Almost every transformer is provided with some measuring, safety, protective and informative devices. Some of them are:
Temperature gauge. Whenever current is flowing in the windings the heat is produced and that heat will ultimately rise the temperature of the oil, cores and winding etc. So a temperature gauge is provided to indicate the temperature of the hot oil in the tank. Nowadays special devices one designed and fitted inside the tank so that sitting in control room we can measure the temperature Of Oil, stampings and winding separately.
Fig. 18.5. Sectional view Of a Buchholz relay
Oil gauge. The level Of the Oil should be maintained in the conservator so that the shortage of the oil in the tank may be sufficiently equipped. So an oil gauge is used. It is provided with an alarm to inform the operator or control room. If the level of the oil goes down there the alarm will caution the operator and the operating circuit to equip the conservator.
Buchholz relay. It is a safety relay provided with the oil immersed transformer. The main function of this relay is to indicate the presence of gas in case of some inner fault. or the level Of transformer oil. It also isolate the transformer in case of serious fault or continuous fault. It is connected between the main and conservator tank. Generally it is observed that the formation of gas in the transformer oil starts if the local temperature exceeds 150C that is the main cause that the momentary faults does not operate the Buchholz relay. In case of serious fault the gas is generated and lower float is pushed towards the trip circuit contacts and finally cut off the input. In case of minor faults the gas is generated slowly which is not able to operate the lower float but the gas accumulates at the top and thus pressing the upper float which operates the alarm circuit to alarm the operator and control room as shown in Fig. 18.5.
Circuit breaker. There are two circuit breakers, one on primary side and other on secondary side. These Circuit breaker will disconnect the supply in case of overloading or short circuit or any other fault or abnormal conditions. In big transformers automatic circuit breakers are used.
Earthing. All the transformers are connected to earth. For maintaining good earthing connections the double earthing is done.
Lightning. A lightning arrester is attached with the body of the big transformer to save it from the sky lightning.