WHM Re-calibration for changing CT ratio 1

[power2engineer]

I am changing a MV feeder which has existing GE type DS WHM presently fed from 400/5 CTs, I am changing the CTs to 600/5. Is it sufficient to change the meter multiplier by a new multiplier 1.5 multiple (6/4) of existing multiplier or a more elobrate recalibration is required? The meter is not used for revenue metering.

 

[rcw retired EE]

Just change the multiplier. Since the CT wiring changed, you may want to verify that teh connections are correct.

An old electrician trick is to open the CT test switch or insert the shorting screws at the CT terminal strip one at a time. The meter should slow down when a phase current is cut out. If it speeds up something is wrong. If it slows down, it might be correct because the test does not find all errors.

 

[scottf]

Meter multiplier is CT effective ratio (600:5A = 120:1) multiplied by the VT effective ratio (if one exists).

 

[LSpark]

Whilst it may work it is a very rough and ready way to do it and may well lead to confusion in the future, unless very clearly labelled and documented. Most relatively modern meters are programmable so you should be able to connect to it and change the CT ratio and pulse multiplier (if applicable) to a suitable value.

You do need to ensure that you do not exceed the maximum pulse rate for the meter, you will be able to find this in the meter technical data sheet. If this rate is exceeded there won't be sufficient discrimiation between pulses and the system won't work correctly.