The overvoltage protection regulations stipulate that the disconnector or circuit breaker of the 110 kV incoming line may often run in open circuit and the line side is charged. Therefore, a set of arrester must be installed close to the disconnector or circuit breaker (proven at home and abroad) , SF6 switch can not be installed, can only install MOA type). According to the practice of domestic power grids, the installation of this group of lightning arresters is carried out by the operating unit itself, because the design department could not determine the operating mode of the line at the beginning, so it is not considered. Some of the power grids have not been able to be fashioned since the substations were put into operation for many reasons. As a result, the circuit breakers were damaged by lightning during hot standby operation. However, when the line is coupled with a coupling capacitor (hereinafter collectively referred to as CC), the line is also struck by lightning, but the circuit breaker in hot standby operation is still safe. Based on this, CC's lightning protection is worth exploring.
1 Thinking about two circuit breaker explosion accidents a) 17:38 June 21, 1996, Shenzhen Power Bureau Fuyong Substation is in hot backup 110kV Fuqiao (Fuyong-Xinqiao) Line 1188 breaker (100-SFM- Type 32B, Japan's Mitsubishi products) L2 arc extinguishers exploded. The direct cause of the accident was a lightning strike. At that time, the string of strings on the circuit flashed, the steel cap broke, and the wire fell to the ground.
b) August 28th, 1998 at 14:18:20 The 110 kV Meihua (Melin-Lianhua Mountain) Line 1153 Circuit Breaker (Model LTB145D1, manufactured by ABB) of the Meilin Substation was in a hot standby state after the lightning stroke was tripped; The circuit breakers L2 and L3 exploded due to the lightning strike again. The direct cause of the accident was a lightning strike. The 7.33 km-long line was struck by lightning at the overhead ground wire at the No. 10 tower, causing the No. 9 and No. 10 wires to lose their overhead ground wire protection.
The similarities in the two accident profiles are as follows: 1) The direct cause is the same as that of lightning; 2) The circuit breaker in the previous example is in hot standby mode; the latter is in hot standby mode after the lightning strike is tripped; 3) The circuit breaker is not added on the line side. Install lightning arresters; 4) Circuit breakers are both internal insulation breakdown explosions; 5) Both plum blossom and Fuqiao are overhead overhead line protection. The differences are as follows: 1) The line L1 of the Meihua Line 1153 line is connected to CC, the L2, L3 phase circuit breaker without CC is broken; 2) The line 1 of Fuqiao Line 1188 is connected to the line CC. The L2 phase circuit breaker arc extinguishment explosion without CC.
From the above phenomenon, it can be seen that the circuit breaker on which the CC is connected has not exploded. The question that this phenomenon gives is that the circuit breaker with CC circuit is not damaged, is it accidental or inevitable? In other words, does CC have lightning protection? If so, how does it play a role in lightning protection? The effect of lightning on the electrical life of CC has no effect. These issues are discussed below.
2 The impact of lightning on the life of the coupling capacitor is known from the structure and lightning protection function. Commonly used valve type and zinc oxide type lightning arresters, the former consists of spark separation and nonlinear resistance (referred to as the valve), the spark gap is mainly responsible for the insulation of the ground Once the thunder and lightning break through the spark gap, the lightning discharge through the non-linear resistance to the earth disappears; the latter is assembled from the zinc oxide resistance sheet, and it is in a very high resistance state to bear the ground insulation during normal operation, and is low when the lightning strikes. The resistance state discharges lightning currents to the ground. Common to both is the release of strong lightning currents through the non-linear resistors and resistors to the earth. However, the coupling capacitor structure does not have a resistive element that conducts a lightning current. Can be seen from Figure 1, which is made of two large capacitive components C1, C2 made. Among them, C1 and C2 are respectively composed of tens of capacitor elements in series with different voltage levels. Each capacitive element is generally composed of three capacitive papers, two polypropylene films, and impregnated dodecylbenzene (OWF type). After C1 and C2 are connected in series, they can withstand the system voltage and the external insulation is a porcelain sleeve. The electric field strength of C1 and C2 (the voltage value per unit thickness of medium) is E=UN/m*d (7)
Type UN - rated voltage, kV;
m - the total number of components in series;
d - the thickness of the dielectric between the poles, mm.
The lower the value of E, the greater the reliability and safety of the work. For general CC type (paper, oil medium) take 9 kV/mm, OWF type take about 8 kV/mm, OWF220/3 type take the lower limit 7.1 kV/mm. The margin is generally more than 30%. In the closed circuit operation, CCs belong to the insulation protection scope (protected by the bus lightning arrester); when the circuit is open in the open circuit (opening end of line) state, the CC will bear a heavy burden - instantaneously receive a large amount of lightning charges, thus Decreasing the steepness of the wavehead makes the lightning voltage at the CC disappear. In contrast to the lightning arrester's de-mining, the CC is to accumulate huge lightning charges on the capacitor plates instead of discharging them through non-metallic insulation. From the perspective of component arrangement and electric field gradient, when a steep thunder and lightning wave hits the CC power supply end with a microsecond speed, theoretically the amount of charge accumulated in each device can be expressed by the following equation:
Ui=mi/Ci (8)
Where ui - the voltage on each capacitive element, V;
Mi - the amount of charge on the plate, C;
Ci - the capacitance of each capacitor, F.
The size of Ci depends on the dielectric constant of the dielectric between the capacitor elements, the area of ​​the plate, and the size of the gap between them, and can be considered as a constant. When the accumulated charge qi on the plate increases, the voltage ui on the element also increases. But the principle that the voltage across the capacitor cannot be abruptly changed is that it takes time for the charge to accumulate on the plate, and the energy storage time is long. When the microsecond-speed high-frequency lightning charge is added to the capacitor, it is like a short circuit instantaneously, so the voltage between the two electrodes cannot be Get increased.
It is considered that overvoltage affects the life of the coupling capacitor. The concept of overvoltage refers to the long-term operation of 1.15UN and 1.95UN of 0.5h. It is also briefly stated that the life of a capacitor is related to the magnitude of overvoltage, the time of action, and the number of interactions.
Regardless of the health condition of the CC from the normal pre-trial or after the lightning, CC's C (total capacitance) breaks one component and the capacitance increases by about 1%; C2 breaks one component and the capacitance increases by about 4%; C1 hits Wearing a component increases the capacity by approximately 1.25%. Replaced when capacitance or tan δ is exceeded. However, from the perspective of engineering management, once an accident such as Meilin 1153 or Fuyong 1188 occurs, an electrical test is performed on CC to grasp the rate of change of its capacity or tan δ, which is undoubtedly valuable.
Although CC has lightning protection, it cannot replace the line arrester. Especially in unattended substations, often the breakers are in hot standby operation, or the operating circuits in the multi-landmine areas are not reunited once they are struck by lightning (this situation is unavoidable). If they are struck by lightning again, they will May cause insulation breakdown in the corresponding switch explosion accident. Therefore, lightning protection should be installed on both sides of the line to avoid recurrence of accidents.
3 Conclusions a) Because of its capacitance between 5 and 20 nF, CC has a significant role in reducing the steepness of lightning waves. This is the key to its lightning protection function, but it is not a lightning wave of any amplitude or steepness. Can defend.
b) CC or wave traps are installed on the line side of the circuit breaker. In addition to reducing the steepness of the wave head, they can also reduce the amplitude of the refracted wave. Under normal circumstances, the lightning wave does not pose a threat to the switch insulation. .
c) Whether the lightning wave has any effect on the electrical life of CC remains to be accumulated in the experiment after it is engaged.
d) The lightning protection function of CC can only serve as a replacement for the system and cannot replace the line arrester.
About the author: Lu Peizhen (1936-), male, Guiyang, Guizhou, senior engineer, is currently engaged in power transformation management.
Author: Shenzhen Power Industry Bureau, Shenzhen, Guangdong 518020
References [1] Solution Guangrun. Power system overvoltage [M]. Beijing: Water Conservancy and Electric Power Press, 1983
[1] Wuhan Institute of Water Conservancy and Electric Power overvoltage protection group. Overvoltage and protection [M]. Beijing: Water Conservancy and Electric Power Press, 1977
1 Thinking about two circuit breaker explosion accidents a) 17:38 June 21, 1996, Shenzhen Power Bureau Fuyong Substation is in hot backup 110kV Fuqiao (Fuyong-Xinqiao) Line 1188 breaker (100-SFM- Type 32B, Japan's Mitsubishi products) L2 arc extinguishers exploded. The direct cause of the accident was a lightning strike. At that time, the string of strings on the circuit flashed, the steel cap broke, and the wire fell to the ground.
b) August 28th, 1998 at 14:18:20 The 110 kV Meihua (Melin-Lianhua Mountain) Line 1153 Circuit Breaker (Model LTB145D1, manufactured by ABB) of the Meilin Substation was in a hot standby state after the lightning stroke was tripped; The circuit breakers L2 and L3 exploded due to the lightning strike again. The direct cause of the accident was a lightning strike. The 7.33 km-long line was struck by lightning at the overhead ground wire at the No. 10 tower, causing the No. 9 and No. 10 wires to lose their overhead ground wire protection.
The similarities in the two accident profiles are as follows: 1) The direct cause is the same as that of lightning; 2) The circuit breaker in the previous example is in hot standby mode; the latter is in hot standby mode after the lightning strike is tripped; 3) The circuit breaker is not added on the line side. Install lightning arresters; 4) Circuit breakers are both internal insulation breakdown explosions; 5) Both plum blossom and Fuqiao are overhead overhead line protection. The differences are as follows: 1) The line L1 of the Meihua Line 1153 line is connected to CC, the L2, L3 phase circuit breaker without CC is broken; 2) The line 1 of Fuqiao Line 1188 is connected to the line CC. The L2 phase circuit breaker arc extinguishment explosion without CC.
From the above phenomenon, it can be seen that the circuit breaker on which the CC is connected has not exploded. The question that this phenomenon gives is that the circuit breaker with CC circuit is not damaged, is it accidental or inevitable? In other words, does CC have lightning protection? If so, how does it play a role in lightning protection? The effect of lightning on the electrical life of CC has no effect. These issues are discussed below.
2 The impact of lightning on the life of the coupling capacitor is known from the structure and lightning protection function. Commonly used valve type and zinc oxide type lightning arresters, the former consists of spark separation and nonlinear resistance (referred to as the valve), the spark gap is mainly responsible for the insulation of the ground Once the thunder and lightning break through the spark gap, the lightning discharge through the non-linear resistance to the earth disappears; the latter is assembled from the zinc oxide resistance sheet, and it is in a very high resistance state to bear the ground insulation during normal operation, and is low when the lightning strikes. The resistance state discharges lightning currents to the ground. Common to both is the release of strong lightning currents through the non-linear resistors and resistors to the earth. However, the coupling capacitor structure does not have a resistive element that conducts a lightning current. Can be seen from Figure 1, which is made of two large capacitive components C1, C2 made. Among them, C1 and C2 are respectively composed of tens of capacitor elements in series with different voltage levels. Each capacitive element is generally composed of three capacitive papers, two polypropylene films, and impregnated dodecylbenzene (OWF type). After C1 and C2 are connected in series, they can withstand the system voltage and the external insulation is a porcelain sleeve. The electric field strength of C1 and C2 (the voltage value per unit thickness of medium) is E=UN/m*d (7)
Type UN - rated voltage, kV;
m - the total number of components in series;
d - the thickness of the dielectric between the poles, mm.
The lower the value of E, the greater the reliability and safety of the work. For general CC type (paper, oil medium) take 9 kV/mm, OWF type take about 8 kV/mm, OWF220/3 type take the lower limit 7.1 kV/mm. The margin is generally more than 30%. In the closed circuit operation, CCs belong to the insulation protection scope (protected by the bus lightning arrester); when the circuit is open in the open circuit (opening end of line) state, the CC will bear a heavy burden - instantaneously receive a large amount of lightning charges, thus Decreasing the steepness of the wavehead makes the lightning voltage at the CC disappear. In contrast to the lightning arrester's de-mining, the CC is to accumulate huge lightning charges on the capacitor plates instead of discharging them through non-metallic insulation. From the perspective of component arrangement and electric field gradient, when a steep thunder and lightning wave hits the CC power supply end with a microsecond speed, theoretically the amount of charge accumulated in each device can be expressed by the following equation:
Ui=mi/Ci (8)
Where ui - the voltage on each capacitive element, V;
Mi - the amount of charge on the plate, C;
Ci - the capacitance of each capacitor, F.
The size of Ci depends on the dielectric constant of the dielectric between the capacitor elements, the area of ​​the plate, and the size of the gap between them, and can be considered as a constant. When the accumulated charge qi on the plate increases, the voltage ui on the element also increases. But the principle that the voltage across the capacitor cannot be abruptly changed is that it takes time for the charge to accumulate on the plate, and the energy storage time is long. When the microsecond-speed high-frequency lightning charge is added to the capacitor, it is like a short circuit instantaneously, so the voltage between the two electrodes cannot be Get increased.
It is considered that overvoltage affects the life of the coupling capacitor. The concept of overvoltage refers to the long-term operation of 1.15UN and 1.95UN of 0.5h. It is also briefly stated that the life of a capacitor is related to the magnitude of overvoltage, the time of action, and the number of interactions.
Regardless of the health condition of the CC from the normal pre-trial or after the lightning, CC's C (total capacitance) breaks one component and the capacitance increases by about 1%; C2 breaks one component and the capacitance increases by about 4%; C1 hits Wearing a component increases the capacity by approximately 1.25%. Replaced when capacitance or tan δ is exceeded. However, from the perspective of engineering management, once an accident such as Meilin 1153 or Fuyong 1188 occurs, an electrical test is performed on CC to grasp the rate of change of its capacity or tan δ, which is undoubtedly valuable.
Although CC has lightning protection, it cannot replace the line arrester. Especially in unattended substations, often the breakers are in hot standby operation, or the operating circuits in the multi-landmine areas are not reunited once they are struck by lightning (this situation is unavoidable). If they are struck by lightning again, they will May cause insulation breakdown in the corresponding switch explosion accident. Therefore, lightning protection should be installed on both sides of the line to avoid recurrence of accidents.
3 Conclusions a) Because of its capacitance between 5 and 20 nF, CC has a significant role in reducing the steepness of lightning waves. This is the key to its lightning protection function, but it is not a lightning wave of any amplitude or steepness. Can defend.
b) CC or wave traps are installed on the line side of the circuit breaker. In addition to reducing the steepness of the wave head, they can also reduce the amplitude of the refracted wave. Under normal circumstances, the lightning wave does not pose a threat to the switch insulation. .
c) Whether the lightning wave has any effect on the electrical life of CC remains to be accumulated in the experiment after it is engaged.
d) The lightning protection function of CC can only serve as a replacement for the system and cannot replace the line arrester.
About the author: Lu Peizhen (1936-), male, Guiyang, Guizhou, senior engineer, is currently engaged in power transformation management.
Author: Shenzhen Power Industry Bureau, Shenzhen, Guangdong 518020
References [1] Solution Guangrun. Power system overvoltage [M]. Beijing: Water Conservancy and Electric Power Press, 1983
[1] Wuhan Institute of Water Conservancy and Electric Power overvoltage protection group. Overvoltage and protection [M]. Beijing: Water Conservancy and Electric Power Press, 1977
Hastelloy C,Hastelloy Forgings,Chlorine Resistance
NiCr alloy Super alloy Co., Ltd. , http://www.chromiumaluminium.com