Do You Know the Differences Between High-Voltage Load Switches, Disconnectors, and Circuit Breakers?
A disconnector is primarily used to reliably isolate the de-energized parts of a high-voltage power distribution system from the live parts, ensuring the safety of maintenance work. The contacts of a disconnector are fully exposed to the air, providing a clear breaking point. Since disconnectors lack arc extinguishing devices, they cannot be used to interrupt load currents or short-circuit currents. Otherwise, under high voltage, the breaking point will generate intense arcs that are difficult to self-extinguish, potentially causing flashovers (phase-to-ground or phase-to-phase short circuits), damaging equipment, and endangering personnel. This is the severe accident known as "operating a disconnector under load." Disconnectors can also be used for certain circuit switching operations to modify system operating modes.
A high-voltage load switch is an electrical device whose functionality lies between a high-voltage circuit breaker and a high-voltage disconnector. It is often used in series with high-voltage fuses to control power transformers. High-voltage load switches are equipped with simple arc extinguishing devices, enabling them to make and break certain load currents and overload currents. However, they cannot interrupt short-circuit currents, so they are typically used in series with high-voltage fuses, relying on the fuses for short-circuit protection. They can isolate power sources, feature clearly visible breaking points, and are commonly used in fixed high-voltage equipment. Without arc extinguishing devices, they can carry normal operating currents and short-circuit currents when closed. They are strictly prohibited from connecting or disconnecting circuits under load and are often used in series with high-voltage circuit breakers. They are used to break load currents and close short-circuit currents, including switching load currents, loop currents, no-load transformers, and cable charging currents, as well as closing short-circuit currents. Load switches equipped with grounding switches can withstand short-circuit currents. Load switches combined with high-breaking-capacity fuses and tripping devices can perform phase-loss tripping, interrupt short-circuit currents, and serve as protective equipment.
A high-voltage circuit breaker, also known as a high-voltage switch, can not only interrupt or close no-load currents and load currents in high-voltage circuits but also cut off overload currents and short-circuit currents when system faults occur, typically through the action of relay protection devices.
Functions and Roles of Circuit Breakers
High-voltage circuit breakers are among the most critical devices in power systems, designed to connect and disconnect circuits under normal conditions and rapidly interrupt fault currents under abnormal conditions. Their functions include:
Interrupting or closing no-load currents in high-voltage lines.
Interrupting or closing load currents in high-voltage lines.
Interrupting or closing fault currents in high-voltage lines.
High-voltage circuit breakers are mainly categorized into multi-oil circuit breakers, low-oil circuit breakers, sulfur hexafluoride (SF₆) circuit breakers, vacuum circuit breakers, and compressed-air circuit breakers. Their characteristics are as follows:
1)Multi-Oil Circuit Breakers: Simple in design and cost-effective, but they require large quantities of oil, are bulky, demand extensive maintenance, and are prone to explosions and fires. These breakers use insulating oil as both the arc extinguishing medium and the primary insulation medium. They are structurally simple with low technical requirements but are large in size and consume significant amounts of steel and insulating oil.
2) Low-Oil Circuit Breakers: Use less oil and feature compact, robust tank designs, saving materials and offering explosion-proof and fire-resistant properties. They are safe to use, significantly simplify power distribution systems, are compact, and easy to transport. Low-oil circuit breakers are simple in structure, have a long history of use, and are backed by extensive operational experience. They still dominate power systems today. In China, low-oil circuit breakers below 20 kV are designed for indoor use, while those rated 35 kV and above are for outdoor use.