JB/T 5894-1991 Guidelines for the use of AC gapless metal oxide arresters
Some standard content:
Mechanical Industry Standard of the People's Republic of China
Guidelines for the Use of AC Gapless Metal Oxide Arrester Subject Content and Scope of Application
This standard is a guiding document for the selection and use of AC gapless metal oxide arresters JB/T 5894 --- 91
This standard applies to gapless metal oxide arresters for limiting overcurrent in AC power systems. This standard does not apply to metal oxide arresters with series or parallel gaps. Reference Standards
GB11032
2 AC gapless metal oxide arresters
GB311.1 Insulation coordination of high-voltage power transmission and transformation equipment GB3117 Insulation coordination guidelines for high-voltage power transmission and transformation equipment GBJ64 Overvoltage protection design specifications for industrial and civil power devices 3 Abbreviations
Gapless metal oxide arresters, because there is neither a series gap nor a parallel gap, eliminate the influence caused by the change of the gap breakdown characteristics, and the protection characteristics are only determined by the residual pressure when the impulse current passes. The nonlinear resistor (valve) of the gapless metal oxide arrester absorbs large energy per unit volume and can be used in parallel to double the energy absorption capacity, which can effectively limit the atmospheric overvoltage and operating overvoltage of the power system.
On the other hand, due to the lack of a series gap, the valve of the metal cyanide arrester must not only withstand the effects of lightning waves and operating wave overvoltages, but also directly withstand the effects of continuous operating voltage and temporary overvoltage. As a result, there are problems of aging, life and thermal stability under these voltages. In addition, in some cases, when the voltage distribution along the arrester is seriously uneven due to factors such as pollution transfer and stray capacitance between adjacent objects, it will cause local overheating of the arrester. Therefore, it is necessary to pay attention to thermal stability during operation during use. Usually, the protection level of the arrester and the reliability of the arrester itself are two contradictory requirements. Therefore, the selection of the arrester is an optimization process, which requires careful consideration of the relevant system parameters and equipment parameters, so that the protection level of the arrester meets the requirements of the protected equipment and the arrester itself has sufficient reliability.
This guideline is formulated to cooperate with GB11032. According to the characteristics of gapless metal oxide arresters and the specific conditions of the power system, the issues that need to be considered in the selection and use of arresters are explained. In the neutral point effectively grounded power system with a rated voltage of 110~500kV, the superiority of metal oxide arresters is more obvious. In the non-effectively grounded system with a rated voltage of 3
63kV, since there is generally no automatic ground fault removal device, it is usually allowed to operate with a ground fault for two hours or longer, so the arrester needs to have a higher reference voltage and rated voltage, so that its residual voltage is close to that of an ordinary valve type arrester. However, due to the lack of a gap, it can have a certain limiting effect on some operating overvoltages. The use of gapless metal oxide arresters to limit parallel compensation capacitor banks and motor operating overvoltages in neutral point non-effectively grounded systems has achieved good results. In special occasions such as protecting old or weakly insulated equipment and indoor substations or switch cabinets with relatively tight space, the use of metal oxide arresters will also have a better effect. 4 Basic characteristics of metal oxide arresters
4.1 General
Approved by the Ministry of Machinery and Electronics Industry on October 24, 1991, 98
Implementation on October 1, 1992
JB/T5894--91
The basic characteristics of metal oxide arresters are their rated voltage and protection level. The protection level of the arrester is determined by the residual voltage of the surge current, the nominal discharge current and the operating surge current. For a given voltage, there are different types of arresters, and therefore different reference voltages and protection levels. In specific applications, the characteristics that need to be considered include continuous operating voltage, power frequency voltage withstand time characteristics, nominal discharge current, long duration current surge withstand characteristics, pressure release level and pollution tolerance. 4.2 Rated voltage (x)
The maximum allowable power frequency voltage effective value between the two terminals of the arrester. The arrester designed according to this voltage can work correctly under the temporary overvoltage determined in the specified action load test. The correct operation of the metal oxide arrester is to withstand the rated voltage for a specified time after one or more impulse currents, and then reach a thermally stable state under the continuous operation voltage. The rated voltage is the reference parameter for various electrical characteristics of the arrester. 4.3 Reference voltage (Urat)
includes power frequency reference voltage and DC reference voltage. The maximum peak value of the power frequency voltage on the arrester measured under the power frequency reference current divided by /2 is the power frequency reference voltage; the voltage on the arrester measured under the DC reference current is the DC reference voltage. The reference voltage of the arrester composed of multiple components is the sum of the reference voltages of each component. The reference voltage is the electrical function near the small current inflection point of the arrester's volt-ampere characteristic curve. 4.4 Continuous operation voltage (U.)
The effective value of the power cheek voltage allowed to be applied between the two ends of the arrester for a long time. An important feature of the metal oxide arrester is that the valve plate may age under the continuous action of the power frequency voltage. The final result of aging is that the DC 1mA voltage of the arrester drops seriously, and loses thermal stability when operating or under continuous operating voltage. 4.5 Charge rate
The ratio of the peak value of the continuous operating voltage to the DC reference voltage: The charge rate directly affects the aging process of the arrester. A high charge rate will accelerate the aging of the arrester. When the continuous operating voltage is unevenly distributed along the arrester, it is possible that the charge rate of some valve plates is high. Reducing the charge rate will not only slow down the aging of the arrester, but also improve the ability to withstand temporary overvoltages. However, when the charge rate is low, the protection performance of the arrester will deteriorate accordingly.
Charge rate is an important parameter that affects the aging performance and protection level of the arrester. 4.6 Power frequency voltage tolerance time characteristics
Under specified conditions, different values of J-frequency voltage are applied to the arrester, and the corresponding maximum duration for which the arrester is not damaged and does not undergo thermal collapse.
The ability of metal oxide arresters to withstand temporary overvoltages is related to the amplitude and duration of the overvoltage and the operating overvoltage deenergization energy absorbed by the arrester before the temporary overvoltage. An overvoltage amplitude that is too high or a duration that is too long may damage the arrester. Arrester of the same type and rated voltage from different manufacturers may have different power frequency voltage withstand time characteristics. The power frequency voltage withstand time characteristics are important for selecting the rated voltage or reference voltage of the arrester according to specific conditions. 4.7
Nominal discharge current (1.)
The peak value of the discharge current of the impulse waveform 8/20 used to classify the arrester level. It is used to determine the protection level under lightning overvoltage. 4.8 Protection level of arrester
The protection level of a gapless metal oxide arrester is entirely determined by its residual voltage. The lightning overvoltage protection level of the arrester is the higher of the following two values: the maximum residual voltage under steep wave impulse current divided by 1.15; a.
The maximum residual voltage under the nominal discharge current.
Note: The regulation of dividing the residual voltage of steep wave impulse current by 1.15 is that the withstand strength of the ironing current residual voltage of the oil-immersed insulation of transformer-type electrical appliances is more than 15% higher than the withstand strength of the nominal current residual voltage. Other types of insulation, such as rotating motors, dry-type transformers, cables and SF. The insulation in the substation (GIS) may have different coefficients. The arrester operation overvoltage protection level is the maximum residual voltage under the operation impulse current. 99
JB/T5894--91
When the rated voltage is constant, the residual voltage is a function of the current passing through the arrester. In the range of lightning impulse current, the residual voltage is also related to the wave head time of the impulse current. Considering the possibility of lightning current in the nearby area, the residual voltage value under steep wave current is given in the characteristics of power station and distribution arresters. The wave head time of the operation impulse current used in the arrester operation impulse current residual voltage test is 3010Gus (there is no obvious effect on the residual voltage value within this range or when the wave head is longer). The current amplitude is specified in different values according to the different nominal current series, different types and different rated voltages of the arrester. This operating impulse current value is only used for the operating residual voltage test of the arrester, and it is not required to reach this value in the long-duration impulse current exposure test. The protection level of the arrester is a basic parameter in the overvoltage protection and insulation coordination of the power system. 4.9 Long-duration current impulse withstand characteristics The ability of the arrester to absorb long-duration discharge energy. Arrester with a system rated voltage of 110kV and above is assessed through a line discharge withstand test. GB11032 is divided into four levels according to the energy size. Generally, the higher the system rated voltage level, the longer the line, and the lower the line wave impedance, the greater the level of the discharge withstand test. Arrester with a system rated voltage of 63kV and below is assessed through a square wave current impulse withstand test.
Long-duration current impulse withstand characteristics are particularly important for arresters used to limit operating overvoltages in ultra-high voltage long-distance transmission systems and large-capacity parallel compensation capacitor groups.
4.10 Pressure square release level
The ability of the arrester to withstand internal fault current. Under the specified short-circuit current, the porcelain sleeve of the arrester with a pressure release device will not explode (that is, the fragments will not fly out of the specified range during the explosion). The pressure release current level is expressed in terms of the effective value of the power frequency current. 4.11 Pollution migration tolerance
The pollution migration tolerance of the arrester is mainly related to its overall structure, the distance between the outer surface of the porcelain sleeve and the shape of the shed. In addition to causing surface flashover, the pollution migration on the surface of the porcelain sleeve will also cause uneven voltage distribution along the resistor, causing local overheating of the resistor and leading to damage. Regular cleaning and application of anti-fouling paint can also improve the anti-fouling ability of the arrester. 5 General procedures for arrester selection
Steps for selecting a lightning arrester
Determine the use conditions of the arrester according to the environmental conditions such as temperature, altitude, wind speed, pollution migration and earthquake in the area of use; b.
Select the type of arrester according to the protected object; determine the continuous operating voltage of the arrester according to the highest voltage of the system; estimate the amplitude and duration of the temporary overvoltage at the installation point of the arrester, select the rated voltage of the arrester and check it with the power frequency voltage tolerance time characteristics;
Estimate the lightning discharge voltage passing through the arrester Current amplitude, select the nominal discharge current of the lightning arrester; estimate the operating impulse current and energy passing through the lightning arrester, and select the line discharge withstand test level, square wave impulse test current amplitude and energy level absorption capacity of the lightning arrester:
Select the protection level of the lightning arrester according to the requirements of insulation coordination; select the pressure release level of the lightning arrester according to the maximum fault current at the installation place of the lightning arrester; select the creepage distance of the lightning arrester porcelain sleeve according to the pollution migration condition at the installation place of the lightning arrester; select the mechanical strength of the lightning arrester according to the lead tension, wind speed and earthquake conditions at the installation place of the lightning arrester. 5.2 Application of arresters
Determine the lightning overvoltage protection level of the arrester according to the rated lightning impulse withstand voltage of the selected protected equipment; if necessary, select the operating overvoltage protection level of the arrester according to the rated operating impulse withstand voltage of the protected equipment; b.
Check the protection range of the arrester according to the number of outgoing lines of the substation; in the selection of insulation level, consider the relationship between the external insulation of the equipment and the altitude and the reduction factor of the internal insulation operation time; when the arrester cannot meet the insulation coordination requirements, one or more of the following methods can be adopted to improve it, and the better solution can be selected through technical and economic comparison: adjust the position of the arrester, reduce the rated voltage of the arrester, increase the nominal discharge current level of the arrester or use a special arrester with a lower protection level. If necessary, the insulation level of the protected equipment can also be improved. 6 Principles for the selection of lightning arresters
6.1 Verification of operating conditions
The operating conditions include external conditions such as ambient temperature, solar radiation, altitude, wind speed, pollution migration and ground expansion. GB11032 divides normal operating conditions and abnormal operating conditions. Temperature has a direct impact on the aging and thermal stability of gapless metal oxide arresters. In addition to the ambient temperature, the temperature rise of solar radiation should also be considered. For this reason, the type test stipulates that the test sample should be preheated to an average weighted temperature of 60°C. If it exceeds this range, it should be negotiated with the manufacturer. For example, in extremely cold areas, the sealing of the lightning arrester should be specially considered. In hot areas, the ability of the lightning arrester to absorb overvoltage energy will be reduced.
Considering pollution migration, GB11032 divides porcelain sleeves into 3 levels and stipulates the minimum nominal creepage distance (ratio of external insulation creepage distance to the highest voltage of equipment or system): 17mm/kV in areas without obvious pollution migration;
20mm/kV in areas with ordinary pollution migration;
25mm/kV in areas with heavy pollution migration.
When selecting the creepage distance, attention should be paid to the effective insulation height of the porcelain sleeve and its effectiveness should be considered. Lightning arresters used in areas with heavy pollution should be tested for artificial pollution in type tests.
When the altitude of the lightning arrester installation exceeds 1000m, or the seismic intensity is above 7 degrees, the maximum wind speed exceeds 35m/s, and the re-icing thickness exceeds 2cm, the manufacturer should be consulted to recalculate the external insulation and mechanical strength of the lightning arrester, and special consideration should be given to the design if necessary.
6.2 The continuous operating voltage of the phase-to-ground arrester is used for the arrester in the system with the ground fault automatic cut-off device, and its continuous operating voltage should be equal to or higher than the highest phase voltage of the system. 110~500kV systems all have ground fault automatic cut-off devices. The continuous operating voltage of the arrester used in such systems can be selected as not less than the highest phase voltage of the system.
The continuous operating voltage of the arrester used in the system with non-effective neutral grounding and no ground fault automatic cut-off device can still be selected as not less than the highest phase voltage of the system.
Considering that the system may often have a long-term operation mode with ground faults, in order to solve the aging and thermal stability problems of the arrester and reduce the accident rate under arc grounding and resonant overvoltage, GB11032 increases the DC 1mA reference voltage of the 363kV power station distribution and parallel compensation capacitor arresters, and increases the test voltage to 1.3 times in the action load test, and the continuous operating voltage is processed.
6.3 Rated voltage of phase-to-ground arrester
The rated voltage of the arrester should be selected based on the temporary overvoltage of the power system. It is generally believed that the arrester must be able to withstand the temporary overvoltage caused by the increase of the voltage of the healthy phase due to a single-phase grounding fault. Temporary overvoltages caused by other reasons should also be considered. The selection of the rated voltage of the arrester should generally be based on the highest value of these overvoltages. Sometimes, temporary overvoltages due to different reasons should be considered (such as sudden load shedding at the same time as the grounding fault), and the probability of these different phenomena occurring at the same time should be taken into account.
6.3.1 Temporary overvoltage caused by grounding fault These overvoltages can be obtained by multiplying the grounding fault factor at the installation point of the arrester by the highest phase voltage in the system. The grounding fault factor can be calculated using an appropriate program.
a. Neutral point effective grounding system
The grounding fault factor is usually not greater than 1.4. The calculation of the grounding fault factor takes into account X./X,, R./X, and R,/X, (see Appendix A). Where: X. —Zero sequence reactance
X,——Positive sequence reactance
R. Zero sequence resistance
R,—Positive sequence resistance
b. Neutral point non-effective grounding system
JB/T5894-91
The ground fault factor is usually 1.73, but it is related to the ground resistance value. In the neutral point non-effective grounding system, when the ground resistance is 37% of the total capacitive reactance of the power grid, the factor reaches the maximum value, which can reach 1.82. Theoretically, if the value of X./X, is between -1 and -20, due to the proximity to the resonance point, the cross
and 2 resonance conditions may occur. The ground fault factor will be higher than 1.82, but the passband X./X, value is far from the range value that causes spectral vibration, and this state can be ignored when selecting the rated voltage of the lightning arrester. 6.3.2 Temporary overvoltage caused by other reasons In addition to ground faults, other important reasons that cause temporary overvoltage include: sudden load shedding leading to generator overexcitation overvoltage; a.
b. Voltage increase at the end of the empty long line (long line capacitance effect). In addition, other types of temporary overvoltages that occur under normal or abnormal conditions also need to be paid attention to, such as: resonance and induction of parallel circuits;
harmonic resonance and transformer saturation caused by load shedding, transformer or capacitor bank. 6.3.3 Determination of rated voltage
Since temporary overvoltage is closely related to the parameters of the system structure, it is difficult to determine the maximum temporary overvoltage and its duration for some complex systems, and it is necessary to estimate through simulation, calculation or investigation of the actual system. In order to simplify the selection procedure of rated voltage, the rated voltage of the lightning arrester is usually selected according to the highest transient overvoltage of the healthy phase under single-phase grounding of the power system and load shedding conditions. For a general neutral point with effective zero-sequence reactance ratio (Z./Z,) between 0 and +3, and zero-sequence resistance to positive-sequence reactance ratio (R./X,) between 0 and +1, in single-phase grounding, the fault factor at the arrester installation point does not exceed 1.4. Therefore, for 110kV and 220kV neutral point effective grounding systems, the rated voltage of the arrester can generally be 1.4 times the system's highest working phase voltage. For 330kV and 500kV systems, although the grounding fault factor is generally low, the influence of factors such as load shedding and long-line capacitance effect is relatively large. For the arresters on the busbar of the substation and the line side of the circuit breaker of these two voltage levels, their rated voltages can generally be selected as 1.3 and 1.4 times the maximum phase voltage respectively.
For neutral point non-effective grounding systems, GB11032. still stipulates the rated voltage of the arrester according to single-phase grounding and load conditions. Harmonic lightning arresters still have to withstand the effects of resonance and arc grounding overvoltage. Therefore, in the power frequency voltage tolerance time characteristic test and action load test, the method of raising the test voltage of the power station, distribution and parallel compensation capacitor arresters to 1.21.3 times the rated voltage has been specially handled.
In recent years, the neutral point has been grounded through a medium or low impedance in 3-63kV systems. The arrester used in this system has not yet been listed in GB11032, and its rated voltage can be negotiated with the manufacturer according to specific conditions. Rated voltage is a comprehensive indicator of the arrester. Selecting a lower rated voltage can improve the protection margin, but it will correspondingly reduce the reliability and service life of the arrester and itself.
6.4 Rated voltage tolerance time characteristics
The ability of a gapless metal oxide arrester to withstand temporary overvoltage is not only related to the amplitude of the rated overvoltage but also to the duration of the power frequency overvoltage and the initial energy absorbed by the arrester. The initial energy of the arrester is because the temporary overvoltage may be caused by a system failure caused by a lightning strike or an operating overvoltage, so the arrester sometimes absorbs a certain amount of overvoltage energy of the operating wave and lightning wave before it withstands the temporary overvoltage (mainly the operating wave overvoltage energy). This part of the initial energy will cause the valve plate temperature to rise, thereby affecting the arrester's ability to withstand temporary overvoltage. The allowable time for the arrester to withstand temporary overvoltage is a function of the temporary overvoltage value applied to the arrester and the initial overvoltage energy. The specific initial energy is specified in GB11032 as the energy generated by the second largest current impact or two long-duration current impact tests. In the test, the predetermined rated voltage amplitude is added immediately to make the power frequency voltage tolerance time characteristic. Some foreign manufacturers provide power frequency tolerance 102
JB/T5894--91
volt-second characteristic curves, and the initial operating overvoltage energy selected is roughly equivalent to the energy generated by two long-duration current impact tests.
The manufacturer should provide the user with the power frequency tolerance volt-second characteristic curve of the arrester in accordance with GB11032. --Generally, after selecting the rated voltage according to technical requirements, it is not necessary to verify the power frequency voltage tolerance characteristics. At the installation point of the arrester, there may be special cases of temporary overvoltages with large amplitude and long duration, or in order to obtain a larger insulation protection margin, when selecting an arrester with a lower rated voltage, it is advisable to check the power frequency voltage tolerance. If the amplitude or duration of the temporary overvoltage exceeds the withstand capacity of the arrester, it is necessary to select an arrester with a higher rated voltage.
The amplitude and duration of the expected temporary overvoltage in the power system are usually determined by the action of the relay protection and circuit breaker during a single-phase grounding fault, and its value varies with the grounding conditions and the relay protection method. Under unfavorable conditions, temporary overvoltages with amplitudes higher than the rated voltage of the arrester or with a relatively long duration may occur. A neutral point effective grounding system will produce high amplitude or long-term temporary overvoltages under the following conditions: In order to limit the ground fault current, the neutral point of a part of the transformer is often not grounded. During the fault tripping or switching operation, some parts of the network may become a non-directly grounded system, which increases the ground fault factor: b. Asynchronous operation of the circuit breaker may produce resonant overvoltage; the time for planned closing and system grid-connected synchronous dispatching operation may be as long as 20 minutes or more. c.
When there is no automatic grounding fault removal device in the neutral point non-effective grounding system, the voltage of the healthy phase of the grounding fault rises to the line voltage, and the duration is usually up to two hours or longer. Sometimes there will be higher amplitude arc grounding and resonant overvoltage. GB11032 stipulates that the lightning arrester for power stations, distribution and parallel compensation capacitors used in non-effective grounding systems must withstand 24 hours at the lightning arrester and rated voltage, and withstand 2 hours at 1.2~1.3 times the rated voltage.
6.5 Lightning discharge current
6.5.1 The main factors affecting the lightning discharge current The amplitude and steepness of the lightning discharge current through the lightning arrester are related to many factors. In a substation with an arrester or lightning conductor for direct lightning protection, the main factors are:
The geometric parameters of the overhead line connected to the substation (mainly height, width and lightning conductor position), usually the geometric parameters are most affected by the rated voltage of the line;
The lightning impulse withstand voltage of the line insulation of the incoming line segment: b.
The length of the incoming line protection segment. The steepness of the discharge current is determined by the steepness of the lightning overvoltage entering the substation. Due to the attenuation of the overhead line conductor and the different geometric shapes of the connecting line, the steepness of the overvoltage is limited to between 150kV/μus and 1200kV/μs; d.
Line wave impedance;
Tower grounding impedance:
The number of lines connected to the substation when the arrester is activated. Due to the refraction and reflection of the traveling wave, the discharge current of the arrester is affected by the parallel wave impedance of other overhead lines and cable lines connected to the bus f.
line. For power facilities without direct lightning protection, such as distribution transformers or the connection between overhead lines and cables, the protected facilities and lightning arresters may be directly struck by lightning, generating very high and steep voltages and large discharge currents. The current passing through the lightning arrester may be close to the lightning current itself.
2 Selection of nominal discharge current
When selecting the nominal discharge current of the lightning arrester, the following factors should be considered: a.
The importance of the power station, that is, the acceptable risk rate of insulation damage, usually increases with the increase of system voltage. The probability of the occurrence of a discharge current higher than the nominal discharge current. b.
According to GBJ64, most of the overhead lines of 110kV and above are equipped with a lightning arrester along the entire line, and the protection angle is relatively small. According to the statistics of the intrusion wave of distant lightning strikes, the vast majority of lightning currents passing through the arrester are: a. 110220kV system, generally not more than 5kA, in areas with particularly strong power demand activities, imperfect incoming line protection or incoming line segment 103
JB/T589491
When the lightning resistance level does not meet the requirements, it may be greater than 5kA, but less than 10kA; b. 330kV system, generally not more than 10kA;
500kV system, when there are multiple groups of lightning arresters in a substation, each group is not more than 20kA. S.
There is no full-line lightning arrester for lines below 110kV, but from the perspective of technical and economic comparison, a certain risk rate of equipment insulation damage is acceptable. According to the use conditions of the arrester type, the nominal current can be selected from 5kA, 2.5kA and 1kA levels. Nearby lightning strikes are generally not used as a basis for selecting the nominal discharge current, but the arrester should have sufficient large current impulse tolerance. The nominal discharge current of the arrester specified in GB11032 is shown in Table 1: Table 1 Nominal discharge current value of the arrester
Arrester type
Neutral point of motor and transformer
Parallel compensation capacitor
Electrified railway
Long duration discharge capability
System or equipment rated voltage, kV (effective value) 3.15~500
0.220~0. 380
3. 15 ~20. 0
110~500
Nominal current, kA (peak value)
Metal cyanide arresters should have the ability to absorb the energy of the operating impulse current under the following operating overvoltages. a.
Line closing and reclosing;
Opening of unloaded transformers and shunt reactors; Analysis of asymmetric faults and oscillation separation of unloaded lines; Opening of unloaded lines and switching on shunt capacitors: Arc grounding of neutral point non-effectively grounded systems: In order to test the ability of arresters to withstand the overvoltage energy stored on the line under actual operating conditions, GB11032 makes provisions for line discharge tests with reference to the IEC draft standard. If a chain-type impulse current generator with distributed parameters is used to simulate the transmission line, the parameters of each chain of the impulse generator can be changed to simulate different line lengths and wave impedances, and different overvoltage multiples can be simulated in proportion according to different voltage levels, and then discharge to the proportion unit of the tested arrester to form a long-duration impulse current similar to the operating overvoltage. GB11032 stipulates that arresters for systems of 110kV and above (excluding neutral point arresters) must undergo this test and are divided into four levels according to the rated voltage of the system (Table 2). Table 2 specifies the parameters of the distributed parameter impulse generator. When the ratio of the operating impulse residual voltage of the arrester to the rated voltage is constant, the energy obtained increases with the increase of the discharge level. The energy generated in the arrester during the withstand test is largely related to the actual operating residual voltage of the tested resistor. This energy can be calculated with sufficient accuracy according to formula (1): UasiU
W\---Specific energy base determined in the test, its value is equal to the ratio of the total energy absorbed by the arrester during the test to the rated voltage U, kJ/kv;
Residual voltage of the test piece during the line discharge test, kV: Z-Line wave impedance, Q;
JB/T5894-91
T--Apparent duration of the current peak, ms. Table 2 Arrester line discharge test parameters
Arrester nominal discharge
current level, kA
Line discharge isoline
Line wave impedance Z,bzxZ.net
The relationship between specific energy and switching impulse residual pressure is shown in Figure 1. w[]
Apparent duration
time of current, ms
Charging voltage U..kV
Equivalent to the rated
voltage level of the system.kV
Figure 1 Relationship curve between the specific energy (kJ) per kV rated value and the ratio of the arrester operating impulse residual voltage Ur to the effective value of the rated voltage UR Parameters Line discharge level The transmission line parameters corresponding to the arrester line discharge test parameters in Table 2 are shown in Table 3: Table 3 Transmission line parameters
Line discharge level
System rated voltage, kV
Note; The standard value is the peak value of the highest phase voltage of the system, the approximate length of the line, km
The line is roughly approximately impedance, 0
If the system conditions meet Table 3, the line discharge level of the arrester can generally be directly selected according to Table 2. Approximate overvoltage multiple (standard value)
If the system conditions do not meet Table 3 or there are high requirements for the energy absorption capacity of the lightning arrester, the energy absorbed by the lightning arrester can be calculated by the electromagnetic transient calculation program (EMTP) or the transient network analyzer (TNA). This energy divided by the rated voltage of the lightning arrester is the actual required specific energy, and then the corresponding line discharge level is found in Figure 1 based on the specific energy. 105
JB/T5894--91
Note; ① When the intersection of the horizontal and vertical barriers falls between two levels, take the higher level: for the lightning arrester with the same rated voltage, the load-bearing current and current selected by the above method may be higher than the corresponding level in Table 2. In the absence of EMTP and TNA, when the influence of phase-to-phase coupling is ignored, the simple single-phase model is applicable in many cases. The following approximate formula can be used to estimate the operating wave current and energy absorbed by the lightning arrester. Curve a in Figure 2 is the arrester volt-ampere
1,= (te-t),2
wherein: Uov-expected overvoltage:
Z.-.-line wave impedance;
1. Lightning arrester operating wave current
\---Lightning arrester operating wave residual voltage;
T—propagation time of the operating wave from the beginning to the end of the line: W
-energy absorbed by the arrester.
Note: Formula (3) calculates the energy received by the arrester in one operation.
For arresters used in 3~63kV systems, it is not required to carry out the line discharge test specified in the transmission line characteristics. Instead, a 2000us impulse current test with an amplitude of 50~400A should be carried out according to the type and use of the arrester: 6-7 Insulation coordination coefficient
When measuring the degree of insulation coordination according to the customary method, the margin between the insulation level of the equipment and the protection level of the arrester is called the coordination coefficient Ks (the product of the safety factor D and the distance factor Ss). Ks=Insulation level of protected equipment
Protection level of lightning arrester
According to the provisions of GB311.7:
Coordination coefficient under lightning overvoltage
Lightning arrester close to protected equipment Ks>1.25
Lightning arrester not close to protected equipment·Ks>1.4b. Coordination coefficient under operating overvoltage Ks>1.15 D·S
For the coordination coefficients of 330kV and 500kV substations, substations with cable sections and gas insulated substations (GIS), computers or simulation tests can be used to verify the insulation coordination status when necessary, and the danger probability of the substation can also be calculated by statistical methods. 6.8 Pressure release level
In order to prevent the fault current passing through the lightning arrester from causing serious explosion of the lightning arrester casing when there is an internal fault in the lightning arrester, the short-circuit current that the lightning arrester can withstand should not be less than the maximum fault current at the installation location of the lightning arrester, and the pressure release current level of the lightning arrester should be selected accordingly. Based on the service life of the arrester, when selecting the pressure release current level, the maximum short-circuit current (periodic component) effective value that may reach 106
in the system development within 10 years at the installation site can generally be considered. Arrester for special purposes
7.1 Parallel capacitor arrester
JB/T589491
Parallel compensation capacitor bank is a device that needs to be frequently switched. At present, the domestic vacuum circuit breaker used for switching capacitor banks still has the phenomenon of reignition during operation, and overvoltage occurs during reignition, and equipment damage accidents often occur due to this overvoltage. The use of metal oxide arresters to limit the reignition overvoltage of the switching capacitor bank has a significant effect. 7.1.1 Protection connection
Bandpass adopts the protection connection of Figure 3, which can effectively limit the development of single-phase reignition, that is, the relative overvoltage of the capacitor and the neutral point overvoltage of the capacitor bank, and at the same time reduce the probability of two-phase reignition, and limit the overvoltage on the capacitor and reactor within a certain range. Figure 31 Type connection mode
L--parallel reactor iC-parallel capacitor V; S;-metal hydride arrester; Cs\-stray capacitance of capacitor neutral point If it is necessary to further limit the capacitor phase-to-phase overvoltage, the two connection modes of Figures 3 and 4 can be used. The I-type connection mode shown in Figure 4 is composed of four arresters, three of which are connected in parallel at both ends of the capacitor bank Sa2, and the other is connected to the neutral point SNz. This can limit the relative overvoltage of the capacitor and the overvoltage between the poles. It is an ideal protection mode, but the arrester in this connection mode absorbs a lot of energy in the two-phase restrike overvoltage, so the arrester should have a large square wave current capacity.
The type 1 protection connection mode shown in Figure 5 is also a connection mode that can limit the relative overvoltage of the capacitor and the overvoltage between the poles of the capacitor, but there is not much operating experience at present. Figure 4
I type connection mode
Figure 5, type connection mode
L--Series reactor C--Parallel capacitor: S, relative to ground or parallel arrester at both ends of the capacitor Ss-Neutral point arrester; Cs--Capacitor neutral point stray capacitance 107
7.1.2 Selection of main parameters of lightning arrester
7.1.2.1 Rated voltage and DC 1mA voltage JB/T5894-91
Parallel compensation capacitors are mainly used in 3~63kV neutral point non-effective systems. The selection of lightning arrester rated voltage can refer to the principles of Article 6.3. The rated voltage of lightning arrester in type 1 connection mode and lightning arrester Sa in type I connection mode can be selected according to Table 6 in GB11032. The arrester in the I-type connection mode and the arrester S in the straight connection mode only bear the phase voltage in the single-phase grounding fault, so the selection of the rated voltage of the arrester is based on the phase voltage, and Table 6 in GB11032 cannot be directly applied. The rated voltage of these arresters should be determined by calculation on the premise of meeting the insulation coordination requirements, 7.1.2.2 Protection level
Since the busbar is generally equipped with a dedicated lightning arrester, the lightning impulse residual pressure of the shunt capacitor arrester can be considered as that of an ordinary valve arrester. For the level of operating impulse protection, according to the overvoltage protection regulations and the national standards for shunt capacitors, the insulation level of the capacitor to the ground is generally 4 times the highest phase voltage peak value: the insulation level between the capacitor poles is 2.15 times the peak value of the capacitor rated voltage. 7.1.2.3 Square wave current carrying capacity
The requirements for the square wave current carrying capacity of the arrester are related to the capacitor group capacity and the system rated voltage. The square wave current carrying capacity of the arrester in the two types of connection methods, Type I and Type II, can be approximately selected according to Table 5. The values in Table 5 are obtained through calculation. For more important capacitor banks and heavy wiring methods, specific calculations can be performed to obtain the square wave current carrying capacity of the arrester. Table 5
Square wave current carrying capacity of parallel compensation capacitor arrester Arrester connection type
Capacitor bank capacity
20 000
20 000
Square wave current carrying capacity under different system rated voltages 10
Note: The unit of system rated voltage (effective value) in the table is kV. Under a certain system rated voltage, when the capacity of the capacitor bank is greater than the value listed in Table 5, the requirements for the square wave current carrying capacity of the arrester should be recalculated. 7.2 Motor and transformer neutral point lightning arresters
Both theoretical analysis and measured statistics show that the amplitude and steepness of lightning currents passing through motor and transformer neutral point lightning arresters are small, and the rated current of the lightning arrester is 1kA. The rated voltage of the lightning arrester is selected according to the voltage rise of the neutral point when single-phase is grounded. 7.2.1 Motor neutral point lightning arrester
For rotating motors directly connected to overhead lines, if the neutral point can be brought out and terminated For direct grounding, a lightning arrester should be installed at the neutral point. The rated voltage of the lightning arrester should not be lower than the highest phase voltage of the motor. 7.2.2 Transformer neutral point lightning arrester
7.2.2.1 For transformers with graded insulation in a neutral point effective grounding system, when the neutral point is not directly grounded, a lightning arrester should be installed at the neutral point. The rated voltage of the lightning arrester should not be lower than the highest phase voltage of the transformer; 7.2.2.2 For 110kV transformers, when the standard lightning impulse insulation level of the neutral point is 185kV, the rated voltage of the lightning arrester is 60kV; 7.2.2.3 For 500kV transformers, the neutral point is usually dead grounded or grounded via a small impedance. The standard lightning impulse insulation level of the latter's neutral point is 325kV, and the rated voltage of the lightning arrester is 100kV; 108
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.