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What is synchronizing?
The overall operation of ensuring that the two
alternating current supplies to be paralleled are
within prescribed limits, in a state of equal
magnitude, equal frequency and phase coincidencefollowed by closure of the appropriate switch to
parallel the two supplies
- Modern Power Station Practice, BEI, London
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Requirements for synchronizing
To achieve the synchronizing the following shall be satisfied
on either side of the circuit breaker
• Voltage Magnitudes are same
• Voltages are in Phase
• Frequencies are equal
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Types of synchronizing
System synchronising:
When two different parts of a system are connected together
(i.e. both Voltage Magnitude, Phase and Frequency cannot
be controlled like generator circuits)
For example Closing of a Bus coupler CB fed by twoTransformer feeders, the voltage magnitude can only be
varied through Tap changing mechanism
Generator synchronizingGenerator is connected to a Grid. The voltage magnitude,
Phase and frequency of the generator supply can be varied.
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Synchronizing methods
Manual synchronisingIt is performed by the operator using following synchronizing
devices. This is generally used for both Generator
synchronisation and System synchronisation
• Synchroscope
• Check Synchronising Relay• DV, DF Meters, Guard Relay
Automatic synchronisingIt is performed through “Automatic Synchronising Relay”. This
provides closed loop control for adjusting Speed & Voltage of
the Generator during synchronization. This is used for
Generator synchronisation
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Synchronizing Equipment
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Slip frequency
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Slip frequency / Frequency error
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Advance Angle
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Load pick-up after synchronising
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Criteria for Generator Synchronising
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Machine slower than system – Sub-synchronous
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Properly Synchronised
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Permissible Synchronising Criteria for Generators
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Procedure for Manual Synchronizing of a Generator
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Procedure for Auto Synchronizing of a Generator
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Sources of errors in Generator Synchronizing
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Mechanism of Wrong Synchonising of Generator
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Possible out of Synchronising
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Effect of Faulty Synchronising on Generator
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Precommissioning checks for Synchronising system
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