The Differences and Applications of Circuit Breakers, Load Switches and Disconnectors

What are circuit breakers, load switches and disconnectors? Presumably most electrical personnel are very clear. But when it comes to the difference and application between circuit breakers, load switches and disconnectors, many electrical personnel may only know one but not the other, and for some electrical beginners, they don't even know what to ask. We all know that the circuit breaker can close, carry and break the current under normal circuit conditions, and can close, carry and break the current under abnormal circuit conditions (including short-circuit conditions) within a specified time. The load switch is a switching device between the circuit breaker and the isolating switch. It has a simple arc extinguishing device, which can cut off the rated load current and a certain overload current, but cannot cut off the short-circuit current.

The isolating switch is a circuit that disconnects the no-load current, so that the maintenance equipment and the power supply have an obvious disconnection point, thereby ensuring the personal safety of the maintenance personnel. The isolating switch does not have a special arc-extinguishing device, so the load current cannot be cut off. Short-circuit current, so the operation of the isolating switch must be performed only when the circuit breaker is disconnected. So the question is, what is the difference between a circuit breaker, load switch and disconnector? Where are the three switches used? The following article will introduce you in detail. After reading the article, I hope that it can deepen the understanding of circuit breakers, load switches and isolating switches for the majority of electrical personnel.

▶ 01 Explanation of terms of load switch, disconnector and circuit breaker

Load switch: It is a switching device that can close and cut off the load current, excitation current, charging current and capacitor bank current under normal working conditions.

Isolation switch: It means that when it is in the divided position, there is an insulation distance between the contacts that meets the specified requirements and an obvious disconnection mark; when it is in the closed position, it can carry the current under normal circuit conditions and the abnormal conditions (such as short circuit) ) of the switching device under current.

Circuit breaker: It is a switching device that can close, carry and break current under normal circuit conditions, and can close, carry and break current under abnormal circuit conditions (including short-circuit conditions) within a specified time.

Because of the requirements of the specification, there are obvious disconnection points required in some circuits, so the load switch can be used alone, because the obvious disconnection point can be seen in the circuit, and the circuit breaker is generally used in conjunction with the isolating switch. Ensure that there is an obvious disconnection point in the circuit. The isolating switch cannot be operated under load, that is, it can be opened and closed when the isolating switch cannot be powered on. The load switch, as the name implies, can be operated under load, that is, it can be switched on and off when it is energized. The situation is first opened and closed.

▶ 02 Type introduction of load switch, disconnector and circuit breaker

Load switches, isolating switches and circuit breakers are divided into high and low voltage;

1. For the load switch:

There are six main types of high voltage load switches:

① Solid gas-generating high-voltage load switch: use the energy of the breaking arc itself to make the gas-generating material in the arc chamber generate gas to blow out the arc. Its structure is relatively simple, and it is suitable for products of 35 kV and below. the

②Pneumatic high-voltage load switch: use the compressed gas of the piston to blow out the arc during the breaking process, and its structure is relatively simple, suitable for products of 35 kV and below. the

③ Compressed air type high-voltage load switch: use compressed air to blow out the arc, and can break a large current. Its structure is relatively complicated, and it is suitable for products of 60 kV and above. ④SF6 high-voltage load switch: SF6 gas is used to extinguish the arc, and its breaking current is large, and the performance of breaking capacitive current is good, but the structure is relatively complicated, and it is suitable for products of 35 kV and above. the

⑤ Oil-immersed high-voltage load switch: Use the energy of the arc itself to decompose and gasify the oil around the arc and cool it to extinguish the arc. Its structure is relatively simple, but it is heavy, and it is suitable for outdoor products of 35 kV and below. the

⑥ Vacuum-type high-voltage load switch: use vacuum medium to extinguish the arc, have long electrical life and relatively high price, and are suitable for products of 220 kV and below.

The low-voltage load switch is also called the switch fuse group. It is suitable for switching on and off the loaded circuit manually infrequently in the AC power frequency circuit; it can also be used for overload and short circuit protection of the line. The circuit breaker is completed by the contact blade, and the overload and short circuit protection is completed by the fuse.

2. For isolating switches

According to the different installation methods, high-voltage isolating switches can be divided into outdoor high-voltage isolating switches and indoor high-voltage isolating switches. Outdoor high-voltage isolating switch refers to a high-voltage isolating switch that can withstand the effects of wind, rain, snow, pollution, condensation, ice and thick frost, and is suitable for installation on the terrace. According to the structure of its insulating pillars, it can be divided into single-column disconnectors, double-column disconnectors, and three-column disconnectors.

Among them, the single-column knife switch directly uses the vertical space as the electrical insulation of the fracture under the overhead busbar. Therefore, it has the obvious advantages of saving the occupied area, reducing the leading wires, and at the same time the opening and closing status is particularly clear. In the case of ultra-high voltage transmission, the effect of saving the floor area is more significant after the substation adopts the single-column knife switch.

In low-voltage equipment, it is mainly suitable for low-voltage terminal power distribution systems such as residential houses and buildings. Main functions: breaking and connecting lines with load

It should be noted here that in the low-voltage terminal power distribution, the isolation switch can be segmented with load! In other cases, and under high pressure, it is not allowed!

3. For circuit breakers

High-voltage circuit breakers are the main power control equipment in power plants, substations, and power distribution rooms. ; When the system fails, it cooperates with the relay protection to quickly cut off the fault current to prevent the expansion of the scope of the accident.

Therefore, the quality of the high-voltage circuit breaker directly affects the safe operation of the power system; there are many types of high-voltage circuit breakers, which can be divided into oil circuit breakers (more oil circuit breakers, less oil circuit breakers) according to their arc extinguishing. , Sulfur hexafluoride circuit breaker (SF6 circuit breaker), vacuum circuit breaker, compressed air circuit breaker, etc.

The low-voltage circuit breaker is also called an automatic switch, commonly known as "air switch", which also refers to a low-voltage circuit breaker. It can be used to distribute electric energy, start asynchronous motors infrequently, protect power lines and motors, etc., and can automatically cut off the circuit when they are seriously overloaded or short-circuited or under-voltage. Its function is equivalent to that of a fuse switch and A combination of overheating and underheating relays, etc. Moreover, it is generally not necessary to change parts after breaking the fault current, and has been widely used.

▶ 03 The difference between load switch, disconnector and circuit breaker

1. The load switch can be broken with load and has the function of self-extinguishing arc, but its breaking capacity is very small and limited. the

2. Generally, the isolating switch cannot be broken with load. There is no arc extinguisher in the structure, and there are also isolating switches that can break the load, but the structure is different from the load switch, which is relatively simple. the

3. Both the load switch and the isolating switch can form an obvious disconnection point. Most circuit breakers do not have the isolation function, and a few circuit breakers have the isolation function. the

4. The isolating switch does not have a protection function. The protection of the load switch is generally protected by a fuse, only quick break and overcurrent.

5. The breaking capacity of the circuit breaker can be made very high in the manufacturing process. It mainly relies on adding current transformers to cooperate with secondary equipment for protection. It can have short circuit protection, overload protection, leakage protection and other functions.