6 kinds of commonly used low-voltage electrical components are fully analyzed, and the harvest is full.

First, low voltage isolation switch

The isolation switch we refer to generally refers to a high-voltage isolating switch, that is, an isolating switch with a rated voltage of 1kv or more. The most used one of the high-voltage switchgear is isolated in the circuit, and its working principle and structure are relatively simple.

When the low-voltage electrical equipment is being repaired, it is necessary to cut off the power supply to separate the maintenance part from the live part and maintain an effective isolation distance, and it is required to withstand the withstand voltage level of the over-voltage between the break points. The knife switch is used as a switching device for the isolated power supply. The knife switch that isolates the power supply is also known as the isolating switch. Isolation knife switches are generally unloaded on/off devices and can only switch on or off "ignorable currents" (referring to the busbar with voltage, the capacitor current of a short cable or the current of a voltage transformer). Some knife switches have a certain on-off capability, and when the on-off capability is compatible with the current required to be turned on, a part of the electrical equipment or the complete set of equipment can be switched on or off under non-fault conditions.

Main features of the isolating switch

1. It has no arc-extinguishing ability and can only be divided and combined without load current;

2. For normal power transmission operation: firstly isolate the switch, and then close the circuit breaker or load switch;

3. When the power is off, first disconnect the circuit breaker or load switch, then disconnect the isolation switch.

The function of the isolating switch

1. For isolating the power supply, disconnecting the high-voltage maintenance equipment from the live equipment, so that there is an obvious visible break point between them;

2. The isolating switch cooperates with the circuit breaker to perform the switching operation according to the needs of the system operation mode to change the wiring mode of the system operation;

3. Used to turn on or off the small current circuit.

Isolation switch parameters

Rated voltage = return road sign voltage *1.2/1.1 times;

Rated current standard value > 150% of maximum load current.

The difference between the isolating switch, the load switch and the circuit breaker

1. The isolating switch plays a role of obvious breaking point in the circuit to ensure the safety of personnel during maintenance. Generally, only the no-load current of the line can be cut off, and the load current and short-circuit current cannot be cut off;

2. The load switch also acts as an isolation and can cut off the load current;

3. The circuit breaker can cut off the load current and the short circuit (fault) current, and can automatically trip when the fault occurs. In addition, some types of circuit breakers are also isolated and can be used as isolated electrical.

Second, the circuit breaker

A circuit breaker is a switching device capable of closing, carrying and breaking current under normal circuit conditions, and capable of closing and carrying current under abnormal loop conditions (including short-circuit conditions) within a prescribed time. Circuit breakers can be used to distribute electrical energy, start asynchronous motors infrequently, protect power lines and motors, and automatically cut off circuits when they are severely overloaded or short-circuited or under-voltage faults. Their functions are equivalent to fuse switches. Combined with over-heat relays and the like. Moreover, it is generally not necessary to change parts after breaking the fault current. At present, it has been widely used.

The circuit breaker is generally composed of a contact system, an arc extinguishing system, an operating mechanism, a trip unit, a casing, and the like. Circuit breakers are classified into miniature circuit breakers, molded case circuit breakers and frame type circuit breakers according to their construction.

The role of the circuit breaker

Cut off and switch on the load circuit, and cut off the faulty circuit to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker is to break 1500V, the current is 1500-2000A arc, these arcs can be extended to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that must be solved by high voltage circuit breakers.

Low-voltage circuit breakers, also known as automatic air switches, can be used to switch the load circuit on and off, as well as to control motors that are not frequently started. Its function is equivalent to the sum of all or all of the functions of the knife switch, over current relay, voltage loss relay, thermal relay and leakage protector. It is an important protection device in the low voltage distribution network.

Low-voltage circuit breakers have a variety of protection functions (overload, short circuit, under voltage protection, etc.), adjustable action values, high breaking capacity, easy operation, and safety, so they are widely used. Structure and working principle The low-voltage circuit breaker is composed of operating mechanism, contacts, protection devices (various trip units), arc extinguishing system and so on.

How the circuit breaker works

When short-circuited, the magnetic field generated by a large current (generally 10 to 12 times) overcomes the reaction force spring, the trip unit pulls the operating mechanism, and the switch instantaneously trips.

When overloaded, the current becomes larger, the heat is increased, and the bimetal is deformed to a certain extent to push the mechanism (the larger the current, the shorter the action time).