Neutral Ground of Delta-Wye Transformer

[shkim2000]

For the temporary commissioning purpose I have one 10MVA, 13.8kV/6.6kV delta/star transformer with 8.23% impendace. The neutral at the secondary is solidly grounded but in this case we may not achieve safety(damage and danger to human during fault) at short-circuit.
For this reason, in general current limiting device is applied to neutral connection.
At the moment, we am not able to affort extra money and time.
At the moment what is optimal/easy countermeaure in achieving safety ?

 

[jvamos]

Using your delta/star transformer you have only two ways to lower the phase-gnd fault current on the secondary side of the transformer. By either grounding the transformer through a resistance or reactance. Just a note - this will not do anything to the three phase fault levels.

 

[rcw retired EE]

Accept the high phase to ground fault current that the transformer can supply and lower the setting on all ground fault and zero sequence relaying to clear any fault faster.

 

[RalphChristie]

Well

If you do not want to spend extra money or time, there is not much you can do, except maybe to do what rcwilson suggested. But it is not always possible to lower these settings and there will always be a danger of touch-potentials and damage during a fault. Touch-potentials are the major issue. A few years back one of my colleagues was electrocuted due to a touch-potential during a ground-fault. It was also a solidly grounded system. (11/6.6kV)

To reduce ground-fault currents: neutral grounded through either resistance (high or low resistance) or reactance.
To limit touch potentials during ground-faults: neutral grounded through resistance (high resistance)


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