ElectroQuest 1

Two coils having equal resistance but diferent inductances are connected in series. the time constant of the series combination is the

• sum of the time constants of the individual coils

• average of the time constants of individual coils

• geometric mean of the time constants of the individual coils

• product of the time constants of the individual coils

The time constant of the network in the figure is

• 2RC

• 3RC

• RC/2

• 2RC/3

What value of C will cause a unity power factor at the ac source

• 68.1 micro F

• 165 micro F

• 0.681 micro F

• 6.81 micro F

Anetwork contains linear resistors and ideal voltage sources. If values of al the resistors are doubled, then the voltage across each resistor is

• Halved

• Doubled

• Increased by four times

• Not changed

The values of I(0+) and I(infinity) is

• 1.5 A and 3 A

• 3A and zero

• 3A and 1.5 A

• Zero and 1.5 A

Th resonant frequency of the given series circuit is

• 1/2 pi(root 3)

• 1/4 pi root(3)

• 1/ 4pi root(2)

• 1/pi root(2)

What is the time of operation of a relay of rating
5 amp 2.2 sec, IDMT and having a relay setting of
125% Tms = 0.6? It is connected to a supply circuit
through a CT, 400 ratio. The fault current is 4000 amp.

• 10 s

• 1.92 s

• 4.5 s

• 2.4 s

A two conductor 1 - phase line operates at 50 Hz. The diameter of each conductor is 2 cm and are spaced 3m apart. What is the line to line capacitance ?

• 9.4*10^-9 F/km

• 4.87*10^-9 F/km

• 3.05*10^-9 F/km

• None of these

A 3 -ф load of 750 kW at 400 V, 50 Hz, operates at a power factor of 0.7 lagging. What is the capacitance per phase of a mesh connected capacitor bank to improve the power factor to 0.95 lagging?

• 3040 uF

• 2500 uF

• 3438 uF

• 2789 uF

A two conductor 1 - 4 line operates at 50 Hz. The diameter of each conductor is 4 cm and are spaced 6 m apart. What is the capacitive susceptance to neutral per km?

• 1.42*10^-9s/km

• 3.25*10^-9 s/km

• 4.8*10^-9 s/km

• 3.06*10^-9 s/km