Advantage of MCR-typed Static VAR Compensator
The MCR-typed static VAR compensator is developed on the basis of the traditional saturable reactor technology. It was put forward by Russia scientists. They creatively introduced the concept of magnetic valve to make just a small part of the cross-section of the iron core saturated. This solves the high-order harmonic problems existing in traditional saturable reactors, because all iron cores in traditional saturation reactor are oversaturated, which results in nonlinearity and thus causes high-order harmonic.
In addition to small harmonics, the MCR-typed SVC also features small size, light weight, low noise, fast response, high voltage withstanding, stable running, and long service life. Therefore, this equipment has experienced rapid development and enjoyed wide application in many countries around the world, such as Russia, Ukraine, America, India, China, etc. It performs well in improving power quality, reducing reactive power loss, filtering system harmonics, stabilizing power grid voltage, as well as improving safety and reliability of the power grid operation.
Due to the adoption of advanced microelectronics technology, the MCR-typed static VAR compensator can regulate reactive power and realize compensation on busbar accurately:
1. The inductive reactive current in main circuit can be adjusted through changing low voltage DC to regulate main circuit impedance quickly and smoothly. In the meantime, through cooperating with capacitor bank connected in parallel to busbar, reactive power compensation can be realized on bus bar, and dynamic response and improved power factor can stabilize bus bar voltage.
2. By properly choosing the parameters of the reactor connected in series with the capacitor bank, compensation on fundamental wave can be obtained and harmonic can also be filtered.
Since the MCR-typed SVC is free from frequent switching, it avoids surge and over-voltage impact caused by MSC, which enhances the reliability and prolongs the service life of the equipment while protecting other instruments.
The static VAR compensator of MCR type fully absorbs advantages and functions of TCR-typed SVC. It also overcomes some disadvantages of the latter. It solves the problems of smooth regulation which can not be realized by MSC and TSC. As the reactor is directly connected to the high voltage main circuit in parallel, it is subjected to extra high voltage and ultra high voltage. At present, the highest voltage of MCR in China reaches 1000KV and the maximum capacity is up to 320MVar. The MCR also has over-load protection function, so it will not cause serious damage to the system except heating. Hence, it is very stable for the MCR-typed SVC to operate in the high voltage circuit. However, the thyristors in TCR-typed SVC are connected to high voltage circuit directly, and over-voltage will result in faults and break.
Working Principle of MCR (take single-phase MCR for instance)
From the above structural scheme of MCR, we know that the main iron core of MCR is divided into two identical parts, iron core 1 and iron core 2. The sectional area of the middle part of the iron core is Ab1 and the sectional area of other parts is Ab, Ab1
From the equivalent circuit diagram of MCR, if both K1 and K2 are non-conductive, the controllable reactor is equivalent to a no-load transformer because of its symmetrical structure. If the voltage of power supply is in positive half cycle, K1 stands for forward voltage and K2 stands for reverse voltage, in case K1 is triggered to conduct (same potential for point a and point b), power supply voltage is coupled by windings with a tap ratio of δ to windings of N2 to supply direct current. The equivalent circuit diagram is as below: