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19 September, 2019

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The Rise of motor applications

02 January, 2019

Rob Wood, ABB’s UK sales manager for LV motors, continues to work through the Rise acronym – Requirements, Infrastructure, Standards and Environment – used to choose the best motor for your application. This month he looks at infrastructure and standards. 

Network voltages and frequencies vary around the world. Additionally, industries and applications may require voltages that are unrelated to the country where the motor is being used or was purchased. 

The ability of the local electrical network to support an application is of particular importance when starting a motor. For fixed-speed motors, an excessively long starting period will cause harmful temperature rises and high currents can cause electromechanical stress. 

This starting period is a function of the load, motor torque and inertia. Between starting speed and nominal speed, the motor torque must be sufficiently high to cope with the greatest possible load torque, even during poor conditions such as having a low voltage across the motor terminals.

Electric motors can generally cope with long starting periods caused by high-inertia loads such as fans, or a pump starting with an open valve leading to the impellor immediately having to push against a body of liquid. The higher torque required to overcome this inertia requires more supply current. Care must be taken to ensure that the local infrastructure can handle these current peaks, and network restrictions on starting current will often influence the specification of large motors.

Another consideration is the growing use of smaller induction motors and variable-speed drives. This combination increases the amount of reactive power taken from the supply. Users who take large amounts of reactive power from the network can be liable to fines and penalties from utilities.

Standards

Knowing the motor’s torque, speed, power and electrical characteristics, it is time to narrow down the selection by turning to the international standards that govern the dimensions, efficiency and performance of electrical motors.

The main international standards bodies are the IEC (International Electrotechnical Commission), Nema (National Electrical Manufacturers Association) and the IEEE (Institute of Electrical and Electronics Engineers). However, in addition to the main standards there can be national or industry-specific standards, and even customer specifications that affect the motor selection. Make sure that you follow all applicable standards and specifications for your project. Finally, the motor might also be subject to local standards which define mandatory minimum efficiency levels. 

Next month, we will look at where the motor will be used, and how that affects its selection.  

For more information, you can watch this video: http://bit.ly/2PyY4fI




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