Protection Engineering Basics and Schemes Protection Engineering | Page 207

Differential setting must account magnetization current and tap changing effect( Voltage regulation effect) of transformer

Two tap positions are there

� For HT, + 10 % tap, Voltage( V max) 34.65KV � For LT,-10 % tap, Voltage( V min) 28.05KV

Now we need to find Average Voltage,

V av =

V av =

Tap Changing Error:

2

( 1

V max

) +( 1

V min

)

2

( 1 34.65) +( 1

28.05) V av = 31.006KV ≅ 31KV

We have three voltages for this system V av = 31KV V max = 34.65KV V min = 28.05KV AtV av = 31KV, Full load current will be,

pg. 207