KR102699221B1 - Earthquake-proof switchboard having real-time deterioration diagnosis function of power capacitor and series reactor - Google Patents

Abstract

The present invention relates to an earthquake-resistant switchboard (high voltage switchboard, low voltage switchboard, motor control panel, distribution board) having a real-time deterioration diagnosis function of power capacitors and series reactors, and more specifically, to an earthquake-resistant switchboard (high voltage switchboard, low voltage switchboard, motor control panel, distribution board) having a real-time deterioration diagnosis function of power capacitors and series reactors, which calculates a resonant frequency through a capacitance calculated based on line current, frequency, and line-to-line voltage and an inductance of a series reactor calculated based on rated voltage and rated current, and isolates and protects a capacitor bank from a power system when a frequency flowing into the capacitor bank approaches the calculated resonant frequency, and diagnoses deterioration of the power capacitor by a temperature detected from the power capacitor and provides a warning about the temperature value of the power capacitor or information on power separation.
[This invention is the result of research on the 2023 Chungbuk Materials, Components, and Equipment Field Technology Development Support Project, a distribution panel project with abnormal state diagnosis and protection function for power capacitors, which is being carried out with the support of Chungcheongbuk-do and Chungbuk Science and Technology Innovation Foundation.]

Description

Earthquake-proof switchboard (high voltage switchboard, low voltage switchboard, motor control board, distribution board) with real-time deterioration diagnosis function of power capacitor and series reactor {EARTHQUAKE-PROOF SWITCHBOARD HAVING REAL-TIME DETERIORATION DIAGNOSIS FUNCTION OF POWER CAPACITOR AND SERIES REACTOR}

The present invention relates to an earthquake-resistant switchboard (high voltage switchboard, low voltage switchboard, motor control panel, distribution board) having a real-time deterioration diagnosis function of power capacitors and series reactors, and more specifically, to an earthquake-resistant switchboard (high voltage switchboard, low voltage switchboard, motor control panel, distribution board) having a real-time deterioration diagnosis function of power capacitors and series reactors, which calculates a resonant frequency through a capacitance calculated based on line current, frequency, and line-to-line voltage and an inductance of a series reactor calculated based on a rated voltage and a rated current, and protects the capacitor bank by isolating it from the power system when the frequency flowing into the capacitor bank approaches the calculated resonant frequency, and diagnoses deterioration of the power capacitor by the temperature detected from the power capacitor and provides a warning about the temperature value of the power capacitor or information on power separation.

In personal power equipment, lights and heating loads have good power factor, but discharge lamps, welding machines, and induction motors have poor power factor, which causes voltage fluctuations and increased power loss.

Power capacitors are power devices that supply leading current by connecting them in parallel with the load to solve these problems.

By using these power capacitors, not only can low power factor be prevented, but also self-power equipment can be managed more effectively. (In the present invention, the term power condenser is described as power capacitor according to the National Institute of Technology and Standards (No. 2020-0098), and the term described as condenser in existing literature is described as condenser.)

In this configuration, the fifth harmonic is the one with the second largest content after the third harmonic due to the characteristics of the power system. The third harmonic can be mostly solved by transformer wiring methods, but the fifth harmonic is solved by a series reactor connected in series with a power capacitor. In this case, if the fifth harmonic occurs at an excessively large value, the terminal voltage of the series reactor increases excessively and the fifth harmonic current exceeds the reference value, causing overheating, so the series reactor is damaged before the capacitor.

Accordingly, in order for the power capacitor to resonate at the fifth harmonic as a substitute for the fifth harmonic filter, a series reactor with a reactor capacity corresponding to 4% of the power capacitor capacity is theoretically required, but in reality, a capacity of 6%, which is slightly larger than the theory, is standard due to frequency fluctuations and economic aspects.

However, a capacitor bank including power capacitors is composed of countless capacitor elements in series and parallel, and when the capacitor bank deteriorates, the capacitor elements are destroyed, causing the electrostatic capacity (C, capacitance) value to change.

Accordingly, as a technology for predicting deterioration of a capacitor bank according to changes in the electrostatic capacitance of the capacitor, a device and method for predicting deterioration of a capacitor bank are disclosed in Patent Publication No. 10-1226474.

The above technology comprises the steps of: a) collecting information on current (I) and voltage (V) input to a capacitor bank, and calculating fundamental voltage (V1) and current (I1), nth (n>1) harmonic voltage (V2) and current (I2), active power (P), power factor, and fundamental and nth harmonic impedance (Z1, Z2); b) calculating leakage resistance (R) of each capacitor of the capacitor bank, impedance (XC) for each capacitor, and impedance (XL) for each series reactor using the power factor and impedance values; c) calculating capacity (L) of each series reactor and capacity (C) of each capacitor by removing a constant component using the fundamental and nth harmonic impedances (Z1, Z2); And d) a step of monitoring and tracking the change status of the capacity (L) of each series reactor, the capacity (C) and leakage resistance (R) of each capacitor, and power consumption, and predicting the deterioration status of each capacitor or series reactor and the performance according to the decrease in the electrostatic capacitance (C) of each capacitor.

However, since the resonant frequency that causes resonance among the incoming frequencies also varies depending on the change in electrostatic capacitance (C), if only the preset harmonics are detected and blocked, the inflow of the varied resonant frequency cannot be prevented, and the inflow of the resonant frequency causes overcurrent in the power capacitor, and there are problems such as heat generation due to the overcurrent, a decrease in the insulating capacity of the dielectric, and insulation breakdown.

Meanwhile, as a technology for predicting the lifespan of a power capacitor through its temperature, an automatic power factor control device having a lifespan prediction function of a phase-shift capacitor for power factor improvement is disclosed in Patent Publication No. 10-1910813.

The above technology comprises a temperature measuring unit which measures the case temperature of the power condenser; and a life prediction unit which predicts the remaining life of the power condenser by using the voltage output from the voltage variable to the power condenser measured by the output voltage and current measuring unit and the case temperature of the power condenser measured by the temperature measuring unit, and then displays the predicted remaining life of the power condenser on a display unit, and is a technology for predicting the life of the power condenser using a mathematical formula based on the allowable temperature of the power condenser and the actual temperature of the power condenser.

However, the above technology has a disadvantage in that the predicted life expectancy is not accurate because the actual temperature detected while the capacitor is operating in the system or the temperature difference between the allowable temperature of the capacitor and the actual temperature is different.

[This invention is the result of research on the 2023 Chungbuk Materials, Components, and Equipment Field Technology Development Support Project, a distribution panel project with abnormal state diagnosis and protection function for power capacitors, which is being carried out with the support of Chungcheongbuk-do and Chungbuk Science and Technology Innovation Foundation.]

Patent Registration No. 10-1226474 (January 21, 2013) Patent Registration No. 10-1910813 (October 17, 2018)

The present invention has been made to solve the above problems, and the problem to be solved by the present invention is to provide an earthquake-resistant distribution panel having a real-time deterioration diagnosis function of a power capacitor and a series reactor, which calculates a resonant frequency in real time through capacitance and inductance based on information such as voltage and current detected in a power system, and, if a frequency flowing into the power system based on the calculated resonant frequency approaches the resonant frequency, isolates the corresponding circuit from the power system to protect the power capacitor.

In addition, the present invention provides an earthquake-resistant distribution panel having a real-time deterioration diagnosis function of a power capacitor and a series reactor capable of detecting the temperature of the power capacitor and diagnosing an abnormal condition of the power capacitor based on the detected temperature.

In order to solve the above-mentioned problem, the present invention provides a seismic distribution board having a real-time deterioration diagnosis function of a power capacitor and a series reactor, the board comprising: a capacitor bank including a power capacitor installed in a cubicle to improve a power factor, and a series reactor connected in series to the power capacitor to correct a current phase and prevent the occurrence of harmonics; and a diagnostic control unit configured to calculate a resonant frequency through a capacitance calculated based on a capacitive capacitance of the power capacitor and an inductance calculated from an inductive inductance of the series reactor, and to control the capacitor bank to be separated from a power system when a frequency flowing into the distribution board approaches the calculated resonant frequency.

Here, the diagnostic control unit is configured to include a capacitance calculation module that calculates the capacitance of each phase of the power capacitor based on the line current, frequency, and line-to-line voltage of the power capacitor; an inductance calculation module that calculates the inductance of the series reactor based on the rated voltage and rated current applied to the series reactor; a diagnostic module that calculates a resonant frequency based on the capacitance calculated by the capacitance calculation module and the inductance calculated by the inductance calculation module and diagnoses the capacitor bank based on the calculated resonant frequency; and a control module that isolates the capacitor bank from the power system according to the diagnostic result of the diagnostic module.

At this time, if the power capacitor is Δ-connected, the electrostatic capacity calculation module is characterized in that the capacitance is calculated by the following formula.

formula)

Here, C _Δ1 is the capacitor capacitance of RS phase, I ₁ is the line current flowing in R and S phases, f is the frequency, V ₁ is the line-to-line voltage of R and S phases, C _Δ2 is the capacitor capacitance of ST phase, I ₂ is the line current flowing in S and T phases, V ₂ is the line-to-line voltage of S and T phases, C _Δ3 is the capacitor capacitance of TR phase, I ₃ is the line current flowing in T and R phases, and V ₃ is the line-to-line voltage of T and R phases.

In addition, if the power capacitor is Y-connected, the electrostatic capacity calculation module is characterized in that the capacitance is calculated by the following formula.

formula)

Here, C _Y1 is the capacitor capacitance of RS phase, I ₁ is the line current flowing in R and S phases, f is the frequency, V ₁ is the line-to-line voltage of R and S phases, C _Y2 is the capacitor capacitance of ST phase, I ₂ is the line current flowing in S and T phases, V ₂ is the line-to-line voltage of S and T phases, C _Y3 is the capacitor capacitance of TR phase, I ₃ is the line current flowing in T and R phases, and V ₃ is the line-to-line voltage of T and R phases.

In addition, the inductance calculation module is characterized in that the inductance is calculated by the following formula.

formula)

Here, L is the inductance value of the series reactor, X _L is the inductive reactance of the series reactor, ω is the angular frequency (2πf), f is the frequency, V _SR is the rated voltage of the reactor, and I _SR is the rated current of the reactor.

In addition, the diagnostic module is configured to calculate a cutoff frequency range that prevents current of the calculated resonant frequency from being applied to a power capacitor when the resonant frequency is calculated, and to control operation of an alarm device when a frequency in the cutoff frequency range is detected or to output a signal that controls separation of the power capacitor from the power system.

In addition, the cutoff frequency is characterized in that it is a frequency that falls within a range having a current value of ±1/√2 of the maximum value (Imax) of the nth harmonic of the resonant frequency.

In addition, the diagnostic control unit further includes a vibration detection module that detects vibration, and is configured to analyze the vibration based on the vibration value detected by the vibration detection module, and control to perform a power separation operation or to control to sound an alarm according to the analysis result.

In addition, the diagnostic control unit further includes a temperature detection module that detects the temperature of the power capacitor, and is configured to diagnose and provide the lifespan due to deterioration of the power capacitor based on the temperature detected by the temperature detection module.

According to the present invention, even if the capacitance value of a capacitor bank changes when applied to a power system, the resonant frequency that may cause a problem in the capacitor bank is calculated in real time based on the changed static capacitance value, thereby preventing the inflow of the resonant frequency, so that failure of power capacitors and series reactors can be prevented, and there is an advantage in that the soundness of the power system can be secured.

In addition, by predicting and providing the lifespan of a power capacitor based on the detected temperature according to the operation of the power capacitor, it is possible to minimize power waste due to malfunction of the power capacitor and has the advantage of enabling efficient use of the supplied power.

Figure 1 is a drawing schematically showing the internal configuration of a seismic distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention.
Figure 2 is a wiring diagram of a capacitor bank and a diagnostic control unit applied to an earthquake-resistant distribution board (high-voltage distribution board, low-voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention.
FIG. 3 shows the configuration of a diagnostic control unit applied to an earthquake-resistant distribution panel (high-voltage distribution panel, low-voltage distribution panel, motor control panel, distribution panel) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention.

Next, a preferred embodiment of an earthquake-resistant switchboard (high voltage switchboard, low voltage switchboard, motor control panel, distribution panel) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention will be described in detail with reference to the drawings.

In the following, the same reference symbols are used for technical elements that perform the same function, and repeated detailed descriptions are omitted to avoid redundant explanations.

In addition, the embodiments described below are provided as examples to effectively demonstrate preferred embodiments of the present invention, and should not be construed to limit the scope of the rights of the present invention.

The present invention relates to an earthquake-resistant switchboard (high voltage switchboard, low voltage switchboard, motor control panel, distribution board) having a real-time deterioration diagnosis function of power capacitors and series reactors, and more specifically, to an earthquake-resistant switchboard having a real-time deterioration diagnosis function of power capacitors and series reactors, which calculates a resonant frequency through a capacitance calculated based on line current, frequency, and line-to-line voltage and an inductance calculated based on rated voltage and rated current, and isolates and protects the capacitor bank from the power system when the frequency flowing into the capacitor bank approaches the calculated resonant frequency, and provides a diagnosis of deterioration of the power capacitor by the temperature detected from the power capacitor.

Here, the capacitor bank is configured to include a power capacitor, a series reactor, and may further include a discharge coil, and the power system means a power line supplied to the capacitor bank.

FIG. 1 is a drawing schematically showing the internal configuration of an earthquake-resistant distribution board (high-voltage distribution board, low-voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention.

Referring to the attached drawing 1, a seismic distribution board having a real-time deterioration diagnosis function of a power capacitor and a series reactor includes a cubicle (10) forming a predetermined frame, various power devices and a capacitor bank (100) and a diagnosis control unit (200) configured inside the cubicle (10).

The power equipment installed inside the above cubicle (10) may include an automatic section switch (AISS), a lightning arrester (LA), a power fuse (PF), a transformer (TR), a metering out fit (MOF), an air circuit breaker (ACB), etc., but the configuration of the power equipment is configured differently depending on the voltage being received and distributed or the power demand on the load side. In addition, various relays that detect the status inside the distribution panel are installed on the inner side of the door.

A capacitor bank (100) is a collection of power devices installed to improve the power factor of a power system, and in the present invention, is configured to include a power capacitor (110, Power Capacitor), a series reactor (120, Series Reactor), and a discharge coil (130, Discharge Coil, see FIG. 2).

In addition, in the present invention, a diagnostic control unit (200) is configured to diagnose the capacitor bank (100) and, if an abnormality is determined to have occurred as a result of the diagnosis, operate an alarm device or isolate the capacitor bank (100) from the power system. The diagnostic control unit (200) is installed on the front door of the cubicle (10).

In the above configuration, the automatic fault section switch (AISS) cooperates with the protective device (circuit breaker, recloser) in front of the automatic fault section switch to open and isolate only the fault section when an overload or fault occurs, thereby preventing the expansion of the fault, and the lightning arrester performs the function of grounding the surge voltage.

Additionally, power fuses safely conduct load current and block abnormal overcurrents to protect circuits and equipment.

Additionally, the transformer transforms the voltage and current supplied to the power line to a certain level and outputs it.

The instrument transformer box has an instrument transformer (PT) and an instrument current transformer (CT) built in. In addition, the front space of the cubicle (10) is configured to display the status of the distribution board.

The above-mentioned instrument transformer box performs the function of transforming high-voltage, high-current power into a predetermined power and supplying it, and is intended to safely connect an integrated power meter in a distribution panel that receives and distributes high-voltage electricity. The inside of the above-mentioned instrument transformer box is configured to transform/transform high voltage and high current into low voltage and small current, respectively, by combining PTs and CTs, so that an integrated power meter can be installed.

A circuit breaker is a switching device that cuts off power in case of abnormal currents such as overload and short circuit.

The power equipment configured in the above earthquake-resistant distribution board can be configured differently depending on the distribution voltage, type, and load capacity of the distribution board. In the present invention, the earthquake-resistant distribution board means any distribution board configured with a power capacitor.

FIG. 2 is a diagram showing a wiring diagram of a capacitor bank and a diagnostic control unit applied to an earthquake-resistant distribution board (high-voltage distribution board, low-voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention.

Referring to the attached Figure 2, a power capacitor (110) is connected in parallel to power lines (R, S, T), and a diagnostic control unit (200) calculates the voltage and resonant frequency applied to the power capacitor (110) to diagnose an abnormal state of the power capacitor (110) and control the power supply.

At this time, a series reactor (120) and a discharge coil (130) are configured at the front end of the power capacitor (110).

A series reactor (120) is installed in front of the power capacitor (110) and removes harmonics, and a discharge coil (130) is installed in parallel between the power capacitor (110) and the series reactor (120) and performs the function of discharging residual charges remaining in the power capacitor (110).

That is, the power capacitor (110) is connected in parallel to the main circuit (R, S, T) to improve the power factor of the system, and is connected in series with the series reactor (120) to also perform the role of a filter that absorbs harmonic current generated by a nonlinear load.

At this time, the power capacitor (110) does not generate harmonics, but when it operates as a power factor improvement and harmonic filter, it transforms the frequency response characteristics of the power system.

In the present invention, the capacitor bank (100) is defined as consisting of a power capacitor (110) and a series reactor (120) as illustrated in FIG. 1, or further including a power capacitor (110), a series reactor (120), and a discharge coil (130) as illustrated in FIG. 2.

Meanwhile, resonance occurring in a power system means a phenomenon in which impedance becomes minimum or maximum at a specific frequency due to inductive inductance and capacitive capacitance. In series resonance, the current is maximum, and in parallel resonance, the voltage is maximum, and during resonance, considerable electrical stress is applied to the power capacitor (110).

In the power factor improvement compensation system, the resonant frequency greatly shortens the life of the power capacitor (110) or causes failure. Accordingly, in order to avoid the resonant frequency, the series reactor and discharge coil are designed below the resonant point.

However, harmonic waves generated under specific conditions by abnormal state signals applied from the outside may cause deterioration of the power capacitor (110).

When the above power capacitor (110) deteriorates, the electrostatic capacitance (C, capacitance) capacity of the power capacitor (110) decreases. This decrease in the electrostatic capacitance (capacitance) capacity changes the resonant frequency value, and it becomes relatively lower compared to the resonant frequency at the time of system design.

That is, the resonant frequency calculated during system design is fixed.

However, the resonant frequency is lowered by the capacitance due to the deterioration of the power capacitor. As a result, a difference value occurs between the resonant frequency at the time of system design and the resonant frequency due to the system operation. Accordingly, if a harmonic current of the lowered resonant frequency flows into the system with the lowered resonant frequency, the inflow of the lowered resonant frequency cannot be blocked because the resonant frequency at the time of design is applied as it is. The resonant frequency that flows in this way causes deterioration or damage to the power capacitor and series reactor.

Accordingly, in the present invention, when the electrostatic capacity (capacitance) of a power capacitor (110) is varied, a diagnostic control unit (200) is configured to detect this in real time, calculate a resonant frequency that may cause a problem in a power system, and prevent the inflow of a frequency close to the calculated resonant frequency, thereby safely protecting a capacitor bank (100) including a power capacitor (110).

The above diagnostic control unit (200) calculates a resonant frequency through a capacitance calculated based on the capacitive capacitance of the power capacitor (110) and an inductance calculated from the inductive inductance of the series reactor (120), and performs a function of controlling the capacitor bank (100) to be separated from the power system when the frequency flowing into the distribution board approaches the range of the calculated resonant frequency.

At this time, a circuit breaker (201) is configured to cut off the power line according to a trip signal output from the diagnostic control unit (200) so as to isolate the capacitor bank (100) from the power system according to the diagnostic result of the diagnostic control unit (200).

In addition, the diagnostic control unit (200) may further include an AD converter and a display.

Here, the AD converter performs the function of converting analog signals for voltage and current applied to the power capacitor (110) into digital signals and outputting them.

The above converter includes a current transformer (CT) to detect the current of the main circuit (R, S, T) applied to the power capacitor and a potential transformer (PT) to detect the voltage of the main circuit (R, S, T) applied to the power capacitor (110).

An instrument transformer (PT) is a device that transforms the voltage of a high-voltage circuit into low voltage so that it can be used for various instruments such as voltmeters, wattmeters, frequency meters, power factor meters, and protective relays. The primary side varies depending on the voltage, but the rated voltage on the secondary side is configured to output 110 V.

A current transformer (CT) is a device that is connected in series with a circuit to transform a large current in a high-voltage circuit into a small current.

Additionally, the display displays the diagnosis and control results of the diagnostic control unit (200) in real time.

In this way, the above diagnostic control unit (200) detects the electrostatic capacity of the power capacitor (110) in real time, calculates the resonant frequency based on the detected electrostatic capacity, and if the calculated resonant frequency and the frequency transmitted from the system approach the resonant frequency that may cause an abnormality, it determines this as an abnormality signal and operates an alarm device or isolates the power capacitor (110) from the power system.

In detail, the diagnostic control unit (200) calculates a resonant frequency through a capacitance calculated based on the capacitive capacitance of the power capacitor (110) and an inductance calculated from the inductive inductance of the series reactor (120), and performs a function of controlling the capacitor bank (100) to be separated from the power system when the resonant frequency flowing into the capacitor bank (100) approaches the calculated resonant frequency.

If the resonant frequency is explained through the attached Fig. 2, the power capacitor (110) is connected in series with the series reactor (120), and thus, if simplified as a simple circuit, an RLC series circuit is formed having the inductance (L) of the series reactor (120) and the capacitance (C) and line resistance (R) of the power capacitor (110).

In an RLC series circuit, the inductive reactance (X _L (jwL)) and capacitive reactance (X _C (1/jwC)) cancel each other out, and when the current and voltage are in phase, it is resonance. The condition for resonance is given by the following equation 1.

Formula 1)

Here, ω is the angular frequency (2πf), L is the inductance of the series reactor, and C is the capacitance of the power capacitor.

If the frequency (f) in the above equation 1 is organized into the resonant frequency (f _r ), the resonant frequency (f _r ) is expressed by the following equation 2.

Formula 2)

Here, f _r is the resonant frequency, L is the inductance of the series reactor, and C is the capacitance of the power capacitor.

The above resonant frequency can be calculated using Equation 2 by detecting the electrostatic capacity (capacitance, C) of the power capacitor (110) and the inductance (L) of the series reactor (120).

When the resonant frequency is calculated, a range of cutoff frequencies that prevent the current of the calculated resonant frequency from being applied to the power capacitor is calculated, and when a frequency is detected within the range of the cutoff frequency, the diagnostic control unit (200) controls to operate an alarm device or to isolate the power capacitor from the system, thereby protecting the power capacitor (110) including the capacitor bank (100).

In the above, the cutoff frequency can be defined as a frequency that falls within a range having a current value of ±1/√2 of the maximum value (Imax) of the nth harmonic of the resonant frequency, and when a harmonic current having a frequency within this range flows in, the power capacitor (110) is configured to be protected by operating an alarm device or isolating the power capacitor (110) from the system.

FIG. 3 shows the configuration of a diagnostic control unit applied to an earthquake-resistant distribution panel (high-voltage distribution panel, low-voltage distribution panel, motor control panel, distribution panel) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention.

Referring to the attached Figure 3, the diagnostic control unit (200) applied to the present invention is configured to include a correction capacity calculation module (210), an inductance calculation module (220), a diagnostic module (230), a control module (240), a vibration detection module (250), and a temperature detection module (260).

The capacitance calculation module (210) calculates the capacitance of each phase of the power capacitor (110) based on the line current, frequency, and line-to-line voltage of the power capacitor.

The internal wiring method of the power capacitor (110) is Δ wiring at low voltage (1,000 V or less). However, at high voltage (7,000 V or less) and extra high voltage (over 7,000 V), the wiring of the power capacitor (110) is configured as Y wiring. In the case of the Y wiring method, the phase voltage is lowered to 1/√3 of the line-to-line voltage, so that the internal voltage of the power capacitor can be lowered.

The current (Ic) flowing through the power capacitor is calculated as ω × C × V (where ω is the angular frequency, C is the electrostatic capacitance, and V is the rated voltage), and the rated capacity (Qc) of the power capacitor is defined by the following equation 3.

Formula 3)

Here, Qc is the rated capacity of the capacitor (KVar), V is the rated voltage, I is the rated current, C is the electrostatic capacity (μF) (capacitance), ω is the angular frequency, and f is the rated frequency.

The rated capacity of the capacitor of the △ connection (Q _△ ) is three times that of the capacitor of the Y connection (Q _Y ), and when this is organized into a formula, it is defined as the following formula 4.

Formula 4)

Here, Q _△ is the rated capacity of the capacitor of △ connection, _CΔ is the electrostatic capacitance of the capacitor of Δ connection, f is the frequency, V _L is the line-to-line voltage, and Q _Y is the rated capacity of the capacitor of Y connection.

Therefore, the capacitor capacitance (C _Δ ) of the Δ connection is defined by the following equation 5.

Formula 5)

Here, _CΔ is the capacitor capacitance of Δ connection, _QΔ is the rated capacitor capacitance of Δ connection, f is the frequency, and V _L is the line-to-line voltage.

Also, in the Y connection, the phase voltage is 1/√3 times the line-to-line voltage, and this is defined as the following formula 6.

Formula 6)

Therefore, the capacitor capacitance (C _Y ) of the Y connection is defined by the following equation 7.

Formula 7)

Here, C _Y is the capacitor electrostatic capacitance of the Y connection, Q _Y is the rated capacitor capacity of the Y connection, f is the frequency, and V _L is the line-to-line voltage.

By the above formulas 5 and 7, the capacitance of the power capacitor can be calculated by the voltage and frequency applied to the power capacitor, and by comparing the calculated capacitance of the power capacitor with the capacitance in the steady state, the change in the current capacitance (capacitance) of the power capacitor can be calculated in real time.

In the above, the electrostatic capacitance of the power capacitor in the normal state is calculated by the line voltage and the fundamental frequency (60 Hz). If the deviation of the calculated electrostatic capacitance of the power capacitor from the electrostatic capacitance of the power capacitor in the normal state is in the range of 95 to 110%, it can be judged to be normal.

Accordingly, a case where the electrostatic capacity of the power capacitor produced is less than 95% of the electrostatic capacity in the normal state or where the electrostatic capacity of the power capacitor exceeds 110% of the electrostatic capacity in the normal state can be judged as an abnormal state.

In addition, the electrostatic capacity (capacitance) of each phase of the power capacitor is defined as Equation 8 below when derived from Equation 3.

Formula 8)

Here, C is the phase capacitance of the power capacitor, Qc is the rated capacity of the power capacitor, f is the frequency, and V is the rated voltage.

For the above formula 8, if each power line of the power system is defined as R, S, and T, and the current flowing in RS phase is I ₁ , the current flowing in ST phase is I ₂ , and the current flowing in TR phase is I ₃ , then in the △ connection, the line voltage and phase voltage are the same, so the capacitor capacitance of each phase of the △ connection is defined by the following formula 9.

Formula 9)

Here, C _Δ1 is the capacitor capacitance of RS phase, I ₁ is the line current flowing in R and S phases, f is the frequency, V ₁ is the line-to-line voltage of R and S phases, C _Δ2 is the capacitor capacitance of ST phase, I ₂ is the line current flowing in S and T phases, V ₂ is the line-to-line voltage of S and T phases, C _Δ3 is the capacitor capacitance of TR phase, I ₃ is the line current flowing in T and R phases, and V ₃ is the line-to-line voltage of T and R phases.

Also, since the phase voltage in the Y connection is 1/√3 times the line-to-line voltage, the capacitor capacitance for each phase of the Y connection is defined by the following equation 10.

Formula 10)

Here, C _Y1 is the capacitor capacitance of RS phase, I ₁ is the line current flowing in R and S phases, f is the frequency, V ₁ is the line-to-line voltage of R and S phases, C _Y2 is the capacitor capacitance of ST phase, I ₂ is the line current flowing in S and T phases, V ₂ is the line-to-line voltage of S and T phases, C _Y3 is the capacitor capacitance of TR phase, I ₃ is the line current flowing in T and R phases, and V ₃ is the line-to-line voltage of T and R phases.

Using the above formulas 9 and 10, the capacitance calculation module (210) calculates the electrostatic capacity, i.e., capacitance, of each phase of the power capacitor according to frequency, current, and voltage.

The inductance calculation module (220) performs the function of calculating the inductance of the series reactor (120) based on the rated voltage and rated current applied to the series reactor (120).

Among the harmonics generated by power capacitors, the third harmonic circulates in the delta connection of the transformer, so in order to remove the fifth harmonic, which is the most problematic, the capacity of the series reactor is 4% of the rated capacity (Qc) of the power capacitor due to the resonance conditions of capacitance and inductance. However, considering frequency fluctuations and economic aspects, it is actually applied as 6% of the rated capacity (Qc) of the capacitor.

The inductance of the series reactor (120) is calculated using the reactor rated voltage and reactor rated current.

Here, the phase voltage is line-to-line voltage/√3, and the capacity of the series reactor is 6% of the capacity of the power capacitor.

If expressed as a formula, it is expressed as the following formula 11.

Formula 11)

Here, V _SR is the series reactor rated voltage and V _L is the circuit voltage.

In the above, the circuit voltage refers to the voltage applied to a series reactor connected in combination with a power capacitor.

In addition, the reactor rated current (I _SR ) is calculated by the reactor rated capacity (Q _L ) of the series reactor, and since the reactor rated capacity (Q _L ) is calculated by the reactor rated current (I _SR ) × reactor rated voltage × 3, when this is organized into the reactor rated current (I _SR ), it is expressed as the following equation 12.

Formula 12)

Here, I _SR is the reactor rated current, Q _L is the reactor rated capacity, and V _SR is the reactor rated voltage.

The reactor rated capacity (Q _L ) is calculated as 0.06 times the capacitor rated capacity (Qc) of the power capacitor, and the reactor rated voltage (V _SR ) is calculated by Equation 11.

Accordingly, the inductive reactance (X _L ) is calculated as ωL, but can be calculated as the ratio of the reactor rated voltage (V _SR ) and the reactor rated current (I _SR ).

If this is expressed as a formula, it is expressed as the following formula 13.

Formula 13)

Here, X _L is the inductive reactance, V _SR is the reactor rated voltage, I _SR is the reactor rated current, ω is the angular frequency, and L is the inductance.

If the above equation 13 is organized into inductance (L), the inductance (L) of the series reactor is organized into the following equation 14.

Formula 14)

Here, L is the inductance, ω is the angular frequency (2πf), f is the frequency, V _SR is the reactor rated voltage, and I _SR is the reactor rated current.

Accordingly, the inductance calculation module (220) calculates the inductance of the series reactor (120) using Equation 14.

The diagnostic module (230) calculates the resonant frequency based on the capacitance calculated by Equation 9 or Equation 10 in the electrostatic capacity calculation module (210) and the inductance calculated by Equation 14 in the inductance calculation module (220), and diagnoses the capacitor bank (100) based on the calculated resonant frequency.

In detail, the above diagnostic module (230) calculates a cutoff frequency range that prevents the current of the calculated resonant frequency from being applied to the power capacitor when the resonant frequency is calculated, and outputs a signal to control the operation of an alarm device or to control the disconnection of the power capacitor from the system when a frequency is detected within the cutoff frequency range.

At this time, the resonant frequency is calculated by the above formula 2.

The control module (240) separates the capacitor bank (100) from the power system or operates an alarm device according to the diagnosis result of the diagnosis module (230).

In addition, although not shown in the drawing, the control module (240) may be configured to provide the control status of the distribution panel by transmitting it to an HMI (Human Machine Interface) or the like in connection with a communication device.

Meanwhile, the distribution board is installed firmly fixed to the ground so that it does not shake or fall over due to vibrations such as earthquakes. However, if the distribution board is firmly fixed to the ground, there is a risk of damage or destruction due to direct vibration applied to the internal power equipment when an earthquake occurs.

Accordingly, the cubicle of the present invention is equipped with an earthquake-resistant device to reinforce the corner portion connected to the frame so as to withstand vibration transmitted from the ground.

The above-mentioned earthquake-resistant device can be formed of a conventional plate spring structure, and stably fixes the frame so that the frame's joint state can be maintained against vibration by reinforcing the frame-to-frame joint strength through the plate spring to transmit vibration.

Even if a seismic device that increases the seismic resistance to vibration is applied in this way, there is a problem in that vibration can be transmitted to the cubicle, and if the seismic resistance of the seismic device is exceeded, the vibration transmitted to the cubicle can damage the internal power equipment or cause abnormal current to flow to the load side.

Accordingly, in the present invention, a vibration detection module (250) is configured to detect vibration and output a signal or cut off power, etc. according to the detected vibration.

The above vibration detection module (250) detects the size of the vibration by installing a sensor, such as a displacement sensor, in the earthquake-resistant device to detect the displacement of the vibration and output the result. That is, the displacement sensor can be attached and installed in the earthquake-resistant device of the plate spring that is coupled to the frame corner of the cubicle.

The above control module (240) is configured to control (cut off power, etc.) based on the vibration value transmitted from the vibration detection module (250).

In addition, factors affecting the insulation deterioration of power capacitors include conditions such as voltage and current supplied to the power capacitor, but the internal and external temperatures of the power capacitor also have a significant impact on the insulation deterioration.

Accordingly, by increasing the withstand voltage margin to enhance the withstand of harmonic voltage and current, and managing the ambient temperature where the power capacitor is installed so that it does not exceed 45℃, the current supplied to the power capacitor and the internal/external temperature are regularly checked to prevent the rupture of the power capacitor.

However, since these tasks require human resources, they not only take up a lot of time and money to manage, but can also create gaps in management.

In the present invention, a temperature detection module (260) for detecting the surface temperature of a power capacitor is configured to provide a prediction of the remaining life of a power capacitor based on the temperature of the power capacitor, and a diagnosis module (230) is configured to calculate the life of the power capacitor based on the temperature detected by the temperature detection module (260).

The above temperature detection module (260) may be configured to include a temperature sensor capable of detecting the temperature of the power capacitor (110).

The above temperature sensor may be either a contact or non-contact type, but a contact temperature sensor may be applied considering the type of distribution panel, installation location, or power distribution power. At this time, the temperature sensor may be attached to the surface of the casing of the power capacitor, and the attachment may be configured to be easily detached using a magnet or the like.

Meanwhile, the Arrhenius model is expressed as a master curve and relationship of time-temperature by judging the time point at which a certain change in the initial characteristic value occurs at various temperatures as the life. From this relationship, the predicted life at a specific temperature can be calculated, and the life due to natural aging at room temperature can be predicted using the data obtained as the results of an accelerated test.

The cause of temperature rise in power equipment is due to current. That is, the greater the amount of current flowing, the higher the temperature generated in the power equipment.

Accordingly, when expressed as the current applied to the power capacitor from the above equation 3, it is expressed as the following equation 15.

Formula 15)

Here, I _C is the current applied to the power capacitor, C is the capacitance of the power capacitor, f is the frequency, and V is the voltage applied to the power capacitor.

According to the above equation 15, the current (I _C ) is determined by the frequency (f), the capacitance (C) and the rated voltage, and the capacitance (C) of the power capacitance can be calculated using equation 9 or equation 10.

At this time, the above equations 9 and 10 are for calculating the resonant frequency, but since its size is ㎌, even if its size changes, the effect on the current applied to the power capacitor may be minimal.

Here, if the capacitance (C) is assumed to have a small amount of change and the power capacitor is used as a passive filter connected in series with a series reactor to provide reactive power, stabilize voltage, improve power factor, and reduce harmonics generated in the power system, when the voltage increases, the current also increases, generating heat in the power capacitor. Accordingly, if the Arrhenius model is applied to the temperature generated inside the power capacitor, the remaining life of the power capacitor is expressed by the following equation 16).

Formula 16)

Here, L _i is the remaining life of the power capacitor, A is a characteristic constant of the dielectric material, and n is the overvoltage exponent.

In the above, for the immersion paper, n is 7 to 8, and for the film, n has a value between 10 and 12.

Referring to the above equation 16, the main causes of insulation destruction or deterioration due to electrical stress in power capacitors are voltage and temperature.

In the Arrhenius model, there is an empirical model called the 2 ⁿ model when accelerating the life of a product or component. The 2 ⁿ model applies the theory that the life is halved for every 10℃ increase in temperature.

At this time, if the change in temperature at which the life of the power capacitor is halved is △θ, the relationship between the remaining life (L _i ) for the total life (L _IO ) and the temperature for the initial temperature (θ ₀ ) and the detection temperature (θ) of the power capacitor is expressed by the following equation 17).

Formula 17)

Here, L _i is the remaining life of the power capacitor, L ₀ is the total life of the power capacitor, θ is the detection temperature, θ ₀ is the initial temperature, and △θ is the temperature change that is halved.

Using the above equation 17, the temperature change that is reduced by half of the power capacitor is approximately 10℃, and when this is organized into a case where the voltage and temperature applied to the power capacitor increase simultaneously, it is expressed as the following equation 18.

Formula 18)

Here, L _i is the remaining life of the power capacitor, V is the detection voltage, V ₀ is the initial voltage, n is the overvoltage index, L ₀ is the total life of the power capacitor, θ is the detection temperature, and θ ₀ is the initial temperature.

In the present invention, the diagnostic module (230) of the diagnostic control unit (200) calculates the remaining life of the power capacitor through Equation 18 based on the detected voltage and temperature, and the calculated remaining life is configured to be displayed on a display through the control module (240) or transmitted to an HMI (Human Machine Interface) or the like in connection with a communication device, thereby providing the remaining life of the power capacitor configured in the distribution panel.

Although the above has described preferred embodiments of an earthquake-resistant distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor according to the present invention, the present invention is not limited thereto, and various modifications may be made within the scope of the claims, the description of the invention, and the attached drawings, and this also falls within the scope of the present invention.

10: Cubicle 100: Capacitor Bank
110: Power capacitor 120: Series reactor
200: Diagnostic control unit 210: Electrostatic capacity calculation module
220: Inductance calculation module 230: Diagnostic module
240: Control module 250: Vibration detection module
260: Temperature sensing module

Claims (9)

A capacitor bank (100) including a power capacitor (110) installed in a cubicle (10) to improve the power factor and a series reactor (120) connected in series to the power capacitor (110) to correct the current phase and prevent the occurrence of harmonics; and
A diagnostic control unit (200) that calculates a resonant frequency through a capacitance calculated based on the capacitive capacitance of the power capacitor (110) and an inductance calculated from the inductive inductance of the series reactor (120), and controls the capacitor bank (100) to be separated from the power system when the frequency flowing into the distribution board approaches the calculated resonant frequency;
Including,
The above diagnostic control unit (200)
A capacitance calculation module (210) that calculates the capacitance of each phase of the power capacitor based on the line current, frequency, and line-to-line voltage of the power capacitor (110);
An inductance calculation module (220) that calculates the inductance of the series reactor (120) based on the rated voltage and rated current applied to the series reactor (120);
A diagnostic module (230) that calculates a resonant frequency based on the capacitance calculated by the electrostatic capacity calculation module (210) and the inductance calculated by the inductance calculation module (220) and diagnoses the capacitor bank (100) based on the calculated resonant frequency;
A control module (240) that separates the capacitor bank (100) from the power system according to the diagnosis result of the above diagnosis module (230);
A vibration detection module (250) that detects vibration; and
A temperature detection module (260) that detects the temperature of the above power capacitor (110);
Including,
Based on the vibration value detected by the vibration detection module (250), the vibration is analyzed, and the power cut-off operation is controlled or an alarm is notified according to the analysis result.
An earthquake-resistant distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor, characterized in that the lifespan due to deterioration of the power capacitor (110) is diagnosed and provided based on the temperature detected by the temperature detection module (260), and the remaining lifespan due to deterioration of the power capacitor (110) is calculated using the following formula.
formula)

Here, L _i is the remaining life of the power capacitor, V is the detection voltage, V ₀ is the initial voltage, n is the overvoltage index, L ₀ is the total life of the power capacitor, θ is the detection temperature, and θ ₀ is the initial temperature.
delete In claim 1,
If the power capacitor (110) is Δ-connected, the electrostatic capacity calculation module (210) is characterized in that the capacitance is calculated by the following formula: an earthquake-resistant distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor.
formula)

Here, C _Δ1 is the capacitor capacitance of RS phase, I ₁ is the line current flowing in R and S phases, f is the frequency, V ₁ is the line-to-line voltage of R and S phases, C _Δ2 is the capacitor capacitance of ST phase, I ₂ is the line current flowing in S and T phases, V ₂ is the line-to-line voltage of S and T phases, C _Δ3 is the capacitor capacitance of TR phase, I ₃ is the line current flowing in T and R phases, and V ₃ is the line-to-line voltage of T and R phases.
In claim 1,
If the above power capacitor (110) is Y-connected, the above electrostatic capacity calculation module (210) is characterized in that the capacitance is calculated by the following formula: an earthquake-resistant distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor.
formula)

Here, C _Y1 is the capacitor capacitance of RS phase, I ₁ is the line current flowing in R and S phases, f is the frequency, V ₁ is the line-to-line voltage of R and S phases, C _Y2 is the capacitor capacitance of ST phase, I ₂ is the line current flowing in S and T phases, V ₂ is the line-to-line voltage of S and T phases, C _Y3 is the capacitor capacitance of TR phase, I ₃ is the line current flowing in T and R phases, and V ₃ is the line-to-line voltage of T and R phases.
In claim 1,
The above inductance calculation module (220) is an earthquake-resistant distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor, characterized in that the inductance is calculated by the following formula.
formula)

Here, L is the inductance, X _L is the inductive reactance of the series reactor, ω is the angular frequency (2πf), f is the frequency, V _SR is the reactor rated voltage, and I _SR is the reactor rated current.
In claim 1,
The above diagnostic module (230) is
An earthquake-resistant distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor, characterized in that when the above resonant frequency is calculated, a cutoff frequency range that prevents the current of the calculated resonant frequency from being applied to a power capacitor is calculated, and when a frequency in the above cutoff frequency range is detected, a signal is output to control an alarm device to operate or a control signal to disconnect the power capacitor from the system is output.
In claim 6,
An earthquake-resistant distribution board (high voltage distribution board, low voltage distribution board, motor control board, distribution board) having a real-time deterioration diagnosis function of a power capacitor and a series reactor, characterized in that the above-mentioned cutoff frequency is a frequency that falls within a range having a current value of ±1/√2 of the maximum value (Imax) of the nth harmonic of the above-mentioned resonant frequency.
delete delete