AC Supply Insulated, isolated or ungrounded neutral system

Summary

This video script delves into the concepts of earthed and insulated neutral systems in AC supply. It explains the fundamental differences between the two, highlighting that an earthed neutral system connects the neutral to the earth at the substation, while an insulated neutral system keeps the neutral isolated. The script further discusses the implications of faults in these systems, emphasizing that an insulated neutral system allows continuous operation of equipment during a fault between line and earth, which is crucial for applications like ships and chemical industries where uninterrupted function is vital. It also touches on the use of isolating transformers and safety measures like enclosures to prevent electrical hazards.

Takeaways

• 🔌 The Earth Neutral System: In this system, the neutral is connected to the earth at the substation, providing a path for fault current to flow, causing the MCB to trip and interrupting the AC supply.
• 🛡️ The Insulated Neutral System: Here, the neutral is not connected to the earth, preventing fault currents from flowing in the event of a line-to-earth fault, thus maintaining the AC supply and avoiding MCB tripping.
• 🚫 Fault Handling: In an Earth Neutral System, a fault between the line and earth will cause a short circuit, leading to an MCB trip, whereas in an Insulated Neutral System, such a fault will not result in a short circuit or MCB trip due to the lack of a return path.
• ⚠️ Single Fault Protection: The Insulated Neutral System offers protection against the first fault between the line and earth but not subsequent faults, which can cause the system to trip.
• 🔄 Isolating Transformer: An isolating transformer can be used in an Earth Neutral System to create an Insulated Neutral System, preventing short circuit currents from flowing and keeping the equipment operational.
• 🏭 Industrial Applications: Insulated Neutral Systems are particularly useful in industries where continuous operation of equipment is critical, such as in ships, train engine VFDs, chemical industries, and telecommunication.
• 🔍 Selective Use: Insulated Neutral Systems are not universally applied but are used selectively in areas where their benefits in maintaining continuous operation are most needed.
• 🌐 Utility Connections: Even if an Insulated Neutral System is desired, the neutral-to-earth connection made by the electricity board at the substation cannot be avoided without using an isolating transformer.
• 💡 RCD as an Alternative: Connecting a resistor-capacitor (RC) network between the neutral and earth can provide high impedance, allowing minimal fault current to flow and preventing the MCB from tripping.
• 🛡️ Safety Precautions: For safety, enclosures are used in Insulated Neutral Systems, with the enclosure body connected to the earth to prevent unauthorized access and potential hazards.
• 🔄 Comparison of Systems: The Earth Neutral System is more prone to MCB tripping after a fault, while the Insulated Neutral System maintains operation unless a second fault occurs, emphasizing the importance of timely repairs.

Q & A

What is an earth neutral system?

An earth neutral system is an electrical system where the neutral wire is connected to the earth at the substation. This connection allows for a return path for electrical current in case of a fault, such as a short circuit.

What is an insulated neutral system?

An insulated neutral system is one where the neutral wire is not connected to the earth. This system is used to maintain continuous operation of equipment in certain applications where a fault between the line and earth does not cause a short circuit current to flow, preventing the MCB from tripping.

What is the primary difference between an earthed neutral system and an insulated neutral system?

The main difference lies in the connection of the neutral wire to the earth. In an earthed neutral system, the neutral is connected to the earth at the substation, while in an insulated neutral system, the neutral is insulated and not connected to the earth.

Why would an MCB trip in an earth neutral system during a fault?

An MCB trips in an earth neutral system during a fault because the fault creates a complete path for the short circuit current to flow, causing a high current that the MCB detects and interrupts to prevent damage.

Why does an MCB not trip in an insulated neutral system during a fault between line and earth?

In an insulated neutral system, a fault between line and earth does not provide a return path for the current, so no significant short circuit current flows, and the MCB does not trip, allowing the equipment to continue operating.

What is the purpose of using an insulated neutral system in certain applications?

The insulated neutral system is used in applications where high function continuity is required, and it prevents the MCB from tripping during a fault between line and earth, ensuring the equipment continues to operate.

What happens if a fault occurs between line and neutral in an insulated neutral system?

If a fault occurs between line and neutral in an insulated neutral system, a short circuit current will flow, causing the MCB to trip and the equipment to stop working, as there is now a direct path for the current.

How can an isolating transformer be used to prevent an MCB from tripping in an earth neutral system?

An isolating transformer can be used to create an insulated neutral system within an earth neutral infrastructure. It electrically isolates the load from the earth, preventing short circuit current from flowing in case of a fault between line and earth, thus preventing the MCB from tripping.

What is the role of an RC connection between neutral and earth in an insulated neutral system?

The RC connection, consisting of a resistor (R) and capacitor (C), provides a high impedance path to the earth. In case of a short circuit, the high impedance limits the current flow, preventing the MCB from tripping and allowing the load to continue working.

Why is an enclosure provided in an insulated neutral system, and how is it connected?

An enclosure is provided in an insulated neutral system for safety reasons to prevent unauthorized access to the electrical components. The enclosure body is connected to the earth to ensure that any fault current is safely directed to the earth, protecting personnel from electric shock.

In which industries or applications is the insulated neutral system commonly used?

The insulated neutral system is commonly used in industries and applications where continuous operation of equipment is critical, such as in ships, train engine VFDs, chemical industries, and telecommunication systems.