24kV Load Switch in Ring Main Unit (RMU) Applications

What Is a Load Switch?

  A Load switch, also known as a load break switch (LBS), is a medium-voltage switching device designed to open and close electrical circuits under load conditions. Unlike an isolator, which must operate under no-load conditions, a load break switch can safely interrupt rated current without causing excessive arc energy or equipment damage.

  At 24kV, load switches are widely used in RMUs, secondary substations, and compact distribution systems for power utility and industrial customers.

Structure of a 24kV Load Switch in RMU Switchgear

A typical 24kV load switch includes several key components engineered for compact installation and long service life within a ring main unit:

1. Switching Contacts

The main electrical contacts handle normal load switching. These contacts are designed to withstand frequent operations and provide robust electrical performance.

2. Arc-Extinguishing Chamber

A dedicated arc-quenching unit (often using SF6, gas, vacuum, or air-insulated arc chambers depending on model) ensures that load currents are safely interrupted with minimal erosion.

3. Mechanical Linkage & Operating Mechanism

The operating mechanism—manual, spring-charged or motorized—drives the contacts and provides quick break and quick close capability.

4. Insulation System

For 24kV systems, insulation may be SF6-insulated, solid insulated (SIS), or air-insulated based on the RMU design. Solid insulation is increasingly preferred due to environmental considerations.

5. Position Indicators & Interlocks

To ensure operator safety, RMU load switches include:

Mechanical ON/OFF position indicators

Door interlocks

Padlocking options

Optional electrical interlocks for automation or remote control

6. Earthing Switch (Optional)

Many RMUs integrate a dedicated earthing switch beside the load switch to allow safe grounding of feeders during maintenance.

Working Principle of a 24kV Load Switch

A 24kV load switch operates on the principle of controlled arc interruption. When the switch opens under load:

1.The contacts separate, initiating an arc.

2.The arc enters the arc-extinguishing chamber, where high dielectric strength (via SF₆, vacuum or insulated arc plates) rapidly reduces ionization.

3.Arc extinction occurs, enabling the current to be safely interrupted.

4.The dielectric recovers, allowing a safe open-gap for isolation.

During closing, the mechanism ensures quick and firm contact engagement, minimizing bounce and preventing arc re-ignition.

Why Load Switches Are Critical in RMUs

  RMU switchgear typically features configurations such as Load Switch + Load Switch + Circuit Breaker (L-L-CB) or Load Switch + Load Switch + Load Switch (L-L-L).

The load switch ensures safe sectionalizing of distribution feeders, improves power reliability, and limits outage areas during faults.

  Key RMU functions supported by load switches:

1.Load transfer between feeders

2.Network sectionalizing

3.Backup or alternative supply switching

4.Transformer protection (in combination with fuses)

5.Fault isolation in ring networks

Advantages of Using 24kV Load Switches in RMUs

The integration of a 24kV load switch in a ring main unit offers several technical and operational benefits:

1. High Operational Safety

Clear contact separation

Built-in interlocks

Reliable insulation

Fast, predictable switching

2. Compact & Space-Saving Design

Ideal for underground substations, roadside kiosks and compact distribution cabinets.

3. High Reliability & Long Service Life

Engineered to withstand thousands of operating cycles with minimal maintenance.

4. Environmental Adaptability

RMUs with 24kV load switches maintain performance under:

High humidity

Coastal climates

Dusty environments

High-temperature regions

5. Low Maintenance Requirements

Simplifies utility operations and reduces lifetime cost.

6. Flexible Configurations

Supports RMU arrangements like:

LBS + Fuse

LBS + Earthing switch

Multi-switch modular RMUs (L-L-L or L-L-CB)

7. Suitable for Automation & SCADA

Motorized options and auxiliary contacts allow remote switching and smart grid integration.

Conclusion

  The 24kV Load switch plays a critical role in Ring Main Unit (RMU) architecture by enabling safe load switching, network flexibility, and reliable power distribution. Its compact structure, strong arc-extinguishing capability and adaptability to modern medium-voltage systems make it essential equipment for utilities, industrial facilities, and renewable energy projects.

  By selecting a well-designed load break switch and integrating it within high-quality RMU switchgear, end users benefit from improved safety, reduced outages, and optimized network performance.