Introduction
In order to obtain optimum performance, motors used for 50 Hz applications should be specifically engineered and manufactured for 50 Hz.
Frequently, the delivery of 50 Hz products is such that an alternate course of action, utilizing 60 Hz products, is desirable.
General Guidelines
The general guidelines for operating 60 Hz motors on 50 Hz systems relate to the fact that the volts per cycle have to remain constant with any change in frequency. Also, since the motor will operate at only five sixths of 60 Hz speed the output horsepower capability of 50 Hz is limited to a maximum of five sixths of nameplate H.P.
Simplified Selection
In order to simplify selection, a derate factor table has been prepared by Engineering.
The table is applicable to 2, 4 and 6 pole 60 Hz Drip-proof and TEFC motors. 8 Pole applications should be referred to Engineering.
All results are based on the derated motor having a 1.0 Service Factor.
| Required 50 Hz HP | |||
| Minimum 60 Hz HP | = | Derate Factor | Or |
HP Capacity @ 50 Hz = Nameplate HP (60Hz) x Derate Factor
|
60 Hertz Voltage |
50 Hertz Optional Voltage Rating (+or- 5%) |
|||
|
230 |
190 |
200 |
208 |
|
|
460 |
380 |
400 |
415 |
|
|
575 |
475 |
500 |
520 |
|
|
Derate |
ODP |
.85 |
.80 |
.75 |
|
Factor |
TEFC |
.80 |
.75 |
.70 |
Motor Over Current Protection
Motor running over-current protection is established by selecting starter heater elements as follows:
Open Drip-proof Motors
Motor Nameplate Amps x 1.1
Totally Enclosed Fan Cooled
Motor Nameplate Amps x 1.0
Using The Table
Example #1
For a 10 HP, 4 Pole, 50 Hz, 380 volt TEFC requirement, the derate factor using a 460 volt motor would be .80
Minimum 60 Hz HP = 10/.80 = 12.5 HP
A 15 HP, 4 Pole, TEFC, 230/460 60 Hz motor could be utilized.
Example #2
A customers machine has a load of 13 HP. Supply voltage is 415 volts 50 Hz.
Open Drip-proof, 4 Pole motor is adequate.
Minimum 60 Hz HP =13/ .75 = 17.3 HP
A 20 HP 60 Hz ODP motor could be applied.