Checking Three Phase Motor Phase Sequence and Generator Set Instruments

1. Phase Sequence Detection of Three-Phase AC Motors Without a Phase Sequence Meter

When a phase sequence meter is unavailable, connect a three-phase AC motor with a known rotation direction. If the motor rotates correctly after corresponding connections, the phase sequence of the tested generator’s output terminals is correct; otherwise, it is incorrect.

2. Inspection of Indicator Instruments on Generator Set Control Panels

During no-load and full-load operation, simultaneously record the readings from high-precision test bench instruments (installed on test benches as specified by test standards, typically with required accuracy classes) and generator set instruments (installed on the unit’s control panel). For ammeters and power meters using current sensors, the actual current and power values must be calculated.

The accuracy of the generator set instruments is determined by the percentage of the difference between the set instrument reading and the test bench instrument reading relative to the full-scale range of the set instrument. The result must meet the accuracy class marked on the control panel instruments.

Example: If the test bench voltmeter (0.5 accuracy class) reads 400V, and the generator set voltmeter (full-scale 500V, marked 1.5 accuracy class) reads 395V, the actual accuracy of the set voltmeter is calculated as follows:

Accuracy=(∣395−400∣500)×100%=1.0% \text{Accuracy} = \left( \frac{|395 - 400|}{500} \right) \times 100\% = 1.0\% Accuracy=(500∣395−400∣)×100%=1.0%

This meets the 1.5 accuracy class requirement, confirming the voltmeter is qualified.

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