AHOP Start without alarm


Thread Starter


AHop start in our unit with out any alarm of 63HQ of Frame VI machine having Mark VI control system. Actual reason of AHOP is unknown. May be the possibility of MHOP problem or Servo current changed from -4.5 to -31.1 before AHOP start.

1.GT-1 load dropped to 17.7 MW from 24.2MW in a matter of 960 msec.

2.GCV position changed from 45.48 % to 32.15%, whereas command for GCV opening was 46.2-47.8%

3.GCV servo current changed -4.35 to -31.6 %

4.All parameters started moving towards previous values, approx 500msec before AHOP running alarm appeared

In mark vi system above observation were found before AHOP start.
Please suggest to analyze the problem
Check your nitrogen precharge in the accumulators.

Sounds like there has been system upset which caused all the gas valves and IGV to rapidly move. The flow rate of the MHOP can not satisfy the transient consumptions, causing a drop in hydraulic oil pressure and the 88HQ to start on low pressure. The purpose of the accumulators, AH1-1/3, is to smooth out, or temporarily supply oil during short high demand periods. Precharge should be about 50% of nominal hydraulic pressure.

In an ideal world an alarm would be given, but that requires robust software ....