During our most recent start-up, we had a problem with the auxiliary hydraulic supply pump not securing once the turbine was at break away speed. We had to open the breaker in order to secure the pump so the sequence would complete to full speed no load.

I have an alarm in now on my Mark V stating "Auxiliary Motor Overload." This is alarm drop 230.

The alarm is 49X_ALM. The point 49X is a logic 1. I have manually reset the overload for both the hydraulic ratchet motor and the aux hydraulic supply motor but 49X does not reset. Has anyone experienced this condition. Any help would be appreciated.

 

The 49X circuit is usually one long, series string of overload contacts. Most of the overloads do not utilize an auxiliary TOL relay, but a few manufacturers utilized relays that were de-energized when the overload condition was detected.

If this is not the case for your unit, you then need to go to each and every motor starter one at a time and reset the overload while having someone watch the Alarm Display and tell you as soon as the alarm is cleared. While sometimes it's possible to feel a small click when depressing the TOL reset button when the TOL relay latches in after being reset, sometimes if the MCC is located on-base there is too much noise and vibration to be able to sense it.

If you do this for every motor starter and the alarm doesn't clear, then you need to find the MCC elementary drawing and find the 49X circuit drawing and work through the string until you find the one that's tripped and won't reset. You would use a voltmeter to check each TOL's terminals to find the open set(s) of contacts.

Sometimes, but not very often, more than one TOL is actuated, and when the contacts are in a series string this can be maddening.

One of the things more owners/operators complain about on GE-design heavy duty gas turbines, especially the ones packaged by GE, is this 49X string. Without good drawings, this can be difficult to troubleshoot, but not impossible, if one understands that it's usually a long, series string of TOL contacts. And, then by using a voltmeter one can work through the starters to find the problem(s) if the clicks can be detected.

When the Aux. Hyd. Pump is still running when the unit reaches FSNL, it will inhibit Auto Synchronization. All one needs to do to shut down the Aux. Hyd. Pump is to go to the pump motor's starter, and rotate the HOA (Hand-Off-Auto) switch to the OFF position <b>while someone is watching the hydraulic pressure gauge!</b> If the hydraulic pressure stays around normal when the Aux. Hyd. Pump stops with the switch held in the OFF position, you can release the switch back to the AUTO position and the pump motor should stay off.

If the Main Hyd. Pump pressure isn't high enough and the hydraulic pressure falls quickly when the Aux. Hyd. Pump motor stops release the HOA switch and the Aux. Hyd. Pump will start again. If the pressure drops but doesn't drop quickly but is still less than the low pressure switch setting, then the Main Hyd. Pump pressure compensator needs to be adjusted to get the pressure above the low pressure switch setting.

Some sites, when calibrating the IGVs, also use a scheme where they shut off the Aux. Hyd. Pump and then bleed down the Hyd. Accumulator pressure for safety reasons. This is a good idea, but if one forgets to close the bleed valve on the Accumulator or doesn't close it fully, the hydraulic pressure will be lower than it should be when only the Main Pump is running.

Also, some sites don't properly adjust the hydraulic system pressure relief valves. These relief valves are <b>NOT</b> the way to set the hydraulic pressure! These are to protect against failures of the pump compensators, and should not be used to adjust system pressure. (The only to properly set these relief valves is to use the pump compensators to raise pump pressure above the setting of the relief valves and make sure they relieve or are adjusted to the proper pressure.)

But, if you don't have a proper set of MCC elementaries, best to use the next shutdown to work through the motor starters and make your own drawing for this 49X circuit!

 

Thank you for the assistance. I have my MCC elementaries and I am starting my drawing for the 49X ckt.