Westinghouse Modules 1C-,5X- Emerson VE-,KJ-
Honeywell TC-,TK- Fanuc motor A0-
Rosemount transmitter 3051- Yokogawa transmitter EJA-
The electrical resistance of a winding, at a specified temperature,
is determined by the length, gauge and composition (i.e, copper,
aluminum, etc.) of the wire used to construct the winding. The
winding in the vast majority of industrial servomotors are
constructed using film coated copper magnet wire. Based on the 1913
International Electrical Commission standard, the linear
temperature coefficient of electrical resistance for annealed
copper magnet wire is 0.00393/o C. Hence, knowing a copper
winding’s resistance at a specified reference or ambient
temperature, the windings at temperatures above or below this
ambient temperature is given by: R(T) = R(T0)[1+0.00393(T-T0)] (eq
a) Where : T = Winding’s Temperature (0 C) T0 = Specified Ambient
Temperature (0 C).
Using equation (a), a 1300 C rise (1550 C-250 C) in a copper
winding’s temperature increases its electrical resistance by a
factor of 1.5109. Correspondingly, the motor’s mechanical time
constant increases by this same 1.5109 factor while its electrical
time constant decreases by a factor of 1/1.5109 = 0.662. In
combination, the motor’s mechanical to electrical time constant
ratio increases by a factor of 2.28 and this increase definitely
affects how the servomotor dynamically responds to a voltage
command. In consulting published motor data, many motor
manufacturers specify their motor’s parameter values, including
resistance, using 250 C as the specified ambient temperature. NEMA,
however, recommends 400 C as the ambient temperature in specifying
motors for industrial applications, Therefore, pay close attention
to the specified ambient temperature when consulting or comparing
published motor data. Different manufacturers can, and sometimes
do, use different ambient temperatures in specifying what can be
the identical motor.
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