How to find your motor replacement in five simple steps.
You need to replace your electric motor and want to know which electric motor you need.
It is not always easy to find the correct replacement motor.
You might need to replace an older model that is obsolete or discontinued.
To help you, we will explain in 5 steps how to choose the right electric motor.
In this video, we assume a three-phase motor, as this is the most commonly used type of electric motor.
In many cases, all the information can be obtained from the nameplate on the motor.
Step 1 Determine nominal power
The nominal power of an electric motor is normally expressed in kilowatts.
On older motors, the power may also be expressed in horsepower.
The conversion is 1 horsepower equals 0.75 kilowatts.
The power of an electric motor is based on the maximum power for a constant load.
In this example, the electric motor has a nominal power of 1.5 kilowatts, or 2 horsepower.
When you select 1.5 kilowatts, however, the new motor will have the same nominal power, you still need to select the motor's other specifications.
We will explain how to do this in the following steps.
Step 2 Determine the motor mounting.
An electric motor can be mounted in several ways, such as with a foot only, an inner flange, an outer flange, or a combination of these.
The design, or mounting method, is defined by a code from the European IEC 34-7 standard.
The five most commonly used mounting methods are: B3 Foot only B5 Outer flange Flange diameter exceeds that of the motor B14 Inner flange Flange diameter is smaller than that of the motor B35 Foot mounted plus outer flange Combination of B3 and B5 B34 Foot mounted plus inner flange Combination of B3 and B14The design can often be read from the nameplate.
However, it can also be determined using this drawings.
The electric motor in our example has mounting B14.
This is an inner flange.
This design can be identified by the threaded holes in the face of the motor.
For a B5 design, the diameter of the flange exceeds the diameter of the motor and the bolt holes are unthreaded.
Step 3 Determine nominal speed.
The nominal speed is usually stated on the nameplate.
This is the actual rotational speed of the output shaft and is expressed in revolutions per minute or RPM.
The RPM on our nameplate is 2860 revolutions per minute.
An alternative way of expressing this speed is by listing the number of poles.
A two pole motor has an RPM equivalent to 3000.
For four poles, this is 1,500 RPM, 1,000 RPM for six poles, and so on.
Due to technical reasons, the actual speed of the shaft always deviates slightly and is lower than the figures given in this picture.
So make sure you always round up correctly.
The common rule of thumb is speed of the motor equals 6,000 divided by the number of poles.
So, a four-pole motor has 6,000 divided by 4 is equal to 1,500 RPM.
We select the nearest speed, round it up.
For the example used here we have a 2-pole motor with a nominal speed of 3000 rpm.
This 3000 rpm is the theoretical speed.
So, select the correct speed by rounding up the required speed.
In our example, a 2-pole motor with 3000 revolutions per minute.
Step 4 Determine the frame size.
The frame size of the electric motor is another important characteristic.
As the dimensions for the European market have been laid down in the IEC standard, electric motors of different brands, but with matching characteristics, are often interchangeable.
Most manufacturers use the same dimensions for a particular size.
The most important dimensions according to the IEC standard are: A.
Distance between mounting holes, perpendicular to motor.
B.
Distance between mounting holes parallel to motor C.
Shoulder of shaft to the first mounting hole D.
Diameter of output shaft at drive end D E.
Shaft length H.
Shaft height For electric motors adhering to IEC standards, most dimensions are directly related to the shaft height or frame size of the motor.
This is the distance between the center of the output shaft and the center and bottom of the feet of AB3 style motor as indicated in this diagram by the letter H.
In our example, the electric motor has a frame size of 90.
Select 90 as the IEC frame size.
Step 5.
Determine the correct efficiency class.
From June 16th, 2011, most motors on the market must be marked in accordance with the IE directive and classified with an efficiency class.
The efficiency classes for electric motors are: IE1 Standard Efficiency IE2 High Efficiency IE3 Premium Efficiency IE4 Super Premium Efficiency Since January 1st, 2017,All new electric motors with a power rating of 0.75 kilowatts or above must meet the IE3 standard.
However, there are exceptions to this rule.
The electric motor in our example has an energy efficiency of IE1.
In order to meet current regulations, select IE3.
26 сен 2024
