JPH0378423A - Electric power system circuit - Google Patents

Abstract

PURPOSE:To prevent a ferroresonant phenomenon stably for a prolonged term by setting natural frequency by the inductance of the saturated region of a transformer for an instrument and capacitance connected at a terminal to the half or less of commercial frequency. CONSTITUTION:The circuit of a transformer 4 for an instrument is installed, and an external ground capacitance 5, a coupling capacitance 6 and voltage 7 related with induction are provided. The inductance of the saturated region of the transformer 4 for the instrument and capacitance 5 connected at a terminal are set so that natural frequency by these inductance and capacitance 5 may be the half or less of commercial frequency. Accordingly, a countermeasure is considered so that a ferroresonant phenomenon is not generated theoretically on the basis of the fundamental principle of the ferroresonant phenomenon, thus stably preventing the ferroresonant phenomenon for a prolonged term without losing an effect even by a quantity of condition change.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to power system circuits, and in particular, to solving the so-called ferroresonance phenomenon that sometimes occurs in circuits to which potential transformers are connected. Regarding technology for prevention.

(Prior art) Conventionally, the principle of this type of fero-resonance phenomenon has not been fully elucidated, and therefore prevention efforts have been made based on inferences and assumptions rather than on theories and principles. Appropriate preventive measures are determined and implemented by devising means and confirming the absence of resonance through numerical calculations or actual measurements. In various power circuits that implement such prevention measures, even a slight change in the circuit constants can significantly change the effect of preventing ferroresonance phenomenon.
Furthermore, there is a large variation in the phenomenon each time. Therefore, even if conventional means for preventing ferroresonance phenomena can prevent ferroresonance within the range of calculation and actual measurement conditions, in actual use, ferroresonance will continue to occur over a long period of time in response to slight changes in conditions. It was difficult to prevent this.

(Problems to be Solved by the Invention) The present invention was proposed in order to solve the problems of the prior art as described above, and its purpose is to theoretically solve the problems of iron To provide an excellent power system circuit that can stably prevent ferroresonance over a long period of time without losing its effectiveness even with slight changes in conditions by taking countermeasures to prevent resonance from occurring. It is.

[Structure of the Invention] (Means for Solving the Problems) A power system circuit according to the present invention is a circuit to which a voltage transformer is connected, and when disconnected from a power supply, the power system circuit is connected to the power supply or another power supply. In a power system circuit that generates a resonant abnormal voltage at an odd fraction of the commercial frequency due to the capacitive coupling of the optical circuit, the nonlinear inductance of the voltage transformer, and the capacitance connected to the voltage transformer terminal, ,
It is characterized in that the inductance in the saturated region of the potential transformer and the capacitance connected to the terminal are set so that the natural frequency due to these inductances and capacitances is 1/2 or less of the commercial frequency.

(Function) In the present invention having the configuration as described above, the natural frequency due to the inductance in the saturation region of the potential transformer and the capacitance connected to the terminal is set to 1/2 or less of the commercial frequency. Based on the basic principle of ferroresonance, it is possible to theoretically prevent the occurrence of ferroresonance, so the effect will not be lost even with slight changes in conditions, and the ferroresonance will be stable over a long period of time. can be prevented.

That is, the inventor analyzed the fero-resonance phenomenon in detail to elucidate the basic principle, and based on this basic principle, provided the present invention.

Below, the basic principle of the iron resonance phenomenon elucidated by the inventor will be explained.

First, FIG. 1(a) is a diagram showing a circuit to which a potential transformer is connected. Potential transformer (hereinafter abbreviated as PT)
The circuit No. 4 can be expressed as shown in this figure. Furthermore, although there may be a plurality of external ground capacitances 5, coupling capacitances 6, and voltages 7 related to induction, each of them can be collectively shown as one equivalent value. That is, regarding the external ground capacitance 5 and the coupling capacitance 6,
The voltage 7 related to induction is set to match the sum of multiple voltage sources, and with the voltage transformer 4 and external ground capacitance 5 removed, multiple voltage sources and their corresponding coupling capacitances are used. It is clear from Thevenin's theorem that it is sufficient to match the voltage generated at point "P" in the figure.

Figure 1(b) shows (b) to make the phenomenon more clear.
The Thevenin's theorem is again applied to the range indicated by "X" (the part related to coupling) to simplify it. Here, the composite capacitance 12 is the external ground capacitance 5, the coupling capacitance, and the internal is equal to the sum of the capacitances. induced voltage 1
1 corresponds to the commercial frequency induced voltage that would occur if the switch 3 were opened and the nonlinear inductance 21, series resistance 22, and equivalent parallel resistance 23 of the PT 4 were removed. That is, 11 is an induced voltage due to capacitive coupling.

FIG. 2 is an example of the phenomenon after opening the switch 3 in the circuit of FIG. 1(b). EMTP (Transient Phenomenon Analysis Program) was applied to analyze the phenomenon. Here, the constant is 500k
The following was chosen as an example of a practical value for a V power system.

Power supply voltage peak value = 449000V Induced voltage = 0.15X449000V Combined capacitance = 1320pF Series resistance = 200Ω Equivalent parallel resistance = 2GΩ Characteristic current of nonlinear reactor (A) Magnetic flux (Wb) -9, 32-0, 77E5 -1. 54E-2-0, 43E4 1.54E-20, 43E4 9.32 0.77E5 In Figure 2, A is the voltage at the terminal of PT4, C is the induced voltage, and B is the value obtained by subtracting C from A. , which is equal to the charging voltage of the composite capacitance 12. D is PT4
and the current flowing through the composite capacitance 12. “Y
'' part, a period in which the resonance conditions are broken and the resonance gradually attenuates (resonance decay period), and a period in which the "Z" part resonance rises again (resonance increase period).

Figure 3 is a greatly expanded time axis of the "Y" part in Figure 2, and AI, Bl, C1, DI are A, B, and C in Figure 2.
, D, respectively.

B1 in FIG. 3 clearly shows how the resonance is attenuated. In the horizontal period of B1, Dl, i.e. P
It can be seen that no current flows through T4 and the composite capacitance 12 (in fact, a minute current flows), and PT4 traces the extremely high inductance part in the non-saturation region on the current-magnetic flux characteristic curve. . At this time, no current (almost) flows through the composite capacitance 12,
Since the charge does not change, the voltage remains constant. In addition, during the period when the voltage polarity of B1 is reversed,
A large current flows through Dl. This period is a period in which the current-magnetic flux characteristic curve of the PT traces the saturation region, and since the inductance in the saturation region is relatively small, current flows. 3 to 3 in FIG. 3 indicate such voltage inversion periods. It is clear when compared with Fig. 1(b) that during the period when the voltage of B1 is constant, the inductance of PT4 is in a very high state, so no current flows even due to the induced voltage of C1, and the combined capacitance is 12
This is a period that is unrelated to the attenuation and rise of resonance because the voltage of On the other hand, during the period from ■ to ■, since PT4 has a relatively low inductance, current flows and C
The more the polarities of the induced voltage of 1 and the PT/capacitance current of Dl match, the more the current increases, and when the polarity is reversed, the amplitude of B1 increases, that is, the resonance rises, and the more the polarities do not match, the more it attenuates. be. Here, the relationship between polarity and amplitude for each of the voltage inversion periods (1) to (2) in FIG. 3 is as follows.

Period Polarity Amplitude■...First half matched, second half inconsistent - Slightly free decay■・
・・First half matching, second half not matching – Slightly free decay ■・・・・
Mismatch - Large attenuation■...Possible match
→Amplitude increase■...Inconsistency -Large attenuation Also, Figure 4 is a greatly expanded time axis of the "Z" portion of Figure 2, and shows A2. B2. C2 and B2 are the second
The same items as A, B, C, and D in the figure are shown. Fourth
2 to 0 in the figure are voltage inversion periods similar to 2 to 2 in FIG. 3, and the relationship between polarity and amplitude for each voltage inversion period 2 to 3 is as follows.

Period Polarity Amplitude■...Consistent→Amplitude increase■...First half coincide, second half mismatch - Slightly free decay■...Habo coincidence →Amplitude increase■・・・Concurrence
- Amplitude increase [stock]...Slightly inconsistent → Slightly attenuated 0...First half consistent, second half inconsistent →Slightly more than free decay, the relationship between the time when the current flows greatly in the PT4 saturation region and the polarity of the induced voltage The degree to which resonance rises depends on this. However, from Figures 3 and 4, it is clear that the time interval at which the polarity of B1 is reversed changes depending on the voltage value, and it is difficult to avoid resonance by intentionally adjusting the relationship with the polarity. It is.

Here, P in Figure 1(b), and ■~ in Figures 3 and 4.
Consider a state in which a large current flows through T4.

If there is no induced voltage 11, the charge on the composite capacitance 12 passes through the inductance in the saturation region of PT4, and the polarity of the charge and voltage on the composite capacitance 12 is reversed over a time period of ]/2 of the natural period determined by the values of both. . The absolute value of the voltage at this time hardly changes, with only slight attenuation. -When the universal conductive voltage 11 exists,
According to the principle of superposition, the amplitude increases by the amount that the voltage of the composite capacitance 12 is charged only by the induced voltage 11. FIG. 5(a) is a circuit diagram in which only the inductance in the saturation region of the power supply voltage e1 and the capacitance C1 is extracted. In Fig. 5(a), when the capacitance C has no initial charge, the switch is closed for 1/2 of the natural period determined by the inductance L and the capacitance C, and the capacitance C is charged with the power supply voltage e. Charging voltage V
c corresponds to the one that best matches the polarity mentioned above and increases the amplitude the most. The horizontal axis in Fig. 5(b) is the natural frequency fo due to the inductance L and capacitance C.
The ratio fs/fo of the frequency fs of the power supply voltage e to (fo = 1/ (2πJLC)) is shown, and the vertical axis is 1/of the natural period due to the inductance L and capacitance C.
2 shows the ratio of charging voltage Vc to power supply voltage e when power supply voltage e is applied. The phase of the power supply voltage e with respect to the application period of the power supply voltage e is also the charging voltage Vc after application.
FIG. 5(b) concerns the phase in which the charging voltage Vc becomes the highest. As can be seen from FIG. 5(b), when the frequency ratio fs/fo is small (that is, when fs is always the commercial frequency, the natural frequency due to the inductance L and capacitance C is sufficiently higher than the commercial frequency), for example At 1/2 or less (that is, the natural frequency due to inductance L and capacitance C is more than twice the commercial frequency), charging voltage Vc is equal to power supply voltage e
, and there is a possibility that the rise of resonance will become large. On the other hand, when the frequency ratio fs/fo is 2 or more (that is, the natural frequency due to inductance L and capacitance C is 1/2 or less of the commercial frequency), Ve is almost zero,
Even if all other conditions are met, resonance will not rise and will attenuate.

Taking all of the above into account, and based on the basic principle of how fero-resonance occurs, resonance occurs when the natural frequency of the inductance in the PT saturation region and the total capacitance connected in parallel is higher than the commercial frequency. It has been found that there is no resonance rise when the frequency is less than 1/2 of the commercial frequency.

Therefore, as mentioned above, by setting the natural frequency due to the inductance in the saturated region of the potential transformer and the capacitance connected to the terminals to be less than 1/2 of the commercial frequency, the ferroresonance phenomenon can be generated. It can effectively prevent
Ferro-resonance phenomenon can be prevented stably over a long period of time.

(Example) Below, an example of the power system circuit according to the present invention will be described.

First, in order to lower the natural frequency due to the sum of the inductance in the PT saturation region and all capacitances connected to the PT, it is necessary to increase the capacitance or increase the inductance in the PT saturation region. be.

Among these, examples of increasing capacitance include locations with large capacitance in power system circuits,
For example, in the case of a bus bar, a configuration can be considered in which the PT is connected to a long point, or the PT is connected to a circuit to which a device with relatively large capacitance is connected.

On the other hand, as an example of increasing the inductance in the saturation region of the PT, for example, a configuration in which the diameter of the coil is increased can be easily considered.

In this case, it is not necessarily required to increase the cross-sectional area of the core.

Also, by combining the above embodiments, the capacitance and P
Of course, a configuration in which both the inductances in the saturation region of T are increased is also possible.

[Effects of the Invention] As explained above, in the present invention, the ferro-resonance phenomenon is explained based on the basic principle, and based on this principle, the inductance in the saturation region of the potential transformer and the capacitance connected to the terminal are calculated. The natural frequency is set to 1/1 of the commercial frequency.
By setting the value to 2 or less, we have provided an excellent power system circuit that can stably prevent ferroresonance over a long period of time without losing its effectiveness even with slight changes in conditions compared to conventional circuits. can.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the circuits to which the PT (potential transformer) is connected, and Figure 1 (a) is representative of all the circuits to which the PT (potential transformer) is connected. The circuit shown in FIG. 1(b) is an equivalent simplified circuit of FIG. 1(a) with respect to the fero-resonance phenomenon. Figure 2 is a waveform diagram showing the voltage and current waveforms when the fero-resonance phenomenon occurs and disappears repeatedly after the PT section is disconnected from the power supply in the circuit of Figure 1(b). A waveform diagram showing an expanded time axis of the resonance attenuation period “Y” in Figure 2,
FIG. 4 is a waveform diagram showing an expanded time axis of the resonance increase period "Z" in FIG. 2. FIG. Figure 5 is a diagram for explaining the rising conditions of fero-resonance. Figure 5 (a) is a circuit diagram in which only the power supply voltage, capacitance, and inductance in the saturation region are extracted, and Figure 5 (b) is a diagram for explaining the rising conditions of fero-resonance. , is a diagram showing capacitance charging voltage characteristics when AC voltages of various frequencies are applied during 1/2 of the natural period due to capacitance and inductance. 1...Power supply voltage, 2...Power supply impedance, 3.
... Switch, 4... Potential transformer, 5... External ground capacitance, 6... Coupling capacitance, 7... Voltage related to induction, 11... Induction voltage, 1
2...Combined capacitance, 21...Nonlinear inductance, 22...Series resistance, 23...Equivalent parallel resistance. "X"... Part related to coupling, "X1"...
・Equivalent circuit of "X" part, "Y"...resonance decay period, "Z"...resonance increase period. A (Al, A2)...terminal voltage of the voltage transformer, B
(Bl, B2)...Voltage obtained by subtracting C from A, C(
C1, C2)...Induced voltage, D (DI, D2)...
- Current flowing through the potential transformer and composite capacitance. ■~0... Voltage inversion period.

Claims (1)

[Scope of Claims] A circuit to which a potential transformer is connected, which when disconnected from a power source, includes capacitive coupling between the power source or another power source and the circuit, nonlinear inductance of the potential transformer, In a power system circuit that generates a resonant abnormal voltage with a frequency of an odd fraction of the commercial frequency due to the capacitance connected to the terminal of the voltage transformer, the inductance in the saturation region of the voltage transformer and the A power system circuit characterized in that the inductance and capacitance are set such that a natural frequency due to these inductances and capacitances is 1/2 or less of a commercial frequency.