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What are the considerations for motor selection?

The pump is a general rotating machine, and its operating power comes from the motor. The types of pumps include sealless magnetic drive pumps, mechanical seal pumps or other forms of centrifugal pumps, all of which must be connected to a motor to deliver the fluid.


Motors can be divided into general motors, inverter duty motors and explosion-proof motors. The specifications of the motors are also different according to the application and environment. The following describes about how to select a suitable motor according to the requirements when using a pump.


For different purposes, it can be based on motor specifications, such as the number of poles (Pole), RPM, the frequency (Hz), voltage (V), the install location, IP Rating, and the energy efficiency index to decide which model to choose.


Pole, RPM, Frequency(Hz)

Pole represents the number of magnet poles in the stator magnetic field of the motor. According to the different connection forms of the stator coil windings, different numbers of poles in the stator magnetic field can be generated. The number of poles affects the rotational speed of the motor.


RPM stands for revolutions per minute. For example, the rotational speed of the motor is 3,600RPM, which means that the motor can rotate 3,600 revolutions per minute.


Frequency (Hz) refers to the frequency of the alternating current (AC) is the number of cycles per second in an AC sine wave. Frequency is the rate at which current changes direction per second, in the international measure Hz as the unit, we use 50Hz or 60Hz in the general worldwide.


RPM formula: RPM= Hz x 60(sec/min) x 2 ÷ number of poles

Therefore, under normal circumstances, when the frequency is 60Hz, 2P runs 3600 rpm, 4P runs 1800 rpm, 6P runs 1200 rpm, and so on. It can be seen from the formula that the number of poles, frequency and rotational speed are closely related to each other.


Voltage (V)

The voltage is proportional to RPM, that is, the higher the input voltage, the faster the motor rotates; the lower the input voltage, the slower the motor rotates.


IP Rating& Install Location

IP rating is usually marked with IPXX, such as IP54, IP55, IP56, etc. The first number after it represents the protection against contact and intrusion of solid foreign objects, and the second number represents the protection against ingress of liquid.

The motor can be installed indoors or outdoors according to the IP rating, depending on whether it can resist damage caused by wind, sun, rain, as well as customer operation requirements, noise problems and other conditions.


Energy Efficiency Index

International Efficiency is defined by the International Electrotechnical Commission (IEC), and the energy efficiency levels are divided into IE1, IE2, IE3, and IE4. The larger the number, the better the efficiency and the more power saving.


The above are the relevant specifications that must be referred to when selecting a motor. Next, the differences and applications of general motors, inverter duty motors  and explosion-proof motors will be introduced.

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