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