Securing a Spare HV Power Transformer 1

[constantlylearning]

I'm trying to get a feel for the standard practices of other utilities with respect to how spare transformers are stored on-site (ready to be placed in service), with minimal risk to the transformer.

In our case, we have a single-phase auto that is a spare member of a three-phase bank. My philosophy is that the safest way to keep this unit ready to be placed in service is to make sure all terminals are disconnected from the system (including the H0X0-neutral) and shorted to the tank with the tank being grounded to the ground grid.

My feeling is that connecting the terminals to a phase or neutral bus, even if de-energized, exposes the transformer to unnecessary risk, including lightning strikes that might make it through the station shielding. (I admit this is not likely, but I think it is technically possible.) Also, I feel that connecting the H0X0 to the neutral bus (even though this bus is grounded) might offer some exposure to fast transients affecting the system neutral. I think this is highly unlikely as well, but is also an unnecessary risk.

I would really appreciate other opinions or points of view.

 

[prc]

Believe it is a 400 or 765 kV auto-transformer. There are several solutions followed by utilities.We should remember that chances of moisture ingress and accumulation is more in a spare transformer than in a running unit.So it is better to keep the spare energised and keep it warm so that it can be brought in to operation with minimum time delay. In that situation you will have to keep the coolers partiallly shut as only no-load loss will be there.Surge arresters are a must on all terminals as transferred surge to delta tertiary will be more in single phase mode.The disadvantage is extra cost by way of protection scheme, HV and IV breakers. Another alternative is to adopt a isolator switching scheme by running an additinal bus for spare so that within minimum time you can switch in the spare.Normally spare unit will be rotated in to operation with running units.