Necessity of Starter in DC Motor

The necessity of a starter in a DC motor is crucial because it controls high inrush currents, ensures smooth acceleration, protects against damage, enables automation, and enhances energy efficiency.

DC motors are widely used in industrial and commercial applications due to their controllability, reliability, and efficiency. However, starting a DC motor without a starter can lead to several operational challenges and potential damages. This article need of a starter in a DC motor, detailing its functions and protective role.

There is a necessity of starter in a DC motor for the following reasons.

Table of Contents

Reasons for Use of Starter in DC Motor

1. High Initial Current (Inrush Current) Control

One of the main reasons why a starter is used in a DC motor is to manage the high inrush current during startup. When a DC motor is powered on, it can draw current several times higher than its rated operating current because of:

Low Armature Resistance: At startup, the armature resistance is very low, leading to a surge in current. The resistance increases after running the motor because it increases with the increase in motor temperature.
Absence of Back EMF: The motor has not yet started to generate back electromotive force (EMF), which normally opposes the supply voltage and limits current. The back EMF develops when the motor starts rotating and is zero when the motor is at a standstill.

Mathematically, the armature current is expressed as,

high starting current at the start of DC motor

This shows that the DC motor draws a high starting current. To limit this, the starter of a DC motor adds resistance in series with the armature, controlling the initial current flow.

High inrush currents can lead to:

Electrical Stress: Excessive current can lead to overheating and potential damage to the motor windings.
Power Supply Fluctuations: A high initial current can cause voltage drops in the power supply network, affecting other connected devices.
Increased Wear: The sudden torque can cause mechanical stress on the motor and associated machinery.

Starters limit the inrush current by gradually increasing the current supplied to the motor, ensuring a smoother startup, protecting both the motor and the power network.

2. Controlled Acceleration

Directly starting a DC motor may result in rapid acceleration, which is undesirable due to:

Mechanical Stress: Sudden acceleration can cause mechanical shock to the motor and the load it drives, leading to wear and tear or mechanical failure.

Safety Concerns: Rapid, uncontrolled acceleration in machinery can pose significant safety risks to operators and nearby personnel.

The starter DC motor allows controlled acceleration by gradually increasing voltage or current, ensuring smooth operation and minimal mechanical stress.

3. Motor Protection

Starters are equipped with various protective features that safeguard the motor during both startup and normal operation:

Overcurrent Protection: Starters can detect and limit excessive current, preventing overheating and potential damage.
Under-Voltage Protection: If the supply voltage falls below a critical level, the starter can disconnect the motor to prevent damage from under-voltage conditions.
Thermal Protection: Many starters include thermal overload protection, which disconnects the motor if it overheats.

These protections extend the motor’s lifespan and maintain reliability in industrial operations.

4. Automation and Remote Control

Motors are started and stopped frequently in many industrial applications, sometimes under varying conditions. Manual control of each operation can be impractical and inefficient. Starters enable:

Automated Control: Starters can be programmed to start and stop motors based on predefined conditions, such as time schedules, temperature, or load demands.

Remote Operation: Modern starters often allow for remote control, facilitating motor operation from a central control system or a remote location.

This automation reduces manual intervention and enhances operational safety and control.

5. Energy Efficiency

Modern starters, such as thyristor drives, optimize voltage and current supply for DC motors, ensuring energy-efficient operation. This reduces power consumption, lowers operational costs, and minimizes environmental impact.

Necessity of Starter in Induction Motor

Just like DC motors, induction motors require starters to ensure safe and efficient operation. When an induction motor is started, it can draw a very high inrush current, often 5 to 7 times its rated current. This sudden surge can cause:

Electrical stress on the motor windings
Voltage drops in the supply network

Mechanical stress on the motor and connected machinery

To prevent these issues, starters are used to limit the starting current and provide controlled acceleration. Common types of starters for induction motors include:

Direct-On-Line (DOL) Starter: Simple and cost-effective for small motors.

Star-Delta Starter: Reduces starting current by connecting the motor in a star configuration initially, then switching to delta.
Auto-Transformer Starter: Provides reduced voltage at startup for smoother acceleration of large motors.

Using a starter in an induction motor not only protects the motor but also ensures energy-efficient and safe operation, especially in industrial applications where motors are frequently started and stopped.

Conclusion

The necessity of a starter in a DC motor is clear: it limits high inrush currents, provides controlled acceleration, protects the motor, enables automation, and improves energy efficiency. Using the right starter of DC motor ensures safe, reliable, and efficient operation in industrial and commercial applications. Understanding your motor’s requirements helps in selecting the appropriate starter, enhancing both performance and longevity.

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