1. EE 2353 HIGH VOLTAGE ENGINEERING
D.ELANGOVAN M.E.,
AP / EEE
SVCE
Lecture# 2
UNIT 4 – Measurements of AC High Voltages

2. Unit 4 Measurements MEASUREMENT OF HIGH DC VOLTAGES
Series Resistance micro ammeter
Resistance potential divider
Generating Voltmeters
Sphere Gaps 2

3. Unit 4 Measurements MEASUREMENT OF HIGH AC VOLTAGES
Series impedance voltmeter
Potential Transformers (CVT)
Electrostatic Voltmeters
Potential Dividers
Sphere gaps 3

4. Unit 4 Measurements
MEASUREMENT OF HIGH AC HIGH FREQUENCY & IMPULSE VOLTAGES
Potential Dividers (R & C)
Peak voltmeters
Sphere gaps 4

5. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
1.Series Resistance micro ammeter
Circuit diagram: 5

6. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
1.Series Resistance micro ammeter
Construction:
A large value of resistance (few hundreds of mega ohms) is connected in series with uA
Protective device (Zenor diode, neon glow tube)connected across the uA 6

7. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
1.Series Resistance micro ammeter
operation
R should be high
High DC voltage is applied
Voltage drop across the resistance
The current flowing thro’ R is measured in uA 7

8. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
1.Series Resistance micro ammeter
Note:
Voltage V=IR
Drop in Ammeter is negligible
R should be chosen such that 1 to 10 uA is allowed for full scale deflection
500 kv can be measured
Accuracy : 0.2% 8

9. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
1.Series Resistance micro ammeter
Need for protective device
If R fails, heavy current will flow thro’ uA
To divert protective device is used 9

10. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
1.Series Resistance micro ammeter
Drawbacks
More power dissipation
Temperature effects 10

11. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
2.Resistance potential divider
Need
To avoid high loading of R
Another resistor is added 11

12. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
2.Resistance potential divider
Circuit diagram 12

13. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
2.Resistance potential divider
Construction
R1 R2 connected in series
Voltage is measured across R2 13

14. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
2.Resistance potential divider
Operation
DC voltages are measured using resistance voltage divider
R2 <<< R1
High DC voltage applied.
Drop across R1
Measure the voltage directly across R2 14

15. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
2.Resistance potential divider
Note
Power Dissipation in resistor R1
Need for cooling
Series connection of resistors 15

16. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
3.Generating Voltmeter
Principle
Variable electrostatic generator which generates a current proportional to the applied external voltage 16

17. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
3.Generating Voltmeter
Time variant capacitance system can be developed between the high voltage electrode and earthed electrode, then current flowing to earth electrode will be a measure of the voltage 17

18. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
3.Generating Voltmeter
Connect High voltage source to disc electrode H
L1,L2,L3 are earthed electrode
The L1 has vanes and its rotated at constant speed
The rotor vanes of L1 periodically cover and uncover the static sensing electrode L3
Capacitance between H & L3 changes periodically 18

19. Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
3.Generating Voltmeter
The shape and No of vanes of L1,L2 are designed that they produce sinusoidal variation in the capacitance
The generated ac current is rectified and read by a moving coil instrument 19

20. Unit 4 Measurements MEASUREMENT OF HIGH AC VOLTAGES
Series impedance voltmeter
Potential Dividers
Electrostatic Voltmeters
Potential Transformers (CVT)
Sphere gaps 20

21. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Potential Dividers
1.R Dividers
Power loss
Temperature Effects
2.Series impedance
3.C dividers 21

22. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
C dividers
Series capacitance Dividers
Apply the voltage
Drop Across C
Charging Current s measured using Micro ammeter 22

23. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
C dividers capacitance potential Dividers 23

24. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
C dividers capacitance potential Dividers
Need to measure
1.Withstand-RMS voltage
2.Breakdown-Peak voltage
RMS = Peak/√2 for only sine wave 24

25. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Peak value measurement
1.Chubb-Frotscue method ( Series capacitor peak voltmeter)
2.Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit)
3.Digital peak voltmeter
4.Sphere gap 25

26. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
RMS value measurement
1.Peak voltmeter with potential voltmeter(Davies , Bowdler ,stand ring circuit)
2.Electrostatic voltmeter 26

27. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Peak value measurement
1.Series capacitor peak voltmeter:
Principle
Measure of charging current
Ic=VὡC
Construction
Stand. Capacitor Diode & Meter 27

28. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
1.Series capacitor peak voltmeter:
Operation
Apply voltage
Charging current is rectified by
D1 and measured
Other half cycle no conduction 28

29. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Peak value measurement
1.Series capacitor peak voltmeter:
Current leads the voltage 29

30. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Peak value measurement
1.Series capacitor peak voltmeter:
Drawbacks
Voltage wave shape is not pure
Sinusoidal. Contains oscillations
Current may not be uniform
Calibration is wrong 30

31. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit) 31

32. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit)
The voltage to be measured is applied across C1&C2 divider.
The voltage appears on C2 is rectified into DC and charge the Cs.
Meter read the peak value of C2
Multiplying Divider ratio we can get the voltage to be measured 32

33. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit)
Discharge Error
Rest Charge Error 33

34. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
RMS value measurement
1.Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit) 34

35. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Electrostatic Voltmeter
Principle
Force between the parallel plate electrodes is given by
F=1/2 €V2A/D2 35

36. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
RMS value measurement
Electrostatic Voltmeter 36

37. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Electrostatic Voltmeter
Construction
HV Electrode insulated
from earth
LV electrode – central point is movable
Light beam
Scale 37

38. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Electrostatic Voltmeter
Operation
High voltage is applied
Due to electrostatic forces
deflection of rotating
Element
Light focused on the mirror
Gets reflected & measured 38

39. Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
Electrostatic Voltmeter
Drawback
For a Constant distance d, the sensitivity is small
Advantage
No source loading
Continuous Reading also possible 39