JPH0682135B2 - Load electricity quantity measurement circuit of AC power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a load electricity amount measuring circuit of an AC power supply device in a three-phase three-wire circuit network.

B. Summary of the Invention The present invention is a load electricity amount measurement circuit for an AC power supply device, in which a current detector composed of a current transformer is provided for each phase of the output end on the power supply side, and the output current of the current detector for each phase is added. However, by providing the connecting portion so that the added output becomes zero, the load electricity amount in the three-phase three-wire circuit network can be measured at the output end on the power source side.

C. Conventional technology For example, as shown in Fig. 3, in a three-phase three-wire network such as a general distribution line consisting of a three-phase unbalanced load in which the power supply side is three-phase balanced and the load side is distributed, In order to obtain the load, at the output end on the power supply side, the three-phase power (both active and reactive) is measured from the detectable line voltage and line current by using a measuring means such as a two-power meter method even when unbalanced. Measurement is possible. In particular, when considering the load on the power source for the unbalanced load, there is a great merit if the power loaded between the lines can be measured and grasped from the output end on the power source side. The advantages of this are as follows. If the active / reactive power or power factor between each line can be easily measured at the output end on the power supply side, the equivalent load impedance between each line can be grasped, which is convenient for the operation, maintenance and inspection of electrical equipment.

As for the effect of the unbalanced load on the power supply, various estimates can be made based on the imbalance of the line current and line voltage that can be detected at the output end on the power supply side, protection against the power supply and load, load limitation, etc. Was going on.

FIG. 4 shows the load of FIG. 3 replaced equivalently with a concentrated load in order to simplify the consideration. If each branch current component inside the Δ power supply in FIG. 4 can be equivalently detected including the phase at the output end on the power supply side, the effective power P applied between each line of the power supply is given by the following equation.

P = line voltage × Δ power supply phase current × cos θ Reactive power Q is expressed by the following equation.

Q = line voltage × Δ power supply phase current × sin θ where θ is the phase difference between the voltage and current of each corresponding phase.

From the above P and Q equations, it becomes possible to measure with a normal measuring circuit. However, most generators in general electrical equipment And for a transformer, Also, there is a delta connection, but even in the case of a delta connection transformer, a current detection circuit must be provided inside the equipment.
Generally, it is impossible to detect the current in each branch of the Δ connection when the power supply equipment is equivalently replaced by the Δ connection.

D. Problems to be solved by the invention In the circuit as shown in FIG. 4, the line voltage at the output end on the power supply side,
In order to measure the load electric quantity such as valid and invalid only by detecting the line current, the calculation assumptions (for example, Must be analyzed and calculated by complex vector expansion and complex number calculation. In order to monitor this promptly, an arithmetic circuit such as an electronic computer is required, and there is a problem that it cannot be instructed by an instrument attached to an ordinary switchboard.

Further, in the circuit shown in FIG. 4, a current detection circuit is provided in each phase on the Δ load side in order to measure active power and reactive power applied between each line at the output end on the power supply side viewed from the terminal on the power supply side. Information transmission to remote (requires telemeter etc. if remote)
Had to do. However, in this case, equipment for information transmission is required, in the case of distributed load, a current detection circuit is required in each branch of the load between distributed lines, and if there are many distributed loads, a huge amount of equipment is required. However, there is a problem that the equipment is not feasible.

E. Means for Solving Problems The first aspect of the present invention is a three-phase three-wire circuit network, in which a current detector is provided for each phase of the power supply side output terminal and the output current of the current detector for each phase is provided. Is added, and a connection portion is provided so that the added output becomes zero. A second invention provides the first invention with a current circuit selection switching unit, a voltage detection unit, a voltage detection phase selection switching unit, three-phase and single-phase power converters, and a measuring instrument.

F. Action In order to indicate the amount of load electricity with a measuring device attached to the switchboard by measuring only the output end on the power supply side, a current component equivalent to each phase current of the Δ connection, which represents the power supply equivalently from the line current, is calculated. It is designed to be detected.

G. Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, PWR is a power supply device, and this power supply device PWR is composed of an AC generator, a transformer and the like. Usually the generator Alternatively, although there is a Δ connection, this embodiment will be described below assuming that they are all converted into equivalent Δ connections. Each phase R, S, T of the power supply device PWR having an equivalent Δ connection is connected to a load LD having an equivalent Δ connection via a line. Current transformers CT _R , CT _S , and CT _T , which are current detectors, are installed in each phase line near the output end of the power supply PWR.
And the other end of the secondary side of the current transformer CT _R of the secondary side of the one end and the current transformer CT _S connected, the secondary side of the secondary side end and current transformer CT _T of a current transformer CT _S Is connected to the other end of the current transformer CT _T and the other end of the current transformer CT _R is connected to the other end. Each connection point CO ₁ , C
O ₂ and CO ₃ are connected to the connecting portion COT where the added output of the CT circuit secondary side combined currents _A , _B and _C becomes zero. The ratio of the current transformers CT _R , CT _S , and CT _T is assumed to be 1: 1. In the figure,
_RS , _ST , _TR are combined impedances of delta connection load,
_RS , _ST , and _TR are active power between lines as seen from the PWR output end of the power supply unit, and Q _RS , Q _ST , and Q _TR are active power between lines as seen from the PWR output end of the power supply unit.

In addition, _RS , _ST and _TR are power supply internal induced voltages, _RS , _ST and _TR are power supply side terminal (line) voltages, _R , _S and _T are power supply output line currents, and _RS , _ST and _TR are power supply equivalent. Δ connection phase current, _A , _B , _C are CT circuit secondary side combined currents, _S is power supply device internal impedance (Δ connection conversion value) Next, the operation of FIG. 1 will be described using mathematical expressions. The power supply device output line currents _{R 1} , _{S 2} , and _{T 3} shown in FIG. 1 are expressed by equation (1) according to Kirchhock's law. _R + _S + _T = 0 (1) _R , _S , and _T are given by equations (2) to (4). _R = _RS - _TR (2) _S = _ST - _RS (3) _T = _TR - _ST (4) Generally, the internal impedance _{S of the} power supply device is 3 Since the phases are equal and the internal induced voltage can be regarded as three-phase equilibrium, the following equation is obtained.

( _RS + _ST + _TR ) _S = _RS + _ST + _TR = 0 ∴ _RS + _ST + _TR = 0 (5) Similarly, if Kirchhock's law of the secondary circuit of the current transformer is applied (6) ~ Equation (8) is obtained. _A = _R - _S (6) _B = _S - _T (7) _C = _T - _R (8) From the above, _A , _B , and _C are calculated ( Expressions 9) to (11) are obtained. _A = 2 _RS- ( _TR + _ST ) = 3 _RS .. (9) _B = 2 _ST- ( _RS + _TR ) = 3 _ST .. (10) _C = 2 _TR- ( _ST + _RS ) = 3 _TR.・ (11) From equations (9) to (11), the CT secondary side combined currents _A , _B ,
_C is in phase with _RS , _ST , and _TR of the power supply equivalent Δ connection phase current, and a value that is three times larger in magnitude is obtained. That is, detection measurement can be performed as _RS = _A / 3 (12) _ST = _B / 3 (13) _TR = _C / 3 (14).

On the other hand, at the output end on the power supply side, the line voltages _RS , _ST , and _TR can also be easily detected, so in addition to the above, the following electric quantities can be easily measured.

(B) The active power and the reactive power applied between each line at the output end of the power supply device are as follows.

W _RS = V _RS・ I _RS・ cos θ _RS = V _RS・ I _A・ cos θ _RS / 3 W _ST = V _ST・ I _ST・ cos θ _ST = V _ST・ I _B・ cos θ _ST / 3 W _TR = V _TR・I _TR・ cos θ _TR = V _TR・ I _C・ cos θ _TR / 3 Q _RS = V _RS・ I _RS・ sin θ _RS = V _RS・ I _A・ sin θ _RS / 3 Q _ST = V _ST・ I _ST・ sin θ _ST = V _ST , I _B , sin θ _ST / 3 Q _TR = V _TR , I _TR , sin θ _TR = V _TR , I _C , sin θ _TR / 3 In addition, the three phases are W _RS + W _ST + W _TR , Q _RS + Q _ST + Q
Become _TR .

Note that θ _RS , θ _ST , and θ _TR are _RS , _ST , _TR and _A ,
It is the phase difference between _B and _C. In addition, the effect of the internal equivalent impedance of the power supply is actually included, but it is generally small compared to the load impedance and is therefore omitted.

(B) The power factor between each line at the output of the power supply is _RS ,
_It can be measured by detecting the phase difference between _ST , _TR and _A , _B , _C. The power factors for the synthesis between the _RS , _ST , and _TR phases are cos θ _RS , cos θ _ST , and cos θ _TR .

(C) The value of the combined load impedance connected between each line at the output terminal of the power supply device is obtained as follows. In addition, R-
Let _RS , _ST , and _TR be the power vector representations between S, S-T, and _TR , respectively. From the above, the load impedance can be easily obtained as follows. _RS = V ² _RS / (W _RS + jQ _RS ) _ST = V ² _ST / (W _ST + jQ _ST ) _TR = V ² _TR / (W _TR + jQ _TR ) Note that the power ₁ in a single-phase circuit is the load impedance
_{Assuming that} the terminal voltage of ₁ is ₁ and the current flowing therein is ₁ , the vector representation ₁ of electric power is as follows.

From this formula, ₁ = V ₁ ² / (W + jQ) is obtained.

From the above embodiment, it is possible to easily obtain the amount of electricity that could not be easily measured at the output end on the power supply side. This is because, by detecting the line current at the output end (transmission end) on the power supply side, each branch current of the power supply that is equivalently represented by Δ connection can be detected. In addition, active and reactive power between each line of the three-phase power supply,
There is an advantage that the power factor can be detected from the line voltage and the power supply branch current.

FIG. 2 shows another embodiment of the present invention, in which the load circuit is omitted and the same parts are designated by the same reference numerals.
In Fig. 2, a current circuit selection switching unit ISW is provided at the connection COT of the current transformers CT _R , CT _S , and CT _T. This ISW switches the output of one of the three phases and outputs it to the terminal 1 of the single-phase power converter SCV.
Input to S, 1L. PT is a transformer that serves as a voltage detector, and the primary side of this transformer PT is connected to the output terminal of the power supply device PWR. The secondary side of the transformer PT is the terminal P1, of the three-phase power converter PCV.
Connected to P2 and P3. The current transformer C is connected to the PCS current input terminals 1S and 1L.
T _R, one end and the other end of the secondary side of the CT _S is connected, 3S, current transformer CT _T, one end and the other end of the secondary side of the CT _R is connected to the 3L.
PCV obtains three-phase power at the + and-terminals from the voltage and current amount.

VSW is a voltage detection phase selection switching unit, VSW is connected to the secondary side of PT, and two of the three phases are selected to obtain the output voltage. The obtained voltage is applied to SCV terminals P1 and P2. Is entered. SCV
Obtains single-phase power from the amount of voltage and current at terminals P1, P2 and 1S, 1L.
The obtained three-phase and single-phase power is supplied to the power meter via the switch SW.
Connected to PWM.

Using the above-described embodiment, single-phase / three-phase power and the like can be measured at the output end on the power source side with one measuring instrument.

H. Effects of the Invention As described above, according to the present invention, the load electric quantity in the three-phase three-wire circuit network can be measured at the output end on the power source side in the first invention. In the second invention, in addition to the effects of the first invention, single-phase and three-phase electricity quantities can be measured with one measuring instrument.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram showing one embodiment of the present invention, FIG. 2 is a circuit configuration diagram showing another embodiment of the present invention, and FIG. 3 is a schematic configuration diagram showing a three-phase three-wire network. FIG. 4 is an equivalent circuit diagram of FIG. PWR ... power _{supply, CT R, CT S, CT} T ... current transformer, COT ... connecting portion, ISW ... current circuit selecting switch unit, PT ... transformer, VSW ... voltage detection phase selection switching unit, for PCV ... three-phase Power converter, SCV ... Single-phase power converter, PWM ... Measuring instrument.

Claims (2)

[Claims] 1. In a three-phase three-wire circuit network, a current detector is provided for each phase of a power supply side output terminal, and the output currents of the current detectors of the respective phases are added so that the added output becomes zero. A circuit for measuring the amount of load electricity of an AC power supply device, which is provided with various connecting portions. 2. In a three-phase three-wire circuit network, a current detector is provided for each phase at the output end on the power supply side, and the output currents of the current detectors for each phase are added so that the added output becomes zero. , A current circuit selection switching unit is provided at the connection unit,
A voltage detector for detecting the voltage between each phase of the power source side output terminal is provided, and the output of this voltage detector and the output of the current detector are supplied, and a three-phase power conversion for obtaining a three-phase power output at the output terminal And a voltage detection phase selection switching unit that obtains a two-phase output from the outputs of the voltage detector, and the output of this switching unit and the two-phase output from the current circuit selection switching unit are supplied.
Provide a single-phase power converter that obtains single-phase power output at the output end,
A load electricity quantity measuring circuit for an AC power supply device, characterized in that the outputs of the single-phase power converter and the three-phase power converter are supplied to a measuring instrument via a switching circuit.