MGVCL Exam Paper (30-07-2021 Shift 1)
For sea water with σ = 5 mho/m and ε_r = 80, what is the distance for which ratio signal can be transmitted with 90% attenuation at 25 kHz?
Condition of good conductor: σ/ϵω >> 1 Equation is given by: The constant ratio = σ/ϵω = 44913.6 σ/ϵω >> 1. hence sea water is a acting as a good conductor Since attenuation is 90%, so transmission is 10% So, e^(-αx) = 0.1
Attenuation constant = √(σμϵ/2) = 0.702 -αx = ln(0.1) x = 3.27 m
Bus Type - Known Parameter - Unknown Parameter Load Bus -P, Q - V, phase angle Generator Bus - P, V (magnitude) - Q, Voltage phase angle Slack Bus Voltage - magnitude and phase angle - P, Q
Power factor for purely inductive circuit is 0 and power factor angle is 90 degree. Power factor for purely capacitive circuit is 0 and power factor angle is 90 degree Power factor for purely resistive circuit is 1 and power factor angle is 0 degree
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".
EXAMIANS