Motors starters are a device that is used to start a motor from stop. Motor starters consist of the switching means necessary to start and stop the motor and overload protection device.
Motor starters let you turn an electric motor on and off, while providing overload protection. Now, we have a power control device that offers more than just a manual on/off control, such as a knife blade switch. The manual motor starters also provide a means to protect the motor from overload conditions.
There are two main types of motor starters:
1. Manual Motor Starters
A starter which the force for closing the main contacts is provided exclusively by manual energy. Operating manual motor starters is fairly simple and straightforward. You press a button or toggle (mounted directly on the starters) to start or stop the motor. Mechanical linkages from the buttons or toggle force the contacts to open and close, starting and stopping the motor.
2. Magnetic Motor Starters
A starter which the force for closing the main contacts is provided by an electromagnetic energy.Magnetic motor starters consist of magnetic contactor and overload relay. Magnetic motor starters offer some additional capabilities not available in manual motor starters, most importantly, remote and automatic operation.
Types of magnetic motor starters
Motor starters are classified as either full voltage or reduce voltage starting.
1. Full Voltage Starting Motor Starters
This starter connects the incoming power directly to the motor. We also call across the line motor starters or direct on line motor starters.
1.1 Full Voltage Non-Reversing Motor Starters (FVNR)
It can be used in any application where the motor runs in only one direction, at only one speed, and starting the motor directly across the line. This type of motor starters is the most commonly used general purpose starters.
1.2 Full Voltage Reversing Motor Starters (FVR)
A starter intended to cause the motor to reverse the direction of rotation by reversing the motor primary connections while it is running. The motor starters reverse motor by reversing any two lead to the motor. This accomplished with two contactors and one overload relay. One contactor is for the forward direction and other is for reverse. It has both mechanically and electrically interlocked sets of contactors to prevent line shorts and energizing both contactors simultaneously.
1.3 Full Voltage Two-Speed Motor Starters
Motor windings in two-speed motor require special starter which can be connected to the motor to obtain different motor speeds.
Two-speed motor starters are designed to control re-connectable squirrel case induction motor for operation at two different constant speeds depending on the construction of the motor. The speed of an induction motor is a function of the supply frequency and the number of poles of the motor windings. To obtain different speeds with fixed supply frequency, the number of magnetic poles of the motor must be changed.
1.3.1 Two Speed One Winding Motor Starters (2S1W)
A single winding two-speed motor carries current in various configurations to provide either constant torque, variable torque, or constant horsepower at each speed. This type of starter is designed for motor which has a single winding for two speeds. Extra winding taps are brought out for reconnection for different number of stator poles. We also call this type of motor as consequent pole motor.
1.3.2 Two Speed Two Winding Motor Starters (2S2W)
A two-winding two speed motor carries current in only one of its windings at each speed.This type of starter is designed for motor which has separate winding for each speed. This motor construction is relatively simple. Separate winding motor with delta connected motor winding require one corner to be opened on each un-used winding.
2. Reduced Voltage Motor Starters
This starter intended to start and accelerate a motor to normal speed by connecting the line voltage across the motor terminals in more than one step or by gradually increasing the voltage applied to the terminals.Two main reasons to use reduced voltage motor starters are reducing the inrush current and limiting the torque output and mechanical stress on the load.
2.1 Reduced Voltage Auto-Transformer Motor Starters (RVAT)
Reduced voltage auto transformer motor starters use an auto transformer to reduce the voltage applied to a motor during start. Reduced voltage auto-transformer motor starters should be used with hard to start loads such as reciprocating compressors, grinding mills, and pumps.
2.2 Part Winding Motor Starters (PW)
Part winding motor starters first connect a part of the motor winding to the supply lines as the first starting step and then connect the remaining portion of the winding to the supply lines as the second step. Part winding motor starters are suited to low starting torques loads such as fans, blowers.
2.3 Wye Delta Motor Starters (YD)
Wye delta motor starters connect the phase windings first in wye relationship for the effect of reduced voltage starting and, subsequently, reconnect these phase winding in delta relationship for running. With wye delta starting, the starting current on the wye connection is equal to 0.33 times the locked rotor current on the delta connection. Wye delta motor starters are applicable to high inertia loads with long acceleration times such as centrifugal compressors.
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