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.
The methods often employed in practice to improve system stability are:
1. Increasing System Voltage
2. Reduction in Transfer Reactance
3. Using High Speed Circuit Breaker
4. Automatic Reclosing
5. Transient Stability
6. Turbine Fast Valving
7. Application of Braking Resistors
8. Single Pole Switching:
Z = √(L/C)
C = L/Z²
C = 50*10⁻⁹/(50*50)
C = 0.02 nF
C = 20 pF