Mechanically switched capacitors (MSC and MSCDN)

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. The MSCDN additionally offers a damping network to avoid resonance conditions in the electrical system. 

Simple and most economical: mechanically switched capacitors (MSC), mechanically switched reactors (MSR) or filter circuits (FC) 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 – solutions and filter circuits from Siemens Energy have been successfully proven in practice.