Get in Step with Synchronization


This paper presents a review of power-system synchronization. When two sources are paralleled, it is crucial to close the interconnecting circuit breaker when both sources are in voltage, frequency, and phase coincidence.

Operators can synchronize manually, or use the latest, state-of-the-art autosynchronizers (device 25A) and sync-check relays (ANSI/IEEE device 25) to automate closing. Generator and bus synchronization share most principles, with some important differences for each type of synchronization. For generation plants, closing manually or applying an automatic synchronizer primarily depends on the plant configuration and operating mode. For bus-line applications, synchronizing depends on power-system stiffness, motor loads, and whether a wye-delta transformer is between the line and bus. Methods for attaining proper synch-check and fast synchronization are discussed.

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 DECS-250 Digital Excitation Control System
 DECS-250N Digital Excitation Control System with Negative Forcing
 DECS-250E Digital Excitation Control System
 DECS-2100 Static Excitation System
 Hydroelectric Generator

Synchronization is the process of matching the voltage, frequency, and phase angle of a source (a generator) to an existing power system, making it possible to operate these systems in parallel. When paralleled, the synchronized power systems can exchange power and load flows. Sources must have (nearly) identical voltage magnitude, frequency, and phase-angle relationships to safely parallel two systems. Proper synchronization provides the following outcomes:

  • Minimum disturbance to the two paralleled systems
  • Minimum shock to an oncoming generator (mechanical and electrical)
  • Money saveis because equipment lasts longer
  • Quick power to loads provided by rapid loading of the oncoming generator

When two segments of a grid are disconnected, these segments cannot exchange power and load again until the systems are brought back into synchronization.

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