1. GENERATION AND MEASUREMENTS
HIGH VOLTAGE TESTING
GENERATION AND MEASUREMENTS
1. INTRODUCTION
why high voltage test ?
2. HIGH VOLTAGE GENERATION
a) Generation of direct high voltages
b) Generation of alternating high voltages
c) Generation of impulse voltages

2. 3. HIGH VOLTAGE MEASUREMENTS
a) Measurement of direct voltages
b) Measurement of alternating voltages
c) Measurement of impuls voltages
4. GENERATION OF HIGH IMPULSE CURRENTS
MEASUREMENT OF IMPULS CURRENTS
a) Rogo wski coil method
b) Current shunt method

3. 1. INTRODUCION Difinition : high voltage = voltage > 1 kV
Aims of HV test
i) Test HV equipment used in power systems
Non-destructive test (NTD) consist of
 Type tests  Routine tests
 Monitoring tests
Used to measure
 Loss angle  Partial disharge level
 Withstand level
ii) Study of overvoltage effects on equipment
External overvoltages (lightNing)
System overvoltages (switching, temporary)

4. HIGH VOLTAGE TESTS RELATED STANDARDS AND ORGANISATION
IEC : International Electrotechnical Committee
BSI : British Standard Institution
IEC 60 (Part I and Part II) = BS 923 : high voltage testing techniques
IEC 71 (Part I and Part II) = BS 5622 : insulation Co-ordination
IEC 52 = BS 358 : Method for the measurement of voltage with sphere gaps.
Other bodies
CIGRE : Conférence International des Grands Réseaux Electriques
ISH : International Symposium on High Voltages Engineering

5. 2. HIGH VOLTAGE GENERATION
a) Generation Of High Direct Voltage
Existing methods
Rectifier circuits
Multiplier rectifier circuits
Cascaded transformer/rectifier circuits
Special circuits; Engetron, Deltatron
Electrostatic generators

8. I) Rectifier Circuits : Background definition
i) Ripple V :
which gives
To reduce ripple
Increase size of smoothing capacitor
Increase frequency
Increase number of phases (if possible)
ii) Amlitude V

9. iii) Ripple Factor
iv) Ripple Factor
Ripple factor  3 %
Regulation
Change / variation of voltage
1 minute tests   1%
More than 1 minute tests    1%

10. Voltage doubler circuit
Greinacher doubler circuit = (Villard doubler + rectifier/smoothing) circuit
Loaded multipliers
If unloaded the diodes do not conduct and the ripple is

11. Because of charge transfer, the capacitors Ci are charged to a voltage equal (Vci - Vi)
The total voltage drop is then,

12. 4-stage cascade rectifier
Voltages at nodes ‘1’ are oscillating
Voltages at nodes ‘1’ are constant 9dc)
HV out is 2* 4* Vmax

13. Loaded cascade circuit, definitions of voltage drop  Vo and ripple V

14. GENERATION OF ALTERNATING VOLTAGE
i) Test transformer ii) Casaded transformer iii) Resonant circuit
I. Test Transformer
Simple design ; usually, one side is earthed
IEC Standard Specifikations
 f = 45 – 65 Hz
 Shape :
 V (1 minute test)  1%
 Transformer ratings
* dry tests: current rating of  100mA
* wet tests: current rating of  500mA
* pollution tests: current rating  15 A

15. Cascaded transformers
Power is shared by the three units
Voltage stress is reduced (shared along the cascade)
Basic circuit of cascaded transformers. (1) Primary widings. (2) Seconddary h.t. widings. (3) Tertiary exciting windings.

16. Series Resonant Circuits
For testing large capacitive loads (cable and GIS) and inductive loads (HV reactors)
For an RLC series circuit the resonant frequency is
The output voltage acros the test object is
At resonance, Zc = Zl
In practice Zc >> R
Which gives V2 >> V1 (20 to 50 times)

17. Advantages
Better waveshape (fundamental times 50)
Better
rkVA output
Voltage callapse after flashover (no damage to equipment)
Easily cascaded, lighter than transformers.

18. Resonant Circuits
a) Previous designs (no reactors)

19. b) Modern designs

20. GENERATION OF IMPULSE VOLTAGE
Why impulse voltage
To study the effect of transient overvoltages generated by lightning or swiching operations on the system
I. Standard Definition of Lightning Surges
T1 front time 1.2 s
T2 time to half-value 50 s
Surge defined T1/T2 = 1.2 /50 s
Tolerances : (IEC60, BS923)
peak value  3%
front time  30%
time to half-value  20%

21. Surge defined as T1 /T2 = 250/2500 s
II. Standard Definition of Switching Surges
Tp time to peak (also known as T1) 250 s
T2 time to half-value 2500 s
TD time above 90% is sometimes specified
Surge defined as T1 /T2 = 250/2500 s
Tolerances : (IEC60, BS923)
peak value  3%
front time  20%
Time to half-value 60%

22. Analysis of impulse generators

23. With >>
Parameters of V out (t)
Time to peak
Time to half peak value