Resistor & Earthing Transformer Rating 1

[Kulog]

The secondary winding of a 6.6/0.100KV earthing transformer(Y-Delta)is connected in broken delta with resistor. The resistor is intended to limit the ground fault current to 30A. How to calculate the Resistor rating and the Earthing Transformer rating.

Any help is highly appreciated.

 

[rbulsara]

Refer to this link:

http://www.edsa.com/Shared Documents/GroundingXfrmrs.pdf

If the link truncates type in "/GroundingXfrmrs.pdf"
after the ...documents/

 

[busbar]

In unfaulted conditions, the grounded-wye/broken-delta transformer set will have 58V on each secondary, producing zero volts across broken delta. In a zero-impedance fault condition on the 6.6kV bus, two primary windings of the grounding-transformer set will see 6.6kV each increasing from the steady-state/unfaulted 3.8kV. The grounding-transformer secondary will see 100 volts on two of three windings, with 173 volts at the broken delta.

[In a faulted condition, voltage phasors on the transformer set can be visualized as 'open-delta' primary/'open-wye' secondary.]

Is “30 amperes” a prmanry or secondary quantity in the grounding transformer?

 

[jbartos]

Suggestion: Visit

http://www.ipc-resistors.com/pdf/GADDMKIII.pdf

for:
2.2 Artificial neutrals
See Table 1. For systems with voltages in excess of 4160V it is usually more convenient to use a broken-delta transformer arrangement and close the secondary delta with a current limiting Resistor. See Application Guide for Ungrounded and High-Resistance Grounded Systems C-400E for more details or call IPC.

 

[jbartos]

Suggestion: Visit

http://www.ipc-resistors.com/pdf/highres_grd.pdf

for the resistor calculation
However, the system grounding calculation should be performed first to determine which system grounding method is applicable.

 

[jbond]

I couldn't get that link to work Rbulsara, has the address changed? I understand that I'm replying to an old post, I'm trying to learn more about earthing transformers and how to size them.

Cheers,
Matt.