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Cumulative rotor current

(12.10)
(12.3)
I, = negative phase sequence current component
Vu = unbalanced voltage Further reading
R; = rotor resistance referred to stator
X; = rotor reactance referred to stator I Beeman, D., Industrial Power Systems Handbook, McGraw-
Hill, New York (1955).
Stator heat on an unbalanced voltage 2 Dommer, R. and Rotter, N.W., ‘Temperature sensors for thermal
over-load protection of machines’, Siemens Circuit, XVII, No.
(a) Maximum theoretical heat 4, October (1982).
3 Ghosh, S.N., ‘Thermistor protection for electric motors’, Siemens
He, (max.) = (If + I,’ + 21, x I, ) (1 2.4) Circuit, XI, No. 3, July (1976).
4 Kaufmann, R.H. and Halberg, M.H., System over- voltages,
(b) Minimum theoretical heat causes und protective measures.
5 Kolfertz, G., ‘Full thermal protection with PTC thermistors of
He, (min.) = (I: + I: + I, x I, ) (12.5) three-phase squirrel cage motors’ , Siemens Review, 32, No. 12
( 1965).
Actual heat generated 6 Lythall, R.T., AC Motor Control (on earth fault protection and
thermistor protection).
He, = (I: + 61,’) (12.6) 7 Ramaswamy, R., ‘Vacuum circuit breakers’, Siemens Circuit,
XXIII, April (1988).
Actual current on unbalance
I,, = Jrn (1 2.7) Source material

Rotor power during an unbalance
Unbalanced Voltages and Single Phasing Protection,
M/s Minikc Controls Private Ltd.
High Voltage HRC Fuses, Publication No. MFG/47, The English
Electric Co. of India Ltd.
(12.8) Surge Suppressors-Bulletin No. T-109, Jyoti Ltd.
Thermistor Motor Protection Relay Catalogue-SP 50125/5482,
I,, = positive sequence current in the rotor circuit, and Larsen and Toubro.
12- = negative sequence current in the rotor circuit Motor Protection Relay, English Electric Co. of India I.td, Catalogue
Ref. PR. 05:101:A/6/85.
Total rotor heat Negative Phase Sequence Relay, M/s English Electric Co. of India
Ltd, Catalogue Ref. PR:01:306:A.
0~ (I; + 3I:” ) (12.9) Thermal Bimetallic Overload Relays, Bhartiya Cuttler Hammer.
I,, = negative sequence rotor current Product Catalogue C-305 MC 305/ANA3/6/85.