In high revenue areas such as universities, shopping malls
and business centres, taking CT’s offline for testing is not
an option, so a reliable live CT test alternative is required.
Live CT testing using admittance…
A component of a good CT’s characteristic performance is
a low admittance value. This admittance value can be measured while in-circuit using the 505B (pictured).
The 505B is placed in series with an in-circuit CT and it
superimposes a small 1.6kHz signal onto the live 50 or 60Hz
secondary metering circuit.
A filter on board the 505B extracts the 1.6kHz admittance
reading and from this a quick determination is made on the
CT’s general health.
Admittance testing only adds an extra 10 minutes to a polyphase
meter test and is quickly becoming part of a routine test requirement
for some utilities.
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