Fault tester 1

[tulum]

Hello,

I have a 13800-1050Y/606 transformer that is resistance grounded on the secondary with a 17.4K NGR. All the necessary GF relays are in-place. However, we would like to install a ground fault test unit on one of the phases to ground. It basically consists of a fused (2A fuse) contact from a test contactor in series with a 15K,100W variable resistor.

My question is:

Is a 600V rating sufficient for the fuse, contactor arrangment? Or is the line voltage of 1050V required?

I know the phase voltage is all the tester will normally see, however during a fault on another phase will the tester phase not see a larger value than Vphase? If so what would be the value?

 

[jbartos]

Suggestions marked ///\\I have a 13800-1050Y/606 transformer that is resistance grounded on the secondary with a 17.4K NGR. All the necessary GF relays are in-place. However, we would like to install a ground fault test unit on one of the phases to ground. It basically consists of a fused (2A fuse) contact from a test contactor in series with a 15K,100W variable resistor.

My question is:

Is a 600V rating sufficient for the fuse, contactor arrangement? Or is the line voltage of 1050V required?
///Supposing that the ground is already experiencing an impression of a phase voltage to the ground, then by connecting your tester rated 600V from another phase to ground, the tester would experience 1050V phase to phase voltage. Therefore, 1050V rating or higher is recommended to be on the safe side.\\I know the phase voltage is all the tester will normally see, however during a fault on another phase will the tester phase not see a larger value than Vphase?
///Yes, see my comment above.\\ If so what would be the value?
///1050V rms nominal or higher during overvoltages and transients.\\

 

[tulum]

Thanks again Jbartos...

I will use a rating higher than 1050v... Good explanation.

regards,
Tulum

 

[busbar]

If the neutral terminal of the 1050Y/606V winding is not solidly grounded, then using 600V components would be a misapplication. There is a method used for ground detection and transient damping in wye-connected medium voltage generators, and a version of that here would be to connect a 600:120V transfomer primary between the winding neutral and ground, and the load the secondary with a 600V-class resistor, {and contactor as desired} and a low-pickup, high-continuous-withstand ground-voltage relay—typically termed a 59G device.

Machine-tool control-power transformers at this voltage seem the be catalog items up to 750VA. It would not be desirable nor recommended practice to fuse the grounding-transformer primary.