JP4258119B2 - Current measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a means for measuring a current flowing through a power line such as a power transmission line, a distribution line, and a power line of equipment, and a current measuring device characterized by the power supply means.
[0002]
[Prior art]
In general, the power supply of the measuring device is supplied by a voltage input such as a transformer or a secondary battery whose input level is relatively stable, and is usually separated from the input for measurement.
There is no system that shares the measurement input and control input with the power supply, but the power supply circuit power supply has many very small units with very small current, and the power consumption is relatively large, with power consumption of several amperes or more. However, there is no system that can measure a wide range of input current.
[0003]
As a system for supplying power from the power line of the power system, p. 75, a DC voltage conversion circuit, a single power supply DC output amplifier circuit, which is an example of a power supply circuit from a current source, and p. No. 35 Nitech's power donut (a donut-shaped sensor attached directly to the transmission line to measure the voltage, current, etc. of the transmission line and take power supply by electromagnetic induction), P. Of "Collaborative Research" Vol. 53 No. 2 The power supply circuit by CT to the optical fiber gyro described in 112-114, etc. are available.
[0004]
[Problems to be solved by the invention]
Regarding the current measurement of transmission and distribution lines, it must be possible to measure a wide range of current values, such as fluctuations in load flow due to system faults and system load conditions, or power outages. When the current information of the transmission / distribution line is to be measured at multiple points, there is a problem with the transmission means of the measurement information, the power supply method to the measurement device, and the like.
When power is supplied from a transmission / distribution line by voltage input, there is a problem of insulation measures in consideration of the voltage class of the system and surge voltage, and it is difficult to make the device compact.
[0005]
From this point of view, the power supply of the device is supplied from the CT current source installed on the transmission and distribution line, and the device itself is also installed directly on the power line, eliminating the problem of device insulation and making the device compact. Become. Furthermore, if the current measurement CT and the power supply CT are shared by the same one, the cost is reduced accordingly, and the configuration of the entire system can be simplified and the size can be reduced.
[0006]
However, when wireless is used as a transmission method of measurement information, synchronous measurement by GPS (Global Positioning System) is performed for measurement, or a memory for recording measurement data, a CPU for high performance calculation, etc. are required, the device The current consumption required for the whole also increases. That is, the burden on the secondary side of the power supply CT increases accordingly, causing the saturation of the CT and the inability to obtain a stable output, and the selection of the CT becomes difficult. On the other hand, it is required that a stable power supply can be supplied for a wide range of current inputs and that the power supply circuit and the measurement circuit can be normally measured without being broken even when overcurrent is input (about 40 times the CT rating). However, at present, no current measuring device that satisfies these requirements has been provided.
[0007]
Therefore, the present invention combines the current measurement and power supply with a single CT to reduce the size and cost of the apparatus, enable measurement for a wide range of current inputs and stable power supply, and An object of the present invention is to provide a current measuring device that also has a protective function.
[0008]
  In order to solve the above-mentioned problem, the invention according to claim 1 is a current measuring device for measuring a current flowing through the power line by CT installed in the power line.
  The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
  Connected to the secondary side of the CTVariable resistance means;
  The input side was connected to this variable resistance meansA rectifier circuit;
  A constant voltage DC output circuit connected to the output side of the rectifier circuit and outputting a substantially constant DC voltage by ON / OFF control of the switching element;
  A backup power supply circuit connected to the constant voltage DC output circuit and charged with a capacitor for the backup power supply by the output current;
  A level conversion circuit that converts the output voltage of the constant voltage DC output circuit or the backup power supply circuit to a predetermined level and supplies power to the current measurement calculation / monitoring means, and
  When the output voltage of the constant voltage DC output circuit decreases, power is supplied by the backup power supply circuit.With
  The current measurement calculation / monitoring means suppresses the input of overcurrent to the rectifier circuit due to the saturation of the CT by changing the resistance value of the variable resistance means according to the current measurement value on the secondary side of the CT, Protect the power supplyIs.
[0009]
  The invention according to claim 2 is a current measuring device for measuring a current flowing through the power line by CT installed in the power line.
  The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
  Variable resistance means connected to the secondary side of the CT;
  A rectifier circuit whose input side is connected to the variable resistance means;
  A constant voltage DC output circuit connected to the output side of the rectifier circuit and outputting a substantially constant DC voltage by ON / OFF control of the switching element;
  This constant voltage DC output circuit is connected to the output currentVia switch or relayA backup power supply circuit in which a capacitor for the backup power supply is charged;
  thisThe output voltage of the backup power circuitVia switch or relayA level conversion circuit that converts to a predetermined level and supplies power to the current measurement calculation / monitoring means,
  SaidThe current measurement calculation / monitoring means suppresses the input of overcurrent to the rectifier circuit by saturation of the CT by changing the resistance value of the variable resistance means according to the current measurement value on the secondary side of the CT, and the power supply While protecting the part
  The current measurement calculation / monitoring means is
  Monitoring means for outputting an alarm when the magnitude of the measured current on the secondary side of the CT is outside a predetermined range;
  Power supply switching means for controlling the operation of each switch or relay to control charging and discharging of the capacitor, andIs.
[0010]
Invention of Claim 3 is the electric current measuring apparatus which measures the electric current which flows through the said electric power line by CT installed in the electric power line,
The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
A switch or relay connected to the secondary side of the CT, a rectifier circuit whose input side is connected to the switch or relay, and an almost constant direct current connected to the output side of the rectifier circuit and on / off control of the switching element A constant voltage DC output circuit for outputting a voltage, a backup power supply circuit connected to the constant voltage DC output circuit and charged with a capacitor for a backup power supply by the output current, and the constant voltage DC output circuit or the backup power supply circuit. A level conversion circuit that converts the output voltage to a predetermined level and supplies power to the current measurement calculation / monitoring means, and
While supplying power by the backup power supply circuit when the output voltage of the constant voltage DC output circuit decreases,
The current measurement calculation / monitoring means is
Monitoring means for outputting an alarm when the magnitude of the measured current is outside the predetermined range, and operating the switch or relay to shut off the input current to the rectifier circuit when the magnitude of the measured current is outside the predetermined range. Power supply switching means for switching to power supply by the backup power supply circuit.
[0011]
Invention of Claim 4 is the electric current measurement apparatus which measures the electric current which flows through the said electric power line by CT installed in the electric power line,
The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
A rectifier circuit connected to the secondary side of the CT, a constant voltage DC output circuit connected to the output side of the rectifier circuit and outputting a substantially constant DC voltage by on / off control of the switching element, and the constant voltage DC A backup power supply circuit connected to the output circuit and charged with a capacitor for a backup power supply via the switch or relay by the output current, and the output voltage of the backup power supply circuit is converted to a predetermined level via the switch or relay A level conversion circuit for supplying power to the current measurement calculation / monitoring means,
The current measurement calculation / monitoring means is
Monitoring means for outputting an alarm when the magnitude of the measured current is outside a predetermined range, and power supply switching means for controlling charging and discharging of the capacitor by controlling the operation of each switch or relay It is.
[0012]
  The invention according to claim 5Item 2, 3 or 4 in the current measuring device,
  It is provided with backup power supply monitoring means for monitoring the charging voltage of the capacitor of the backup power supply circuit and outputting an alarm when the magnitude is outside a predetermined range and sending a signal for power supply switching to the power supply switching means. is there.
[0013]
The invention according to claim 6 is the current measuring device according to claim 1, 2, 3, 4 or 5,
The current measurement calculation / monitoring means includes input range control means for switching the input range according to the magnitude of the measurement current.
[0014]
  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 shows the present invention.referenceFunctional block diagram showing formInThe This current measuring device is a current measurement in which a measurement / power supply CT 20 attached to a power line 10, a power supply unit 30 connected to the secondary side thereof, a measurement input from the CT 20 and a DC power supply from the power supply unit 30 are applied. The calculation / monitoring unit 40, the wireless transmission unit 50 to which the DC power supply from the power supply unit 30 and the output signal of the current measurement calculation / monitoring unit 40 are added, the wireless antenna 51 connected to the wireless transmission unit 50, and the necessity The GPS antenna 42 and the measurement CT 45 are installed accordingly.
[0015]
  thisreferenceThe mode is to supply the power of the apparatus from the measurement / power supply CT 20 connected to the power line 10 and measure the current of the power line 10 detected by the CT 20, whereby the current information (magnitude, Phase, frequency, etc.) and power supply are performed simultaneously. However, a CT45 for measurement may be installed separately depending on measurement conditions.
[0016]
The power supply unit 30 includes a rectifier circuit 31 connected to the secondary side of the CT 20, a constant voltage DC output circuit 32 by self-excited chopper control, a backup power supply circuit 33 connected to the output side, and a constant voltage DC output circuit. 32 and a backup power supply circuit 33, and a diode circuit 34 composed of a pair of diodes connected to the output side of the backup power supply circuit 33, and a level conversion circuit 35 connected to the cathode side to obtain a DC power supply voltage of a predetermined level. The output of the backup power supply circuit 33 is input to the current measurement calculation / monitoring unit 40, and the state (voltage) of the backup power supply can be monitored.
[0017]
The current measurement calculation / monitoring unit 40 connected to the secondary side of the measurement / power supply CT 20 includes a GPS synchronization unit 41 provided as necessary, a measurement input circuit 43 having an A / D converter, and a measurement input circuit. 43 output signals are added to calculate the system current, monitor the input current level and backup power supply status, and perform transmission control to wirelessly transmit the measured current value and monitoring result to the remote central unit CPU44.
[0018]
The system current measurement enables multipoint synchronous measurement using GPS, and the measurement calculation data is sent to a relay radio station (not shown) via the radio transmission unit 50 and the radio antenna 51, and further to the central device. Is transmitted. In this central device, it is possible to check the display of the device status including the measurement information and the power supply.
In addition, this apparatus is applicable also to the system (Japanese Patent Application No. 2000-179400 "failure point location method") which locates the failure point of a power transmission and distribution line from the electric current measurement information of a system | strain, for example.
[0019]
FIG. 2 is a circuit configuration diagram of the power supply unit 30 in FIG. 1, and FIG. 3 is an operation explanatory diagram thereof.
In the power supply unit 30, the secondary current I2a of CT20 through which the system current I1 flows on the primary side is rectified by the rectifier circuit 31, and the output current I2b is from a self-excited chopper control circuit including a comparator 32a and an FET 32b as a switching element. The constant voltage DC output circuit 32 is converted into a constant DC voltage Va.
[0020]
The constant voltage DC output circuit 32 suppresses the input current from the CT 20, and when the overcurrent is input, the FET 32b is turned on by the output signal of the comparator 32a to transiently stop the current supply to the output side. Operates to reduce Va.
That is, a constant output voltage Va is maintained by repeating the on / off control of the FET 32b. Usually, the current measurement calculation / monitoring unit 40 and the wireless transmission unit 50 are caused by the current I2c flowing through the diode 34a on the upper side of the diode circuit 34. Will be supplied with power.
[0021]
Further, the backup power supply circuit 33 is provided with a large-capacity backup capacitor 33a into which a shunt current of the output current of the constant voltage DC output circuit 32 flows through a resistor and a diode, and this capacitor 33a is always charged. Yes.
In the state where the capacitor 33a is sufficiently charged, when the supply voltage from the CT 20 decreases or becomes unstable due to a power failure of the system, the diode 34b is turned on when a potential difference occurs between the anode and the cathode of the diode 34b. Thus, the current I2d flows, and the power supply is automatically switched to the backup power supply circuit 33.
That is, the power supply by the current I2c is switched to the power supply by the current I2d. The backup state by the power supply circuit 33 is transmitted to the measurement input circuit 43 in FIG.
[0022]
Further, the backup power supply circuit 33 has not only a backup function when the power supply from the CT 20 is impossible, but also a compensation function when the output voltage of the constant voltage DC output circuit 32 becomes unstable for some reason. The power supply unit 30 generally contributes to supplying a stable DC power supply voltage to each unit.
[0023]
FIG. 3 shows the operation of the power supply unit 30. The secondary current I2a of the CT 20, the output current I2b of the rectifier circuit 31, the on / off operation of the FET 32b, the output voltage Va of the constant voltage DC output circuit 32, and the output of the diode circuit 34. The voltage Vb and the output voltage Vo of the power supply unit 30 are shown.
As described above, the output voltage Va of the constant voltage DC output circuit 32 fluctuates in the vicinity of the rated value of the constant voltage due to the on / off operation of the FET 32b. In such a case, the operation shifts to the power supply operation by the current I2d of the backup power supply circuit 33 as shown in the figure.
[0024]
When this device is applied to a power transmission / distribution line, the backup power supply circuit specification should be sufficient if it can be backed up for several minutes in consideration of the reclosing time (particularly the power distribution system) at the time of a system fault. Think.
Even if the power failure continues such as when reclosing fails, it is only necessary that the measurement data at the time of the accident can be transmitted to the central unit by wireless transmission while the backup power supply circuit is alive. In other words, measurement data can be sufficiently collected with a backup time of several minutes, so that there is no particular problem even during a power outage.
[0025]
By the way, when the FET 32b of the constant voltage DC output circuit 32 in FIG. 2 is not turned on, the secondary load of the CT 20 is determined by the power supply capacity to the device, but when the FET 32b is turned on, the FET 32b is turned on. It depends on the CT internal resistance and the CT resistance such as the winding resistance of CT20. Since the conditions under which CT20 is saturated depend on these burdens, care must be taken with respect to the selection of CT (particularly the rated burden and overcurrent constant).
[0026]
In general, the fault current of the transmission and distribution line should be 40 times the rating. That is, in the power supply unit 30 of FIG. 2, the circuit must operate normally even when a current equivalent to 40 times the secondary-side rated current value of the CT 20 flows through the transmission and distribution line.
On the other hand, in order to stably supply power to the apparatus even during operation below the rating of the power system (several tens% of the rating), a CT having a relatively large secondary side rating must be selected. If the secondary side rating of CT20 is 5A, the maximum rating of power supply unit 30 needs to be considered up to 200A.
[0027]
For example, assuming that the power flow of the transmission and distribution line needs to operate normally even at 20% of the rating, the power supply of the device must function normally even when the secondary current value of CT20 is 1A. (If the CT secondary side rating is 1A, the maximum rating of the power supply unit 30 may be 40A, but the power supply of the apparatus must operate normally at 0.2A, and the power supply condition becomes severe).
In order to reduce the size and cost of power supply units and electronic circuit elements under such conditions, a certain degree of secondary rated current value is required. It is difficult, and the maximum rated value is about several tens of A at most. Further, as the rated value increases, circuit heat generation due to a large current also becomes a problem.
[0028]
By the way, paying attention to the saturation phenomenon of CT, a considerable current does not flow to the secondary side with respect to the overcurrent input. That is, depending on the saturation point of CT, a large current such as 200 A may not be output even with an overcurrent input at the time of a system fault for a CT with a secondary side rated value of 5 A.
[0029]
A general CT current output characteristic is as shown in FIG. 4, and an approximate characteristic can be grasped by an overcurrent constant n at a rated load. As described above, this characteristic also changes depending on the circuit load on the secondary side. If the circuit load is smaller than the rated load of the CT, it becomes more difficult to saturate, and a secondary output current is generated according to the primary input. .
On the other hand, since the load on the circuit is small when the FET is turned on, an overcurrent may occur depending on the duration of the circuit, and sufficient caution is required.
[0030]
  First of the present invention1In the embodiment, the power supply unit is protected by utilizing the saturation phenomenon of CT as described above.
  Figure 5 shows this1Embodiments are shown and claimed.1,This corresponds to the embodiment of the invention described in 2. As shown in the figure, the switch SW0 is controlled by a signal from the CPU 44, and the secondary burden resistance of the CT 20 is made variable by resistors R0 to Rn, thereby controlling the saturation characteristics of the CT 20. These resistors R0 to Rn measure the input current by the auxiliary CT21 connected to the secondary side of the CT20, and the CPU 44 of the current measurement calculation / monitoring unit 40 sends a signal to the switch SW0 according to the measured value. .
  According to the present embodiment, even if the FET 32b continues to be in the ON state, the CT 20 can be saturated by selecting the resistance value, and the input current to the power supply unit 30A can be suppressed.
[0031]
In addition, it is possible to correct variations in the saturation characteristics of CT20 by using a variable resistor including resistors R0 to Rn. Further, the power supply unit 30A is reliably protected by saturating the CT 20 while measuring the input current value by the CPU 44, and the heat generation of the circuit can also be suppressed by the operation with the optimum current value.
When the input current becomes unstable due to saturation of CT20, stable power supply may be performed using the backup power supply circuit 33 as described above.
[0032]
The power input value suppressed by the saturation of CT 20 can be monitored by the current measurement function of the current measurement calculation / monitoring unit 40, and an alarm is generated as described later when an abnormality occurs. The load adjustment (variable resistance) circuit constituted by the resistors R0 to Rn also has an advantage that the optimum saturation characteristic can be detected and controlled even when CT having different specifications is used.
[0033]
  Next, FIG.2An embodiment is shown. This embodiment corresponds to an embodiment of the invention described in claims 3, 5 and 6.
  In the present embodiment, the power supply by the secondary current of the CT 20 and the power supply by the backup power circuit 33 can be switched by software.
  In FIG. 6, 43A is a measurement input circuit connected to the auxiliary CT 21, and this circuit 43A includes a parallel circuit of a circuit in which a switching element 43a and resistors Rk0 to Rkn are connected in series, and a Zener connected in parallel to them. A diode series connection circuit 43b, a filter circuit 43c connected to both ends thereof, and A / D converters 43d and 43e are provided.
[0034]
The output of the filter circuit 43c is input to the input measurement / monitoring means 44b in the CPU 44 via the A / D converter 43d, and the voltage of the backup capacitor 33a in the power supply unit 30B is supplied to the A / D converter 43e. To the backup power supply monitoring means 44c in the CPU 44.
The input measurement / monitoring means 44b and the backup power supply monitoring means 44c output an abnormal alarm and a status display signal indicating an abnormality in the input current and an abnormality in the backup power supply, and the monitoring outputs of these means 44c and 44d are power supplies. It is also input to the supply switching means 44d. The output of the input measuring / monitoring means 44b is also input to the input range (full scale) control means 44a.
[0035]
The output signal of the input range control means 44a is applied to each switching element 43a of the measurement input circuit 43A, and the output signal of the power supply switching means 44d is applied to the switch SW1 provided on the input side of the rectifier circuit 31. . Note that the switch SW1 is composed of a pair of interlocking switches, and is normally in a connected state as shown in FIG. 6 (with a switch on), and the secondary side of the CT 20 is connected to the rectifier circuit 31.
[0036]
Next, the operation of this embodiment will be described with reference to the flowchart of FIG. FIG. 7 shows measurement / power supply monitoring processing and power supply switching control processing by the CPU 44.
In FIG. 7, it is first determined whether the switch SW1 is turned on or off (S1). If it is turned on, a current input value less than the overcurrent level (n times the rated input current) is measured (S3). It is assumed that a current exceeding the overcurrent level is measured (S2). Here, the current measurement process is executed while controlling the input range by sequentially changing the resistances Rk0 to Rkn of the measurement input circuit 43A as shown in the upper right of FIG.
[0037]
Here, when the input full scale of the A / D converter 43d of the measurement input circuit 43A is adjusted to the input level at the time of a system fault, the measurement is performed with a small number of bits for a low input level that is usually lower than the rated current. The quantization error becomes large and measurement with high accuracy becomes impossible. Therefore, in accordance with the magnitude of the measurement value detected by the input measurement / monitoring means 44b, the input range control means 44a makes the selection of the resistors Rk0 to Rkn of the input measurement circuit 43A by software processing and changes the input of the A / D converter 43d. The full scale is made variable so that high-precision measurement can be performed with the optimum measurement resolution.
[0038]
When the input measurement / monitoring means 44b detects that the input current measured via the A / D converter 43d in FIG. 6 exceeds the overcurrent level (S4), an alarm for abnormal power input is output. At the same time, the switch SW1 is turned off via the power supply switching means 44d, and the process ends (S9, S10). Note that the process proceeds to step S2 when the switch SW1 is turned off.
If the input current level is insufficient and power supply is not possible (S5), an alarm for abnormal power input is output (S11) and the process proceeds to step S7.
[0039]
If the input current level does not exceed the overcurrent level and is not insufficient (S5), the input measuring / monitoring means 44b determines whether CT20 is saturated (S6), and is saturated. If so, the backup power supply monitoring means 44c determines whether backup is possible from the voltage of the capacitor 33a (S7). Note that the process proceeds to step S7 even after the process of step S2.
[0040]
If the backup by the capacitor 33a is possible, the switch SW1 is kept off (S8) and the process is terminated. If backup is not possible, the backup power supply monitoring means 44c outputs an alarm indicating that the preparation of the backup power supply is incomplete and normal measurement is impossible (S12), and the switch SW1 is connected via the power supply switching means 44d. And finishes (S13).
[0041]
That is, in this embodiment, when the input current exceeds the overcurrent level, the switch SW1 is turned off to make it impossible to supply power from the CT 20, and the power supply is automatically switched to the backup power source by the capacitor 33a. Since the operation is performed while measuring and monitoring the input current value in this way, when a power input abnormality such as an overcurrent is detected, the alarm information of the device is notified to the central device through wireless transmission, and the power supply unit 30B is protected. However, the apparatus can be operated normally. As described above, if the power supply of the apparatus can be backed up for several minutes, it is sufficient to measure and analyze the fault phenomenon of the system.
[0042]
  Here, while FIG. 6 monitors the input current level by software and switches the switch SW1 when an overcurrent is input, the switch shown in FIG.3In the embodiment, the switch SW1 is controlled by monitoring the input level with hardware.
  The input monitoring circuit 36 in the power supply unit 30E of FIG. 8 includes a circuit that generates an overcurrent input determination reference voltage Vref1 from the control power supply Vcc, a circuit that converts the output of the input current rectifier circuit 31 into a voltage Vi1, and Vref1 The comparator 36b compares the level with Vi1, and the off-delay timer 36a that holds the output signal of the comparator 36b for a certain period of time.
  Compared to the above-described monitoring control by software, when the overcurrent is detected by hardware as shown in FIG. 8, the switching of the switch SW1 becomes faster, and the overcurrent protection effect of the power supply circuit and the element subsequent to the switch SW1 is enhanced.
[0043]
FIG. 9 shows the operating state of the embodiment of FIG. When the input current increases, Vi1 increases, and when this Vi1 exceeds Vref1, a high level signal is output from the comparator 36b. The output signal of the comparator 36b is maintained for a predetermined time Toff by the off-delay timer 36a.
As a result, the switch SW1 is switched for an overcurrent input exceeding a certain current level to cut off the supply of the input current to the power supply circuit, and the power is supplied from the backup capacitor 33a as described above. Is.
[0044]
By the way, when the circuit protection method based on the above-mentioned CT saturation phenomenon is applied, it becomes impossible to measure the overcurrent region in the event of a system fault. For example, the CT for measurement and the CT for power supply are installed separately. It is necessary to take measures such as However, in the circuit configuration shown in FIGS. 6 and 8, when an overcurrent input such as a system fault is detected, the power supply unit is immediately switched to the backup side by the switch SW1, and the power supply unit is switched from the secondary side of the CT20. The current from CT20 is used only for measurement. Since the circuit load of the measurement input circuit 43A is much smaller than that of the power supply unit, even a circuit having the same rating as the above-described CT is less likely to be saturated. As a result, overcurrent at the time of a system fault can be measured without saturating the CT.
[0045]
In the embodiment of FIGS. 6 and 8, the backup power supply monitoring means 44c is configured to always monitor the charging state (voltage level) of the capacitor 33a, and the power supply cannot be performed because the capacitor voltage drops. Is operated by switching the power supply circuit from the backup power supply to the power supply using the secondary current of CT20 under the control of the switch SW1 (S7, S12, S13). At this time, if the secondary current of the CT 20 is an overcurrent, a normal measurement value of the system current cannot be obtained due to the saturation phenomenon of the CT 20, so that the system current value is accurate until the backup power supply is charged again. Measurement becomes impossible and the function stops.
[0046]
  FIG. 10 shows the first aspect of the present invention.4Embodiments are shown and correspond to the embodiments of the invention described in claims 4, 5, and 6.
  As described above, when the current consumption value of the apparatus power supply is relatively large, selection of the power supply unit and CT becomes difficult. However, as shown in FIG. 10, the apparatus power is not directly supplied from the CT 20, but the CT 20 is used only for measuring the system current and charging the capacitor 33a of the backup power circuit, and the power is supplied exclusively from the backup power circuit. Then, the secondary side rated current of CT20 can be made small and the rated burden of CT20 can also be suppressed.
[0047]
In FIG. 10, a different part from embodiment of FIG. 6, FIG. 8 is a structure of the power supply part 30C.
A switch SW2 is connected to one end of the capacitor 33a of the backup power supply circuit, and the capacitor 33a is normally connected to the constant voltage DC output circuit 32 and charged in a connected state (ON state) as shown in FIG. .
The switch SW2 is on / off controlled by software monitoring control by the CPU 44. In FIG. 10, the switch SW2 is on / off controlled by the output of the power supply switching means 44d of the CPU 44.
[0048]
FIG. 11 is a diagram for explaining the operation of this embodiment. When the switch SW2 is OFF, the capacitor 33a is discharged and the power is supplied by the discharge current. At this time, the CPU 44 is in a normal operation mode and performs current measurement and wireless transmission of measurement data.
The voltage Vc of the capacitor 33a is input to the backup power supply monitoring means 44c of the CPU 44 via the A / D converter 43e. When it is detected that the voltage Vc has become below a certain value, the power supply switching means 44d Switch SW2 is turned on. As a result, the capacitor 33a is in a charged state, and the CPU 44 interrupts the current measurement operation and wireless transmission to enter a standby mode for low power consumption operation, and only monitors the capacitor voltage Vc.
[0049]
  In the embodiment of FIG. 10, when the switch SW2 is in the ON state (during charging of the capacitor 33a), it is necessary to operate the voltage of the backup power source by the CPU 44 at a minimum, so that the current consumption increases and charging takes time.
  For this reason, the first shown in FIG.5In the embodiment, the charging voltage of the backup capacitor 33a is monitored by hardware, and charging / discharging of the backup capacitor 33a is controlled without operating the CPU 44.
[0050]
The embodiment of FIG. 12 differs from FIG. 10 in that a switch SW2 including a pair of interlocked switches SW2a and SW2b is connected to one end of a backup capacitor 33a in the power supply unit 30F. Connection state (a state in which SW2a is off and SW2b is on).
In addition, a charge / discharge control circuit that detects full charge of the backup capacitor 33a by hardware and controls the switch SW2 that switches between charge and discharge is provided. This charge / discharge control circuit includes a circuit for generating a full charge determination reference voltage Vref2 for the backup capacitor 33a from the control power supply Vcc, a circuit for converting the level of the backup voltage Vc to the voltage Vi2, and a comparator for comparing the levels of Vref2 and Vi2. 37 and an output holding circuit 38 for holding the output signal of the comparator 37 until the backup power source is exhausted.
[0051]
FIG. 13 shows the operation of this embodiment. As described above, normally, the switch SW2a is off and the SW2b is on, so that the capacitor 33a is charged. When the voltage Vc rises due to the charging of the capacitor 33a, Vi2 rises accordingly, and when Vi2 becomes larger than the full-charge determination reference voltage Vref2, the output signal of the comparator 37 becomes High level. This output signal is held by the output holding circuit 38.
As a result, the switch SW2a is turned on, the SW2b is turned off, and the backup capacitor 33a is discharged. Accordingly, the power supply to the measurement input circuit 43A and the CPU 44 becomes effective, and various measurement / monitoring functions and transmission functions work. The voltage of the backup capacitor 33a decreases due to the discharge, and when it becomes below a certain value, the CPU 44 stops and the output holding circuit 38 returns to the normal state, the switch SW2 returns to the normal state and the capacitor 33a is charged again. Is to be done.
[0052]
The charging time of the capacitor 33a is determined by the resistance value of the resistor 33d connected to the constant voltage DC output circuit 32. Since the charging current can be suppressed by this resistor 33d, the CT 20 is charged during charging. Secondary burden can be kept small.
[0053]
  In the embodiment of FIGS. 10 and 12, it is necessary to interrupt current measurement and transmission in the standby mode in which the capacitor 33a is charged.
  Therefore, as shown in FIG.6As in the embodiment, the backup power supply circuit is provided with two capacitors 33b and 33c, and these voltage levels are monitored by the backup power supply monitoring means 44c and 44e in the CPU 44A via the A / D converters 43e and 43f. By switching the power supply by the switching means 44d and the switches SW3 and SW4 and charging the unused capacitors, the time for stopping the current measurement and transmission by the CPU 44A is reduced as much as possible.
[0054]
In FIG. 14, the switches SW3 and SW4 are each composed of a pair of interlocking switches. FIG. 14 shows that the switch SW3 is turned off and the switch SW4 is turned on. Reference numerals 33e and 33d denote resistors connected between one end of each of the capacitors 33b and 33c and the constant voltage DC output circuit 32.
[0055]
FIG. 15 shows a processing flow of the CPU 44A in the embodiment of FIG.
Similarly to the above, the current input value is measured while controlling the input range (S21), and when the input current exceeds the overcurrent level, an alarm indicating a power supply input abnormality is output (S22, S27). Note that the load resistance control shown in FIG. 5 and the power source switching control by the switch SW1 in FIG. 6 are added as necessary.
Also, an alarm indicating a power input abnormality is output even when the input current level is insufficient (S23, S28).
[0056]
Next, if the voltage of the capacitor 33b monitored by the backup power supply monitoring means 44c is sufficient, the power supply switching means 44d switches on the switch SW3 to discharge the capacitor 33b, and supplies power by the discharge current. (S24, S25). On the other hand, the switch SW4 in the on state is turned off to charge the capacitor 33c (S26), and the process ends.
If the voltage of the capacitor 33b is insufficient in step S24, the voltage of the other capacitor 33c monitored by the backup power supply monitoring means 44e is confirmed (S29). If this voltage is sufficient, the switch SW4 is turned on. The capacitor 33c is discharged and power is supplied (S30). On the other hand, the switch SW3 in the on state is turned off to charge the capacitor 33b (S31), and the process ends.
[0057]
If the voltage of the capacitor 33c is insufficient in step S29, neither of the capacitors 33b and 33c of the backup power supply circuit is prepared and an alarm is output that power supply is impossible (S32). Thereby, the CPU 44A shifts to the standby mode.
[0058]
In addition, you may comprise switch SW1-SW4 used in each embodiment mentioned above by a relay (relay contact).
[0059]
【The invention's effect】
As described above, according to the present invention, a stable power supply can be supplied from a wide range and unstable current input of a power transmission and distribution line, and a highly reliable power supply can be provided. In particular, even in places where it is difficult to supply control power such as commercial power, if there is a power line with a power flow such as a transmission and distribution line, it will be possible to supply a relatively stable power from there, and installation of equipment is also possible It becomes.
[0060]
In addition, if the system current measurement and power supply CT are shared, the apparatus can be miniaturized, the cost can be reduced, and a wide range of input currents can be measured with relatively high accuracy.
In addition, because the saturation characteristics of CT for measurement and power supply can be controlled, it is possible to operate while correcting the characteristics using the same hardware even if a CT with different specifications is selected. Therefore, it is easy to select a relatively low cost CT for measurement / power supply.
[Brief description of the drawings]
FIG. 1 of the present inventionreferenceIt is a functional block diagram which shows a form.
FIG. 2 is a circuit configuration diagram of a power supply unit in FIG.
FIG. 3 is an operation explanatory diagram of FIG. 2;
FIG. 4 is a diagram showing current output characteristics of a general CT.
FIG. 5 shows the first of the present invention.1It is a circuit block diagram which shows embodiment.
FIG. 6 shows the first of the present invention.2It is a circuit block diagram which shows embodiment.
7 is a flowchart showing processing of a CPU in FIG.
FIG. 8 shows the first of the present invention.3It is a circuit block diagram which shows embodiment.
9 is an operation explanatory diagram of FIG. 8. FIG.
FIG. 10 shows the first of the present invention.4It is a circuit block diagram which shows embodiment.
11 is an operation explanatory diagram of FIG. 10; FIG.
FIG. 12 shows the first of the present invention.5It is a circuit block diagram which shows embodiment.
13 is an operation explanatory diagram of FIG. 12. FIG.
FIG. 14 shows the first of the present invention.6It is a circuit block diagram which shows embodiment.
15 is a flowchart showing processing of a CPU in FIG.
[Explanation of symbols]
10 Power line
20 CT for measurement and power supply
21 Auxiliary CT
30, 30A, 30B, 30C, 30D, 30E, 30F Power supply
31 Rectifier circuit
32 Constant voltage DC output circuit
32a comparator
32b FET (switching element)
33 Backup power circuit
33a, 33b, 33c Backup capacitor
33d, 33e resistance
34 Diode circuit
35 level conversion circuit
35a DC / DC conversion circuit
35b Smoothing capacitor
36 Input monitoring circuit
36a Off-delay timer
36b, 37 comparator
38 Output holding circuit
40 Current measurement calculation and monitoring unit
41 GPS synchronization unit
42 GPS antenna
43,43A Measurement input circuit
43a Switching element
43b Zener diode series connection circuit
43c filter circuit
43d, 43e, 43f A / D converter
44, 44A CPU
44a Input range control means
44b Input measurement and monitoring means
44c, 44e Backup power supply monitoring means
44d Power supply switching means
45 CT for measurement
50 Wireless transmission unit
51 Wireless antenna
SW0, SW1, SW2, SW3, SW4 switch
R0-Rn, Rk0-Rkn resistance

Claims (6)

In a current measuring device for measuring a current flowing through the power line by CT installed in the power line,
The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
Variable resistance means connected to the secondary side of the CT ;
A rectifier circuit whose input side is connected to the variable resistance means ;
A constant voltage DC output circuit connected to the output side of the rectifier circuit and outputting a substantially constant DC voltage by ON / OFF control of the switching element;
A backup power supply circuit connected to the constant voltage DC output circuit and charged with a capacitor for the backup power supply by the output current;
A level conversion circuit that converts the output voltage of the constant voltage DC output circuit or the backup power supply circuit to a predetermined level and supplies power to the current measurement calculation / monitoring means, and
While supplying power by the backup power supply circuit when the output voltage of the constant voltage DC output circuit decreases ,
The current measurement calculation / monitoring means suppresses the input of overcurrent to the rectifier circuit due to the saturation of the CT by changing the resistance value of the variable resistance means according to the current measurement value on the secondary side of the CT, A current measuring device characterized by protecting a power supply unit . In a current measuring device for measuring a current flowing through the power line by CT installed in the power line,
The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
Variable resistance means connected to the secondary side of the CT;
A rectifier circuit whose input side is connected to the variable resistance means;
A constant voltage DC output circuit connected to the output side of the rectifier circuit and outputting a substantially constant DC voltage by ON / OFF control of the switching element;
A backup power supply circuit connected to the constant voltage DC output circuit and charged with a capacitor for a backup power supply via a switch or a relay by the output current;
And a level converting circuit for supplying power to the current measuring operation and monitoring means the output voltage of the backup power supply circuit is converted to a predetermined level via a switch or relay,
The current measurement calculation / monitoring means suppresses the input of overcurrent to the rectifier circuit due to the saturation of the CT by changing the resistance value of the variable resistance means according to the current measurement value on the secondary side of the CT, While protecting the power supply,
The current measurement calculation / monitoring means is
Monitoring means for outputting an alarm when the magnitude of the measured current on the secondary side of the CT is outside a predetermined range;
A current measurement apparatus comprising: power supply switching means for controlling the operation of each switch or relay to control charging and discharging of the capacitor . In a current measuring device for measuring a current flowing through the power line by CT installed in the power line,
The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
A switch or relay connected to the secondary side of the CT;
A rectifier circuit whose input side is connected to this switch or relay;
A constant voltage DC output circuit connected to the output side of the rectifier circuit and outputting a substantially constant DC voltage by ON / OFF control of the switching element;
A backup power supply circuit connected to the constant voltage DC output circuit and charged with a capacitor for the backup power supply by the output current;
A level conversion circuit that converts the output voltage of the constant voltage DC output circuit or the backup power supply circuit to a predetermined level and supplies power to the current measurement calculation / monitoring means, and
While supplying power by the backup power supply circuit when the output voltage of the constant voltage DC output circuit decreases,
The current measurement calculation / monitoring means is
Monitoring means for outputting an alarm when the magnitude of the measured current is outside a predetermined range;
Power supply switching means for operating the switch or relay to cut off the input current to the rectifier circuit and switching to the power supply by the backup power supply circuit when the magnitude of the measured current is outside a predetermined range; A current measuring device characterized by In a current measuring device for measuring a current flowing through the power line by CT installed in the power line,
The power supply unit of the current measurement calculation / monitoring means provided on the secondary side of the CT,
A rectifier circuit connected to the secondary side of the CT;
A constant voltage DC output circuit connected to the output side of the rectifier circuit and outputting a substantially constant DC voltage by ON / OFF control of the switching element;
A backup power supply circuit connected to the constant voltage DC output circuit and charged with a capacitor for a backup power supply via a switch or a relay by the output current;
A level conversion circuit that converts the output voltage of the backup power supply circuit to a predetermined level via a switch or relay and supplies power to the current measurement calculation / monitoring means, and
The current measurement calculation / monitoring means is
Monitoring means for outputting an alarm when the magnitude of the measured current is outside a predetermined range;
A current measurement apparatus comprising: power supply switching means for controlling the operation of each switch or relay to control charging and discharging of the capacitor. The current measuring device according to claim 2 , 3 or 4,
A backup power supply monitoring means for monitoring the charging voltage of the capacitor of the backup power supply circuit and outputting an alarm when the magnitude is outside the predetermined range and sending a signal for power supply switching to the power supply switching means is provided. Characteristic current measuring device. In the current measuring device according to claim 1, 2, 3, 4 or 5,
The current measurement calculation / monitoring means is
A current measuring apparatus comprising an input range control means for switching an input range according to the magnitude of a measuring current.

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