Grounding point for CT secondary star neutral 3

[prc]

When star neutral point of CT secondary is formed in substations where this is to be grounded -at CT secondary box near to instrument transformer in the yard or at the panel in control room?

 

[scottf]

Practice varies by user. From an instrument transformer's perspective, all are acceptable...just make sure the ground is not applied at multiple points. My personal preference is to ground at the meter/relay.

 

[davidbeach]

Our practice is to ground at the first terminal inside the control house.

 

[Distribution73]

I would suggest having a look at IEEE Std c57.13.3 "IEEE Guide for the Grounding of Instrument Transformer Secondary Circuits and Cases". It provides helpful information and guidelines on this subject.

 

[RRaghunath]

'Grounding at the first terminal inside control house' as davidbeach indicated is the popular practice I believe.

 

[prc]

Thank you for the guidance.

 

[LincolnKeith]

About 40 years ago, myself and a theoretically senior colleague went to Saudi Arabia to commission a series of 13.8kV substations.
I quickly decided that it would be better for us to split the substations and work individually, rather than as a team.
After successfully having my third substation energised, I decided to check how my colleagues third substation was progressing (it was due to be energised that day also).
On arriving at my colleagues site, I found that quite a few people "just happened to be passing" at the time of planned energisation.
This may have been due to errors becoming apparent during energisation of his first two substations. In fact the operations guy who energised my substation had earlier told me that he had lost the toss when he was assigned my site to energise, "your sites are boring, they always get energised without problems".
Anyway, energisation happened but there was no indication that it had happened, the voltmeters suggested that there was zero volts on the switchboard.
While everybody was considering what had gone wrong this time, after a short interval, smoke was seen coming from the switchboard.
De-energise and investigate.

It turned out that the VTs were connected in star and earthed in the busbar chamber and then the six wires were run into the control panel. There they were again connected in star and earthed. Unfortunately, on the other side of the windings.

So, as mentioned above, earth Cts and Vts only in one place. Also, get your switchboard commissioned by somebody who knows how to do it in practice (no matter what academic qualifications he may have).