A load switch is a type of control electrical device equipped with a simple arc-extinguishing mechanism. It is capable of opening and closing circuits under load conditions, handling a certain load current and overload current. However, it cannot interrupt short-circuit currents on its own and must be used in series with a high-voltage fuse, which takes over to cut off the short-circuit current when needed.
Example:
- FZW32 Outdoor High-Voltage Isolating Vacuum Load Switch
Functions of a Load Switch:
- Switching Function:
With its arc-extinguishing capability, a load switch can break and close load currents and overload currents up to 3-4 times their normal value. It can also handle operations such as disconnecting large no-load transformers, long no-load lines, or large-capacity capacitor banks.
- Substitute for Circuit Breakers:
When combined in series with a current-limiting fuse, a load switch can replace a circuit breaker. The load switch manages the overload current up to a certain level, while the current-limiting fuse takes over to handle larger overload currents and short-circuit currents.
- Load Switch-Fuse Combination:
When a load switch is integrated with a current-limiting fuse, it is termed a "load switch-fuse combination appliance" per national standards. Depending on the installation, the fuse can be placed either on the power supply or receiving side of the load switch. If frequent fuse replacement is not required, installing the fuse on the power supply side allows the load switch to function as an isolator.
2. What Is an Isolating Switch?
An isolating switch is a control electrical device without an arc-extinguishing mechanism. Its primary function is to isolate the power supply to ensure safe maintenance of electrical equipment. Because it lacks an arc-extinguishing device, it is not designed for switching under load. However, under specific conditions, it may be used to connect or disconnect low-power circuits.
Functions of an Isolating Switch:
- Isolation:
When opened, it establishes a clear insulation gap, separating the circuit or equipment to be maintained from the power supply. This ensures the safety of personnel and equipment.
- Circuit Reconfiguration:
It can alter the circuit configuration as required.
- Low-Current Operations:
It is used to manage small currents, such as those from bushings, busbars, connectors, short cables, capacitive currents, voltage transformer excitation currents, and circulating currents during busbar switching.
- No-Load Transformer Operations:
Depending on its design, it can handle the no-load excitation current of transformers with specific capacities.
Types of Isolating Switches:
- Outdoor High-Voltage Isolating Switches:
Designed to withstand outdoor conditions like wind, rain, snow, and ice, these switches are often used in substations.
- Indoor High-Voltage Isolating Switches:
Used in enclosed environments for similar functions.
- Structural Variants:
Single-column, double-column, and three-column isolating switches differ based on their insulation struts. Single-column switches save space and reduce lead wires, making them ideal for ultra-high-voltage applications.
3. Key Differences Between Load Switch and Isolating Switch
1. Current Handling:
- Isolating Switch:
Only suitable for breaking unloaded currents, not load currents or short-circuit currents. It must only operate when the circuit is de-energized to prevent safety hazards.
- Load Switch:
Equipped to handle overload currents and rated load currents but cannot interrupt short-circuit currents.
2. Arc-Extinguishing Device:
- Load Switch:
Has an arc-extinguishing device that helps manage arcs during switching operations, enhancing safety and reliability.
- Isolating Switch:
Lacks an arc-extinguishing device, limiting its application to non-load operations.
3. Functions:
- Isolating Switch:
Primarily used to isolate power supply sections in high-voltage systems for maintenance or inspection, ensuring personnel safety.
- Load Switch:
Applied in fixed high-voltage equipment to manage fault currents and rated currents. It is commonly used in high-voltage as well as low-voltage systems.
Examples:
- Load Switch Models: 12kV Load Break Switch, 12kV SF6 LBS.
- Isolating Switch Models: 12kV and 24kV Disconnectors.
Both switches are essential in electrical systems but serve distinct purposes, with different operational limitations and applications.
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