TWI640786B - Method for monitoring capacitance value of capacitor of power system - Google Patents

Abstract

The present invention relates to a capacitance value monitoring method for 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 of a power system for improving or absorbing a harmonic of a harmonic filter. And the current value and voltage value transmitted by the comparator, and then calculate the reactive power output of the capacitor according to the current value and the voltage value, and then calculate the capacitance value of the capacitor according to the reactive power output, and the calculated capacitance value and The capacitor's rating is compared to determine if the capacitor is attenuated or damaged.

Description

 Capacitance value monitoring method for capacitors of power systems  

The present invention relates to a capacitor, and more particularly to a method for monitoring a capacitance value of a capacitor for improving power factor or filtering harmonics in a power system.

When the load is connected in the power system, there will be both active power and reactive power, and the sum of the effective power and the reactive power is the total output power called apparent power, wherein the transmission of the invalid power is higher, and Increase the power loss of the transmission line and increase the line current. Therefore, capacitors are installed in the power system to improve the power factor of the power system. In the power system, the power factor is improved. In addition to reducing the supply of reactive power, the line loss between the power supply terminal and the power supply terminal can be reduced, the voltage can be improved, and the capacity of the power system can be increased.

Furthermore, the power factor is too high (such as more than 100%) will also affect the quality of the power supply, that is, in order to improve the power factor, it is not possible to install an oversized capacitor without any limitation, because when the capacitor is installed too large, the power factor improves the efficiency. It is not obvious that in addition to increasing the cost, the over-compensation increases the ineffective current, resulting in double loss of equipment investment and efficiency. Even when the power factor is ahead, the voltage may be too high, which may affect the operational safety of the power system.

In addition, the electricity supplier charges electricity charges to the electricity users according to the power factor. In the current electricity price standard of Taiwan Power Company, when the average power factor is less than 80%, for every 1% lower, the electricity fee for this month needs to increase by 0.1%; When it exceeds 80%, for every 1%, the electricity fee for this month should be reduced by 0.1%, and the average power factor is more than 95%. The power factor is maintained at 80% if the capacitor is properly installed in the power system. Between ~95% will reduce electricity bills.

According to the above, it is necessary to properly install a capacitor in the power system to correct the power factor between appropriate values. In other words, if the capacitor is damaged or malfunctions, the power factor of the power system cannot be maintained at an appropriate level. Between values. However, when the current power system is in operation, it is impossible to measure or monitor the capacitor, and it is impossible to know whether the capacitor is aging or damaged, so that the user cannot replace the capacitor in time, and the power system cannot be maintained at an appropriate power factor. How to effectively measure or monitor the capacitors of the power system in the operating state is an urgent problem to be solved.

In view of the problem that the power system in the prior art operating state cannot measure or monitor the capacitor, one of the objects of the present invention is to measure or monitor the capacitor in the power system under the operating state of the power system. In particular, it is measured or monitored for capacitors in power systems that have filters that improve power factor or absorb harmonics.

According to an object of the present invention, there is provided a method for monitoring a capacitance value of a capacitor of a power system, which is a power monitoring device applied to a power system, comprising the steps of: receiving a tuned filter as a power factor improving or absorbing harmonic in a power system; The current value and voltage value transmitted by the current comparator and the voltage comparator connected to the capacitor are calculated according to the current value and the voltage value, and the capacitance value of the capacitor is calculated according to the reactive power output amount, and then The calculated capacitance value determines whether the capacitor is attenuated or damaged.

The current value may be a primary wave current value or a harmonic current value, and the voltage value may be a primary wave voltage value or a harmonic voltage value.

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 to determine whether the capacitor is attenuated or damaged.

Wherein, the capacitance value is compared with the rated value of the capacitor, and the difference between the capacitance value and the rated value of the capacitor is calculated, and when the difference exceeds the threshold value preset by the power monitoring device, it is lower than the international electrician (IEC60831) The -5% capacitance value standard specified in IEC 60871) means that the capacitor has been attenuated or that the internal capacitive element is partially damaged.

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

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

1. In the operating state of the power system, the live line measurement or the live line monitoring of the capacitor in the power system as a tuning filter for power factor improvement or absorption harmonics.

2. Capacitors in power systems can be accurately measured or monitored regardless of series reactors.

3. Three-phase high-voltage capacitors, low-voltage capacitors and filters, or single-phase high-low voltage capacitors and filters, which are tuned filters for power factor improvement or harmonic absorption in power systems, can accurately measure or monitor capacitance. value.

S101~S104, S201~S206, S301~S306‧‧‧ Step flow

1 is a schematic flow chart of the present invention; FIG. 2 is a schematic flow chart of a single-phase capacitor of the present invention; FIG. 3 is a schematic flow chart of a three-phase capacitor of the present invention.

The spirit and scope of the present invention will be described in the following detailed description of the preferred embodiments of the present invention, which can be modified and modified by the teachings of the present invention. The spirit and scope of the present invention.

Referring to FIG. 1 , the present invention is a method for monitoring a 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 as a power factor for improving the power system or a main system for absorbing the power system. Harmonic Tuned Filter, the method includes the following steps: (S101) receiving a current value and a voltage value transmitted by a current comparator and a voltage comparator connected to a power factor correction capacitor in a power system, wherein the current value The system may be a primary wave current value or a harmonic current value, and the voltage value may be a primary wave voltage value or a harmonic voltage value; (S102) calculating an invalid power output of the capacitor according to the current value and the voltage value; (S103) calculating a capacitance value of the capacitor according to the reactive power output amount; (S104) further calculating a difference between the calculated capacitance value and the rated value of the capacitor, determining whether the capacitor is attenuated according to the difference or partially damaging the internal capacitive element .

Since the fundamental power current value or the harmonic current value, and the primary fundamental wave voltage value or the harmonic voltage value, the difference between the reactive power output amount and the capacitance value of the subsequent capacitor is determined by the primary fundamental wave voltage. The value of the invalid power output and the capacitance value calculated by the value of one basic wave current are the most accurate, and the output of the reactive power and the value of the capacitor calculated by using the harmonic current value or the harmonic voltage value are inaccurate (distortion). However, regardless of the state of the voltage value or voltage value calculation, it can be confirmed whether the capacitor is attenuated or damaged by the calculated capacitance value of the capacitor. In addition, three-phase capacitor or single-phase capacitor correction may be used in the power system. Power factor, and possibly capacitor series reactor or series reactor, therefore, in one embodiment of the invention, one fundamental wave voltage value and one fundamental wave current value, and for the above three-phase capacitor or single The combination of the phase capacitor and the capacitor series reactor or the series reactor does not have different equations. The output of the rate is described as follows for the different combinations of the above: When the capacitor is a three-phase capacitor and the reactor is not connected in series, the calculation formula of the reactive power output of each phase of the three-phase capacitor is as follows: RS phase invalid power output = R Phase primary wave current value × RS phase primary wave voltage value × ; ST phase invalid power output = S phase primary fundamental current value × ST phase primary fundamental voltage value × ; RT phase invalid power output = T phase primary wave current value × RT phase primary wave voltage value × .

When the capacitor is a three-phase capacitor and a series reactor, the calculation formula of the reactive power output of each phase of the three-phase capacitor is as follows: RS phase invalid power output = R phase primary fundamental current value × RS phase primary fundamental voltage value × ×(1-impedance ratio of reactor); ST phase invalid power output = S phase primary fundamental current value × ST phase primary fundamental voltage value × ×(1-impedance ratio of reactor); RT phase reactive power output = T phase primary fundamental current value × RT phase primary fundamental voltage value × × (1 - impedance ratio of reactor).

When the capacitor is a three-phase capacitor, whether or not the series reactor is used, the calculation formula of the capacitance value of each phase of the three-phase capacitor is as follows: RS phase capacitance value = RS phase invalid power output amount / (2 × π × frequency of power system × power system The square of the RS phase voltage value of the supplied power); ST phase capacitance value = ST phase invalid power output amount / (2 × π × frequency of the power system × square of the ST phase voltage value of the power supplied by the power system); RT phase capacitor Value = RT phase invalid power output / (2 × π × frequency of the power system × square of the RT phase voltage value of the power supplied by the power system); when the capacitor is a single-phase capacitor and the reactor is not connected in series, its reactive power output The calculation formula of the quantity is as follows: invalid power output quantity = primary fundamental wave current value × primary fundamental wave voltage value.

When the capacitor is a single-phase capacitor and a series reactor, the formula for calculating the reactive power output is as follows: invalid power output = primary fundamental current value × primary fundamental voltage value × (1 - impedance ratio of reactor).

When the capacitor is a single-phase capacitor, whether or not the reactor is connected in series, the capacitance value of the capacitor is calculated as follows: capacitance value = invalid power output / (2 × π × frequency of the power system × square of the voltage value of the power supplied by the power system) The voltage value of the power supplied by the power system is an R phase voltage or an S phase voltage or a T phase voltage.

In the present invention, the power monitoring device can provide a choice of whether to use a single-phase capacitor, a three-phase capacitor, and whether it is a series reactor in the power system, and can select a corresponding calculation formula of the reactive power output amount and the capacitance value of the capacitor. For the user to operate.

An embodiment of the present invention, as shown in FIG. 2, the power monitoring device monitors a single-phase capacitor for a power system, and the processing flow is as follows: (S201) a current comparator connected to a capacitor as a power factor correction in the power system. And a primary wave current value and a primary wave voltage value transmitted from the comparator; (S202) determining whether the capacitor is in series with the reactor; (S203) when the capacitor is not connected to the reactor, calculating the invalid power output of the capacitor according to the following formula Quantity, and then perform the step (S205): invalid power output amount = primary wave current value × primary wave voltage value; (S204) when the capacitor series reactor, calculate the capacitor's invalid power output according to the following formula, and then perform the steps (S205): Invalid power output amount = primary fundamental wave current value × primary fundamental wave voltage value × (1 - impedance ratio of reactor); (S205) The capacitance value of the capacitor is calculated according to the following formula: capacitance value = invalid power output amount / (2 × π × frequency of the power system × square of the voltage value of the power supplied by the power system), wherein the voltage value of the power supplied by the power system is the R-phase voltage S or will phase voltage T-phase voltage; (S206) and then the difference between one of the calculated rated capacitance value of the capacitor, the capacitor is determined based on a difference whether attenuated or damaged.

In another embodiment of the present invention, referring to FIG. 3, the power monitoring device monitors the three-phase capacitor for the power system, and the processing flow is as follows: (S301) The specific flow connected to the capacitor as the power factor correction in the receiving power system a primary wave current value and a primary wave voltage value transmitted from the comparator and the comparator; (S302) determining whether the capacitor is a series reactor; (S303) when the capacitor is not connected to the reactor, calculating the phases of the capacitor according to the following formula Invalid power output, proceed to step (S305): RS phase invalid power output = R phase primary wave current value × RS phase primary wave voltage value × ; ST phase invalid power output = S phase primary fundamental current value × ST phase primary fundamental voltage value × ; RT phase invalid power output = T phase primary wave current value × RT phase primary wave voltage value × (S304) When the capacitor series reactor, calculate the reactive power output of the capacitor according to the following formula, and then perform the step (S305): RS phase invalid power output = R phase primary fundamental current value × RS phase primary fundamental voltage Value × ×(1-impedance ratio of reactor); ST phase invalid power output = S phase primary fundamental current value × ST phase primary fundamental voltage value × ×(1-impedance ratio of reactor); RT phase reactive power output = T phase primary fundamental current value × RT phase primary fundamental voltage value × × (1 - impedance ratio of reactor); (S305) Calculate the capacitance value of the capacitor according to the following formula: RS phase capacitance value = RS phase invalid power output amount / (2 × π × power system frequency × power supply by the power system Square of voltage value); ST phase capacitance value = ST phase invalid power output / (2 × π × power system frequency × square of voltage value of power supplied by power system); RT phase capacitance value = RT phase invalid power output / (2 × π × power system frequency × square of the voltage value of the power supplied by the power system); (S306) and then calculate the difference between the calculated capacitance value and the rated value of the capacitor, and determine whether the capacitor is based on the difference Attenuated or damaged.

In the above calculation formulas, the primary wave current value and the primary fundamental wave voltage value are described. However, as described above, in the actual implementation of the present invention, one primary wave current value and one primary wave voltage value are used. It can be replaced by harmonic current values and harmonic voltage values.

In the present invention, the impedance ratio of the actual reactor is determined by the main harmonic order on the actual power system. In the current power system, when the capacitor system is used as a power factor for improving the power system, it is common. The impedance ratio of the reactor is 6%, 7% or 13%, but not limited to this. In addition, as a capacitor provided by a tuned filter that absorbs harmonics of the power system, the impedance ratio of the reactor used for the main harmonic problem to be solved is determined. Further, the capacitor described in the present invention is a high voltage capacitor or a low voltage capacitor which is a power factor for improving a power system in an electric power system, and is also suitable for a high and low voltage capacitor for absorbing harmonics.

In summary, the present invention can perform live line measurement or live line monitoring of the capacitor under the operating state of the power system, and 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 device The calculation formula of the invalid power output of the appropriate capacitor and the calculation formula of the capacitance value of the capacitor can be selected to evaluate whether the capacitor is attenuated or damaged. Thus, when the power monitoring device finds that the capacitor is attenuated or damaged, a corresponding warning signal is issued. Such as the signal or sound, so that the consumer can replace the capacitor in time to achieve the purpose of maintaining the power system at the appropriate power factor.

To sum up, this case is not only innovative in terms of technical thinking, but also has many of the above-mentioned functions that are not in the traditional methods of the past. It has fully complied with the statutory invention patent requirements of novelty and progressiveness, and applied for it according to law. Approved this invention patent application, in order to invent invention, to the sense of virtue.

Claims (8)

A capacitor value monitoring method for a capacitor is applied to a power monitoring device of a power system, comprising the steps of: receiving a current transformer and a ratio of a capacitor connected to a tuning filter of a power factor improving or absorbing harmonic in the power system; a current value and a voltage value transmitted from the voltage device; calculating an invalid power output amount of the capacitor according to the current value and the voltage value; calculating a capacitance value of the capacitor according to the reactive power output amount; and calculating the calculated value The capacitance value is used to determine whether the capacitor is attenuated or damaged; wherein, the invalid power output of the capacitor is calculated according to the formula of any one or more of the following combinations: when the capacitor is a single-phase capacitor, and the series reactor is not connected At the time, the invalid power output of the capacitor is calculated by the following formula: invalid power output = current value × voltage value; when the capacitor is a single-phase capacitor and its series reactor, the capacitor is calculated by the following formula Invalid power output: invalid power output = current value × voltage value × (1 - impedance ratio of reactor); when the capacitor When it is a single-phase capacitor, it is first determined whether the single-phase capacitor is a series reactor. When the single-phase capacitor is not connected to the reactor, the invalid power output of the capacitor is calculated by the following formula: invalid power output = current value × a voltage value; wherein, when the capacitor is a three-phase capacitor, the reactive power output of each phase of the three-phase capacitor is separately calculated by a combination of any one or more of the following: when the three-phase capacitor is not connected in series At the time, the invalid power output of each phase of the three-phase capacitor is calculated by the following formula: When the three-phase capacitor is connected in series with the reactor, the reactive power output of each phase of the three-phase capacitor is calculated by the following formula: The capacitance value monitoring method according to claim 1, wherein the capacitance value is calculated by the following formula: capacitance value = invalid power output amount / (2 × π × power system frequency × square of voltage value of power supplied by the power system) ). The method for monitoring a capacitance value according to claim 1, wherein the current value is a primary wave current value or a harmonic current value, and the voltage value may be a primary wave voltage value or a harmonic voltage value. The capacitance value monitoring method according to claim 1, wherein the capacitance value is calculated by the following formula: RS phase capacitance value=the RS phase invalid power output amount/(2×π×power system frequency×power system power supply) The square of the voltage value); ST phase capacitance value = the ST phase invalid power output / (2 × π × power system frequency × the square of the voltage value of the power supplied by the power system); RT phase capacitance value = the RT phase is invalid Power output / (2 × π × power system frequency × square of the voltage value of the power supplied by the power system). The method for monitoring a capacitance value according to claim 1, wherein the current value is a primary wave current value or a harmonic current value, and the voltage value may be a primary wave voltage value or a harmonic voltage value. The method for monitoring a capacitance value according to claim 1, wherein the power monitoring device presets a threshold value, and when the power monitoring device determines that the difference exceeds the threshold, the capacitor is attenuated or damaged. The method for monitoring a capacitance value according to claim 1, wherein when the power monitoring device determines that the difference does not exceed the threshold, it indicates that the capacitor is still available. The capacitance value monitoring method according to claim 1, wherein the impedance ratio of the reactor is one of 6%, 7%, and 13%.