Powering of 5.0 MVA 11/22 kV transformer

[maypot]

Hi,

The utility supply is planning to power a 5.0 MVA transformer without the basic temperature and Bucholtz protection . The transformer will only be protected by overcurrent and earth fault protection .
Is it a sound practice ?

Bob

 

[RRaghunath]

Buchholz protection is considered primary protection for transformers for two reasons
(1) The gas collection device can sense an incipient (or developing) fault and caution the operator in advance.

(2) The surge device is very reliable in detecting a fault in the transformer and also is fast acting.

If a transformer is in service without Buchholz protection, it is certainly a compromise and cannot be said to be good engineering practice.

Having said that, the Buchholz and temperature sensing devices are transformer mounted and it is to be seen on case to case basis if there are any difficulties in wiring the signals to the remote breaker / switchgear room.

Hope the above is helpful.

 

[jghrist]

The protection scheme for power transformers needs to balance the overall economics while considering the cost of repairing damage, the cost of lost production, the adverse effects on the balance of the system, the spread of damage to adjacent equipment, and the period of unavailability of the transformer. According to IEEE/ANSI C37.91-1985, IEEE Guide for Protective Relay Applications to Power Transformers,:
"Fuses are comonly used to provide fault detection for transformers with minimum nameplate ratings up to 5000 kVA, three phase (Category I and II). Transformers larger than 5000 kVA, three phase, minimum nameplate (Category II and IV) are generatlly protected by a combination of potective devices..."

 

[dpc]

I agree with jghrist - the level of protection is a function of the transformer size and cost of replacement/downtime.

There are many, many 5 MVA transformers in service with only primary fuses for protection.