Hermetically Sealed Transformers

Possibly whatever was causing the pressure to increase will get worse and destroy the transformer. Because you didn't investigate. Is this an oil filled transformer? if so, do you know what a Buchholz relay is, and what it is used for?

The electricians keep the relay from energising by constantly bleeding the gas off, thats why I'm asking the question. Is it safe to keep doing this.?

In an oil filled transformer, a sudden and large increase in gas pressure is usually because of severe insulation breakdown and arcing. Gradual gas pressure increase could be because the transformer is being run over its rating and overheating somewhat, but it could mean slight arcing somewhere, in a winding or bushing, or at a badly made connection, for example. This could lead to the need for expensive repairs later. Are the electricians qualified? Have you asked them if the transformer's life expectancy is reduced?

I remember a guy who wrote to the manufacturer of a ground-leakage meter on the main board asking to replace the 10 Amp meter with a 100 Amp model because the needle was over on the stop all the time. The manufacturer wrote back saying that the proper solution was to investigate the high value of leakage. Don't be that guy.

Thanks for that, the electricians have ordered a new transformer which will not arrive for 3 months, so I think they will continue to vent off until replacement. I asked what the worst case was and told transformer could wreck itself internally but no problem externally, I'm not so sure it is a 2500KVA rated transformer, but what do I know, it is not my field.

A transformer is built for a certain rating (e.g. 2500KVA). That means size of winding conductors, size of iron core, cooling oil capacity, cooling design, is calculated so the transformer will run with acceptable level of temperature rise in service. Therefore maintenance cost is acceptable. If that rating is exceeded by a reasonably small level, maintenance cost may be increased due e.g to more frequent attendance by electricians as in your case. Also life may be shortened but if it is being replaced in 3 months that may be OK. It sounds like they may have the situation under control. Maybe they log the pressure readings. If the transformer destroys itself internally there will be at least one external effect, namely loss of supply.

Thanks, I appreciate your replies.