New Yaskawa ELECTRIC 200V Industrial Servo Motor 7000W 22.3N.m SGMSS-70A2A-FD11

In the same published data servomotors are generally rated to operate with either a 1300 C (Class B) or 1550 C (Class F) continuous winding temperature. Although motors with a Class H, 1800 C temperature rating are also available. Assuming the motor’s resistance along with its electrical and mechanical time constants are specified at 250 C, it was just demonstrated that all three parameters significantly change value at a 1550 C winding temperature. If the motor’s winding can safely operate at 1800 C the resistance change is even greater because equation (7.4-24) shows that a 1550 C rise (1800 C-250 C) in winding temperature increases its electrical resistance by a factor of 1.609. Hence, if the servomotor’s dynamic motion response is calculated using the 250 C parameter values then this calculation overestimates the motor’s dynamic response for all temperatures above 250 C.

In all permanent magnet motors there is an additional affect that temperature has on the motor’s mechanical time constant only. As shown in eq (a) a motor’s mechanical time constant changes inversely with any change in both the back EMF, Ke, and torque constant, KT. Both Ke and KT have the same functional dependence on the motor’s air gap magnetic flux density produced by the motor’s magnets. All permanent magnet motors are subject to both reversible and irreversible demagnetization. Irreversible demagnetization can occur at any temperature and must be avoided by limiting the motor’s current such that, even for an instant, it does not exceed the peak current/torque specified by the motor manufacturer. Exceeding the motor’s peak current rating can 7 7 permanently reduce the motor’s Ke and KT thereby increasing the motor’s mechanical time constant at every temperature including the specified ambient temperature. Reversible thermal demagnetization depends on the specific magnet material being used. Currently, there are four different magnet materials used in permanent magnet motors. The four materials are: Aluminum-Nickel-Cobalt (Alnico), Samarium Cobalt (SmCo), Neodymium-Iron-Boron (NdFeB), and Ferrite or Ceramic magnets as they are often called. In the temperature range, -600 C < T < 2000 C, all four magnet materials exhibit reversible thermal demagnetization such that the amount of air gap magnetic flux density they produce decreases linearly with increasing magnet temperature. Hence, similar to electrical resistance, the expression for the reversible decrease in both Ke(T) and KT(T) with increasing magnet temperature is given by : Ke,T(T) = Ke,T(T0)[1-B(T-T0)] (eq b) In equation (b), the B-coefficient for each magnet material amounts to : B(Alnico)= 0.0001/0 C B(SmCo) = 0.00035/0 C B(NdFeB) = 0.001/0 C B(Ferrite) = 0.002/0 C