[English] Why NGR? : Neutral Grounding resistor Part-1

Summary

In this video, Gyan Electrical explains the importance of Neutral Grounding Resistors (NGR) in protecting transformers and generators. When neutral points of large equipment, like transformers or generators, are solidly grounded, a phase-to-earth fault can result in high fault currents that may damage the equipment. To mitigate this, an NGR is used to limit the fault current, preventing harm to the windings or core. The video discusses how NGRs effectively reduce fault current to safe levels, ensuring the safety and longevity of electrical equipment.

Takeaways

• 😊 The video explains the purpose of NGR (Neutral Grounding Resistor) in generators and transformers.
• ⚡ NGR is used to protect large-rating equipment like transformers and generators.
• 🔌 The equipment phases are labeled R (Red), Y (Yellow), and B (Blue), with the neutral or star point connected to the ground.
• 🌍 When the neutral is directly grounded, it is called solid grounding.
• 🔥 In solid grounding, if a phase-to-earth fault occurs, the fault current flows from the fault point to the neutral grounding, which could damage the equipment.
• 🛡️ To protect the equipment from high fault currents that can damage windings or the core, NGR is used.
• 💡 NGR limits the fault current when an earth fault occurs, preventing damage to the equipment.
• 🔧 The resistor in the NGR limits the amount of fault current flowing into the equipment.
• 📉 Limiting the fault current ensures the equipment's safety, preventing harm from excessive current.
• 🔒 NGR is an essential protective device for electrical equipment like generators and transformers, ensuring they operate safely during faults.

Q & A

What does NGR stand for in the context of electrical equipment?

NGR stands for Neutral Grounding Resistor, a device used to limit fault current in electrical equipment like transformers and generators.

Why is solid grounding of the neutral point potentially harmful to equipment?

Solid grounding can lead to very high fault currents in case of a phase-to-earth fault, which can damage the equipment's windings or core.

How does an earth fault occur in a transformer or generator?

An earth fault occurs when there is a fault between a phase (R, Y, or B) and the earth, causing fault current to flow through the system.

What role does the NGR play during an earth fault?

The NGR limits the fault current flowing through the system by introducing resistance, protecting the equipment from high current that could cause damage.

What would happen if the neutral of a transformer or generator is grounded without an NGR?

Without an NGR, a phase-to-earth fault would result in high fault currents that flow directly through the equipment, potentially leading to damage.

How does the NGR protect equipment from damage?

The NGR limits the fault current, reducing the amount of current that reaches the equipment during a fault, thus preventing overheating or damage.

What is the difference between solid grounding and grounding with an NGR?

In solid grounding, the neutral is directly connected to the earth, allowing high fault currents. In grounding with an NGR, a resistor is used to limit the fault current.

What would the consequence be if an NGR were not used in a large rating transformer or generator?

Without an NGR, the equipment could be severely damaged due to high fault currents during a phase-to-earth fault, leading to potential failure of the windings or core.

Can you describe the flow of fault current in a system with an NGR?

In a system with an NGR, the fault current flows from the fault point to the ground, but the NGR limits the current before it reaches the equipment, protecting it from high current.

Why is it important to limit the fault current in large electrical equipment?

Limiting the fault current is crucial because excessive fault current can cause thermal and mechanical stress on the equipment, leading to damage or failure.