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.
Carrier current over the power line provides simultaneous tripping of circuit breakers at both ends of the line in one to three cycles.
Thereby high-speed fault clearing is obtained, which improves the power system stability.
The auto-reclosing simultaneous reclosing signal is sent thereby simultaneous (1 to 3 cycles) reclosing of the circuit breaker is obtained.
For simultaneous faults, carrier-current protection provides easy discrimination.
As per answer key "pilot protection" is true but there is mistake the right answer is "none".
Rotor frequency, f_r = s*f_s
s = 2/50
s = 0.04
Ns = 120f/P
Ns = 1500 rpm
s = (Ns - Nr)/Ns
Nr = Ns(1 - s)
Nr = 1500*(1 - 0.04)
Nr = 1440 rpm