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HIGH VOLTAGE

breakdown behavior in co-axial cylinders

Assistant Professor Suna BOLAT

Eastern Mediterranean University

Electric and electronic department

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Parameters (Definitions) for

cylindrical electrode system

1. Actual electrode separation, d

2. Effective electrode separation,

3. Geometric characteristics, p&q

4. Utilization factor (Electrode efficiency),

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Actual electrode separation, d

=

=

=

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Effective electrode separation,

=

= ln

=

= .

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Geometric characteristics, p&q

In co-axial cylinders:

=+ =

=

=+ ==

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Utilization factor (electrode efficiency)

= =

=

1

=

=

ln =

1

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Breakdown behavior in concentric spheres

Goal:Analyzing the relationship between electrode radii and

electric field and potential.

Change in Emaxwith respect to r

Change in Umaxwith respect to r

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1. Change in

with respect to

and Radius of outer sphere is constant, radius of inner sphere is

variable.

= . =

Q: How do we find the minimum value for Emax?

A: derivative is zero!!!

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= 0

=

. ln =

. l n . l n

=

ln ln 1 . (. l n . l n ) = 0

ln ln 1 = 0

ln = 1 = ln =

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Optimum geometric characteristic

= = = 2.718

=

fittest, optimum geometric char. with regard

to breakdown in co-axial cylinders

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Breakdown behavior

()

()

AB

Breakdown strength of

the insulator

= Breakdown region

No discharge region

No-Breakdown

<

Pre-Breakdown region

Partial discharge region

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1. Change in

with respect to

, = .

= = .

= , = , =

= .

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= . ln = ()

Maximum Voltage will be Maximum

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Maximum value for

Q: how do we find maximum value of ?

A:= 0;

= . ln = . l n . ln

= ln + 0 ln

= 0

ln ln 1 = 0 ln = 1

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= = 2.718 =

Optimum characteristic with regard to

breakdown in cylindrical system.

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=

Breakdown voltage of the

electrode system

Breakdown voltage of the

insulator

Breakdown

Partial

discharge

No

discharge

AB

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Breakdown behavior

>