Electric motors


In the last couple of years, the new trend among the European AC electric motor manufacturers is to increase the efficiency of motors.

Low-power motors up to about 22 kW are produced in a special high-efficiency motor series, the efficiency factor of which has been improved by about 5%. On the other hand, it has always been possible to buy more powerful motors with a slightly higher (by 1–3%) efficiency factor.

Considering the long life of the motors, mostly more than 30 years, and their high number of operating hours, the price of the motor is very low compared to its running costs. The price of a high efficiency motor is insignificant compared to the savings over its lifetime. On the other hand, it is not an optimal decision to replace existing and fully functioning motors with high-efficiency motors, except if the existing motors are in poor condition or if a longer payback time for a new motor is acceptable.

It should be noted that high efficiency motors always have a higher rated speed.

  • Automatic on/off mode is the easiest way to achieve savings. The methods are very diverse and their performance is closely related to use. The aim is to minimise the period of engine idling, following the need to operate the specific equipment. Sensors can be micro-switches, pressure switches, proximity sensors, etc., often combined with a time relay. Sometimes cheap electronic time relays are enough to provide a simple automatic solution.
  • Motor regulators are sometimes referred to as voltage regulators. When the motor controller detects a reduced load, it automatically reduces the voltage and therefore the magnetic flux to the required level to meet the load's energy demand. As a result, losses in the stator are reduced, and the efficiency ratio is increased. The characteristic curves of this device are often integrated parts of modern soft-starters and frequency converters. Step starters have four energy-saving advantages that can be used for motor loads with high starting inertia and torque that increases with speed.
  • Starting the motor at a reduced voltage rather than the rated one and gradually increasing the voltage, and therefore the load, during the start, allows reducing the power required at the moment of starting. As a result, the lower power motor operates closer to full load and with higher efficiency.
  • Similar to other methods that provide variable speed, the frequency converter directly regulates the power to the motor-driven equipment by changing its rotational speed. Unlike, for example, a two-speed motor, the frequency converter can adjust the power very well to the demand, so that the excess power does not have to be diverted by a gate, shunt, valve, etc. Using frequency converters for speed control in existing AC motor equipment is usually more advantageous than other variable speed drives such as variable speed motors, commutator motors and DC motors.

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