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UNIT 4 – Measurements of AC High Voltages. HIGH VOLTAGE ENGINEERING. Unit 4 Measurements. MEASUREMENT OF HIGH DC VOLTAGES Series Resistance micro ammeter Resistance potential divider Generating Voltmeters Sphere Gaps. 2. Unit 4 Measurements. MEASUREMENT OF HIGH AC VOLTAGES

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## HIGH VOLTAGE ENGINEERING

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**UNIT 4 – Measurements of AC High Voltages**HIGH VOLTAGE ENGINEERING**Unit 4 Measurements**MEASUREMENT OF HIGH DC VOLTAGES Series Resistance micro ammeter Resistance potential divider Generating Voltmeters Sphere Gaps 2**Unit 4 Measurements**MEASUREMENT OF HIGH AC VOLTAGES Series impedance voltmeter Potential Transformers (CVT) Electrostatic Voltmeters Potential Dividers Sphere gaps 3**Unit 4 Measurements**MEASUREMENT OF HIGH AC HIGH FREQUENCY & IMPULSE VOLTAGES Potential Dividers (R & C) Peak voltmeters Sphere gaps 4**Unit 4 MEASUREMENT OF HIGH DC VOLTAGES**1.Series Resistance micro ammeter Circuit diagram: 5**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 6**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 7**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% 8**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 9**Unit 4 MEASUREMENT OF HIGH DC VOLTAGES**1.Series Resistance micro ammeter Drawbacks More power dissipation Temperature effects 10**Unit 4 MEASUREMENT OF HIGH DC VOLTAGES**2.Resistance potential divider Need To avoid high loading of R Another resistor is added 11**Unit 4 MEASUREMENT OF HIGH DC VOLTAGES**2.Resistance potential divider Circuit diagram 12**Unit 4 MEASUREMENT OF HIGH DC VOLTAGES**2.Resistance potential divider Construction R1 R2 connected in series Voltage is measured across R2 13**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 14**Unit 4 MEASUREMENT OF HIGH DC VOLTAGES**2.Resistance potential divider Note Power Dissipation in resistor R1 Need for cooling Series connection of resistors 15**Unit 4 MEASUREMENT OF HIGH DC VOLTAGES**3.Generating Voltmeter Principle Variable electrostatic generator which generates a current proportional to the applied external voltage 16**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 17**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 18**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 19**Unit 4 Measurements**MEASUREMENT OF HIGH AC VOLTAGES Series impedance voltmeter Potential Dividers Electrostatic Voltmeters Potential Transformers (CVT) Sphere gaps 20**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**Potential Dividers 1.R Dividers Power loss Temperature Effects 2.Series impedance 3.C dividers 21**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 22**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**C dividers capacitance potential Dividers 23**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 24**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 25**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**RMS value measurement 1.Peak voltmeter with potential voltmeter(Davies , Bowdler ,stand ring circuit) 2.Electrostatic voltmeter 26**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 27**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 28**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**Peak value measurement 1.Series capacitor peak voltmeter: Current leads the voltage 29**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 30**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit) 31**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 32**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit) Discharge Error Rest Charge Error 33**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**RMS value measurement 1.Peak voltmeter with potential voltmeter(Davis , Bowdler ,stand ring circuit) 34**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**Electrostatic Voltmeter Principle Force between the parallel plate electrodes is given by F=1/2 €V2A/D2 35**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**RMS value measurement Electrostatic Voltmeter 36**Unit 4 MEASUREMENT OF HIGH AC VOLTAGES**Electrostatic Voltmeter Construction HV Electrode insulated from earth LV electrode – central point is movable Light beam Scale 37**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 38**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 39

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