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Substation — Welded/EHV
BURNDY
®
Canada: 1-800-387-6487
www.burndy.com
US: 1-800-346-4175
M-6
The sphere is removed and the voltage
raised until there is a corona on the connec-
tor. Since the voltage gradient increases
directly with increases in applied voltage, the
gradient on the conductor at this point can
be readily calculated.
It is important to note that the significant
parameter is the voltage gradient on the
surface of the conductor. It is not necessary
to know the gradient on the connector. The
conductor gradient in any given substation
is controlled by its design parameters and
may be calculated using the following
formulae and nomograms. Once the
gradient is known, it is unnecessary to have
any other information to design connectors.
As long as connectors are corona-free at a
conductor voltage gradient higher than that
planned for the conductor, the connector
will be corona-free under fair weather
operating conditions.
There may on occasion be unusual situations
where choice of
conductor
, station geometry
or clearance problems cause the need for
connectors of special design. Where this is
the case, BURNDY
®
is prepared to design
corona-free devices to operate under such
conditions.
The center conductor has a gradient about 5% higher than the
outside conductors. The gradient on the center phase may be
calculated using the formula for the single conductor.
Single phase system and substituting (h
e
) from the following formu-
la or attached nomograms for the height above ground (h). For the
center phase:
Bundled Conductor - Three Phase
This case may be reduced to the single bundled conductor case by replacing h with h
e
in the equation.
The definition of h
e
is identical to that given for the single conductor –– three phase situation.
The maximum gradient (E
m
) occurs on the side facing the ground
plane.
Formula for Determining The Voltage Gradient
Notations Used
h
= line to ground distance (cm)
h
e
= equivalent single phase line to ground distance (cm)
r
= radius of the individual conductor (cm)
r
e
= equivalent single conductor radius (cm) of bundled
s
= conductor spacing in the bundle (cm)
conductors
d
= phase to phase spacing of the line (cm)
n
= number of conductors in the bundle
V
= line to ground voltage (kV)
E
a
= average gradient at the surface of the conductor (kV/cm)
E
m
= maximum gradient on the surface of a single conductor
It should be noted that h
e
is somewhat smaller than
The value of
is unity for 1-, 2-, and 3- conductor bundles and
1.12 for 4- conductor bundles.
Fig. 1