【Weekly Topic】Week 13 of 2011: What should be noted when using capacitors?

Regularly monitor the temperature of the terminals and the capacitor body, and measure the current in each phase

　Answer: (1) Mainly observe whether there is any oil leakage, overheating, abnormal noises or electrical discharge flashovers on the outside, as well as any swelling. 　　(2) Whether the fuse wire of the fuse is normal, and whether the discharge indicator light has gone out. 　　(3) Are the voltmeter, ammeter, and temperature indicator functioning normally?

(1) The operating voltage must not exceed the rated voltage of the capacitor； 　　(2) The capacitor temperature should not exceed the specified value ； 　　(3) After the protection device trips automatically, power shall not be forced to be supplied; the cause must be identified and the fault corrected. Only after it is confirmed that there is no fault can the capacitor be put back into operation ； 　　(4) The capacitor must be fully discharged before it is put back into operation; it is strictly prohibited to close the switch with the capacitor still charged ； 　　(5) If the capacitor casing expands, leaks electricity, or sparks occur, use should be stopped immediately ； 　　(6) The capacitor enclosure shall be reliably grounded.

The issues that need to be considered during the operation of capacitors, along with the corresponding solutions, are outlined as follows: 1. Ambient temperature – The temperature of the environment surrounding the capacitor should not be too high nor too low. If the ambient temperature is too high, the heat generated by the capacitor during operation cannot dissipate ； And if the ambient temperature is too low, the oil inside the capacitor may freeze, leading to easy electrical breakdown. According to the technical specifications for capacitors, the operating ambient temperature for capacitors is generally limited to 40°C as a maximum. Temperatures in most areas of our country are below this level, so special cooling facilities are generally not necessary. If there is a heat source near the capacitor, it is possible for the room temperature to rise above 40°C; in such cases, ventilation measures should be taken to reduce the temperature, or else the capacitor should be disconnected immediately. 　　The lower limit of the ambient temperature for capacitors should be determined based on the type and properties of the dielectric in the capacitor. The dielectric in YY-type capacitors is mineral oil, which does not freeze even at temperatures below -45°C. Therefore, -40°C is specified as the lower limit for the ambient temperature. The dielectric in YL-type capacitors is prone to freezing; therefore, the ambient temperature must be above -20°C. In northern regions of China, these capacitors should not be used during winter. (Unless it is placed indoors with heating measures in place) 2? Operating temperature The temperature of the dielectric material inside the capacitor should be below 65°C, with a maximum of 70°C; otherwise, it may lead to thermal breakdown or swelling of the capacitor. The temperature of the capacitor casing lies between the dielectric temperature and the ambient temperature, typically ranging from 50 to 60°C, and it must not exceed 60°C. 　　To monitor the temperature of the capacitor, the probe of a tung oil plaster thermometer can be attached to the middle two-thirds height of the large surface of the capacitor casing; alternatively, a temperature-testing wax strip with a melting point of 50–60°C can be used. 　　3? Operating Voltage Capacitors are highly sensitive to voltage, as their losses are proportional to the square of the voltage. Excessive voltage can cause the capacitor to overheat significantly, accelerate the aging of its insulation, shorten its lifespan, and even lead to electrical breakdown. The grid voltage should generally be lower than the rated voltage of the capacitor itself, with a maximum not exceeding 10% of its rated voltage. It should be noted, however, that the maximum operating voltage and the maximum operating temperature cannot occur simultaneously. Therefore, when the operating voltage is 1.1 times the rated voltage, cooling measures must be taken. 　　4? Operating current and harmonic issues When capacitors are installed in a power grid that contains \"harmonic sources\" such as magnetically saturated voltage regulators, large rectifiers, and arc furnaces, high-order harmonics appear in the alternating current. For the n-th harmonic, the reactance of the capacitor is 1/n of that at the fundamental frequency; therefore, the effect of harmonics on the current is quite significant. Such harmonic currents are extremely harmful to capacitors, as they can easily cause the capacitors to break down and lead to inter-phase short circuits. Considering the presence of harmonics, it is stipulated that the operating current of capacitors must not exceed 1/3 of their rated current. If necessary, an appropriate inductive reactance should be connected in series with the capacitor to limit harmonic currents. 　　5? Arcing issue during switching on 　 Certain capacitor banks, especially high-voltage capacitors, experience arcing at the switches or converters due to the large inrush current that occurs when they are switched on and connected to the grid. In such cases, the capacitance value of the capacitor bank should be adjusted or the converter replaced; for high-voltage capacitors, series reactors can be used to eliminate the issue. 　　6? Problem of discharge noise during operation Generally, capacitors make no sound when in operation, but there are exceptions. The causes of the sound are roughly as follows: (1) Bushing discharge. If the capacitor’s bushings are of the assembled type, and it is left outdoors for an extended period of time, rainwater can seep between the two layers of bushings; when voltage is applied, this can result in crackling discharge sounds. In such cases, the outer tube can be loosened, dried, and then reinstalled. 　　(2) Discharge due to lack of oil. If there is a severe lack of oil in the capacitor, to the point where the lower end of the bushing emerges above the oil level, it is possible for a discharge sound to be heard. To this end, capacitor oil of the same specification should be added. 　　(3) Desoldering discharge. If there is a poor solder joint or a detached solder joint inside the capacitor, flashover discharge will occur in the oil. If the discharge noise persists, it should be disassembled for repair. 　　(4) Poor grounding discharge. When the core of a capacitor has poor contact with its casing, a floating voltage appears, causing a discharge sound. At this point, simply shaking the capacitor to bring the core into contact with the casing will eliminate the discharge sound. 　　7? Explosion issue When multiple groups of capacitors are connected in parallel, if one of them breaks down, the remaining capacitors will all discharge through that failed capacitor at the same time. The discharge energy is very high, and the pulse power is extremely high, causing the capacitor oil to vaporize rapidly and leading to an explosion or even a fire; in severe cases, it can also cause damage to buildings. To prevent such accidents, an appropriate reactor or fuse can be connected in series with each capacitor, and then they can be used in parallel. Furthermore, although using a Δ connection for the capacitors used for parallel compensation in power systems has many advantages, when one of these capacitors breaks down and short-circuits, it causes a short circuit between two of the three phases; the resulting short-circuit current is very high, and this can lead to the explosion of the capacitor. This is particularly dangerous for high-voltage capacitors. Therefore, high-voltage capacitor banks should be connected in a star (Y) configuration with an ungrounded neutral point; when their capacity is low (450 kvar and below), they should be connected in a delta configuration. Low-voltage capacitor banks should be connected in a Δ configuration.

Issues to note when using capacitors in operation: 1. Ambient temperature. 　　The temperature of the environment surrounding the capacitor should not be too high nor too low. If the ambient temperature is too high, the heat generated during the capacitor’s operation cannot be dissipated ； If the ambient temperature is too low, the oil inside the capacitor may freeze, leading to easy electrical breakdown. According to the technical specifications for capacitors, the operating ambient temperature for capacitors is generally limited to 40°C as a maximum. 2. Operating temperature. 　　When a capacitor is in operation, the temperature of its internal dielectric should be below 65°C, with a maximum of 70°C; otherwise, it may lead to thermal breakdown or bulging. 3. Operating voltage. 　　Capacitors are highly sensitive to voltage, as their losses are proportional to the square of the voltage. Overvoltage can cause the capacitor to heat up significantly, accelerate the aging of its insulation, shorten its lifespan, and even lead to breakdown. 4. Operating current and harmonic issues. 　　Harmonic currents are very harmful to capacitors, as they can easily cause the capacitors to break down and lead to inter-phase short circuits. Considering the presence of harmonics, it is stipulated that the operating current of capacitors shall not exceed 13 times the rated current. If necessary, an appropriate inductive reactance should be connected in series with the capacitor to limit harmonic currents. 5. Arc problem during closing. 　　When certain capacitor banks, especially high-voltage capacitors, are switched on and connected to the grid, arcing may occur at the switches or converters due to the large inrush current. In such cases, the capacitance value of the capacitor bank should be adjusted or the converter should be replaced; for high-voltage capacitors, series reactors can be used to eliminate this issue. 6. Problem with discharge noise during operation. 　　Capacitors generally make no noise when in operation, but there are exceptions sometimes. 7. Explosion issue When multiple groups of capacitors are connected in parallel, if one of them breaks down, the remaining capacitors will discharge through that faulty one at the same time. The discharge energy is very high, and the pulse power is extremely high, causing the capacitor oil to vaporize rapidly and leading to explosions or even fires; in severe cases, it can also cause damage to buildings. To prevent such accidents, an appropriate reactor or fuse can be connected in series with each capacitor, and then they can be used in parallel.

Pay main attention to whether its connectors are loose or if the temperature is too high； Also, has the volume of the capacitor changed?

In power systems, power capacitors are primarily used for reactive power compensation or phase shifting, and they are installed in large numbers in substations at various levels. The proper operation of these capacitors plays an important role in ensuring the quality and efficiency of power supply in power systems. Below, we introduce the issues that should be noted during the operation of power capacitors and the corresponding handling methods. 1. Ambient temperature: The temperature of the environment surrounding the capacitor should not be too high nor too low. If the ambient temperature is too high, the heat generated during the capacitor’s operation cannot be dissipated ； If the ambient temperature is too low, the oil inside the capacitor may freeze, leading to easy electrical breakdown. According to the technical specifications related to capacitors, the operating ambient temperature for capacitors is generally limited to 40°C as a maximum. Temperatures in most parts of our country are below this level, so special cooling facilities are generally not necessary. If there is a heat source near the capacitor that could raise the room temperature above 40°C, ventilation measures should be taken to cool down the area; otherwise, the capacitor should be disconnected immediately. The lower limit of the ambient temperature for capacitors should be determined based on the type and properties of the dielectric in the capacitor. The dielectric in YY-type capacitors is mineral oil, which does not freeze even at temperatures below -45°C; therefore, -40°C is specified as the lower limit for the operating temperature. The dielectric in YL-type capacitors is prone to freezing; therefore, the ambient temperature must be above -20°C. In northern regions of China, it is not advisable to use such capacitors during winter. (Unless it is placed indoors with heating measures in place) 2. Operating temperature: When the capacitor is in operation, the temperature of its internal dielectric should be below 65°C, with a maximum of 70°C; otherwise, thermal breakdown or bulging may occur. The temperature of the capacitor casing lies between the dielectric temperature and the ambient temperature; it is generally 50–60°C and must not exceed 60°C. To monitor the temperature of the capacitor, a probe from a tung oil lime thermometer can be attached to the capacitor casing at two-thirds of its height along the larger surface, or a temperature-sensitive wax strip with a melting point of 50–60°C can be used. 3. Operating voltage: Capacitors are highly sensitive to voltage, as their losses are proportional to the square of the voltage. Overvoltage can cause the capacitor to heat up significantly, accelerate the aging of its insulation, shorten its lifespan, and even lead to breakdown. The grid voltage should generally be lower than the rated voltage of the capacitor itself, with a maximum of 10% above that rated voltage. It should be noted, however, that the maximum operating voltage and the maximum operating temperature cannot occur simultaneously. Therefore, when the operating voltage is 1.1 times the rated voltage, cooling measures must be taken. 4. Operating current and harmonic issues: When capacitors are installed in a power grid that contains \"harmonic sources\" such as magnetically saturated voltage regulators, large rectifiers, and arc furnaces, high-order harmonics appear in the alternating current. For the n-th harmonic, the reactance of the capacitor is 1/n of that at the fundamental frequency; therefore, harmonics have a significant impact on the current. Such harmonic currents are extremely harmful to capacitors, as they can easily cause the capacitors to break down and lead to inter-phase short circuits. Considering the presence of harmonics, it is stipulated that the operating current of capacitors must not exceed 1.3 times the rated current. If necessary, an appropriate inductive reactance should be connected in series with the capacitor to limit harmonic currents. 5. Arcing issue during switching on: Certain capacitor banks, especially high-voltage capacitors, experience arcing on the switches or converters due to the large inrush current that occurs when they are switched on and connected to the grid. In such cases, the capacitance value of the capacitor bank should be adjusted or the converter replaced; for high-voltage capacitors, series reactors can be used to eliminate the issue. 6. Problem of discharge noise during operation: Capacitors generally make no sound when in operation, but exceptions do occur sometimes. The main causes of sound are as follows: (1) Casing discharge. If the capacitor’s bushing is of the assembled type, and it is left outdoors for an extended period of time, rainwater can seep between the two layers of the bushing; when voltage is applied, this can result in crackling discharge sounds. In such cases, the outer sleeve can be loosened, dried, and reinstalled. (2) Oil-deficient discharge. If there is a severe lack of oil in the capacitor, to the point where the lower end of the bushing emerges above the oil level, it is possible for a discharge sound to be heard. To this end, capacitor oil of the same specification should be added. (3) Desoldering discharge. If there is a poor solder joint or a detached solder joint inside the capacitor, flashover discharge will occur in the oil. If the discharge sound persists, it should be disassembled for repair. (4) Poor grounding discharge. When the core of a capacitor has poor contact with its casing, a floating voltage appears, causing a discharge sound. At this point, simply shaking the capacitor to bring the core into contact with the casing will eliminate the discharge sound. 7. Explosion issue: When multiple groups of capacitors are connected in parallel, if one of them breaks down, the remaining capacitors will discharge through that failed capacitor at the same time. The high discharge energy and high pulse power cause the capacitor oil to vaporize rapidly, leading to explosions or even fires; in severe cases, it can also damage buildings. To prevent such accidents, an appropriate reactor or fuse can be connected in series with each capacitor, and then they can be used in parallel. Furthermore, although using a Δ connection for the capacitors used for parallel compensation in power systems has many advantages, when a capacitor in this configuration breaks down and short-circuits, it causes a short circuit between two of the three phases; the resulting short-circuit current is very high, which can lead to the explosion of the capacitor. This is particularly dangerous for high-voltage capacitors. Therefore, high-voltage capacitor banks should be connected in a star (Y) configuration with an ungrounded neutral point; when their capacity is low (450 kvar and below), they should be connected in a delta configuration. Low-voltage capacitor banks should be connected in a Δ configuration.

During study*, Moderator Xie....

Reply to 1# zhaohh3211: 1. Ambient temperature – The ambient temperature around the capacitor should not be too high nor too low. If the ambient temperature is too high, the heat generated by the capacitor during operation cannot be dissipated ； If the ambient temperature is too low, the oil inside the capacitor may freeze, leading to easy electrical breakdown. According to the technical specifications related to capacitors, the operating ambient temperature for capacitors is generally limited to 40°C as a maximum. Temperatures in most parts of our country are below this level, so special cooling facilities are generally not necessary. If there is a heat source near the capacitor, it is possible for the room temperature to rise above 40°C; in such cases, ventilation measures should be taken to reduce the temperature, or the capacitor should be disconnected immediately. The lower limit of the ambient temperature for capacitors should be determined based on the type and properties of the dielectric in the capacitor. The dielectric in YY-type capacitors is mineral oil, which does not freeze even at temperatures below -45°C; therefore, -40°C is specified as the lower limit for the operating temperature. The dielectric in YL-type capacitors freezes more easily, so the ambient temperature must be above -20°C. 2. Operating temperature: When the capacitor is in operation, the temperature of its internal dielectric should be below 65°C, with a maximum of 70°C; otherwise, it may lead to thermal breakdown or bulging of the capacitor. The temperature of the capacitor casing lies between the dielectric temperature and the ambient temperature; it is generally 50–60°C and must not exceed 60°C. To monitor the temperature of the capacitor, the thermometer probe can be attached to the front surface of the capacitor casing at a height of two-thirds up from the bottom using tung oil and lime, or a temperature-measuring wax strip with a melting point of 50–60°C can be used for measurement. 3. Operating voltage: Capacitors are highly sensitive to voltage, as their losses are proportional to the square of the voltage. Overvoltage can cause the capacitor to heat up significantly, accelerate the aging of its insulation, shorten its lifespan, and even lead to breakdown. The grid voltage should generally be lower than the rated voltage of the capacitor itself, with a maximum not exceeding 10% of its rated voltage. It should be noted, however, that the maximum operating voltage and the maximum operating temperature cannot occur simultaneously. Therefore, when the operating voltage is 1.1 times the rated voltage, cooling measures must be taken. 4. Operating current and harmonic issues: When capacitors operate in a power grid that contains \"harmonic sources\" such as magnetically saturated voltage regulators, large rectifiers, and arc furnaces, higher-order harmonics appear in the alternating current. For the n-th harmonic, the reactance of the capacitor is 1/n of that at the fundamental frequency; therefore, the effect of harmonics on current is significant, equivalent to n2 times the degree of influence on voltage. For example, in the case of the 5th harmonic, if its reactive power is 6% of that of the fundamental wave, then the voltage it causes is only (1/5)×6% = 1.2% of the fundamental voltage rating, whereas the current it generates is as high as 5×6% = 30% of the fundamental current. Such harmonic currents are extremely harmful to capacitors, as they can easily cause the capacitors to break down and lead to inter-phase short circuits. Considering the presence of harmonics, it is specified that the operating current of the capacitor shall not exceed 1.3 times the rated current. If necessary, an appropriate inductive impedance should be connected in series with the capacitor to limit harmonic currents. 5. Arcing issue during closing: Certain capacitor banks, especially high-voltage capacitors, experience arcing on the circuit breaker or converter due to the large inrush current that occurs when they are connected to the grid. In such cases, the capacitance value of the capacitor bank should be adjusted or the converter replaced; for high-voltage capacitors, series reactors can be used to eliminate this issue. 6. Problem of discharge noise during operation: Capacitors generally make no sound when in operation, but exceptions do occur sometimes. The main causes of sound are as follows: (1) Casing discharge. If the capacitor’s bushing is of the assembled type, and it is left outdoors for an extended period of time, rainwater can seep between the two layers of the bushing; when voltage is applied, this can result in crackling discharge sounds. At this point, the capacitor can be taken out of service and discharged, after which the outer tube can be removed, dried, and reinstalled. (2) Discharge due to lack of oil. If there is a severe lack of oil in the capacitor, to the point where the lower end of the bushing emerges above the oil level, it is possible for a discharge sound to be heard. To this end, capacitor oil of the same specification should be added. (3) Desoldering discharge. If there is a poor solder joint or a detached solder joint inside the capacitor, flashover discharge will occur in the oil. If the discharge sound persists, it should be disassembled for repair. (4) Poor grounding discharge. When the core of a capacitor has poor contact with its casing, a floating voltage appears, causing a discharge sound. At this point, the discharge sound can be eliminated by shutting down the capacitor, discharging it, and then ensuring good contact between its core and casing. 7. Explosion issue: When multiple groups of capacitors are connected in parallel, if one of them breaks down, the remaining capacitors will discharge through that faulty one at the same time. The high discharge energy and high pulse power cause the capacitor oil to vaporize rapidly, leading to an explosion or even a fire; in severe cases, it can also cause damage to buildings. To prevent such accidents, an appropriate reactor or fuse can be connected in series with each capacitor, and then they can be operated in parallel.