EE 2353
HIGH VOLTAGE ENGINEERING
SVCE
D.ELANGOVAN M.E.,
AP / EEE
SVCE
Lecture# 2
UNIT 4 – Measurements of AC High Voltages
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Unit 4 Measurements
SVCE
MEASUREMENT OF HIGH DC VOLTAGES
Series Resistance micro ammeter
 Resistance potential divider
 Generating Voltmeters
 Sphere Gaps
2
Unit 4 Measurements
SVCE
MEASUREMENT OF HIGH AC VOLTAGES
 Series impedance voltmeter
 Potential Transformers (CVT)
 Electrostatic Voltmeters
 Potential Dividers
 Sphere gaps
3
Unit 4 Measurements
SVCE
MEASUREMENT OF HIGH AC HIGH FREQUENCY &
IMPULSE VOLTAGES
 Potential Dividers (R & C)
 Peak voltmeters
 Sphere gaps
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
1.Series Resistance micro ammeter
Circuit diagram:
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
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%
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
1.Series Resistance micro ammeter
Need for protective device
If R fails, heavy current will flow thro’ uA
To divert protective device is used
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
1.Series Resistance micro ammeter
Drawbacks
More power dissipation
Temperature effects
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
2.Resistance potential divider
Need
To avoid high loading of R
Another resistor is added
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
2.Resistance potential divider
Circuit diagram
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
2.Resistance potential divider
Construction
R1 R2 connected in series
Voltage is measured across R2
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
2.Resistance potential divider
Note
Power Dissipation in resistor R1
Need for cooling
Series connection of resistors
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
3.Generating Voltmeter
Principle
Variable electrostatic generator which generates a
current proportional to the applied external voltage
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
SVCE
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
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Unit 4 Measurements
SVCE
MEASUREMENT OF HIGH AC VOLTAGES
 Series impedance voltmeter
 Potential Dividers
Electrostatic Voltmeters
 Potential Transformers (CVT)
Sphere gaps
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Potential Dividers
1.R Dividers
 Power loss
 Temperature Effects
2.Series impedance
3.C dividers
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
C dividers
Series capacitance Dividers
 Apply the voltage
 Drop Across C
 Charging Current s measured using Micro
ammeter
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
C dividers
capacitance potential Dividers
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
C dividers
capacitance potential Dividers
Need to measure
1.Withstand-RMS voltage
2.Breakdown-Peak voltage
RMS = Peak/√2 for only sine wave
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
RMS value measurement
1.Peak voltmeter with potential voltmeter(Davies ,
Bowdler ,stand ring circuit)
2.Electrostatic voltmeter
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Peak value measurement
1.Series capacitor peak voltmeter:
Principle
Measure of charging current
Ic=VὡC
Construction
Stand. Capacitor Diode & Meter
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
1.Series capacitor peak voltmeter:
Operation
 Apply voltage
 Charging current is rectified by
D1 and measured
 Other half cycle no conduction
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Peak value measurement
1.Series capacitor peak voltmeter:
Current leads the voltage
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Peak voltmeter with potential voltmeter(Davis ,
Bowdler ,stand ring circuit)
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
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
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Peak voltmeter with potential voltmeter(Davis ,
Bowdler ,stand ring circuit)
 Discharge Error
 Rest Charge Error
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
RMS value measurement
1.Peak voltmeter with potential voltmeter(Davis ,
Bowdler ,stand ring circuit)
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Electrostatic Voltmeter
Principle
Force between the parallel plate electrodes is given
by
F=1/2 €V2A/D2
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
RMS value measurement
Electrostatic Voltmeter
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Electrostatic Voltmeter
Construction
 HV Electrode insulated
from earth
 LV electrode – central point
is
movable
 Light beam
 Scale
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Electrostatic Voltmeter
Operation
 High voltage is applied
 Due to electrostatic forces
 deflection of rotating
Element
 Light focused on the mirror
 Gets reflected & measured
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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
SVCE
Electrostatic Voltmeter
Drawback
 For a Constant distance d, the sensitivity is small
Advantage
 No source loading
 Continuous Reading also possible
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