Functions and Performance Requirements
Elements of an Excitation System
Types of Excitation Systems
Control and Protection Functions
Modeling of Excitation Systems
The functions of an excitation system are
to provide direct current to the synchronous generator field winding, and
to perform control and protective functions essential to the satisfactory operation of the power system
The performance requirements of the excitation system are determined by
Generator considerations:
supply and adjust field current as the generator output varies within its continuous capability
respond to transient disturbances with field forcing consistent with the generator short term capabilities:
rotor insulation failure due to high field voltage
rotor heating due to high field current
stator heating due to high VAR loading
heating due to excess flux (volts/Hz)
Power system considerations:
contribute to effective control of system voltage and improvement of system stability
Functions and Performance Requirements
Elements of an Excitation System
Types of Excitation Systems
Control and Protection Functions
Modeling of Excitation Systems
The functions of an excitation system are
to provide direct current to the synchronous generator field winding, and
to perform control and protective functions essential to the satisfactory operation of the power system
The performance requirements of the excitation system are determined by
Generator considerations:
supply and adjust field current as the generator output varies within its continuous capability
respond to transient disturbances with field forcing consistent with the generator short term capabilities:
rotor insulation failure due to high field voltage
rotor heating due to high field current
stator heating due to high VAR loading
heating due to excess flux (volts/Hz)
Power system considerations:
contribute to effective control of system voltage and improvement of system stability
This Power Point Presentation includes Automatic Generation control :
Learning Objective: To illustrate the automatic frequency and voltage control strategies for single and two
area case and analyze the effects, knowing the necessity of generation control.
Learning Outcome:Upon successful completion of this course, the students will be able to Analyze the generation-load balance in real time operation and its effect on frequency and
develop automatic control strategies with mathematical relations.
Concept of AGC, complete block diagram representation of load-frequency control of an
isolated power system, steady state and dynamic response,
Excitation System & capability curve of synchronous generatorMANOJ KUMAR MAHARANA
Excitation systems perform control and protective functions essential to the satisfactory performance of the power system.
The amount of continuous reactive power a generator can supply is restricted by various limits. In the over-excitation region limits are imposed by rotor heating or amount of field current and second is the stator current. In the under excitation region the limits are imposed by load angle. So in steady state the generator should always operate within this region and the loci of the various limiters are called the capability curve of the generator.
Inter Connected Power System(Turbine Speed Governing Mechanism)Raviraj solanki
Inter Connected Power SystemTOPIC : Turbine Speed Governing Mechanism
Introduction
Turbine Speed Governing Mechanism
Mathematical Modeling
Adjustment Of Governor Characteristics
The speed governing system consists of the following parts .
Speed governor
Linkage mechanism
Hydraulic amplifier
Speed changer
Automatic generation control (AGC) is a system for adjusting the power output of multiple generators at different power plants, in response to changes in the load. Since a power grid requires that generation and load closely balance moment by moment, frequent adjustments to the output of generators are necessary. The balance can be judged by measuring the system frequency; if it is increasing, more power is being generated than used, which causes all the machines in the system to accelerate. If the system frequency is decreasing, more load is on the system than the instantaneous generation can provide, which causes all generators to slow down.
Introduction to reactive power control in electrical powerDr.Raja R
Introduction to reactive power control in electrical power
Reactive power in transmission line :
Reactive power control
Reactive power and its importance
Apparent Power
Reactive Power
Apparent Power
Reactive Power Formula
This Power Point Presentation includes Automatic Generation control :
Learning Objective: To illustrate the automatic frequency and voltage control strategies for single and two
area case and analyze the effects, knowing the necessity of generation control.
Learning Outcome:Upon successful completion of this course, the students will be able to Analyze the generation-load balance in real time operation and its effect on frequency and
develop automatic control strategies with mathematical relations.
Concept of AGC, complete block diagram representation of load-frequency control of an
isolated power system, steady state and dynamic response,
Excitation System & capability curve of synchronous generatorMANOJ KUMAR MAHARANA
Excitation systems perform control and protective functions essential to the satisfactory performance of the power system.
The amount of continuous reactive power a generator can supply is restricted by various limits. In the over-excitation region limits are imposed by rotor heating or amount of field current and second is the stator current. In the under excitation region the limits are imposed by load angle. So in steady state the generator should always operate within this region and the loci of the various limiters are called the capability curve of the generator.
Inter Connected Power System(Turbine Speed Governing Mechanism)Raviraj solanki
Inter Connected Power SystemTOPIC : Turbine Speed Governing Mechanism
Introduction
Turbine Speed Governing Mechanism
Mathematical Modeling
Adjustment Of Governor Characteristics
The speed governing system consists of the following parts .
Speed governor
Linkage mechanism
Hydraulic amplifier
Speed changer
Automatic generation control (AGC) is a system for adjusting the power output of multiple generators at different power plants, in response to changes in the load. Since a power grid requires that generation and load closely balance moment by moment, frequent adjustments to the output of generators are necessary. The balance can be judged by measuring the system frequency; if it is increasing, more power is being generated than used, which causes all the machines in the system to accelerate. If the system frequency is decreasing, more load is on the system than the instantaneous generation can provide, which causes all generators to slow down.
Introduction to reactive power control in electrical powerDr.Raja R
Introduction to reactive power control in electrical power
Reactive power in transmission line :
Reactive power control
Reactive power and its importance
Apparent Power
Reactive Power
Apparent Power
Reactive Power Formula
Condition monitoring of rotating electrical machinesAnkit Basera
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These slides presents an overview of different wind generator systems and their comparisons. Later of the slides the modelling and control strategies of wind generators will be discussed.
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Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
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Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
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CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
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Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
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Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
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Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Halogenation process of chemical process industries
GENERATOR PROTECTIONS
1. PROTECTIONS OF GENERATOR
Prepared by: Dhaval D. Julasana (ELECTRICAL-GET)
Thankful to Electrical department
Date: 23/10/2018
NIRMA LTD. BHAVNAGAR
2. Introduction
Type of power generation
Construction and working of generation
Excitation system
Automatic voltage regulator
Type of generators
Difference between salient pole and cylindrical pole generator
Why protection required?
Generator Protections
Generator connection circuit
Generator with NGT
Various faults
Abnormal operating conditions
Excitation of generator field
Stator fault
Differential protection
Percentage bias differential protection
Rotor fault
Protection against rotor fault
Over speeding
Loss of excitation
Contents
3. • Protection against prime mover failure
• How to provide direction into the relay
• Failure of excitation
• Torque develop strategy
• Why protection is required?
• Earth fault
• Types of earthing
• High impedance earthing
• Compensated
• Hybrid impedance ground earthing
• Rotor earth fault
• Why do we care of nearer earth fault
• Pole sleeping
• Stator ground fault
NIRMA LTD. BHAVNAGAR
4. Introduction
Power system is Biggest men made system in the world
Among this biggest Power system is in india
Installed capacity of the Power system is approx. 344GW (August
2018) ,329.20 Gw (april 30th 2017 , At year of 1941 generation was
1362MW
What is the meaning of grid?
Interconnection of the power system components through ac line
How many grids in India?
Earlier ES= Eastern grid
NR= North Region
SR= South region
NER= North eastern region
6. • At first synchronization done with ES-NER
• Then NR-ES-NER
• WR-NR-NER-ES
• Above combined region called central region
• At last only two region remaining which is CE & SR
• Both have separate frequency
• 31st December 2013 around 20:00 Hrs Southern grid successfully synchronized
with central grid
NIRMA LTD. BHAVNAGAR
8. Type of power generation
Majority three type of generation does in india.
• Thermal
• Nuclear
• Water
• World’s largest solar plant currently building up in to Madhya Pradesh
Name is “RIVA”, It’s total capacity 750MW.
NIRMA LTD. BHAVNAGAR
9. NIRMA LTD. BHAVNAGAR
76%
10%
4%
2%1%3% 4%0%
GENERATION
COAL
LARGE HYDRO
WIND POWER
SOLAR POWER
BIO MASS
NUCLEAR
GAS
DIESEL
Generation data of (2018)
COAL= 986591 Gwh
HYDRO=126123Gwh
Wind power= 52666 Gwh
Wind power = 52666
Solar power= 25871 Gwh
Biomass= 15252Gwh
Nuclear= 38346 Gwh
Gas= 50208Gwh
Diesel= 386Gwh
11. Construction and working of generator
• Alternator is one kind of transducer which converts mechanical energy to electrical energy
working on the principle of ELECTROMAGNETIC INDUCTION
• Alternating current will produce by rotating magnetic field so, DC field will hold on rotor
and armature on stator so static dc flux will link on the armature and it will produce the
alternating power.
NIRMA LTD. BHAVNAGAR
12. Excitation system
• Excitation of generator means current will pass through field winding so it will
produce the flux for synchronous generator DC current is needed for that one extra
pilot generator is there so it will provide DC supply to field of generator.
• Pilot generator connected with same shaft. And it’s output is rectified through
solid state rectifier connected with the slip-ring of main generator rotor
• Pilot generator’s output is AC output and it’s need to rectify and convert in to DC
for main exciter and again main exciter’s output need to convert in to DC by diode
bridge circuit and finally this DC output will feed into main machine.
NIRMA LTD. BHAVNAGAR
16. Synchronous Generator
• Synchronous generator converts mechanical power into electrical power source of
mechanical power maybe any thing it may be diesel engine, steam turbine or any similar
device.
• For high- speed machine the prime movers are usually steam turbine employing fossil
or nuclear energy resources
• Lower speed machine are often driven by hydro-turbines that employ water power for
generation.
• Smaller synchronous machine are sometimes used for private generation and at stand by
units, with diesel engines or gas turbines as prime movers.
17. Types of Generator
• Cylindrical-rotor( non-salient pole)- Machines used in Thermal Power plant
generators. Number of poles will be less. These type of generator are High Speed
generator.
• Salient-Pole machines used in hydro power plantNumber of pole will be High.
These type of generator are low speed generator.
NIRMA LTD. BHAVNAGAR
18. Difference between Salient pole and cylindrical pole
generators
• Salient pole generator
1. It has large diameter and shorter
axis length.
2. As the rotor speed is lower, more
number pole are required to attain
the required frequency frequency is
proportional to number of poles.
3. Flux distribution is relatively poor
than non salient pole rotor, hence
the generator emf waveform is not
as good as cylindrical rotor
4. Salient pole rotors generally need
damper windings to prevent rotor
oscillations during operation.
• Cylindrical pole generator
1. They having smaller diameter but
having longer axial length.
2. Cylindrical rotors are used inhigh
speed electrical machines, usually
1500rpm to 3000rpm.
3. Winding loss as well as noise is less
compare to salient pole rotors.
4. Number of poles is usually 2 or 4.
5. Damper windings are not needed in
Cylindrical pole rotors.
6. Flux distribution is symmetrical so
sinusoidal waveform is there so
better emf waveform.NIRMA LTD. BHAVNAGAR
19. Why protection?
1. To detect fault because huge current will damage the equipment
2. To prevent injury to personal
3. To prevent damage of equipment
4. To monitor parameter continuously
5. Operate quickly whenever necessary
21. Generator protection
Generator protection is challenging problem because it’s system connections on three
different sides as shown in fig1 on the ne side is prime mover second side it is grid third
side for dc excitation system
It has to run synchronism with the grid because of its connection to the power system. On
yet another side generator protection is very complex compared to protection for other
elements of the power system.
In case of a fault on turbo alternator, it is not enough to open main circuit breaker
connecting it to power grid. Ex. When turbo alternator driven by a steam turbine is tripped,
the following must be done.
• Steam supply to the turbine is stopped or bypassed.
• Firing of the boiler is stopped.
• Coal mills are stopped;
• Field circuit of the alternator is interrupted.
• Alternator kept running at slow speed with the help of barring gear till it cools down
uniformly, so as to avoid uneven expansions.
24. Generator protection depends on following:
• Type of prime mover and it’s construction
• MW and voltage rating
• Mode of operation
• Method of connection to the power system
• Method of earthing
26. Continue…
• Please noted that generator is never solidly grounded
• If ground it solidly then at fault like L-G fault time abnormally very high current
will flow from neutral point to rotor it will generate very high vibration in rotor
and mechanically damage it and asymmetric field occurs in it.
• So in practical practice we will ground through NGR or NGT.
• It will limit the fault current
• UAT will provide auxiliary supply to the generators auxiliary equipment, it’s
generally power supply 10% of full load power of generator. In our 82MW power
plant Here 36%
NIRMA LTD. BHAVNAGAR
31. Stator faults
• There is possibility to occurs inter turn fault, phase to phase fault and phase to ground
fault.
• For that longitudinal protection.
NIRMA LTD. BHAVNAGAR
33. Differential protection
• Differential protection make for unit protection system, This protection should
operate due to internal fault of unit but not external fault.
• In healthy condition zero current will flow from operating coil.
• But due to construction of the CT no one CT can same as in terms of construction
there is always error in plus or minus terms. So from operating coil always current
will flow I1-I2 value.
• So due to external fault far from transformer some inrush current will flow so, I1-
I2 current’s value will increases upto relay’s peak up value so mal-operation does
occurs.
• To remove this malfunction need to change this characteristics.
• So it is percentage bias differential relay.
NIRMA LTD. BHAVNAGAR
36. Difference between transformer and generator
differential protection
• POWER TRANSFORMER
1. Primary and secondary voltages are
in general different.
2. Turn-ratio of the CTs are different
because of ratio of transformation of
the transformer
3. Tap changer may be present
• GENERATOR
1. Same voltage for CTs on two sides
of generator winding
2. Turn-ratio of CTs on the two sides
of the generator winding is same
3. No such device is present
NIRMA LTD. BHAVNAGAR
37. Rotor faults
• The rotor carries the field winding which is kept isolated from the ground.
Neither the positive nor the negative terminal of the dc supply is grounded.
Thus, any ground fault on the rotor field winding does not affect the working
of the alternator.
• However subsequent fault would cause a section of the rotor winding to be
short circuited, giving rise to a secondary flux which oppose the main flux.
Flux get concentrated on one pole but dispersed over the other and intervening
surfaces.
• So the asymmetry, in the alternator the inertia of rotation is very large and the
rotor to stator air gap is very small so less chance to permanent damage.
• At first on the field fault it must be detected and the set tripped in a controlled
manner, arrangement for earth fault detection and protection given in to figure.
39. Over-speeding
• Conceder turbo alternator supplying rated power at that time mechanical near
about it’s synchronous speed so at some reason some fault occurs at that time
generator will get tripped so it does not serve any electrical load but constantly
mechanical input is there so at that time abruptly speed go to very high value to
avoid it need to stop steam input should be zero
• For that the speed governing system of the turbine is responsible for detecting this
condition. The over speeding can also be detected either on the generator shaft.
Over speeding can be detected by over frequency relay also.
NIRMA LTD. BHAVNAGAR
40. Over speed ?
Over frequency relay
Techogenerator
output
NO
YES
STOP STEM INPUT
START GENERATOR SHUT DOWN
NIRMA LTD. BHAVNAGAR
41. Loss of excitation
• Possible cause to loss of excitation given below
• Loss of field to main exciter
• Accidental tripping of the field breaker
• Short circuit in the field winding
• Poor brush contact in the breaker
• Loss of ac supply to excitation system
42. Continue…
• The generator delivers both real and reactive power to grid, real power comes
from the turbine while the reactive power is due to the field excitation.
• Corresponding real power from rotor is Pm and corresponding reactive power
from field Qe,
46. Connection of generator
• Direct connection: A generator which connect directly to the load is called direct
connection.
• Via generating transformer: A generator which is connect indirectly with
transformer which step up the voltage.
NIRMA LTD. BHAVNAGAR
51. Generator protection requirements
• To detect faults on the generator
• To protect generator from the effects of abnormal power system operating
conditions
• To isolate generator from system faults not cleared remotely
• Action required depends upon the nature of the fault.
• Usual to segregate protection functions into :
−Tripping
−Alarm
NIRMA LTD. BHAVNAGAR
52. Earth fault protection
• If there is no protection then what happen?
• An earth fault involving the stator core results in burning of the iron at the point of
fault and welds laminations together
• Earth fault protection is therefore a principle feature of any generator protection
Type of
protection
Method of
protection
Connection
of protectionNIRMA LTD. BHAVNAGAR
53. Method of earthing
• Mainly three types of earthing
• Neutral grounding resistance earthing
1. lossy method
2. not useful for higher rating of generators
• Neutral grounding transformer earthing
1. lossless earthing method
2. size is more because of transformer
3. Use for higher rating of generators
• Solidly earthing
1. Rapid damage occurs
2. burning the core iron
3. welding the core laminations
NIRMA LTD. BHAVNAGAR
56. Why ground?
• Improve safety by allowing detection of faulted equipment
• Stop transient overvoltage
• Ability to detect a ground fault before a multiphase to ground fault evolves
• If impedance is introduced, limit ground fault current and associated damage
faults
• Provide good source of protection for other system.
NIRMA LTD. BHAVNAGAR
57. Continue…
• The lower the R the better the ground source
• The lower the R more damage to the generator on
internal ground fault
• Can expansive resistor as rating goes up.
• Ground current typically 200 to 400A.
NIRMA LTD. BHAVNAGAR
58. High impedance
• System ground source obtain from GSU.
• Uses principle reflects:
• Ground fault current typically: <=10A.
𝑅 𝑁𝐺𝑅 =
𝑅 𝑅
𝑉𝑃𝑅𝐼
𝑉𝑆𝐸𝐶
NIRMA LTD. BHAVNAGAR
59. Compensated.
• Most expensive because tuned reactor and
transformer.
• Uses reflected impedance from grounding
transformer, same as high impedance ground system
does
• Generator fault mitigated from ground fault.
• Reactor tuned against generator capacitance to
ground to limit ground fault current to very low
value. (can be less than 1A)
NIRMA LTD. BHAVNAGAR
60. Hybrid impedance grounding
• Has advantages of Low Z and High Z.
• Low Z grounded machine provides ground source for
other under normal condition.
• 51G acts as back protection for uncleared system
ground fault.
• 51G is too slow to protect generator for internal fault.
• Ground fault detected by 87GD element.
• Low Z path opened by vacuum switch.
• Only HighZ ground path is then available ao the high
ground path is limits the curret approximately 10A.
NIRMA LTD. BHAVNAGAR
62. Stator ground fault
• Traditional stator ground fault protection schemes include:
• Neutral over voltage
• Various third harmonic voltage dependent schemes.
• These exhibits sensitivity, security and clearing speed issue that may
subject a generator to prolonged low level ground faults that evolve
into damaging faults.
NIRMA LTD. BHAVNAGAR
64. NGT ratio selected that provides 120 to 240V for ground
fault at machine terminals
Max. L-G volts: 11/1.73 = 6.35kv.
Max. NGT volts at sec.= 6350/120=52.91VTRNIRMA LTD. BHAVNAGAR
65. Why do we care about faults near neutral?
• A fault at or near the neutral shunts the high resistance that saves the
stator from large currents with an internal ground fault.
• If generator operating with an undetected with ground fault near to
neutral is a accident waiting to happen.
• We can use third harmonic or injection technique for complete
coverage.
NIRMA LTD. BHAVNAGAR
66. Pole slipping protection
• The variation of impedance seen at the generator during pole
slipping.
• Trip signal is sent if the measured impedance crosses two
characteristics can be applied to increase the protection selectivity,
such as one or two blinders, MHO or a lenticular characteristics.
• The θ and blinder depends on the value of impedance
NIRMA LTD. BHAVNAGAR
69. • The impedance of the system and generator transformer determines the
forward reach of the lens, ZA and the transient reactance reach ZB.
• Width of the lens is set by the angle α and the line pp’, perpendicular to the
axis of the lens, is used to determine if the center of the impedance swing
during a transient is located in the generator.
• Normal operation is with the measured impedance in zone R1 if a pole slip
develops, the impedance locus will traverse through zone R2,R3, R4, when
entering R4 zone trip signal is issued provided impedance lies below
reactance line pp’ and hence the locus of swing lies within or close to the
generator, the generator is pole slipping with respect to the rest of the
system.
NIRMA LTD. BHAVNAGAR
70. • If the locus lies above line PP’, the swing lies far out in the power
system- i.e. one part of the power system, including the protected
generator, is swinging against the rest of the network. Tripping may
still occur, but only if swinging is prolonged meaning that the power
system is in danger of complete break up. Further confidence checks
are introduce by requiring that the impedance locus spends a
minimum time within each zone for the pole slipping condition to be
valid.
NIRMA LTD. BHAVNAGAR
71. • The trip signal may also be delayed for a number of slip cycles even if
a generator pole slip occurs this is to both provided confirmation of a
pole slipping condition and allow time for other relays to operate if
the cause of the pole slip lies somewhere in the power system.
Should the impedance locus traverse the zones in any other
sequence, tripping is blocked.
NIRMA LTD. BHAVNAGAR
72. Generator Excitation System
• Main task of the excitation is to provide an adjustable DC current to
excite the winding of the generator, to meet the requirement for
generator normal operation. Controlling the excitation of the
synchronous generator is one of the main means to control generator
operation.
• Function of the excitation system:
1. Maintain the end voltage of the generator
2. Control the disturbution of reactive power
3. Improve the stability of synchronous generator paralleling
operation.
NIRMA LTD. BHAVNAGAR
73. • Alternator mainly two types are following:
1. Separately excited system
2. self excited system.
• Separately excited system have PMG powering the automatic voltage
regulator and there is one isolation transformer for sensing the
voltage for AVR and in the other hand for self-excited alternator, there
is residual magnetism in the exciter field to initialize the voltage ramp-
up process and after voltage build-up, isolation transformer which is
responsible for voltage sensing for AVR, start powering the AVR as
well.
NIRMA LTD. BHAVNAGAR
74. Continue…
• Self excited generator is responsible for two things.
1. Sensing voltage
2. Powering AVR after initial voltage build-up due to residual
magnetism.
NIRMA LTD. BHAVNAGAR
76. Self excited alternator problem- lack of
residual magnetism
• Some times there is no voltage build up in the self excited alternator,
the reason is lack of residual magnetism.
• So for that remove the AVR need to connect the field with the battery
and blocking diode to the exciter field and after that start the engine,
if you see now voltage is building up, then It is confirm that exciter
field has been flashed successfully. Now stop the engine and remove
the battery and blocking diode , connect the AVR and again start the
engine to make sure that the alternator is back in operation.
NIRMA LTD. BHAVNAGAR
77. Advantage of PMG Excitation support systems
• A PMG is appropriate regulator which provide constant voltage input
to the generator’s terminal voltage.
• When the load on the generator is nonlinear due to thyristor power
supplies such as UPS system.
• The load may produce notches on the power rectifiers in a shunt
excited generator’s AVR. When this occur generator’s terminal voltage
get unstable.
• PMG have very strong magnetic field. It eliminates field flashing.
• Strong and very fast voltage build-up.
NIRMA LTD. BHAVNAGAR