Measuring starting parameters of squirrel cage induction motor

Question

I am trying to find some numerical solution for finding starting current and starting torque for three phase squirrel cage induction motor.

Some of the data I measured in energy meter such as

• no load test: VA=81.40 , W=20.11 , P.F.=0.255
• block rotor test: VA=899.7 , W=375.3 , P.F.=0.417

The motor rated voltage on the name plate is 150 V and rated frequency is 150 Hz. Power output is 275 W and 2 pole machine. I have some data which is starting torque 60% and starting current 570%.

Here I am confused on how to measure the starting torque and starting current value any way I need to calculate. If it is possible by circle diagram then please tell me how because I have limited data. Any equation so that I can get solution by using RS-485 communication type energy meter.

How can I get the solution?

Answer 1

The starting current and starting torque can be calculated from the per-phase equivalent circuit. The circle diagram is an aid for that calculation. You need to use the data from the no-load and blocked-rotor tests. However the DC resistance is also required and should be measured. You should be able to find the procedure for calculating the equivalent circuit component values in a text book or lecture notes that can be found on the internet. The procedure for calculating torque from the equivalent circuit can also be found.

The rated motor speed and current should be marked on the name plate. The rated torque can be calculated from the rated speed and power. With the rated torque and current, you can use the given percentage values to calculate starting torque and current.

The energy meter is not very useful beyond performing the no-load and blocked-rotor tests.

You should find the procedures mentioned above, work on the solution, then ask for assistance with any parts that you don't understand. The full solution can not be provided here as the answer to a single question.