Ground Fault Setting

[ikhwanmy]

Need advice to setting the Ground Fault for the new motor install: How do I set below setting. If it is base on FLA what is the percentage?
1. GF Inhibit Time
2. GF Trip Delay
3. GF Trip Level
4. GF Warn Level

 

[iwire]

I send an RFI (Request For Information) to the engineer.

 

[ron]

I send an RFI (Request For Information) to the engineer.

You can guess or the engineer can guess. I would expect no GF current, so I set it pretty low (not zero, due to coupling) and adjust if it trips.

 

[Bugman1400]

In general, if the motor is connected 3PH, you can set the ground pickup 10% to 30% of the phase pickup. However, this only applies if you are using the residual of the phase CTs and not one of them 50:5 window CTs. The time delay will depend on the motor curve. You will need to ensure that the delay will coordinate with the upstream device but, generally, 0.2-0.3 seconds is used. As you can see, there are a lot of "generalities" here and more info is needed to give a more informed response.

 

[zog]

You can guess or the engineer can guess. I would expect no GF current, so I set it pretty low (not zero, due to coupling) and adjust if it trips.

Engineers never guess

Seriously though, what the OP needs is to have a coordination study done to determine the settings.

 

[ron]

Seriously though, what the OP needs is to have a coordination study done to determine the settings.

Even with a coordination study, they could lay the trip characteristics of the new GF trip next to an upstream device to gain selectivity, but it is still a guess on the setting relative to the motor characteristics. This is GF and not phase, so it is more of a guess.

 

[ikhwanmy]

Even with a coordination study, they could lay the trip characteristics of the new GF trip next to an upstream device to gain selectivity, but it is still a guess on the setting relative to the motor characteristics. This is GF and not phase, so it is more of a guess.

:happyno:. Thanks Guys. I shall set with the default setting and let see if the ground fault triggered.

 

[topgone]

Even with a coordination study, they could lay the trip characteristics of the new GF trip next to an upstream device to gain selectivity, but it is still a guess on the setting relative to the motor characteristics. This is GF and not phase, so it is more of a guess.

If it is humanly possible, you can do away with the usual guesswork->do a live test and measure the fault current to ground: ground the cables at the farthest end and then supply the line/equipment with a low-power AC source.

 

[Ingenieur]

vfd or fvnr makes a difference
hp, voltage would help
what does it trip? Shunt, uv, etc
start the motor measure with a clamp on
should see almost nothing under any normal circumstance
time til running and use that as the inhibit
the trip delay, low 6 cycles or less, no need for any really other than as a filter to avoid nuisance
I would set it at 5-10 times what you measure

but if a small lv motor I would not mess with any of that
use a zero seq relay
inhibit 5 sec
trip delay 6 cycles
trip 10% of fla or 10 A max, the lower the better
warning 1/2 of trip