Induced voltage from current transformer
Induced voltage from current transformer
(OP)
I was looking for some information regarding a question from an electrician at my facility.
We currently ground out all busswork while doing PM work on it. The reason being is obviously to avoid any induced voltages which could be harmful to the workers.
The question is: Is it possible to get enough of a induced voltage on relay control wiring to induce a voltage on the buswork through the CT?
Thanks
We currently ground out all busswork while doing PM work on it. The reason being is obviously to avoid any induced voltages which could be harmful to the workers.
The question is: Is it possible to get enough of a induced voltage on relay control wiring to induce a voltage on the buswork through the CT?
Thanks






RE: Induced voltage from current transformer
RE: Induced voltage from current transformer
RE: Induced voltage from current transformer
There may be more complex circuits (differentials for example) where multiple ct's feed the same circuit. Even in that case I would think the voltage possible on primary would be low for two reasons:
1 - there would usually be a low impedance path in parallel to the ct with deenergized primary/bus. (we don't put ct secondaries in series).
2 - Voltage is stepped down from secondary to primary. Typically ct saturation condiciton would correspond to about 1 volt on primary (bus).
RE: Induced voltage from current transformer
RE: Induced voltage from current transformer
There are many ways for buswork to become charged with annoying and/or dangerous voltages.
The reason for grounding the buses before any work is to avoid any surprises while you are working. For this reason, I would ask you to continue what you are doing; it is the safest way to work.
RE: Induced voltage from current transformer
As discussed by electricpete, compare a PT to a CT associated with the same bus. The turns ratios are in opposite proportion, making a reverse-fed CT in no way the hazard of a PT in a similar situation.
RE: Induced voltage from current transformer
As was stated above, the CT acts as a step-down transformer when looking from secondary to primary. The actual voltage that would be induced is determined by the ratio. For example, let's say you have a 200:5A (40:1)CT. If there is 10 V induced on the secondary side of the CT, the resulting voltage across the primary of the CT is about 0.25V.
I believe your concern could be based on thoughts about voltage transformers, where there can be dangerous voltage levels induced on the primary winding, with small voltages on the secondary side.
RE: Induced voltage from current transformer
RE: Induced voltage from current transformer
RE: Induced voltage from current transformer
RE: Induced voltage from current transformer
Assuming the voltage applied across the secondary is to the same ground, the voltage induced across the primary winding is from primary to ground, at least the potential to ground is nearly the same as across the winding.\
Regardless...the voltage drop is of no consequence.
RE: Induced voltage from current transformer