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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
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