Ungrounded system (HRG), separately derived system

[fatuus]

Please help right away.

An HRG grounded xfmr secondary feeds a heat wheel type RTU. I am adding a zig-zag transformer in line to clear harmonics.

It is very difficult to add a grounding electrode to the transformer. I argue that since it is an un-grounded system no GE is necessary.

Am I wrong?

 

[texie]

Please help right away.

An HRG grounded xfmr secondary feeds a heat wheel type RTU. I am adding a zig-zag transformer in line to clear harmonics.

It is very difficult to add a grounding electrode to the transformer. I argue that since it is an un-grounded system no GE is necessary.

Am I wrong?

Sorry, but yes. Also note that this is not ungrounded system-it is a high-impedance grounded system.

 

[Ingenieur]

are you saying you have a wye secondary with neutral grounding resistor AND are adding a zig-zag?
do you have a sketch?

 

[Sahib]

A solidly grounded zigzag transformer will defeat the purpose of HRG.

 

[Jraef]

Maybe more fundamentally, if you have devices on the HRG system that are producing harmonics, you may need to rethink the entire setup. Power rectifier systems generally come with surge protection and CM noise mitigation devices that will not like being connected to an HRG system because they are referenced to ground, so they become a lower resistance path than your NGR and try to ground your ENTIRE system until they fail, often catastrophically. You could remove their ground references, but you also reduce their function so the generally recommended practice is to use a Drive Isolation Transformer to feed just those devices, and ground the secondary of that transformer. That could ALSO be a zig-zag isolation transformer if you so desire.