Neutral earthing
Neutral earthing
(OP)
Why are liquid earthing resistors used on powerstaion generator earths and at other parts of the network where the voltage is relatively low, yet solid earths are used on 275Kv etc?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: Neutral earthing
RE: Neutral earthing
RE: Neutral earthing
RE: Neutral earthing
On the LV/station-auxiliary side, typically resistance-grounded design limits ground-fault and circulating-current flow and it’s easier to make lower-voltage windings with proportionately higher BIL design. The lowside exposure to overvoltage is limited by having only relatively short-run bus/localized loads.
Negative-sequence currents can flow on both sides of the transformer; where zero-sequence current will only exist on the high [line] side. Rotating machinery is more easily damaged by heating from negative-sequence current when compared to transformers.
All boils down to economics.
RE: Neutral earthing
High voltage systems are generally solidly grounded to minimize the transient line to ground voltages on unfaulted phases during ground faults and to permit reduced insulation at the neutral of large transformers. It is not uncommon in many Asian countries (and maybe Europe as well) to operate some large generator step-up transformer neutrals ungrounded (or resistance grounded) to reduce the ground fault duty on the high voltage system. A grounding switch is usually provided to permit selectively grounding only certain transformers. This practice results in very expensive transformers at the higher voltages because the neutrals have to be fully insulated. I have not seen this done in North America.