svce 1 ee 2353 high voltage engineering d.elangovan m.e., ap / eee svce lecture# 2 unit 4 –...

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EE 2353HIGH VOLTAGE ENGINEERING

D.ELANGOVAN M.E.,AP / EEE

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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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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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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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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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Need for protective device

If R fails, heavy current will flow thro’ uA

To divert protective device is used

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Drawbacks

More power dissipation

Temperature effects

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2.Resistance potential divider

Need

To avoid high loading of R

Another resistor is added

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Circuit diagram

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ConstructionR1 R2 connected in series

Voltage is measured across R2

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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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NotePower Dissipation in resistor R1

Need for cooling

Series connection of resistors

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3.Generating Voltmeter

Principle

Variable electrostatic generator which generates a

current proportional to the applied external voltage

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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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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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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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C dividers

Series capacitance Dividers

Apply the voltage

Drop Across C

Charging Current s measured using Micro

ammeter

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C dividers capacitance potential Dividers

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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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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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RMS value measurement

1.Peak voltmeter with potential voltmeter(Davies ,


2.Electrostatic voltmeter

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1.Series capacitor peak voltmeter:

Principle

Measure of charging current

Ic=VὡC

Construction

Stand. Capacitor Diode & Meter

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Operation

Apply voltageCharging current is rectified by

D1 and measured

Other half cycle no conduction

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Current leads the voltage

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Drawbacks

Voltage wave shape is not pure

Sinusoidal. Contains oscillations

Current may not be uniform

Calibration is wrong

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Peak voltmeter with potential voltmeter(Davis ,


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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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Discharge Error

Rest Charge Error

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1.Peak voltmeter with potential voltmeter(Davis ,


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Electrostatic Voltmeter

Principle

Force between the parallel plate electrodes is given

by

F=1/2 €V2A/D2

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Construction

HV Electrode insulated

from earth

LV electrode – central point is

movable

Light beam

Scale

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OperationHigh voltage is applied

Due to electrostatic forces deflection of rotating

Element

Light focused on the mirrorGets reflected & measured

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Drawback

For a Constant distance d, the sensitivity is small

Advantage

No source loading

Continuous Reading also possible

svce 1 ee 2353 high voltage engineering d.elangovan m.e., ap / eee svce lecture# 2 unit 4 –...

Documents

high high dc voltage

ua slide

high loading of r

r2 slide

series voltage

resistance voltage divider

high voltage engineering

large value of resistance