svce 1 ee 2353 high voltage engineering d.elangovan m.e., ap / eee svce lecture# 2 unit 4 –...
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SVCE
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EE 2353HIGH 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
operationR 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
ConstructionR1 R2 connected in series
Voltage is measured across R2
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Unit 4 MEASUREMENT OF HIGH DC VOLTAGES
2.Resistance potential divider
OperationDC 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
NotePower 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 VoltmeterTime 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 VoltmeterConnect 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 VoltmeterThe 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 voltageCharging 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 €V2A/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
OperationHigh voltage is applied
Due to electrostatic forces deflection of rotating
Element
Light focused on the mirrorGets 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
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