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# 10EE73: HIGH VOLTAGE ENGINEERING: chapter 5:Presentation part b] chapter 5

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Dear Students/Faculties,
I am uploading detailed notes on HIGH VOLTAGE ENGINEERING_10EE73 for meeting the requirement of VTU, Belagavi syllabus.
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Vineeth Kumar P K
Assistant Professor
Dept. of E&E
SDM Institute of Technology, Ujire, D.K, Karnataka, India

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### 10EE73: HIGH VOLTAGE ENGINEERING: chapter 5:Presentation part b] chapter 5

1. 1. [PART-B] Unit 5 GENERATION OF IMPULSE VOLTAGE AND CURRENT Prepared by Vineeth Nambiar Assistant professor Dept of EEE SDMIT, Ujire 7/21/2017 1Dept. of EEE, SDMIT, Ujire
2. 2. Syllabus Unit 5, GENERATION OF IMPULSE VOLTAGE AND CURRENT: Introduction to standard lightning and switching impulse voltages. Analysis of single stage impulse generator-expression for Output impulse voltage. Multistage impulse generator working of Marx impulse. Rating of impulse generator. Components of multistage impulse generator. Triggering of impulse generator by three electrode gap arrangement. Trigatron gap and oscillograph time sweep circuits. Generation of switching impulse voltage. Generation of high impulse current. 6 Hours 7/21/2017 2Dept. of EEE, SDMIT, Ujire
3. 3. What is impulse voltage?? • Impulse voltage is a unidirectional voltage. • No appreciable oscillation. • It rises rapidly to a maximum value and falls more or less rapidly to zero. • A unidirectional voltage that rapidly rises to a peak value and then drops to zero more or less rapidly. Also known as pulse voltage. 7/21/2017 3Dept. of EEE, SDMIT, Ujire
4. 4. Why Impulse Voltage? • To study the effect of transient overvoltages generated by lightning or swiching operations on the system. 7/21/2017 4Dept. of EEE, SDMIT, Ujire
5. 5. Representation of Impulse Wave t0t1 t2 t3 10 Wave front= 1.5*(t2-t1) Wave tail= t3-t0 7/21/2017 5Dept. of EEE, SDMIT, Ujire t2 is the time taken to reach 90% of peak value t1 is the time taken to reach 10% of peak value
6. 6. Representation of Impulse Wave Contd…… Ref. the text book by C.L WADHWA Page number 101 7/21/2017 6Dept. of EEE, SDMIT, Ujire
7. 7. • Maximum value is called peak value of impulse voltage. • If an impulse voltage develops without causing flashover or puncture is called full impulse voltage. • Due to flash over or puncture sudden collapse of impulse voltage will occur and it is called as chopped impulse voltage. What is impulse voltage?? Contd… CL WADHWA-Page 102 7/21/2017 7Dept. of EEE, SDMIT, Ujire
8. 8. Wave front & Wave tail • A full impulse voltage consists of both wave front and wave tail. • Wave front- Time taken by the wave to reach its maximum value starting from zero value. - difficulty to identify the wave front - wave front is considered as 1.5 times (t2-t1) - where t2 is the time taken to reach 90% of peak value -t1 is the time taken to reach 10% of peak value - (t2-t1) is about 80% of wave front time 7/21/2017 8Dept. of EEE, SDMIT, Ujire
9. 9. • Wave tail- Time measured between the nominal starting point t0 and the point on the wave tail where the voltage is 50% of peak value. - wave tail time (t3-t0) • Part of a signal-wave envelope (in time or distance) between the steady-state value (or crest) and the end of the envelope. Wave front & Wave tail 7/21/2017 9Dept. of EEE, SDMIT, Ujire
10. 10. • Three standards 1. BSS & ISS standard 2. American Standard Association 3. IEC standard Standards for impulse voltage BSS- Basic Safety Standard 7/21/2017 10Dept. of EEE, SDMIT, Ujire
11. 11. Standards for impulse voltage • BSS and ISS standard - standard wave shape specified (1/50) microseconds wave. - ie a wave front of 1 mico second and wave tail of 50 mico seconds. -Tolerance is not more than +50% or -50% on the duration of the wave front . - 20% on the time to half value on the wave tail is allowed. - Complete specification of the wave is 100kV, (1/50) micoseconds , where 100kV is the peak value of the wave 7/21/2017 11Dept. of EEE, SDMIT, Ujire
12. 12. • American Standard Association -Wave shape recommended by American standard is 1.5/40 microseconds. -permissible variation 0.5 microseconds on the wave front and +10 or -10 microseconds for wave tail. -The wave front time is taken as 1.67 times the time taken by the wave to rise from 30% to 90% of its peak value . - Wave tail time is computed same as that of BSS and ISS standard Standards for impulse voltage 7/21/2017 12Dept. of EEE, SDMIT, Ujire
13. 13. • IEC (International Electro technical Commission) -The standard impulse wave shape belonging to 1.2/50μs. -should withstand higher voltage (above 220kV). Standards for impulse voltage 7/21/2017 13Dept. of EEE, SDMIT, Ujire
14. 14. Important Definitions Related to Impulse Voltage (Types of impulse Voltage) 1.Chopped wave -If an impulse voltage is applied to a piece of insulation a flash over or puncture occur and sudden collapse of impulse voltage is called chopped wave. -if the chopping takes place front part of the wave is called front chopped wave 2.Impulse puncture voltage -Peak value of impulse voltage which cause the puncture of the material. 7/21/2017 14Dept. of EEE, SDMIT, Ujire
15. 15. 3. Impulse flash over voltage -When impulse voltage applied to the insulating material flash over may or may not occur. -If the flashover occur more than 50% of number of applications , then it is called as impulse flash over voltage. -Impulse flash over voltage depends polarity, duration of wave front & wave tail and nature of material. Important Definitions Related to Impulse Voltage Contd… 7/21/2017 15Dept. of EEE, SDMIT, Ujire
16. 16. IMPULSE GENERATOR 7/21/2017 16Dept. of EEE, SDMIT, Ujire
17. 17. What is impulse generator? • An impulse generator is an electrical apparatus which produces very short high- voltage or high-current surges. • It can be classified into two types a) impulse voltage generators & b) impulse current generators. 7/21/2017 17Dept. of EEE, SDMIT, Ujire
18. 18. Basic impulse generator 7/21/2017 18Dept. of EEE, SDMIT, Ujire
19. 19. Why impulse Generator? • Impulse generator produce high impulse voltage. • High impulse voltages are used to test the strength of electric power equipment against lightning and switching surges. • steep-front impulse voltages are sometimes used in nuclear physics experiments. • High impulse currents are needed for tests on equipment such as lightning arresters. • Fuse testing. • Technical applications such as lasers, thermonuclear fusion, and plasma devices. 7/21/2017 19Dept. of EEE, SDMIT, Ujire
20. 20. • An impulse generator essentially consists of a capacitor which is charged to the required voltage and discharged through a circuit. • The circuit parameters can be adjusted to give an impulse voltage of the desired shape. • Cs is charged from a dc source until the spark gap G breaks down. • The voltage is then impressed upon the object under test of capacitance Cb. • The wave shaping resistors Rd and Re control the front and tail of the impulse voltage available across Cb respectively. • Overall the wave shape is determined by the values of the generator capacitance (Cs) and the load capacitance(Cb), and the wave control resistances Rd and Re. Basic impulse generator 7/21/2017 20Dept. of EEE, SDMIT, Ujire
21. 21. • The output voltage waveform can be defined by • where, v(t) instantaneous output voltage, Vo DC charging voltage, , roots of the characteristics equation, which depends on the parameters of the generator. where Basic impulse generator 7/21/2017 21Dept. of EEE, SDMIT, Ujire
22. 22. Classification of Impulse Voltage Generator 1. Single Stage Impulse Generator 2.Multi Stage Impulse Generator (Marx generator) 7/21/2017 22Dept. of EEE, SDMIT, Ujire
23. 23. Single stage Impulse Generator Circuit REF. C. L. WADHWA –PAGE NO. 103 External elements, waveform control Wave duration control 7/21/2017 23Dept. of EEE, SDMIT, Ujire
24. 24. 7/21/2017 Dept. of EEE, SDMIT, Ujire 24 Single stage Impulse Generator Circuit
25. 25. • The spark gap act as voltage limiting & voltage sensing switch. • The apparatus which produces the required voltages is the impulse generator. • In high voltage engineering, an impulse voltage is normally a unidirectional voltage which rises quickly without appreciable oscillations, to a peak value and then falls less rapidly to zero. Single stage Impulse Generator Circuit 7/21/2017 25Dept. of EEE, SDMIT, Ujire
26. 26. Importance of each elements in impulse generator circuit 1. Capacitor (C1)- • C1 is the capacitance of generator charged from a dc source to a suitable voltage. • It will discharge through the space gap. • If the generator is single stage C1 is enough. • In the case of multistage impulse generator group of capacitor connected in parallel and discharged in series. 7/21/2017 26Dept. of EEE, SDMIT, Ujire
27. 27. 2. Inductor(L1) -inductance of the generator -The leads of inductor is connecting to the generator - Small value 3. Resistor (R1) -Damping purpose -Output voltage / Output waveform control Importance of each elements in impulse generator circuit contd……… 7/21/2017 27Dept. of EEE, SDMIT, Ujire
28. 28. 4.L3 and R3 -external elements -connected generator for the waveform control/shape 5.R2 and R4 -Control the waveform duration -R4 serve as a potential divider 6.C2 and C4 -Capacitance to the earth of high voltage components and leads 7.C4 -Includes the capacitance of the test object -load capacitance -Hold the voltage to produce required value of wave shape Importance of each elements in impulse generator circuit contd……… 7/21/2017 28Dept. of EEE, SDMIT, Ujire
29. 29. 8. L4 -Inductance of test object -Influence the waveform 9.Grounding -One terminal of impulse generator is solidly grounded -The polarity of output voltage can be changed by changing the polarity of dc charging voltage Importance of each elements in impulse generator circuit contd……… 7/21/2017 29Dept. of EEE, SDMIT, Ujire
30. 30. Performance parameters of single stage impulse generator 1. Efficiency 2.Impulse energy transformed during a discharge is given by 3.The minimum value of generator capacitance is given by 7/21/2017 30Dept. of EEE, SDMIT, Ujire
31. 31. Equivalent circuits of single stage Impulse Generator contd…. REF. C L WADHWA PAGE NO 104 7/21/2017 31Dept. of EEE, SDMIT, Ujire
32. 32. Equivalent circuits of single stage Impulse Generator • Evaluation & analysis is easy as compared to main circuit. Do refer text book of M S Naidu & V Kamaraju – page no 172 7/21/2017 32Dept. of EEE, SDMIT, Ujire
33. 33. 7/21/2017 Dept. of EEE, SDMIT, Ujire 33 Expression for output impulse voltage for single stage impulse generator Refer the text book MS Naidu and V Kamaraju Page number 172 to 173 Assignment
34. 34. Expression for output impulse voltage for single stage impulse generator Assignment Refer the text book MS Naidu and V Kamaraju Page number 172 to 173 7/21/2017 34Dept. of EEE, SDMIT, Ujire
35. 35. Drawbacks of single stage impulse generator • Physical size of the circuit elements are very large. • Large size of sphere. • High dc charging voltage is required. • Suppression of corona is difficult. • Switching of very high voltage with the spark gap is difficult. 7/21/2017 35Dept. of EEE, SDMIT, Ujire
36. 36. Multistage Impulse Generator Introduction • To obtain higher and higher impulse voltage. • In 1923 E. Marx suggested a multiplier circuit which is commonly used to obtain impulse voltage with as high a peak value as possible for a given charging dc voltage. • Depending upon the charging voltage available and output voltage required “the number of identical impulse capacitors are charged in parallel and then discharged in series”. • Obtain total charging voltage multiplied with number of stages. 7/21/2017 36Dept. of EEE, SDMIT, Ujire
37. 37. Why Multistage Impulse Generator??????? • A single capacitor C1 is may be used for voltages up to 200 kV. Beyond this voltage, a single capacitor & charging unit may be too costly & the size becomes very large. 7/21/2017 Dept. of EEE, SDMIT, Ujire 37 Multistage Impulse Generator
38. 38. Multistage Impulse Generator Circuit 7/21/2017 38Dept. of EEE, SDMIT, Ujire Schematic Diagram of Multistage Impulse Generator
39. 39. Multistage Impulse Generator Circuit 7/21/2017 39Dept. of EEE, SDMIT, Ujire Schematic Diagram of Multistage Impulse Generator (modified)
40. 40. • Rs is a charging resistance to limit the charging current. • The generator capacitance C is chosen such that the product of CRs is about 10s to 1 min. • The gap spacing is chosen such that the breakdown voltage of the gap G is greater than the charging voltage V. • All the capacitance are charged to the voltage V in about 1 minute. • Charging time constant=CRs (in seconds) • Discharging time constant = CR1/n (in micro seconds) , where n is the number of stages. 7/21/2017 Dept. of EEE, SDMIT, Ujire 40 Multistage Impulse Generator Circuit
41. 41. Multistage Impulse Generator 7/21/2017 41Dept. of EEE, SDMIT, Ujire A 16 stage Multistage Impulse Generator having a stage capacitance of 0.280μF And maximum charging voltage 300kV . The height of the generator will be about 15m. Area = 3.25m x 3.00 m
42. 42. Construction of Multistage Impulse Generator Refer C.L WADHWA- PAGE NO. 117 7/21/2017 42Dept. of EEE, SDMIT, Ujire
43. 43. Construction of Multistage Impulse Generator • Require a dc power supply for charging the impulse capacitance C1 of the generator. • Supply consists of step up transformer and rectifier. • The value of resistor should be constant & never vary with external factors. • Non-inductive wire wound resistors are commonly used. • Resistors which will be used for the construction for multistage impulse generator flexible to replace. • Oil paper insulated capacitor having high rate of discharge are normally employed and reason for reduced size of capacitor. 7/21/2017 43Dept. of EEE, SDMIT, Ujire
44. 44. • The sphere gap adjusted by a remotely controlled motor conjunction with indicator. • Chimney provided with dust free and dry air. • A series protective resistance should be included in this earthing device to avoid too high discharge current. • Charging resistors are fixed at sphere coloumn. • Front and tail resistor fixed to the generator frame. • All the leads and electrodes should dimensioned properly to avoid corona discharge. Construction of Multistage Impulse Generator contd… 7/21/2017 44Dept. of EEE, SDMIT, Ujire
45. 45. Components of a multistage impulse Generator 1.DC Charging set 2.Charging Resistors -Non inductive high value of resistance about 10 to 100k. -Each resistance will be designed to have a maximum voltage between 50 and 100kV. 3.Generator Capacitors and spark gap - Capacitor designed for several charging and discharging operations. -Capacitors will be capable of having 10kA of current. -Spark gaps will be usually spheres or hemispheres of 10 to 25 cm diameter. 7/21/2017 45Dept. of EEE, SDMIT, Ujire A multistage impulse generator requires several components parts for Flexibility & production of the required wave shape.
46. 46. 4. Wave-shaping Resistors and Capacitors -Non inductive wound type -Capable of discharging 1000A current -50 to 100kV max. designed voltage -Load capacitance will be 1 to 10nF 5.Triggering System -Contain trigger spark gap to cause spark breakdown of the gaps. Components of a multistage impulse Generator contd… 7/21/2017 46Dept. of EEE, SDMIT, Ujire
47. 47. 6.Voltage Dividers -Resistor type or damped capacitor type -oscilloscope with recording arrangement are provided for measurement of voltage across test object 7.Gas insulated impulse generator -Above 4MV impulse generator, tall & large space requirement -4.8MW- nearly 30m height N2, compressed gas and SF6 will provide proper insulation. Components of a multistage impulse Generator contd… 7/21/2017 47Dept. of EEE, SDMIT, Ujire
48. 48. Triggering and Synchronization of the impulse Generator Why triggering & synchronization ????? • Control for charging process of impulse generator. • To integrate the measuring devices. • Chopping gap control. • CRO is used for measuring and studying the effect of impulse wave on the performance of the insulation of the equipment. • Impulse waves are of shorter duration. • It is necessary that operation of the generator and the oscillograph should be synchronized accurately. • Time sweep circuit is main part of oscillograph. • The time sweep circuit of the oscillograph should be initiated at the time slightly before the impulse wave reaches the deflecting plates. • The impulse generator drives both sweep and triggering circuits. • The sweep circuit operating first , triggering circuit works after 0.1 to 0.5 microseconds. 7/21/2017 48Dept. of EEE, SDMIT, Ujire
49. 49. Triggering -3 Stages 1. Fix the gap distance between the spheres and increase the stage applied dc voltage till the flashover occurs. 2. Set the gap distance between the spheres large enough, apply a desired voltage across them and then reduce the gap distance till flashover takes place. 3. Fix both, the desired stage voltage and corresponding gap distance within prescribed limits. Then apply the trigger pulse to the trigatron on the first stage. 7/21/2017 49Dept. of EEE, SDMIT, Ujire
50. 50. • Two methods are available (i) Three electrode gap arrangement (ii) Trigatron gap 7/21/2017 Dept. of EEE, SDMIT, Ujire 50 Triggering and Synchronization of the impulse Generator
51. 51. Triggering of impulse generator by three electrode gap arrangement. Circuit for Triggering of the impulse Generator CL WADHWA PAGE NO 119 7/21/2017 51Dept. of EEE, SDMIT, Ujire
52. 52. Triggering of impulse generator by (i) three electrode gap arrangement. • ‘Three electrode gap arrangement ‘ is one of the method for triggering and synchronization of impulse generator. • The spacing between 2 spheres is adjusted so that two series gap are able to withstand charging voltage of impulse generator. • Central sphere is called control sphere. • A high resistance is connected between the outer sphere and its centre point is connected to control sphere. • The voltage between outer sphere is equally divided between two sphere gap. 7/21/2017 52Dept. of EEE, SDMIT, Ujire
53. 53. How to test the dielectric breakdown strength of three sphere gap arrangement? • First impulse generator is to be charged to a voltage which is slightly less than the breakdown voltage of the gap. • Apply an impulse wave of either polarity & peak voltage not less than (1/5) th of charging voltage to the control sphere. • Check whether the dielectric breakdown occurred or not. 7/21/2017 53Dept. of EEE, SDMIT, Ujire
54. 54. Operation of three sphere gap arrangement • Two ‘three sphere gap arrangement’ is included in the synchronization & triggering circuit Thyratron tube 7/21/2017 54Dept. of EEE, SDMIT, Ujire
55. 55. 1.’Three sphere gap arrangement’- • The switch ‘s’ is closed which initiate the sweep circuit of the oscillograph. • The same impulse is applied to the thyratron tube. • The inherent time delay of thyratron ensure sweep circuit operate first before the starting of high impulse wave. • We can able to create further delay by using Capacitance- Resistance (R1C1) circuit. • The tripping impulse is applied through capacitor C2. • During charging period the voltage across thyratron is about +20kV. Operation of three sphere gap arrangement contd… 7/21/2017 55Dept. of EEE, SDMIT, Ujire
56. 56. 2.Trigatron gap • A device, known as "Trigatron", is used to control the flash over at the spark gaps in order to get a desired magnitude of the output voltage repeatedly. • Function- used as ‘First gap of impulse generator’ • "Trigatron", consists essentially of three-electrodes. • three electrodes are • (1)High voltage electrode is a sphere- indication of HV • The (2)Earthed electrode is also a sphere • The spherical configuration gives homogeneous field • (3)Metal rod electrode/ Trigger electrode be the third electrode Operation of three sphere gap arrangement contd… 7/21/2017 56Dept. of EEE, SDMIT, Ujire
57. 57. Diagram for “Trigatron spark gap” 7/21/2017 57Dept. of EEE, SDMIT, Ujire
58. 58. • A small hole is drilled into earth electrode into which metal rod projects (trigger rod). • The annular gap between the rod and the surrounding hemisphere is 1 mm. • A glass tube is fitted over rod electrode. • The potential of metal electrode and earth electrodes are same. • Both are connected through a high resistance. • Tripping pulse or control pulse applied between metal and earth electrodes. • When the tripping pulse is applied, main field is distorted. • Reason for dielectric breakdown. Construction of “Trigatron spark gap” 7/21/2017 58Dept. of EEE, SDMIT, Ujire
59. 59. • Single stage or multi stage impulse generator maintaining a definite “trigatron” distance. Construction of “Trigatron spark gap” go on…. 7/21/2017 59Dept. of EEE, SDMIT, Ujire
60. 60. Tripping circuit of trigatron 7/21/2017 60Dept. of EEE, SDMIT, Ujire
61. 61. • The capacitor C1 is charged through high resistance R1 • Switch S is closed • A pulse is applied to a sweep circuit of the oscillograph through the capacitor C3 • Same time capacitor C2 is charged • Triggering pulse is applied through trigger electrode (metal rod electrode) • The requisite delay in triggering the generator can be provide by R2 and C2 • The residual charge on the C2 can discharged through R2 • Now a days laser is used for tripping the spark gap Operation of Tripping circuit of trigatron 7/21/2017 61Dept. of EEE, SDMIT, Ujire
62. 62. • The trigatron also has a phase shifting circuit associate with the synchronization of initiation time with external Alternating voltage. • Design is to prevent the overcharging of capacitor • An indicating device shows whether the generator is going to fire properly or not Operation of Tripping circuit of trigatron contd… 7/21/2017 62Dept. of EEE, SDMIT, Ujire
63. 63. Generation of switching surges/ switching impulse voltage • Switching surges has an important role in the design of insulation for extra high voltage transmission line (EHV) & power systems. • Switching surge is a short duration transient voltage produced in the system due to sudden opening or closing of switch or circuit breaker. • Switching surges may be produced due to arcing at faulty power systems. • The transient voltage may be oscillatory wave or damped oscillatory wave having frequency of a few hundred Hz to a few kilo Hz. 7/21/2017 63Dept. of EEE, SDMIT, Ujire
64. 64. • Wave front time= 0.1 to 10ms • Wave tail time ~ 1ms • Switching surges contain higher energy than lightning impulse voltage. • Types of circuit produced switching surges Generation of switching surges/ switching impulse voltage Modified impulse generator for long duration wave shapes Power transformer or testing transformer With dc excitation or with tesla coil7/21/2017 64Dept. of EEE, SDMIT, Ujire
65. 65. Circuits for producing switching surge voltage 7/21/2017 65Dept. of EEE, SDMIT, Ujire
66. 66. Impulse Current Generation • A high impulse current generator consists of large number of capacitor connected in parallel to a common discharge path. Ie by using ‘capacitor bank’. • The generation of impulse current waveforms of high magnitude (nearly 100 KA) find applications like - test work -basic research on non-linear resistors -electric arc studies -electric plasma state 7/21/2017 66Dept. of EEE, SDMIT, Ujire
67. 67. Definition of impulse current waveforms • The waveshapes used in testing surge diverters are (4/10 micro seconds-wave front) and (8/20 micro seconds –wave tail). • Tolerance allowed in between +10% and -10%. • Waveshapes are normally rectangular shape. 7/21/2017 67Dept. of EEE, SDMIT, Ujire
68. 68. Circuit for Impulse Current Generation 7/21/2017 Dept. of EEE, SDMIT, Ujire 68 Arrangement of capacitors in Impulse Current generation circuit.
69. 69. Types of Impulse current waveforms 7/21/2017 Dept. of EEE, SDMIT, Ujire 69
70. 70. Circuit producing impulse current wave Refer MS NAIDU & V Kamaraju Page 188 & fig.6.217/21/2017 70Dept. of EEE, SDMIT, Ujire
71. 71. Circuit producing impulse current wave • Number of capacitors connected in parallel & discharged in parallel in the circuit. • In order to minimize the value of inductance capacitance are subdivided into smaller units. Components -DC charging unit giving variable voltage to capacitor bank. -additional air core inductor having high current value. -oscillograph- measurement purpose. -triggering units & spark gap. 7/21/2017 71Dept. of EEE, SDMIT, Ujire
72. 72. Generation of Rectangular Current Pulses • The generation of rectangular current pulse can be done by ‘discharging a pulse network or cable previously charged’ • To produce a rectangular pulse a coaxial cable of surge impedance Z0 is used. 7/21/2017 72Dept. of EEE, SDMIT, Ujire
73. 73. THANK YOU 7/21/2017 73Dept. of EEE, SDMIT, Ujire