What is a Three-Point Starter?
An electrical device known as a three-point starter is used to start and maintain the speed of a DC shunt motor. The connection of resistance in this circuit is in series which decreases the initial high current and protects the equipment against any electrical failures. Here, the event of back e.m.f plays an essential part in operating the motor. This EMF extends when the motor’s armature begins to rotate in the magnetic field by acting against the voltage supply.
A 3-point starter helps to start and run DC shunt or compound wound DC motors.
Now let’s discuss why these type of DC motors require the starter in the first place?
Well, it is because there is back EMF (Eb), which plays a critical role in governing the operation of the motor. The back emf creates as the motor armature begins to rotate in presence of the magnetic field, by generating action and counters the supply voltage. Consequently the back emf at the starting of the motor is zero, but it develops continuously as the motor gathers speed.
The general motor emf equation is:
E = Eb + Ia Ra
Where
E=Supply Voltage
Eb=Back EMF
Ia=Armature Current
Ra=Armature Resistance
E = Ia since Eb = 0,
Then
E = Ia.Ra.
Subsequently we can modify for the armature current Ia
Ia = E / Ra
We can see from the above equation that the current will be dangerously high at starting (as the armature resistance Ra is small) this end we really must used a device like the 3 point starter toward limit the starting current to acceptably low value.
Three Point Starter
The primary errand of a motor starter is to start as well as stop the motor to which it is united. Starters, like relays, are electromechanical switches designed specifically to protect the motor from overload. The starter gives the supply to the motor manually or automatically as well as protects the motor from faults or overload. It based on the types of motors, the motor starters are available in various sizes with different ratings in the market. This article discusses 3 point starter which is used in business as well as industrial applications.
Table of Content
- What is a Three-Point Starter?
- Construction
- Working
- 3-Point Starter Vs 4-Point Starter
- Advantages
- Disadvantages
- Applications