FAQ | Avco Engineers

FAQ

1. Can a 1500 RPM motor be run at 3000 RPM by frequency inverter application
No. It will have mechanical problems like bearing failure.

2. Why one has to buy higher frame size motor if it is to be used with frequency inverter applications?
If the motor is run at lower speed, cooling will be insufficient. With a higher frame motor more
surface area for cooling will be available.

3. What is the significance of using only a particular speed motor with a particular application? What are the consequences if 3000 RPM motor is used in place of 1500 RPM motor or vice versa?
Driven equipment is designed to run at particular speed only. If it is run at higher speed, mechanical
damage and accident may occur. If it is run at lower speed, output will be less than rated.

4. What is the full load current of the motor?
Please refer the performance chart for the motor in the relevant section on this website.

5. What is the starting current of the motor?
Please refer the performance chart for the motor in the relevant section on this website.

6. What is the size of starter and overload relay range required for a particular motor?
his has to be obtained from the starter supplier.

7. What is the full load torque of the motor?
Please refer the performance chart for the motor in the relevant section on this website.

8. What is the starting torque of the motor?
Please refer the performance chart for the motor in the relevant section on this website.

9. What is the method of starting for a particular motor.- DOL, Star-Delta, Rotor Resistance
Normally for small motors upto 10 HP – DOL, for 10 HP and above ratings star-delta and for slipring
motors- Rotor resistance.

10. How many times a motor can be started in an hour without any harmful effect on the winding?
2 Hot, 3 Cold and 4 Equally spaced starts for S1 duty motors.

11. What is the safe limit of the body temperature of the motor?
As per insulation class of the winding. Please refer relevant chart for insulation in the related section on this web site.

12. What is the significance of Ambient Temperature on performance of the motor?
Increase in ambient temperature will affect the output/KW of the motor.

13. What is the difference between Class ‘B’ and Class ‘F’ insulations? Which is better?
Temperature withstanding capacity of the motor winding differs with the class of insulation material used. Class ‘B’ insulation temperature limit is 130 0C. Class ‘F’ insulation temperature limit is 155 0C. Naturally Class ‘F’ is better than Class ‘B’.

14. Can the motor winding withstand heavy fluctuations in the supply voltage? What is the effect of surges on the winding?
Yes, to a certain limit. Apart from insulation failure, mechanical stresses also take place due to voltage surges in motor winding.

15. At what minimum supply voltage the motor can be safely started without harmful effect on the winding?
90 % of rated voltage.

16. What is the minimum time required by the motor to attain full speed at the rated load?
As per IS 325.

17. What are the percentage efficiencies of the motor at full, half and quarter loads?
Please refer the performance chart for the relevant motor in the related section on this web site.

18. What is the motor power factor at full, half and quarter load?
Please refer the performance chart for the relevant motor in the related section on this web site.

19. What is the value of per phase winding resistance of the motor?
Please refer the performance chart for the relevant motor in the related section on this web site.

20. What is the rated speed of the motor?
Please refer the performance chart for the relevant motor in the related section on this web site.