Megger Testing In-Service CT or PT secondary winding
Megger Testing In-Service CT or PT secondary winding
(OP)
What are the thoughts on megger testing in-service CT or PT secondary wiring? What precautions would you follow. Would it be done at all at your company? Thanks.






RE: Megger Testing In-Service CT or PT secondary winding
An applicable reference may be §7.10 of NETA Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems 2001 Order info www.NETAworld.org
RE: Megger Testing In-Service CT or PT secondary winding
Assuming the wiring was disconnected from the units during the test (i.e. with shorting bars, knife switches, etc...) and from the connected devices, it should be no problem.
I don't believe it to be possible to megger test the units themselves while energized, or for it to be advisible to try!
RE: Megger Testing In-Service CT or PT secondary winding
Ichabod
RE: Megger Testing In-Service CT or PT secondary winding
RE: Megger Testing In-Service CT or PT secondary winding
I can see how it's possible on CT circuits, but not on VT circuits.
Remember, if you apply a potential to the secondary of a VT (without is being shorted), a potential will be induced on the primary. If the unit is in-service, this will probably cause the VT to saturate, and potentially fail (i.e. blow-up).
RE: Megger Testing In-Service CT or PT secondary winding
RE: Megger Testing In-Service CT or PT secondary winding
Norm
RE: Megger Testing In-Service CT or PT secondary winding
RE: Megger Testing In-Service CT or PT secondary winding
RE: Megger Testing In-Service CT or PT secondary winding
Is the control wiring connected to the PT secondary during these tests? If so, lifting the ground could be big trouble!! If there is a system transient, etc... and there is no ground reference on the PTs secondary, the secondary can float to very high voltages and it could be very dangerous.
RE: Megger Testing In-Service CT or PT secondary winding
RE: Megger Testing In-Service CT or PT secondary winding
It's up to you...
However...as a manufacturer of VTs and CTs, I wouldn't recommend it! Quite frankly, in my humble opinion, it's a good way to get somebody killed.
Inclement weather is not the only thing that can cause transients...line switching, equipment failure, etc...can all be causes of voltage rise or high-frequency transients on the line.
Also....isn't a megger test DC? Have you considered the effect of applying a DC voltage to the secondary of a VT with the primary energized?
RE: Megger Testing In-Service CT or PT secondary winding
The CT meggering in service may become difficult if the CTs secondary windings are connected in grounded wye connection.
RE: Megger Testing In-Service CT or PT secondary winding
Sorry....I missed any comments about removing fuses (and still don't see them)...I asked earlier if the vt was removed from the circuit and I understood milliamp to say that the connections to the VT were left in tact.
RE: Megger Testing In-Service CT or PT secondary winding