The Different DC/AC Motor Starters and Their Applications, Advantages, and Flaws
The motor starters are primarily used for reducing the current or voltage at the time the motor starts initially, and are not used in the self-starting motors. Because abnormally high or very low voltage can damage the components of a motor, the use of motor starters is necessary. Starters also keep the starting speed of the motor constant and avoid problems including short circuit and overloading. In lieu of the circumstances, other components like a circuit breaker or a contractor may also be used along with a starter. In accordance with the types of current viz. AC and DC), starters may also be of two types, viz. DC motor starters and AC motor starters.
DC Motor Starters
The DC motor starters are used for starting and stopping the DC motor safely. They are cheaper when compared to the AC motor starters and also have a simpler construction and built.
When the motor is turned “off”, the armature winding is devoid of any back EMF. The armature winding has a very low resistance. Therefore, when a high or full supply voltage is provided to the motor during its starting phase, a large current amount flows through the winding. This high amount of current may burn the winding or damage components (for instance brushes). If there is a large voltage fluctuation within the voltage main supply, the equipment can be damaged. All these issues are resolved through the use of the DC motor starters. The 3 main varieties of the DC motor starters, along with their benefits and flaws are given below.
2 Point Starters- The starters are used with DC series motors. They find application in cranes and in the railways where they can be used to stop the rail. 2 point starter does not allow the motor to draw high current during starting. It protects the motor in incidences including single phasing, no voltage, over voltage and under voltage.
3 Point Starters- The 3 point motor starters are used typically in the DC shunt motors. They are commonly used in areas including spinning mills and the lathe factories. The 3 point starters offer a number of advantages. They protect the motor from the current surges and in the instances of short circuit fault or overload. We can also use other equipment along with the starter so that it can control the speed of the motor as well. The only disadvantage associated with starters is that they are not useful when combined with the variable speed motor.
4 Point Starters - The 4 point starters are commonly used with the DC compound motor. They can also be used with the DC shunt motors. These starters are commonly used in the rolling mills and the process industries. When you have to protect the variable speed motors, the four-point starters are the best option.
AC Motor Starters
The induction and the AC Motors require the AC starter so that they can start safely. Adverse conditions such as power surges, overload, under load, and circuit failures do not affect the motor adversely when AC starters are used.
When an induction motor is connected directly to the large voltage supply, EMF of high-value effects induction motor’s rotor. Because of the exceptionally large EMF, a high current will flow in the rotor winding. For balancing this, a current also makes way through the stator winding. This current may damage the winding itself. A large fluctuation may also occur in the supply voltage, which damages the other components that may be connected to the line. Below is a brief description of the AC motor starter types.
DOL or Direct Online Starter- These starters are used in compressor, conveyor belts, and in the induction motors having a capacity of 7.5 KW. The cheap starters have a simple construction and can protect motor components in cases of short circuit and overload. The drawback of the starter is that it cannot reduce the starting current of the motor, but only acts as an "off/on” switch.
Stator Resistance Starter- The starters can also be used for motors having a rating greater than 7.5 KW. The starter can reduce the starting current and is quite affordable. The drawback is that the starter can also reduce that torque of the motor.
Auto Transformer Starter- These starters are quite easy to control and are energy efficient (no loss due to resistance). The flaw of the autotransformer starter is that it can also reduce the torque of the motor.
You can concert and a leading supplier to know about the best motor starters options and deals available to you. The starters may prevent an accident, reduce electricity consumption, and enhance the longevity of the motor and components.