Electrical

Why synchronizing is required in an electrical power system?

What is synchronizing?

In an electrical power system synchronizing is the process of interconnecting two AC power sources and this must be done with fewer disturbances. We can connect different power systems by using a circuit breaker. In order to connect two power systems certain factors must be considered like the magnitude of the voltage must be the same, both the voltage must be in the same phase, and the frequencies should be equal. Collectively, frequency and voltage matching is called synchronization.

What is the requirement of a control system for synchronizing?

  • It should compare the magnitude and frequency and should indicate their relative status
  • The adjustment and of the voltage and frequency must be facilitated
  • Check for synchronism
  • Synchronism breaker closure must be facilitated
  • The synchronizing systems must be isolated after breaker closure

What is the operational requirement which will be needed for synchronization?

The speed and voltage must be kept higher so that the reverse power and reverse KVAR trip can be prevented. Check the neutral isolator condition. In case of medium and low resistance grounding the neutral of any of the machines should be kept closed and this is done to prevent the earth fault relay operation.

What could happen if the synchronization is faulty?

  • The equipment could be damaged
  • There will be system disturbances such as power oscillations and voltage depression
  • In the case of the relay, there could be reverse operation and loss of field

How to do the pre-commissioning checks in a synchronizing system?

  • Check if the wire connection to the terminal block or the synchronizing machine is proper or not
  • Phase sequence should be checked by a phase sequence indicator
  • The voltage across the terminals should be measured
  • Check the synchronizing relay
  • Waveform measurement should be taken

What are the different types of synchronization?

Manual synchronization  

This synchronization is done by the operator by using certain synchronizing devices such as synchroscope, check synchronizing relay, and DF meters. This type of synchronization is used to synchronize the generator and the system. This type of synchronizing is done for many machines, while doing this synchronization the operator controls the speed and voltage of the machine or system. The major advantage of manual synchronization is that it is really simple and economical. In this process, we can use a sync check relay and the sync check relay would only allow the breaker closure only if the phase angle, frequency, and voltage are within the predetermined limits. The manual method will be useful for the no-load operation and for the normal frequency condition. The major disadvantage of a manual operation is that in case of an emergency it is not possible to synchronize quickly. So in the substation or for any industrial purpose auto-synchronization will be used.

Auto synchronization

The automatic synchronization is done by using a synchronizing relay. By using this closed-loop control can be done in order to adjust the speed and voltage of the generator while synchronization and this type of synchronization are mostly done for the generator. In case of emergencies, we would require automatic devices to turn off the main switch of an incoming machine and this can be easily done by auto-synchronization.

Advantages of auto synchronization

  • It would verify if the phase sequence of the incoming machine is proper, and if not it will take required actions
  • The frequency of the machine will be compared to the busbar frequency and it would adjust the frequency if required
  • Machine voltage will be checked to that of the busbar and it would take required actions for that if necessary
  • The changes are done by using the software so no wire changing won’t be required
  • There is no need for manual intervention
  • PLC is used in this synchronization and because of this the number of relays and contactors will be reduced

Advanced synchronizer

  • Sensing and control signal switching can be removed by using programmable I/O and VT input
  • Peer to peer synchrophasors  
  • The remote control is possible by fiber optics

A synchroscope can be used to determine the synchronization between two-system. By using this the operator indication can be improved and there is no need for physical signal switching.

What are the different sources of errors which can be seen in a synchronizing system?

  • Burdens
  • Phase error and the voltage transfer ratio
  • Lead resistance, there must not be any voltage drop in the interconnecting cable
  • Interposing potential transformer
  • Errors during connecting instruments manually

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