Page 53 - Industrial Power Engineering and Applications Handbook

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List of formulae used for S high, I, = - (1.7a)
e2
5s
E< x2
Theory of operation
Motor output and torque
T = (Pm . [rr (1.1)
(1.8)
$ = $,,, sin (ut
P, = rotor power
T = torque developed
&,, = maximum field strength (1.8a)
I, = rotor current
T.N
p=- P, = synchronous power
974
P = rotor power in kW P, - P, = s . P, (1.9)
T = torque in mkg P, - P, = slip loss
N = speed in r.p.m.
(1.10)
(1.3)

S= slip
R2 = rotor resistance per phase System harmonics
,,X2 = standstill rotor reactance per phase and
,,e2 = standstill rotor induced e.m.f. per phase.
(1.1 1)
(1.3a) n

Tst = starting torque HVF = harmonic voltage factor
V, = per unit harmonic voltages
n = harmonic order not divisible by 3
(1.3b)
(a) Eddy current loss
T, = rated torque
Le =t:.f2.B2Ip (1.12)
dt)
e2=-zI.- (1.4) tl = thickness of steel laminations
dt
B = flux density
zr = number of turns in the rotor circuit per phase and p = resistivity of the steel laminations
d@dt = rate of cutting of rotor flux
e2 = 4.44 Kw . @,,, . zr . ,f, (1.5) (b) Hysteresis loss
Lh = f . (Bm)'3 to 2 (1.13)
Kw = winding factor
f, = rotor frequency = S . f

N, = synchronous speed
N, = rated speed Further reading
120. f
N, = - (1.6a) 1 Golding, E.W., Electrical measurements and measuring
r.p.m.
P Instruments, The English Language Book Society and Sir Isaac
Pitman & Sons Ltd, London.
f= frequency of the supply system in Hz 2 Humphries, J.T., Motor and Controls for l-$ motors. Merrill,
p = number of poles in the stator winding Columbus, OH.
3 Puchstein, A.F., Lloyd, T.C. and Conard, A.G., Alternating
Rotor current 4 Current Machines, Asia Publishing House, Bombay (1959).
Say, M.G., The Perjkrmancr und Design ofAlternating Current
Machines, Pitman & Sons Ltd, London (1958).
(1.7) 5 Smeaton, R.W., MotorApplication and Maintenance Hand Book,
McGraw Hill, New York (1969).