Isolating switch

Disconnecting switch: (what we call the isolating switch, generally refers to the high pressure isolating switch, the rated voltage in above 1 kv and isolating switch) high voltage switch to use a kind of most electrical appliances, isolation effect in the circuit, its working principle and structure is simple, but, because of the large amount work reliability requirement is high, It has great influence on the design, establishment and safe operation of substation and power plant.

The main features of disconnecting switch:

1, is no arc extinguishing ability, can only be in the case of no load current, circuit.

2, general power transmission operation: first close the isolation switch, then close the circuit breaker or load switch; 3, power off operation: first disconnect the circuit breaker or load switch, and then disconnect the isolation switch.

Function of disconnecting switch:

1, used to isolate the power supply, disconnect the high-pressure maintenance equipment from the live equipment, so that there is a visible disconnect point.

2, isolating switch and circuit breaker, according to the system operation mode needs to reverse operation, to change the system operation wiring mode.

3, used to connect or disconnect the small current circuit.

Parameters of disconnecting switch:

Rated voltage (KV) = circuit nominal voltage *1.2/1.1 times. The rated current standard value should be greater than 150% of the maximum load current.

The circuit breaker

Circuit breaker: it refers to the switch device that can close, carry and break the current under normal loop condition, and can close, carry and break the current under abnormal loop condition (including short circuit condition) within specified time. Circuit breaker can be used to distribute electric energy, infrequently start asynchronous motor, the power line and motor protection, when they occur serious overload or short circuit and undervoltage fault can automatically cut off the circuit, its function is equivalent to fuse switch and underheat relay combination. And there is generally no need to change parts after breaking the fault current. At present, it has been widely used.

Circuit breaker is divided into high voltage circuit breaker by its use scope, and low voltage circuit breaker, high and low voltage boundary is divided more fuzzy, generally called high voltage electrical appliances above 3kV.

Circuit breaker generally consists of contact system, arc extinguishing system, operating mechanism, tripping device, shell and so on.

The function of circuit breaker: cut off and connect the load circuit, and cut off the fault circuit, prevent the expansion of accidents, ensure safe operation. And the high voltage circuit breaker to break 1500V, the current of 1500-2000A arc, these arc can be stretched to 2m still continue to burn not extinguished. Therefore, arc extinguishing is a problem that high voltage circuit breaker must solve.

Low-voltage circuit breakers, also known as automatic air switches, are used to switch on and off load circuits and to control motors that start infrequently. Its function is equivalent to the knife switch, over-current relay, voltage loss relay, thermal relay and leakage protector and other electrical parts or all of the total function, is an important protection of low-voltage distribution network.

Low-voltage circuit breaker has a variety of protection functions (overload, short circuit, under-voltage protection, etc.), adjustable action value, high breaking capacity, convenient operation, safety and other advantages, so it is widely used. Low-voltage circuit breaker consists of operating mechanism, contact, protection device (all kinds of tripping device), arc extinguishing system, etc.

Working principle of circuit breaker:

When the short circuit, the magnetic field generated by the large current (generally 10 to 12 times) overcomes the counterforce spring, the tripping device pulls the operating mechanism, and the switch trips instantaneously.

When the overload, the current increases, heat intensifies, the deformation of the bimetal sheet to a certain extent to promote the mechanism action (the greater the current, the shorter the action time).

The main contact of a low-voltage circuit breaker is closed manually or electrically. After the main contact is closed, the free tripping mechanism locks the main contact on the closing position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit, and the coil of the undervoltage release is connected in parallel with the power supply. When the circuit is short-circuited or seriously overloaded, the armature of overcurrent tripping device is closed to make the free tripping mechanism move and the main contact disconnects the main circuit. When the circuit is overloaded, the thermal element of the thermal release device heats up and bends the bimetallic sheet, which pushes the free release mechanism to act. When the circuit is undervoltage, the armature of undervoltage trip is released. Also enables free tripping mechanism action. Shunt trip is used for remote control. In normal operation, the coil is powered off. When distance control is required, press the start button to make the coil energized, and the armature drives the free trip mechanism to disconnect the main contact.

Now there are electronic ones. The transformer is used to collect the current of each phase. Compared with the set value, when the current is abnormal, the microprocessor sends out a signal to make the electronic tripping device drive the operation mechanism.

Circuit breaker parameters:

Rated operating voltage (Ue) : This is the voltage at which the circuit breaker operates under normal (uninterrupted) conditions.

Rated current (In) : The maximum current that a circuit breaker equipped with a special overcurrent trip relay can withstand indefinitely at ambient temperature specified by the manufacturer, without exceeding the temperature limit specified for the current bearing part.

Short-circuit relay Trip current setting value (Im) : short-circuit trip relay (instantaneous or short delay) is used to make the circuit breaker trip quickly when high fault current value occurs, and its trip limit is Im.

Rated short-circuit breaking capacity (Icu or Icn) : The rated short-circuit breaking current of a circuit breaker is the maximum (expected) current at which the circuit breaker can break without damage. The current value provided in the standard is the ROOT mean square value of the AC component of the fault current, and the DC transient component (always present in the worst-case short-circuit) is assumed to be zero when calculating the standard value. Industrial circuit breaker ratings (Icu) and household circuit breaker ratings (Icn) are usually given in the form of kA root mean square values.

Short-circuit breaking capacity (Ics) : the rated breaking capacity of circuit breakers is divided into rated limit short-circuit breaking capacity and rated operating short-circuit breaking capacity.

Double power switch

Double power switch: it is the switch that automatically switches to another power supply when the power fails. General double power switch is widely used in high-rise buildings, residential areas, hospitals, airports, docks, fire, metallurgy, chemical, textile and other important places do not allow power outage.

Classification of double power switch:

1. STS static switch: Also called static switch to alternative power supply automatic switching system, the first after failure of STS automatically switch to the first two all the way to power a load (normal and premise of the first two electricity all the way and the first basic synchronization), the acoustic fault STS automatically switches to the all the way to power a load (if the normal electricity all the way and the 2 basic synchronization).

Suitable for continuous power conversion of any two power sources, such as UPS-UPS, UPS- generator, UPS- mains, mains - mains, etc. Synchronous devices are required between all the above power sources to ensure the basic synchronization of the two power sources, otherwise THE STS cannot be switched.

It is mainly composed of intelligent control board, high speed thyristor and circuit breaker. The standard switching time is less than or equal to 8ms, which does not cause IT load power outages. It not only provides reliable power supply to the load, but also ensures the safety of STS when switching between different phases.

2. ATS automatic transfer switch: ATS is mainly used in emergency power supply system, which automatically transfers the load circuit from one power supply to another (standby) power supply to ensure the continuous and reliable operation of important loads. The ATS is a mechanical structure. The conversion time is more than 100 ms, which may power off the load. Suitable for lighting, motor load.

contactor

Contactor: divided into AC contactor (voltage AC) and DC contactor (voltage DC), it is used in power, distribution and electricity. Contactor in a broad sense refers to the industrial electric coil through the current to generate a magnetic field, so that the contact closed, in order to control the load of the electrical appliances.

Contactor role:

Because it can quickly cut off the main circuit of AC and DC and can be frequently connected with the large current control (some types of up to 800 amperes) circuit device, so it is often used in the motor as a control object, It can also be used to control the load of factory equipment, electric heater, working machine and various power sets. The contactor can not only connect and cut off the circuit, but also has the protection of low voltage release. Contactor control capacity, suitable for frequent operation and remote control. It is one of the important components in automatic control system.

In industrial electrical, contactor models are many, the current in 5A-1000A range, its use is quite extensive.

Working principle of contactor:

When the contactor coil is energized, the coil current will generate a magnetic field, which will make the static core generate electromagnetic suction to attract the moving core, and drive the AC contactor point action, normally closed contact is disconnected, normally open contact is closed, the two are linked. When the coil is powered off, the electromagnetic attraction disappears, the armature is released under the action of the release spring, so that the contact is restored, normally open contact is disconnected, normally closed contact is closed. Dc contactors work in a similar way to temperature switches.

Current transformer

Current transformer principle is based on the principle of electromagnetic induction. The current transformer consists of a closed core and windings. It's a little winding circle number, string in the current need to measure the line, so it often have all the current flows through the line, the secondary winding circle number is more, concatenated in measuring instrument and protection circuit, current transformer at work, its secondary side circuit is always closed, so the measuring instrument and protection circuit in series with the coil impedance is very small, The current transformer is close to short circuit. The current transformer converts the large current at the primary side to the small current at the secondary side for measurement. The secondary side cannot be open circuit.

Functions of current transformers:

In power generation, substation, transmission, distribution and electricity lines, the size of the current varies widely, ranging from a few ampere to tens of thousands of ampere. In order to facilitate measurement, protection and control need to convert to a more uniform current, in addition to the line voltage is generally relatively high, such as direct measurement is very dangerous. The current transformer plays the role of current conversion and electrical isolation.

Thermal relay (used with contactor)

The working principle of the thermal relay is that the current flowing into the thermal element generates heat, so that the bimetal sheet with different expansion coefficients will be deformed. When the deformation reaches a certain distance, the connecting rod will be pushed to action, so that the control circuit will be disconnected, so that the contactor will lose power, the main circuit will be disconnected, and the overload protection of the motor will be realized. As the overload protection element of motor, relay has been widely used in production for its advantages of small size, simple structure and low cost.

Parameters of thermal relay:

Rated voltage: the highest voltage value that thermal relay can work normally, generally 220V, 380V, 600V AC.

Rated current: The rated current of thermal relay mainly refers to the current that passes through the thermal relay

Rated frequency: generally speaking, the rated frequency is designed according to 45~62HZ.

Setting current range: The setting current range is determined by its own characteristics. It describes a thermal relay under certain current conditions.