Substation Transformer Windings
Substation Transformer Windings
(OP)
What benefits\liabilities would be involved in constructing a 3Ph 10MVA Delta\GndY 69KV\12.47KV Transformer with Rectangualr vs Circular wound cores? Secondly what industry standards exist for Gnd protection on the high side of such a unit?






RE: Substation Transformer Windings
RE: Substation Transformer Windings
With the transformer full load current of 83.7A, a CT ratio of 100:5A would be selected. The ground fault relay can be set down to around 15% of the CT rating, which allows for unequal CT saturation during inrush conditions (lower setting possible with detailed calculation). An instantaneous ground overcurrent relay setting can also be applied, as there is no zero sequence current source on the transformer side of the feeder breaker - any zero sequence ground current flowing in the circuit can only be as the result of a ground fault in the transformer 69 kV feeder or the HV winding.
RE: Substation Transformer Windings
1. It appears that the transformer efficiencies are normally taken into consideration since the transformers usually run 24hr per day and 7days per week. Lower resistance of the transformer windings will lead to smaller RI**2 watt losses. This works in favor of square windings if one does not have to be committed to industry standards.
2. HV side delta is normally not required to have the ground protection.
RE: Substation Transformer Windings
RE: Substation Transformer Windings
RE: Substation Transformer Windings
generally the HV will be conducter type and the core is rectangular in nature. the core is held in position by s frame which is welded in construction.
the foil type rectangular winding have good short circuit withstand capacity due to the even distribution of the fault current in the foil and can have lower resistance with lower losses.
i would be intrested to know about the ABB design but the rectangular construction can be benefitial but the repairs of the same are a costly affair.
RE: Substation Transformer Windings
RE: Substation Transformer Windings
RE: Substation Transformer Windings