Understanding STAR-DELTA Starter !

Summary

This video script delves into the necessity and practical implementation of the Star-Delta starting technique for high power rating three-phase induction motors. It explains the motor's operation, highlighting the stator and rotor's roles in producing a rotating magnetic field (RMF) that induces current in the rotor, leading to motion. The script addresses the challenge of high starting current, which can cause voltage drops and affect other devices. The Star-Delta connection is introduced as a solution, reducing the starting current by initially connecting the motor in star configuration. The use of contactors and a timer to automate the transition from star to delta configuration is also discussed, ensuring a smooth and efficient start-up process.

Takeaways

• 🔧 Three-phase induction motors are crucial in industry due to their robustness and simplicity.
• 🌟 The Star-Delta starting technique is used for high power rating induction motors to reduce inrush current.
• 🏗️ An induction motor consists of two main parts: the stator, which receives input power, and the rotor, which turns due to the rotating magnetic field (RMF).
• 🔌 The stator's three coil sets, when excited by a three-phase AC supply, produce a two-pole RMF essential for motor operation.
• 🔁 The rotor's operation is based on electromagnetic induction, where the RMF induces electricity in the rotor bars, causing it to rotate.
• ⚡ At start-up, the rotor's speed is zero, leading to a high rate of flux cut and consequently high induced EMF and current in the rotor bars.
• 🔌 The high start current in the rotor also causes a high stator current, which can lead to voltage drops and affect other devices on the line.
• 📡 The Star-Delta connection mitigates the high start current issue by initially connecting the stator coils in star configuration, reducing the input voltage and current.
• 🔄 Contactors are used to automatically switch between star and delta configurations, simplifying the process and ensuring proper motor operation.
• ⏱️ A timer controls the exact timing of when the contactors switch the motor from star to delta configuration, ensuring smooth operation.

Q & A

Why are three-phase induction motors considered the workhorse of modern industry?

Three-phase induction motors are considered the workhorse of modern industry due to their robustness and simplicity, which make them reliable and easy to maintain.

What is the Star-Delta starting technique used for?

The Star-Delta starting technique is used to start high power rating induction motors by reducing the initial inrush current and providing a smooth start.

What are the two main parts of an induction motor?

The two main parts of an induction motor are the stator and the rotor.

How does the stator of a three-phase induction motor produce a rotating magnetic field?

The stator of a three-phase induction motor produces a rotating magnetic field when connected to a three-phase power supply, which induces electricity in the rotor bars.

What is the role of the rotor in an induction motor?

The rotor in an induction motor is like current-carrying bars immersed in a magnetic field, which induces an electromagnetic force causing the rotor to rotate in the same direction as the rotating magnetic field.

Why is a star double starter needed for starting an induction motor?

A star double starter is needed to reduce the initial high current draw during the start of an induction motor, which can cause voltage drop and affect other devices on the same line.

How does the rotor's interaction with the rotating magnetic field change at the start of the motor?

At the start of the motor, the rotor speed is zero, causing the rotating magnetic field to cut the rotor bars at a very high rate, inducing a high EMF and current. As the rotor speed increases, the current induced decreases to a normal value.

What is the purpose of the Star Delta Connection in an induction motor?

The Star Delta Connection is used to reduce the initial inrush current during the start of the motor by initially connecting the stator coils in star configuration, which reduces the voltage across each coil, and then switching to delta configuration once the motor is running.

How does the use of contactors facilitate the Star Delta starting process?

Contactors are used to automatically switch between star and delta configurations without manual rearrangement of terminals, making the starting process more practical and efficient.

What determines the exact timing of the contactor action in a Star Delta starter?

The exact timing of the contactor action in a Star Delta starter is determined by a timer, which ensures the motor transitions from star to delta configuration at the appropriate speed.

Why is it important to understand the operation of an induction motor before discussing the Star Delta connection?

Understanding the operation of an induction motor is imperative before discussing the Star Delta connection because it provides the necessary background on how the motor works and why the connection method is necessary for starting high power rating motors.

Outlines

00:00

🔌 Understanding Star-Delta Starter for Induction Motors

This paragraph introduces the necessity of a star-delta starter for high power rating induction motors. It explains the basic operation of a three-phase induction motor, which consists of a stator and rotor. The stator, when connected to a three-phase power supply, generates a rotating magnetic field (RMF) that induces current in the rotor bars, causing the rotor to turn. The paragraph highlights the problem of high starting current due to the interaction between the RMF and the stationary rotor at startup. To mitigate this, the star-delta connection is introduced as a solution. Initially, the motor starts in star configuration, reducing the voltage and current across the stator coils, and once the rotor gains speed, it switches to delta configuration for normal operation. The use of contactors for automatic switching between star and delta configurations is also mentioned.

05:04

🛠 Practical Implementation of Star-Delta Connection

The second paragraph delves into the practical implementation of the star-delta connection using contactors. It describes how contactors can be used to establish a star connection by connecting the second terminals of the stator coils together, which reduces the starting current. For delta configuration, an additional contactor is used to branch the second terminal cables and connect them to the input supply. The paragraph explains that a timer determines the exact moment when the contactors switch the motor from star to delta configuration. The video script concludes with a call to action for support on Patreon to help achieve the channel's goals.

Keywords

💡Three-Phase Induction Motors

Three-phase induction motors are a type of AC motor commonly used in industrial applications due to their robustness and simplicity. They operate on the principle of electromagnetic induction and are known for their reliability and low maintenance requirements. In the video, the focus is on understanding the starting techniques for these motors, which is crucial for their efficient operation in high power rating scenarios.

💡Star-Delta Starter

The Star-Delta starter is a method used to start high power rating induction motors. It involves initially connecting the motor's stator windings in a star configuration to reduce the starting current, and then switching to a delta configuration once the motor is up to speed. This method is essential for protecting the motor and the electrical supply from high inrush currents during startup, as explained in the video.

💡Stator

The stator is the stationary part of an induction motor that houses the windings through which the three-phase AC power supply is connected. It is responsible for generating the rotating magnetic field that drives the motor's operation. The video script explains that the stator's design and connection method play a critical role in the motor's starting process.

💡Rotor

The rotor is the rotating part of an induction motor, which is energized by the rotating magnetic field created by the stator. It is designed to turn within the stator's magnetic field, converting electrical energy into mechanical energy. The video emphasizes the interaction between the stator's rotating magnetic field and the rotor at startup, which influences the motor's starting current.

💡Rotating Magnetic Field (RMF)

The rotating magnetic field is a fundamental concept in the operation of three-phase induction motors. It is produced by the stator windings when excited by a three-phase AC supply. The RMF is what induces current in the rotor and causes it to turn. The video script simplifies the understanding of this field by illustrating the coil arrangement that produces it.

💡Electromagnetic Induction

Electromagnetic induction is the process by which an electromotive force (EMF) is generated in a conductor due to a changing magnetic field. In the context of the video, electromagnetic induction is the mechanism by which the rotor of an induction motor is energized, leading to its rotation. The script uses this concept to explain the motor's operation without a direct electrical connection to the rotor.

💡Lorentz Force Law

The Lorentz Force Law describes the force on a charged particle moving through a magnetic field. In the video, it is mentioned to explain how the induced current in the rotor bars experiences a force that causes the rotor to rotate. This law is crucial for understanding the mechanical motion resulting from the interaction between the rotor and the stator's magnetic field.

💡Transformer Action

The transformer action refers to the principle by which an induction motor operates, where the stator acts like the primary winding of a transformer, and the rotor acts like the secondary. This action is responsible for the transfer of energy from the stator to the rotor, as described in the video. Understanding transformer action is key to grasping the motor's starting and operational characteristics.

💡High Starting Current

High starting current is a challenge faced by induction motors, especially those with high power ratings. When the motor starts, the rotor is stationary, and the rate at which the rotor cuts through the magnetic field lines is high, leading to a large induced EMF and current. The video script discusses how the Star-Delta starter mitigates this issue by initially reducing the voltage and current at startup.

💡Contactors

Contactors are electrically operated switches used to make or break connections in an electrical circuit. In the context of the video, contactors are used to automatically switch the stator windings from a star to a delta configuration once the motor has reached a sufficient speed. The script explains how contactors simplify the process of changing the motor's connection method, which would otherwise be manually complex.

💡Timer

A timer is a device used to control the operation of other devices by turning them on or off at preset times. In the video, a timer is used to determine the exact moment when the motor's stator windings should be switched from a star to a delta configuration. This ensures that the transition occurs at the optimal time for the motor's performance, as discussed in the script.

Highlights

Three-Phase induction motors are essential in modern industry due to their robustness and simplicity.

Star-Delta starting technique is used for high power rating induction motors.

Understanding induction motor operation is crucial for grasping the need for Star-Delta connection.

Induction motors consist of two main parts: the stator and the rotor.

The stator of a three-Phase induction motor produces a rotating magnetic field when connected to a three-Phase power supply.

The rotating magnetic field (RMF) is responsible for making the rotor turn.

A simplified coil arrangement can produce a two-pole rotating magnetic field.

The rotor acts like current-carrying bars immersed in a magnetic field.

The induction motor operates due to electromagnetic induction rather than direct connection.

The stator coil acts as the primary of a transformer, and the rotor bar as the secondary.

At the start of the motor, the rotor's interaction with the RMF is significant.

High EMF and current are induced on the rotor bars at the start of the motor.

As the rotor speed increases, the current induced on the bars decreases.

The stator current is high at the start, leading to a large voltage drop in the line.

Star-Delta Connection is a common solution to overcome high starting current issues.

In a star connection, each coil receives a much reduced voltage compared to a Delta configuration.

Reduced input voltage in star connection leads to reduced current at the stator coil.

Contactors are used to switch between star and delta configurations automatically.

The timing of contactor action is determined by a timer.

Supporting the channel on Patreon helps in achieving educational goals.

Transcripts

Three-Phase induction motors are the workhorse of modern industry due to their robustness and simplicity.

You might have seen that in order to start a high power rating induction motor a starting technique called [Star-Delta] is used.

In this video we will understand why a star double starter is needed and how it is accomplished practically.

To understand why a star delta connection is needed [a] proper [understanding] of induction motor operation is imperative.

The induction Motor has two main parts a stator and rotor.

The input power is given to the stator

When connected to a three-Phase power supply the stator of a three-Phase induction motor produces a rotating magnetic field.

The RMF is the one which makes the rotor turn.

Let's simplify this winding to understand the connection

This is the simplest coil arrangement to produce an RMF. We have three coil sets as shown

let's Denote it with U

V and w

The ends of each coil are represented as [one] and [two] respectively

When excited by a three-Phase ac power supply this simple coil configuration will produce a two pole rotating Magnetic field.

This rotating Magnetic field will induce electricity in the rotor bars according to electromagnetic induction

So the ruler is like current carrying bars immersed in a magnetic field

This will induce an electromagnetic force according to lorentz Force law and the rotor will rotate in the same direction as the RMS

This is how the induction motor works.

Electricity is induced on the rotor bars due to electromagnetic induction rather than direct connection

So it is clear that the induction motor works due to transformer action

The stator coil acts like the primary of a transformer and the rotor bar as the secondary

Here comes a really interesting problem think of the rotor RMF interaction at the starting of the motor

When the induction motor starts the rotor speed is zero and slowly increases

This means the rotating Magnetic field will cut the rotor bars at a very high rate

As the rotor Gain speed the rate of Flux cut will decrease

So a high Emf and current will be induced on the bars at the start

As the rotor speed increases the current will lower to the normal value

At the start stator current also must be high since the rotor and stator current are coupled due to transformer action

Due to this the stator coils will draw a huge amount of current when the motor starts

This will produce a large voltage drop in the line and affect other devices when a heavy rating induction motor starts

How does one overcome this problem?

Star Delta Connection is one of the most commonly used solutions for this

You can see in the current design that all the ends of the coils are free

We could connect one free end of each of the coils in two different ways

Either as star where the end terminals are together

Or as Delta, with the one coil is connected to the start of the next coil. This is clearly depicted in the schematic.

When we apply a three-Phase voltage across a star connection each coil will receive a much reduced voltage

Whereas if one applies a three-Phase voltage across the Delta configuration we will get the same applied voltage

So the trick to overcome the high start and current is simple just connect the coils in star at the starting

Reduced input voltage means reduced current at the stator coil

To necessitate disconnection all the terminals of the coils are fed to the junction box of the motor they are arranged in the following manner.

input power is given to the terminal one of the coils.

To connect in star what we have to do is just connect the second terminals together

After the rotor reaches a considerable speed, the stator current will be normal so that we can switch to Delta configuration.

To switch to Delta you just have to connect the terminals as shown

However such a manual rearrangement of terminals is practically difficult in practice in order to achieve this, we use contactors.

Use of contactors are simple, just draw three cables from the second end of the terminal

If these three cables are connected together it is clear that it will result in a star connection

This is exactly what a contactor does

When this contactor is activated that will result in a star connection

To achieve Delta connection the second terminal cables are branched and one more contactor is introduced

The second Branch is connected to the input supply as shown

So if the second contactor is closed it will result in a delta configuration.

The exact timing of contactor action is determined by a timer

We hope you developed a clear insight it to start all the connections

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