JP2011002297A - Residual magnetic flux measuring device, residual magnetic flux measuring method, and synchronous switching controller of circuit breaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem wherein, in the case of a transformer having a non-grounded neutral point, a DC component sometimes remains superimposedly in a transformer voltage after being cut off by a circuit breaker, and a DC offset component remains in the transformer voltage, and thereby residual magnetic flux cannot be calculated accurately.SOLUTION: In a three-phase transformer provided in a power system, wherein a primary side has a Δ-connection, a secondary side has a Y-connection, and the neutral point is non-grounded, a current transformer is provided on a surge absorber in each phase on the primary side of the three-phase transformer, and a voltage to the ground in each phase is determined from a detected value of the current transformer, and a voltage to the ground in each phase on the secondary side is operated, to thereby determine the residual magnetic flux.

Description

  The present invention relates to a measurement technique and a circuit breaker control for accurately measuring a residual magnetic flux generated when a transformer is interrupted and the iron core is demagnetized.

When the transformer is shut off to stop, the iron core is demagnetized and residual magnetic flux remains. As a result, a large magnetizing inrush current may flow when the circuit breaker is turned on again after recovery. In order to prevent detection of abnormal current in this case, power should be supplied to each phase at a timing corresponding to the residual magnetic flux. For this reason, a residual magnetic flux measuring device has been proposed for calculating the residual magnetic flux of the transformer after interruption from the primary coil voltage.
In the conventional residual magnetic flux detection device, a voltage detector for measuring each phase voltage is provided on the downstream side of the circuit breaker for connecting / cutting off the three-phase transformer to the three-phase power source.
The voltage induced in the iron core leg of each phase is proportional to the phase voltage, and the temporal change in the amount of magnetic flux in the iron core leg becomes the induced voltage of the iron core leg phase. Therefore, to obtain the magnetic flux, the phase voltage may be integrated.
In the residual magnetic flux measuring device, the residual magnetic flux is obtained by measuring the voltage waveform of each phase when the three-phase transformer is interrupted and calculating the magnetic flux by integrating the voltage value. (For example, see Patent Document 1)

Japanese Patent No. 2685574

In the case of a three-phase transformer whose neutral point is ungrounded, a DC component may remain superimposed on the three-phase transformer voltage after being interrupted by the circuit breaker. As a result, a DC offset component remains in the three-phase transformer voltage, the residual magnetic flux calculated by integrating this voltage drifts, and the residual magnetic flux cannot be calculated accurately.
Moreover, it is necessary to install a voltage detection circuit for measuring the residual magnetic flux, which increases the cost.

  The present invention has been made to solve the above-described problems. In a three-phase transformer, the voltage is integrated by eliminating the influence of the DC offset component after being cut off at low cost, and the magnetic flux of each phase is calculated. An object of the present invention is to obtain a residual magnetic flux measuring device that can accurately detect the residual magnetic flux.

The residual magnetic flux measuring device according to the present invention is a three-phase transformer provided in an electric power system in which a primary side is Δ-connected, a secondary side is Y-connected, and a neutral point is ungrounded. A current transformer is provided in each surge absorber, the ground voltage of each phase is obtained from the detected value of the current transformer, and the residual magnetic flux is obtained by calculating the ground voltage of each phase on the secondary side.

  The present invention opens the circuit breaker from the output of the current transformer provided in the surge absorber of each phase on the primary side without newly installing a branch circuit for measuring the voltage for each phase of the three-phase transformer. It becomes possible to obtain the ground voltage of each phase after the pole and accurately obtain the residual magnetic flux of each phase.

It is a block diagram which shows the structure of Embodiment 1 of this invention. It is a figure which shows the behavior (a) (b) for every phase of the three-phase transformer of Embodiment 1 of this invention. It is a figure which shows the behavior (c) (d) (e) for every phase of the three-phase transformer of Embodiment 1 of this invention. It is a block diagram which shows the structure of Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a residual magnetic flux measuring apparatus 1 according to Embodiment 1 of the present invention. The residual magnetic flux measuring apparatus 1 includes a current transformer installed in a surge absorber 13 connected to a three-phase transformer 30 and a three-phase circuit breaker 10.
The three-phase transformer 30 has a Δ-connected three-phase primary winding 31 and a Y-connected secondary winding 32 whose neutral point is ungrounded. Is connected to the other line.
The three-phase circuit breaker 10 includes three switches 10R, 10S, and 10T, and is arranged between the generator-side lines of the R phase 1R, S phase 1S, and T phase 1T and the three-phase transformer 30. Connected. The three switches 10R, 10S, and 10T can be opened or closed simultaneously or independently.
On the primary side of the three-phase transformer 30, a surge protector 13 for system protection is installed for each phase as 13R, 13S, and 13T. This surge absorber prevents the voltage and current downstream of the system from being shaken by noise on the primary side (generator side).

The instantaneous value of the current flowing through the surge absorbers 13R, 13S, and 13T for each phase is provided between the primary-side (generator-side) buses 11R, 11S, and 11T of the three-phase transformer 30 and the surge absorbers 13R, 13S, and 13T. Measured for each phase by the current transformers 12R, 12S, and 12T.
The current values Isr, Iss, Ist measured by the current transformers 12R, 12S, 12T are transmitted to the three-phase transformer primary side ground voltage calculation means 4 of the residual magnetic flux measuring device 1. The three-phase transformer temporary side ground voltage calculation means 4 integrates the current value before and after the circuit breaker is opened for each phase, and the integrated value is static for the surge absorbers 13R, 13S, and 13T for each phase. By dividing by the capacitances Cr, Cs, and Ct, the ground voltages Vδr, Vδs, and Vδt for each phase can be obtained.

Cr · Vδr = ∫ (Isr) dt (1)
Cs · Vδs = ∫ (Iss) dt (2)
Ct · Vδt = ∫ (Ist) dt (3)

From (1), (2), (3)

Vδr = (1 / Cr) ∫ (Isr) dt (4)
Vδs = (1 / Cs) ∫ (Iss) dt (5)
Vδt = (1 / Ct) ∫ (Ist) dt (6)

The three-phase ground voltage on the primary side of the transformer determined by the transformer primary side ground voltage calculation means 4 is transmitted to the transformer secondary side ground voltage calculation means 5.
The transformer secondary side ground voltage calculation means 5 calculates the difference between the primary side ground voltages of the transformer and obtains Y-connected secondary side ground voltages Vyr, Vys, and Vyt.

Vu = Vδr−Vδs (7)
Vv = Vδs−Vδt (8)
Vw = Vδt−Vδr (9)

The ground voltage on the secondary side of the transformer thus obtained is transmitted to the residual magnetic flux calculation means 6.
The residual magnetic flux calculation means 6 integrates the secondary side ground voltages Vu, Vv, Vw obtained by the transformer secondary side ground voltage calculation means for each phase, and calculates the residual magnetic flux of each phase.

FIG.
The method of calculating the residual magnetic flux of the three-phase transformer 30 from the phase voltage by the residual magnetic flux calculating means 6 is as follows.
The voltage induced in the core leg of each phase of the three-phase transformer 30 is proportional to the phase voltage of the Y connection of the three-phase transformer 30. Further, since the temporal change in the amount of magnetic flux in the iron core leg becomes an induced voltage of the phase of the iron core leg, the phase voltage may be integrated in order to obtain the magnetic flux from the phase voltage. However, the magnetic flux contains a calculated DC component depending on the time point at which integration is started, and it is necessary to eliminate this.
Now, the voltage and the amount of magnetic flux in the steady state with respect to the ground voltages Vu, Vv, Vw of each phase of the secondary coil 32 are expressed by the following equations.

Vu = Vm · sin (ωt) (10)
Vv = Vm · sin (ωt−2 / 3π) (11)
Vw = Vm · sin (ωt + 2 / 3π) (12)

φu = −φm · cos (ωt) (13)
φv = −φm · cos (ωt−2 / 3π) (14)
φw = −φm · cos (ωt + 2 / 3π) (15)

here,
Vm: Phase voltage peak value
ε: Angular frequency
t: time
Φm: Maximum value of magnetic flux in the core leg during steady state
Vu, Vv, Vw: Phase voltage of each phase
Φu, Φv, Φw: Magnetic flux of the core leg of each phase
Now, it is assumed that the phase voltage data for calculating the residual magnetic flux is taken into the calculation means 6 at least one cycle before the breaker 10 starts breaking. Then, the maximum value and the minimum value of the AC waveform exist at least once for both the phase voltage and the magnetic flux before the transient change of the phase voltage after the start of the interruption starts.
Taking the transient phase voltage and magnetic flux at the time of interruption of each phase as Vut, Vvt, Vwt, Φut, Φvt, and Φwt, taking Φut as an example, Φut is calculated as a time function from the following equation.
t
φut (t) = ∫Vut dt−φu0 (16)
t0

here,
t0: Integration start time
t: time
Φu0: DC component correction term for calculation that changes depending on the integration start time t0

Since the integration start time t0 is at least one cycle before the start of interruption as described above, the maximum value and the minimum value in the steady state AC waveform should appear as well as the phase voltage, and the maximum value Since the minimum value is equal in size and opposite in sign, Φut (t) is obtained in the form of a time function by integrating the equation (16), and the maximum value of Φut (t) is obtained. And Φu1 and Φu1, respectively, ΦU0 can be obtained from the above-described conditions, and the following equation is obtained.
Φu0 = (Φu2 + Φu1) / 2 (17)

In this way, by setting an arbitrary time before one cycle that becomes a transient phenomenon waveform due to interruption as the integration start time, it is possible to integrate the phase voltage and calculate the residual magnetic flux of the iron core leg. For Φvt and Φwt, the same equation as ΦUt is established by simply changing the index.
There are roughly two types of methods for actually calculating the residual magnetic flux by such a calculation method, one of which is a digital calculation by a computer, and the other is an analog calculation circuit. It is a method. Since the frequency of the target circuit is 50 Hz or 60 Hz, which is a commercial frequency, there is no problem in calculation time even with digital calculation by a computer, and even if analog calculation is adopted, existing analog calculation circuits should be combined. Since it is relatively easy to produce an arithmetic circuit, it is necessary to consider which one to select from different conditions. However, digital calculation by a computer is better than analog calculation for calculating the optimum input phase described later. As shown in Fig. 1, the residual magnetic flux calculation is also appropriate to convert the phase voltage into a digital signal by A / D conversion and make it a digital calculation by a computer. is there.

2 to 4 show a surge absorber current waveform, a transformer primary-side ground voltage waveform, a transformer secondary-side ground voltage waveform, a transformer magnetic flux, and a transformer secondary-side current waveform, respectively.
FIG. 2A shows current values Isr, Iss, and Ist flowing into the surge absorbers 13R, 13S, and 13T, which are obtained from the outputs of the current transformers 12R, 12S, and 12T in FIG. By integrating this current value and dividing by the electrostatic capacity Cr, Cs, Ct of the surge absorber as in the equations (4), (5), (6), the primary for each phase shown in FIG. The ground voltages Vδr, Vδs, and Vδt of the side coil can be obtained.
The secondary side ground voltage can be calculated from the difference between these voltage values using equations (7), (8), and (9), and Vu, Vv, and Vw shown in FIG. .
The ground voltage Vu, Vv, Vw of the secondary coil can be integrated as shown in equation (16) to obtain the three-phase transformer magnetic flux, which is shown in FIG.
Moreover, FIG.3 (e) is the electric current which flows into a secondary side coil.

  Therefore, without installing a new branch circuit for measuring the voltage for each phase of the three-phase transformer, the circuit breaker was opened from the output of the current transformer installed in the surge absorber of each phase on the primary side. The ground voltage of each subsequent phase is obtained, and the residual magnetic flux of each phase can be obtained accurately.

As can be seen from the surge absorber current in FIG. 2A, the surge absorber current continues to flow for a while even after the switch is opened.
Therefore, in order to avoid the influence of this oscillating current, a more accurate residual magnetic flux calculation value can be obtained by determining the residual magnetic flux after the oscillating current has sufficiently converged after a lapse of a predetermined time after the interruption.

Further, the surge absorber current of FIG. 2 (a) continues to flow while oscillating for a while, and as shown in FIG. 2 (b) and FIG. 3 (c), the oscillation of ground voltage on the primary side or secondary side of the three-phase transformer It appears.
Therefore, in order to avoid the influence of this ground voltage oscillation, if the residual magnetic flux is calculated after the oscillation current after interruption becomes smaller than the predetermined amplitude and sufficiently converges, the amplitude of the oscillation voltage varies depending on the power supply voltage, interruption timing, etc. Even when the time until convergence changes, it can be directly detected from the amplitude of the oscillation voltage that a sufficient convergence has occurred, and a more accurate residual magnetic flux calculation value can be obtained with the shortest waiting time.

  Also, comparing the coil voltage of each phase, not the oscillation amplitude of each phase coil, and determining the residual magnetic flux after the absolute value of these differences becomes smaller than a predetermined value, the more accurate residual magnetic flux calculation value is the shortest Can be obtained in a waiting time.

As described above, in the first embodiment, the following residual magnetic flux measurement method has been described.
In a three-phase transformer installed in the power system, the primary side is Δ-connected, the secondary side is Y-connected, and the neutral point is ungrounded, the current flowing through the surge absorber for each phase installed between the primary-side power supply circuit and the circuit breaker Measure for each phase by current transformer. By integrating the measured current value of each phase and dividing by the capacitance of each surge absorber, the ground voltage of each primary side phase is calculated. The ground voltage of each phase on the secondary side is obtained from the calculated ground voltage of each phase on the primary side by difference calculation. The residual magnetic flux remaining in the iron core of each phase of the three-phase transformer can be measured by integrating the ground voltage of each phase on the secondary side, which is the result of this calculation, for each phase.
By implementing such a measurement method, a current transformer provided in the surge absorber of each phase on the primary side without newly installing a branch circuit for measuring the voltage for each phase of the three-phase transformer It is possible to obtain the ground voltage of each phase after the circuit breaker is opened from the output of, and accurately obtain the residual magnetic flux of each phase.

Embodiment 2. FIG.
FIG. 5 is a block diagram showing a configuration of a circuit breaker synchronous switching control device 7 according to Embodiment 2 of the present invention. The circuit breaker synchronous switching control device 7 includes a residual magnetic flux measuring device 1 and a switching control device 8, and includes voltage detection wirings 9 R, 9 S, 9 T of the generator side lines 1 R, 1 S, 1 T and a three-phase circuit breaker 10. An open / close command signal line 14 for operating the three switches 10R, 10S, and 10T and an information line 15 for receiving residual magnetic flux information from the residual magnetic flux calculation means 6 are configured.
The switching control device 8 commands the opening and closing of the three-phase circuit breaker 10 via the switching command signal line 14, and monitors the voltage of the generator side lines 1R, 1S, 1T via the voltage detection wiring and remains. The residual magnetic flux information is received from the residual magnetic flux calculation means 6 of the magnetic flux measuring device 1 through the residual magnetic flux information line 15, the optimum input phase of the three-phase circuit breaker 11 is determined, and the input of the three-phase circuit breaker 11 is commanded.

A large magnetizing inrush current may flow due to the residual magnetic flux in the iron core when the circuit breaker is turned on again after the transformer is shut off due to a shutdown.
After obtaining the residual magnetic flux of the iron core of the three-phase transformer, this can be prevented by obtaining the optimum input phase for each phase. When the three-phase transformer is turned on in a phase in which the residual magnetic flux in the iron core of the three-phase transformer and the magnetic flux when a voltage is applied to the transformer in a steady state, the inrush current does not flow.
In each phase operation type circuit breaker, first, the circuit breaker is turned on at an optimum phase for one phase, and the remaining two phases are turned on with a time difference, thereby suppressing the magnetizing inrush current.
Even in a circuit breaker that can only be turned on at the same time, the inrush current can be minimized by simultaneously turning on the three phases with the phase with the least exciting current.

  The circuit breaker synchronous switching device using the residual magnetic flux measuring device can determine the accurate residual magnetic flux of the three-phase transformer after the breaking operation, and the correct target closing phase when the three-phase circuit breaker synchronous switching device is turned on It is possible to set the three-phase circuit breaker of the power system stably by minimizing the magnetizing inrush current when the three-phase circuit breaker is turned on.

DESCRIPTION OF SYMBOLS 1 Residual magnetic flux measuring apparatus 1R, 1S, 1T Generator side line 2U, 2V, 2W Electric power system side line 4 Transformer primary side ground voltage calculation means 5 Transformer secondary side ground voltage calculation means 6 Residual magnetic flux calculation means 7 Breaker Synchronous switching control device 8 Switching control devices 9R, 9S, 9T Voltage detection wiring 10 Three-phase circuit breakers 10R, 10S, 10T Switches 11R, 11S, 11T Three-phase transformer primary buses 12R, 12S, 12T Current transformer 13 , 13R, 13S, 13T Surge absorber 14 Open / close command signal line 15 Residual magnetic flux information line 30 Three-phase transformer 31 Primary coil 32 Secondary coil

Claims (6)

Measures the current flowing through the surge absorber for each phase installed between the primary power supply circuit and the circuit breaker of the three-phase transformer, which is installed in the power system and the primary side is Δ-connected, the secondary side is Y-connected, and the neutral point is ungrounded Measuring means, a primary side voltage calculating means for calculating a ground voltage of each phase on the primary side from the current, and a secondary side calculating a ground voltage of each phase on the secondary side from the ground voltage of each layer on the primary side. A residual magnetic flux measuring device comprising: ground voltage calculating means; and residual magnetic flux calculating means for calculating residual magnetic flux remaining in the iron core of each phase of the three-phase transformer from the ground voltage of each phase on the secondary side.   The residual magnetic flux measuring device according to claim 1, wherein the residual magnetic flux calculation means determines the residual magnetic flux after a predetermined time has elapsed since the circuit breaker started to interrupt the power supply to the power supply circuit of the three-phase transformer. .   The voltage signal of each phase output by the primary-side ground voltage calculation means or the secondary-side ground voltage calculation means after the circuit breaker starts to cut off the power supply to the power supply circuit of the three-phase transformer is less than a predetermined amplitude The residual magnetic flux measuring device according to claim 1, wherein the residual magnetic flux calculating means determines the residual magnetic flux after becoming.   The absolute value of the difference between the voltage signals of the respective phases output from the primary side ground voltage calculation means or the secondary side ground voltage calculation means after the circuit breaker starts to cut off the power supply to the power supply circuit of the three-phase transformer. The residual magnetic flux measuring device according to claim 1, wherein the residual magnetic flux calculating means determines the residual magnetic flux after the predetermined value or less is reached. In a three-phase transformer provided in the power system, the primary side is Δ-connected, the secondary side is Y-connected, and the neutral point is ungrounded, the current flowing through the surge absorber for each phase installed between the primary-side power supply circuit and the circuit breaker Measure the ground voltage of each phase on the primary side from the current, calculate the ground voltage of each phase on the secondary side from the ground voltage of each phase on the primary side, and calculate the ground voltage from the ground voltage of each phase on the secondary side. A residual magnetic flux measuring method, comprising: calculating a residual magnetic flux remaining in an iron core of each phase of a phase transformer.   Synchronous switching of a circuit breaker, characterized in that a target application phase is calculated from the residual magnetic flux calculated by the residual magnetic flux measuring device according to any one of claims 1 to 4 and the circuit breaker is inserted at the target application phase. Control device.

Images