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09873171145 [email protected]
Generator Basics
• Generator is a machine which converts
Mechanical energy to Electrical energy
• Magnetic Induction Principle
• An emf is induced in a coil whenever
a) a coil cuts through a magnetic field
b) a magnetic field cuts through a coil
Generator Structure
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Generator Basics
• emf induction is due to relative motion
between two parts ( coil & magnetic field)
• Relative motion is by Rotation
• Two mechanical parts :
Field - Part which produces magnetism (Rotor)
Armature – part where emf is induced (Stator)
Generator Structure
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Generator BasicsGenerator Structure
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Generator Basics
• Prime Mover
• Rotor (Exciter)
• Stator
Generator components
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Generator Basics
• Source of mechanical power for
relative motion
• Two classes of Prime movers :
High Speed : Steam & Gas Turbines
Low Speed : IC engines, Water turbines and
DC motors
Generator components- Prime mover
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Generator Basics
• Type of prime mover plays an important role
in a generator installation
Many characteristics of alternator
and its construction depend upon
Speed at which the rotor is turned.
Generator components- Prime mover
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Generator Basics
• Two types are used in rotating field alternators
- Turbine driven rotor
( used where prime mover is a high speed turbine)
- salient pole rotor
( used with low speed prime movers)
Generator components- Rotors
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Generator BasicsGenerator components- Rotors
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Generator Basics
• Many types based on
- Power out put
- Voltage output
- Type of cooling
- Number of phases
Generator components- Stators
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Generator BasicsGenerator components-
Simplified schematic of 3 ph. Stator
• Three single phase windings
displaced by 120 degrees
• Star or Delta connection
• Neutral may or may not be
brought out
• No. of terminals can be
3,4, or 6
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Generator Basics
Out-puts from a Generator
Three phase ac power at :
-Rated Voltage
-Rated Frequency
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Generator Basics
Out-puts from a Generator – Common Ratings
Small Generators : 25 kVA to 300 kVA
Medium Size Generators : 500 kVA to 1 MVA
Large size Generators : 1 MVA to 25 MVA
Power Plant Generators: 110 MW to 500 MW
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Generator Basics
Out-puts from a Generator - Frequency
• Frequency depends up on the
Speed of Rotation ( direct proportion)
• F = PN / 120 where
F = frequency in Hz
P = No. of poles
N = speed of rotation in RPM
( 120 is a constant to convert minutes to seconds
and poles to pole pairs)
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Generator Basics
Out-puts from a Generator - Frequency
• Nominal frequency = 50 Hz
• Generator frequency can vary due to
load fluctuations
• Frequency Regulation is mainly
by adjusting the speed
• speed is controlled by varying the fuel
input to the prime mover ( Governor control)
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Generator Basics
Out-puts from a Generator - Governors
• Governor ensures frequency at a set value
by increasing / decreasing the fuel input
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Generator Basics
Out-puts from a Generator - Governors
Two types of Governors :
Pneumatic : Fuel flow is controlled by
valve position control
Control Input : DC Voltage
Electronic : Fuel flow is controlled by
a total servo mechanism
Control input : DC Voltage pulses
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Generator Basics
Out-puts from a Generator - Voltage
• Voltage is induced in the stator winding
• Terminal voltage depends upon :
1) No. of conductors in series per winding
2) Speed at which magnetic field cuts the winding
3) Strength of the magnetic field
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Generator Basics
Out-puts from a Generator – Voltage Control
• Nominal Voltage = 415 V, 11 kV
• Voltage can vary due to load fluctuations
• Terminal voltage is controlled by
varying the Strength of magnetic field
= varying the current through the field coil
= varying the voltage applied to the field coil
(Exciter control)
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Generator BasicsTypical Exciter
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Generator Basics
Out-puts from a Generator – Exciters
External to Exciter Transformer
Generator Rectifier Unit
Controls
Built on the Small DC machine
Generator attached to same shaft
of generator
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Generator Basics
Neutral terminal
• Very important from the point of view of
a) reducing the fault currents
b) providing effective protection
• should be used for medium size and above
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Generator Basics
Neutral Grounding Resistors
Protect generators from excessive fault currents
Provides safety for operators
Provides protection for connected equipment
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Generator Basics
Generator Impedance
R
X
Synchronous Reactance
Transient reactance
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GENERATOR PROTECTION
ϕϕϕϕ = 0o (360O) FORWARD RESISTIVE
ϕϕϕϕ = +30o FORWARD RESISTIVE + FORWARD CAPACITIVE
ϕϕϕϕ = +60o FORWARD RESISTIVE + FORWARD CAPACITIVE
ϕϕϕϕ = +90o FORWARD CAPACITIVE (LOSS OF FIELD)
ϕϕϕϕ = +120o REVERSE RESISTIVE + FORWADRD CAPACITIVE
ϕϕϕϕ = +150o REVERSE RESISTIVE + FORWARD CAPACITIVE
ϕϕϕϕ = +180o REVERSE RESISTIVE
ϕϕϕϕ = +210o (-150O) REVERSE RESISTIVE + FORWARD INDUCTIVE
ϕϕϕϕ = +240o (-120O) REVERSE RESISTIVE + FORWARD INDUCTIVE
ϕϕϕϕ = +270o (-90O) FORWARD INDUCTIVE
ϕϕϕϕ = +300o (-60O) FORWARD INDUCTIVE + FORWARD RESISTIVE
ϕϕϕϕ = +330o (-30O) FORWARD INDUCTIVE + FORWARD RESISTIVE
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Generator Basics
Generator Behaviour
Influence of Rotor on Stator
Influence of Stator on Rotor
Effect of Load on Generator
Effect of excitation on Generator Impedance
Influence of generator on prime mover
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Generator Basics
Generator Behaviour
Influence of Rotor on Stator
• Only variable is excitation current
• Terminal voltage is proportional to
Excitation current
• Will influence Generator impedance
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Generator Basics
Generator Behaviour
Influence of Stator on Rotor
• Only variable is the load
• Unbalance loads can cause rotor heating
• Excessive loads can cause out of step
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Generator Basics
Generator Behaviour
Effect of Load on Generator
• Load will decide the pF of generator
• Over loads can cause speed reduction
• Unbalance loads can cause over heating
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Generator Basics
Generator Behaviour
Effect of excitation on Generator Impedance
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Generator Basics
Power output from Generator
Active power kW Controlled by Governor
Reactive Power kVA Controlled by Exciter
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GENERATOR PROTECTION
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� TURBO GENERATOR
� DIESEL GENERATOR
� HYDRO GENERATOR
� WIND GENERATOR
GENERATOR PROTECTION
TYPES OF GENERATORS
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SUB SYSTEMS OF GENERATORS
� PRIME MOVER
� EXCITATION SYSTEM
� VOLTAGE REGULATOR
� GOVERNOR
� COOLING SYSTEM
GENERATOR PROTECTION
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FAULTS IN GENERATOR
� EXTERNAL FAULTS
� INTERNAL FAULTS
� ROTOR EARTH FAULT
� FAULTS RELATED TO SUB SYSTEMS
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EXTERNAL FAULTS
OVER LOADING
UNBALANCE LOADING
SHORT CIRCUIT
EARTH FAULT
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INTERNAL FAULTS
� PHASE TO PHASE FAULTS IN WINDINGS
� PHASE TO EARTH FAULTS
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FAULTS RELATED TO SUB-SYSTEMS
� UNDER VOLTAGE
� OVER VOLTAGE
� UNDER FREQUENCY
� OVER FREQUENCY
� REVERSE POWER
� LOSS OF EXCITATION
� LOW-FORWARD POWER
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GENERATOR PROTECTION
TYPES OF FAULTS (STATOR SIDE)
VOLTAGE RESTRAINED OVER CURRENT
THERMAL OVER LOAD
CURRENT UNBALANCE
OVER VOLTAGE
UNDER VOLTAGE
OVER FREQUENCY
UNDER FREQUENCY
LOSS OF FIELD
REVERSE POWER
UNDER POWER
OUT OF STEP
INADVERTANT ENERGISATION
EARTH FAULT (100%)
EARTH FAULT (95%)
GENERATOR DIFFERENTIAL
OVER EXCITATION (V/Hz)
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GENERATOR PROTECTION
TYPES OF FAULTS (ROTOR SIDE)
ROTOR EARTH FAULT
EXCITATION UNDER VOLTAGE
EXCITATION UNDER CURRENT
DIODE FAILURE
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SINGLE LINE DIAGRAM
GENERATOR PROTECTION
G
rrrr
49 46 40
81
32
87G
51V 37 64
5927
11 kV
6.6 MW
400/5
400/5
400/5
11000/110v
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GENERATOR PROTECTION
VOLTAGE RESTRAINED OVER CURRENTVOLTAGE RESTRAINED OVER CURRENT
- WHEN O/C FAULT, TERMINAL VOLTAGE REDUCES.
- RELAY MAY NOT TRIP, SINCE FAULT CURRENT
THROUGH RELAY MAY BE LESS THAN SET POINT
NECESSARY TO VARY THE O/C PICK UP SETTING
WITH RESPECT TO VOLTAGE
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GENERATOR PROTECTION
VOLTAGE RESTRAINED OVER CURRENTVOLTAGE RESTRAINED OVER CURRENT
V/Vs
I*/ [I>]
0.2 0.8
0.2
1.0
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GENERATOR PROTECTION
LOSS OF FIELD IN GENERATORS
GENERATOR WILL OVER SPEED &
OPERATE AS AN INDUCTION GENERATOR
(OVER SPEEDS OF THE ORDER OF 2 TO 5% )
GENERATOR WILL CONTINUE TO DELIVER POWER
WILL DERIVE EXCITATION FROM THE SYSTEM
STATOR CURRENT WILL BE 200%
THERE WILL BE HEAVY ROTOR CURRENT
RESULTS IN OVER HEATING
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GENERATOR PROTECTION
LOSS OF FIELD IN GENERATORS
PHASE ANGLE BETWEEN
ANGLE ϕϕϕϕ VOLTAGE & CURRENT
IMPEDANCE REPLICA OF
ANGLE αααα PHASE ANGLE
αααα = 360O - ϕϕϕϕ
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GENERATOR PROTECTION
ϕϕϕϕ = 0o (360O) FORWARD RESISTIVE
ϕϕϕϕ = +30o FORWARD RESISTIVE + FORWARD CAPACITIVE
ϕϕϕϕ = +60o FORWARD RESISTIVE + FORWARD CAPACITIVE
ϕϕϕϕ = +90o FORWARD CAPACITIVE (LOSS OF FIELD)
ϕϕϕϕ = +120o REVERSE RESISTIVE + FORWADRD CAPACITIVE
ϕϕϕϕ = +150o REVERSE RESISTIVE + FORWARD CAPACITIVE
ϕϕϕϕ = +180o REVERSE RESISTIVE
ϕϕϕϕ = +210o (-150O) REVERSE RESISTIVE + FORWARD INDUCTIVE
ϕϕϕϕ = +240o (-120O) REVERSE RESISTIVE + FORWARD INDUCTIVE
ϕϕϕϕ = +270o (-90O) FORWARD INDUCTIVE
ϕϕϕϕ = +300o (-60O) FORWARD INDUCTIVE + FORWARD RESISTIVE
ϕϕϕϕ = +330o (-30O) FORWARD INDUCTIVE + FORWARD RESISTIVE
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GENERATOR PROTECTION
R
X
Z
LOSS OF
FIELD
NORMAL
LOSS OF FIELD
PROTECTION
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GENERATOR PROTECTION
R
X
Z
LOSS OF
FIELD
NORMAL
K1
K2
LOSS OF FIELD
PROTECTION
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GENERATOR PROTECTION
REVERSE POWER GENERATORS
GENERATOR WILL BECOME MOTOR
HARMFUL TO THE PRIME MOVER
( STEAM TURBINE WILL OVER HEAT)
(DIESEL ENGINE WILL EXPLODE DUE
TO UNBURNT FUEL)
(HYDRAULIC TUBINE WILL HAVE CAVITATION)
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GENERATOR PROTECTION
STATOR EARTH FAULT
95% EARTH FAULT NORMAL RELAY
100% EARTH FAULT SPECIAL RELAY
SENSES ABSENCE
OF 3RD HARMONICS
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GENERATOR PROTECTION
INADVERTANT ENERGISATION
- APPLICATION OF FULL VOLTAGE AT
STANDSTILL
COASTING TO STOP
BEFORE SYNCHRONISM
- PRESENCE OF UNBALANCE VOLTAGE DUE TO
FLASH OVER AT IONE OR TWO POLES OF BREAKER
GENERATOR FORCED TO START AS
INDUCTION MOTOR RESULTING IN MECHANICAL
DAMAGES TO PRIME MOVER AND EXCESSIVE
HEATING IN THE ROTOR
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GENERATOR PROTECTION
V/Hz PROTECTION
- INCORRECT VOLTAGE REGULATOR ACTION
- LOAD THROW - OFF
- SUDDEN OVER VOLTAGE / OVER FREQUENCY
RESULTS IN OVER FLUXING OF GENERATOR
AND OVER HEATING
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rrrr rrrr
rrrrrrrr rrrr
-
BC1 BC2
B1 B2 B3
G1 G2 G3
PT1 PT2 PT3
CT1 CT2 CT3
BUS-1 BUS-2 BUS-3
PULSES FOR
GOVERNOR &
EXCITER
PULSES FOR
GOVERNOR &
EXCITER
PULSES FOR
GOVERNOR &
EXCITER
LOAD SHARING OF GENERATORS
LSR = LOAD SHARING RELAY
Fig. -1
L
S
R
L
S
R
L
S
R
L
S
R
L
S
R
L
S
R
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rrrr
GRID ISLANDING SCHEME
rrrr
REVERSE POWER RELAY
LOW FORWARD POWER RELAY
UNDER VOLTAGE RELAY
DIRECTIONAL O/C + E/F RELAY
dF/dT RELAY
UNDER FREQ. RELAY
OVER FREQ. RELAY
VECTOR SURGE RELAY
DG
GRID INCOMER
TRANSFORMER
PLANT
LOADS
rrrrrrrrrrrr
Fig. -2
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SYNCHRONISATION OF GENERATORS
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SYNCHRONISING IS THE PROCESS OF
ELECTRICALLY CONNECTING
TWO AC POWER SOURCES WITH
ROTATING MACHINES
WITHOUT ANY DISTURBANCE TO
EXISTING SYSTEM AND
WITHOUT ANY DAMAGE TO THE
EXISTING SYSTEM
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SYNCHRONISATION
SINGLE GENERATOR TO A BUS
(DEAD BUS / LIVE BUS SYNCH.)
MULTIPLE GENERATORS TO A BUS
(SIZE, VINTAGE, RESPONSE TIMES)
AUTO CHANGEOVER IN BUS CONNECTIONS
MANUAL & AUTO SYNCHRONISATION
REVERSE SYNCHRONISATION
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rrrrrrrr B1 B2
G1 G2
PT1 PT2
COMMON BUS
SYNCHRONISING OF GENERATORS
SCM 21
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RESULTS OF INCORRECT SYNCHRONISATION
FREQUENCY ACTIVE POWER FLOW
HIGH FREQ. TO LOW FREQ.
PHASE ANGLE JOLT TO THE SYSTEM
FATIGUE TO SHAFT
DAMAGE TO BEARINGS
OVER HEATING OF STATOR
VOLTAGE REACIVE POWER FLOW
HIGH VOLTAGE TO LOW VOLTAGE
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rrrr
REVERSE SYNCHRONISATION
rrrr
DG
GRID INCOMER
TRANSFORMER
PLANT
LOADS
rrrrrrrrrrrr
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GENERATORS IN PARALLEL
TYPES OF PARALLEL OPERATION
�MULTIPLE GENERATORS ON A COMMON BUS
WITHOUT CONNECTION TO GRID
�GENERATORS CONNENCTED TO GRID IN
IMPORT ONLY MODE
�GENERATORS CONNECTED TO GRID IN
IMPORT + EXPORT MODE
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GENERATORS IN PARALLEL
ISSUES TO BE ADDRESSED
BASIC PROTECTIONS
•SEQUENTIAL STARTING & SYNCHRONISATION
•NEUTRAL SWITCHING LOGIC
• INSTABILITY & HUNTING AT HIGHER POWER O/P
•CASCADED TRIPPING ON LOAD FLUCTUATION
•REVERSE POWER FLOW DUE TO BREAKER FAILURE
•POOR POWER FACTOR
•EFFECT OF GRID DISTURBANCES &
GRID ISLANDING SCHEMES
•LOAD MANAGEMENT AFTER ISLANDING
•REVERSE SYNCHRONISATION
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GENERATORS IN PARALLEL
BASIC PROTECTIONS
OVER CURRENT + E/F
THERMAL OVER LOAD
UNDER VOLTAGE + OVER VOLTAGE
UNDER FREQUENCY + OVER FREQUENCY
LOSS OF FIELD
CURRENT UNBALANCE
REVERSE POWER
DIFFERENTIAL + REF
ROTOR E/F
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GENERATORS IN PARALLEL
SEQUENTIAL STARTING & SYNCHRONISATION
AMF SCHEME
STARTING LOGIC
AUTO SYNCHRONISATION
- DEAD BUS SYNCHRONISATION (FIRST MACHINE)
STARTING/ STOPPING OF GENERATOR NEXT IN LINE
- LIVE BUS SYNCHRONISATION
(SUBSEQUENT MACHINES)
PT SWITCHING LOGIC
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GENERATORS IN PARALLEL
SEQUENTIAL STARTING & SYNCHRONISATION
MAINS FAILURE
DETECTION
I/C TRIP &
STARTING LOGIC
3 ATTEMPT
STARTERS
PT SWITCHING
LOGIC
AUTO SYNCH. OF
GENERATORS
CUT IN – CUT OUT
LOGIC
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GENERATORS IN PARALLEL
NEUTRAL SWITCHING LOGIC
MASTER GENERATOR NEUTRAL TO BE GROUNDED
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GENERATORS IN PARALLEL
INSTABILITY AT HIGHER O/P & CASCADED TRIPPING
ERRATIC RESPONSE TO LOAD FLUCTUATIONS
- DIFFERENT SIZES OF GENERATORS
- DIFFERENT VINTAGES OF GENERATORS
IMROPER LOAD ALLOCATION TO
EACH GENERATOR
OPERATOR’S LIMITATIONS
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rrrr rrrr
rrrrrrrr rrrr
-
BC1 BC2
B1 B2 B3
G1 G2 G3
PT1 PT2 PT3
CT1 CT2 CT3
BUS-1 BUS-2 BUS-3
PULSES FOR
GOVERNOR &
EXCITER
PULSES FOR
GOVERNOR &
EXCITER
PULSES FOR
GOVERNOR &
EXCITER
GENERATORS ON COMMON BUS – AUTO LOAD SHARING SCHEME
LSR = LOAD SHARING RELAY RRS
Fig. -1
L
S
R
L
S
R
L
S
R
L
S
R
L
S
R
L
S
R
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GENERATORS IN PARALLEL
REVERSE POWER FLOW
rrrr
rrrrrrrr
-
BC1
B1 B2
G1 G2
PT1 PT2
CT1 CT2
BUS-1 BUS-2
Fig. -2
RELAY
R1
RELAY
R2
G1 STOPS DUE TO
MECHANICAL PROBLEMS
B1 WILL NOT TRIP
G2 WILL FEED G1
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GENERATORS IN PARALLEL
POOR POWER FACTOR
rrrr
G1
PT1
CT1
BUS-1
PULSES FOR
GOVERNOR &
EXCITER
LSR = LOAD SHARING RELAY
L
S
R
L
S
R
rrrr
REFERENCE
VOLTAGE
SOURCE
GRID
KEEP RATIO OF
KW/KVAr CONSTANT
Fig. -3
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GENERATORS IN PARALLEL
HANDLING OF GRID DISTURBANCES
� GRID FAILURE
� GRID FAULT
� OVER LOAD IN THE GRID
� UNDER / OVER VOLTAGE IN THE GRID
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GENERATORS IN PARALLEL
rrrr
GRID ISLANDING SCHEME
rrrr
REVERSE POWER RELAY
LOW FORWARD POWER RELAY
UNDER VOLTAGE RELAY
DIRECTIONAL O/C + E/F RELAY
dF/dT RELAY
UNDER FREQ. RELAY
OVER FREQ. RELAY
VECTOR SURGE RELAY
DG
GRID INCOMER
TRANSFORMER
PLANT
LOADS
rrrrrrrrrrrr
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GENERATORS IN PARALLEL
LOAD MANAGEMENT AFTER ISLANDING
� LOAD SHEDDING- FREQUENCY BASED
- POWER BASED
� LOAD SHADING
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GENERATORS IN PARALLEL
REVERSE SYNCHRONISATION
� AUTO SYNCHRONISING
� LOCATION OF SYNCHRONISING
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THANK YOU