GP7 Ground Relay tripping.

[Pat Masterson]

Our GP7 has begun to trip the relay quite often. It seems to happen most when changing run levels, say from 3 to 2, or down to idle. We can reset it and go for quite aways, until we change notches again.
How does one figure out what the problem is? We have looked for burnt/broken wiring in all of the cabinets to no avail. Whats a good way to diagnose this problem? What else can we look for? thanks. -pat masterson

[csxengineer98]

can be some bad wireing down around the traction motors...or a traction motor itself... is there a traction motor cut out on the back wall? if so.. let it trip..then cut out a motor.. try it agin.. if it trips agin..cut out a differnt motor.. and so on till you cut out the problem motor.. if that dont help..you have to major problems else where..no matter what it is in my advice is call an electriction...

csx engineer 

[oltmannd]

Start with inspecting the traction motor commutators.  Look for broken/burnt brush leads. Also, you'll probably need to do a hi-pot test to see if the wiring insulation is good. 

[Rodney Beck]

I have done what csx said after finding out what caused the problem I tone up the mech department.

 

Rodney

[Pat Masterson]

oltmannd, is there a way to cut out one traction motor at a time? How does one do this?  -pat

[csxengineer98]

oltmannd, is there a way to cut out one traction motor at a time? How does one do this?  -pat

in the cab..on the back wall on the same door as the isolation switch..is there a traction motor cut out switchs there? it should say traction motor cut out on it if there is one...

csx engineer 

[oltmannd]

Doubtful that his GP7 had traction motor cutouts.

[csxengineer98]

Doubtful that his GP7 had traction motor cutouts.

depends on how long ago it was rebuilt..

csx engineer 

[rrboomer]

If the isolation switch is still inside the lower left elect cab door (facing toward long hood) there may be another three position switch in there also.  The arrow points straight up if all motors cut in, then nine o'clock position cuts out one truck and three o'clock the other truck. It's the same truck c/o switch EMD used on their SW models, been too many years I don't remember which position is which truck.

If it only KGR when changing throttle positions you may have a low voltage ground.  A couple of places to check would be the ER relay wiring and inside the throttle stand. Might also check for frayed wiring at the governor plug.

Is transition involved when the throttle changes/GR occurs?

[Rodney Beck]

Bad order the unit and let the mech department deal with it, I have done it before on the road yes it cost me some speed but I did not have the headache anymore.

 

Rodney

[Pat Masterson]

>Is transition involved when the throttle changes/GR occurs?

No, this will occur at very low speeds. no transition.  -pat

 

[Randy Stahl]

If it's happeneing when you throttle off look at the Generator field decay resistor and the companion contacts on the shunt field contactor. You may have either a bad resistor, wiring , interlock or quite possibly by now a bad main generator

[silicon212]

If it's happeneing when you throttle off look at the Generator field decay resistor and the companion contacts on the shunt field contactor. You may have either a bad resistor, wiring , interlock or quite possibly by now a bad main generator

Pat, Randy is a locomotive electrician, so I would probably consider this an excellent start.