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Motors and Generators | Abb AC Servo motors
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How to interpret motor information
“Rated” voltage/speed
“Rated” conditions refer to measurement points, and are selected as an easy and convenient “reference” or “measurement”
point. Manufacturers select a “rated voltage”, operate with a “rated torque”, to verify that “rated speed” is reached.
Note that any voltage may be applied to the BSM series of brushless servo motors so either 160 Vdc, 300 Vdc, or 650 Vdc
may be applied. However the design limits must be observed. And those are: 1) maximum speed (rpm) limit, 2) demagnetization
(max torque/current) limit, and 3) 650 Vdc maximum.
Motor data
All BSM motors are 3-phase WYE connected. Connection is important because the motor/feedback is phase sensitive. All
motor parameters are expressed as phase to phase (line-to-line) figures. This includes voltage constant, resistance and
inductance.
The phase to phase voltage constant (back-emf) is a sinusoidal wave, which is measured while driving the motor (as a
generator) at 1000 rpm, and measuring the output voltage. The peak of this measured output voltage is shown in the literature
as Vpk/krpm; the RMS of the output voltage is Vrms/krpm.
Some data in the motor tables are expressed as “cold” figures (25°C), while others are “hot” (155°C) values. The cold figures
are: voltage constant, torque constant, resistance, inductance, peak torque and peak current. The hot figures are: continuous
stall torque continuous stall current.
The temperature coefficient between cold and hot voltage constant (and torque constant) is 0.90 for N-series, 0.80 for C-series
and 0.85 for BSM132 series. Motor resistance changes by a factor of 1.5 from 25°C to 155°C.
Motor temperature
The BSM series of servo motors are rated for a maximum continuous winding temperature of 155°C. These conditions are
ploted in a 25°C ambient on the motor speed-torque curves. For operation at 40°C ambient derate by 6%.
The temperature rise of the motor windings depends upon the amount of torque which is being delivered to the load. In this
brochure, the thermal limit line (line dividing dark and light shaded areas on the speed-torque curves) indicates the 155°C limit.
Temperature range - normal operating range of bearing grease is - 29°C to 155°C.
Altitude - the motors are rated for operation at 1000m or lower; derate 10% per 1000m.
The BSM motors include an internal thermal switch (bi-metallic) which is normally closed. It opens at 155°C ±5°. This switch
may be connected to the input of a motion controller, programmable logic device, or other type of machine control via an
isolating relay. Any of these devices could then sense this switch and shut power down when the thermal switch opens.
Abb AC Servo motors