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The alternating current module 3.2 measures the phase currents on the consumer side and neutral side of a generator. The ACM3.2 uses the measurements to detect phase-to-phase faults or phase-to-earth faults in earthed generator systems. The protection consists of:

  • A stabilised stage that uses a dual-slope operating characteristic. This current restraint approach is also known as biased differential protection.
  • A high set differential stage (non-stabilised).

Physical connections

  • 1 × 3-phase current measurement consumer side
    • 1 or 5 A AC (nominal)
  • 1 × 3-phase current measurement neural side
    • 1 or 5 A AC (nominal)

Current measurement characteristics

The ACM3.2 has two sets of terminals for current measurement. 

  • The first set of terminals measures the current at the consumer side of the generator. 
  • The second set of terminals measures the current at the neutral side of the generator. 
  • The ACM3.2 uses these measurements for logging, alarms and protective functions relating to differential current protection in the system.

Frequency measurements

  • Provides robust frequency detection in environments with electrical noise.


  • ANSI 87G differential protection for generators