Temperature-dependent amperometric correction system and method

Abstract

The temperature-dependent current measurement correction system according to the present invention comprises: a distribution line; a transformer that transforms the voltage of power transmitted from the distribution line into low-voltage power that can be used by a consumer; and a terminal device (FRTU) formed around the transformer that monitors the three-phase distribution line connected between the utility pole and the transformer, measures the voltage and current, calculates the temperature coefficient (α) of the resistance, and corrects the current measurement value. By calculating the temperature coefficient of the resistance to correct the current measurement value according to temperature, the system has the effect of enabling more precise measurement.

Description

Technology Field

[0001] The present invention relates to a temperature-dependent current measurement correction system and method, and more specifically, to a temperature-dependent current measurement correction system and method capable of improving current measurement precision by correcting the current calculation formula of a distribution automation terminal device currently connected to a distribution network without the need to install additional devices. Background Technology

[0003] Conventional technology requires a step of applying voltage or current to a fixed load and continuously measuring for a set period of time using a measurement module, deriving a correction value using sampling data and Ohm's law, and correcting for each sample.

[0004] In particular, conventional technology improves the measurement precision of voltage and current based on a fixed load, but it has a problem in that it cannot resolve the phenomenon where the magnitude of resistance changes with temperature, affecting the precision of the current.

[0005] In addition, Patent Document 2 below has the cumbersome problem of requiring the installation of a separate device in a manner that involves installing a separate sensor and measuring device near a control device intended for line protection operation, and correcting the voltage and current measurement values ​​of the control device using the magnitude and phase of the voltage and current measured by the measuring device. Prior art literature

[0007] Patent Document 1: Korean Registered Patent Publication No. 10-1446669 (September 25, 2014) Patent Document 2: Korean Registered Patent Publication No. 10-1227653 (January 23, 2013) The problem to be solved

[0008] To solve the problems described above, the present invention aims to provide a temperature-dependent current measurement correction system and method that can improve current measurement precision by correcting the current calculation formula of a distribution automation terminal device currently connected to the distribution network, without requiring any additional devices to be installed. means of solving the problem

[0010] To achieve the above-mentioned objective, the temperature-dependent current measurement correction system according to the present invention comprises: a distribution line; a transformer that transforms the voltage of power transmitted from the distribution line into low-voltage power usable by a consumer; and a terminal device (FRTU) formed around the transformer that monitors a three-phase distribution line connected between a utility pole and a transformer, measures voltage and current, calculates a temperature coefficient (α) of resistance, and corrects the measured current value; wherein the terminal device (FRTU) has a current gain (I) on the fundamental wave gain Correcting the current calculation process by multiplying by ) to obtain the current gain (I gain ) mathematical expression Calculated as such, and a current gain (I) reflecting the temperature coefficient (α) of the above resistance to improve current precision. gain ) mathematical expression Characterized by calculating as follows, wherein the temperature coefficient (α) of the resistance is given by a mathematical formula It is characterized by calculating as.

[0011] In another embodiment, to achieve the above-described objective, the temperature-dependent current measurement correction method according to the present invention measures voltage and current while monitoring a three-phase distribution line formed around a transformer and connected between a utility pole and a transformer, and calculates a temperature coefficient (α) of resistance to correct the measured current value, wherein the method comprises: (a) a step in which a current measurement unit (110) of a terminal device measures the current value of the distribution line; (b) a step in which an A / D converter of the terminal device converts the current value into a digital signal; (c) a step in which a main board of the terminal device applies a current gain (I) to the current value converted into a digital signal gain (d) a step of applying the current gain (I) by the DSP of the main board gain A step of calculating RMS (Root Mean Square: RMS value) by applying the ) value; and (e) a step in which the HMI board of the terminal device displays the RMS current value calculated by the DSP on an LCD; wherein the main board, in step (c), the current gain (I gain It is characterized by calculating by reflecting the temperature coefficient (α) of resistance when applying ). Effects of the invention

[0013] The temperature-dependent current measurement correction system and method according to the present invention have the effect of enabling more precise measurement by calculating the temperature coefficient value of resistance to correct the temperature-dependent current measurement value and applying the correction to the measurement value.

[0014] In addition, the temperature-dependent current measurement correction system and method according to the present invention have the effect of enabling more accurate fault current determination through current measurement values ​​that consider the amount of current change according to temperature. Brief explanation of the drawing

[0016] FIG. 1 is a configuration diagram of a temperature-dependent current measurement correction system according to the present invention. FIG. 2 is a block diagram of a terminal device of a temperature-dependent current measurement correction system according to the present invention. FIG. 5 is a circuit diagram of the current measurement unit of a terminal device in a temperature-dependent current measurement correction system according to the present invention. Figure 4 is a flowchart of a current measurement correction method according to temperature according to the present invention. FIG. 5 is a reference drawing for explaining a current measurement correction method according to temperature according to the present invention. Specific details for implementing the invention

[0017] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0018] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely one preferred embodiment of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0019] Hereinafter, a temperature-dependent current measurement correction system and method according to the present invention will be described with reference to the attached drawings.

[0020] FIG. 1 is a diagram illustrating peripheral technology for explaining a temperature-dependent current measurement correction system according to the present invention.

[0021] As shown in FIG. 1, the current power distribution system includes a terminal unit (FRTU: Feeder Remote Terminal Unit: 100), a transformer (200), and a DCU (Data Concentration Unit: 300). When power is transmitted from a high-voltage line to the transformer (200), the transformer (200) can transform the power into low-voltage power that can be used at a consumer and supply it.

[0022] At this time, the DCU (300) monitors the low-voltage line formed at the lower output terminal of the transformer and connected to a plurality of consumers.

[0023] The above terminal device (FRTU:100) is formed at predetermined distances on the upper part of the transformer (200) and monitors the high-voltage line at the input end between the three-phase high-voltage line connected from the utility pole and the transformer, measures the voltage and current, and transmits them in real time to the upper system, the distribution system server (400).

[0024] The above distribution system server (400) generates various data such as fault, inrush, and PQM using voltage and current measurement values ​​received from the terminal device (100).

[0025] As shown in FIG. 2, the above terminal device (100) includes a current measuring unit (110), a surge board (130), a main board (140), an HMI (Human-Machine Interface) board (150), and a communication module (160).

[0026] The above current measuring unit (100) is configured with a current measuring circuit as shown in FIG. 3, and when a current value is input, it measures the current value based on the magnitude of the voltage across the resistor.

[0027] It can be seen that the current measured by the above current measuring unit (100) has a different precision as the magnitude of the resistance changes depending on the change in temperature.

[0028] As described above, in order to correct the current measurement value measured by the current measuring unit (100) according to the temperature, the temperature coefficient value of the resistance is calculated and the correction is applied by reflecting the temperature coefficient value of the resistance in the measurement value, thereby enabling more precise current measurement.

[0029] The temperature coefficient of the above resistance can be calculated as shown in [Equation 1] below.

[0030]

[0031] R a : Resistance value according to reference temperature

[0032] T a : Reference temperature

[0033] R: Resistance value according to arbitrary temperature

[0034] T: arbitrary temperature

[0035] In the above [Mathematical Formula 1] (RR a ) / R a represents the rate of change of the resistance value, and the temperature coefficient of resistance is defined in the component's resistance datasheet.

[0036] For example, it is defined as shown in [Table 1] below.

[0037] Rated power Previous term value range (ohm) TCR (Temperature Coefficient) Zen Buddhism 1W 0.1~0.18 710 ppm / ℃ Alloy 60 0.2~0.56 490 ppm / ℃ Alloy 90 0.62~43 100 ppm / ℃ CNW 47~180 260 ppm / ℃ NCNW

[0038] By using the temperature coefficient of such resistance, the rate of change of the resistance value can be calculated using the reference temperature (25℃) and the current temperature, and this calculated value can be used to detect minute changes in the resistance magnitude. By calculating the rate of change of the resistance value and correcting the measured value of the terminal device for this rate, the actual measured value can be determined more accurately.

[0039] The surge board (130) transmits the current value measured by the current measuring unit (110) to the main board (140).

[0040] The main board (140) includes a DSP (Digital Signal Processor: 141) and a CUP (Central Processing Unit: 142). The DSP (310) receives the current value and calculates the amount of electricity, and the CPU (142) transmits the amount of electricity calculated by the DSP (141) to the HMI board (150).

[0041] The DSP (141) converts the current value that has passed through the CT (Current Transformer) of the surge board (130) into a digital signal, and then applies a current gain (GAIN) value to calculate the RMS (Root Mean Square: RMS value) and transmits the current value to the HMI board (150).

[0042] Meanwhile, the above DSP (141) performs a fault detection function by calculating various electrical quantities using the converted digital data.

[0043] The above DSP (141) utilizes the fundamental wave current of each phase, which is the FFT result value every 1ms, to perform a fault detection function when the minimum operating current of the set value is exceeded and to notify of the fault.

[0044] Meanwhile, the above DSP (141) calculates various electric quantities as shown in [Table 2] below.

[0045] Operation item formula Effective phase voltage (Va, Vb, Vc / Vr, Vs, Vt) Calculation of average RMS voltage value for 12 cycles per phase RMS value line currents Ia, Ib, Ic, In, Iz Calculation of average RMS current value for 12 star cycles Active power by phase Calculated as a one-cycle average of the sum of the products of the instantaneous current and voltage for each phase, and then calculated as a 12-cycle average. Phase-specific reactive power 12-cycle average of the product of 1-cycle effective current and voltage Apparent power by phase 12-cycle average of the product of 1-cycle effective current and voltage 3-phase bundled active power Calculate the active power for each phase as the three-phase sum 3-phase combined reactive power Calculate the reactive power for each phase as the three-phase sum 3-phase lump-sum apparent power Calculate the apparent power of each phase as the three-phase sum

[0046] The above HMI board (150) is composed of an LCD and an LED, and the status is displayed on the LCD and LED.

[0047] That is, on the above LCD (status display), the effective voltage and current (average of 12 cycles) for each phase, the faulty phase (occurs when the current value of each phase exceeds the minimum operating current every 1ms / fault is released when the fault release function is performed), and the live / dead line status for each phase (live line status notification when the voltage value of each phase exceeds the live line level <set value> and is maintained for more than the live line maintenance time <set value> every 1ms / dead line status notification when it is below the live line level) can be checked.

[0048] The above LED (front notification lamp) allows you to check whether a malfunction has occurred and whether the line is live or dead.

[0049] Here, the DSP (141) improves current precision by correcting the current calculation process.

[0050] That is, as mentioned, the DSP (141) applies the current gain to the fundamental wave in the current calculation process, and the current gain is as shown in [Equation 2] below.

[0051] R is the resistance value according to any temperature.

[0052] If the temperature coefficient (α) value of the resistance is reflected in the above [Equation 2], it is as shown in [Equation 3] below.

[0053]

[0054] In the above mathematical formula, R a is the resistance value at a reference temperature for being measured as a sample of voltage and converted into current.

[0055] The external CT ratio refers to the ratio of the measuring CT of the switch or circuit breaker, and is 1000:1.

[0056] The internal CT ratio refers to the ratio of the measuring CTs of the terminal device or circuit breaker, and is 100:1.

[0057] V REF is a reference voltage, which serves as a standard voltage. This voltage is used as the reference voltage value for the ADFullScale and is a parameter provided in the datasheet specified by the manufacturer for each component.

[0058] The above ADFullScale is a value obtained by dividing the reference voltage of the AD Converter by the resolution, and is a parameter given on the data sheet for each manufacturer of the AD Converter.

[0059] At this time, it is preferable that the temperature coefficient (α) of the resistance in [Equation 3] above be calculated as in [Equation 1] above.

[0060] Therefore, unlike conventional technology, the present invention does not require the installation of additional devices by correcting the resistance value differently according to temperature.

[0061] The above communication module (160) transmits current data corrected by reflecting temperature information measured by the terminal device (FRTU: Feeder Remote Terminal Unit: 100) to the above distribution system server (400).

[0062] As mentioned above, the distribution system server (400) can generate various data such as fault, inrush, and PQM (Product Quality Manager?) using voltage and current measurement values ​​received from the terminal device (100).

[0063] A correction method using a temperature-dependent current measurement correction system according to the present invention having the configuration described above will be explained with reference to FIGS. 4 and 5.

[0064] First, the current measuring unit (110) of the terminal device (100) performs the step of measuring the current value of the power distribution line (S100).

[0065] The A / D converter (120) of the above terminal device (100) performs the step of converting the current value into a digital signal (S200).

[0066] The main board (140) of the terminal device (100) stores the sampling data converted into digital samples (128 samples per cycle) by the A / D converter (120) in a memory buffer.

[0067] The main board (140) of the terminal device (100) performs the step of applying the current gain of [Equation 2] to the current value converted into a digital signal (S300).

[0068] At this time, it is preferable for the main board (140) to calculate the temperature coefficient (α) as described in [Equation 3] when applying the current gain.

[0069] The DSP (141) of the main board (140) performs the step of calculating the RMS (Root Mean Square: RMS value) by applying the current gain (GAIN) value (S400).

[0070] The HMI board (150) of the terminal device (100) performs the step of displaying the RMS current value calculated by the DSP (141) on the LCD (S500).

[0071] Meanwhile, the data flow for measurement, fault monitoring, etc. is explained in more detail with reference to Fig. 5.

[0072] The Sampled Data section acquires sample data by passing the current and voltage of each phase of the analog signal through an AD converter, and acquires 128 samples from a 60Hz electrical signal.

[0073] FFT & Metering stands for Fast Fourier Transform and is performed once every 8 samples, or 1ms. By performing the FFT, information regarding the magnitude and phase from DC to the 63rd harmonic can be obtained, and based on this data, calculations regarding various power quantities are performed.

[0074] The Disturbance Detector monitors once every 0.5 cycles based on an electrical frequency of 60 Hz and monitors the voltage status (instantaneous voltage drop, instantaneous voltage rise, instantaneous power outage, etc.) as a measure of electrical quality.

[0075] The calculation of power data in the Measurements section is performed in accordance with “61000-4-30 Test and Measurement Techniques - Methods for Measuring Electrical Quality”. Accordingly, power data such as RMS and Power represent the average value over 12 cycles, and other aspects are performed in accordance with the performance standards of IEC 61000-4-30.

[0076] Zero Crossing Signal calculates the frequency by tracking the point where the voltage passes the zero value to calculate the time period and taking the reciprocal of it.

[0077] The Fault Detection Protection Fault Location section utilizes the fundamental wave components of each current phase calculated by FFT every 1ms to detect overcurrent every 1ms. It operates by comparing the fundamental wave components of each current phase with the minimum operating current setting value, and notifies of an electrical fault if the fundamental wave components exceed the minimum operating current setting value. Terminal devices around the point where the fault occurred can locate the fault by notifying of the fault.

[0078] Although the technical concept of the present invention has been described above together with the accompanying drawings, this is merely an illustrative explanation of preferred embodiments of the present invention and is not intended to limit the invention. Furthermore, it is evident that anyone with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and imitations within the scope of the technical concept of the present invention without departing from its scope. Explanation of the symbols

[0079] 100 : Terminal device (FRTU: Feeder Remote Terminal Unit) 110: Current measuring unit 130 : Surge Board 140 : Motherboard 141: DSP (Digital Signal Processor) 142: CUP(Central Processing Unit) 150 : HMI (Human-Machine Interface) board 160 : Communication module 200 : Transformer 300 : DCU (Data Concentration Unit)

Claims

Claim 1 A distribution line; a transformer that transforms the voltage of power transmitted from the distribution line into low-voltage power usable by a consumer; and a terminal device (FRTU) formed around the transformer that monitors the three-phase distribution line connected between the utility pole and the transformer, measures voltage and current, calculates the temperature coefficient (α) of the resistance, and corrects the measured current value; wherein the terminal device (FRTU) includes a current measuring unit that measures the current value based on the magnitude of the voltage across the resistance; a surge board that transmits the current value measured by the current measuring unit to a main board; and a current gain (I) that converts the current value passing through the CT (Current Transformer) of the surge board into a digital signal. gain A temperature-dependent current measurement correction system characterized by comprising: a main board composed of a DSP (Digital Signal Processor) that transmits a current value calculated using RMS (Root Mean Square: RMS value) by applying a value to an HMI board, performs a fault detection function and notifies of a fault when the minimum operating current of a set value is exceeded by utilizing the fundamental wave current of each phase, which is the FFT result value every 1ms, and a CPU that transmits the electric quantity data calculated by the DSP to the HMI board; an HMI (Human-Machine Interface) board on which the calculated current value or the electric quantity data status is displayed on an LCD; and a communication module that transmits the corrected current data, reflecting temperature information measured by a terminal device (FRTU: Feeder Remote Terminal Unit), to a power distribution system server. Claim 2 delete Claim 3 In claim 1, the terminal device (FRTU) has a current gain (I) that reflects the temperature coefficient (α) of the resistance. gain ) mathematical expression Calculated as follows, wherein in the above mathematical formula, the external CT ratio is the ratio of the measuring CTs of the switch or circuit breaker, and the internal CT ratio is the ratio of the measuring CTs of the terminal device or circuit breaker, and V REF is the reference voltage, which serves as the standard voltage, and ADFullScale is the value obtained by dividing the A / D converter's reference voltage by the resolution, and R a A temperature-dependent current measurement correction system characterized in that is a resistance value according to a reference temperature, Ta is a reference temperature, and T is the temperature at the time of current measurement. Claim 4 In Clause 3, the temperature coefficient (α) of the resistance is the mathematical formula Calculate as, but R a is the resistance value according to the reference temperature, T a is the reference temperature, R is the resistance value according to an arbitrary temperature, and T is an arbitrary temperature, and (RR a ) / R a A temperature-dependent current measurement correction system characterized by being the rate of change of resistance value. Claim 5 A temperature-dependent current measurement correction method for monitoring a three-phase distribution line formed around a transformer and connected between a utility pole and a transformer, measuring voltage and current, and calculating a temperature coefficient (α) of resistance to correct the measured current value, comprising: (a) a step in which a current measuring unit (110) of a terminal device measures the current value of the distribution line; (b) a step in which an A / D converter of the terminal device converts the current value into a digital signal; (c) a step in which a DSP constituting the main board of the terminal device calculates a current gain (I gain A method for correcting current measurement according to temperature, characterized by comprising: a step of calculating the RMS (Root Mean Square: RMS value) of a current value converted into a digital signal by applying a value, and utilizing the fundamental wave current of each phase, which is the FFT result value every 1ms, to perform a fault detection function and notify of a fault when the current exceeds the minimum operating current of a set value; and a step in which the HMI (Human-Machine Interface) board of the terminal device displays the RMS current value calculated by the DSP (Digital Signal Processor) on an LCD. Claim 6 In claim 5, the main board is the current gain (I) in step (c). gain A temperature-dependent current measurement correction method characterized by calculating by reflecting the temperature coefficient (α) of resistance when applying ). Claim 7 In claim 6, the above current gain (I gain ) reflects the temperature coefficient (α) It is calculated as follows, wherein the external CT ratio is the ratio of the measuring CTs of the switch or circuit breaker and the internal CT ratio is the ratio of the measuring CTs of the terminal device or circuit breaker, and V REF is the reference voltage, which serves as the reference, and ADFullScale is the value obtained by dividing the A / D converter's reference voltage by the resolution, and R a is the resistance value according to the reference temperature, Ta is the reference temperature, T is the temperature at the time of current measurement, and the temperature coefficient (α) of the resistance is It is calculated as, but R a is the resistance value according to the reference temperature, T a is the reference temperature, R is the resistance value according to an arbitrary temperature, and T is an arbitrary temperature, and (RR a ) / R a A temperature-dependent current measurement correction method characterized by the fact that is the rate of change of resistance value.

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