Different Types Of Starters Used In Motor, AC Starters, DC Starters

July 22, 2020January 20, 2023 CS Electrical And Electronics

Hello Guys, welcome back to our blog. In this article, we will discuss different types of starters used in motors, different types of ac starters, and different types of dc starters, such as DOL starters, soft starters, auto-transformer starters, and star-delta starters.

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Different Types Of Starters Used In Motor

Guys, first I will tell you why we will use starters instead of starting the motor directly. At starting the motor is under the stationary condition and there is no back emf present in the armature, the resistance of the armature will be low at starting if we connect the motor directly to the supply then the motor will draw heavy current which is harmful to the dc motor.

Example: Consider a 5hp motor, 230v, 20A rated current and armature resistance of 0.5 ohms at starting.

When we give supply to the motor without a starter then the motor will draw more current i.e.,

I=V/R

I=230/0.5

=460 amps

which is 20 to 21 times greater than the full-load current. So to reduce the heavy current at starting, starters are always used in the motors. To limit the starting current starters are used. Connecting the motor directly will result, in the burning of the armature due to the heating effect, and the commutator or brushes will also get damaged due to heavy speaking. Now I will discuss different types of starters used for ac motors as well as dc motors.

Starter Used For AC Motors

The starters used for ac motors are:

01. Soft Starter
02. Direct Online Starter
03. Autotransformer Starter
04. Star-delta Starter
05. Rotor Resistance Starter

01. Soft Starters

a. In some applications, we need the smooth operation of controlling starting current at that time we can use a soft starter. In the soft starter, the thyristor voltage control method is used.
b. A total of six triacs are used in the soft starter. Two triacs are connected antiparallel with each other. Let’s give name as T1, T1′, T2, T2′, T3, and T3′.
c. By controlling the firing angle of the triac, the voltage applied to the motor can be controlled.
d. 60 degrees is the interval between successive firing. The firing frequency is 6 times the input frequency.
e. When the triac T3′ is fired, T1 & T3′ conduct for 60 degrees. Then later T2 is fired, T3′ and T2 will conduct for the next 60 degrees, and the cycle repeats.
f. Once fired, each triac conducts for 120 degrees.
g. As far as the triac is fired, the voltage is supplied to the motor.
h. We came to know that by controlling the firing angle, the voltage can be controlled.

02. Direct Online Starter

a. If the motor is below 5 hp, then a DLO starter is used.
b. For motors below 5 hp, there is no need to reduce current such type of motor can withstand the starting current. Direct online starters are used to connect the starter directly to the supply without controlling the current.
c. This starter is not used to reduce starting current but this starter is used for protecting the motor from abnormal conditions like single phasing, overloading, etc.
d. The normally open(NO) contact is open and normally closed(NC) is closed.
e. To start the motor, the NO button is pushed for a few seconds which energizes the coil and attracts the contractor, thus the stator gets direct supply.
f. To off the motor, press the NC button which opens the circuit of the coil and the coil gets de-energized then contractors get released and the motor will no get supplied.
g. When overload occurs the thermal overload relay will get opened.

03. Autotransformer Starter

a. The autotransformer starters are used to reduce the voltage applied to the stator.
b. The autotransformer starter consists of a suitable change-over switch. At the start, the stator is supplied by reduced voltage because the autotransformer is provided with tappings, by varying the knob voltage can be controlled. As the motor comes to 80% of the normal speed, the change-over switch is thrown into the run position. By this rated voltage will be applied to the stator and the motor runs at the normal speed.
c. This type of starter is used for high-rating motors.

04. Star-delta Starter

a. This type of starter is commonly used for the induction motor and it is very cheap.
b. In this type of starter, the stator of the motor is connected to the star at the starting and the voltage gets reduced by factor one divided by root three. Thus the voltage will be reduced and the current is limited.
c. When the motor obtains normal speed the switch is thrown on the other side, the winding gets connected in Delta, across the supply and it gets rated voltage.
d. This type of starter requires less maintenance.

Now I will discuss different types of starters used for dc motors.

Starters Used For DC Motors

The starters are: