How to specify electrical motors for mixers ?
The power required for mixing is generally delivered through 3 phase electrical motors. In some cases, pneumatic or hydraulic motors may be used where-in variable speed operation is required, or mixer installation is in a hazardous zone.
The parameters to be specified for electrical motors used for mixing equipment are as follows:
- Single-phase power / Three-phase power – The use of single phase motors in mixing equipment is limited to household applications, small bakeries or in hotel kitchens. Industrial mixers are equipped with three-phase motors because they have higher starting torque, lower current requirement and are more efficient compared to single phase motors.
- Supply Voltage – Supply voltage for three phase power in most Asian countries is 415 volts. In USA, the supply voltage for three-phase supply is 460 volts.
- Supply Frequency – The frequency of the alternating current supply is to be specified for motors. The supply frequency in Asian and European countries is 50 Hz and that in USA is 60 Hz.
- Motor Power – Motor power is commonly specified in horsepower (HP) or kilowatts (kW).
1 HP = 0.746 kW
The motor power required for mixing equipment should be decided based on the estimated power for mixing, and the drive system losses. The drive system losses depend on the configuration, mechanical components of the drive system.
It is preferred that electrical motors should not be rated beyond 90% of the full load current specified on the motor name plate.
- Motor Speed – Three-phase motors are available in different speeds. Motors operating at 50 Hz frequency have speeds of 750 rpm, 1000 rpm, 1500 rpm, 3000 rpm. Likewise motors operating at 60 Hz frequency have speeds of 900 rpm, 1200 rpm, 1800 rpm, 3600 rpm.
Motors are designed to operate within 2 – 3% of their synchronous speed. The synchronous speed of motors depends on the number of poles in the motor winding.
Motor speed (in rpm ) = 120 x Frequency (Hz) / No. of Poles.
Thus a motor with 2 poles in motor winding and operating at 50 Hz frequency, shall operate at a speed of 3000 rpm.
- Motor Duty – Mixer motors are specified for continuous duty operation.
- Motor Amperage - Motor amperage is the measure of current required to operate the motor. The full load current of a motor is the current required when the motor is operated at its rated power. The full load current is generally specified on the motor name plate.
- Motor Efficiency – Motors are available in different efficiency classes such as Eff 1, Eff 2, etc. Depending on the application, appropriate efficiency class of motors should be specified.
- Motor Frame Size – The motor frame sizes are set by standards such as IEC (International Electrotechnical Commission), NEMA (National Electrical Manufacturers Association). The motor dimensions for a given frame sizes remain constant.
- Insulation Class – The motor insulation class establishes the maximum safe operating temperature of a motor.
- Enclosure Classification – This consists of specifying the type of motor enclosure, flameproof or non-flameproof operation, motor operating class, and group.
- Motor Mounting – Electrical motors are available in foot mounted and flange mounted constructions.
Unique Mixers & Furnaces Pvt Ltd
Contact Person: Mr Jayesh R Tekchandaney
Phone – +91-22-25801214/25822385
Website – www.uniquemixer.com