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Industrial Motor Control in the broadest sense of the term encompasses the different methods used to control an electrical system’s performance. With reference to machinery, it involves the start-up, acceleration, d eceleration, reversal and stopping of the motor and the applied load. Here, we take a look at the electrical control of three-phase alternating systems.

Industrial circuitry can be very complex and can’t be explained briefly and the information on this blog is restricted to elementary circuits. But the basic principles that are mentioned here are applicable to all types of control systems, regardless of how complex they are.

Control devices

A control circuit is made up of numerous basic interconnected components that achieve the desired performance. The components will vary in size depending on the motor’s power; however the operation principles stay the same. It’s possible to design a complex industrial control system, using these few basic components:

  • Manual circuit breakers
  • Disconnecting switches
  • Pushbuttons
  • Cam switches
  • Magnetic contactors
  • Relays
  • Thermal relays and fuses
  • Limit switches and other special switches
  • Pilot lights
  • Resistors, transformers, capacitors and reactors

Fuses haven’t been included in this list because they aren’t control devices; they are categorised as protective devices. Here is a more detailed look at what some of these components do:

Disconnecting switch

This switch isolates the system’s motor from the main power source. It is made up of three line fuses and three knife-switches that are enclosed in a metallic box. The latter can be closed & opened simultaneously with the use of an external handle. These switches are selected to carry the motor’s nominal full-load current as well as to withstand short-circuit currents for short intervals.

Manual circuit breakers

This breaker closes and opens a circuit just like any toggle switch. When it trips, it can be reset manually. These types of breakers are commonly used in place of disconnecting switches because you don’t need to worry about replacing fuses.

Cam switches

A cam switch is used to control the motion as well as the position of callenders hoists, machine tools etc.

Push-buttons

A push-botton switch is activated via finger pressure. Two/more contacts close or open when the switch is depressed. A push-button is usually spring-loaded so it returns to its normal position once the pressure is removed.

Control relays

This is an electromagnetic switch that closes & opens a set of contacts whenever the relay coil gets energized. This relay coil produces a very strong magnetic field that attracts a movable armature that has the contacts. A control relay is largely used in a low-power circuit.

Thermal relays

This is essentially a temperature-sensitive/overload device whose contacts close/open whenever the motor’s current exceeds its pre-set limit. The current then flows through a calibrated heating element that raises the relay’s temperature. A thermal relay is a basic component in any time-delay device because the system’s temperature can’t follow instantaneous alterations in current.

Magnetic contactors

They are control relays that are designed to close and open a power circuit. They have a magnetic plunger and a relay coil that carries a complete set of movable contacts. Magnetic contactors are utilized to control motors ranging from 0.5 hp – several hundred hp.

Power contactors for switching motors

There is a very wide range of power contactors used for switching motors, such as 3-pole standard contactors, vacuum contactors, 4-pole power relays, coupling relays, and miniature contactors.

Proximity detectors

These sealed devices are able to detect objects without actually coming into direct contact with them.

Pilot light

Pilot lights indicate the on/off state of remote components in a control system.

These are just a few of the basic components used in industrial motor control systems. If you want to know more about our power products and services, don’t hesitate to contact us at KaRaTec Power Supply Pty. You can give us a call at 612 9808 1127. You can also fill in this contact us form.

Thanks for reading,
Karatec Power Supply Pty
612 9808 1127

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