The coupling capacitor may be part of a capacitor voltage transformer used for voltage measurement.

The capacitor voltage transformer uses a capacitance potential divider and is used at higher voltages due to a lower cost than an electromagnetic VT.

Capacitor voltage transformer: Transformer in which capacitor divider is used to reduce high voltage before application to the primary winding.

A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay.