PT Rating
PT Rating
(OP)
Hi,
I visited a site where they used a potential transformer to sense ground fault on their 22 kV / 400 V transformer. The PT is rated at 13 k V/ 110 V . This sound strange as the PT should have been sized at the rated line/line voltage of the transformer.
Any comment !
Grundig
I visited a site where they used a potential transformer to sense ground fault on their 22 kV / 400 V transformer. The PT is rated at 13 k V/ 110 V . This sound strange as the PT should have been sized at the rated line/line voltage of the transformer.
Any comment !
Grundig






RE: PT Rating
It depends on how the PT's are arranged. If the three PT's are arranged in a "wye" configuration then the voltage across each on of the PT's would be 22/1.73 = 12.7kV. This would get you close to the 13kV necessary to produce the 110V on the secondary.
RE: PT Rating
RE: PT Rating
davidbeach
I'm curious, why does the 22kV need to be solidly grounded in order for the VT's to be connected in "wye"
RE: PT Rating
RE: PT Rating
Alwasy spec the grounding VT's for full phase-phase votlage or make sure there are suitable damping resistors in the circuit.
ANSI C37.102 had a good explanation (5.2.2).
RE: PT Rating
Thanks for the replies. The 22 k V transformer is grounded through this PT that is the PT is connected to the star point of the 22 k V transformer. I understand that the fault current should be high enough to induce a voltage in the secondary. But my understanding is that this PT should be sized for line/line voltage.
Regards.
Grundig
RE: PT Rating
This are rather different and distinct applications. Either can be done, but generally not both at the same time. Clear, concise, and precise terminology can certainly help narrow down the range of answers and keep them more focused on the real issue.
RE: PT Rating
Grundig
RE: PT Rating
Distribution transformer from power transformer neutral to ground with resistor on the low side of the distribution transformer should be sized for the line-neutral voltage of the power transformer. Ground one of the phases of the power transformer and now you have L-N neutral voltage across the distribution transformer; that's as bad as it will get, no need for a higher voltage rating.