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In many cases, the simplest solution for controlling reactive power is just sufficient. That makes mechanically switched capacitors (MSC) and mechanically switched reactors (MSR) the most economical power compensation devices for mainly constant or predictable voltage. Both devices are connected to the grid via high-voltage circuit breakers. Under heavy load conditions, MSCs provide voltage control and grid stabilization in a simple and cost-efficient way. MSRs provide stability under low load conditions or can be used at the end of long, radial AC lines. However, usage is somewhat limited as the capacitors need to discharge for several minutes after switching off an MSC bank.
Filter circuits are often used in industrial plants. The filter circuits damp the generated harmonics which are produced by inverters and nonlinear loads.
MSC/MSCDN at a glance
Simple and most economical: mechanically switched capacitors (MSC), mechanically switched reactors (MSR) or filter circuits are well proven in many applications.
When speed is not the main focus, mechanically switched capacitors (MSC) are a simple and low-speed solution that provides grid stabilization and voltage control under heavy load conditions, while mechanically switched reactors (MSR) provide stabilization under low load conditions.
A more advanced variant is a mechanically switched capacitor with damping network (MSCDN). This filter circuit provides reactive power to the grid by using a capacitive filter structure. This limits the amplification of existing harmonics in the grid, and further enhances grid stability. In industrial plants filter circuits reduce harmonics and improve the power factor. Switched filters enable a slow power factor control.
MSC/MSCDN/FC are available in different branches that provide various benefits. Number and type of selected branches depend on the specific application and are project tailored.
Mechanically switched capacitors (MSC) or filter circuits (FC) allow automatic switching of the capacitor banks according to the requirement of the network system and can also be switched on and off manually. MSC increase voltage at the point of connection.
Mechanically switched reactors (MSR) have the opposite effect of mechanically switched capacitors. MSR therefore decrease voltage at the point of connection.
MSCDN and FC provide reactive power to the grid through a capacitive filter structure. It provides capacitive reactive power under power frequency conditions. When its tuning frequency is exceeded, the MSCDN provides inductive reactive power. At high-frequency conditions it acts as a damping resistor. Filter circuits are specific designed in order to damp the harmonics on its junction point.
MSC/MSCDN – solutions and filter circuits from Siemens have been successfully proven in practice.
Delivery of seven MSCDNs with different operating ranges (20-80 MVar) for the “275-kV Mambong and Entinggan substation extension” project
Component design, to ensure its proper interaction with the grid, implementation and commissioning
Providing voltage support and filtering of specific frequencies at the Mambong substation
When the advantages of static VAR compensators (SVC) aren’t required, mechanically switched reactors, capacitors or filter circuits (FC) provide a simple, robust, and cost-efficient solution for grid stabilization and voltage control.