Abstract:
Embodiments of an electric power measuring system capable of computing accurate electric power information using a low voltage measuring instrument in a small-scale electric power system are provided. The electric power measuring system may include a first measuring instrument for measuring and detecting a current and a zero-cross point from a distribution line and for generating and outputting current information of the distribution line from the current and the zero-cross point, and a second measuring instrument for computing electric power information of the distribution line according to a voltage thereof and the current information output from the first measuring instrument.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2015-0099936, filed on Jul. 14, 2015 entitled “ELECTRIC POWER MEASURING SYSTEM”, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present disclosure relates to an electric power measuring system, and more particularly, to an electric power measuring system capable of computing accurate electric power information using a low voltage measuring instrument in a small-scale electric power system. 
         [0004]    Description of the Related Art 
         [0005]    Generally, an electric power measuring system measures a voltage and a current flowing at an electric power system in a distribution panel or a panel board, that is, a load of a distribution line to compute electric power information such as electric energy and the like through various computations. 
         [0006]    The electric power measuring system includes a measuring instrument for measuring a voltage and an amount of a current from a distribution line to generate various measuring information. The measuring instrument is classified into a high voltage measuring instrument and a low voltage measuring instrument. 
         [0007]    The high voltage measuring instrument measures all of a voltage and an amount of a current from a distribution line to generate first data, for example, data including voltage information, current information, power factor information and the like, and processes the first data to generate second data, for example, electric power information of the distribution line. The low voltage measuring instrument measures one of a voltage and an amount of a current from a distribution line to generate first data. 
         [0008]    Meanwhile, in a small-scale distribution panel or panel board, an electric power measuring system is established with only a low voltage measuring instrument due to a manufacture cost factor. And, the low voltage measuring instrument measures one of a voltage and an amount of a current of a distribution line and generates first data according to the measurement to transmit the first data to an external side through a communication. 
         [0009]      FIG. 1  is a diagram schematically illustrating a configuration of a typical electric power measuring system. 
         [0010]    As shown in  FIG. 1 , a typical electric power measuring system  1  includes a low voltage measuring instrument, that is, a current measuring instrument  20  which measures a current from a distribution line  10  to generate current information I in a distribution panel or a panel board. 
         [0011]    In the distribution line  10  configured with a three-phase balanced line having phase terminals of an R-phase, an S-phase, and a T-phase, the current measuring instrument  20  measures a current value with respect to one of the R-, S-, and T-phases. 
         [0012]    The current measuring instrument  20  generates the current information I of the distribution line  10  from the measured current value to transmit the current information I to an integrated measuring instrument  30  of an external side through a communication. 
         [0013]    The integrated measuring instrument  30  computes electric power information P of the distribution line  10  from the current information I transmitted from the current measuring instrument  20  on the basis of voltage information V, for example, alternating current (AC) voltage information of the distribution line  10 , provided from the external side. The electric power information P is information regarding an AC electric energy. 
         [0014]    As described above, in the typical electric power measuring system  1 , the current measuring instrument  20  is installed inside the distribution panel or the panel board, and the current information I of the distribution line  10  is transmitted from the current measuring instrument  20  to the integrated measuring instrument  30  of the external side to compute the electric power information P of the distribution line  10 . 
         [0015]    In the typical electric power measuring system  1 , however, when the current measuring instrument  20  transmits the current information I to the integrated measuring instrument  30 , a problem in which a phase of the current information I is not synchronized with that of the voltage information V may occur due to a time delay and the like. 
         [0016]    As a result, when the integrated measuring instrument  30  computes the electric power information P of the distribution line  10 , a phase error between the voltage and the current may occur in the typical electric power measuring system  1 . Consequently, it is difficult to accurately compute the electric power information P of the distribution line  10  to cause a problem in which reliability of the typical electric power measuring system  1  is degraded. 
       SUMMARY 
       [0017]    Therefore, to address the problems described above, an object of some embodiments of the present disclosure is to provide an electric power measuring system capable of computing accurate electric power information of a distribution line using a current measuring instrument installed inside a distribution panel or a panel board. 
         [0018]    An electric power measuring system according to one embodiment of the present disclosure includes a first measuring instrument configured to measure and detect a current and a zero-cross point from a distribution line and to generate and output current information of the distribution line from the current and the zero-cross point, and a second measuring instrument configured to compute electric power information of the distribution line according to a voltage thereof and the current information output from the first measuring instrument. 
         [0019]    The first measuring instrument may convert a phase of the current from the zero-cross point and generate the current information including a magnitude of the current and the converted phase thereof. 
         [0020]    The first measuring instrument may include a measurement unit configured to measure the current from the distribution line, a converter configured to convert the current into digital data, a zero-cross detector configured to detect and output one or more zero-cross points from the voltage of the distribution line, a main processor (MCU) configured to compute the magnitude of the current and an absolute phase thereof from the digital data, convert the absolute phase of the current into a relative phase thereof according to the one or more zero-cross points, and generate and output the current information including the magnitude of the current and the relative phase thereof, and a communication unit configured to transmit the current information to the second measuring instrument. 
         [0021]    The first measuring instrument may further include a power generator connected to the distribution line to generate an operational power of the first measuring instrument. 
         [0022]    The zero-cross detector may detect the one or more zero-cross points with respect to the voltage provided from the distribution line to the power generator. The second measuring instrument may compute an apparent power by multiplying the voltage by the magnitude of the current, calculate an active power of the distribution line by multiplying the apparent power by the relative phase of the current, and generate the electric power information including the active power. 
         [0023]    An electric power measuring system of some embodiments of the present disclosure detects a zero-cross point of a distribution line through a zero-cross detector provided in a current measuring instrument. And, using the detected zero-cross point, a phase of a current measured at the distribution line may be converted into a relative phase between the current and a voltage. 
         [0024]    Consequently, phases of the voltage and the current measured at the distribution line are exactly synchronized with each other, such that an integrated measuring instrument may generate accurate electric power information of the distribution line to improve a measurement reliability of the electric power measuring system. 
         [0025]    Also, the electric power measuring system of some embodiments of the present disclosure computes and transmits the relative phase between the current and the voltage of the distribution line through the current measuring instrument, such that a computation amount of the integrated measuring instrument may be drastically reduced in comparison with the typical electric power measuring system. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1  is a diagram schematically illustrating a configuration of a typical electric power measuring system, according to the prior art. 
           [0027]      FIG. 2  is a diagram schematically illustrating a configuration of an electric power measuring system, according to an embodiment of the present disclosure. 
           [0028]      FIG. 3  is a flow chart illustrating an operation of the electric power measuring system shown in  FIG. 2 , according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Hereinafter, an electric power measuring system according to some embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 
         [0030]      FIG. 2  is a diagram schematically illustrating a configuration of an electric power measuring system according to an embodiment of the present disclosure. 
         [0031]    With reference to  FIG. 2 , an electric power measuring system  100  may include a current measuring instrument  120  and an integrated measuring instrument  130  which are connected to each other through wire/wireless communication networks (not shown) to perform a data communication. 
         [0032]    One or more current measuring instruments  120  may be installed inside a panel board or a distribution panel. The current measuring instrument  120  may generate current information according to a current measured from a distribution line  110  inside the panel board or the distribution panel to transmit the current information to the integrated measuring instrument  130 . 
         [0033]    The distribution line  110  may be a three-phase balanced line including phase terminals of an R-phase, an S-phase, and a T-phase, but it is not limited thereto. And, the current measuring instrument  120  may measure a current of one of the R-, S-, and T-phases of the distribution line  110  to compute current information thereof based on the measured current. 
         [0034]    The current measuring instrument  120  may include a current measurement unit  121 , an analog-digital converter (hereinafter, referred to as an A/D converter)  123 , a zero-cross detector  125 , a main processor (hereinafter, referred to as an MCU)  127 , and a communication unit  129 . 
         [0035]    The current measurement unit  121  may measure a current flowing at a load (not shown) from the distribution line  110  to output an amount of a current, for example, a current value in a form of analog data according to the measured current. 
         [0036]    The A/D converter  123  may convert the current value output from the current measurement unit  121  from analog to digital to output current data in a form of digital data. The A/D converter  123  may sample the current value from the current measurement unit  121  to convert the sampled current value into the digital data. 
         [0037]    The MCU  127  may compute a magnitude of the current and a phase thereof, for example, an absolute phase of the current flowing at the distribution line  110  from the current data output from the A/D converter  123 . 
         [0038]    Also, the MCU  127  may convert the computed absolute phase of the current into a relative phase between the current and a voltage according to a zero-cross point output from the zero-cross detector  125  which is to be described later. 
         [0039]    And, the MCU  127  may generate current information of the distribution line  110 , which includes the computed magnitude of the current and the relative phase thereof. 
         [0040]    The zero-cross detector  125  may detect and output one or more zero-cross points from the distribution line  110 . The zero-cross detector  125  may detect and output a voltage of the distribution line  110 , that is, a point at which an instantaneous value of an induced voltage of the distribution line  110  is ‘0’ as a zero-cross point. The zero-cross point may be output to the MCU  127 . 
         [0041]    The communication unit  129  may transmit the current information of the distribution line  110 , which is output from the MCU  127 , to the integrated measuring instrument  130 . The communication unit  129  may be configured with one of a power line communication modem, an RS-485 serial communication modem, a radio frequency (RF) modem, and a Zigbee modem. 
         [0042]    The integrated measuring instrument  130  may compute electric power information of the distribution line  110  from the current information transmitted from the current measuring instrument  120 . The integrated measuring instrument  130  may receive information regarding a magnitude of the voltage of the distribution line  110  to compute the electric power information regarding an induced power of the distribution line  110  from the current information transmitted from the current measuring instrument  120  using the received information. 
         [0043]      FIG. 3  is a flow chart illustrating an operation of the electric power measuring system shown in  FIG. 2 . 
         [0044]    Hereinafter, with reference to  FIGS. 2 and 3 , an operation of computing electric power information of a distribution line in the electric power measuring system of some embodiments of the present disclosure will be described in detail. 
         [0045]    Firstly, the current measurement unit  121  of the current measuring instrument  120  may measure a current from the distribution line  110  to output a current value in a form of analog data in Operation S 10 . 
         [0046]    Also, the A/D converter  123  of the current measuring instrument  120  may convert the current value output from the current measurement unit  121  into digital data to output current data in Operation S 20 . 
         [0047]    And, the zero-cross detector  125  of the current measuring instrument  120  may detect and output one or more zero-cross points from the distribution line  110  in Operation S 15 . 
         [0048]    For example, the current measuring instrument  120  may further include a power generator (not shown) for generating an operational power capable of operating all components of the current measuring instrument  120  from the distribution line  110 . And, the zero-cross detector  125  may detect and output a zero-cross point regarding a voltage of the distribution line  110 , that is, an induced voltage flowing at the distribution line  110  from one or more lines extending from the distribution line  110  to the power generator. Here, the current measurement unit  121  and the zero-cross detector  125  may operate at the same time. 
         [0049]    The MCU  127  of the current measuring instrument  120  may compute a magnitude and an absolute phase of the current of the distribution line  110  from the current data output from the A/D converter  123 . Thereafter, the MCU  127  may convert the absolute phase of the current into a relative phase between the current and the voltage using the zero-cross point output from the zero-cross detector  125  in Operation S 30 . 
         [0050]    And, the MCU  127  may generate and output current information, which includes the magnitude of the current computed from the current information and the relative phase of the current generated from the zero-cross point, of the distribution line  110  in Operation S 40 . 
         [0051]    The communication unit  129  of the current measuring instrument  120  may transmit the current information of the distribution line  110 , which is generated in the MCU  127 , to the integrated measuring instrument  130  through wire/wireless communication networks in Operation S 50 . 
         [0052]    The integrated measuring instrument  130  may generate electric power information of the distribution line  110  from voltage information of the distribution line  110 , which is provided from an external side, and the current information thereof, which is transmitted from the current measuring instrument  120 , in Operation S 60 . 
         [0053]    For example, the integrated measuring instrument  130  may compute an apparent power of the distribution line  110  by multiplying a magnitude of the voltage of the voltage information by the magnitude of the current of the current information. And, by multiplying the computed apparent power by the relative phase cos Φ of the current information, an active power of the distribution line  110  may be computed. The integrated measuring instrument  130  may output the electric power information of the distribution line  110 , which includes the active power. 
         [0054]    As described above, the electric power measuring system  100  of some embodiments of the present disclosure may detect the zero-cross point of the distribution line  110  through the zero-cross detector  125  provided in the current measuring instrument  120  to convert the phase of the current measured at the distribution line  110  into the relative phase between the current and the voltage using the detected zero-cross point. 
         [0055]    Consequently, phases of the voltage and the current measured at the distribution line  110  are exactly synchronized with each other, such that the integrated measuring instrument  130  may generate accurate electric power information of the distribution line  110 . 
         [0056]    In other words, a measuring reliability of the electric power measuring system  100  may be improved. 
         [0057]    Also, the electric power measuring system  100  of some embodiments of the present disclosure computes and transmits the relative phase between the current and the voltage of the distribution line  110  through the current measuring instrument  120 , such that a computation amount of the integrated measuring instrument  130  may be drastically reduced in comparison with the typical electric power measuring system. 
         [0058]    Although the description has been set forth in detail, it should be construed as illustrative embodiments not to be taken in a sense for limiting the scope of the present disclosure. Therefore, the scope of the present disclosure should be construed by the appended claims, along with the full range of equivalents and to which such claims are entitled. 
         [0059]    While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the protection. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the protection. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the protection. Various components illustrated in the figures may be implemented as hardware and/or software and/or firmware on a processor, ASIC/FPGA, dedicated hardware, and/or logic circuitry. Also, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Although the present disclosure provides certain preferred embodiments and applications, other embodiments that are apparent to those of ordinary skill in the art, including embodiments which do not provide all of the features and advantages set forth herein, are also within the scope of this disclosure. Accordingly, the scope of the present disclosure is intended to be defined only by reference to the appended claims.