Why Motor Start in Star and Run in Delta| Star delta Starter| Why Motor Connected in Delta

Summary

The video script discusses the concept of using a star-delta starter for electric motors, addressing a viewer's question about the logic behind running the motor in delta configuration after starting in star. It explains that starting a motor in star reduces the high starting current, protecting the motor and electrical system from damage. However, after the initial start, the motor is switched to delta for the required high starting and running torque, ensuring the motor can handle the load effectively. The explanation aims to clarify the benefits and necessity of this switching mechanism in electrical engineering applications.

Takeaways

• 😀 The video discusses the concept of using a star-delta starter for electric motors and the logic behind changing from star to delta configuration.
• 🔧 When starting a motor through star-delta starting, the starting current is significantly reduced compared to full-load current, which can be six to seven times higher.
• ⚡ The high starting current in a direct start can cause the motor's circuit breaker to trip due to overcurrent, and it can also affect other feeders due to voltage drop.
• 🌟 Star-delta starters are used to avoid these issues by applying reduced voltage during the starting phase, thus controlling the inrush current.
• 📐 In star configuration, the phase voltage is approximately 1.3 times the line voltage, which means starting with reduced voltage compared to the full line voltage.
• 🔄 The transition from star to delta configuration is necessary because star configuration does not provide the high starting and running torque required by some applications.
• 🛠 High starting torque is essential for applications that need the motor to overcome high inertia during startup, ensuring the motor can start effectively.
• 🔄 High running torque is necessary for the motor to handle the load effectively and maintain rotation under the required torque conditions.
• ⏱ The changeover from star to delta usually occurs after a short period, typically 8 to 10 seconds, to provide the motor with high starting and running torque.
• 🔌 The script mentions that if the motor is not switched to delta configuration, it may not meet the required torque demands, leading to potential tripping of the motor.
• 🔧 The video aims to clarify a common question about why motors are not run continuously in star configuration and the necessity of the changeover to delta for meeting torque requirements.

Q & A

What is the main purpose of using a star-delta starter for motors?

The main purpose of using a star-delta starter is to reduce the inrush current during the starting phase of the motor, thereby preventing damage to the motor and electrical system due to high starting torque.

Why is the motor not allowed to run continuously in star configuration?

The motor is not allowed to run continuously in star configuration because it does not provide the high starting and running torque required by certain applications, which can lead to the motor not being able to handle the load properly.

What is the relationship between line voltage and phase voltage in star configuration?

In star configuration, the phase voltage is related to the line voltage by the formula V_phase = V_line / √3, which means the phase voltage is approximately 1.3 times less than the line voltage.

How does the starting current of a motor compare to its full-load current during a direct start?

During a direct start, the starting current of a motor can be six to seven times higher than its full-load current, which can lead to significant electrical stress on the motor and the electrical system.

Why might the panels around a large motor trip due to under-voltage when starting?

When a large motor draws a high starting current, it can cause a significant voltage drop in the system, leading to under-voltage conditions that may trip the panels around it.

What is the function of a reduced voltage starter like the star-delta starter?

A reduced voltage starter, such as the star-delta starter, is used to apply reduced voltage across the motor terminals during the starting phase, which in turn reduces the starting current and torque.

Why is it necessary to switch from star to delta configuration after a few seconds of motor operation?

Switching from star to delta configuration after a few seconds is necessary to provide the motor with the required high starting and running torque to handle the load effectively and prevent motor trip due to insufficient torque.

What are the disadvantages of running a motor in star configuration for an extended period?

Running a motor in star configuration for an extended period can result in insufficient starting and running torque, which may not meet the application requirements and could cause the motor to trip.

How does the star-delta starter help in avoiding the issues related to high inrush current?

The star-delta starter helps in avoiding issues related to high inrush current by initially starting the motor with reduced voltage in star configuration, which significantly lowers the inrush current, and then switching to delta configuration to provide full torque.

What is the typical time frame for the switch from star to delta configuration in a star-delta starter?

The typical time frame for the switch from star to delta configuration in a star-delta starter is between 8 to 10 seconds after the motor starts.

Why is high running torque important for certain applications?

High running torque is important for certain applications because it ensures that the motor can handle the load effectively and maintain smooth operation, preventing the motor from tripping due to overload.