3 point starter | 3 point starter dc motor | three point starter of dc motor | three point starter

Mind of Engineer

4 Feb 202408:03

Summary

TLDRThis lecture delves into the workings of a three-point starter, a device used to protect DC motors from high starting current. It explains the construction, working principle, and important components like the series-connected resistance, which reduces the current to prevent machine damage. The lecture also covers the starter's terminals, the starting position, the under-voltage protection, and overload protection mechanisms. It highlights the advantages of using a three-point starter for smooth motor starting and speed control in various industrial applications, while also discussing its drawbacks and the concept of back EMF in DC motors.

Takeaways

😀 A three-point starter is a device used to protect DC motors from high starting current.
🔧 It includes a series resistance that reduces the high starting current, thus protecting the machine from damage.
🔌 There are three main terminals in a three-point starter: Line Terminal, Armature Terminal, and Field Terminal.
🔄 The Line Terminal is connected to the positive side of the battery, the Armature Terminal to the motor's armature winding, and the Field Terminal to the motor's field winding.
🔑 The construction, working principle, and important components of the three-point starter are discussed in the lecture.
🌀 The starter uses a series of components to limit the current, including a variable resistor known as the 'r' series, which includes R1, R2, R3, and R4.
🛠 The starter provides under-voltage protection by ensuring that the electromagnetic field's strength is reduced if the supply voltage drops or is off.
🔄 Overload protection is provided by an overload trip coil, which trips the circuit if the motor is overloaded, preventing motor burnout.
🔄 The speed of the DC motor can be controlled using the three-point starter, which is beneficial in applications like factories and spinning mills.
🔄 The three-point starter reduces high starting current and provides protection against short circuits and overload issues in the motor.
🔄 The term 'back EMF' is introduced, which is the voltage induced in the armature conductors when the stationary flux is cut by the rotating armature, affecting the speed and performance of the DC motor.

Q & A

What is a three-point starter and why is it used?
-A three-point starter is a type of device used to protect a DC motor from high starting currents. It includes a series resistance that reduces the high starting current, thereby preventing damage to the motor.
What are the main terminals of a three-point starter?
-The main terminals of a three-point starter are the Line Terminal, Armature Terminal, and Field Terminal. The Line Terminal is connected to the positive line, the Armature Terminal to the motor's armature winding, and the Field Terminal to the motor's field winding.
How does the handle of the three-point starter function during the motor start-up?
-The handle, initially in the 'Off' position, is manually moved to the start position. As the handle moves over resistance studs, the motor begins to start, with resistances reducing the armature current to a safe value until the motor reaches full speed.
What is the role of the NVC coil in the three-point starter?
-The NVC (No Voltage Coil) provides under-voltage protection. It holds the starter handle in the 'Run' position when the motor is running at full speed. If the supply voltage drops, the magnetic field weakens, causing the handle to return to the 'Off' position, cutting off the motor's supply.
How does the OLC coil protect the motor from overload?
-The OLC (Overload Coil) provides overload protection by tripping the circuit if the motor draws excessive current. This prevents the motor from burning out by cutting off the supply when an overload condition is detected.
What are the drawbacks of using a three-point starter?
-The main drawback of a three-point starter is the large speed variation it can cause in the motor. The NVC coil's magnetic strength can decrease, leading to the handle moving to the 'Off' position unintentionally. This type of starter is also not suitable for variable speed motors.
Why was the four-point starter introduced?
-The four-point starter was introduced to overcome the drawbacks of the three-point starter, such as the large speed variation and unintentional handle movement to the 'Off' position.
What is back EMF and why is it important in DC motors?
-Back EMF (Electromotive Force) is the voltage generated in the armature conductors of a DC motor due to the generator action when the armature cuts through the magnetic flux. It opposes the supply voltage and is crucial for regulating the current in the motor.
How does the resistance in the three-point starter help during motor startup?
-The resistance in the three-point starter helps limit the armature current to a safe value during motor startup by creating voltage drops across the resistances, which reduces the overall current flowing through the motor.
Where are three-point starters commonly used?
-Three-point starters are commonly used in applications like lathe machines, factories, and spinning mills where controlling the speed and protecting the motor from high starting currents is essential.

Outlines

00:00

🔌 Understanding Three-Point Starters for DC Motors

The script discusses the function and construction of a three-point starter used in DC motors to protect them from high starting current. It explains the connection of a series resistance that reduces the starting current, thus preventing machine damage. The three main terminals—line, armature, and feed—are detailed, along with the starter's construction, working principle, and important components like the series resistance, handle, and electromagnetic coil. The text also covers the operation of the starter, including the reduction of current during starting, the gradual increase to full speed, and the role of the electromagnetic field in holding the handle in the run position. Additionally, it touches on under-voltage protection and overload protection mechanisms that safeguard the motor from potential damage.

05:02

🛠 Advantages and Drawbacks of Three-Point Starters

This paragraph delves into the advantages and limitations of three-point starters. It highlights how these starters enable smooth and controlled starting of DC motors, which is beneficial for various industrial applications. The script mentions the variable speed regulation that three-point starters provide, which is not possible with other types of starters due to the lack of additional resistance in series with the field winding. However, it also points out the drawbacks, such as the large speed variation and reduced magnetic strength of the electromagnet during normal operation, which can lead to issues with speed regulation. The paragraph concludes by emphasizing the importance of understanding the back EMF and its role in the operation of DC motors, and encourages viewers to subscribe to the channel for more informative content.

Mindmap

Keywords

💡Three-Point Starter

A three-point starter is a type of device used to protect DC motors from high starting current. It is integral to the video's theme as it is the main subject discussed. The script explains its construction, working principle, and important applications in various industrial settings.

💡High Starting Current

High starting current refers to the large amount of current drawn by a motor when it starts, which can be damaging. The video discusses how the three-point starter mitigates this issue to protect the motor, using a series resistance to reduce the current, as mentioned in the script.

💡Series Resistance

Series resistance is used in the three-point starter to reduce the high starting current. The script describes how this resistance is connected in series with the motor to limit the current, thus protecting it from damage during startup.

💡Terminals

Terminals are connection points in electrical devices. The script specifies three main terminals in a three-point starter: Line Terminal, Armature Terminal, and Field Terminal, each serving a distinct function in the operation of the starter.

💡Overload Protection

Overload protection is a safety feature that prevents damage to the motor due to excessive current draw. The video explains how the three-point starter incorporates an overload trip coil, which is an electromagnet that triggers a circuit break in case of an overload, as described in the script.

💡Under Voltage Protection

Under voltage protection ensures that the motor does not operate below the required voltage, which could lead to inefficiency or damage. The script explains how the three-point starter provides this protection by using an under voltage coil that disengages the motor from the power supply if the voltage drops.

💡Electromagnet

An electromagnet is a type of magnet whose magnetic field is generated by an electric current. In the context of the video, the electromagnet is part of the overload trip coil and under voltage protection mechanism, attracting or releasing components to protect the motor.

💡Field Winding

Field winding is the part of a motor that creates a magnetic field to induce motion. The script discusses how the field winding in a three-point starter receives full supply voltage, which is then reduced by the series resistance to protect the motor.

💡Armature Winding

Armature winding is the winding in a motor that rotates when the magnetic field interacts with it. The video explains how, in a three-point starter, the armature current is reduced by the series resistance to prevent damage during startup.

💡Speed Regulation

Speed regulation refers to the ability to control the speed of a motor. The script points out that the three-point starter does not allow for speed regulation due to the lack of additional resistance in series with the field winding, which is a key point in understanding its limitations.

💡Back EMF

Back EMF, or electromotive force, is the voltage induced in the motor's windings as it rotates. The script mentions back EMF in the context of explaining how the three-point starter operates and the protective measures it provides during the motor's operation.

Highlights

Introduction to the concept of a three-point starter used to protect DC motors from high starting current.

Explanation of the construction and working principle of the three-point starter.

The starter connects a resistance in series to reduce high starting current, protecting the machine from damage.

Three main terminals: Line terminal (connected to positive supply), Armature terminal (connected to motor's armature winding), and Field terminal (connected to motor's field winding).

The starting handle is manually moved from 'off' to 'start' position to gradually increase motor speed.

No-Volt Coil (NVC) provides undervoltage protection by returning the handle to the 'off' position if supply voltage drops.

Overload Trip Coil (OLC) provides overload protection by tripping the circuit when motor current exceeds a safe value.

The magnetic strength of the NVC holds the handle in the 'run' position during normal operation.

A key drawback of the three-point starter is that it causes large variations in motor speed.

Introduction of the four-point starter to address the drawbacks of the three-point starter.

The three-point starter is not suitable for variable speed motors due to its inability to regulate speed.

The three-point starter is effective in reducing high starting current and providing short circuit and overload protection.

Explanation of back EMF in DC motors, which opposes the supply voltage and current during operation.

The use of the three-point starter in industrial applications like lathe factories and spinning mills.

The significance of understanding the topic in an easy way and subscribing to the channel for more educational content.