During a recent, planned S/D on one of our Fr.6 turbines we experienced a failed compressor bleed valve and the unit was tripped via "the big red button". We were then gonna setup the unit for an offline water wash. Our electric hydraulic pump motor (set for auto) didn't start during the trip. Should the electric hydraulic pump motor have started during the trip or could this be a sequencing issue? Thank you, Patrick.

 

The cut in sequence of the aux. hydraulic pump can be easily checked from the logic. Verify this by checking the sequence for L4HQ. If it's used the logic signal L14HS (HP speed <95%)will initiate the pump cut in signal (maybe via L4HQ_ON signal to the MCC).

In any case during coasting down post a trip, the hydraulic pressure is NOT required (the IGV, SRV and the GCV must be relieved from hydraulic pressure in order to close and remain closed)

Good Luck,
A. Oztas

 

Hydraulic oil pump does not come online during a machine trip. The hydraulic oil is used only in servo valve for fuel control and IGV control and it is not needed when the machine trip happens. further after machine coasts down only the AOP comes on line as it is needed for maintaining the bearing lube oil header pressure and also for ratcheting. so there is nothing wrong with the sequencing of the hydraulic oil pump (AHOP).

 

Here's the logic that A. Oztas was referring to:
<pre>
L14HSX L63HQ1LY L52HQ L4HQZ
---| |--------| |--------|/|------------------( )
| |
| |
L4 | L14HSZ |
---|/|-------------------|/|-----
</pre>
It's correct that Hyd. Pressure isn't required during a coastdown after a trip, and the above logic indicates that when the unit is above 14HS and the Aux. Hyd. Pump has been shut down and is operating on the Main Hyd. Pump that when the unit trips (L4 drops out when the unit is tripped) L4HQZ will remain a logic "1" which will keep the Aux. Hyd. Pump from running during a trip.

There will be pressure from the Main Hyd. Pump during the coastdown from a trip.

[The above logic is part of GE's "drop-out-to-run" philosophy. L4HQZ will be a logic "0" (<b>Z</b>ero) when the Aux. Hyd. Pump is to be started and running. When L4HQZ is a logic "1", the Aux. Hyd. Pump is to be stopped and not running.]