TWI693768B - Method for monitoring capacitance value of capacitor in power system - Google Patents

Abstract

The invention is a method for monitoring the capacitance value of a capacitor of a power system, which is applied to a power monitoring device of a power system, which includes a current transformer connected to a capacitor as a tuned filter for power factor improvement or harmonic absorption in the power system The current value (specifically the fundamental wave current or the current value containing harmonics) and voltage value (specifically the fundamental wave voltage or the voltage value containing harmonics) from the voltage comparator are calculated according to the current value and the voltage value After the invalid power output of the capacitor, the capacitance value of the capacitor is calculated based on the calculated invalid power output, and the calculated capacitance value is compared with the rated value of the capacitor to judge whether the capacitor is attenuated or damaged.

Description

Method for monitoring capacitance value of capacitor in power system

The present invention relates to capacitors, in particular to a method for monitoring the capacitance value of capacitors for improving power factor or filtering harmonics in power systems.

When the load is connected in the power system, there will be both effective power and ineffective power, and the effective power is the total output power (called apparent power), in which the transmission of ineffective power requires a higher voltage and increases the transmission line Power loss and increase line current. Therefore, capacitors are installed in the power system to improve the power factor of the power system. In the power system, improving the power factor, in addition to reducing the supply of invalid power, can also reduce the line loss between the power supply end and the power consumption end, improve the voltage and increase the capacity of the power system.

Furthermore, too high a power factor (eg more than 100%) will also affect the quality of power supply, which means that too large capacitors cannot be installed without restrictions in order to improve the power factor, because when the capacitor is installed too large, the power factor improvement benefit It is not obvious that, in addition to increasing the cost, the excessive compensation will increase the invalid current, which will cause a double loss of equipment investment and performance. Even when the power factor is ahead, it may cause a situation where the voltage is too high, affecting the operation safety of the power system.

In addition, power suppliers charge electricity to consumers based on power factor. In terms of the current electricity tariffs of the Taiwan Power Company, when the average power factor is less than 80%, for every 1% lower, the electricity fee needs to increase by 0.1% in that month; and When it exceeds 80%, for every 1%, the electricity bill should be reduced by 0.1% in that month, and the average power factor exceeding 95% will not be deducted. Therefore, if the power system is appropriate Installing capacitors on the ground and maintaining the power factor between 80% and 95% will reduce electricity costs.

According to the above, capacitors need to be properly installed in the power system to correct the power factor to an appropriate value. In other words, if the capacitor is damaged or does not operate normally, the power factor of the power system cannot be maintained at an appropriate value. Between values. However, when the current power system is in operation, it cannot measure or monitor the capacitor, nor can it know whether the capacitor is aging or damaged, so that the user cannot replace the capacitor in time, resulting in the power system unable to maintain an appropriate power factor. How to effectively measure or monitor capacitors in the power system under active operation is a problem that needs to be solved urgently.

In view of the problem that the power system in the operating state in the prior art cannot lively measure or monitor the capacitor, an object of the present invention is to measure or monitor the capacitor in the power system under the operating state of the power system. Especially for the power system to measure or monitor the capacitors of filters that improve power factor or absorb harmonics.

In order to achieve the above purpose, the present invention provides a method for monitoring the capacitance value of a capacitor of a power system, which is applied to a power monitoring device of a power system and includes the following steps: receiving tuning in a power system as power factor improvement or harmonic absorption The current value (specifically the fundamental wave current or the current value containing harmonics) and the voltage value (specifically the fundamental wave voltage or the voltage value containing harmonics) from the current transformer and voltage regulator connected to the capacitor of the filter ), calculate the reactive power output based on the current and voltage values, and then calculate the capacitor's capacitance based on the reactive power output to determine whether the capacitor is attenuated or damaged based on the calculated capacitance.

Among them, the way to judge whether the capacitor is attenuated or damaged is to compare the calculated capacitance value with the rated value of the capacitor, and then determine whether the capacitor is attenuated or damaged.

Among them, the way of comparing the capacitance value with the rated value of the capacitor is to calculate the difference between the capacitance value and the rated value of the capacitor, and when the difference exceeds the threshold value preset by the power monitoring equipment, it is lower than the international electrician (IEC60831 With the -5% capacitance value standard stipulated by IEC60871) regulations, it means that the capacitor has been attenuated or the internal capacitive components are partially damaged.

Among them, when the difference does not exceed the threshold value preset by the power monitoring equipment, it means that the capacitor and the filter are still usable.

According to the above, the present invention has one or more of the following advantages:

1. Under the operating state of the power system, live line measurement or live line monitoring can be performed on the capacitor as a tuned filter for power factor improvement or harmonic absorption in the power system.

2. Whether the capacitor of the power system is connected in series or not, it can be accurately measured or monitored.

3. Whether it is a three-phase high-voltage capacitor, low-voltage capacitor and filter, or a single-phase high and low-voltage capacitor and filter as a tuned filter for power factor improvement or harmonic absorption in the power system, the capacitance can be accurately measured or monitored value.

S101~S104, S201~S206, S301~S306

Fig. 1 is a schematic flow diagram of the present invention; Fig. 2 is a schematic flow diagram of a single-phase capacitor series or non-series reactor of the invention; Fig. 3 is a schematic flow diagram of a three-phase capacitor series or non-series reactor of the invention .

The spirit of the present invention will be illustrated in the following figures and in detail. Any person with ordinary knowledge in the art can understand what is preferred by the present invention after understanding the preferred embodiments of the present invention. The technology is changed and modified without departing from the spirit and scope of the present invention.

Please refer to FIG. 1, which is a schematic flowchart of the present invention. As shown in the figure, the present invention is a method for monitoring the capacitance value of a capacitor of a power system, which is applied to a power monitoring device of a power system, wherein the capacitor is used to improve the power factor of the power system or absorb the main harmonics generated by the power system For tuned filters, this method includes the following steps: (S101) Receive the current value (specifically the fundamental current or harmonics) from the current transformer and the voltage transformer connected to the power factor correction capacitor in the power system (Current value of the wave) and voltage value (specifically the fundamental voltage or the voltage value with harmonics); (S102) calculate the reactive power output of the capacitor based on the current value and voltage value; (S103) calculate the reactive power output based on the reactive power output The capacitance value of the capacitor; (S104) The difference between the calculated capacitance value and the rated value of the capacitor is determined according to the difference to determine whether the capacitor is attenuated or the internal capacitance element is partially damaged.

Since three-phase capacitors or single-phase capacitors may be used to modify the power factor in the power system, and capacitors may be connected in series or not in series, in the present invention, for different combinations of states, there are different The equation calculates the reactive power output of the capacitor. The different combinations of the above are explained as follows:

Please refer to FIG. 2, which is a schematic flow chart of the present invention using single-phase capacitors connected in series or not in series. As shown in the figure, when the capacitor is a single-phase capacitor and its series reactor is used, the calculation formula of its reactive power output is as follows: R-phase secondary reactive power output = (R-phase secondary current value × R-phase secondary voltage value ÷ ( 1-Reactor impedance ratio))×(Capacitor rated voltage/(R-phase secondary voltage value÷(1-Reactor impedance ratio))) ² ; S-phase secondary power output = (S-phase secondary current value×S Phase voltage value÷(1-Reactor impedance ratio))×(Capacitor rated voltage/(S-phase secondary voltage value÷(1-Reactor impedance ratio))) ² ; T-phase secondary power output = (T Phase current value × T phase secondary voltage value ÷ (1-reactor impedance ratio)) × (capacitor rated voltage/(T phase secondary voltage value ÷ (1-reactor impedance ratio))) ² .

When the capacitor is a single-phase capacitor and no reactor is connected in series, the calculation formula of its reactive power output is as follows: R-phase secondary reactive power output = R-phase secondary current value×R-phase secondary voltage value×(capacitor rated voltage/R Phase voltage value) ² ; S phase secondary reactive power output = S phase secondary current value × S phase secondary voltage value × (capacitor rated voltage/S phase secondary voltage value) ² ; T phase secondary reactive power output = T phase Secondary current value × T phase secondary voltage value × (capacitor rated voltage/T phase secondary voltage value) ² .

However, regardless of whether the single-phase capacitor is connected in series or not, the calculation formula of the secondary capacitance value of each phase of the single-phase capacitor is the following formula: R-phase secondary capacitance value=the R-phase secondary ineffective power output/(2×π×power supply Frequency×capacitor rated voltage ² ); S-phase secondary capacitance value=the S-phase secondary reactive power output/(2×π×supply frequency×capacitor rated voltage ² ); T-phase secondary capacitive value=the T-phase secondary reactive power output Amount/(2×π×power supply frequency×capacitor rated voltage ² ).

As such, when the power monitoring equipment monitors the single-phase capacitor for the power system, the processing flow is as follows:

(S201) The current transformer connected to the power factor correction capacitor in the receiving power system and Current value and voltage value transmitted by voltage regulator;

(S202) Determine whether the capacitor is connected in series with the reactor;

(S203) When the capacitor is connected in series with the reactor, calculate the reactive power output of the capacitor according to the following formula, and then proceed to step (S205): R-phase secondary reactive power output = (R-phase secondary current value × R-phase secondary voltage value ÷ ( 1-Reactor impedance ratio))×(Capacitor rated voltage/(R-phase secondary voltage value÷(1-Reactor impedance ratio))) ² ; S-phase secondary power output = (S-phase secondary current value×S Phase voltage value÷(1-Reactor impedance ratio))×(Capacitor rated voltage/(S-phase secondary voltage value÷(1-Reactor impedance ratio))) ² ; T-phase secondary power output = (T Phase current value × T phase secondary voltage value ÷ (1-reactor impedance ratio)) × (capacitor rated voltage/(T phase secondary voltage value ÷ (1-reactor impedance ratio))) ² .

(S204) When the capacitor is not connected in series with the reactor, calculate the reactive power output of the capacitor according to the following formula, and then proceed to step (S205): R phase secondary reactive power output = R phase secondary current value×R phase secondary voltage value×( Capacitor rated voltage/R phase secondary voltage value) ² ; S phase secondary reactive power output = S phase secondary current value × S phase secondary voltage value × (capacitor rated voltage/S phase secondary voltage value) ² ; T phase secondary invalid power Output = T-phase secondary current value × T-phase secondary voltage value × (capacitor rated voltage/T-phase secondary voltage value) ² .

(S205) Calculate the capacitance value of the capacitor according to the following formula: R-phase secondary capacitance value=the R-phase secondary reactive power output/(2×π×power supply frequency×capacitor rated voltage ² ); S-phase secondary capacitance value=the S-phase Secondary reactive power output/(2×π×power supply frequency×capacitor rated voltage ² ); T-phase secondary capacitance value=the T-phase secondary reactive power output/(2×π×power supply frequency×capacitor rated voltage ² ).

(S206) The difference between the calculated capacitance value and the rated value of the capacitor is determined according to the difference to determine whether the capacitor is attenuated or damaged.

However, the calculation method for the single-phase capacitors of each phase mentioned above can be integrated into the following calculation formula:

When a single-phase capacitor is connected in series with the reactor: reactive power output = (current value × voltage value ÷ (1-reactor impedance ratio)) × (capacitor rated voltage/(voltage value ÷ (1-reactor impedance ratio)) ) ² .

When a single-phase capacitor is not connected in series with reactor: reactive power output = current value × voltage value × (capacitor rated voltage / voltage value) ² .

Capacitance value of single-phase capacitor: capacitance value = the reactive power output/(2×π×power supply frequency×capacitor rated voltage ² ).

For example, the actual R-phase secondary capacitor operating voltage is 1,925V, the capacitor's actual R-phase secondary capacitor operating current is 96.6Amp, the capacitor rated voltage is 2,310V, and the reactor impedance ratio is 6%, when a single-phase capacitor is connected in series with the reactor If the above formula is introduced, the reactive power output of the R phase is: (1,925V×96.6Amp÷(1-6%))×(2,310V/(1,925V÷(1-6%)) ) ² =251.708kvar

And the capacitance value of its R-phase secondary capacitor will be: 251.708kvar÷(2×π×60Hz×2,310V ² )=125 microfarad.

However, when no reactor is connected in series with the R-phase secondary capacitor, the reactive power output of the R-phase secondary capacitor is: 1,925V×96.6Amp×(2,310V/1,925V) ² =267.775kvar.

The capacitance value of the R-phase secondary capacitor will be: 267.775kvar÷(2×π×60Hz×2,310V ² )=132 microfarad (microfarad).

In this way, the capacitance value obtained above can be subtracted from the rated value of the capacitor to obtain a difference, so as to determine whether the capacitor is attenuated or damaged according to the difference.

In addition, even if the single-phase capacitor group is connected in series with more than six capacitors, even hundreds or thousands of capacitors, you can use the calculation formula disclosed above to calculate the capacitance of each capacitor, which is effective Calculate the capacitance of multiple capacitors to determine whether each capacitor is attenuated or damaged.

Please refer to FIG. 3, which is a schematic flow chart of the present invention using three-phase capacitors connected in series or not in series as an example. As shown in the figure, when the capacitor is a three-phase capacitor and its reactor is connected in series, the calculation formula of the reactive power output of each phase of the three-phase capacitor is as follows:

器額定電壓/RS相次電壓值)²；

However, when the capacitor is a three-phase capacitor, and the reactor is not connected in series, the calculation formula of the ineffective power output of each phase of the three-phase capacitor is as follows:

Device rated voltage/RS phase voltage value) ² ;

However, regardless of whether the three-phase capacitors are connected in series or not, the calculation formula of the secondary capacitance value of each phase of the three-phase capacitor is the following formula: RS phase secondary capacitance value = the RS phase secondary reactive power output/(2×π×power supply Frequency×capacitor rated voltage ² )÷2; ST phase secondary capacitance value=the ST phase secondary reactive power output/(2×π×power supply frequency×capacitor rated voltage ² )÷2; RT phase secondary capacitor value=the RT phase Secondary reactive power output/(2×π×power supply frequency×capacitor rated voltage ² )÷2.

In the present invention, the power monitoring equipment can provide a choice of whether to use single-phase capacitors, three-phase capacitors and whether they are connected in series in the power system. In this embodiment, the power monitoring equipment monitors the three-phase capacitors of the power system, and its processing The process is as follows:

(S301) Receiving the current value and voltage value from the current transformer and the voltage transformer connected to the power factor correction capacitor in the power system.

(S302) It is judged whether the capacitor is connected in series with the reactor.

器之阻抗比))×(電容器額定電壓/(RS相次電壓值÷(1-電抗器之阻抗比)))²；

(S303) When the capacitor is connected in series with the reactor, calculate the reactive power output of each phase of the capacitor according to the following formula, and then proceed to step (S305):

Impedance ratio))×(capacitor rated voltage/(RS phase secondary voltage value ÷(1-reactor impedance ratio))) ² ；

(S304) When the capacitor is not connected in series with the reactor, calculate the reactive power output of the capacitor according to the following formula, and then proceed to step (S305):

(S305) Calculate the capacitance value of the capacitor according to the following formula: RS phase secondary capacitance value = the RS phase secondary reactive power output / (2 × π × power supply frequency × capacitor rated voltage ² ) ÷ 2; ST phase secondary capacitance value = the ST phase secondary reactive power output/(2×π×power supply frequency×capacitor rated voltage ² )÷2; RT phase secondary capacitance value=the RT phase secondary reactive power output/(2×π×power supply frequency×capacitor rated voltage ² )÷2;

(S306) The difference between the calculated capacitance value and the rated value of the capacitor is determined according to the difference to determine whether the capacitor is attenuated or damaged.

For example, if the capacitor's actual RS-phase secondary capacitor operating voltage is 380V, the capacitor's actual R-phase secondary operating current is 60.8Amp, the capacitor's rated voltage is 480V, and the reactor impedance ratio is 6%, when three-phase capacitors are connected in series, If the above formula is introduced, the reactive power output of the RS phase is:

The capacitance of the RS phase capacitor will be: 60.019kvar÷(2×π×60Hz×480V ² )÷2=345.5 microfarad.

However, when the three-phase capacitors are not connected in series with reactors, the reactive power output of the RS phase is:

The capacitance value of the RS phase capacitor will be: 63.846kvar÷(2×π×60Hz×480V ² )÷2=367 microfarad.

In this way, the capacitance value obtained above can be subtracted from the rated value of the capacitor to obtain a difference, so as to determine whether the capacitor is attenuated or damaged according to the difference.

In the present invention, the impedance ratio of the actual reactor depends on the main harmonic order on the actual power system. In the current power system, when the capacitor system is used to improve the power factor of the power system, it is common The impedance ratio of the reactor is 6%, 7% or 13%, but it is not limited to this. In addition, the capacitor used as a tuned filter to absorb harmonics of the power system depends on the impedance ratio of the reactor used to solve the main harmonic problem. In addition, the capacitors described in the present invention are high-voltage capacitors or low-voltage capacitors used to improve the power factor of power systems in power systems, and are also suitable for high- and low-voltage capacitors for absorbing harmonics.

In summary, in the present invention, the present invention can Line measurement or line monitoring, and regardless of whether the capacitor is a three-phase capacitor or a single-phase capacitor, and whether the capacitor is connected to the reactor, the power monitoring equipment can select a suitable formula for calculating the reactive power output of the capacitor and the capacitance of the capacitor The calculation formula of the value, in order to evaluate whether the capacitor is attenuated or damaged, so when the power monitoring equipment finds that the capacitor is attenuated or damaged, it sends out a corresponding warning signal, such as a light or sound, so that the user can replace the capacitor in time to achieve power The purpose of the system to maintain an appropriate power factor.

In summary, this case is not only innovative in terms of technical ideas, but also possesses the above-mentioned multiple effects that traditional methods do not match. It has fully met the requirements of novelty and progressive legal invention patents. Approve this application for a patent for invention to encourage invention and achieve good results.

S301~S306‧‧‧Step flow

Claims (10)

A method for monitoring the capacitance value of a capacitor, which is applied to a power monitoring device of a power system, and includes the following steps: receiving a capacitor connected to the power system as a power factor improving and absorbing harmonic, or a tuned filter for absorbing harmonics The current value and voltage value transmitted by the current comparator and the voltage comparator; calculate the reactive power output of the capacitor according to the current value and the voltage value; calculate the capacitance value of the capacitor based on the reactive power output; then The calculated capacitance value determines whether the capacitor is attenuated or damaged; where, when the capacitor is a three-phase capacitor and its reactor is connected in series, the reactive power output of each phase of the three-phase capacitor is calculated according to the following formula :

Among them, when the capacitor is a single-phase capacitor and its reactor is connected in series, the reactive power output of the single-phase capacitor is calculated by the following formula: reactive power output = (current value × voltage value ÷ (1-reactor Impedance ratio))×(Capacitor rated voltage/(Voltage value÷(1-Reactor impedance ratio))) ² . The capacitance value monitoring method as described in item 1 of the patent application scope, wherein, when the capacitor is a three-phase capacitor, the capacitance value is calculated according to the following formula: RS phase secondary capacitance value = RS phase secondary invalid power output Quantity/(2×π×power supply frequency×capacitor rated voltage ² )÷2; ST phase secondary capacitance value=the ST phase secondary power output/(2×π×power supply frequency×capacitor rated voltage ² )÷2; RT Phase capacitance value = RT phase secondary power output / (2 × π × power supply frequency × capacitor rated voltage ² ) ÷ 2. The capacitance value monitoring method as described in item 1 of the patent application scope, wherein, when the capacitor is a single-phase capacitor, the capacitance value is calculated according to the following formula: capacitance value=the reactive power output/(2×π× Power supply frequency × rated voltage of capacitor ² ). The capacitance monitoring method as described in item 1 of the patent application scope, wherein the power monitoring device presets a threshold, and when the power monitoring device determines that the difference exceeds the threshold, it indicates that the capacitor has been attenuated or damaged. The capacitance value monitoring method as described in item 1 of the patent application range, wherein the current value is a fundamental current or a harmonic current value, and the voltage value is a fundamental wave voltage or a harmonic voltage value. A method for monitoring the capacitance value of a capacitor, which is applied to a power monitoring device of a power system, and includes the following steps: receiving a capacitor connected to the power system as a power factor improving and absorbing harmonic, or a tuned filter for absorbing harmonics The current value and voltage value transmitted by the current comparator and the voltage ratio device; based on the current value and the voltage value, the reactive power output of the capacitor is calculated; based on the reactive power output, the capacitance value of the capacitor is calculated; and Determine whether the capacitor is attenuated or damaged by calculating the calculated capacitance value; where, when the capacitor is a three-phase capacitor and there is no reactor in series, the invalid power of each phase of the three-phase capacitor is calculated by the following formula Output:

Among them, when the capacitor is a single-phase capacitor and the reactor is not connected in series, the reactive power output of the single-phase capacitor is calculated according to the following formula: reactive power output = current value × voltage value × (capacitor rated voltage/ Voltage value) ² . The capacitance value monitoring method as described in item 6 of the patent application scope, wherein, when the capacitor is a three-phase capacitor, the capacitance value is calculated according to the following formula: RS phase secondary capacitance value = RS phase secondary invalid power output Quantity/(2×π×power supply frequency×capacitor rated voltage ² )÷2; ST phase secondary capacitance value=the ST phase secondary power output/(2×π×power supply frequency×capacitor rated voltage ² )÷2; RT Phase capacitance value = RT phase secondary power output / (2 × π × power supply frequency × capacitor rated voltage ² ) ÷ 2. The capacitance value monitoring method as described in item 6 of the patent application scope, wherein, when the capacitor is a single-phase capacitor, the capacitance value is calculated according to the following formula: capacitance value = the reactive power output/(2×π ×Power supply frequency×Capacitor rated voltage ² ). The capacitance value monitoring method as described in item 6 of the patent application scope, wherein the power monitoring device presets a threshold value, and when the power monitoring device determines that the difference exceeds the threshold value, it indicates that the capacitor has been attenuated or damaged. The capacitance value monitoring method as described in Item 6 of the patent application range, wherein the current value is a fundamental current or a current value containing harmonics, and the voltage value is a fundamental wave voltage or a current containing harmonics Voltage value.

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