Construction of 11/0.
4KV substation
Substation
Types of substation
Construction requirements
Work procedure
Site location
INITIAL AND ULTIMATE REQUIREMENTS
Cooperatives should consider both short- and long-range plans in the development of their
systems. Timely development of plans is not only essential for the physical and financial integrity of
electrical Systems, it is also essential in supplying customers with adequate service. The long-range plan
identifies the requirements of a substation not only for its initial use but also for some years in the future.
Consider ultimate requirements during the initial design. Make economic comparisons to discover what
provisions are necessary for ease of addition. Remember that development plans embrace philosophies
of equipment and system operation and protection before construction is started. Changes in the
cooperative’s standard design philosophies should be reviewed by the personnel who design, operate,
and maintain the proposed equipment. Departures from standard designs could jeopardize the operation
of the system.
SITE CONSIDERATIONS
Two of the most critical factors in the design of a substation are its location and siting. Failure to
carefully consider these factors can result in excessive investment in the number of substations and
associated transmission and distribution facilities. It is becoming increasingly important to perform initial
site investigations prior to the procurement of property. Previous uses of a property might render it very
costly to use as a substation site.
Such previous uses might include its use as a dumping ground where buried materials or toxic waste
has to be removed prior to any grading or installation of foundations.
The following factors should be evaluated when selecting a substation site:
a. Location of present and future load center
b. Location of existing and future sources of power
c. Availability of suitable right-of-way and access to site by overhead or underground transmission and
distribution circuits
d. Alternative land use considerations
e. Location of existing distribution lines
f. Nearness to all-weather highway and railroad siding, accessibility to heavy equipment under all weather
conditions, and access roads into the site
g. Possible objections regarding appearance, noise, or electrical effects
h. Site maintenance requirements including equipment repair, watering, mowing, landscaping, storage, and
painting
i. Possible objections regarding present and future impact on other private or public facilities
DISTRIBUTION SUBSTATIONS
Distribution substations are usually characterized by voltages up to 230 kV on the primary side and
12.5Y/7.2 kV, 13.2Y/7.6 kV, 13.8Y/8.0 kV, 24.9Y/14.4 kV, or 34.5Y/19.9 kV on the secondary side.
In recent years, the trend has been toward increasing system voltages. It is becoming more common to
eliminate the intermediate transmission substations and directly reduce the transmission voltages to
primary distribution levels. The distribution substations discussed are generally limited to the traditional
type characterized by simple bus arrangements and minimal equipment. However, the arrangements can
be expanded for use in larger distribution substations with higher voltages.
4.3.1 Basic Distribution Substation
Figure 4-2 is a one-line diagram for a basic distribution substation. Depending on the load being served,
it is possible that initial construction may be limited to one distribution circuit.
The subtransmission circuit enters the substation through a primary disconnect switch used principally to
isolate the substation from the subtransmission system for maintenance or when replacement of substation
equipment is required. It is usually of the three-pole, single-throw, group-operated typeBulletin 1724E-300
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To permit voltage regulator maintenance without feeder or bus de-energization, bypass facilities are
provided as illustrated in Figure 4-3.
Figure 4-3: Voltage Regulator Bypass Arrangements
The switches normally used for regulator bypassing automatically combine all switching operations and
perform them in the correct operating sequence. Each combined switch can usually be installed in the
same space as one single-pole disconnect switch.
For a detailed discussion concerning the application of voltage regulators, see RUS Bulletin 1724D-114,
“Voltage Regulator Application on Rural Distribution Systems.”
4.3.4 Circuit Breaker/Recloser Bypass Facilities
Bypass facilities permit circuit breaker or recloser maintenance or repair without circuit de-energization.
Figure 4-4 illustrates a typical bypass arrangement.
The bypass switches usually consist of three independently operated hook stick switches, but a three-pole
group-operated switch can also be used. In some applications, it may be desirable to combine some of the
switches to facilitate installation. Figure 4-5 illustrates one possible configuration.
In this configuration, a tandem switch is used to combine the bypass switch and the load side disconnect
switch onto a single switch base. The combined switch can be installed in nearly the same space as one
single-pole disconnect switch.
To provide circuit protection during bypassing, the bypass switch can be replaced by a fuse.
