ee 2353 high voltage engineering

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EE 2353HIGH VOLTAGE ENGINEERING

D.ELANGOVAN M.E.,AP / EEESVCE

Lecture# 2

UNIT 4 – Measurements of AC High Voltages

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Unit 4 Measurements

MEASUREMENT OF HIGH DC VOLTAGESSeries 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 highHigh DC voltage is appliedVoltage drop across the resistanceThe current flowing thro’ R is measured in uA

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Note:Voltage V=IRDrop in Ammeter is negligibleR should be chosen such that 1 to 10 uA is allowed for full scale deflection500 kv can be measuredAccuracy : 0.2%

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Need for protective deviceIf R fails, heavy current will flow thro’ uATo divert protective device is used

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DrawbacksMore power dissipationTemperature effects

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2.Resistance potential divider

NeedTo avoid high loading of R

Another resistor is added

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Circuit diagram

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ConstructionR1 R2 connected in seriesVoltage is measured across R2

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OperationDC voltages are measured using resistance voltage dividerR2 <<< R1High DC voltage applied.Drop across R1Measure the voltage directly across R2

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NotePower Dissipation in resistor R1Need for coolingSeries connection of resistors

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3.Generating VoltmeterPrincipleVariable 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 HL1,L2,L3 are earthed electrodeThe L1 has vanes and its rotated at constant speedThe rotor vanes of L1 periodically cover and uncover the static sensing electrode L3Capacitance 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 capacitanceThe 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 DividersElectrostatic 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 DividersApply the voltageDrop Across CCharging 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 , Bowdler ,stand ring circuit)

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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OperationApply voltageCharging current is rectified by D1 and measuredOther half cycle no conduction

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Current leads the voltage

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DrawbacksVoltage wave shape is not pure

Sinusoidal. Contains oscillationsCurrent may not be uniformCalibration is wrong

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Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit)

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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 C2Multiplying Divider ratio we can get the voltage to be measured

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Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit)

Discharge ErrorRest Charge Error

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1.Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit)

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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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ConstructionHV Electrode insulated

from earthLV electrode – central point is movableLight beamScale

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Electrostatic VoltmeterOperationHigh voltage is applied

Due to electrostatic forces deflection of rotating Element

Light focused on the mirrorGets reflected & measured

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DrawbackFor a Constant distance d, the sensitivity is small

AdvantageNo source loadingContinuous Reading also possible

ee 2353 high voltage engineering

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