The following contents take 400V reactive power compensation cabinet as an example to give you a general introduction of reactive power compensation cabinets and components in cabinets. This content can be used as a basic knowledge for salesperson of reactive power compensation products.
A. reactive compensation cabinet?
In the 400V system, the reactive power compensation cabinet is a set of low-voltage cabinet for providing reactive power to the distribution system.
Remember two points:
1) it's a low pressure cabinet
2) it provides reactive power for the user's electrical equipment.
Another saying: a device that corrections the power factor of the system. (this statement sounds tall)
C. overvoltage protection element
The effect of Overvoltage on the equipment in the cabinet is reduced, and the damage to the components in the cabinet is prevented by overvoltage.
Every reactive compensation cabinet is made up of several reactive compensation branches. The branches are included: protection elements, switching switches, reactors, and electric capacitors.
D. protection element
It protects the components and faults on the compensation branch.
The protective components on the branch are often used as fuses, and the parameters need to be matched with the capacitor on the branch.
E. switching switch
The function of the switch is to connect the capacitor and reactor on the compensation branch to the system or to exit the component of the system.
The capacitance reactance is connected to the system, that is, the constant input of the capacitor; the capacitance reactance is removed from the system, that is, the commonly said capacitor is excised.
PS: when capacitors are put into operation, there is inrush current, which is the basic characteristic of capacitor input. Therefore, switching switch has another function, which is to reduce the inrush current of capacitors.
The common capacitor switching switches are:
Capacitor special contactor
Capacitor special contactor
Remember, it must be a special capacitor.
The contactor of the capacitor is more than one pair of contacts of the conventional contactor, and the resistance value in the circuit is larger than that in the loop, leading to the reduction of the inrush current of the capacitor.
Advantages: less fever during operation
Shortcomings: Although the capacitor inrush is effectively limited, the flow value is still larger.
This device is called more, often seen or heard of thyristor switch, non-contact switch, regulator all refers to it.
The switching of the thyristor is used to realize the switching of the capacitor.
Advantages: the "zero crossing" can be realized, that is, the flow of capacitor can be limited to the minimum.
Shortcomings: a large amount of heat.
Thyristor is very sensitive to heat, and the superheat will damage to thyristor. In addition, emitting a lot of heat will also cause a significant increase in the temperature of the reactive power compensation cabinet, and the high ambient temperature has great influence on the life of the capacitor.
Therefore, when using the thyristor switch, we must pay attention to the heat dissipation.
The heat dissipation of the 1. thyristor switch is often done by its own cooling fan. When the temperature of the thyristor is higher than the limit, the fan is started; when the temperature is lower to the limit, the fan stops working. When the temperature rises above the dangerous temperature, the thyristor switch protection system will leave the thyristor out of the working state.
2. the heat dissipation of the reactive power compensation cabinet.
A composite switch is a product that combines the advantages of a thyristor switch and a contactor, which is composed of a thyristor and a mechanical contact.
The switching of capacitors is accomplished by thyristor, which ensures the zero crossing switching of capacitors. After the capacitor is put into operation, the mechanical contact is used as the conduction circuit to avoid the heat generated by the thyristor for long term operation.
The reactor is the companion of the capacitor, which has appeared together in many times. As an important component in the reactive power compensation cabinet, it must be understood.
The reactor has two main functions:
1. suppression of capacitor inrush
2. suppression harmonics
To know the appearance of a common reactor, see the picture below.
Our common reactor has two types of wire wound and foil.
According to the different material, the wire wound reactor has copper wire and aluminum wire, and the same reason, there are two kinds of copper foil and aluminum foil.
Reactors are usually protected by over temperature. They have a pair of contacts (usually closed much). When the reactor is over heated, the contacts are open, which can be used to remove the reactor from the system.
The parameters often described by the reactor are "reactance".
The reactor that is specially used to suppress the flow of capacitors is not more than 1%.
The reactance rate is based on the number of main harmonics in the system. For example: to suppress the influence of the 5 and 7 harmonics, the common 5.6%, 6%, 7% reactance rates, the 3 harmonic suppression, and the common 12%, 13%, 14% reactance rates.
The main components of the reactive power compensation cabinet. Because of the existence of capacitors, the reactive power compensation cabinet is often called "capacitor cabinet".
In the low pressure system, our common capacitors are self-healing capacitors (made of metallized films).
According to the difference in the internal filling agent of the capacitor, several kinds of different kinds can be divided. For example, we often hear the word "dry capacitor".
Oil immersed capacitor, as the name implies that filling agent is liquid, the defect of liquid is leakage risk, and oil is flammable.
The dry capacitor has solved the above disadvantages of the oil immersed capacitor, which is usually filled with filled resin and inert gas.
Shape and installation
There are many shapes and sizes of capacitors, such as oval, circular, square and so on.
Different configurations determine the different installation methods.
Wiring terminals are common with screw and European terminals, such as drawings.
Screw connection, the contact area is big, the connection is firm. The wiring column is exposed to the outside, usually with a protective cover.
European terminal with exquisite structure and small contact area. When the most common fault occurs, the terminal terminal is loose, and the contact point heat causes the terminal to burn out.
In order to prevent the explosion of capacitors, explosion-proof devices are usually installed.
The capacitor itself is a energy storage element. When the capacitor is out of operation, its own charge needs to be released, and the discharge resistance is used to complete the capacitor. The discharge resistance can be built outside and can be built in. The discharge voltage is required below 75V within the prescribed time.
More about capacitor knowledge, please pay attention to the other content of the micro signal "Zheng ER technology".
H. power factor controller
The power factor controller is the control center of the reactive power compensation cabinet, and it is the core of the automatic switching of the compensator (compensation branch).
Basic working principle
Power factor controller monitoring system is lack of reactive power or power factor index, control capacitor (compensation branch) automatic switching, so as to adjust the power factor to be qualified.
The power factor controller can be understood from the following aspects
1. control parameters
The power factor controller is based on the parameters of the power factor? The lack of reactive power? Or something else?
Common power factor, reactive component, and a variety of parameters are mixed.
2. compensation method
Three phase complements and phase separation compensation.
The three-phase co compensation means to send a command, at the same time the system A, B, C three-phase reactive vacancy compensation.
Compensation refers to issue a command, the system can only A, B, C three in one phase of vacancy compensation, which can realize the independent control of reactive power compensation for each.
The hybrid compensation means that the three phase publication and phase separation compensation can be realized simultaneously.
3. compensation control output type and loop number
The controller usually has two output command types, one is the contact point output, the other is mainly used for contactor control, the other is level output, which is mainly used to control thyristor switch and compound switch.
The number of output circuits of the controller determines the number of compensation branches that can be controlled by a controller. There are 6 roads, 12 roads and 18 roads.
4. controller monitoring parameters
As an intelligent device, many power factor controllers can monitor a lot of electrical parameters at the same time.
For example, current, voltage, reactive power, harmonic distortion rate and so on.
5. The monitor interface of the controller
The common controller interface consists of digital display and liquid crystal display.
6. record of protection function and fault information
As the intelligent equipment in the reactive power compensation cabinet, the power factor controller usually has a perfect protection function to ensure the safe operation of the reactive power compensation cabinet. Such as overvoltage, undervoltage, over temperature protection and so on.
The fault information can be recorded in full, and the included time mark is recorded.
7. data sharing
As an intelligent device, its data can be shared to third parties.
That is: whether it has a standard communication interface and whether the communication protocol is open.
Again, it is often heard that the device has a RS485 interface, is it a Modbus communication protocol.
For each equipment in the type of low voltage cabinet, we all have to consider the following problems, and the reactive power compensation cabinet is no exception.
1) cabinet and cabinet size
The cabinet type of the reactive power compensation cabinet and the low pressure switch cabinet.
2) measurement system
For a complete set of equipment, the instrument is generally required to measure the electrical parameters.
That is, usually the reactive power compensation cabinet will configure the power meter.
3) heat dissipation system
The heat dissipation of the reactive compensation cabinet must be done well, otherwise the overheating of the temperature in the cabinet will directly cause the damage of the capacitor.
The heat dissipation can be achieved by the conventional temperature controller + exhaust fan and the special air-conditioner of the switch cabinet.
4) the top of the cabinet is connected to the main bus, bus switch cabinet top cabinet
Why when it comes to specified bus? This is a place that is easily overlooked by some people.
If you are a low-voltage cabinet factory, the project all cabinets are done by your family, including the reactive power compensation cabinet, then the provisions of the bus nature is provided with complete cabinet factory.
If the reactive power compensation cabinet is provided by third parties alone, the general reactive power compensation cabinet at this time do not contain provisions and provisions of bus connection to the bus line of the main switch cabinet. At this point the user needs to be aware that this part of the device should not be missed.
5) the two wiring of this equipment and the external
The other wiring of the reactive power compensation cabinet is handed over to the technical engineer to deal with. As a salesperson, do not pay attention to such details, because the content needs many words to make it clear.
Through the above content, everyone is basically clear of the reactive compensation cabinet. It is a low voltage cabinet combined with a large number of power components. Therefore, I suggest to users that the main components in reactive power compensation cabinet, such as capacitors, reactors, power factor controllers, switching switches, etc., should be selected after the brand and specifications are selected, and the assembly of other components and equipment will be handed over to the whole plant. In this way, the quality of the components is controlled and the quality of the complete set of cabinet is guaranteed.