Introduction of High and Low Voltage Devices for Reactive Power Compensation

Reactive power compensation, the full name of reactive power compensation, is a technology that plays a role in improving the power factor of the power grid in the power supply system, reducing the loss of power supply transformers and transmission lines, improving power supply efficiency, and improving the power supply environment. Therefore, the reactive power compensation device is in an indispensable and very important position in the power supply system. Reasonable selection of compensation devices can minimize the loss of the power grid and improve the quality of the power grid. On the contrary, if it is improperly selected or used, it may cause many factors such as power supply system, voltage fluctuation, and harmonic increase. The basic principle, meaning, switching method, circuit, controller, high and low voltage devices, compensation method, existing problems, etc. of reactive power compensation are introduced in detail.

1. Basic introduction of reactive power compensation

1.1 Basic Principles

The power output by the power grid includes two parts: one is active power: it directly consumes electric energy, converts electric energy into mechanical energy, heat energy, chemical energy or sound energy, and uses these energy to do work. This part of power is called active power; the other is reactive power : consume electric energy, but only convert electric energy into another form of energy, this energy is a necessary condition for electrical equipment to do work, and this energy is periodically converted with electric energy in the grid, this part of power It is called reactive power (such as the electric energy occupied by electromagnetic components to establish a magnetic field, and the electric energy occupied by capacitors to establish an electric field).

1.2 Significance

1.2.1 Compensating reactive power can increase the proportional constant of active power in the grid.

1.2.2 Reduce the design capacity of power generation and power supply equipment and reduce investment. For example, when the power factor cosΦ=0.8 increases to cosΦ=0.95, installing a 1Kvar capacitor can save equipment capacity by 0.52KW; on the contrary, increasing 0.52KW is for the original equipment , which is equivalent to increasing the capacity of power generation and power supply equipment. Therefore, for new construction and reconstruction projects, reactive power compensation should be fully considered, so that the design capacity can be reduced, thereby reducing investment.

1.2.3 To reduce the line loss, it can be obtained from the formula ΔΡ%=(1-cosθ/cosΦ)×100%, where cosΦ is the power factor after compensation, and cosθ is the power factor before compensation:

cosΦ>cosθ, so after increasing the power factor, the line loss rate also decreases, reducing design capacity, reducing investment, increasing the transmission ratio of active power in the grid, and reducing line loss all directly determine and affect the economic benefits of power supply enterprises. Therefore, the power factor is an important indicator for assessing economic benefits, and it is imperative to plan and implement reactive power compensation.

1.3 Commonly used reactive power compensation methods in the power grid include:

1.3.1 Centralized compensation: install parallel capacitor banks in high and low voltage distribution lines;

1.3.2 Group compensation: Install parallel compensation capacitors on the low-voltage side of the distribution transformer and the distribution panel of the user workshop;

1.3.3 On-site compensation of a single motor: Install shunt capacitors at the single motor.

The installation of reactive power compensation equipment can not only reduce power consumption and improve power factor, but also fully tap the potential of equipment transmission power.

1.4 When determining the reactive power compensation capacity, the following two points should be noted:

1.4.1 Overcompensation should be avoided at light load, and it is not economical to increase power loss due to reversed reactive power.

1.4.2 The higher the power factor is, the less the effect of reducing losses per kV compensation capacity will be. Normally, increasing the power factor to 0.95 is a reasonable compensation.

The in-situ reactive power compensation capacity can be determined according to the following empirical formula: Q≤UΙ0 where: Q---reactive power compensation capacity (kvar); U---rated voltage of the motor (V); Ι0---no-load motor Current (A); however, reactive power compensation also has its disadvantages: it cannot fully replace high-voltage centralized compensation and low-voltage group compensation; as we all know, reactive power compensation can be divided into high-voltage centralized compensation and low-voltage Group compensation and low pressure local compensation. Among them, the in-situ compensation area is the largest and the effect is good. But its total capacitor installation capacity is larger than the other two methods, and the capacitor utilization rate is also low. The capacitor capacity of high-voltage centralized compensation and low-voltage group compensation is relatively small, and the utilization rate is also high, and can compensate the reactive power loss of the transformer itself. For this reason, these three compensation methods have their own scope of application, and the use occasions should be determined in combination with the actual situation, and each performs its own duties and classification.

2. Different devices for reactive power compensation

2.1 Introduction to switching

The delay switching method is commonly known as the "static" compensation method. The purpose of delay switching is to prevent the capacitor from being damaged by too frequent actions, and more importantly, to prevent the continuous switching of the capacitor from causing the power supply system to oscillate, which is very dangerous.

Delay switching mode The device used to control capacitor switching can be a special contactor for switching capacitors, a composite switch or a synchronous switch (also known as a phase selection switch).

The special contactor for switching capacitors has a set of auxiliary contacts connected in parallel with the main contacts after series resistance. During the input process, the auxiliary contact is closed first, and the resistor connected in series with the auxiliary contact precharges the capacitor, and then the main contact is closed again, thus limiting the inrush current when the capacitor is input.

The compound switch is to use the thyristor and the relay contact in parallel, but the compound switch uses both the thyristor and the relay, so the structure becomes more complicated and the cost is relatively high, and because the thyristor is sensitive to overcurrent, overvoltage and dv/dt Sex is also relatively easy to damage. In practical applications, most composite switch failures are caused by damage to thyristors.

Synchronous switch is the latest technology developed in recent years. As the name suggests, it is to make the contacts of mechanical switches close or break accurately at the required moment. The synchronous switch for controlling the capacitor is to be closed when the voltage at both ends of the contact is zero, so as to realize the non-inrush input of the capacitor, and to be disconnected when the current is zero, so as to realize the arc-free breaking of the switch contact. Because synchronous switching omits the thyristor, not only the cost is reduced, but also the reliability is improved. Synchronous switch is the product of the perfect combination of traditional mechanical switch and modern electronic technology, which fully demonstrates the characteristics of high reliability and low loss of mechanical switch while having unique technical performance.

When the load of the grid is inductive, such as motors, electric welding machines and other loads, the current of the grid lags behind the voltage by an angle; when the load is capacitive, such as in an overcompensation state, the current of the grid is ahead of the voltage by an angle Angle, power factor leading or lagging refers to the phase relationship of current to voltage. The controller of the compensation device detects the physical quantity of the power supply system to determine the switching of the capacitor. This physical quantity can be power factor or reactive current or reactive power.

The following is an example of the power factor type. When this physical quantity meets the requirements, such as cosΦ leading and >0.98, lagging and >0.95, within this range, the controller does not send out control signals at this time, and the capacitor banks that have been put in will not exit, and the capacitor banks that have not been put in will not exit. put in. When it is detected that cosΦ does not meet the requirements, such as cosΦ lagging and <0.95, then put a group of capacitors into it, and continue to monitor cosΦ. If the cosΦ still does not meet the requirements, the controller will delay for a period of time (delay time can be set), and then turn on A bank of capacitors until they are all put in. When detecting a leading signal such as cosΦ<0.98, that is, a capacitive load, the controller will cut off the capacitor banks one by one. The principle to be followed is: the capacitor bank that is put in first will be cut off first when it is cut off. If the delay time is set to 300s, and this compensating device has ten capacitor banks, then the time for all input is 5 minutes, and the same is true for cutting off. During this period of time, reactive power loss compensation can only be gradually put in place. This may happen if the delay time is set very short, or if no delay time is set. When the controller detects that cosΦ<0.95, it quickly puts in the capacitor banks one by one. During the input period, the power grid may already have a capacitive load, that is, overcompensation, and the controller controls the removal of the capacitor banks one by one. system breakdown. Whether oscillation can be formed is closely related to the nature of the load, so this parameter needs to be set according to the site conditions, and the compensation effect should be considered under the condition of ensuring the safety of the system.

2.2 AC input type

Since the capacitor is a device whose voltage cannot be transient, a large inrush current will be formed when the capacitor is switched on, and the maximum inrush current may exceed 100 times the rated current of the capacitor. Inrush currents can adversely affect the grid and reduce the service life of capacitors. In order to reduce the inrush current, most compensation devices use a special contactor for capacitor switching. This contactor has a set of auxiliary contacts connected in series with the current limiting resistor and the main contact in parallel. When the contactor is pulled in, the auxiliary contacts first Turn on, so that the capacitor is connected to the circuit through the current limiting resistor for pre-charging, and then the main contact is connected to connect the capacitor to the circuit normally. In this way, the inrush current can be limited to less than 20 times the rated current of the capacitor.

This type of compensation device is cheap, reliable and widely used. Since the contact life of the AC contactor is limited, it is not suitable for frequent switching, so this type of compensation device is not suitable for frequently changing load conditions.

2.3 Input type setting

This type of compensating device is the TSC subclass of the SVC classification. Since the thyristor is easily damaged by the impact of the inrush current, the thyristor must be triggered at zero crossing, that is, a trigger signal is sent when the voltage across the thyristor is zero. The zero-crossing trigger technology can realize no inrush current into the capacitor, and because there is no limit to the triggering times of the thyristor, it can realize quasi-dynamic compensation (response time is in milliseconds), so it is suitable for frequent switching of capacitors and is very suitable for frequently changing load conditions . The conduction voltage drop of the thyristor is about 1V, and the loss is very large (taking a compensation device with a rated capacity of 100Kvar as an example, the rated current of each phase is about 145A, and the rated conduction loss of the thyristor is 145×1×3=435W), it must be used Large cooling fins and use of ventilation fans. The thyristor is very sensitive to the voltage change rate (dv/dt). It is easy to be misconducted and damaged by the inrush current when encountering sudden voltage changes such as operating overvoltage and lightning strikes. The rate of voltage change cannot be reduced.

This type of compensating device has complex structure, high price, poor reliability, and large loss. Except for occasions where the load changes frequently, it has almost no use value in other occasions.

2.4 Composite device

The composite switch technology is to use the thyristor and the relay contact in parallel. The thyristor realizes the voltage zero-crossing input and the current zero-crossing cut-off, and the relay contact passes the continuous current. the surge. However, the composite switch technology uses both thyristors and relays, so the structure becomes quite complicated, and the thyristors are relatively easy to damage due to their sensitivity to dv/dt.

2.5 Synchronous input device

Synchronous switch technology is the latest technology developed in recent years. As the name suggests, it is to make the contacts of mechanical switches close or break accurately at the required moment. For a synchronous switch that controls a capacitor, it is meant to be closed when the voltage across the switch contacts is zero.

Synchronous switching technology refuses to use thyristors, so it is still not suitable for frequent switching. However, because the synchronous switch is more energy-saving, safer and more reliable, and more resource-saving than the composite switch and AC contactor, and the phase selection switch uses single-chip technology, it can not only control up to 64 capacitors through the RS485 communication control method, but also has The communication function can send the electrical measurement information of the grass-roots units to the upper-level power grid in real time, and it is a seamless connection with the smart grid that is being developed in the country and many other factors.

3. Instantaneous reactive power compensation

Instantaneous switching mode is the well-known "dynamic" compensation mode. It should be said that it is the technical crystallization of semiconductor power devices and digital technology. It is actually a set of fast servo system. Sampling and calculation are completed within one cycle, and when two cycles arrive, the controller has already issued a control signal. The thyristor is turned on by the pulse signal, and the switching capacitor bank completes a complete action within about 20-30 milliseconds. This control method cannot be realized by mechanical action contactors. As a new generation of compensation device, the dynamic compensation method has a broad application prospect. Many switch industry factories have tried to produce and manufacture such devices and some manufacturers have produced very good devices. Of course, compared with similar foreign products, there is still a certain gap in performance, component quality and product structure.

4. Line for reactive power compensation

4.1 Series connection method

This method adopts the series connection of inductance and capacitance to adjust the reactance to achieve the purpose of compensating for reactive power loss. Analyzing from the principle, this method has a fast response speed, and when it is used in a closed loop, it can achieve zero-difference adjustment, so that the reactive power loss can be reduced to zero. In terms of component selection, one set of capacitors can be selected according to the amount of compensation, and there is no need to divide them into multiple circuits. Since there are so many advantages, it should be an ideal compensation device. However, due to the large value of the inductance required to be selected, it needs to be adjusted within a large dynamic range, so the volume is relatively large, and the price is also higher. Coupled with some technical reasons, this technology has not been widely used or Very few users.

4.2 Devices used

As the switching switch of the capacitor bank, the wiring method is more commonly used. BK is a semiconductor device, and C1 is a capacitor bank. This wiring method uses 2 sets of switches, and the other phase is directly connected to the grid to save a set of switches, which has many advantages.

The semiconductor devices used as compensation devices generally use thyristors, which have the advantages of convenient material selection, mature and economical circuits. Its shortcoming is that the component itself cannot be shut down quickly, and it is easy to burn out in an accidental situation, so the protection measures must be perfect. When the protection problem is solved, it should be an ideal device as a switching switch for capacitor banks. The compensation effect of dynamic compensation also depends on whether the controller has high performance and parameters. A very important item is to require the controller to have good dynamic response time, accurate switching power, and high self-identification ability, so as to achieve the best compensation effect.

When the controller collects the signal that needs to be compensated and sends out an instruction (an instruction to put in one or more sets of capacitors), at this time, the trigger pulse is used to trigger the conduction of the thyristor, and the corresponding capacitor bank is also incorporated into the line for operation. It should be emphasized that the condition for the conduction of the thyristor must satisfy that the terminal voltage of the capacitor in its phase is zero, so as to avoid damage to the components caused by the inrush current, and the semiconductor device should be switched without inrush current. When the control command is withdrawn, the trigger pulse disappears immediately, and the thyristor is naturally turned off with zero current. The capacitor voltage after shutdown is the AC peak value of the line voltage, which must be discharged by the discharge resistor as soon as possible to prepare the capacitor for re-introduction.

Components can choose single-phase thyristor anti-parallel or bidirectional thyristor, or solid-state contactor suitable for capacitive loads, which can save the pulse circuit triggered by zero crossing, thereby simplifying the circuit, and the withstand voltage and current of the components should be selected reasonably , radiators and cooling methods should also be considered.

4.3 Switching method

In fact, it is a mixture of static and dynamic compensation. Some capacitor banks use contactor switching, while other capacitor banks use power semiconductor devices. This method can achieve complementary advantages to a certain extent, but as far as its control technology is concerned, there are also complete control software. This method is used for ordinary networks such as industrial and mining, residential areas, and domain network transformation. Compared with a single switching method The scope of application is broadened, and the effect of energy saving is better. The compensation device chooses a non-constant capacitance capacitor bank, and the compensation effect in this way is more detailed and ideal. The phase-splitting compensation method can also be used, which can solve the loss caused by the three-phase non-parallel of the line.

4.4 Var generator

Using PWM rectification control technology, through real-time sampling of the voltage and current of the grid and high-performance DSP to calculate the reactive power of the grid, and realize the compensation of reactive power compensation. The characteristic of SVG is that it can realize dynamic continuous reactive power compensation, and can realize the compensation of inductive reactive power and capacitive reactive power, so that the power factor of the power grid can be stabilized above 0.98. SVG not only compensates for reactive power, but also compensates for harmonic current.

5. Controller for reactive power compensation

Which compensation method to choose depends on the status of the power grid. First of all, you must have an understanding of the line to be compensated. For working conditions with large loads and rapid changes, the lines of electric welding machines and motors use dynamic compensation to save energy. The effect is obvious. For lines with relatively stable loads, static compensation methods should be used, and dynamic compensation devices can also be used. Generally, the working time of electric welding is more than a few seconds, and the start-up of the motor is also more than a few seconds, while the response time of dynamic compensation is tens of milliseconds. Considering 40 milliseconds, it is a relatively stable state from 40 milliseconds to 5 seconds. state process, the dynamic compensation device can complete this process.

5.1 Control method

The reactive power compensation controller has three sampling methods, power factor type, reactive power type, and reactive current type. The choice of which physical control method is actually the choice of the reactive power compensation controller. The controller is the command system of the reactive power compensation device, and functions such as sampling, calculation, and switching signals, parameter setting, measurement, and component protection are all completed by the compensation controller. Over the past ten years, it has experienced a rapid development process from discrete components-integrated circuits-single chip microcomputers-DSP chips, and its functions have become more and more perfect. As far as the overall situation in the country is concerned, due to the large market demand and the increasing number of manufacturers, their performance and internal quality vary greatly. Another problem that needs to be paid attention to when selecting is that the names of domestically produced controllers are all "XXX reactive power compensation controllers", and the meaning of "reactive power" appearing in the names is not the sampling physical quantity of this controller. The sampling physical quantity depends on the model number of the product, not the name of the product.

5.2 Power factor type

The power factor is represented by cosΦ, which represents the proportion of active power in the line. When cosΦ=1, there is no reactive power loss in the line. Improving power factor to reduce reactive power loss is the ultimate goal of this type of controller. This control method is also a very traditional method, and sampling and control are also relatively easy to implement.

5.2.1 "Delay" setting, the switching delay time should be adjusted within the range of 10s-120s "Sensitivity" setting, the current sensitivity should not be greater than 0-2A.

5.2.2 The input and cut-off threshold setting, the power factor should be able to be set within the range of 0.85 (lag) -0.95 (lead).

5.2.3 Overvoltage protection settings

5.2.4 Display settings, cycle switching and other functions

This sampling method should not only ensure the stability of the line system and no oscillation phenomenon during operation, but also take into account the compensation effect. This is a pair of contradictions, and the parameters can only be set in a better state depending on the specific situation on site. Even if the adjustment is better, it cannot make up for the defects of this method itself, especially when the line is heavily loaded. For example: set input threshold; cosΦ=0.95 (lag). At this time, the line is heavily loaded. There will be no compensation command for the inverter, and there will be no capacitor bank input, so this control method is not recommended as the recommended method.

5.3 Rate type

The reactive power (reactive current) type controller perfectly solves the defects of the power factor type. A well-designed reactive power controller is intelligent, has strong adaptability, can take into account the stability of the line and the effect of detection and compensation, and can perform perfect protection and detection of the compensation device. This type of controller is generally Both have the following functions:

5.3.1 Four-quadrant operation, automatic and manual switching, self-identification of the power of each capacitor bank, automatic adjustment of switching time according to the load, harmonic overvoltage alarm and protection, line resonance alarm, overvoltage protection, line low current alarm, voltage , Current distortion rate measurement, display capacitor power, display cosΦ, U, I, S, P, Q and frequency.

From the above functions, it can be seen that its control function is complete. Because it is a reactive power controller, the effect of the compensation device can be brought into full play. If the line is under heavy load, even if the cosΦ has reached 0.99 (lag), as long as another set of capacitors does not cause overcompensation, another set of capacitors will be added to make the compensation effect reach the best state. Using the controller of the DSP chip, the operation speed is greatly improved, and the Fourier transform is realized. Of course, not all reactive power controllers have such complete functions. There is still a certain gap between domestic products and foreign products.

5.4 Dynamic Compensation

The requirements for this kind of controller are even higher. Generally, it is considered together with the trigger pulse forming circuit. It is required that the controller has strong anti-interference ability, fast operation speed, and more importantly, it has a good dynamic compensation function. Since this type of controller is also based on the reactive type, it has the characteristics of the static reactive type.

Domestic controllers used for dynamic compensation have a large gap compared with similar foreign products. First, the dynamic response time is slow, and the repeatability of dynamic response time is not good; Large, the system characteristics are easy to drift, the maintenance cost is high, and the overall investment cost of the equipment is high. In addition, the corresponding national standards have not yet been seen, and this aspect lags behind development.

Since the application of modern semiconductor devices is more and more common, the power is also greater, but its negative effect is to generate a large non-sinusoidal current. The harmonic voltage of the power grid increases, the distortion rate increases, and the power supply quality of the power grid deteriorates.

If there is a large harmonic voltage on the power supply line, especially above the 5th order, these harmonics will be amplified by the compensation device. The capacitor bank and the line resonate in series, which increases the voltage and current distortion rate on the line, and may cause equipment damage. In this case, the compensation device cannot be used. The best solution is to connect reactors in series with the capacitor bank to form a harmonic filter. The design of the filter should be capacitive in the case of power frequency to compensate the reactive power compensation of the line, and it should be an inductive load for harmonics to absorb part of the harmonic current and improve the distortion rate of the line. After adding the reactor, the problem of voltage increase at the capacitor terminal should be considered.

The filter compensation device not only compensates the reactive power loss but also improves the line quality. Although the cost increases a lot, it should be considered as much as possible for the line with a large harmonic component. It cannot be considered that there is no problem if the device does not have a problem for a while. In many cases, the use of fifth-order, seventh-order, eleven-order or high-pass filters can eliminate harmonics in the system while compensating for reactive power compensation.

6. High and low voltage devices for reactive power compensation

6.1 Low voltage installation

It is suitable for electric power, automobile, petroleum, chemical industry, metallurgy, railway, port, coal mine, oil field and other industries with AC 50 Hz, rated voltage below 660 V, large load power changes, and high requirements for voltage fluctuation and power factor.

Basic technical parameters and working environment:

Ambient temperature: -25oC~+40oC (outdoor type); -5oC~+40oC (indoor type), the maximum daily average temperature is 30oC

Altitude: 1000m

Relative Humidity: < 85% (+25oC)

Maximum rainfall: 50 mm/10 min

Installation environment: The surrounding medium has no explosion and flammable hazards, no gas that can damage insulation and corrode metals, and no conductive dust. No violent vibrations and bumps, installation inclination <5%.

Technical indicators: rated voltage: 220 V, 380 V (50 Hz)

Judgment basis: reactive power, voltage

Response time: < 20 ms

Compensation capacity: 90 kvar~900 kvar

Allowable error: 0~10%

6.2 High pressure installation

Applicable to 6kV~10kV substations, 1~4 groups of capacitors can be arbitrarily arranged on the busbars of section I and section II, adapting to various operation modes of substations.

Basic technical parameters and working environment:

Normal working temperature: -15~+50oC, relative humidity <85%, altitude: 2000 m

Technical indicators: Rated voltage: 6 kV~10 kV

AC voltage sampling: 100 V (PT secondary line voltage)

AC current sampling: 0~5 A (if the PT takes the secondary A and C line voltage on the 10 kV side, the CT should take the B-phase current)

Voltage setting value: 6~6.6 kV 10~11 kV adjustable

Transformation ratio of current transformer: 200~5000 /5 A adjustable

Action interval time; 1~60 min adjustable

System stabilization time required for action: adjustable from 2 to 10 minutes

Power factor setting: 0.8~0.99 adjustable

Technical features: Voltage priority: automatically switch capacitors according to voltage quality requirements, so that the bus voltage is always within the specified range.

Automatic compensation: Automatic switching of capacitor banks according to the size of reactive power compensation, so that the system does not overvoltage, overcompensate, and reactive power loss is always in the minimum state.

Record monitoring: The monitoring data, operation records, voltage pass rate statistical table, etc. can be called out automatically or at any time (optional).

Intelligent control: before automatically issuing each action control command, first inquire about all possible over-limit values after the action to reduce the number of actions.

Abnormal alarm lockout: When the capacitor control circuit relay protection action, refusal to operate, and controller power failure, it will send out sound and light alarm, display the fault location and lock the exit.

Safety protection: Manually exit the self-switching state of any capacitor bank, and the controller automatically locks and exits the control.

Fuzzy control: How to implement the comprehensive control principle when the system is at the high end of the qualified voltage range and in a specific environment is the difficulty in the design of this series of products. Frequent actions caused by many factors on site, such as configuration environment, power status, action time, user's limit on the number of actions, etc., are the most worrying for users. The application of fuzzy control is to consider the above factors and make this "blind area" be reasonably resolved.

6.3 Low pressure compensation device

Using high-power thyristor switching switch, the controller can control the thyristor switch according to the system voltage, reactive power, and two-phase criteria to quickly switch the multi-level capacitor bank. The thyristor switch adopts the zero-crossing trigger mode, which can realize the input of the capacitor without inrush current and impact, stabilize the system voltage, compensate the reactive power of the grid, improve the power factor, and increase the bearing capacity of the transformer. It can be widely used in industrial and mining enterprises and community power distribution systems such as electric power, metallurgy, petroleum, ports, chemicals, and building materials.

6.3.1 Device structure and technical performance of main components

6.3.1.1 Device structure

The low-voltage reactive power dynamic compensation device is composed of a controller, a non-contact switch group, a parallel capacitor group, a reactor, a discharge device and a protection circuit, and the whole machine is designed as an electromechanical integration.

6.3.1.2 Technical performance of main components

6.3.1.2.1 Controller

The controller of the low-voltage reactive power dynamic compensation device is a new digital design, software and hardware modularization, high integration, electromagnetic compatibility, and strong anti-interference ability. There are 12 output terminals, which can realize three methods: phase separation, balance, and phase separation and balance. compensate. It has a wide range of applications and can meet the compensation needs of loads of different natures. It can control the switching of the non-contact switch group according to the system voltage and reactive power compensation. There are two operation modes: manual and automatic. It also has protection functions such as overvoltage cutoff, overvoltage lockout, undervoltage cutoff, and overtemperature alarm.

6.3.1.2.2 Non-contact switch group

The non-contact switch group is the main executive element of the device, which is composed of thyristor switch, radiator, fan, temperature control switch, zero-crossing trigger module and resistance-capacitance absorption circuit. The maximum controllable capacity of a single group of integrated design is 90kvar. Imported components, high power, high safety factor.

6.3.1.2.3 Parallel capacitor banks

High-quality self-healing shunt capacitors are selected, which can be flexibly coded and combined according to different capacities. There are many switching stages, and large-capacity compensation can be in place at one time.

6.3.2 Basic working principle

When the device is working, the controller monitors the changes of system voltage and reactive power in real time. When the system voltage is lower than the power supply standard or the reactive power compensation reaches the set switching threshold of the capacitor bank, the controller will give a switching command. The zero-crossing circuit quickly detects the voltage across the thyristor (that is, the voltage difference between the capacitor and the system), and triggers the thyristor when the voltage across the thyristor is zero, and the capacitor bank realizes no inrush current input or no inrush current cut off.

6.3.3 Main technical parameters

6.3.3.1 Rated voltage AC220V/380V±10% 50Hz

6.3.3.2 Wiring method Three-phase four-wire

6.3.3.3 Switching basis System voltage and reactive power

6.3.3.4 Response time ≤20ms

6.3.3.5 Switching delay 0.1～30s (continuously adjustable)

6.3.3.6 Switching accuracy average≤+2%

6.3.3.7 Compensation capacity 60kvar～1080kvar

6.3.3.8 Switching series 1～18

6.3.4 Environmental conditions for use

6.3.4.1 Working environment temperature -25℃～+45℃

6.3.4.2 Relative air humidity ≤ 85%

6.3.4.3 Altitude ≤2000m (plateau type is used above 2000m)

6.3.4.4 Installation environment No flammable, explosive, chemical corrosion, flooding and severe vibration places

6.3.4.5 Installation method Indoor screen type, outdoor box type

6.3.4.6 Installation conditions The harmonic content in the grid complies with the provisions of the 0.38kV clause in GB/T14549

6.3.5 Protection functions

It has multiple protections for overcurrent, overvoltage, undervoltage, and overtemperature. The device can automatically exit the operation in case of external failure and power failure, and automatically recover after power on.

6.4 High voltage compensation device

Suitable for 6KV, 10KV large and medium-sized industrial and mining enterprises and other substation power distribution systems with large load fluctuations and frequent adjustment of power factor. This device is based on factors such as system voltage and reactive power shortage, and through comprehensive calculation, automatically switches capacitor groups to improve voltage quality, improve power factor and reduce line loss. This device is suitable for unattended substations and occasions where the harmonic voltage and harmonic current meet the allowable values specified in the national standard GB/T14548-93. If the on-site harmonic conditions exceed the standard, 1%-13% reactance can be equipped according to the situation to resist harmonics from entering compensation equipment.

6.4.1 Structure and basic working principle

The high-voltage reactive power automatic compensation device is composed of a controller, a high-voltage vacuum switch or vacuum contactor, a high-voltage capacitor bank, a reactor, a discharge coil, a lightning arrester and some necessary protection auxiliary equipment. The digital high-voltage reactive power automatic compensation controller decides whether to switch the capacitor bank according to the nine-zone map combined with the fuzzy control principle, voltage priority, load reactive power compensation, and switching times limit, so that the bus voltage is always within the standard range. Make sure not to overfill to minimize losses. Within the allowable voltage range, switch the capacitor bank in place at one time according to the reactive power requirements of the load. Before investing in capacitors, estimate the amount of voltage increase. If it exceeds the standard, reduce the capacity or not invest. In the case of abnormal conditions, the controller issues an instruction to exit all capacitor banks, and at the same time sends out an audible and visual alarm. After troubleshooting, the manual disarming of the alarm can be put into the automatic working mode again.

6.4.2 Technical features

6.4.2.1 Voltage priority

Automatic switching of capacitors according to voltage quality requirements. When the voltage exceeds the maximum set value, the capacitor bank will be cut off step by step until the voltage is qualified. When the voltage is lower than the minimum set value, the capacitor bank is gradually put into operation under the condition of ensuring no overload, so that the bus voltage is always within the specified range.

6.4.2.2 Automatic reactive compensation function

Under the principle of voltage priority, the capacitor bank is automatically switched according to the reactive power compensation of the load, so that the system is always in the state of minimum reactive power loss.

6.4.2.3 Intelligent control function

Before automatically issuing an action command, first inquire about all possible over-limit values after the action to reduce the number of actions.

6.4.2.4 Abnormal alarm function

When the relay protection action of the capacitor control loop refuses to move and the controller automatically blocks the automatic control of the reorganized capacitor.

6.4.2.5 Fuzzy control function

When the system is at the high end of the qualified voltage range and in a specific environment, how to implement the comprehensive control principle is the difficulty in the design of this series of products. ) caused by frequent actions is what users are most worried about, and the application of fuzzy control is to consider the above factors so that this "blind spot" can be reasonably resolved.

6.4.2.6 Comprehensive protection function

Each device has switch protection (optional), overvoltage, loss of voltage, overcurrent (short circuit) and zero sequence relay protection, double star unbalance protection, fuse overcurrent protection, zinc oxide arrester, grounding protection, quick break protection wait.

6.4.3 Main technical parameters

6.4.3.1 Rated voltage (AC) 6KV, 10KV

6.4.3.2 System voltage sampling (AC) 100V (PT secondary line voltage)

6.4.3.3 AC current sampling 0～5A (if the PT takes the secondary A and C phase line voltage on the 10KV side, the CT should take the B-phase current)

6.4.3.4 Voltage setting value 6～6.6KV 10～11KV adjustable

6.4.3.5 Action interval time adjustable from 1 to 60 minutes

6.4.3.6 Power factor setting value 0.8～0.99 adjustable

6.4.3.7 Change of current transformer 50～5000/5A adjustable

6.4.3.8 Action requires system stabilization time, adjustable from 2 to 10 minutes

6.4.4 Use environment

6.4.4.1 Ambient temperature -15℃～+45℃

6.4.4.2 Relative humidity ≤85%

6.4.4.3 Altitude ≤2000m (plateau type is used above 2000m)

6.4.4.4 There are no explosive and flammable dangerous goods in the surrounding medium, no gas enough to damage insulation and corrode metals, no conductive dust, no violent vibration and no bumps in the installation site.

6.4.4.5 The power supply complies with the national standards and does not have strong harmonic components.