Dual-speed motors

Dual-speed motors are a cost-saving solution for applications requiring only two speeds that moreover reduces the risk of failure. Typically, these motors are designed for an operating speed and a slower speed to facilitate startup. Dual speed motors can propel fans, pumps, hoists, and other machines at two different speeds without a frequency inverter. 

Menzel is a German motor manufacturer and offers you an extensive range of large electric larger dual-speed motors in low and medium voltage up to frame sizes IEC 560 mm.

Large two speed three-phase motors from German manufacturer

Two speed three-phase motors continue to be seen as a simple alternative to realizing two operating speeds, even if their use has been greatly reduced by the use of frequency converters. Nevertheless, dual-speed designs of large motors have become a rare exception. However, Menzel continues to offer large two speed three-phase motors – low and medium voltage.

We manufacture large pole-changing motors for countries with 50 Hz or 60 Hz mains frequency. Of course, like all of our electric motors, they comply with the current standards EN60034 and IEC60034, VDE, DIN and ISO. As a German manufacturer, we are able to implement specific special designs in our Berlin (Germany) plant at any time. We also offer a wide range of additional designs for our two speed motors, such as special braking systems and more.

Dual speed motors up to 1000 kW and 11 kV

• Power range: from 100 kW to 1000 kW
• Voltage: from 380 V to 11000 V
• Mounting: B3 and V1 (special designs can be implemented at any time)
• Shaft heights: from 315 to 560
• Cooling: IC01 / IC 411 / IC 81W / IC 611 (special designs can be implemented at any time)
• Protection: IP23, IP55, IP67
• Number of poles: various number of poles possible
• Motor housing: cast iron or welding steel
• Thermal utilization: according to B or F, optionally H

6000V dual-speed motors for cement plant in Central Asia

In a current project, the end customer had explicitly specified 6000V pole-changing motors. To implement the particular speed ratios, Menzel manufactured three-phase asynchronous motors with two independent stator windings, a 6-pole and an 8-pole winding combined in one housing.

The dual-speed motors intended to power fans in a cement plant have a rated voltage of 6000 V with rated operating speeds of 988 min-1 and 746 min-1 at rated outputs of 850 kW and 500 kW respectively. As another special feature, these customized motors withstand ambient temperatures from -38 °C to 40 °C.

The principle of dual speed motors

Dual speed motors are designed for operation with two, sometimes three constant speeds, between which you can switch back and forth. The speeds result from the respective number of pole pairs of the motor. They are a simple alternative to frequency inverters as you can economically implement two or three operating speeds in industrial machines and systems.

With a two-speed motor, speed and power can be easily adapted to the requirements of the application, which can lead to considerable energy savings. By lowering the motor speed, power consumption can be minimized and CO2 emissions can be reduced.

Dahlander circuit or two separate stator windings

Pole-changing motors can be divided into two groups: winding in Dahlander connection on one hand, and two separate stator windings on the other hand.

A Dahlander motor is a motor with two speeds that offers a 1:2 switchover (example 2: 4, 4: 8 or 6:12, etc.). Motors with Dahlander circuit are designed for a direct grid start and are operated with only one voltage. Only one winding is used, which enables two different circuits in the terminal box for the individual speeds. The two circuit types ∆/ΥΥ (triangle / double star) and Υ/ΥΥ (star / double star) are common for a Dahlander circuit.

While you can only achieve a speed ratio of 1:2 with a winding in Dahlander circuit, two separate stator windings offer the possibility of different speed ratios. Pole-changing motors with two separate windings have different polarities, for example 4/6, 6/8 etc. Circuits types for separate windings: ∆/∆, Υ/Υ, ∆/Y. Separate stator windings can either be connected together in one single terminal box. Alternatively, they can be arranged in separate terminal boxes.

Typical applications of dual-speed medium voltage motors

Dual-speed medium voltage motors are used, for example, in the transport industry, e.g. for the transport of bulk goods as well as in hoists, pumps or ventilation systems.

• Fans
• Ventilators
• Conveyors
• Pumps
• Hoists and more

The advantages of MENZEL dual speed motors

• Two speeds combined in one motor
• No frequency inverters / power electronics required
• Robust solution for environments in which the installation of power electronics is not appropriate
• Well-designed robust package for high load capacity
• Low acquisition and operating costs
• Good vibration values ​​and low maintenance costs
• Various customization options