In bias differential protection for transformer,
There are two basic settings required to setup the percentage biased differential protection.
1. Minimum pickup
2. The slope.
The minimum pick-up covers the transformer magnetizing current typically 1-4% of transformer rating.
A pick up of 0.2 to 0.3 times the TAP is recommended for general cases.
The slope is defined by determining the potential sources of differential current.
E→EMF in volt
φ→Flux in weber
A→Parallel path (for wave winding = 2)
Z→No. of armature conductors
N→speed in rpm
P = Number of poles
E = PφNZ/(60A)
E = 8*0.020*625/(60*2)
E = 500 V
A voltage dip is a short temporary drop in the voltage magnitude in the distribution or customer's electrical system.
Common causes of voltage sags and under voltages are short circuits (faults) on the electric power system, motor starting, customer load additions and large load additions in the utility service area.
Sags can cause computers and other sensitive equipment to malfunction or simply shut off.
For the given circuit shown in figure,
D1 is forward bias mode - On state
D2 is in reverse bias mode - off state
D3 is in reverse bias mode - off state.