Static var compensator (SVC) with MCR
Overview
A Static VAR Compensator (or SVC) is an electrical device for providing fast-acting reactive power on high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulating voltage and stabilizing the system. The term “static” refers to the fact that the SVC has no moving parts (other than circuit breakers and disconnects, which do not move under normal SVC operation).
The SVC of MCR type adopted adjustable iron core reactor to control inductive reactive power through changing magnetic permeability of iron core with DC excitation. Because MCR is the real reactor that inductance can be adjusted compared with TCR, the MCR typed SVC has become more and more popular in dynamic reactive power compensation application fields.
The main functions of MCR typed SVC
① Enhance power factor and Reduce line loss;
② Adjust and Stabilize power grid voltage;
③ During short-circuit, reactive power has a function of sustaining instantaneous voltage to avoid generator breaking.
④ Increase power transfer capability.
The comparison between MCR and TCR:
From the above diagram, the main difference is at blue section.
The SCR of SVC with MCR is coupled with reactor through iron core; it just needs to withstand lower voltage of 380V, so it has a very high stability.
The SCR of SVC with TCR is connected in series to high voltage main circuit; it needs to withstand high voltage and big current, so it is easy to damage.
The dynamic compensation theory of SVC of MCR type
From the left diagram on above primary circuit diagram:
QF: Impact reactive power of load
QC: Capacitive reactive power supplied by fixed capacitor bank on bus bar—Constant
QL: Inductive reactive power supplied by magnetically controllable reactor—Dynamic adjustment
The most important is to control the pass angle of the thyristors prospectively to obtain the needed currents in order to provide the needed reactive power of QL.
Therefore, the system must try to satisfy the equity:
QS=QF+ (QL-QC) =0, so that the power factor is a constant and there will be no fluctuation of the voltage, here, QS is generated reactive power on bus bar.
Why choose SVC of MCR Type
● High reliability: The SCR is installed in low voltage circuit, not in main circuit, so, the withstanding voltage is just 1% of main circuit voltage.
● Low harmonic contents: THD is below of 5%, which comply with related national criterion, if the multiple connections are adopted, the THD can be reduced below of 1.2%.
● Small dimension: the dimension of MCR is about 2/5 of TCR.
● It can be able to connect in high voltage power grid, the cost and floor space are reduced dramatically.
