The control power transformer
provides control power for the bank as well
as a voltage signal for the power factor controller.
In most cases the control power transformer
is connected phase-to-phase, but in some instances,
it may be connected phase-to-ground.
The control power transformer voltage and power rating are chosen
based upon the system voltage, control power transformer connection,
and load requirements. Additional load requirements
to allow for bank expansion are considered
in sizing the control power transformer.
The control power transformer may be of the oil-filled type or
of the cast-coil type. NEPSI chooses the type
of control power transformer based upon cost, technical preference,
customer preference, and reliability. For
both types, the control power transformer is fused on the primary
side.
The control power transformer 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.
