
Comparison of EMVTs Vs CVTs
S.No. Characteristic Electromagnetic VT Capacitor VT1 Burden >= 300 VA <= 300 VA2 Reliability More Less3 Cost Expensive Less expensive4 Transient response Very Good Poor
5 Distance Protection accuracy
Very Good Over Reaches
The figure below shows an overview of standard protective relays for generator transformer units. A recommended minimum of relays for different types and sizes of generators is given under section protective relay schemes.
Fig. Protective relays for a generator-transformer unit
Types of Fault and their Protection
Stator earth-fault protection
Common practice in most countries is to earth the generator neutral through a resistor , which gives a maximum earth–fault current of 5-10 A. Tuned reactors which limit the earth –fault current to less than 1 A are also used . In both cases, the transient voltages in the stator system during intermittent earth –faults are kept within acceptable limits , and earth-faults which are tipped within some few seconds will only cause negligible damage to the laminations of the stator core .
The generator earthing resistor normally limits the neutral voltage transmitted from the high voltage side of the unit transformer in case of an earth fault on the high voltage side to max. 2-3% of rated generator phase voltage.
Short -circuits between the stator winding in the slots and the stator core are the most common electrical faults in generator s. The fault is normally initiated by mechanical or thermal damage to the insulating material or the anti-corona paint on a stator coil. Interturn faults, which normally are difficult to detect, will quickly develop into an earth –fault and will be tipped by the stator earth–fault protection.
Stator earth –fault Protection for Generators with unit Transformers
95% stator earth- fault protection
A neutral point overvoltage relay , fed either from a voltage transformer connected between the generator neutral and earth or from the broken delta winding of three –phase voltage transformers on the generator line side , will depending on the setting , protect 80-95% of the stator winding . The relay is normally set to operate at 5% of phase voltage with a time –delay of 0.3-0.5 s. With generator bus, the low voltage winding of the unit transformer and the high-voltage winding of the unit auxiliary transformer.
Fig. 95% stator earth fault protection
Units with generator breaker between the transformer and the generator should also have a three phase voltage transformers connected to the bus between the low voltage winding of the transformer and the breaker. The broken delta connected secondary are connected to a neutral point overvoltage relay , normally set to 20-30% of phase voltage , which will provide earth –fault protection for the low voltage winding and the section of the bus connected to it when the generator breaker is open . Normally, voltage limiting capacitors will be required for this bus section.
Loss of Excitation protection
A complete loss-of- excitation may occur as a result of:
Unintentional opening of the field breaker
an open circuit or a short circuit of the main field
a fault in the automatic voltage regulator (AVR), with the result that the field
current is reduced to zero
When a generator with sufficient active load losses the field current, it goes out of
synchronism and starts to run asynchronously at a speed higher than the system,
absorbing reactive power ( VAR ) for its excitation from the system.
The maximum active power that can be generated without loss of synchronism
when the generator losses its excitation depends on the difference between the
direct axis and quadrature axis synchronous reactance. For generators with salient
poles , the difference is normally sufficiently large to keep the machine running
synchronously ,even with an active load of 15-25% of rated load .
The generator terminal voltage varies periodically due to the large generator
auxiliary induction motor stall, which would lead to complete shutdown of
thermal power station .Reduced excitation ,causing excessive heating at the end
region of the stator core , may be obtained during normal system condition ,when
there is a continuous tendency towards an increasing system voltage (dropping of
reactive loads ). in that case, the normal tendency towards an increasing system
voltage (dropping of reactive loads). In that case, the normal automatic voltage
regulator (AVR) action will reduce the field excitation.
Loss of Excitation relay RAGPK is used to protect Generator
Fig. Loss of excitation relay
Thermal overload protection
Overloads up to 1.4 times the rated current are not normally detected by the
impedance or over-current protection. Sustained overloads within this range are
usually supervised by temperature monitors (resistance elements) embedded at
various points in the stator slots. The temperature monitoring system enables
measurements measuring points.
As an additional check of the stator winding temperature, an accurate thermal
overload down to some few minutes, which is required for adequate thermal
protection of directly cooled machines.
The temperature rise of the stator winding is , in addition to the magnitude of the
current ,also influence d by the coolant flow , the coolant temperature , etc.
Thermal overload relay RAVK is a microprocessor based thermal overload
relay . The relay has output contact for alarm when the measured thermal content
is 95% of operate value.
Fig. Thermal overload relay
Rotor earth –fault protection
The rotor circuit can be exposed to abnormal mechanical or thermal stresses due
to e.g. vibrations, excessive currents or choked cooling medium flow. This may
result in a breakdown of the insulation between the field winding and the rotor
iron at one point where the stress has been too high. The field circuit is normally
kept insulated from earth. A single earth –fault in the field winding or its
associated circuits, therefore, gives rise to a negligible fault current and does not
represent any immediate danger. if ,however, a second earth fault should occur,
heavy fault current and severe mechanical unbalance may quickly arise and lead
to serious damage .It is essential ,therefore ,that any occurrence of insulation
failure is discovered and that the machine is taken out of service as soon as
possible . Normally ,the machine is tripped after a short time delay.
Rotor earth-fault relay with dc injection
The rotor earth –fault relay type RXNB 4 a dc voltage of 48 v to the rotor field
winding and measures the current through the insulation resistance . When a fault
occurs , a certain contribution to the injection voltage is obtained depending on
the field voltage and where in the rotor winding the fault occurs.
Rotor earth-fault relay with ac injection
For small generators with rotating dc exciters, a suitable rotor earth-fault
protection can be arranged with ac injection and a time –over current relay as
shown in fig. With current setting 15 mA , the protection operates for earth-faults
with fault resistance up to about 3.3 kilo ohm ,independent of fault location .
Fig. Rotor earth-Fault with Ac injection
Fig. Rotor earth-Fault with Dc injection
Negative phase sequence current protection
When the generator is connected to a balanced load , the phase current are equal
in magnitude and displaced electrically by 120º.The ampere-turns wave produced
by the stator currents rotate synchronously with the rotor and no eddy current are
induced in the rotor parts .
Unbalanced loading gives rise to a negative sequence current component in the
stator current. The negative-sequence current produces an additional ampere-turn
wave which rotates backwards, hence it moves relatively to the rotor at twice the
synchronous speed. The double frequency eddy currents induced in the rotor may
cause excessive heating, primarily, in the surface of cylindrical rotors and in the
damper windings of rotors with salient poles.
The approximate heating effect on the rotor of a synchronous machine for various
unbalanced fault or severe load unbalance conditions is determined by the product
I22t=K, where I2 is the negative sequence current expressed in per unit (P.U.)
stator current, t the duration in seconds and K a constant depending on the heating
characteristics of the machine, i.e. the type of machine and the method of cooling
adopted.
Table:
Type of generator Max. permitted
I22t=K(seconds)
Max. permitted
continuous I2 (percent)
Cylindrical rotor
Indirectly cooled 30 10
Directly cooled 5-10 8
Salient pole
With damper winding 40 10
Without damper winding 40 5
Example on load dissymmetry which gives rise to negative–sequence currents in the
generator are:
Unbalanced single –phase loads, such as railroads and induction furnaces
Transmission line dissymmetric due to non- transposed phase wires or open
conductor (circuit -breaker pole failure )
An open conductor may give rise to a considerable negative–sequence current, as a
maximum of more than 50% of rated machine current. The combination of two or
more of the above mentioned dissymmetry can give rise to harmful negative sequence
currents ,even if each of them give rise to a relatively small unbalance.
Negative sequences current relay RARIB with thermal memory
The measuring unit for I2t has the setting range 1-63 s in steps of 1s. The unit is
provided
with a thermal memory and the cooling down time of the relay is settable in 7 steps in
the
(2.65-1.70)×k. The blocking relay resets when the heat content in the memory is 50%
of the tripping level.
The memory function secures adequate protection, even in case of repeated periods of
Unbalanced loading which eventually results in excessive heating of the machine, if it
is not tripped.
Over-voltage protection
If the generator circuit–breaker is tripped while the machine is running at full load
and rated power factor, the subsequent increase in terminal voltage will normally be
limited by a quick acting AVR. However, if the AVR is faulty, or, at this particular
time, switched for manual control of a voltage level, severe overvoltage will occur.
This voltage rise will be further increased if simultaneous over-speeding should
occur, owing to a slow acting turbine governor. In case of a hydro electric generator,
a voltage rise of 50-100% is possible during the most unfavorable conditions.
An excessive high set voltage relay can be include to trip the generator quickly in
case of excessive over–voltages following a sudden loss of load and generator over
speeding .
For high impedance earthed generators, the over-voltage relay is connected to the
voltage between phases to prevent faulty operation in case of earth-faults in the stator
circuits .
Over-voltage relay RAEDK
The microprocessor based time over/under-voltage relay RXEDK 2H has two voltage
stages with definite time delay.
Over–excitation protection
The excitation flux in the core of the generator and connected power transformers is directly proportional to the ratio of voltage to frequency (V/Hz) on the terminals of
the equipment. The losses due to eddy current s and hysteresis and hence, the temperature rise, increase in proportion to the level of excitation.An example on the V/Hz capability curve for a generator and the unit transformer is shown infigure.
Fig. V/Hz characteristics of generator-transformer units
As long as the generator –transformer unit is connected to the network, the risk of over-excitation is relatively small .However, when the generator transformer unit is disconnected from the network; there is an obvious risk for over-excitation, mainly during generator start-up and shut down. From cases reported in existing literature it can be concluded that over-fluxing occurs relatively often compared to the number of other electrical incidents. The risk of over-excitation is, obviously, largest during periods when the frequency is below rated value. Hence, overvoltage relays cannot be used to protect the generator-transformer unit against over-fluxing. The proper way of doing this to use a relay which measures the ratio between voltage and current (V/Hz relay).
Over-Excitation relay RALK
The microprocessor based over-excitation relay RXLK 2H has two V/Hz measuring stages with time delay and wide setting range: 0.2-9.6 V/Hz. The relay provides a precise measurement of the relationship between voltage and frequency within the frequency range 5-100 Hz.
Generator differential relays
For modern generators, the time constant of the dc component in the short-circuit
current is large, typically more than 200ms. The risk of saturation of the current
transformers in case external short-circuits is obvious .It is, therefore, important
that generator differential relay remains stable even when the current transformers
are heavily saturated.
The principle of the RADHA high –impedance differential relay is shown in Fig.
The current transformers on the generator neutral and the line side shall have
identical turn’s ratio and similar magnetizing characteristics. Hence, under normal
service condition and external faults with unsaturated current transformers, the
voltage across the relay measuring circuit is negligible.
In case of an external short-circuit, one of the current transformers may saturate
more than the others .The worst case will be if one is completely saturated and the
other is completely unsaturated. The maximum voltage across the relay will be:
Umax=Isn (Rct+Rl) where
Isn= secondary sub transient short-circuit current, symmetrical (ac) component
Rl= resistance of pilot wire between current transformer (CT) and relay
Rct=resistance of the secondary winding of the saturated current transformer
The relay operate voltage is set higher than Umax
The minimum operate current depends mainly on the voltage setting of the relay,
the magnetizing characteristics and the current ratio of the CT’s.
For internal faults, with fault current equal to or above the minimum operate
value of the relay, the voltage across the relay goes up to the full saturation
voltage of the CT’s and the relay operates in 10-15ms.
A voltage dependent resistor across the differential relay limits the voltage to a
safe level .
The primary operate current is normally between 1-5%of rated generator
current .The relay requires dedicated CT cores.
Generator and unit transformer differential relay
The transformer differential relay RADSB is used generator- transformer units. It
is a static relay with threefold restraint:
1. Through–fault restraint for external faults
2. Magnetizing in rush restraint
3. Over–excitation restraint to counteract operation at abnormal magnetizing
currents caused by high voltage
The magnetizing in rush restraint is required to keep the relay stable when a
nearby fault on an adjacent feeder is cleared.
During the time of the fault, the terminal voltage of the main transformer is
practically zero and at the instant of fault clearance, i.e. when the circuit–breaker
of the faulty feeder opens, the transformer terminal voltage quickly rises. This
may cause severe magnetizing in rush currents.
For generator-transformer units with separate generator breaker, the in rush
restraint is also required when the unit transformer is energized from the H.V.
bus.
The over-excitation restraint is important for generator –transformer differential
relays .Without the restraint, there is an obvious risk that the differential relay
may trip the generator due to overvoltage if a substantial part of the load is
disconnected when clearing a fault. The voltage then rises immediately and
remains high until the automatic voltage regulator (AVR) of the machine has
brought it back to the normal value.
Reverse power protection
The purpose of the reverse power relay is basically to prevent damage on the prime
mover (turbine or motor).
If the driving torque becomes less than the total losses in the generator and the prime
mover, the generator stars to work as a synchronous compensator, taking the
necessary active power from the network. In case of steam turbines, a reduction of the
steam flow reduces the cooling effect on the turbine blades and overheating may
occur.
Hydro turbines of the Kapalm and bulb type may also be damaged due to the fact that
the turbine blades “surf “ on the water and set up an axial pressure on the bearing .
The total losses, as a percentage of rated power of a prime mover/generator unit
running at rated speed, are approximately:
Steam turbine 1-3%
Diesel engine 25%
Hydraulic turbine 3%
Gas turbine 5%
These values apply to the case when the power input to the prime-mover is
completely cut off. Thus, in the case when the total losses of a unit are covered partly
by the prime –mover and partly by electric power from the system, the actual power
drawn by a generator, during certain motoring conditions, may be much less than the
above percentage values.
Reverse power relay RXPE 40
The reverse power relay shown in figure contains one static directional current unit
RXPE 40 and one static timer RXKT 2.The directional unit measures the 1x Cos
§ ,where §is the angle between the polarizing voltage and the current to the relay .
When connected to phase current and phase voltage, the relay cannot operate when
there is a direct earth-fault on the generator bus in the phase selected for
measurement.
The RXPE 40 unit is normally connected to phase current and phase voltage .For
generators with V-connected voltage transformers, the current voltage circuits are
connected in accordance with Figure1.
Impedance Relay RAZK
The microprocessor based impedance relay RXZK 22H has two impedance
measuring stages and definite time delay. The impedance measuring characteristics is
polygonal with independent setting of the reach in the X and R directions see Figure2.
Impedance stage Z1 is set to reach only into the unit transformer and will provide a
fast back-up protection for phase short-circuits on the generator terminals, the
generator bus and the low voltage winding of the unit transformer.
Impedance stage Z2 is normally set to operate at 70% of rated generator load
impedance, corresponding to an operate current of 1/0.7 =1.4 times rated current at
rated voltage .
Figure1: Reverse Power Relay
Figure2: Impedance Relay RAZK
Phase Interterm Short-circuit protection
Modern medium size and large size turbo-generators have the stator winding
designed with only one turn per phase per slot .For these machines, interterm faults
can only occur in case of double earth-faults or as a result of severe mechanical
damage on the stator end windings. The latter is considered rather unlikely to occur.
It is generally considered difficult to obtain a reliable protection against short-
circuiting of one turn if the stator winding has a large numbers of turns per phase.
For generators with split neutrals, the conventional inter-turn fault protective scheme
comprises a time delayed low–set over-current relay which senses the current flowing
in the connection between the neutrals of the stator winding , see Fig. 13.The fault
current can be extensively large in case of interterm faults , hence , the time delay
must be short , 0.2 to 0.4 sec, and the over-current relay must be set higher than the
maximum unbalanced current incase of external faults and the minimum unbalanced
current for single–turn short-circuits have to be obtained from the manufacturer of the
machine.
Interturn short-circuit current relay RAIDK
The microprocessor based time over-current relay RXIDK 2H is used for the
interterm protection
Mechanical Faults
Failure of Prime mover
When a generator operating in parallel with others losses its power input, it remains
in synchronism with the system and continues to run as a synchronous motor,
drawing sufficient power to drive the prime mover. This condition may not appear to
be dangerous and in some circumstances will not be so. However, there is a danger of
further damage being is caused.
Over speed
The speed of a turbo-generators set rises when the steam input is in excess of that
require to drive the load at nominal frequency .The speed governor can normally
control the speed ,and, in any case , a et running in parallel with others in an
interconnected system cannot accelerate much independently even if synchronism is
lost .However ,if load is suddenly lost when the HV circuit breaker is tripped , the set
will begin to accelerate rapidly .The speed governor is designed to prevent a
dangerous speed rise even with a 100% load rejection , but nevertheless an additional
centrifugal over speed trip device is provided to initiate an emergency mechanical
shutdown if the over speed exceeds 10%.
To minimize over speed on load rejection and hence the mechanical stress on the
rotor, the following sequence is used whenever electrical tripping is not urgently
required:
Trip prime mover or gradually reduce power input to zero.
Allow generated power to decay towards zero.
Trip generator circuit breaker only when generated power is close to zero or
when the power flow starts to reverse, to drive the idle turbine.
Protection Application in plant
With the development in the field of electronics and induction type relay have been replaced by much compact and accurate kind of electronic relays.
One of the latest innovations which took place in the field is the advent of Numerical relays.
GRP stands for GENERATOR RELAY PANEL comprises of mainly REG, RET and SPAJ .The combination of the three are used in protection scheme of generator.
REG built by ABB incorporate following features in it:
Selectable protection functions
Setting menu-assisted with personal computer by means of the windows-based operator program.
Continuous self –monitoring by hardware
Setting of parameters and recording of the settings
display of events , their acknowledgement and printout
Serial port for communication
Design :
The REG belongs to the generation of fully numerical generator protection terminals, i.e. analogue to digital conversion of the input variables takes place immediately after the input transformers and all further processing of the resulting numerical signals is performed by microprocessors and controlled by programs.
Standard Interface enables REG to communicate with other control systems. Provision is thus made for the exchange of data such as reaction less reporting of binary of binary states, events, measurements and protection parameters or the activation of a different set of settings by higher level of control systems.
The menu based HMI (human machine interface) and the REG small size makes the tasks of connection, configuration and setting simple.
Figure 1 .Generator Relay panel
Hardware
The hardware concept for the REG generator protection equipment comprises four different Plug-in units, a connection mother PCB and housing .In the analog input unit an input transformer provides the electrical and static isolation between the analogue input variables and the electronic circuits and adjusts the signals to a suitable level of processing.
Every analog variable is passed through a first order R/C low-pass filter on the main CPU unit to eliminate what is referred to as the aliasing effect and to suppress HF interferences. They are then sampled and converted to digital signals. The analog /digital conversion is performed by a 16 Bit converter .A DSP carries out part of the digital filtering and makes sure that the data for the protection algorithms are available in the memory to the main processor. Binary signals from the main processor are relayed to the corresponding inputs of the I/O unit and thus control the auxiliary output relays and the light emitting diode (LED) signals .The main processor unit is equipped with an RS232C serial interface via which among other things the protection settings are made, events are
read and the data from the disturbance recorder memory are transferred to a local or remote PC.
Fig. Connection of Generator Relay Panel
Application
The main areas of application of the REG terminal are the protection of the generators, motors and unit transformers .All important protection functions required for the protection of generators, motors and unit transformers are included .The system can therefore replace several relays of a conventional protection schemes .The following table gives a survey of the most significant protection functions of REG.
PROTECTION FUNCTIONS
1. Generator differential ,Transformer differential
2. Definite time over-current (under current)
3. Instantaneous Over-current(undercurrent)
4.Voltage-controlled Over-current
5. Inverse Time Over-current
6. Negative phase sequence current
7. 100 % stator earth fault(= rotor earth fault)
8. Under-impedance
9. Minimum Reactance
10. Power, Overload, Over-temperature
11. Frequency, Over-excitation
12.Inverse negative Phase-sequence current
13. Logical Functions ,Poor slip functions
All setting is extremely wide to make the protection functions suitable for a multimedia of Application.
Digital input and output signals can also be connected together logically:
The tripping outputs of each protection function can be allocated to channels of the tripping auxiliary relay assembly in a manner corresponding to a matrix.
The pick-up and tripping signals can be allocated to the channels of the signaling auxiliary relay assembly.
Provision is made for blocking each protection function with digital signals (e.g. digital inputs or the tripping signal of another protection function). Digital input and output signals can also be connected together logically.
The tripping outputs of each protection function can be allocated to channels of the tripping auxiliary relay assembly in a manner corresponding to a matrix.
The pick-up and tripping signals can be allocated to the channels of the signaling relay assembly.
Provision is made for blocking each protection function with a digital signal (e.g. digital inputs or the tripping signal of another protection function).
SPAJ
Combined over current and earth-fault relay
Features
Three-phase, low –set phase over current unit with definite time or inverse definite minimum time (IDMT) characteristics.
Three-phase., high-set phase over current unit instantaneous or definite time function.
Low-set, non-directional earth fault unit with definite time or inverse definite minimum time.
(IDMT) characteristics
High-set ,non –directional earth fault unit with instantaneous or definite time function
Built-in breaker failure protection function
Two heavy-duty and four light-duty output relays with field-selectable configuration
Numerical display of setting values, measured values, memorized fault values, fault codes etc.
Application
The combined over current and earth-fault relay SPAJ 140C is intended to be used for the
selective short-circuit and earth-fault protection of radial feeders is solidly earthed,
resistance earthed or impedance earthed power-systems. The integrated protection relay
includes a phase over current unit with flexible tripping and signaling facilities .The over
current and earth-fault relays can also be used in other applications requiring single ,two
or three phase over current protection and non-directional earth-fault protection .The
combined over current and earth-fault relays also features circuit breaker failure
protection .
Protection arrangement in plant:
There are many protections which have not been shifted to REG and SPAJ due to its own advantage. The following Protections are the old once itself:
UAT differential Protection –Old
Generator Differential Protection-Old
Local Backup breaker(LBB)-Old
Dead Machine Protection –Old
The following Protection has been shifted to REG:
Overall Differential Protection –REG
Reverse Power Protection –REG
Under Frequency Protection –REG
Negative Phase Sequence Protection-REG
Over Voltage Protection –REG
Loss of Excitation Protection –REG
Under Impedance Protection –REG
Over Fluxing Protection –REG
Stator Earth Fault Protection –REG
The following Protection has been shifted to SPAJ:
UAT Over Current and Earth Fault Protection –SPAJ
GT Over Current Protection –SPAJ
References
1. The ART and Science of protective relaying
2. ABB site- www.abb.com
3. Fundamental of protection Practice
4. NUMERICAL Generator Protection by ABB
5. www.wikipedia.com
6. Internet
