Hello friends, in today’s article we will see how many types of motor starters there are and what they are and how many methods to turn on the motor and much more about it.
What is a Motor Starter?
A motor starter is an electric device by which we can turn any motor on or off. Its function is very similar to that of a relay that turns the motor on and off and Provides protection to the motor against over voltage and under voltage from the relay.
The following are the main functions of a motor starter.
- Turn on the motor safely.
- Turn off the motor safely.
- The need for the motor to change the direction of time.
- Provide protection against motor overvoltage and Undervoltage.
The motor starter consists of two main components which are used to protect and control the motor.
Electrical Contactor: The main function of a contactor is to turn on/off the power supply in the motor by making or breaking contact terminals.
Overload Protection Circuit: This can be identified by its name and what its function is. It works to isolate the main current from experiencing even the slightest overheating of the motor. Due to which the stator and rotor of the motor are not damaged in any way.
Why We Need a Starter with a Motor?
When current is given to the induction motor, the current of the magnetic field moving in the rotor winding and the AMF behind the current produced increases the motor torque, which leads to a higher rotor current.
In the time between the application of the electric supply to the motor and the actual acceleration of the motor at its full speed, a large amount of current is drawn from the supply through the stator. The amount of starting current is 5 to 6 times higher than the full load.
This current is only for a short time. Due to the large current flowing in the cable, the voltage drop in the system can cause damage to the electrical equipment. For this reason, a certain method of starting the motor is required.
How does a Motor Starter work?
A starter is an electrical device used to easily turn the motor on and off. Contacts are made easier with the help of a starter so that the motor can be turned on and off.
With the manual starter, we can turn the small motor on and off. In this, the hand-operated lever is operated manually by moving the contact position and turning it on and off. The disadvantage of a manual starter is that it has to be restarted in case of power failure. In other words, both its actions are done manually.
Occasionally such a position can also be caused by the motor winding force due to the high current being carried in the motor. Due to this situation, this starter is not used much. This is why other alternative motor starters with protection such as automatic starters are used instead.
Automatic starters use electrochemical relays and contactors, which are used to switch the motor on/off operation. When this is powered, the power passes through the contactor coil and forms an electromagnetic field, which pulls or pushes the contacts to connect the motor windings to the power supply.
The starter uses pushbuttons called start and stops which cause the motor to start and stop. The contactor is de-energized using stop buttons. So that the coil leads to de-energies. Thus a spring is used between the contacts of the contactor so that the contactor returns to its original position and the motor stops working.
Types of Motor Starters Based on Different Techniques And Starting Methods:
Various starting techniques are used to turn on the induction motor in the industry. Before we talk about the type of motor, we will look at some of the techniques used in motor starters.
- Full Voltage or Across The Line Starter.
- Full Voltage Reversing Starter.
- Multispeed Starter.
- Reduced Voltage Starter.
#1. Full Voltage or Across The Line Starter:
In such a starter the motor is given direct power from the electric line. The power rating of the motor connected to such a starter is low. So that large voltage drops are not made in those power lines. Such a starter is used in places where the motor rating is low and needs to be driven in one direction.
#2. Full Voltage Reversing Starter:
3 phase induction We can change the direction of the motor by switching any 2 phases. Such a starter consists of two mechanically connected magnetic contacts with alternating phases in the forward and opposite directions. Such a starter is used where the motor needs to be driven in both directions and is used for contact.
#3. Multispeed Starter:
To change the speed of an ac motor it is necessary to vary the frequency of the given power supply or to vary the number of poles of the motor (by reconnecting the windings in some). This type of starter drives the motor at a slightly pre-selected speed to complete its applications.
#4. Reduced Voltage Starter:
The most common way to turn on a motor is to drastically reduce the voltage at the start of the motor to reduce the current flow so that the windings of the motor can be damaged as a result of a drastic reduction in voltage. This type of starter is used for high rated motors.
Type of Motor Starters:
The types of motor starters are as follows and their advantages and disadvantages are also shown.
|Sr.No.||Type of Motor Starters|
|#1||Direct Online Starter (DOL)|
|#2||Stator Resistance starter|
|#3||Rotor Resistance or Slip Ring Motor Starter|
|#5||Star Delta Starter|
|#7||Variable frequency drive (VFD)|
There are many types of motor starters but they are mainly divided into two parts which are as follows:
- Manual Starter.
- Magnetic Starter.
#1. Manual Starter:
This type of starter does not require any skills to turn it on. Anyone can turn it on normally. A push-button is used to turn it on and off. There is a mechanical switch on the back of the push button. Completes the circuit when turned on and breaks or opens the circuit when closed.
The manual starter provides protection against overload but does not protect against low voltages. That is, in case of power failure it cannot break the circuit which can be a catastrophe for some applications.
The motor has to be restarted when the power is restored. This is used for low power motors. Direct on-line (DOL) starter is a type of manual starter that provides overload protection but not against low voltage.
#2. Magnetic Starter:
Magnetic Starter is used for high power AC motors. It uses electromagnetic relays to create magnets which help in disconnecting the circuit.
This provides low and safe voltage when starting the motor. It protects the motor against low voltage and overcurrent in such a starter. In the condition of power failure, this starter breaks the circuit automatically. Unlike manual starters, this includes automatic and remote operations that exclude the operator.
There are mainly two circuits of a magnetic starter.
- Power circuit: This is mainly responsible for powering the motor. Its electrical contacts are included. Due to which the power supplied to the motor from the supply line by the overload relay turns on / off.
- Control circuit: This is used to control the contact that supplies power to the motor. The electromagnetic coil gives strength to pull or push the contactor, or de-energizes. Thus providing a remote control for the magnetic starter.
#3. Direct Online Starter (DOL):
The dol starter is the simplest form of starter in which the motor is connected directly to an incoming electric current. It includes a magnetic contactor that connects it to the incoming power and also protects it from overload. Which type of voltage is not dropped while starting the motor.
So such a starter is used for motors with a rating of less than 5 HP. Thus 2 simple push buttons are used to turn the motor on and off. Pressing the start button of the motor gives strength to the coil which pulls the contacts together to complete the circuit of the circuit. And pressing the stop button stimulates the contact coil and pushes its contacts forward and thus breaks the circuit.
This does not provide a safe starting voltage to the starter motor. But overlapping relays also provide protection against overheating and overcurrent. Overload relays usually have closed contacts that excite the coils of contacts. When the relay trips, the coil of the contactor excites the circuit and breaks.
Advantages of DOL Motor Starter:
- The design of this starter is simple and easy.
- It is easy to understand and operate.
- Generates high torque due to high starting current
Disadvantages of DOL Motor Starter:
- High currents can damage the windings of the motor.
- Not suitable for high ratings.
- This shortens the life of the motor.
#4. Stator Resistance Starter:
The stator resistance starter method uses a reduced voltage starter technique to connect an external resistor to each winding series of the motor. The main function of a resistor is to reduce the line voltage applied to the stentor. At the start of the motor, the variable resistor is kept in the state of maximum resistance. Due to the voltage drop of the resistor the motor gets a safe amount of voltage.
Low stator voltage limits the initial inrush current that damages the motor windings. As the speed of the motor increases, the resistance is reduced and the motor is connected to direct power.
As the current is directly proportional to the amount of voltage and the torque varies with the square of the current, the torque decreases 4 times as the voltage decreases 2 times. Thus the initial torque using such a starter is very low and needs to be maintained.
Advantages of Stator Resistance Motor Starter:
- This can be used in both Star and Delta.
- The variable voltage supply allows easy acceleration
- It provides relief in the initial characteristics.
Disadvantages of Stator Resistance Motor Starter
- Starting torque is equal to lack of voltage.
- Resistors have proven to be very expensive for motors of large ratings.
- Resistors strip power.
#5. Rotor Resistance or Slip Ring Motor Starter:
This type of starter operates on full voltage. It is also known as a slip ring motor starter as it only works for one slip ring induction motor.
The external resistance is connected to the rotor in a star combination with the help of a sleep ring. This resistance limits the rotor current and helps to increase the torque instead of reducing the initial stator current. It also helps to improve the power factor.
The resistors used in this way are used only at the beginning of the motor. Once the motor reaches its proper speed then this is removed.
Advantages of Rotor Resistance Motor Starter:
- This method improves the power factor.
- Motion control can be done easily.
- Due to the high torque, the motor can start even under motor load.
- It provides an initial current using full voltage.
Disadvantages of Rotor Resistance Motor Starter:
- Only works for slip ring induction motor.
- The cost of the rotor increases and so does the weight.
#6. Autotransformer Starter:
A step-down or autotransformer is used to reduce the voltage applied to the stator at the beginning of the motor. This type of transformer can be connected to both star and delta type motors.
The secondary winding of the autotransformer is connected to each phase of the motor. Autotransformer Multiple tapings provide a fraction of the rated voltage.
At the start of the motor, the relay stays at the starting point so the motor gets the voltage only in low. The tap point providing the voltage. Rotate the relay between the tape points to increase the voltage with the speed of the motor. And finally, connect the motor with full voltage.
Compared to other voltage reduction techniques, it provides a higher voltage for a specific starting current. It has been shown to help provide better starting torque.
Advantages of Autotransformer Starter:
- It can also be used at a manual speed.
- It provides torque to the motor perfectly.
- It also gives relief to the initial features.
Disadvantages of Autotransformer Starter:
- Due to the large size of the transformer takes up more space.
- Circuits are very complex and expensive in proportion.
#7. Star Delta Starter:
Star Delta Starter Nose is used in industries for large-rated motors. The winding of 3 phase induction motor is converted from star to delta
The star connection of the induction motor is connected using that triple pole double throw relay. Due to the star connection, the phase voltage is reduced by a factor of 1/3 and it reduces the initial current as well as the initial torque by 1/3 of the normal rated value
When the motor reaches its proper speed, the timer relay acts to turn the star connection of the stator windings into a delta connection, so that each phase receives full voltage and the motor works properly.
Advantages of Star Delta Starter:
- It does not need maintenance.
- Simple design.
- Used for motors of large rating.
- It is best for long acceleration times.
- Provide low bounce current.
Disadvantages of Star Delta Starter:
- Operates only on motors with a delta connection.
- More wire connections are found.
- The motor feels a normal jerk as it rotates from star to delta.
- The initial characteristics are there is very limited flexibility.
#8. Soft Starter:
The Soft Starter works on the same voltage reduction system as other starters. This motor uses a semiconductor switch like the TRIAC to control the voltage as well as the current supplied to the induction motor.
Fuse control TRIAC is used to provide variable voltage. In voltage, TRIAC’s carrier angle or firing angle can be separated. The minimum carrying angle is kept to give this reduced voltage to the motor. The carrying angle is increased and the voltage is gradually increased. At the maximum carrying angle, the full line voltage is applied to the induction motor and it runs at the prescribed speed.
The starting current and voltage provide a slow and smooth increase in torque so that no one feels the shock, which makes the motor work smoothly, which increases the life of the machine.
Advantages of Soft Starter:
- It is small in size.
- Increases the age of the system.
- Reduces power surges in the system.
- Provides smooth acceleration so no shock is felt.
- Reduces power surges in the system.
- Efficiency is high Lack of maintenance required.
Disadvantages of Soft Starter:
- The system is very expensive.
- Dissolves energy in the form of heat.
#9. Variable frequency drive (VFD):
Variable Frequency Drive (VFD) can also vary the given voltage and frequency like a soft starter. Variable Frequency Drive (VFD)
Is mainly used to control the speed of the induction motor as it depends on the given supply frequency.
Converts from the supply line to DC using AC rectifiers. Pure DC is converted to AC with adjustable frequency and voltage using pulse width modulation technology through power transistors such as IGBTs.
Gives complete control over the determined speed of the motor from start to finish. Speed adjusting option with variable voltage provides better current and current acceleration.
Advantages of Variable Frequency Drive:
- It offers full speed control with easy acceleration and distraction
- It increases life expectancy due to the absence of electrical and mechanical stress.
- Provides good and easy acceleration for large-rated motors.
Disadvantages of Variable Frequency Drive:
- Dissipates heat.
- The cost of the system increases if speed control is not required.
- VFDs create harmonics in electric lines that affect electronic devices and the power factor.
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