NEPSI's Metal-Enclosed Capacitor Banks and Harmonic Filter Banks come equipped with a control power transformer (CPT). This CPT provides control power for the bank as well as a voltage signal for the power factor controller. In most cases the CPT is connected phase-to-phase, but in some instances, it may be connected phase-to-ground.

The CPT voltage and power rating are chosen based upon the system voltage, CPT connection, and load requirements. Additional load requirements to allow for bank expansion are considered in sizing the CPT.

The CPT may be of the oil-filled type or of the cast-coil type. NEPSI chooses the type of CPT based upon cost, technical preference, customer preference, and reliability. For both types, the CPT is fused on the primary side.

The CPT is typically connected to the line-side terminals of the air-disconnect switch. This connection location allows for the testing of the bank controls and components while being disconnected from the medium voltage system. If desired by the customer, the connection location can be changed to the load-side terminals of the air-disconnect switch.