Specifications

40
Secondary Unit Substations Some customers require an integrated assembly, called a
secondary unit substation, to provide electrical service to a
facility. A secondary unit substation consists of a primary switch
and one or more transformers mechanically and electrically
connected to switchboard or switchgear sections. All elements
of the substation are engineered to the specific needs of the
application.
The incoming service to the primary switch is typically rated
for 2.4 to 13.8 kV. The primary switch is used to connect and
disconnect the secondary unit substation from the incoming
service. The transformer section can be liquid filled, ventilated
dry type, or cast coil type and is used to step down the voltage
to below 600 volts. The outgoing section can be switchboard or
WL low voltage switchgear sections.
Primary Switch
Transformer
Switchboard or
Switchgear Sections
Small Industrial Facility An example of the power system for a small industrial facility
Power Distribution Example is one shown in the following illustration. For simplicity, only
a few circuits are shown. In this example, incoming voltage
is stepped down to 4160 volts and applied to the facility’s
secondary unit substation. A transformer in the secondary
unit substation steps the voltage down to 480 volts which is
distributed to various switchboards and panelboards. A 1-phase
transformer reduces the voltage to 120 volts.
Transmission
Voltage
4.16 kV
Power Company
Sub Station
Secondary Unit Substation
Primary
Switch
Transformer
Switchboard
480 V
480 V
Panelboard
Panelboard Panelboard
Switchboard
Transformer
480 V120 V
480 V