transformer replacement, different power rating
transformer replacement, different power rating
(OP)
For replacing transformers with spares of same voltage ratio but different kVA rating, what do I need to consider for replacing on the same protection network, ie which side do I need to construct fault currents for and how?






RE: transformer replacement, different power rating
RE: transformer replacement, different power rating
RE: transformer replacement, different power rating
A change in fault current requires checking he capability of the c.t.'s supplying the relays. The CTs must (1)supply enough secondary amps to permit pickup, and(2) not saturate during a fault. Lower kVA ratings will affect (1); higher kVA ratings will affect (2). In addition the fault level on the secondary must be calculated to see that the switchgear can interrupt the fault.
RE: transformer replacement, different power rating
RE: transformer replacement, different power rating
As recommended by "njengr1", you shoud consider and check the CT ratio of primary and secondary side of transformers and protective relay settings.
RE: transformer replacement, different power rating
RE: transformer replacement, different power rating
RE: transformer replacement, different power rating
I agree with jghirst, adding 2Mva could bring the switchgear out of spec. and become a danger.
regards,
Danny
RE: transformer replacement, different power rating
You need to check your CT knee voltage, ratio and burden. with the new short cir. current.
RE: transformer replacement, different power rating
New transformer approximate short circuit current level on its secondary is:
Isec=6000kVA/(sqr3 x 3.3kV) ~ 1050Amps
Isec,sc=(1.0/0.068) x 1050 ~ 15441Amps
Old transformer approximate short circuit current level on its secondary is:
Isec=4000kVA/(sqr3 x 3.3kV) ~ 700Amps
Isec,sc=(1.0/0.069) x 700 ~ 10145Amps
and
6000kVA/4000kVA=1.5 ~ 1050Amps/700Amps ~ 15441Amps/10145Amps
RE: transformer replacement, different power rating
I think my posting could make you confused.