Gas Turbine 125 V DC Ground 1

[ARAMCAWEE]

Greetings,

We have GE frame five gas turbines and we are suffering from intermittent 125 VDC ground. The DC ground is existed as long as the turbine is running, as soon as soon the turbine is down the ground disappeared. Sometimes the ground is going on and off while the turbine is running, yet, it will not be existed as soon the turbine is down. There is only two wires that carry the DC from the battery to all DC devices in the turbine which make it almost impossible to detected it.

On of the proposal we are studying is having a separate DC circuit for each DC device in the turbine. Yet, my question is that: is there any type of equipment or a device that can detect the DC ground in a turbine while the turbine is running?? Is there any DC grounding online monitoring system available in the market that can be used in the gas turbine???

Regards,,

 

[ScottyUK]

Aramcawee,

Lets clarify your requirement a little:

1) Do you want to detect the ground fault

or

2) Do you want to locate the ground fault

As you already know there is a ground fault, I'll assume that 2) applies and 1) is already taken care of.

One method is 'divide and conquer' - split the system in half, determine which half is faulted, split again, repeat... very labourious, and tricky or impossible if the unit is running. One thing that springs to mind is that a solenoid coil supply or similar is a likely cause. Typically these aren't energised until the unit is running, hence the reason that the fault doesn't show up when the unit is shut down.

There are a number of instruments which inject low frequency current on to the DC pole with the earth fault, with the return current passing through earth. A receiver unit is used to trace the signal to the fault. One such instrument is the 'Grouser' which is available in the UK. There are a few others which have been mentioned previously in Eng-Tips. They are effective, although some skill is required in their application.



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If we learn from our mistakes,
I'm getting a great education!

 

[mc5w]

You can get split core window type direct current transducers from Flex-Core. These are a similar on concept to split core current transformers. You would also need to connect a grounding resistor such as a baseboard electric heater to the 125 VDC power source to provide enough current to actuate the transducer but without creating a high current ground fault.

 

[abeltio]

GE has different control systems.
the more advanced the vintage of your control system the troubleshooting of the 125vdc ground fault will be easier.

your comment that the ground is detected with the unit running is not clear.

if this is a new situation: check for water, damaged cables in all junction boxes.

what is important is WHEN the ground is detected... i.e. at what speed or load level.


at different speeds, different things happen... solenoids energize or de-energize, excitation starts etc.
i.e. if the ground is detected after the start sequence is complete but the unit is not synchronized... may be the ground is related to the bleed valves or the excitation

if the ground is detected after the unit is synchronized, may be it is related to the generator breaker circuit.

a complete troubleshooting will require shutting the unit down and isolating each circuit, eventually you will find it checking each termination.

saludos.
a.

saludos.
a.

 

[Sargardani]

As Scotty indicated your best bet would be to use a Battery Ground Fault Locator. I have personally used it to locate ground faults in hydro power plants. I would say it's a great piece of equipment.... allowing you to trace ground faults without having to shut the unit down. In fact without the need to sectionalize by switching off the dc supply....which could lead to other problems.



Sarg