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

The expression for voltage regulation of a short transmission line for lagging power factor is given by: ___, where, 'I' is the line current, 'V_r' is the receiving end voltage, 'R' is the line resistance and 'X' is the line reactance.

For lagging power factor = (IR*cosφ + Ixsinφ)/Vr
For leading power factor = (IR*cosφ - Ixsinφ)/Vr
Zero voltage regulation occurs on leading power factor only.

A single phase motor connected to 400 V, 50 Hz supply takes 30 A at a power factor of 0.7 lagging. Calculate the capacitance required in parallel with the motor to raise the power factor to 0.9 lagging.

For single phase induction motor,
P = VIcosφ
P = 400*30*0.7
P = 8400 W
Q1 = P*tan(φ) = 8400*1.020
Q = 8568.82 VAR
Now power factor change to 0.9
So, φ' = 25.84 degree
Q = 8400*tan(25.84)
Q = 4067.95
Qnet = Q - Q'
Qnet = 8568.82 - 4067.95
Qnet = 4500.8
C = V²/(2ᴨf)
C = (400*400)/(2ᴨ*50)
C = 8.95*10⁻⁵
C = 89.5 μF

Determine the ohmic value of the current limiting reactor per phase external to a 30 MVA, 11 kV, 50 Hz, three phase synchronous generator which can limit the current on short circuit of 5 times the full load current. The reactance of the synchronous generator is 0.05 pu.

The ratio of full load current to short circuit current = 1/5
Xsc = j/(1/5)
External reactance required = j*((1/5) - 0.05))
= j*0.15 pu
Full load current = (30*1000)/(√3*11)
= 1574.6 A
Per unit reactance = j*0.15 = (I*Xr)/V
j*0.15 = (1574.6*Xb)/((11/√3)*1000))
= 0.60 ohm

Stability of power system can be improved by
1. Reducing voltage of transmission
2. Using parallel transmission lines
3. Using series compensators
Which of the above statements are correct?

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:

In Microsoft Word, which of the following menu is used to add Headings that are displayed automatically in the top margin of all pages?