CT polarity check for transformer ct
CT polarity check for transformer ct
(OP)
Hi,
While testing polarity check on transformer ct and the battery applied to the primary, a dangerous voltage and arcing may be generated while disconnecting the battery from the transformer winding. This happened to a very experienced technician last week.
I just want to be sure that i understand why this happen. Is it that the reactor of the transformer is opposed to current variation.
This isn't happening habitually, but this time a 36 V instead of a lower voltage battery was used because of some reading problem by the ampmeter connected at the secondary.
How do you check polarity safely?
Thanks
While testing polarity check on transformer ct and the battery applied to the primary, a dangerous voltage and arcing may be generated while disconnecting the battery from the transformer winding. This happened to a very experienced technician last week.
I just want to be sure that i understand why this happen. Is it that the reactor of the transformer is opposed to current variation.
This isn't happening habitually, but this time a 36 V instead of a lower voltage battery was used because of some reading problem by the ampmeter connected at the secondary.
How do you check polarity safely?
Thanks






RE: CT polarity check for transformer ct
RE: CT polarity check for transformer ct
RE: CT polarity check for transformer ct
If you think this might be the cause of your issue, just reapply the DC voltage and gradually (slowly) dial it back to zero. Remove your test leads at this point. This should be standard practice whenever doing this work.
RE: CT polarity check for transformer ct
Be careful, with a bigger core that could have turned out nasty for the commissioning tech involved.
RE: CT polarity check for transformer ct
Perhaps the low impedance ammeter is the problem. Usually this check is done with an analog voltmeter. Residual magnetization shouldn't be an issue, since the switch isn't closed long enough for current to rise.
RE: CT polarity check for transformer ct
RE: CT polarity check for transformer ct
In the past when used to use a battery, the contact was a just a momentary tap of the battery lead to the bushing using an insulated hot stick. Hopefully you do not connect, measure and then disconnect the battery. If you have magnetized the CT, you will need apply a voltages of alternate polarity and decreasing magnitude to demagnetize it.
RE: CT polarity check for transformer ct
Thanks,
Vijay