These are special air transformers designed to optimal transmission of static converters power into the distribution network using coupling filters.
They can be classified by voltage level to which the Ripple Control is emitted:
MV (22 kV and 35 kV) coupling transformers for inside use
These are air transformers without steel magnetic core. The Static frequency converter is connected to primary winding through C1 capacitor battery (single multi-capacity capacitor per phase). C2 coupling capacitor battery consists of one, two or three high-voltage capacitor is connected to the secondary winding.
HV (110 kV) coupling transformers, outside use
Windings are placed in tubular, oil-filled tank. There is expansion tank on top allowing for oil cooling. C1 capacitor batery includes one or two high-capacity capacitor on phase. There is a capacitor battery (consists of 8 or 10 capacitors in series on phase) connected to HV winding.