JPS61194370A - Voltage/current detection circuit of multiphase ac line - Google Patents

Abstract

PURPOSE:To make it possible to detect line voltage or a line current by using the lower numbers of transformers than the number of the phases of a multi phase AC lines, by providing (n-1) sensors to n-phase lines to be measured and adding the outputs of the sensors. CONSTITUTION:Line voltage vectors V12, V23 of three-phase lines 1, 2, 3 are respectively inputted to rectifiers 12a, 13b through voltage transformers 11a, 11b and the output of an adder 13 is inputted to a rectifier 12c to form DC voltages corresponding to vectors V12, V31, V23. Line current vectors I1, I3 are respectively inputted to the rectifiers 16a, 16c through current transformers 15a, 15c and the output of an adder 17 is inputted to the rectifier 16b to form DC currents corresponding to line current vectors I1, I2, I3 while the outputs of multipliers 19a, 19b are inputted to an adder 20 to output a signal having a level corresponding to the magnitude of effective power.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to voltage and
This relates to a current detection circuit.

[Technical Background of the Invention] In addition to measuring active power and reactive power supplied from IT power lines, polyphase wattmeters are used to monitor power equipment by checking whether the load is almost evenly applied to each phase line. To ensure efficient operation, some are equipped with the ability to measure line voltage and line current.

Among such multiphase wattmeters, a typical configuration example of a three-phase wattmeter, which is relatively commonly used, is shown in FIG. The outline will be explained with reference to Figure 3.
Line voltage protection for three-phase lines 1, 2.3 12. *23. *31
For example, the desired voltage levels 912', 923', 923',
ψ31', and the line voltages V12, V are converted from these converted voltages by rectifiers 5a, 5b, 5c, etc.
23. DC voltage V1 at a level corresponding to the magnitude of ψ31
2'.

V23' and V31' are formed.

Similarly, the line currents It, I2 and I3 of the three-phase lines 1 and 2.3 are also currents i1' at desired levels through, for example, three current transformers f3a+6b*6c.

12', i3' and rectifiers 7 a, 7 b, 7
The line current t1゜' is calculated from these converted currents by c, etc.
DC current at a level corresponding to the size of 12gIz■1'
, ■2', and ■3' are formed.

Regarding the electric power, the multipliers 8a and 8b calculate the scalar product P1'=V12'・11' from the converted voltage *12' and the converted currents 11' and 13', respectively.
and P2' = V2:! ``T:I'' is determined, and these two values P1' and P2' are added together via an adder 9. In this case, as is well known, in a three-phase line, three line current 11
．． Since the sum of I2.13 becomes "0", the sum of the converted currents II' + I2' + Ico' also becomes "0". Utilizing this condition, a power value W3φ' at a level corresponding to the magnitude of the active power W3φ of the three-phase line is obtained from the above P1′ and P2′ by the so-called two-set force meter method.

The electrical quantities thus determined are sent to a measuring section (not shown), converted into digital values, and then displayed on a display or the like. .

As is clear from the above explanation, in the conventional three-phase car meter illustrated in Fig. 2, when determining the line voltage and line current of the three-wire Sanwa electric line, three It is necessary to incorporate three voltage transformers 4a to 4C and three current transformers 6a to 6c. It is also possible to replace each of these transformers with a small portable clamp sensor or the like.

In any case, the large number of such measurements increases the external dimensions of the product and increases the number of superpositions, which is undesirable because it increases the burden on the operator, whether indoors or outdoors.

[Object of the Invention] This invention was made in view of the above points, and its purpose is to focus on the fact that the vector of the instantaneous values of line voltage and line current of a multiphase AC line is closed.

To provide a voltage/current detection circuit suitable for a multiphase wattmeter in which a thin capacity such as line voltage or line current is required using voltage transformers and current transformers whose number is smaller than the number of phases. It is in.

[Example] Hereinafter, the present invention will be explained in detail with reference to an example shown in FIG. 1 of the accompanying drawings.

Referring to the same figure, for detecting line voltage, the input sides of voltage transformers 11a and llb are connected between 1 and 2 and 2 and 3 of the three-phase line, respectively, and their outputs The side is connected to the input side of rectifiers 12a and 12b, for example. Further, the output sides of the voltage transformers 11a and llb are also connected to the input side of the adder 13, for example.
The output side of this adder 13 is connected to the input side of a rectifier 12c. The output sides of these three rectifiers 12a to 12c are connected to a measuring section (not shown) or the like via output terminals 14a to 14c, respectively.

Regarding detection of line current, clamp type current transformers 15a and 15c are connected to, for example, 1 and 3 of the three-phase line 1゜2.3.
etc., and their output sides are connected to the input sides of rectifiers 16a and 16e, for example. Also,
The output sides of the current transformers 15a and 1.5c are also connected, for example, to the input side of an adder 17.
The output side of 7 is connected to the input side of rectifier 16b.

The output sides of these three rectifiers 16a to 16e are connected to the above-mentioned measuring section, etc. (not shown) via output terminals 18a to 18c, respectively.

Regarding power detection, the circuit configuration is almost the same as that of the conventional polyphase wattmeter illustrated in FIG. For example, the input side of the multiplier 19a is connected to the input side of the multiplier 19a. Further, the output side of the voltage transformer 11b and the output side of the current transformer 15c are connected to, for example, the input side of the multiplier 19b. The output sides of these two multipliers 19a and 19b are connected, for example, to the input side of an adder 20, and the output side of this adder 20 is connected via an output terminal 21 to a measuring section (not shown) in the same manner as described above.

Next, to explain the operation of this voltage/current detection circuit, the line voltage protectors 12 and 23 of the three-phase lines 1, 2.3 detect a desired voltage level V via voltage transformers 11a and 11b, respectively. 12' and V23', and the rectifier 12
a, 12b, from these converted voltages a DC voltage v at a level corresponding to the magnitude of the line voltage *12 and 923 above.
12' and v23' are formed.

DC voltage v at a level corresponding to the magnitude of line voltage *31
31' is obtained as follows. That is, in the three-phase lines 1, 2, and 3, the sum of the instantaneous vectors of the line currents is "0" as described above, but similarly, the sum of the instantaneous vectors of the line voltages is also "0" as shown below. ”.

*12+gu23+Ω31=0 Than this.

Vl　3　+V23　=　Vyo1 is obtained.

Therefore, if we assume that the converted voltage is *31' for the line voltage Ω31 in the three-phase lines 1, 2.3, the difference between the other two converted voltages V12' and 23' is , following the above formula, Vl 2 ' + V2 : I ' + Vs
1' = 0 holds, and from this point on, do the same thing.

*1゜・＋※23・=−gu、1・ is obtained.

Therefore, as shown in Fig. 1, when the above converted voltages *12' and 23' are added together via the adder 13, the output side has the above-mentioned assumption for the line voltage *31. The desired level of the inverted conversion voltage (-)V 31 '
appears. This converted voltage (-) *1' is the rectifier 1
2c, thereby forming a DC voltage V s 1 ' at a level corresponding to the magnitude of the line voltage '7:Ii.

Regarding the line currents II and i:I, the desired current levels 11' and i3' are determined by current transformers 15a and 15c, respectively.
The line currents 11 and i3 are converted from these converted currents by the rectifiers 18a and 18c.

Direct currents 1' and 13' with levels corresponding to the magnitudes are formed.

Regarding the line current 12, this is because the sum of the instantaneous vectors of the three line currents, 1 x + I 2 + I 3, is "0".

I 1 + I 3 = I 2 It is.

Therefore, assuming that the converted current of the line current 12 is I2', these three converted currents 11' and 12' as in the case of the converted voltage (-) 931'.

Between I3', following the above formula, i,・+i3・＝　−I　　　’ The relationship holds true.

Therefore, when the converted currents 11' and I3' are added together via the adder 17, the line current 1 is added to the output side.
2, the desired level of inversion conversion current (-)iz'
appears. This converted current (-) 12' is transferred to the rectifier 16
b, thereby forming a direct current 2' having a level corresponding to the magnitude of the line current 12.

As for how to obtain the active power W3φ of the three-phase lines 1 and 2.3, the double force meter method is applied as in the conventional example, so
Briefly, the multipliers 19a and 19b calculate the scalar products P1' and P27 of the converted voltage *12' and the converted currents L1', 923' and I3', respectively. These values are input to the adder 20, and the active power value W at a level corresponding to the magnitude of the above-mentioned active power W3φ is obtained.
3φ' is obtained from the output side of the adder 20.

The electrical quantities detected in this way at levels corresponding to the magnitudes of the line voltage, line current, active power, etc. are sent to a measuring section (not shown), where they are subjected to appropriate signal processing and displayed on a display, etc. Is displayed.

[Effect] As explained above, the voltage/current detection circuit of the polyphase wattmeter according to the present invention can detect the line-to-line voltage *1, ψ2,...*31 when the line to be measured is a three-phase line, for example. and line current I
f, 1. ? , I3 and two voltage transformers 11a, Ilb and two current transformers 15a.

15b, and the extracted converted voltage *12'.

Two multipliers 19a and 19b for obtaining a power value W3φ' at a level corresponding to the magnitude of the active power W-4φ of the three-phase line by the double force meter method from ÷23' and the converted currents i1/ and I3'. and adder 2 that adds their outputs.
0, and the above two converted voltages *12',
923', and a voltage adder 13 and a current adder for adding the converted currents II' and I% to form another converted voltage (-)*1' and converted current (-) I2', respectively. It is equipped with 17. These converted voltages and converted currents are converted into DC voltages and DC currents at levels corresponding to the magnitudes of the line voltages and line currents through rectifiers 12a to 12c and 16a to 16c, respectively, and then measured. The data is sent to the department, digitized, and displayed on a display.

Therefore, according to a polyphase wattmeter to which the circuit of the present invention is applied, the number of voltage transformers and current transformers built into the wattmeter body is generally the same as the number required for polyphase power measurement. The number of lines is one less than the number of phases of the line, and the weight burden on the measurer can be reduced. Additionally, since the wattmeter is operated while the line under test is live, the number of voltage transformers and current transformers that govern the size and weight of the product is reduced, which is also important in terms of handling. It is extremely desirable for people.

Although the above description has been made for a wattmeter on a three-phase line, it goes without saying that the technique of the present invention can also be applied to a wattmeter on a line with more than three phases.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the voltage/current detection circuit of a polyphase wattmeter according to the present invention applied to a three-phase wattmeter, and FIG. 2 is a block diagram of a conventional three-phase wattmeter. FIG. 3 is an explanatory diagram showing an example of the mutual relationship between voltage and current in a three-phase line. In the figure, 1, 2.3 are three-phase lines to be measured, and 11a. 11b is a voltage transformer, 12a, 12b, 12c, ・
16a, 16b, 16c are rectifiers, 13.17.20 are adders, 15a, 15c are current transformers, 19a. 19b is a multiplier.

Claims (1)

[Claims] Converting the line voltage and line current levels of the n-phase line to be measured (n=3, 4, 5, . . .) using a voltage sensor and a current sensor at predetermined ratios, respectively; and an adder that takes the extracted converted voltage and converted current as inputs, respectively, and a DC voltage and DC voltage that correspond to the levels of the line voltage and line current from the converted voltage and converted current and the output of the adder. In a voltage/current detection circuit for a multiphase AC line having a rectifier that forms a current, the voltage sensor and the current sensor are coupled to the n-phase line to be measured and send their converted outputs to the rectifier, respectively.
It receives "n-1" converted voltages from the voltage sensors and adds them to the converted voltage of one phase to which the voltage sensor in the n-phase line to be measured is not coupled. a voltage adder that forms a voltage with a corresponding level and reversed polarity and sends it to the rectifier; and a voltage adder that receives "n-1" converted currents from the current sensor and adds these to the device to be measured. A current adder is provided for forming a current having a level corresponding to a converted current of one phase to which the n-phase line current sensor is not coupled and having an inverted polarity and sending the current to the rectifier. Voltage/current detection circuit for multiphase AC lines.