JP7570282B2 - Transformer-equipped watt-hour meter - Google Patents

Description

This disclosure relates to a transformer-equipped watt-hour meter that measures the amount of power in a circuit in combination with a meter transformer.

A watt-hour meter with a transformer is installed on the secondary side of an instrument transformer to measure the amount of power in circuits in switchboards, distribution boards, etc. A watt-hour meter with a transformer is an instrument that converts the high current and high voltage of the main circuit, which is located on the primary side of the instrument transformer, into voltage and current values that can be measured by an instrument, using the instrument transformer to perform measurements.

In an instrument transformer, it is necessary to prevent the load on the instrument transformer from fluctuating, causing changes in detection accuracy, depending on the connection state of the instrument connected to the secondary side. For this reason, in Patent Document 1, in areas where the load is small, an adjustment load is connected to the secondary side of the instrument transformer, and in areas where the load is large, the adjustment load is disconnected from the secondary side of the instrument transformer, suppressing load fluctuations.

Japanese Patent Application Publication No. 3-283416

In recent years, there has been an increase in cases where automatic meter reading is performed via communication, and an increasing number of configurations have been created in which a communication module is combined with the watt-hour meter to give it a communication function. In such configurations, since the communication module can be combined later, the usage burden varies depending on whether or not the communication module is present, resulting in a new issue of greater fluctuations in the burden on the secondary side of the instrument transformer.

This disclosure has been made in consideration of the above, and aims to provide a watt-hour meter with a transformer that can keep the usage load of the instrument transformer constant regardless of whether a communication module is connected or not.

In order to solve the above-mentioned problems and achieve the object, a transformer-equipped electricity meter to which a communication module can be detached comprises a power transformer that reduces the voltage of a measurement signal of an instrument transformer, outputs a first output which is an insulated output of the reduced voltage measurement signal to the communication module via a first connecting line, and outputs a second output which is a non-insulated output of the reduced voltage measurement signal to a second connecting line, a dummy resistor connected between the first connecting line and ground, and a series circuit with a switching element, and is characterized in that the switching element is turned off when the communication module is connected to the electricity meter, and the switching element is turned on when the communication module is not connected to the electricity meter.

The watt-hour meter with a transformer disclosed herein has the effect of providing a watt-hour meter with a transformer that can keep the usage load of the meter transformer constant regardless of whether a communication module is connected or not.

FIG. 1 is an overall configuration diagram showing a circuit configuration including a watt-hour meter with a transformer according to an embodiment of the present invention; Circuit configuration diagram of a watt-hour meter with a transformer according to an embodiment FIG. 2 is a diagram showing a specific circuit configuration of a dummy resistor and a switching element according to the embodiment; 1 is a flowchart showing an example of the operation of a transformer-equipped watt-hour meter according to an embodiment; FIG. 1 is a diagram showing a modified example of a transformer-equipped watt-hour meter according to an embodiment;

The following describes in detail the embodiment of the watt-hour meter with transformer with reference to the drawings.

Embodiment
Fig. 1 is an overall diagram showing a circuit configuration including a watt-hour meter with a transformer according to an embodiment. In Fig. 1, a current transformer 20, a current transformer 30, and an instrument transformer 1 are connected to power supply wiring 11, 12, and 13 that flows from the power supply side to the load side of a main circuit. For example, the current transformer 20 is connected to the power supply wiring 11, and the current transformer 30 is connected to the power supply wiring 13. The current transformers 20 and 30 convert a large current that flows from the power supply side of the main circuit to the load side into a small current that can be measured by the watt-hour meter with a transformer 2. The current transformers 20 and 30 input a voltage value corresponding to the measured current value to the watt-hour meter with a transformer 2.

The voltage transformer 1 is connected to the power supply wiring 11, 12, and 13, and converts the high voltage related to the main circuit into a low voltage that can be measured by the watt-hour meter with transformer 2. The voltage transformer 1 inputs the measured voltage value to the watt-hour meter with transformer 2. The output of this voltage transformer 1 is used to measure the amount of electricity and is also used as the operating power source for the watt-hour meter with transformer 2.

The watt-hour meter 2 with transformer is connected to the current transformer 20, the current transformer 30, and the voltage transformer 1. The watt-hour meter 2 with transformer measures the amount of power related to the main circuit by taking in the voltage corresponding to the current taken from the current transformer 20 and the current transformer 30 connected to the main circuit, and the voltage taken from the voltage transformer 1.

The power transformer 22 is connected to the communication module 3. The communication module 3 is detachable from the watt-hour meter 2 with a transformer. The communication module 3 acquires the measurement values measured by the watt-hour meter 2 with a transformer, for example, using a smartphone or a personal computer. The communication module 3 can use wireless communication using Bluetooth (registered trademark), specific low-power radio, or wired communication such as CC-Link (Control Communication Link, registered trademark), or PROFIBUS (Process Field Bus, registered trademark).

Figure 2 is a circuit diagram of a transformer-equipped watt-hour meter 2 according to an embodiment. The instrument transformer 40 shown in Figure 2 shows a circuit configuration including a current transformer 20, a current transformer 30, and an instrument transformer 1. The transformer-equipped watt-hour meter 2 has a rectifier circuit 21 to which the instrument transformer 1 is connected, a power transformer 22, a power supply control circuit 23, a dummy resistor 24, a switching element 25, an internal meter power supply 26, a measurement control unit 27 as a control unit, an input circuit 28, and a display unit 29. The input circuit 28 is connected to the current transformer 20, the current transformer 30, and the instrument transformer 1, and converts each input signal into a voltage signal for measurement. The display unit 29 displays the amount of power calculated by the measurement control unit 27.

The rectifier circuit 21 converts the low-voltage AC power (e.g., AC 110V) converted by the voltage transformer 1 into DC power for use as the operating power source for the transformer-equipped watt-hour meter 2. The input circuit 28 converts the AC signal output from the voltage transformer 40, which includes the current transformer 20, the current transformer 30, and the voltage transformer 1, into a voltage signal that can be read by the measurement control unit 27. The power transformer 22 step-down converts the converted DC voltage to a low voltage that can be driven by the circuitry in the transformer-equipped watt-hour meter 2 and the communication module 3. The power transformer 22 also electrically insulates the primary circuitry of the power transformer 22 from the communication module 3.

The power supply control circuit 23 includes, for example, a feedback circuit that performs feedback control for controlling the output voltage of the power supply transformer 22.

The dummy resistor 24, which will be described later, is a circuit configuration for maintaining the output voltage of the isolated output of the power transformer 22. The switching element 25 electrically disconnects the dummy resistor 24 from the circuit and electrically connects the dummy resistor 24 to the circuit. The series circuit of the dummy resistor 24 and the switching element 25 is connected between the power output of the power supply used to drive the communication module 3 and ground.

The instrument internal power supply 26 converts the voltage output generated by the power transformer 22 as a non-insulated output into a low voltage that can be driven by the measurement control unit 27.

The measurement control unit 27 is a CPU (Central Processing Unit) used for measurement and control of the transformer-equipped watt-hour meter 2. The measurement control unit 27 measures the amount of power in the main circuit using the current output from the current transformer 20 and current transformer 30 obtained from the power transformer 22 via the meter internal power supply 26, and the voltage output extracted from the instrument transformer 1. The measurement control unit 27 also monitors the connection of the communication module 3 and controls the on/off of the switching element 25.

The circuit configuration shown in FIG. 2 requires that the rectifier circuit 21 and power transformer 22 are configured as a flyback-type switching power supply, and that the secondary output voltage of the power transformer 22 is monitored and controlled by configuring a feedback circuit using a power supply control circuit 23 for voltage control to stabilize the output voltage. By configuring a feedback circuit, the internal power supply 26 of the instrument becomes a non-isolated output.

However, in FIG. 2, the voltage and current input of the transformer-equipped watt-hour meter 2, which is connected to the secondary side of the instrument transformer 40, and the communication module 3 generally need to be configured in an insulated manner to avoid the effects of noise or surges.

Therefore, in this embodiment, the power supply used inside the transformer-equipped electricity meter 2 has a two-output configuration of non-insulated and insulated, with the non-insulated output being used by the meter's internal power supply 26 and the insulated output being used to drive the communication module 3.

In this way, in the circuit configuration of the transformer-equipped electricity meter 2 constituting this embodiment, the secondary output stepped down by the power transformer 22 consists of two outputs, a non-insulated output and an insulated output, and the first output, which is the insulated output of the stepped-down secondary output, is output to the communication module 3 via the first connection line L1, and the second output, which is the non-insulated output of the stepped-down secondary output, is output to the meter internal power supply 26 and the measurement control unit 27 via the second connection line L2.

The second output, which is a non-insulated output, has its output voltage controlled by the power supply control circuit 23. However, the first output, which is an insulated output supplied to the communication module 3, is not output voltage controlled, and if the communication module 3 is not connected to the watt-hour meter 2 with transformer, it is expected that the output voltage will be significantly high. For this reason, in the watt-hour meter 2 with transformer of the embodiment, a dummy resistor 24 is implemented for the purpose of maintaining the output voltage.

When the communication module 3 is connected with the dummy resistor 24 installed, the power consumption of the communication module 3 is added to the power consumption of the watt-hour meter 2 with transformer. In other words, the usage load on the voltage circuit of the watt-hour meter 2 with transformer increases.

For example, if the watt-hour meter 2 with transformer is a certified meter, the total burden of the watt-hour meter 2 with transformer combined with the instrument transformer 40 used must be kept within the usage burden of the instrument transformer 40.

As mentioned above, if the usage load of the transformer-equipped watt-hour meter 2 changes when the communication module 3 is attached or detached from the transformer-equipped watt-hour meter 2, there is a concern that the usage load of the instrument transformer 40 may be exceeded.

Therefore, in this embodiment, a switching element 25 is implemented, and the measurement control unit 27 turns the switching element 25 on and off. In other words, a series circuit of a dummy resistor 24 and the switching element 25 is provided between the first connection line L1 and the ground.

Here, the switching element 25 is a simple switch circuit composed of, for example, a transistor or a thyristor.

Figure 3 is a diagram showing a specific circuit configuration of the dummy resistor 24 and the switching element 25 in the embodiment. In Figure 3, the switching element 25 is a transistor 25a.

In FIG. 3, the measurement control unit 27 monitors whether the communication module 3 is connected to the transformer-equipped watt-hour meter 2. When the communication module 3 is not connected, the measurement control unit 27 controls the transistor 25a to be on. This electrically connects the dummy resistor 24, forming a circuit in which the dummy resistor 24 is a usage burden. On the other hand, when the communication module 3 is connected, the measurement control unit 27 controls the transistor 25a to be off. This disconnects the dummy resistor 24, forming a circuit in which the communication module 3 is a usage burden.

The resistance value of the dummy resistor 24 is adjusted so that the usage load is the same as that of the communication module 3. As a result, by turning the transistor 25a on and off depending on whether the communication module 3 is connected or not, the usage load of the transformer-equipped watt-hour meter 2 can be kept constant regardless of whether the communication module 3 is connected or not.

Figure 4 is a flowchart showing an example of the operation of the transformer-equipped electricity meter 2 according to the embodiment. Figure 4 shows the operation of the measurement control unit 27.

First, the measurement control unit 27 determines whether or not the communication module 3 is connected to the transformer-equipped watt-hour meter 2 (step S11). If the communication module 3 is connected (step S11: Yes), the measurement control unit 27 turns off the switching element 25 (step S14). This disconnects the dummy resistor 24 from the circuit (step S15). As a result, the communication module 3 becomes a load on the transformer-equipped watt-hour meter 2.

If the communication module 3 is not connected (step S11: No), the measurement control unit 27 turns on the switching element 25 (step S12). This connects the dummy resistor 24 to the circuit (step S13), and the dummy resistor 24 becomes a load on the transformer-equipped electricity meter 2.

Figure 5 is a diagram showing a modified example of the watt-hour meter 2 with a transformer according to the embodiment. In the modified example shown in Figure 5, the communication module 3 controls the on/off of the switching element 25 using a control signal. That is, as shown in Figure 4, the communication module 3 determines whether or not it is connected to the watt-hour meter 2 with a transformer, and controls the on/off of the switching element 25 according to the determination result. In other words, when the communication module 3 is connected to the watt-hour meter 2 with a transformer, the communication module 3 turns off the switching element 25.

Thus, according to this embodiment, when the communication module 3 is connected, the switching element 25 is turned off and the dummy resistor 24 is disconnected from the circuit, and when the communication module 3 is not connected, the switching element 25 is turned on and the dummy resistor 24 is connected to the circuit. Therefore, regardless of whether the communication module 3 is connected or not, the load on the meter can be kept constant, and measurement accuracy can be ensured. Furthermore, by using a dummy resistor, which is a component of the power supply circuit inside the meter, it is possible to reduce the number of additional parts. In addition, since the load on the meter in this embodiment is controlled by a DC circuit, it can be realized with relatively small and inexpensive parts.

The configurations shown in the above embodiments are examples of the contents of this disclosure, and may be combined with other known technologies. Parts of the configurations may be omitted or modified without departing from the spirit of this disclosure.

1 Instrument transformer, 2 Watt-hour meter with transformer, 3 Communication module, 11, 12, 13 Power supply wiring, 20, 30 Current transformer, 21 Rectifier circuit, 22 Power supply transformer, 23 Power supply control circuit, 24 Dummy resistor, 25 Switching element, 25a Transistor, 26 Internal power supply of meter, 27 Measurement control section, 28 Input circuit, 29 Display section, 40 Instrument transformer.

Claims (5)

A transformer-equipped watt-hour meter having a detachable communication module,
a power transformer that reduces the voltage of a measurement signal of an instrument transformer, outputs a first output, which is an insulated output of the measurement signal after the voltage reduction, to the communication module via a first connection line, and outputs a second output, which is a non-insulated output of the measurement signal after the voltage reduction, to a second connection line;
a dummy resistor connected between the first connection line and ground and a series circuit including a switching element;
a switching element that is turned off when the communication module is connected to the watthour meter, and that is turned on when the communication module is not connected to the watthour meter. 2. The watt-hour meter with a transformer according to claim 1, wherein the resistance value of the dummy resistor is adjusted so that the usage load is the same as that of the communication module. 3. The watt-hour meter with a transformer according to claim 1, wherein a control unit of the watt-hour meter detects whether the communication module is connected to the watt-hour meter and controls the switching element. 3. The watt-hour meter with a transformer according to claim 1, wherein the communication module turns off the switching element when the communication module is connected to the watt-hour meter. The watt-hour meter with a transformer according to any one of claims 1 to 4, further comprising a measurement control unit that measures an amount of watt-hour based on the second output obtained from the second connection line.

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