JP2005043232A - Wattmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a phase connected with single-phase three wires, to enhance working efficiency, to reduce an expense by dispensing with a dedicated apparatus, and to enhance detection precision, in measurement of electric power, inspection, wiring work and the like in a different capacity three-phase four-wire type electric power source. <P>SOLUTION: This wattmeter for measuring electric power of a three-phase alternating current is provided with a voltage detecting means for detecting voltages between transmission lines and the grounding for the three-phase alternating current with the grounding potential as a reference, and a detecting means for detecting the prescribed phase of the three-phase alternating current connected with a single-phase three-wire load, based on the result of vector operation by combining two of the grounding voltages. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wattmeter that measures a power value of a three-phase alternating current, and in particular, when a single-phase three-wire load is connected to a predetermined three-phase phase, the single-phase three-wire load can be detected. Related to wattmeters.

  Equipment installed in factories, etc. is supplied with 200V three-phase power as a power source, and Scott connection is made to a predetermined phase among them to create a 100V system power supply, and a single phase is used for loads such as electric lights. Power is being supplied. Such a connection system is called a different capacity three-phase four-wire system.

When measuring or inspecting electric power, wiring work, etc. in a different capacity three-phase four-wire system, the reliability is low even if there is no wiring diagram, and the single-phase three-wire is connected from any phase of the three-phase three-wire power source. There is an unknown site, and it is necessary to check the wiring.
Conventional wattmeters do not have a function to check the connected phase of a single-phase three-wire load. As a dedicated device to check the wiring, the signal is superimposed on each phase line of the power supply and the signal on the single-phase load side The method of detecting is used.

This will be described with reference to the drawings.
FIG. 2 is an explanatory view showing detection of a conventional single-phase three-wire load.
In FIG. 2, a three-phase power source 30 is configured by three-phase three-wires, and supplies three-phase power to loads RL1, RL2, and RL3 connected to each phase. The R-S phase of the three-phase power supply 30 is grounded at an intermediate position N, so that single-phase power is supplied to loads RL4, RL5 connected between R-N and S-N.

The signal superimposing unit 20 superimposes a minute signal having a frequency sufficiently higher than commercial frequencies such as 4 kHz and 50 mV by clamping the transmission line of each phase of the three-phase power supply 30. The signal detector 21 has a function of detecting a superimposed signal from a line in which a single-phase three-wire load is wired to the three-phase power supply 30 and notifying the operator. That is, when the signal detector 21 detects the superimposed signal, the phase in which the single-phase three-wire load is wired can be determined depending on which phase the signal is superimposed on.
Prior art documents related to a power meter for measuring three-phase power include the following.

JP-A-6-34678 Japanese Patent Laid-Open No. 11-344514

  In the conventional example shown in FIG. 2, a dedicated device for wiring confirmation is required and the power source side and the load side are separated. For example, when the positions of the power source and the load are separated, two people are in contact with each other. The work efficiency is poor. In addition, since the signal detector handles a minute signal, it may be weak to noise and cannot be detected correctly.

  Therefore, the problem to be solved by the present invention is that it is possible to detect the phase in which the single-phase three-wire is connected in the measurement and inspection of the power of the different capacity three-phase four-wire power source, and the wiring work, improving the work efficiency, The purpose is to reduce costs and improve detection accuracy by not using dedicated equipment.

(1) In a wattmeter that measures three-phase AC power,
Voltage detection means for detecting a ground-to-ground voltage between the three-phase AC transmission line with reference to the ground potential;
Detecting means for detecting a phase of a three-phase alternating current to which a single-phase three-wire load is connected based on a result of a vector operation combining the two voltages between the grounds;
A wattmeter characterized by the provision of

(2) The detection means determines whether the single-phase three-wire load is connected depending on whether the result of the vector calculation of the voltage between the grounds exceeds a predetermined ratio with respect to the rated voltage of the single-phase three-wire load. The power meter according to (1), wherein the power meter is determined.

(3) The voltage detecting means has three amplifiers, one of the input terminals of each amplifier is connected to a ground potential point, and the other input terminal is connected to a three-phase AC transmission line. The wattmeter as described in (1) or (2) characterized by the above-mentioned.

  According to the first to third aspects of the present invention, it is possible to detect in advance information about the phase of the three-phase three-wire, to which the single-phase three-wire load is connected, using the measured voltage. Therefore, there is no need to investigate using a dedicated device separately, and it is possible to prevent an increase in cost and deterioration in work efficiency and improve detection accuracy.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention.
In FIG. 1, the three-phase power supply 30 shows a case where each phase is grounded at an intermediate position. When the phase is between the R and S phases, the phase is N1. Is grounded at N3.
The portion surrounded by the broken line is the wattmeter of the present invention.
In each of the amplifiers 1, 2, and 3, one of the input terminals is connected to the terminal Nin of the wattmeter, and this terminal Nin is grounded outside the wattmeter and connected to a common potential point in the wattmeter.

The other input terminals of the amplifiers 1, 2, 3 are connected to the terminals Vin1, Vin2, Vin3 of the wattmeter, respectively. The voltages Vrn (R-N1 phase voltage), Vsn (S-N2 phase voltage), and Vtn (T-N3 phase voltage) of each transmission line with respect to the ground potential are applied to the terminals Vin1, Vin2, Vin3, respectively. Each amplifier normalizes and outputs the voltage.

The A / D converter 4 simultaneously holds the output voltages of the amplifiers 1, 2, 3 by the sample hold function, and sequentially performs A / D conversion by switching the held voltages. The converted digital data is taken into the MPU 6 which is a processor through an insulating circuit 5 including a photocoupler, a transformer, or an insulating element instead of them. The portion so far corresponds to voltage detection means.

The MPU 6 vector-adds the voltages of the respective transmission lines with respect to the detected ground potential according to the following expression, and based on the result, detects which phase of the three-phase three-wire is connected to the single-phase three-wire load. This corresponds to detection means. The display 7 displays the detection result of the single-phase three-wire load.

The output voltages Vrn, Vsn, and Vtn of the amplifier indicate the RN phase, SN phase, and TN phase voltages with respect to the ground potential, respectively, and these voltages are obtained when the single-phase three-wire voltages are balanced. The relationship is as follows.

Ｓ−Ｔ相間に単相３線の負荷が接続されている場合。

Ｔ−Ｒ相間に単相３線の負荷が接続されている場合。

When a single-phase three-wire load is connected between the RS phases.

When a single-phase three-wire load is connected between the ST phases.

When a single-phase three-wire load is connected between the TR phases.

That is, it can be seen from which phase of the three-phase three-wire the single-phase three-wire load is connected by measuring the voltage of each transmission line with respect to the ground potential and adding the vectors.
Even if the voltage of the single-phase three-wire load is unbalanced, the result of the above equation can be expected to be a sufficiently low value with respect to the rated voltage (for example, 100 V), so the right side of the above equation is not 0. Determination can be made if the voltage is 10% or less. This determination is made by the MPU 6.

ここで、Ｔは１周期、ｖｒｎ，ｖｓｎ，ｖｔｎは、時刻ｔにおけるサンプリングデータである。 The voltage vector calculation may be performed by adding the sampling data of the A / D converters having the same timing to each other as shown in the following equation to obtain the effective value.

Here, T is one cycle, and vrn, vsn, and vtn are sampling data at time t.

FIG. 1 mainly explains the characteristics of the present invention, and the configuration of a conventional wattmeter for power measurement is omitted.

Moreover, the input part comprised from three amplifiers in the wattmeter of this invention can be used also as a voltage input of a three-phase four-wire system. Specifically, the input terminal Nin of the wattmeter is connected to the neutral point of the star connection, Vin1 is connected to the R-phase transmission line, Vin2 is connected to the S-phase transmission line, and Vin3 is connected to the T-phase transmission line. Thereby, the phase voltage of R phase, S phase, and T phase can be measured. Therefore, the present invention can be applied to any three-phase four-wire wattmeter without changing hardware.

As described above, since it is possible to detect information on which phase of the three-phase three-wire is connected to the phase to which the single-phase three-wire load is connected using a power meter, there is no need to separately investigate using a dedicated device. In addition, it is possible to prevent an increase in expenses and deterioration in work efficiency, and improve detection accuracy.
Therefore, it is effective when there is no wiring diagram or there is no reliability even if there is no wiring diagram at the time of power measurement, inspection and wiring work of a three-phase four-wire power source of different capacity.

It is the block diagram which showed one Example of this invention. It is explanatory drawing which showed the detection of the phase by which the conventional single phase 3 line was connected.

Explanation of symbols

1, 2, 3 Amplifier 4 A / D converter 5 Insulation circuit 6 MPU
7 Display

Claims (3)

In a wattmeter that measures three-phase AC power,
Voltage detection means for detecting a ground-to-ground voltage between the three-phase AC transmission line with reference to the ground potential;
Detecting means for detecting a phase of a three-phase alternating current to which a single-phase three-wire load is connected based on a result of a vector operation combining the two voltages between the grounds;
A wattmeter characterized by the provision of   The detection means determines whether the single-phase three-wire load is connected depending on whether the result of the vector calculation of the voltage between the grounds exceeds a predetermined ratio with respect to the rated voltage of the single-phase three-wire load. The wattmeter according to claim 1. The voltage detecting means has three amplifiers, one of the input terminals of each amplifier being connected to a ground potential point, and the other input terminal being connected to a three-phase AC transmission line. The wattmeter according to claim 1 or 2, characterized by the above.

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