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High voltage
measurements
To be measured
• Arrangement
– electric field
– voltage
– capacity
– charge
– resistance to ground
– discharge current
• Material
– Resistivity
– Specific surface resistance
Influenced by:
• Temperature
• Relative humidity
– Relative permittivity
To be measured
Types of test voltages:
•AC
•DC
•aperiodic voltage impulse
•high frequency damped voltage impulse
Measurement of high voltages
Measurement of the voltage peakSpark gap
a) asymmetric; b) symmetric
for AC
Measurement of the voltage peak
(Chubb-Fortescu method)
Chubb-Fortescu method
?)( =tic
Measurement of the voltage peak
t
UCd
d)( =tic ∫∫ ==
max
min
U
U
T/2
0
UT
Ct
t
UC
Tdd
d
d1mi
maxminmax2UCfUU
T
C=−= )(mi
2fCUpeak
mi
=
⇒
⇒
Chubb-Fortescu method
Measurement of the voltage peak
Measurement of the peak voltage
Impulse:
a) circuit;
b) error caused by the time constant
a)
b)
MCRD=τ
Measurement of RMS
RMS value
Urms/Ucs
Linear mean
value
Um/Ucs
Um/Urms
707,02
1=
5,02
1=
707,02
1=
612,08
3=
318,01=
π
637,02=
π
5,02
1=
637,02=
π
900,08=
π
816,03
2=
0 0
Electrostatic voltmeter:
22
2
1AUU
d
dC
d
dWM ≈==
ϕϕ
Measurement of RMS
Starke-Schröder voltmeter:
2
2
2
2
1
2
1U
a
AU
da
dCF
ε==
da
dWF =
Measurement of RMS
Generator voltmeters
dt
dCtU
dt
dUtC
dt
dQic )()( +==
Voltmeter with oscillating measuring electrode:
Generator voltmeters
Field mill:
N high voltage electrode; F grounded shielding electrode;
M1 and M2 fixed measuring electrodes
Generator voltmeters
Voltage dividers
Resistive voltage divider with strayed capacitor (C):
Capacitive voltage divider:
a) open circuit currents; b) secondary load currents
Voltage dividers
capacitive divider :
C1 CA1
C2 CA2
Independent
measuring systems
Cs : Capacity if shielding
Ck : Capacity of the head
Cs , Ck can be neglected generally.
Compenzated impulse divider
Voltage dividers
Measurement of resistivity
ρ Ohm m
Guard electrode
Measurement of surface resistance
ρ Ohm
Measurement of surface resistance
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