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 Considerable time and expense can be saved if a coordination study is performed in conjunction
with the construction work plan (see subparagraph 8.4.3.1 (e)). Much of the data required for a
coordinating study can be accumulated while performing studies required for the construction
work plan.
To determine if system sectionalizing is adequate, the device at each sectionalizing point should
be tested for:
(a)
Correct voltage rating.
(b)
Adequate load current.
(c)
Adequate interrupting current rating.
(d)
Adequate continuous current rating.
(e)
Correct pickup current rating.
(f)
Coordination with adjacent devices.
These tests are performed by comparing system parameters to device ratings or characteristics
and can be easily accomplished by the use of computer applications. Tests for correct voltage,
load current, and interrupting current ratings require only that, for each sectionalizing point, the
device at that point and its ratings are on file storage. They can be compared to system
parameters of voltage level, load current, and maximum fault current, also on file storage. If the
system voltage level does not fit within the acceptable device voltage level range, then the
voltage level test has failed. Load current must be less than the continuous current rating and
maximum fault must be less than the device interrupting current rating to pass load current and
interrupting current tests. It is often beneficial to apply a constant multiplier to all load currents,
before the load current test, to adjust for load growth or imbalance conditions on multi-phase
lines.
The minimum pickup current rating test must search the system controlling the device under
evaluation to find the minimum fault current available through that device (as defined by some
given fault impedance - usually 40 ohms for Rural Electrification Administration studies). The
value must be greater than the requirements for minimum and maximum fault current available
through the device being evaluated and must fall within the range of coordination as defined for
the device with the source side device that it is protecting. The range of coordination, with
adjacent devices, can be defined for each test using methodical representations of the device TCC
curves. The coordination test need only be performed on the source side device if all devices on
a circuit are evaluated. Coordination with load side devices will be tested when the load side
device is evaluated.
8.4.6 Economic Conductor Analysis. An economic conductor analysis is performed to
reduce electric system energy losses to the lowest possible level. Although cost minimization is
important, the first consideration in the design of primary lines for an electric distribution system
is assurance that the conductor size specified is adequate from a voltage drop standpoint. When
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