NEMA and IEC Standard
NEMA standard used in northern America, especially the United States must be added that states that use the technology or buying plants from the United States. Meanwhile, the IEC adopted by some countries in the world except in America. In addition to other standards such as BS2613 British, German VDE and Japanese JIS 0530. Usually another standard that is adopted IEC metric.
NEMA or the National Electrical Manufacturers Association based in the United States.
IEC, International Electrotechnical Commission based in Europe.
Below is an example specification of an electric motor as an example for discussion in connection with the use of frequencies. What is difficult to avoid is that we bought a standard NEMA motors to be installed in the country that use IEC standard or vice verse. Requiring knowledge of electricity specifications and mechanical specifications of both standards.
Example: 100HP Motor, 230/460 V, 60 Hz,
Understanding of these specifications, are as follows:
- NEMA write with horse power capacity, 100 HP as the capacity or ability to move a load by the motor 100 horse power. Usually IEC stated capacity with KW (100 HP = 74.57 KW)
- 230V, motor winding consists of two sets of each phase and connected in parallel
- 460V, motor winding consists of two sets of each phase and connected in series.
- 60Hz, the frequency of electricity networks should be available for these motors.
(Retrieved from the table Leeson Motor Catalog)
Install the motor on 60 Hz 50 Hz Frequency
Power-grid in Europe and in almost all other countries use the system frequency 50Hz, except for North America to use 60Hz.
What is the effect of performance, put the motor in the frequency 60Hz. 50Hz? Is safe enough?
The answer to doubt "yes" or maybe "yes no".
So motor 60Hz, 460V at 50Hz, if installed, 380V will produce a satisfactory performance according to nameplate horsepower, and the rotation axis of rotation of 50/60 is only listed on the nameplate. So if 60Hz to 50Hz, that should Voltage 5 / 6 × 460V = 383V
Motor 60Hz 230V at 50Hz if installed 230V, may not satisfy without reducing horsepower for 0,80-0,85 factors. So HP mobilized rated load should be decreased, this relationship with the heat effects arising in the winding.
With the guidance table, it can be concluded that 100HP Motor, 230V/460V, 60 Hz, motor 1800Rpm connected 230V winding mounted on 220V / 50 Hz will occur as follows:
- Full load torque required 120%
- Round synchronous stator falls to 5 / 6 or 83.3% of 0833 × 1800 = 1500 Rpm
- Full load current to 115%
- Efficiency at full load down 2%
- Power factor down 3-4%
- Locked rotor torque rated up from the 130 to 135%
- Breakdown torque, up from rated to 120 to 125%
- Locked rotor currents from the rated up to 106%
- Heat in motor up to 153%
- Magnetic noise increases.