LRS vs VFD| What is Liquid Resistance Starter| What is VFD| Function of VFD| Motor Starting Method

Summary

In this video, Abhishek Joshi discusses the basic differences between VRD (Variable Reluctance Drive) and VFD (Variable Frequency Drive), explaining their purposes in the industry. He clarifies that VRD is used for high starting torque in slip-ring induction motors, while VFD is for smooth starting and speed variation. He emphasizes that these two cannot replace each other due to their distinct functions and applications.

Takeaways

• 😀 Abhishek Joshi, an electrical engineer, discusses the basic differences between VRD (Variable Reluctance Drive) and VFD (Variable Frequency Drive).
• 🔌 The primary purpose of VRD is to provide high starting torque to slip-ring induction motors by adding external resistance to the rotor circuit.
• 🔄 VFD, on the other hand, is mainly used to provide smooth starting and speed variation for any motor.
• 🚀 VRD is used specifically during the starting period of slip-ring induction motors, whereas VFD operates throughout the entire motor operation.
• 🔧 VRD cannot provide variable speed to motors, focusing only on high starting torque, while VFD can adjust motor speed as per requirements.
• 🌀 Slip-ring induction motors cannot add external resistance in their rotor circuit, unlike slip-ring motors which can incorporate external resistance for better performance.
• 📈 High starting torque is a key feature provided by VRD, which is essential for starting slip-ring induction motors.
• ⏱ VFD offers a gradual increase in motor RPM, preventing jerks and high starting torque, thus providing a smooth start.
• 🔄 VFD allows for continuous motor operation with variable speed, which is useful in applications requiring frequent changes in motor RPM.
• 🛠 The choice between VRD and VFD depends on the specific requirements of the application, such as the need for high starting torque or variable speed control.
• 📚 For a deeper understanding of VRD, Abhishek Joshi has created several videos that can help clarify the concept, which are linked in the description.

Q & A

What is the main topic of discussion in the video?

The main topic of discussion in the video is the basic differences between VRD (Variable Reluctance Drive) and VFD (Variable Frequency Drive) and whether they can be used interchangeably.

What is the primary purpose of using VRD in slip-ring induction motors?

The primary purpose of using VRD is to provide high starting torque to the slip-ring induction motors by adding external resistance in the rotor circuit.

How does VRD help in starting slip-ring induction motors?

VFD helps in starting slip-ring induction motors by adding external resistance to the rotor circuit, which provides extra starting torque.

What is the main function of a Variable Frequency Drive (VFD)?

The main function of a VFD is to provide smooth starting and speed variation to any motor, allowing for gradual acceleration and deceleration.

Why is high starting torque not provided by VFD?

High starting torque is not provided by VFD because its main purpose is to provide smooth starting, not high torque. It gradually increases the motor's RPM, avoiding jerks and high starting torque.

How does the motor's RPM change when started with VFD?

When a motor is started with VFD, it gradually increases the RPM from a lower value (e.g., 500 RPM) to the rated RPM (e.g., 1500 RPM) in a step-by-step manner, providing a smooth start.

What are the applications where VFD is commonly used?

VFD is commonly used in applications where speed variation is required, such as in applications where the motor's RPM needs to be changed frequently based on the requirements.

Can VRD and VFD be used interchangeably in all applications?

No, VRD and VFD cannot be used interchangeably as they serve different purposes. The choice between them depends on the specific requirements of the application, such as the need for high starting torque or smooth speed variation.

How does the operation of VRD differ from VFD during the motor's running condition?

VFD remains in the motor circuit throughout the motor operation, allowing for continuous speed variation, whereas VRD is only used during the starting period of the slip-ring induction motor and is disconnected once the motor reaches about 80% of its rated RPM.

What are the key parameters to consider when choosing between VRD and VFD?

Key parameters to consider include the need for high starting torque, smooth starting, the ability to vary motor RPM, and the specific application requirements.

Where can viewers find more information about VRD?

Viewers can find more information about VRD in the videos created by the speaker, which are linked in the description or accessible through the provided links.