High voltage measurement

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

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

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

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Unit 4 Measurements
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
1.Series Resistance micro ammeter
Circuit diagram:

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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

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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

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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%

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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

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

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

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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
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
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
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
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
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
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
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
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
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
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
C dividers capacitance potential Dividers

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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

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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

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

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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

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

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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

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Unit 4 MEASUREMENT OF HIGH AC VOLTAGES
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
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
Electrostatic Voltmeter
Principle
Force between the parallel plate electrodes is given
by
F=1/2 €V2
A/D2

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

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