Tom Bishop. P.E. 
EASA Technical Support Specialist 

It should not be assumed that because a motor can drive a running load, it also has the capability to accelerate the load up to rated speed. During starting, a mo­tor must deliver the energy required to accelerate the load. To do this, the motor torque must exceed that needed to ac­celerate the load. The motor torque value in excess of the load torque requirement is termed the “torque available for ac­celeration,” as shown in Figure 1. 

Though this explanation appears to be relatively simple and straightfor­ward, there are some complex condi­tions. Namely, that the motor torque during starting is not constant, and unless the load is a pure inertia load (very rare), it does not have a constant speed-torque relationship. Therefore, the torque available for acceleration is the difference between the speed-torque curves for the motor and the load. 

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