5.2)

It is a gas operated relay used for the protection for oil immersed transformer against all internal faults

A Buchholz relay is used to detect

Loss of oil

Presence of gas generated by minor interwinding faults

Catastrophic insulation breakdown

Initially, a loss of oil initiates an alarm. If the oil loss continues, then the relay will initiate disconnection of the transformer. The presence of gas initiates an alarm. Catastrophic insulation breakdown initiates the disconnection of the transformer.

5.4)

Silica gel crystals are commonly used in the breather of a transformer.

Silica gel breathers provide an economic and efficient means of controlling the level of moisture entering the conservator tank during the breathing process.

(5.1)

A 230 V DC supply is connected across 300 in series to a unknown resistor R.

The Voltmeter connected across 300 resistor has internal resistance of 300 and reads 30 V.

Let be the unknown resistance.

Draw a circuit using above specifications.

Redraw the circuit replacing the voltmeter with its equivalent internal resistance.

Voltage in a parallel network is same.

Hence current through 300 is

Current flowing in the voltmeter is 0.1 A.

Hence total current flowing in the circuit is .

Step 2:

Total resistance of the network is .

Calculate the equivalent resistance of the circuit.

and are parallel then .

Equivalent resistance is .

Substitute and in .

The value of unknown resistance .

Solution:

The value of unknown resistance .