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The distribution system may also be divided into three distinct
subsystems.
 Distribution substation
 Primary distribution system
 Secondary distribution system

The remainder of this unit will focus on each of these three
subsystems.

3 Read and translate Text 2:

Text 2
Distribution substations

The distribution substation receives power from one or more
transmission or subtransmission lines at the corresponding
transmission or subtransmission voltage level and provides that
power to one or more distribution feeders that originate in the
substation and comprise the primary network. Most feeders
emanate radially from the substation to supply the load.

There are five main functions of the distribution substation:

1. Voltage transformation: One or more transformers will always
be located within the substation to step down the voltage to the
primary distribution voltage level. These transformers will
always be three-phase banks, or they will be three single-phase
banks connected in a three-phase configuration. The standard
primary distribution voltage levels include 4.16kV, 7.2kV,
12.47kV, 13.2kV, 14.4kV, 23.9kV, and 34.5kV.
2. Switching and protection: Different kinds of switchgear will be
located at the substation, including the following:
a. Switches: devices that can carry and interrupt normal load
current and thus disconnect portions of the network.
b. Circuit breakers: devices that can carry and interrupt
normal load current, like switches; in addition, they
interrupt short-circuit (fault) current. Circuit breakers are
always paired with a relay which senses short-circuit
condition using potential transformers (PTs) and current
transformers (CTs).
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