Measurement of high_voltage_and_high_currentunit_iv_full_version

SVCE

1

EE 2353HIGH VOLTAGE ENGINEERING

D.ELANGOVAN M.E.,AP / EEESVCE

Lecture# 2

UNIT 4 – Measurements of AC High Voltages

SVCE

2

Unit 4 Measurements

MEASUREMENT OF HIGH DC VOLTAGESSeries Resistance micro ammeter Resistance potential divider Generating Voltmeters Sphere Gaps

SVCE

3

Unit 4 Measurements

MEASUREMENT OF HIGH AC VOLTAGES Series impedance voltmeter

Potential Transformers (CVT) Electrostatic Voltmeters Potential Dividers Sphere gaps

SVCE

4

Unit 4 Measurements

MEASUREMENT OF HIGH AC HIGH FREQUENCY & IMPULSE VOLTAGES Potential Dividers (R & C) Peak voltmeters Sphere gaps

SVCE

5

Unit 4 MEASUREMENT OF HIGH DC VOLTAGES

1.Series Resistance micro ammeter

Circuit diagram:

SVCE

6



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

SVCE

7



operationR should be highHigh DC voltage is appliedVoltage drop across the resistanceThe current flowing thro’ R is measured in uA

SVCE

8



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%

SVCE

9



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

SVCE

10



DrawbacksMore power dissipationTemperature effects

SVCE

11


2.Resistance potential divider

NeedTo avoid high loading of R

Another resistor is added

SVCE

12



Circuit diagram

SVCE

13



ConstructionR1 R2 connected in seriesVoltage is measured across R2

SVCE

14



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

SVCE

15



NotePower Dissipation in resistor R1Need for coolingSeries connection of resistors

SVCE

16


3.Generating VoltmeterPrincipleVariable electrostatic generator which generates a current proportional to the applied external voltage

SVCE

17


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

SVCE

18


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

SVCE

19


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

SVCE

20

Unit 4 Measurements

MEASUREMENT OF HIGH AC VOLTAGES Series impedance voltmeter Potential DividersElectrostatic Voltmeters Potential Transformers (CVT)Sphere gaps

SVCE

21

Unit 4 MEASUREMENT OF HIGH AC VOLTAGES

Potential Dividers 1.R Dividers

Power loss Temperature Effects

2.Series impedance

3.C dividers

SVCE

22


C dividers

Series capacitance DividersApply the voltageDrop Across CCharging Current s measured using Micro ammeter

SVCE

23


C dividers capacitance potential Dividers

SVCE

24


C dividers capacitance potential Dividers

Need to measure

1.Withstand-RMS voltage

2.Breakdown-Peak voltage

RMS = Peak/√2 for only sine wave

SVCE

25


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

SVCE

26


RMS value measurement

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

2.Electrostatic voltmeter

SVCE

27



1.Series capacitor peak voltmeter:

Principle

Measure of charging current

Ic=VὡC

Construction

Stand. Capacitor Diode & Meter

SVCE

28



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

SVCE

29




Current leads the voltage

SVCE

30




DrawbacksVoltage wave shape is not pure

Sinusoidal. Contains oscillationsCurrent may not be uniformCalibration is wrong

SVCE

31


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

SVCE

32


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

SVCE

33


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

Discharge ErrorRest Charge Error

SVCE

34



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

SVCE

35


Electrostatic Voltmeter

Principle

Force between the parallel plate electrodes is given by

F=1/2 €V2A/D2

SVCE

36




SVCE

37



ConstructionHV Electrode insulated

from earthLV electrode – central point is movableLight beamScale

SVCE

38


Electrostatic VoltmeterOperationHigh voltage is applied

Due to electrostatic forces deflection of rotating Element

Light focused on the mirrorGets reflected & measured

SVCE

39



DrawbackFor a Constant distance d, the sensitivity is small

AdvantageNo source loadingContinuous Reading also possible

Measurement of high_voltage_and_high_currentunit_iv_full_version

Engineering

Transcript of Measurement of high_voltage_and_high_currentunit_iv_full_version