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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

, 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:

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.

= line to ground distance (cm)

e

= equivalent single phase line to ground distance (cm)

= radius of the individual conductor (cm)

e

= equivalent single conductor radius (cm) of bundled

= conductor spacing in the bundle (cm)

conductors

= phase to phase spacing of the line (cm)

= number of conductors in the bundle

= line to ground voltage (kV)

a

= average gradient at the surface of the conductor (kV/cm)

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.