Transformers in parallel
Transformers in parallel
(OP)
I wonder if somebody could help me. I want to know if it is possible to connect 2x 40 MVA transformers in parallel. The transformers does not have LTC's and their impedance don't vary more the 1% with each other. Would this be okay ? All the athor attributes are matched!
RE: Transformers in parallel
Unmatched neutral-grounding resistors or dissimilar configurations need investigation. Be aware of incraaesed fault duties in the paralleled configuration.
Also, you might anticipate significant var circulation between the two units—potentially on the order of 1MVAR.
RE: Transformers in parallel
RE: Transformers in parallel
1. The power output of the largest Tfo should not be more than twice that of the smallest unit.
2. Transformers must be supplied by the same network.
3. Connections must be the same length and have similar characteristics between the LV terminals (if you have MV/LV Tfo)or MV terminals (if you have HV/MV Tfos)and the coupling circuit breaker.
4.Couplings ( vector group) must be identical.
5.Short-circuit voltages must be identical (+-10%
6.Differences in secondary voltages between the different
Tfos must not exceed 0.4%.
7. The switch(tap-off) shall be positioned identically on each Tfo.
8.If the power outputs of the Tfos are different,the total available combined power output will be approx. 10% less
that the sum of power outputs for each Tfo.
RE: Transformers in parallel
The impedance difference will mean that one transformer will carry more load than it's higher impedance twin, so use CTs in each xfmr to provide overload protection.
RE: Transformers in parallel
Also, I just want to emphasize busbar's point on the increased fault current. If your customers purchased equipment based on a 40 MVA transformer upstream, then parallelling the transformers will nearly double their available fault current. This could be a serious issue.
dpc
RE: Transformers in parallel