Handbook of Electrical Engineering

INDUCTION MOTORS 119

R22N,X22N,R33NandX33N. The cycle is repeated using the ‘old’ values (call theseR22O,X22O,R33O
andX33O) plus a small amount of the error between the ‘new’ and ‘old’ values, i.e.,

R 22 =R22O+k(R22N−R22O)

X 22 =X22O+k(X22N−X22O)

R 33 =R33O+k(R33N−R33O)

X 33 =X33O+k(X33N−X33O)

The value of ‘k’ should be chosen to be between+ 0 .001 and+ 0 .01 to ensure stability. The
process is stopped once the absolute error in each of the parameters has fallen below a suitably small
value, e.g. 0.001 per-unit of its absolute value. Tables 5.9 and 5.10 for two-pole induction motors
were complied from Tables 5.1, 5.2, 5.5 and 5.6, to show the results of the method.

5.3 Construction of Induction Motors

The physical construction of an induction motor is greatly influenced by the environment and ambient
conditions. The environmental conditions include considerations for explosion, corrosion, dampness,
ingress of dust and solid particles, proximity to human operators, cost and economics. Ambient con-
ditions relate to surface temperature, methods of cooling, fan design and appropriate derating factors.

Table 5.9. Per-unit resistances for equivalent double-cage two-pole motors

Rated power

(kW)

Slip (pu) R 20 R 21 R 22 R 33

LV — — — — —

11 0.0433 0.0323 0.0398 0.0434 0.11308

15 0.0355 0.0270 0.0411 0.05127 0.05491

22 0.0282 0.0218 0.0421 0.05865 0.03391

30 0.0237 0.0186 0.0425 0.06165 0.02619

37 0.0216 0.0167 0.0425 0.06342 0.02232

45 0.0191 0.0152 0.0423 0.06389 0.01967

55 0.0173 0.0138 0.0419 0.06402 0.01737

75 0.0150 0.0120 0.0410 0.06378 0.01461

90 0.0138 0.0111 0.0403 0.06312 0.01332

110 0.0126 0.0103 0.0393 0.06210 0.01222

132 0.0117 0.00955 0.0384 0.06119 0.01120

160 0.0108 0.00888 0.0372 0.06007 0.01032

200 0.00995 0.00820 0.0357 0.05840 0.00945

250 0.00917 0.00759 0.0341 0.05685 0.00868

315 0.00846 0.00705 0.0323 0.05485 0.00802

HV — — — — —

630 0.00887 0.00771 0.0183 0.03660 0.00920

800 0.00896 0.00776 0.0175 0.03491 0.00995

1100 0.00901 0.00777 0.0172 0.03587 0.00989

2500 0.00883 0.00740 0.0205 0.06099 0.00841

5000 0.00842 0.00672 0.0303 0.12957 0.00709