FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A method for determining core loss in a 3f squirrel cage induction motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Dr. Jaiswal Vinay, of Crompton Greaves Ltd, Analytics Lab, Global R&D Centre,. Kanjur Marg, Mumbai 400 042, Maharashtra, India, and Dr. Deshmukh Narayan Kashirao, D-505, Powai Park, to the right of D-Mart, High Street, Hiranandani Garden, Powai-Mumbai- 400 067, Maharashtra, India; both Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention :

FIELD OF THE INVENTION
This invention relates to a method for determining core loss in a 3$ squirrel cage induction motor.
BACKGROUND OF INVENTION
Electrical appliances/machines like fans, punching presses or lathes are generally driven by 3$ squirrel cage induction motors. A 3(J) squirrel induction motor comprises a hollow cylindrical magnetic material stator formed with a plurality of teeth around the circumference thereof. Phase windings are inserted in slots formed between adjacent teeth of the stator and are wound around the stator circumferentially. The phase windings are connected to the corresponding phases of a 3<}) power supply. The motor also comprises a magnetic material rotor formed with a plurality of teeth around the circumference thereof. Phase windings are inserted in the slots between adjacent teeth of the rotor. Core loss or iron loss is a form of energy loss that occurs in the 3$ squirrel cage induction motors due to eddy current loss and hysteresis loss in the magnetic cores of the stator and rotor at fundamental and harmonic frequencies. Eddy current loss is related to the resistivity of the core of the stator and rotor. Hysteresis loss is related to the molecular friction between the magnetic particles of the core of the stator and rotor when they move continuously to align themselves to the changes in the rotating magnetic field. If the core loss is high, the efficiency of the motor decreases and the power output of the electrical appliance or machine reduces with decrease in efficiency of the motor. Core loss will also heat up and damage the motor thereby reducing its life. Therefore, it is essential to accurately determine the core loss of the motor to ensure healthy and efficient running of the motor and to increase the life of the motor. Core loss of a motor is generally determined by calculating the back emf of the motor at fundamental frequency , calculating the magnetic flux density in the stator teeth at fundamental frequency using the calculated back emf and calculating the magnetic flux density in the stator core at


fundamental frequency using the calculated back emf. The calculated values of the magnetic flux density of the stator teeth and the stator core are compared with a reference set of values of magnetic flux density and core loss provided by the manufacturer of electrical steel used in the motor, to determine the core loss of the motor [M. G. S A Y, "The Performance and Design of Alternating Current Machines," CBS Publishers & Distributors, Third edition, 1983]. Due to large differences between the calculated values of core loss and measured values of core loss this method is not accurate and reliable and it is not possible to determine core loss of a 3(j) squirrel cage induction motor accurately using this method.
OBJECTS OF THE INVENTION
An object of the invention is to provide a method for determining core loss in a 3(J) induction motor, which method is accurate and reliable.
Another object of the invention is to provide a method for determining core loss in a 3$ induction motor, which method is simple and easy to carry out.
DESCRIPTION OF THE INVENTION
According to the present invention there is provided a method for determining core loss in a 3(}) squirrel cage induction motor comprising the following steps:
a) calculating the back emf of the motor at fundamental frequency and at (6£±1)th harmonics where £=1,2, 3...i.e. 5th, 7th, 11th, 13th, 17th, 19th, 23rd, 25th, 29th, 31st, 35th, and nth (n < Ns that is number of stator slots) using



where,
ns _n is synchronous speed for the nth harmonics
kwn = kpnkdn is winding factor for the nth harmonics
¦ is frequency
Nph is the number of turns per phase
fn is the flux per pole for the nth harmonics
En is the back e.m.f. for the nth harmonics (voltage across Xm_n)
b) calculating the iron loss in the stator teeth of the motor at fundamental frequency and at (6A:±1)th harmonics where k=\, 2, 3...i.e. 5th, 7th, 11th, 13th, 17th, 19th, 23rd, 25th, 29th, 31st, 35th, and n,h (n < Ns that is number of stator slots) using:

where,
B"m s, is the peak value of flux density in stator teeth for the nth harmonics p is no. of pole pairs ws is width of stator teeth L is effective core length
Resultant value of magnetic flux density (peak) in stator teeth
n=n
b (i) comparing the value of B ms, with the reference set of values of magnetic flux density as provided by the manufacturer of the electrical steel used in the motor so as to determine ^(loss per Kg for the teeth).


b (ii) calculating the total core loss in the stator teeth as follows:


where,
Wst is the weight of stator teeth
c) calculating the iron loss in the stator core at fundamental frequency and at (6A±1)* harmonics where k=1, 2, 3...i.e. 5th, 7th, 11th, 13th, 17th, 19*, 23rd, 25th, 29*, 31st, 35th, and nth (n < Ns i.e. no. of stator slots) using:

where,
B"sc is flux density in stator core for the nth harmonics wc is effective core depth
Resultant value of magnetic flux density (peak) in stator core

c (i) comparing the value of Bsc with the reference set of values of magnetic flux density as provided by the manufacturer of the steel so as to determine Psc (loss per Kg for the stator core).
c (ii) Calculating the total core loss in the stator core as follows:


where,
Wsc is the weight of stator core


d) calculating the iron loss in the rotor teeth (tooth pulsation losses) at fundamental frequency and at (6&±1)th harmonics where k=1, 2, 3...i.e. 5th, 7th, 11th, 13th, 17th, 19th, 23rd, 25th, 29th, 31st, 35th, and n,h (n