TRANSFORMER

1.       Transformers Transformation Ratio

          

       V1/V2=N1/N2=I1/I2=K or NS/NP=VS/VP=IP/IS=K

2.       Explain the function of Buchholzs Relay for Transformer protection?

It is the gas and oil operated relay. It has two circuits, on is trip and second is alarm. Any minor fault develops that time the evaporated gas will actuate the alarm circuit; otherwise any major fault rush of oil will actuate the Trip Circuit.

3.       What are the protections for Transformers?

a)      Buchholzs relay

b)      Overheated relay

c)       Earth fault relay

d)      Temperature sensor

For higher transformer additionally

a)      Restricted Earth fault relay

b)      Differential relay

4.       How to check Transformer oil? What should be value?

a)      To collect oil from bottom drain in Test kit.

b)      Adjust Test kit spears (2.5mm or 4mm)

c)       Increase the voltage gradually up to tripping point

The oil should withstand 30KV for 1 minute gap with a gap of 2.5mm

5.       What is the breather? Details about the Silica gel

It is a small container, contains silica gel and oil. It absorbs the moisture from the atmospheric air and allow the fresh air to the conservator.

6.       What is C.T. and P.T.

C.T. is Current Transformer which step down the current. It is used for current measurement and protection.P.T. is Transformer Tap changing on HT side. Transformer is working at mutual induction action.

1.       YPM of Transformer

a)      Obtain the work permit

b)      Transfer the load to the other transformer

c)       Switch “ON” the Earth Switch on primary and secondary side

d)      Physically clean the Transformer

e)      Check the insulation resistance of primary and secondary winding and check the winding resistance

f)       Check the terminal tightness

g)      Check the Earth connections of Transformer

h)      Carry out B.D.V. test of Transformer oil

i)        Control box cleaned with contact cleaner

j)        Check the Silica gel

k)      Check the HT and LT bushings

l)        Open the Earth switch

m)    Energize the Transformer an d give load

n)      Close the permit.

2.       Which are the Paralleling conditions of Transformers?

a)      Voltage must be same as check tap-changer position

b)      Frequency must be same

c)       Phase sequence must be same

d)      Impedance of both the Transformers has to be same

e)      Vector group of both must be same.