A coil having an inductance of 100 mH is magnetically coupled to another coil having an inductance of 900 mH. The coefficient of coupling between the coils is 0.45. Calculate the equivalent inductance if the two coils are connected in series aiding.

Mutual inductance (M) = k*√(L1*L2)
k = 0.45
M = 0.45*√(900*100*10⁻⁶) = 135 mH
Leq = L1 + L2 + 2M
Leq = 900 + 100 + 270
Leq = 1270 mH

Two-wattmeter method is used to measure the power taken by a 3-phase induction motor on no load. The wattmeter readings are 375 W and –50 W. Calculate the reactive power taken by the load.

Reactive power taken, Q = √3*(W1 - W2)
Q = √3*(375 + 50)
Q = √3*425 kVAR

If a 415 V, 50 Hz, star-connected, three-phase squirrel-cage induction motor is operated from a 415 V, 70 Hz supply, the torque that the motor can now provide while drawing rated current from the supply

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A 16 A, Type B Miniature Circuit Breaker (MCB) will disconnect a fault in 0.1s when the fault current is

Class B trip curve:
The MCB with class B trip characteristics trips instantaneously when the current flowing through it reaches between 3 to 5 times rated current. These MCBs are suitable for cable protection.
Hence, For 16 A current Type B MCB disconnect fault at 3*16 = 48 A to 5*16 = 80 A.

An RLC series circuit consists of R = 16 Ω, L = 5 mH and C = 2 μF. Calculate the quality factor.

For series RLC circuit,
Q = (1/R)*√(L/C)
Q = 1/16*√(5 mH/2 μF)
Q = 50/16
Q = 3.125