Status and development of static var compensation

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The status and development of static var compensation technology in power system

Abstract: This paper summarizes the development status of static var compensation technology in power system in detail, analyzes the principles, advantages and disadvantages of various static var compensation technologies and their current applications in power system, and puts forward the development trend of Static Var Compensation Technology in the future

key words: development trend of static var compensation (SVC ASVG) power system 1 introduction the reactive power balance of each node of the power system determines the voltage level of the node, because there are a large number of devices with frequent changes in reactive power among users of the power system; Such as rolling mill, electric arc furnace, 3. Electrified railway during pressure test, etc. At the same time, users also have a large number of precision equipment with high requirements for system voltage stability, such as computers, medical equipment, etc. Therefore, it is urgent to compensate the reactive power of the system

the traditional reactive power compensation equipment includes shunt capacitor, condenser and synchronous generator. Because the impedance of shunt capacitor is fixed, it can not dynamically track the change of load reactive power; However, the compensation equipment such as condenser and synchronous generator are rotating equipment, which have great loss and noise, and are not suitable for too large or too small reactive power compensation. Therefore, these devices have been increasingly unable to meet the needs of the development of power system

since the 1970s, with the further deepening of research, a static var compensation technology has emerged. After more than 20 years of development, this technology has experienced a process of continuous innovation, development and improvement. The so-called static reactive power compensation refers to the use of different static switches to switch capacitors or reactors, so that they have the ability to absorb and emit reactive current. It is used to improve the power factor of the power system, stabilize the system voltage, inhibit system oscillation and other functions. At present, this kind of static switch is mainly divided into two types: circuit breaker and power electronic switch. As the circuit breaker is used as the contactor, its switching speed is slow, about 10 ~ 30s, so it is impossible to quickly track the change of load reactive power. In addition, switching the capacitor often causes serious impact inrush current and operating overvoltage, which is not only easy to cause contact point welding, but also internal breakdown of the compensation capacitor, resulting in large stress and large maintenance

with the development of power electronics technology and its application in power system, the emergence of AC contactless switches SCR, GTR, GTO, etc. as switching switches, the speed can be increased by 500 times (about 10 μ s) For any system parameter, reactive power compensation can be completed within one cycle and can be adjusted by single phase. At present, the static var compensation device refers to the var compensation equipment using thyristors, mainly including the following three types: one is the static var compensation device with saturated reactor (sr:saturatedrector); The second type is thyristor controlreactor (TCR) and thyristor switchcapacitor (TSC). These two devices are collectively referred to as SVC (staticvar compensator); The third type is the static var generator (asvg:advanced static var generator) which is a successful compensation device for the static reactive gold plate with self commutation phase change flow technology and processed with phase change wrapped thermal insulation energy storage technology

the following three types of static var compensation technologies are introduced one by one, mainly SVC and ASVG, and the development trend of static var compensation technology in the future is pointed out

2 value of wear amount of reactive power compensation device (SR) with saturated reactor saturated reactor is divided into self saturated reactor and controllable saturated reactor, and the corresponding reactive power compensation device is also divided into two types. The reactive power compensation device with self saturated reactor relies on the inherent ability of the reactor to stabilize the voltage. It uses the saturation characteristics of the core to control the amount of reactive power emitted or absorbed. The controllable saturation reactor controls the saturation degree of the core by changing the working current in the control winding, so as to change the inductive reactance of the working winding and further control the reactive current. The static var compensation device composed of such devices belongs to the first batch of static compensators. As early as 1967, this device was made in Britain. Later, General Electric Company (GE) of the United States also made such a static var compensation device [1]. However, due to the high cost of the saturated reactor in this device, which is about 4 times that of the general reactor, and the silicon steel sheet of the reactor is in a saturated state for a long time, the core loss is large, which is 2 ~ 3 times larger than that of the shunt reactor. In addition, this device also has vibration and noise, and the adjustment time is long, The speed of dynamic compensation is slow. Due to these shortcomings, static var compensators of all saturated reactors are rarely used at present, and are generally only used in EHV transmission lines

3 thyristor controlled reactor (TCR)

two anti parallel thyristors are connected in series with one reactor, and its single-phase schematic diagram is shown in Figure 1. The three phases are connected into triangles, and such a circuit is incorporated into the electricity, which is equivalent to that the AC voltage regulator circuit is connected to the inductive load. The effective phase shift range of this circuit is 90 ° ~ 180 °. When trigger angle α= At 90 °, the thyristor is fully conductive, and the conduction angle δ= 180 °, at this time, the reactor absorbs the maximum reactive current. According to the relationship between trigger angle and equivalent admittance of compensator:

bl = blmax( δ- sin δ)/ π and blmax = 1/XL. Increasing the trigger angle can increase the equivalent admittance of the compensator, which will reduce the fundamental component of the compensation current. Therefore, by adjusting the trigger angle, the reactive power absorbed by the compensator can be changed to achieve the effect of adjusting the reactive power. In engineering practice, the step-down transformer can be designed as a reactance transformer with large leakage reactance, and the reactance transformer can be controlled by thyristor, so there is no need to connect a transformer separately or install a circuit breaker. The primary winding of the reactance transformer is directly connected to the high-voltage line, and the secondary winding is connected to the thyristor valve through a small reactor. If appropriate device circuit is selected in the third winding of reactance transformer, such as adding filter, reactive power compensation can be further reduced

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