IEEE 1290:2015 pdf free download – IEEE Guide for Motor-Operated Valve(MOV) Motor Application,Protection,Control, and Testing in Nuclear Power-Generating Stations
4.3 Motor torque
Motor temperature and terminal voltage affect torque output (Appendix R [B1]’). Some motors may berequired to start after being exposed to elevated ambient temperatures for several hours. It is prudent toevaluate the minimum available motor torque at the highest motor temperature and minimum voltage.
This internal temperature should be based on worst-case operating conditions.For valves that may berequired to stroke more than once in succession, a temperature rise obtained from the motor performancecurve should be added to the motor ambient temperature to account for the internal heat generated duringthe preceding strokes. For operations in changing ambient conditions, the thermal lag of the motor shouldbe considered.High temperature fluid in pipes may provide a localized ambient temperature rise.
The distinction between rated start torque and locked-rotor torque is an important factor in valve actuatormotor application. Locked-rotor torque is, by definition, the torque the motor produces at zero speed atrated voltage and frequency.Because variations in the manufacturing process allow some tolerance in theVAM resistance and inductance, and because all motors are not typically tested during the manufacturingprocess unless this was specified by the purchaser, a specific locked-rotor torque for a specific VAM maybe unavailable.The manufacturer therefore determines a rated start torque that it will guarantee. Thisrated start torque is usually a rather conservative value.For example, a motor that has a locked-rotortorque design value of 342 t × lbf(464 N x m) has a rated start torque of 300 ft × 1bf (407 N x m).
lf the user has no other data available on a specific motor, he or she has to use the rated start torque valuein the calculation to determine the torque margin. If the user is able to perform testing, he or she willusually find more torque capability than would be given by the rated start torque value. This testing canbe in the form of dynamometer testing at the plant of the manufacturer or user, or other testing where themotor current and voltage can be measured and the motor torque at zero speed determined by a thrust ortorque measuring device. There are a number of diagnostic systems presently available to measureactuator thrust and torque. It is beyond the scope of this guide to discuss methods for determining motortorque from these diagnostic systems. In general, the locked-rotor torque capability of the motor itselfshould be determined,not the effect of rotational inertia of the actuator components. Where the outputtorque of the motor is assumed to be greater than the rated starting torque of the motor,each of theparameters (such as power factor，locked-rotor current,and locked-rotor torque) in the equation toestimate the output of the VAM should be determined by testing the specific VAM being evaluated.
For applications where the hammerblow feature of the motor operator has been supplied, the VAM wouldstart unloaded, thus requiring less voltage to start and shortening the inrush current for a few millisecondsbefore actuating the hammerblow feature and loading the motor. Therefore, the VAM is only required to supply the torque associated with seating or unseating the valve while the motor is operating above zerospeed. The current associated with this torque can be as much as 50% less than the locked-rotor current.The voltage requirement for the unloaded motor would be expected to be reduced; however, this shouldbe confirmed with the valve actuator supplier. The user may use this torque and current value in his or heranalysis. The cases where the hammerblow feature could be negated are valves that have nonlocking gearsets with the valve position maintained by motor brakes,or valves that have last been seated by manualaction. However，plant procedures generally require stroking the valve electrically after any manualmanipulations.