10_chapter 4
TRANSCRIPT
91
4.3 DESCRIPTION OF APPARATUS
4.3.1 POINT PLANE ELECTRODE SYSTEM ARRANGEMENT
The plane electrode is made up of mild steel and has very smooth
finished surface [Fig. 4.1]. The point electrode is a hemispherically
capped cylinder [Fig. 4.2 ]. The different materials used for point
electrode are stainless steel, copper [Fig. 4.3], brass [Fig. 4.4 ], silver
plated brass [Fig. 4.5], chromium plated brass [Fig. 4.6 ] and nickel
plated brass[Fig. 4.7]. The diameter of point electrode used are 1mm,
1.5mm, 2mm, 3mm, 4mm and 5mm for copper ; 1mm, 1.5mm, 2mm and
3mm for stainless steel, 1mm, 1.6mm, 2mm, 2.5mm, 3mm, 4mm and
5mm for brass. The minimum length of hemispherically capped electrode
used in experiments is 130mm [ > 2.5 gap length ]. This electrode is
mounted horizontally using brass holders [Fig. 4.8] 50mm in length and
with one side rounded off to a radius of 12.5mm and all surfaces very
smooth finished. The length of the brass holder is 50mm [Fig4.9]. The
inner portion of the brass holder is threaded to accommodate an
aluminum rod which in turn is supported by vertically placed 8.27cm dia
stands. The horizontal axis of the point plane gap is at a height of 80cms.
This is achieved by use of vertical insulating end supports. [Fig.4.10] The
plane electrode is brazed on to a brass holder[Fig. 4.11] with ½ “BSW
threads in the inner portion, which in turn is supported by vertically
placed 8.27cm dia stands of length 80cm which in turn is placed on a
wooden table.
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4.3.2 HIGH VOLTAGE D.C. SUPPLY
The high voltage D.C. supply is obtained from voltage doubler circuit
arrangement. The rating of HV transformer used is 240V / 100KV /
5KVA [Fig. 4.12]. The HV winding of transformer has small number of
turns near the ground end
HVfgryrrghthrtrhtrthhhhdndn4trRFGRYFGRGR of the HV winding which
is used for measurement of HVAC output voltage. The LV side of the HV
transformer is supplied through an oil filled 240 V / 0 – 240 V Variac
with all controls [Fig.4.13]. The circuit diagram of voltage doubler circuit
is shown in Fig. 4.26. A current limiting resistance of 30 kiloohms, 200
watts [ non inductive type ] has been used in series with the HV
electrodes in all the experiments [Fig. 4.12]. The connections to the
capacitors from HV rectifiers [Fig. 4.15] are made through corona free
arrangements made from aluminum material. A suitable set of corona
free connectors facilitate changeover of polarity of D.C supply to point
plane electrode system [Fig. 4.15 & 4.16].
The output voltage of HVDC test set is connected to an accurate
HVDC measuring arrangement. The HV arm of the HVDC measuring
arrangement is a compensated type HV resistance [Fig. 4.17]. The
measured resistance value is 29.3 Mega ohms. The HVDC resistor in
series with an accurate reading DC milliammeter [Fig. 4.18] was used for
accurate measurement of HVDC voltage applied to HV electrode of the
point plane experimental electrodes. As a verification procedure, a
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100mm diameter sphere gap assembly[Fig. 4.19] has also been used for
checking the HVDC output voltages.
4.3.3 THE ULTRAVIOLET LIGHT SOURCE
A mercury discharge lamp [ Fig. 4.20 ] 125 watt, 200-250V (1N.HPL-
N BC) Philips make was used to provide ultraviolet radiation required to
release the initial photoelectric current IO from the cathode. The
ultraviolet lamp was mounted at a distance of 30 cm from horizontal axis
of the gap and was directed to the entire gap and point electrode. An
initial warming up period of 30 minutes was allowed for stabilization.
4.3.4 DETAILS OF DIGITAL STORAGE OSCILLOSCOPE
Yokogawa make (window based ) DSO [ Fig. 4.21] was used for
recording the corona pulses. The details of the oscilloscope are:
Model number : 9140L(701311)
Maximum sampling rate : 5 GS/s
Frequency bandwidth : 1 GHz
Input channels :4 (CH1 to CH4)
Input impedance :1 MΩ ±1.0% in parallel with 20 pF
Capacitance
Voltage axis sensitivity : 2mv/div to 5V/div (1-2-5 steps)
Vertical axis accuracy :For 1MΩ INPUT:±1.5% of 8 divTime base accuracy
:± 0.001%
Display : 8.4 inch(21.3cm) color TFT liquid
Display
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Storage :Built-in memory media
Media type :Compact flash
Capacity :32 MB
USB peripheral interface connector
Connector type :USB type A connector(receptacle)
PB 500 (10:1 passive probe) :10MΩ *10
4.4 GENERAL DESCRIPTION OF LABORATORY CONDITIONS
The laboratory is situated about 4 KM from the main traffic road. The
area is almost totally free from disturbances and the atmospheric
conditions are steady without abrupt changes. Experiments have been
conducted during the time periods 11.0 a.m to 5.0 p.m of the day during
which disturbances and fluctuations are minimum. Only the days on
which fair weather conditions prevailed have been selected for carrying
out experimental investigations. However, as a precautionary measure,
atmospheric conditions- pressure, dry bulb temperature and wet bulb
temperature have been recorded at every two hours period while carrying
out experimental investigations.
4.5 MEASUREMENT OF INITIATORY CURRENT IO
An Electrometer (Keithley make) has been used for measurement of
initiatory current. A known gap was set up and the connection made
with input supply to UV lamp, HVDC supply and Electrometer and the
output voltage to point electrode was set at zero value. The whole system
was maintained under these conditions for 30 minutes for allowing time
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duration for stabilization of the experimental setup. After stabilization,
initiatory current was measured by applying a voltage of 1KV to HV
electrode (i.e., point electrode). These measurements were carried out for
several gap spacings and several diameters of the point electrode. The
average value of measured current was same and the current did not
vary with gap spacing or change in radius of hemispherical electrode.
The magnitude of the measured average initial current is 1*10-12 Amp.
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4.6 DESIGN AND CONSTRUCTION OF HV RESISTANCE WITH
VOLTAGE BALANCING CAPACITORS
It consists of 15 sections of (330KΩ *3 ) resistances connected in
parallel with 0.01 microfarad 2000V rated voltage balancing capacitors.
Component of each section is tested for 2000volts DC, one minute
withstand. Only good components, which did not vary in value more than
±1% are selected for building the voltage divider. Before testing, each
resistor is thoroughly cleaned using Trichloroethylene (to remove grease,
moisture and soluable materials ) and a coating of epoxy resin is applied
over external surface and allowed to set for 24 hours.
The complete HV resistance is built using above tested components
and assembled inside a insulating tube with leads suitably brought out.
The space inside the insulating tube is filled with good quality
transformer oil. The above HV resistor is used along with an accurate
reading D.C. milliammeter and with calibration resistors for accurate
measurement of HVDC voltages upto 15 KV. The schematic circuit
diagram of the arrangement is shown in Fig. 4.22
4.7 VERIFICATION OF OUTPUT VOLTAGE INDICATED BY HVDC
METER USING 100MM DIA STANDARD SPHERE GAP
ASSEMBLY
The connections were made as shown in Fig. 4.24. The surface of
both the spheres ( 100 mm dia ) were cleaned using a good clean dry
cloth. The surface of both the spheres were again cleaned using cloth
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dipped in Trichloroethylene. The atmospheric pressure in mm of
mercury, dry bulb and wet bulb temperatures were noted. Using the
standard slip gauge ( Accurately machined thickness blocks ), the gap
distance between the two spheres was adjusted to 5 mm. A UV lamp was
used for irradiation of the gap and it was kept at a safe distance from the
spheres such that the mounting of the UV lamp does not influence the
sparkover characteristics of the standard sphere gap assembly. The
output voltage of the DC set was varied till the sparkover of the sphere
gap occurred. Just at sparkover the reading indicated by HVDC meter
was recorded. The experiment was repeated 5 times at intervals of 1
minute. The average value of 5 readings indicated by the meter was
compared with the sparkover value given in the standards corresponding
to the gap spacing after the correction factor [Table 4.1 ]. This showed
very good agreement within the accuracies of measurement.
TABLE 4.1
RELATION BETWEEN CORRECTION FACTOR K AND AIR DENSITY
FACTOR d
d 0.70 0.75 0.80 0.85 0.90 0.95 1.0 1.05 1.10 1.15
K 0.72 0.77 0.82 0.86 0.91 0.95 1.0 1.05 1.09 1.12
98
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4.8 MEASUREMENT OF CORONA INCEPTION VOLTAGES
[ POSITIVE POLARITY]
The schematic diagram of connection for measurement of corona
inception voltages in point plane gaps is as shown in fig 4.23. For
measurement of current at inception, an accurate digital multimeter [ 4
½ digit, LCD ] with an accuracy of 0.5% was used. Initially, the point and
plane electrodes were cleaned using Trichloroethylene. Using corona free
connectors, the connections were made so as to connect positive DC
supply to point electrode Fig. 4.15. The laboratory dry bulb, wet bulb
temperatures and pressures were noted down. Using accurately
machined thickness blocks corresponding to required gap spacing, the
point plane gap was set to a desired value, say 10mm. The voltage
applied to point electrode was steadily increased untill the corona
current measurement meter indicated current of 1.0 microamperes.
The voltage corresponding to corona onset current of 1 microampere
has been considered as corona onset potential (In few cases corona onset
current was less than 1.0 μA. However, the difference between the
voltage at actual inception and that required for corona current to be 1.0
μA was within measurement accuracy ). At inception, oscillograph
showed current pulses of varying magnitude occuring at different
intervals of time. At near 1.0 µA current as indicated by the DC
microammeter, the pulsed behaviour of corona was relatively lower. For
each gap spacing, five readings of inception potentials were recorded at
100
one minute time interval. The average of five readings is taken as corona
inception potential magnitude.
The experiment was repeated for different gap spacing between point
and plane electrode. Further, the experiments were also conducted for
different radii of hemispherical tip of the point plane gap and for different
materials of point electrode. The experimental results are tabulated in
Table 4.2. The tabulated corona inception voltages are values at STP
which are values after applying air density and humidity correction
factors to measured values. If Va is the corona inception voltage at
prevailing atmospheric conditions, the corona inception voltage at STP is
given by Vs=Va*h/d where h is humidity correction factor and d is air
density correction factor given by d=0.386p/(273+Td). Humidity
correction factor „ h „ is obtained from the recorded temperatures of wet
and dry bulb thermometers and by using the graphs provided in the
standards which are shown in Fig.s 4.25 and 4.26.
4.9 MEASUREMENT OF CORONA INCEPTION VOLTAGES ( NEGATIVE
POLARITY )
Using the HVDC supply set up for negative polarity (Fig. 4.16 ), the
experiments were conducted for measurements of corona inception
voltages in a similar way as described in above section. However, the
experiment was repeated by irradiation of the gap with the help of a UV
lamp placed at a distance 30cm from the gap. At onset, negative corona
consisted of Trichel pulses. In case of negative point plane corona,
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humidity correction factor h=1. The experimental results are tabulated in
Table 4.2.
102
Fig. 4.1 :- Plane Electrode
103
Fig. 4.2 Hemispherically capped cylinder
104
Fig. 4.3 Copper Electrodes
105
Fig. 4.4 :- Brass Electrode
106
Fig. 4.5 Silver Plated Brass Electrode
107
Fig. 4.6 Chromium Plated Brass electrode
108
Fig. 4.7 Nickel Plated Brass Electrode
109
Fig. 4.8 Brass holders
110
Fig. 4.9 Brass holder electrode assembly
111
Fig. 4.10 Point electrode support system
112
Fig. 4.11 Plane electrode support system
113
Fig. 4.12 100KV HV Transformer
114
Fig. 4.13 Control panel with oil filled variac
115
Fig. 4.14 A Passive probe across 100 Kilo ohm Resistor
116
Fig. 4.14b Digital microammeter for corona current measurement
117
Fig. 4.15 Rectifiers and Connections for positive polarity
118
Fig. 4.16 Rectifiers and connections for Negative polarity
119
Fig. 4.17 Compensated HV resistor
120
Fig. 4.18 KV Meter
121
Fig. 4.19 100mm dia sphere gap assembly
122
Fig. 4.20 Mercury discharge lamp
123
Fig. 4.21 Yokogawa 1000 MHz DSO
124
Fig 4.22 HV Resistance with voltage balancing capacitors
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Fig. 4.23 SCHEMATIC DIAGRAM OF TEST SET FOR POINT PLANE ELECTRODES
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TABLE 4.2
EXPERIMENTAL VALUES OF CORONA INCEPTION POTENTIALS
[ POSITIVE AND NEGATIVE POLARITY ]
Sl.no MATERIAL DIAMETER
IN MM
GAP
LENGTH
IN MM
POSITIVE
CORONA
INCEPTION
VOLTAGE IN
KV
NEGATIVE
CORONA
INCEPTION
VOLTAGE
IN KV
1 Brass 1mm 20 7.672 7.659
30 8.1668 8.3407
50 9.5418 9.966
1.6 20 9.73778 9.745
30 10.4037 10.466
50 11.871 11.94
2.0 20 11.234 11.74
30 12.163 12.824
50 13.078 13.841
2.5 20 11.78 12.643
30 13.36 13.885
50 15.043 15.048
3.0 20 13.077 13.4929
30 14.499 14.2948
127
50 16.315 15.604
4.0 20 16.25
30 16.4344 17.76
50 19.91158 19.49
5.0 20 18.2449
30 20.22 20.933
50 23.0529 21.38
COPPER 1.0 20 7.732 7.33
30 8.6928 7.913
50 9.9876 9.798
1.5 20 9.8289 10.315
30 10.9332 11.1047
50 12.0319 12.635
2.0 20 11.4553 11.599
30 12.554 12.929
50 14.4087 13.94
3.0 20 14.1156 14.208
30 15.0593 15.6
50 16.1831 16.71
4.0 20 16.658
30 18.1513 18.014
50 20.6189 20.162
128
5.0 20 18.505
30 20.079 19.6446
50 22.5 21.64
STAINLESS
STEEL
1.0 20 8 8.157
30 8.319 9.041
50 9.222 11.425
1.5 20 9.7338 12.01
30 10.7012 12.338
50 11.5165 13.9546
2.0 20 11.3078 12.776
30 12.362 13.37
50 13.696 14.189
3.0 20 13.79 15.129
30 15.032 16.95
50 16.846 18.78
NICKEL
PLATED
BRASS
1.0 20 7.9746 8.188
30 8.3494 8.792
50 9.389 9.574
1.5 20 9.8107 9.834
129
30 10.6557 10.689
50 12.1933 12.1058
2.0 20 10.866 11.34
30 12.113 12.522
50 13.354 13.7997
2.5 20 12.274 13.0856
30 13.609 14.1779
50 15.333 15.704
3.0 20 13.637
30 15.2436 14.98
50 17.856 16.445
4.0 20 14.7018
30 18.585
50 19.005 20.223
5.0 20 16.65
30 20.68 20.493
50 21.248 22.33
CHROMIUM
PLATED
BRASS
1.0 20 8.293 7.7898
30 8.84 8.5351
50 9.875 9.7544
130
1.5 20 9.977 9.933
30 10.9927 10.92027
50 12.35 12.0697
2.0 20 10.129 11.87
30 12.084 12.77
50 13.422 13.969
3.0 20 14.04 15.184
30 15.359 16.40849
50 16.836 18.0057
4.0 20 16.3426
30 18.6026 18.516
50 19.198 19.89
5.0 20 21.08
30 20.6225 20.856
50 23.2936 23.06
SILVER
PLATED
BRASS
1.0 20 7.9835 7.862
30 8.4938 8.825
50 9.8052 9.904
1.5 20 9.3923 10.446
30 10.3974 11.317
131
50 12.088 12.412
2.0 20 11.1818 11.613
30 12.129 12.062
50 13.7815 12.137
2.5 20 12.213 12.935
30 13.342 13.848
50 15.468 4.96
3.0 20 13.788 15.16
30 15.86 15.797
50 17.9179 17.2
4.0 20 16.148 17.129
30 17.8109 17.164
50 18.019 18.77
5.0 20 18.9 18.939
30 20.336 19.4
50 22.86 22.247
4.10 POLARITY EFFECTS ON CORONA INCEPTION POTENTIALS
On observations of results reported in Tables 4.2 for positive and
negative polarity corona inception potentials for same type of electrode
material and geometry, we observe that the negative polarity inception
voltages are generally higher as compared to positive polarity corona
inception voltages. In order to analyse this phenomena in a general way,
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Fig. 4.74-4.75 are drawn to indicate movement of electrons which are
primary charge carriers that cause ionization as they move in electric
field regions for which the ratio E/P is greater than (E/P)critical. The
critical E/P is the value at which α=η for air and in the Fig. the distance
dc is the value of distance from point electrode to the position on the axis
where (E/P)= (E/P)critical. Viewing the phenomena in this manner, we
observe from the Fig. that near corona inception, for the positive polarity
of the point electrode electrons at distance dc from point electrode move
towards the +ve point electrode causing ionization in the path of
movement. During this path of movement, electrons travel into regions of
progressively increasing electric fields ( higher electric field regions ) and
thus can cause greater number of ionization collissions in their path
before reaching the anode. However, for the case of -ve polarity of the
point electrode, the situation is the converse. That is, electrons move
from point electrode into regions of progressively relatively lower values
of electric fields in their path as they reach towards point of distance dc.
Therefore, there can be much lower number of ionization collisions for
this case of negative polarity as electrons travel from point electrode
towards the critical distance and subsequently towards the cathode.
Hence higher voltage has to be applied to point electrode to cause
corona. It may be also noted here that for negative polarity the electrons
can get attached to neutral molecules forming negative ions which do not
cause ionization. Also, the negative ions being heavy move slowly in low
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field regions which situation is same for movement of positive ions in low
field regions for the case of positive polarity of point electrode. These are
possible considerations for a higher voltage required to be applied for
negative polarity of point electrode to cause corona inception as
compared to the voltage that is required to be applied to cause corona
inception for positive polarity of the electrode system.
4.11 EFFECT OF MATERIAL OF ELECTRODE ON CORONA
INCEPTION VOLTAGES
POSITIVE POLARITY
From experimental results we observe that for same diameter of point
electrode and for different gap distances the lowest corona inception
voltages are obtained for pure brass point electrode (not plated). By
change of material of point electrode whether using electroplated brass
electrodes or different material for point electrode the values of corona
inception potentials do not increase considerably for 1mm diameter of
the gap. The maximum increase in corona inception potential is about
7% in this case. Except for only few values of corona inception potentials
for nickel plated point electrode the trend is same for experimentally
determined corona inception potentials for other diameters of the
hemispherically capped point electrode upto diameter of 5.0mm.
However, the maximum difference in corona inception voltage for point
electrodes of other materials (for diameter of point electrode in range of
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1.5mm to 5.0mm ) is approximately 10 % above the value measured for
pure brass electrode of same electrode geometry.
NEGATIVE POLARITY
For the case of negative polarity, we do not observe any consistent
behaviour of corona inception potentials as observed for the case of
positive polarity (Refer Table 4.2 ). With change of material of point
electrode whether electroplated brass or other material for point electrode
different from brass, the corona inception potentials are higher in certain
cases as compared to value obtained for pure brass point electrode and
certain other cases, the corona inception potentials are lower.
4.12 TRICHEL PULSE FREQUENCIES WITH NEGATIVE POLARITY
CORONA
The negative polarity corona consists of Trichel pulse behaviour from
occurrence of corona inception. As voltage is further increased after
corona inception, the DC microammeter records increase in current and
corresponding to increase in current there is increase in frequency of
Trichel frequencies. Even with UV rays shining directed to the gap of the
point plane electrode there were small variations in value of Trichel pulse
frequencies oscillographically recorded for a given value of DC current. In
all our experiments, in order to avoid possible damage to point electrode
the magnitude of corona current was limited to 5 microamperes. In
general for all the cases studied, the average value of Trichel pulse
frequencies increased with increase in DC corona current [ Maximum
135
corona current limited to 5 microamperes ]. For same value of DC corona
current, Trichel pulse frequencies decrease with increase in gap length.
Also, the average Trichel pulse frequencies decrease with increase in
diameter for same value of corona current. The results are shown in Fig.
4.68-4.70.
The average value of Trichel pulse frequencies for given corona
current changed with change in material of the cathode from brass to
nickel, silver and chromium plated brass electrode.[Fig 4.71-4.73]
4.13 CORONA PULSE RISE TIME MEASUREMENTS
The rise time measurements of corona pulse at inception for +ve
polarity was measured by recording the voltage pulse across 100KΩ
resistor using yokogawa make DSO. During studies on corona inception
phenomena, it was observed that for +ve polarity of the point plane
electrode geometry, the rise time of corona pulses just at corona
inception was very fast and in range of approximately 50 nanoseconds to
150 nanoseconds. In addition, extremely fast rise HV pulses have
applications in engineering topics such as electrostatic discharges (ESD),
electromagnetic interference (EMI), and also in medical sciences for study
of electroporation effects on biological cells[ 4.1 to 4.3 ]. From these
considerations, investigations were carried out to achieve extremely fast
rise time electric pulses. The oscilloscopically recorded waveforms of
corona pulses for positive polarity are shown in Fig.s 4.27 to 4.36 for
different materials, for different diameters and different gap lengths.
136
The lowest rise time have been observed for pure brasss and silver
plated brass material. These are shown in Fig. 4.54 to 4.63. For pure
brass material, generally, for a given value of DC corona current, the rise
time of corona pulse is decreasing with gap spacing. For pure brass
electrode, the minimum rise time observed for 1.0mm diameter is 61
nanoseconds for DC corona current and for a gap spacing of 50mm.
Experimental investigations were carried out for achieving possible
improvements in rise time of corona pulses by sudden application of over
voltage to a pre stressed point plane gap. The pre-stress voltage selected
was 65% (approximately) of the magnitude of steady state corona
inception voltage in air under fair weather conditions. The circuit
diagram is shown in Fig. 4.76. For these investigations point plane
electrode of 1 mm dia for point and 10mm gap distance was selected. The
oscillographic record of voltage pulse obtained under these conditions is
shown in Fig. 4.77. We observe from the Fig., the rise time of pulse
recorded is 29.5 nano seconds.
For further study of the phenomena, the voltages corresponding to
108 multiplication [This value corresponds to threshold value for
streamer development and critical distance is the distance
correspondimg to (E/P)CRI in air under fair weather condition for α= η]
and the critical distances from centre of point electrodes for various gap
distances and different diameters of hemispherical tip of point electrode
were calcluted. These are shown in Fig.s 4.78 to 4.83.
137
When the voltage corresponding to 108 multiplication (within about
+1%) was suddenly applied, there was a sound and this was
accompanied by an approximately small spot luminosity moving from tip
of HV electrode to the ground. It was clearly a transitory conduction of
gap and not at all a permanent conduction across the gap. Repetition of
this experiment for various gap distances indicated, that the phenomena
of transitory conduction (very short duration time conduction for times of
order of about few tens of nanoseconds) appeared very close to the
voltage corresponding to 108 multiplication for all gap spacings.
4.14 CONCLUSIONS
Point plane electrode geometry for experimental investigations has been
constructed.
1. A High voltage DC measuring device is built which uses accurately
measured RC components in order to measure the HVDC voltages
to good accuracy by measuring the DC current flowing through the
resistor ( ±1% accuracy ).
2. Experimentally determined values of corona inception potentials
for the -ve polarity of point electrode are higher than the values
obtained for the positive polarity.
3. The effect of material on corona inception voltage magnitudes is
not considerable and is observed to be consistently higher
(Maximum increase of 7%) for the positive polarity as compared to
corona inception voltages determined for brass electrode.
138
4. Even with UV light directed into the gap of electrodes, there are
small variations in Trichel pulse frequencies for a given value of DC
corona current.
5. Average value of Trichel pulse frequencies decrease with increase
in diameter.
6. Average value of Trichel pulse frequencies decrease when the
material is changed from brass to silver, nickel and chromium.
7. The lowest rise time for positive polarity corona inception voltage is
observed for silver plated brass electrode for steady state voltage
applications.
8. With suitable arrangement for sudden overvoltage application on
prestressed point plane gap (prestress voltage being 65% steady
state corona inception voltage) with magnitude of voltage
corresponding to 108 multiplication, it is possible to reduce the rise
time of positive polarity corona pulse voltage.
139
Figure. 4.24 Circuit Diagram indicating arrangement for application of
positive polarity and negative polarity voltages to point elctrodes.
140
Fig. 4.25
141
Fig. 4.26
142
Fig. :- 4.27 Recorded waveforms of corona pulse
Brass, diameter 1mm gap distance 30mm
143
Fig. :- 4.28 Recorded waveforms of corona pulse
Brass, diameter 5mm gap distance 20mm
144
Fig. :- 4.29 Recorded waveforms of corona pulse
Copper, diameter 1mm gap distance 20mm
145
Fig. 4.30 Recorded waveforms of corona pulse
Copper Diameter 4mm gap distance 20mm
146
Fig. 4.31 Recorded waveforms of corona pulse
Stainless steel, Diameter 1.5mm gap distance 30mm
147
Fig. 4.32 Recorded waveforms of corona pulse
Nickel plated brass, Diameter 2mm gap distance 30mm
148
Fig. 4.33 Recorded waveforms of corona pulse
Silver plated brass, Diameter 1mm gap distance 50mm
149
Fig. 4.34 Recorded waveforms of corona pulse
Nickel plated brass, diameter 2.5mm gap distance 20mm
150
Fig. 4.35 Recorded waveforms of corona pulse
Chromium plated brass, Diameter 2mm gap distance 50mm
151
Fig. 4.36 Recorded waveforms of corona pulse
Chromium plated brass, Diameter 3mm gap distance 20mm
152
Fig. 4.37 Recorded waveforms of Trichel pulse frequencies
Brass, Diameter 1mm gap distance 20mm
153
Fig. 4.38 Recorded waveforms of Trichel pulse frequencies
Brass, Diameter 3.1mm gap distance 50mm
154
Fig. 4.39 Recorded waveforms of Trichel pulse frequencies
Copper, Diameter 1mm gap distance 20mm
155
Fig. :- 4.40 Recorded waveforms of Trichel pulse frequencies
Copper , Diameter 1mm gap distance 20mm
156
Fig. 4.41 Recorded waveforms of Trichel pulse frequencies
Stainless steel, Diameter 1mm gap distance 20mm
157
Fig. 4.42 Recorded waveforms of Trichel pulse frequencies
Stainless steel, Diameter 1.5mm gap distance 30mm
158
Fig. 4.43 Recorded waveforms of Trichel pulse frequencies
Nickel plated brass, Diameter 1mm gap distance 20mm
159
Fig. 4.44 Recorded waveforms of Trichel pulse frequencies
Nickel plated brass, Diameter 1.5mm gap distance 50mm
160
Fig. 4.45 Recorded waveforms of Trichel pulse frequencies
Chromium plated brass, Diameter 1mm gap distance 20mm
161
Fig. 4.46 Recorded waveforms of Trichel pulse frequencies
Chromium plated brass, Diameter 2.5mm gap distance 20mm
162
Fig. 4.47 Recorded waveforms of Trichel pulse frequencies
Silver plated brass, Diameter 1mm gap distance 20mm
163
Fig. 4.48 Recorded waveforms of Trichel pulse frequencies
Silver plated brass, Diameter 2mm gap distance 50mm
164
Fig. 4.49 Recorded waveforms of Trichel pulse frequencies
Silver plated brass, Diameter 5mm gap distance 50mm
165
Fig. 4.50 Comparison of positive corona inception voltage for Brass
and Nickel plated Brass.
166
Fig. 4.51 Comparison of positive corona inception voltage for Brass
and Chromium plated Brass.
167
Fig. 4.52 Comparison of positive corona inception voltage for Brass
and Silver plated Brass.
168
Fig. 4.53 Comparison of positive and negative Corona Inception
Voltages
169
Fig. 4.54 Positive corona: Plot of rise time vs gap distance for Brass,
Diameter 1mm
170
Fig. 4.55 Positive corona: Plot of rise time vs gap distance for Brass,
Diameter 2mm
171
Fig. 4.56 Positive corona: Plot of rise time vs gap distance for
Stainless steel, Diameter 1mm
172
Fig. 4.57 Positive corona: Plot of rise time vs gap distance for
Stainless steel, Diameter 1.5mm
173
Fig. 4.58 Positive corona: Plot of rise time vs gap distance for Silver
plated Brass, Diameter 1mm
174
Fig. 4.59 Positive corona: Plot of rise time vs gap distance for Silver
plated Brass, Diameter 1.5mm
175
Fig. 4.60 Positive corona: Plot of rise time vs gap distance for Silver
plated Brass, Diameter 2.0mm
176
177
Fig. 4.61 Positive corona: Plot of rise time vs gap distance for Silver
plated Brass, Diameter 2.5mm
178
179
Fig. 4.62 Positive corona: Plot of rise time vs gap distance for Silver
plated Brass, Diameter 3mm
Fig. 4.63 Positive corona: Plot of rise time vs gap distance for Silver
plated Brass, Diameter 4mm
180
Fig. 4.64 Positive corona: Plot of rise time vs gap distance for
Chromium plated Brass, Diameter 1.5mm
181
Fig. 4.65 Positive corona: Plot of rise time vs gap distance for
Chromium plated Brass, Diameter 2mm
182
Fig. 4.66 Positive corona: Plot of rise time vs gap distance for
Chromium plated Brass, Diameter 5mm
183
Fig. 4.67 Positive corona: Plot of rise time vs gap distance for Nickel
plated Brass, Diameter 1.5mm
184
Fig. 4.68 Plot of Average Trichel Pulse frequencies in KHz vs Corona
current for Brass, Diameter 1mm
185
186
Fig. 4.69 Plot of Average Trichel Pulse frequencies in KHz vs gap
length in mm
187
188
Fig. 4.70 Plot of Average Trichel Pulse frequencies in KHz vs
Diameter in mm
Fig. 4.71 Plot of Average Trichel Pulse frequencies in KHz for Brass
and Silver plated Brass vs gap length in mm
189
Fig. 4.72 Plot of Average Trichel Pulse frequencies in KHz for Brass
and Chromium plated Brass vs Gap length
190
Fig. 4.73 Plot of Average Trichel Pulse frequencies in KHz for Brass
and Nickel plated Brass vs Gap length
191
Fig 4.74 Pictorial Representation of polarity effect (Positive)
Fig. 4.75 Pictorial Representation of polarity effect (Negative)
192
Fig. 4.76
193
Fig. 4.77 Oscillographic record for Rise time in over voltage gap
194
Fig. 4.78 Plot of critical distance vs gap length corresponding to
108 Multiplication D=1.5mm
195
Fig. 4.79 Plot of critical distance vs gap length corresponding to 108
Multiplication D=2.0mm
196
Fig. 4.80 Plot of voltage in KV on tip corresponding to
108Multiplicatio arround diameter 1.0mm
197
Fig. 4.81 Plot of voltage in KV on tip coresponding to
108Mutiplication Diameter=1.5mm
198
Fig. 4.82 Plot of critical distance vs gap length corresponding to 108
Multiplication D=2.5mm
4.15 REFERENCES
1. IEEE standard surge withstand capability (swc) tests for protective relays
and relay systems P472/D9, c37.90.1-198X. Draft document of the
power system relaying committee,june 8, 1987.
2. Recommended transient voltage tests applicable to transistorized relays,
The British Electrical and Allied manufacturer‟s association (inc)
publication number 219, november 1966.
3. M.Behrend et al, “Pulse Generators for pulse electric field exposures of
Biological cells and tissues”, IEEE Transactions on Dielectrics and
Electrical insulation, vol 10, no. 5, october 2003,pp 820-825.
199
Fig. 4.83 Experimental Setup for Over voltage Application