GB/T 2900.19-1994 Electrical terminology High voltage test technology and insulation coordination
Some standard content:
National Standard of the People's Republic of China
Electrical terminology
High-voltage test technique and insulation coordination
Electrotechnical terminologyHigh-voltage test technique and insulation coordinationGB/T 2900.19--94
Replaces GB 2900.19-82
This standard refers to and adopts IEC71 "Insulation Coordination", IEC60 "High Voltage Test Technique" and IEC50 "International Electrotechnical Vocabulary (IEV)" of the International Electrotechnical Commission.
1 Subject content and scope of application
This standard specifies the definitions of common terms in the scope of high-voltage test technique and insulation coordination. This standard is applicable to the formulation of standards, the preparation of technical documents, the writing and translation of professional manuals, teaching materials and books. Special terms with too narrow a scope of use may be specified in relevant standards. 2 General terms
2.1 High-voltage techniques High-voltage techniques Relevant technical issues under high voltage, such as high-voltage electric field, high-voltage insulation, overvoltage and insulation coordination, high-voltage test technology, etc. 2.2 High-voltage electric power equipment High-voltage electric power equipment General term for high-voltage equipment used for power generation, transmission and distribution in power systems. Transmission and distribution equipment equipment for electric power transmission and distribution 2.3
General term for power equipment and materials used in power systems for transmission and distribution of electric energy and corresponding control, measurement and protection of power systems.
Nominal voltage of a (three phase) system An appropriate setting value used to nominally or distinguish the phase-to-phase voltage (effective value) of the system. 2.5 Highest voltage of a (three phase) system The highest value of the phase-to-phase voltage (effective value) that appears at any time and at any point in the system under normal operating conditions. Note: It does not include various transient voltages (such as those caused by operation in the system) and various transient voltages that appear under abnormal conditions (such as faults or sudden load shedding). 2.6 Rated voltage for equipment The phase-to-phase voltage (effective value) marked on the equipment and related to certain operating characteristics of the system. Note: For equipment that is not applicable to this definition, it can be specified in relevant professional standards. 2.7 Highest voltage for equipment The highest value of the phase-to-phase voltage (effective value) used to determine the insulation or other characteristics of the equipment. Note: "Other characteristics" here refer to the characteristics related to the maximum voltage of the equipment specified in the relevant equipment standards. 2.8 Insulation configuration terminal Insulation configuration terminal In the insulation structure, any electrode that can apply voltage to the insulation. The insulation configuration terminals are divided into: Phase terminal: In operation, the system relative voltage is applied. Neutral terminal: Represents or is connected to the neutral point of the system (such as the neutral terminal of the transformer, etc.). Guohao Technical Supervision Bureau approved on May 19, 1994 and implemented on January 1, 1995
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Grounding terminal: In operation, it is usually directly grounded (such as transformer housing, circuit breaker base frame tower frame, etc.). 2.9 Insulation configuration In operation, the overall geometric structure of the insulation is composed of the insulator and the insulation configuration terminal. The insulation structure includes all components that affect the dielectric state (insulating and conductive). Various types of insulation structures can be divided into three-phase insulation structure, relative insulation structure, phase insulation structure and longitudinal insulation structure.
2. 10 Voltage stress Any single or group of voltages applied to the terminals of an insulating structure. For two-terminal insulation structures, such as phase-to-ground insulation structures, the voltage is characterized by its peak value (or effective value) and waveform. For three-terminal insulation structures, such as phase-to-phase insulation structures and longitudinal insulation structures, the voltage is a combined voltage, which consists of two phase-to-ground voltages. The voltage is characterized by the peak values (or effective values), waveforms, and the difference between the peak values of the two components. Note: When the peak values of the two components do not coincide, the combined voltage can be fully characterized by the following data: a. At the peak value moment of one component, the instantaneous value of the other component; b. When different from the above situation, the combined voltage peak value and the instantaneous values of each component at the combined voltage peak moment are used. 3 Overvoltage and insulation coordination
3. 1 Overvoltage and its reference value overvoltage and its reference value valueU㎡ represents the highest voltage of the three-phase system, then the relative-to-earth or phase-to-phase voltage of any waveform whose peak value exceeds the highest relative-to-earth voltage peak value (2/3Um) or the highest phase-to-phase voltage peak value (2U) of the system is respectively the relative-to-earth or phase-to-phase overvoltage. When the overvoltage value is expressed in per unit value, the reference values of the relative-to-earth and phase-to-phase overvoltages are 2/3Um and 2U. (expressed in pu) respectively.
3. 2 Per unit of phase-to-earth overvoltage The ratio of the relative-to-earth overvoltage peak value to the relative-to-earth voltage reference value. 3.3 Per unit of phase-to-phase overvoltage The ratio of the phase-to-phase overvoltage peak value to the phase-to-phase voltage reference value. 3. 4 Classification of voltage and overvoltage "Its waveform and duration, voltage and overvoltage are divided into: a. Continuous (power frequency) voltage; b. Temporary overvoltage: c. Transient overvoltage; d. Combined overvoltage.
.continuous(power-frequency)voltage3.5Continuous (power) voltage
Power frequency voltage continuously applied to any two terminals on an insulating structure. 3.6 Temporary overvoltagetemporary overvoltageAn overvoltage that oscillates (at the power frequency or a certain multiple or fraction thereof) for a long time at a given installation point without attenuation or with a weak attenuation.
Transient overvoltagetransient overvaltage3.7
An overvoltage that lasts for a few milliseconds or less, usually with strong damping or non-oscillating. It can be superimposed on a temporary overvoltage. Transient overvoltages include slow-front overvoltage, fast-front overvoltage and steep-front overvoltage. 3.8
Slow-front overvoltageslow-front overvolage;Switching overvoltageA transient overvoltage, usually unipolar and with a peak time between 20μs and 5000us, and a duration of less than 20ms. 3.9. Fast-front overvoltage fast-front overvoltage, lightning overvoltage52
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A transient overvoltage. Usually unipolar, with a wavefront time between 0.1μs and 20μs, and a half-peak time of less than 300μus. 3.10 Very-fast-front overvoltage A transient overvoltage. Usually unipolar and with superimposed oscillations, with a wavefront time of less than 0.1pμs, a total duration of less than 3ms, and an oscillation frequency between 30kHz and 100MHz. Combined overvoltage combined overvoltage3.111
An overvoltage consisting of two voltage components applied simultaneously between each end of the phase insulation or longitudinal insulation and the ground. Representative voltages and overvoltages3.12
A voltage and overvoltage that can produce the same effect on insulation as the various applied voltages that occur during operation, and that has a given waveform and value (one, a group or a frequency distribution). 8. Continuous (power frequency) voltage
waveform: a power frequency oscillation wave, the duration of which is equal to the expected life of the equipment. Value: corresponds to the highest voltage of the system (effective value). b. Temporary overvoltage
waveform: standard power frequency short-time voltage.
value: root mean square value (effective value, peak value divided by 2). c. Slow wavefront (operation) overvoltage
waveform: standard operation impulse, that is, an impulse with a wavefront time of 250μs and a half-peak time of 2500gμs. Value: peak value.
d. Fast wavefront overvoltage
waveform: standard lightning impulse, that is, an impulse with a wavefront time of 1.2μs and a half-peak time of 50μs. Value: peak value.
e. Steep front overvoltage
waveform: The waveform parameter range is: front time Tt≤0.1us, total duration less than 3ms, and with an impulse of superimposed oscillation rate of 30kHz to 100MHz. The test waveform is specified in the relevant equipment standards. Value: peak value.
f. Interphase slow front (operation) overvoltage
waveform: The combination of two standard operation impulses with the same beep value and opposite polarity. Value: The arithmetic sum of the peak values of the two components. 3.13 Neutral point insulated system isolated neutral system A system in which the neutral point is not grounded except for high impedance grounding for protection and measurement. 3.14 Neutral point solidly earthed neutral system A system in which all or part of the neutral points of the transformers are directly grounded or grounded through low impedance. E resonant earthed system
Resonant earthed system
A system in which the neutral point is grounded through a reactor. Its inductance value can make the power frequency inductive current flowing through the reactor when single-phase is grounded basically compensate for the capacitive component of the fault current.
3.16 Impedance earthed system impedance earthed system system with neutral point grounded by appropriate impedance. 3.17 Earth fault factor earth fault factor when a ground fault occurs in a three-phase system (one-phase or two-phase ground fault at any point), the ratio of the maximum power frequency voltage effective value of a selected point (generally refers to the equipment installation point) relative to the ground in good condition to the effective value of the power frequency voltage of the point relative to the ground when there is no fault. 3.18 Lightning current lightning current
The current flowing when lightning directly strikes an object with low ground impedance used in lightning protection calculation. 3.19 Earth resistance earth resistance53
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The ratio of the maximum potential difference of the grounded object (such as the neutral point of the equipment housing, transformer, etc.) to the zero potential surface in the soil to the maximum current flowing through it.
3.20 Overvoltage protective devices Overvoltage protective devices Devices that limit the amplitude of overvoltage, or limit its duration, or both, such as lightning arresters. 3.21 Protection level of a protective device protection level of a protective device The peak value of the highest voltage that may appear at both ends of the protective device under specified conditions. 3.22 Protection factor of a protective device protection factor of a protective device The ratio of the protection level of a protective device to 2/3U. 3.23 Insulation coordination insulation coordination The process of reasonably determining the insulation level of the equipment based on the possible overvoltage, the insulation characteristics of the equipment and the factors that may affect the insulation characteristics after considering the overvoltage protection measures adopted. 3.24 External insulation external insulation The exposed surface of the air gap and solid insulation of the equipment. It bears voltage and is affected by external conditions such as atmosphere, pollution, moisture, foreign matter, etc.
3.25 Internal insulation internal insulation The solid, liquid or gaseous part of the internal insulation of the equipment. It is basically not affected by external conditions such as atmosphere, pollution, moisture, foreign matter, etc. 3.26 Indoor external insulation Indoor external insulation Indoor external insulation designed for operation inside buildings and not exposed to the open air. 3.27 Outdoor external insulation Indoor external insulation designed for operation outside buildings and exposed to the open air. 8 Self-restoring insulation Self-restoring insulation 3.28
Insulation that can fully recover its insulation properties after destructive discharge caused by voltage application. 3.29: Non-self-restoring insulation Insulation that loses or cannot fully recover its insulation properties after destructive discharge caused by voltage application. 3.30 Rated insulation level Rated insulation level A set of standard withstand voltages sufficient to prove that the required insulation withstand capacity is met. A. For equipment with a maximum voltage equal to or less than 252kV, the rated insulation level is expressed in standard lightning impulse and standard short-duration power frequency withstand voltage.
b. For equipment with a maximum voltage greater than 252kV, the rated insulation level is expressed in standard lightning impulse and switching impulse or short-duration power frequency withstand voltage.
3.31 Standard insulation level standard insulation level The rated insulation level corresponding to the standard value of the highest voltage U. 3.32 Standard switching [lightning] impulse withstand voltage standard switching [lightning] impulse withstand voltage The standard value of the switching [lightning] impulse voltage that the equipment insulation can withstand during the withstand voltage test. 3. 33 “Standard short duration power-frequency withstand voltagestandard short duration power-frequency withstand voltageThe standard value (effective value) of the power frequency voltage that the equipment can withstand when tested under specified conditions and time.Conventional switching[lightningJimpulse withstand voltage3.341
Under specified conditions, the insulation can withstand a certain number of operating [lightning] impulse withstand voltage without any destructive discharge or damage: standard value. This concept is particularly applicable to non-self-recovering insulation.3.35Conventional maximum switching [lightning] overvoltageIn the conventional insulation coordination method, the operating [lightning] overvoltage peak value used as the maximum overvoltage.3.36”Insulation coordination factorinsulation co-ordination factorThe ratio of the standard withstand voltage of the equipment to the corresponding protection level of the protective device. 54
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Note: ①The definition here is written based on the insulation coordination method actually used in my country, which is different from the definition in the IEC standard. ② When there is no protective device or the protective device cannot protect against a certain overvoltage, the overvoltage level on the equipment replaces the protection level. ③ According to the conventional method and statistical method of insulation coordination, there are two types of insulation coordination factors: conventional coordination factors and statistical coordination factors. 3.37 Standard voltage shapes The following standard voltage shapes are used in this standard: Rated short-time power frequency: sinusoidal voltage with a frequency in the range of 48 to 62 Hz. - Standard operating impulse: impulse with a wave front time of 250ps and a half-peak time of 2500us. Standard lightning impulse: impulse with a wave front time of 1.2us and a half-peak time of 50us. 3.38 Withstand voltage (assumed and statistical) withstand voltage (assumed and statistical) The voltage with a representative voltage waveform that the insulation can withstand with a given reference probability. - The reference probability of the assumed withstand voltage is 100%. - The reference probability of the statistical withstand voltage is 90%. 3.39 Performance criterion of insulation The benchmark that is considered acceptable in terms of economy and operation. Usually it is expressed by acceptable insulation failure indicators (number of failures per year, mean time between failures MTBF, failure rate, etc.). 3.40 Deterministic method for insulation coordination Conventional procedure for insulation coordination In this insulation coordination method, the maximum lightning and switching overvoltage that may act on the equipment should first be determined based on the overvoltage limit and the protection level of the protective device, and taking into account some unfavorable factors (such as distance, waveform, etc.) that may cause the overvoltage acting on the equipment to exceed the protection level. This maximum overvoltage is multiplied by the conventional coordination factor, and the standard withstand voltage of the equipment is selected from the standard series based on the value obtained.
3.41 Switching [lightning] overvoltage probability density function f. (U)
The probability density function of the peak value of the switching [lightning] overvoltage acting on the equipment (or a certain point of the line) as a result of a specific event in the system (line closing, reclosing, fault and lightning discharge, etc.). f. (U) is equal to the limit of the ratio of the probability that the overvoltage is in the interval U.U1, (U2>U,) to the interval width U.-U, as shown in Figure 1. Then the probability that the overvoltage peak value appears between U1 and U is:
corresponds to the area of the shaded part in the figure. f. (U) varies with the system, the installation location of the equipment, the operating conditions and the cause of the overvoltage.
jo(u) d
Figure 1 Operation [lightning] overvoltage probability density f. (U) 3.42: Switching [lightning] overvoltage upper side probability Q(U) switching [lightning] overvoltage upper probability Q. (U) The probability that the operation [lightning] overvoltage peak value acting on the equipment (or a certain point of the line 55
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) is greater than U as a result of a specific event in the system (line closing, reclosing, fault and lightning discharge, etc.). The relationship between Q(U) and f. (U) is shown in Figure 2 or by the following formula: Q(U)=1-
. fo(U)dU=1-F. (U)
Figure 2 Operation [Lightning overvoltage upper side probability Q. (U) 3. 43 Probability of disruptive discharge phu)
Probability of disruptive discharge caused by insulation under the action of voltage of certain waveform and amplitude. 3.44
Probability of withstand The probability that insulation can withstand the action of voltage of certain waveform and amplitude without causing destructive discharge, which is equal to (1-p). 3.45
Statistical switching [Lightning Jovervoltage Us The peak value of the operating [lightning] overvoltage corresponding to the upper side probability of Us equals a certain reference probability. In insulation coordination, this reference probability is generally taken as 2%. 3. 46: Statistical switching [lightning] impulse withstand voltage Uw statistical switching [lightning] impulse withstand voltage Uw under the same waveform and different amplitude of the operating [lightning] impulse voltage, the corresponding operating [lightning] impulse voltage peak value when the probability of destructive discharge of insulation is equal to a certain reference probability P\ When the probability of destructive discharge of insulation P(U) is known and the reference probability P\ is given, Uw is uniquely determined, as shown in Figure 3. P(u)
Figure 3 Statistical operating [lightning] impulse withstand voltage Uw 3.47 Statistical procedure of insulation coordination
statistical procedure of insulation co-ordination A method of using statistical methods to design insulation coordination under the premise of allowing a certain insulation failure rate. This method is generally only applicable to self-restoring insulation.
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3. 48 Simplified statistical procedure of insulation coordination simplified statistical procedure of insulation co-ordination A simplified statistical method of insulation coordination. At this time, some assumptions are made about the probability distribution of a certain type of overvoltage and the probability distribution curve of the insulation withstanding this overvoltage (such as a normal distribution with known standard deviation and expectation), and the curve is represented by a point corresponding to a certain probability value. The abscissa of this point in the overvoltage probability curve is called the "statistical overvoltage", and the abscissa of this point in the withstand probability curve is called the "statistical impulse withstand voltage". Then, a margin is selected between the statistical impulse withstand voltage and the statistical overvoltage, that is, the statistical coordination factor. The statistical withstand voltage can be determined by multiplying the statistical overvoltage by the statistical coordination factor. 3.49 Insulation failure rate risk of failureof the insulation The probability of destructive discharge caused by the insulation complying with a certain waveform overvoltage is calculated by statistical methods. It can be calculated by the following formula: R
f.(U) - Pr(U)dU
Numerically, it is equal to the area of the shaded part in Figure 4. R(U)
High voltage test technology
Flashoverflashover
Figure 4 Insulation failure rate R
Destructive discharge along the surface of the insulating medium. 4.2 Spark dischargesparkover
Destructive discharges in gas or liquid media. 4.3 Puncture
Destructive discharges in solid media. 4.4 Destructive dischargedisruptive dischargeUbzxz.net
The phenomenon of loss of dielectric strength under high voltage in solid, liquid, gaseous media and combined media. During destructive discharge, the voltage between electrodes drops rapidly to zero or close to zero. 4.5 Destructive discharge voltagedisruptivedischargevoltageThe voltage value that causes destructive discharge in the medium can be expressed as peak value, effective value or arithmetic mean value according to different types of tests. 50% destructive discharge voltageUso50%disruptive dischargevoltageUso4.6
The expected voltage value that causes a 50% probability of destructive discharge on the test piece. 4.7 Standard reference atmosphere Standard reference atmosphere The standard reference atmosphere is:
Temperature: tg20℃,
Air pressure: bo-101.3kPa;
Absolute humidity hg-11g/m°.
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4r8: Atmospheric correction factor The destructive discharge voltage of external insulation is related to the atmospheric conditions. Using the atmospheric correction factor, the measured destructive discharge voltage can be converted to the voltage value U under standard atmospheric conditions. Conversely, the test voltage specified under standard atmospheric conditions can be converted to the equivalent value under actual test conditions.
The atmospheric correction factor K is the product of the air density correction factor k (see 4.9) and the humidity correction factor z (see 4.10), that is, K, k, z.
The destructive discharge voltage value is proportional to the atmospheric condition correction factor, i.e.: U=KU.
4.9 Air density correction factor The air density correction factor depends on the relative air density k, = (8)m
When the air temperature t and are expressed in degrees Celsius, the weather pressure 6 and 6. are expressed in the same unit, the relative air density is: b(273+to)
b. The (273+t)
m value is related to the test voltage type, polarity, test sample type and discharge distance. Its value can be found in the relevant standards. 4.10 Humidity correction factor The humidity correction factor can be expressed as:
kz (k)u
Where is a parameter that depends on the test voltage type, its value can be found in the relevant standards. is a parameter that depends on the test voltage type, polarity and discharge distance, its value can be found in the relevant standards. 4.11 Ripple
Ripple is a periodic pulsation of the arithmetic mean value of the DC voltage. 4.11.1 Amplitude of the ripple Half the difference between the maximum and minimum values of the ripple. 4.11.2 Ripple factor
Ratio of the ripple amplitude to the arithmetic mean value of the DC voltage. Impulse
Non-periodic transient voltage or current applied during the test. It usually rises rapidly to a peak value and then drops to zero more slowly. Note: The English term "impulse" is different from the term "surge." "Surge" refers to the transient process of voltage and current occurring in the system during operation. 4.13 Fast-front impulse Lightning impulse
Impulse with a wavefront time of 20μs or less. 4.14, Slow-front impulse switching impulse
Impulse with a wavefront time of more than 20μs. 4.15, Full-wave lightning impulse full lightning impulse Lightning impulse that is not interrupted by destructive discharge, the waveform is shown in Figure 5. 58
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Figure 5 Full-wave lightning impulse
4.16 Standard lightning impulse standard lightning impulse T = 1. 67T
T'=0.3T,=0.5T
Standard lightning impulse is a full-wave lightning impulse with a wavefront time of 1.2us and a half-peak time of 50μus. It is called 1.2/50 impulse. 4.17
front time of a lightning impulseT, front time of a lightning impulseT, is an apparent parameter, which is 1.67 times the time interval T between the moment when the lightning impulse reaches 30% of its peak value and the moment when the lightning impulse reaches 90% of its peak value (points A and B in Figure 5). If the wave front is oscillating, first make an average curve of the oscillating wave and determine points A and B as defined above.
4.18 Apparent origin O1virtualoriginO1 It is the instant O that is 0.3T ahead of the instant equivalent to point A, as shown in Figure 5. For waveforms with a linear time scale, it is the intersection of the straight line drawn through points A and B with the time axis. 4.19time to half value of a lightning impulseT2time to half value of a lightning impulseT2 The time interval between the apparent origin of a lightning impulse and the moment when the voltage drops to half of its peak value, as shown in Figure 5. 4.20 Chopped lightning impulse A chopped lightning impulse is a lightning impulse in which the voltage drops rapidly to zero or near zero due to destructive discharge. It can be of oscillatory or non-oscillatory type.
Note: The chopping can be accomplished by an external chopping gap or by discharges in the insulation inside or outside the test specimen. 4.21 Standard chopped lightning impulse A standard lightning impulse chopped by an external gap, with a chopping time T of 2 us to 5 us as shown in Figure 6b. 4.22
Instant of chopping The instant of chopping is the moment of rapid voltage drop at which chopping begins. 4.23 Characteristics of voltage collapse during chopping The apparent characteristics of the voltage collapse during chopping are defined by points C and D, which are 70% and 10% of the voltage value at the instant of chopping (see Figure 6). The duration of the voltage collapse is 1.67 times the time interval between points C and D. The steepness of the voltage dip is the ratio of the voltage at the moment of chopping to the duration of the voltage dip.
Note: Points C and D are used for definition purposes only. It does not mean that the duration and steepness of the voltage dip can be measured with any accuracy using conventional measurement systems.
(a) Lightning impulse truncated at the wavefront
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(b) Lightning impulse truncated at the wavetail
Figure 6 Lightning impulse chopping wave
Lightning impulse chopping time T: time to chopping of a lightning impulse T4.24
The time interval between the apparent origin and the moment of chopping of the lightning impulse is shown in Figures 6a and 6b. It is an apparent parameter. Standard switching impulse standard switching impulse4.25
The wavefront time T is 250μs and the half-peak time T2 is 2500μs. 4.26
Switching impulse front time T, time to peak of a switching impulse T, the time interval from the actual origin ○ to the moment when the voltage reaches the peak value of the switching impulse, as shown in Figure 7. u
Figure 7 Switching impulse
Switching impulse cut-off time T. time to chopping of a switching impulse T. The time interval from the actual origin to the moment of cut-off of the switching impulse. Half-peak time of a switching impulse T, time to half value of a switching impulse T4.28
The time interval from the actual origin ○ to the moment when the switching impulse first drops to half its peak value, as shown in Figure ? 4.29Time above 90% peak value of a switching impulse Tatimeabove90%TaThe duration of the switching impulse exceeding 90% of its peak value, as shown in Figure 7. 60
4.30Time to zero
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The time interval from the actual origin to the first time the impulse passes through the zero value. Linearly rising impulse4.31
An impulse that rises with an approximately constant steepness before being cut off by a destructive discharge. It is applicable to lightning impulses and switching impulses. 4.32
Linearly rising front-chopped impulseAn impulse that rises linearly until it is cut off by a destructive discharge. As shown in Figure 8. The impulse is defined by the following parameters:
peak value U
wavefront time T,
apparent steepness S
S=U/T,
S is the slope of the straight line passing through points E and F, usually expressed in kilovolts per microsecond. If the wavefront from the 30% bat value to the moment of cut-off falls completely within two straight lines parallel to the EF line with a time displacement of ±0.05T1, this impulse chopped wave is considered to be approximately linearly rising (see Figure 8). Note: The value and allowable deviation of the apparent steepness S should be specified by the relevant standards. U
Figure 8 Linearly rising wavefront truncated impulse
4.33 Voltage/time curve for impulse with constant waveform Under the condition of constant waveform, the relationship curve between the impulse discharge voltage and the corresponding discharge time of the test piece, the truncation can occur at the wavefront, peak or wave tail, as shown in Figure 9.
Note: Due to the dispersion of discharge voltage and discharge time, the actual volt-second characteristic curve obtained during the test is a package. 61
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Figure 9 Impulse volt-second characteristic curve
4.34 Voltage/time curve for linearly-rising impulse When the test piece is discharged, the relationship curve between the peak voltage and wavefront time of the linearly rising impulse is shown in Figure 10. This curve is obtained by applying linearly rising impulses of different steepness.
Note: Due to the dispersion of discharge voltage and discharge time, the actual volt-second characteristic curve obtained during the test is a package. Figure 10 Linear rising impulse volt-second characteristic curve 4.35 Impulse current is a non-periodic transient current. There are two waveforms: the first is that the current rises from zero to the peak value in a very short time, and then drops to zero in an approximately exponential law or damped sine waveform. The waveform of this impulse current is represented by the wavefront time T and the half-peak time T, which is recorded as Ti/T2. As shown in Figure 11(a). The second waveform is approximately rectangular, called square wave impulse current, as shown in Figure 11(b). 62
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