Page 128 - Handbook of Electrical Engineering

110 HANDBOOK OF ELECTRICAL ENGINEERING

0.02208 per-unit. The following ohmic values apply at 415 V for an equivalent star-wound stator:-

R 1 = 0.179 X 1 = 0.438
R 20 = 0.0145 X 20 = 0.8230
R 21 = 0.253 X 21 = 0.333
R c = 115.0 X m = 17.0

Calculate the following:-

• Full-load current from the supply.

• Full-load power factor.
• Full-load efficiency.
• Full-load torque.

• Starting current from the supply.

• Starting power factor.
• Starting torque.

Figure 5.1 is the appropriate equivalent circuit for the calculations.

a) Solution for full-load.
The applied voltage per phase V p is:-

415.0
V p = √ = 239.6 volts
3

The rotor resistance R 2 and reactance X 2 are:-

R 2 = (0.253 − 0.145) × 0.02208 + 0.145 = 0.1474 ohms
X 2 = (0.333 − 0.823) × 0.02208 + 0.823 = 0.8122 ohms

The rotor ‘output power’ resistance R out at the given slip is:-
1 − s 1 − 0.02208

R out = R 2 = 0.1474 = 6.5273 ohms
s 0.02208
The total rotor impedance Z 22 is:-

Z 22 = R 2 + jX 2 + R out = 0.1474 + j0.8122 + 6.5273

= 6.6747 + j0.8122