JPH11215713A - System fault current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a fault with accuracy at high speed, in systems linked through a high-speed current-limiting interrupt device formed by connecting a direct-current reactor for current limitation between the direct-current terminals of a single-phase rectifying bridge circuit. SOLUTION: When this system fault current detector 21 is in a normal state, a direct current at almost a constant level is passed through its direct-current reactor L. At fault occurrence, an overcurrent is passed transiently through the direct-current reactor L, and an overcurrent is detected through a search coil 22. Filtering is performed via a detecting circuit 23, and full-wave rectification and peak detection is performed through a full-wave rectifying circuit 26 via an amplifier 25. The detected peak value is compared with a specified settling value through a comparator 29 to determine the fault. Consequently, this device requires only several milliseconds for fault detection and contributes to increase in fault detection speed, whereas ordinary methods using current transformer(CT) or potential transformer(PT) requires at least one cycle. Since fourth harmonic waves are removed by the detecting circuit 23, malfunctions due to the introduction of a static capacitor can be prevented with this method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply system having one or a plurality of power generating devices and a large number of loads, such as a commercial power supply system and a private power generation system, or a power supply system and a load system. It is preferably applied to a system in which the two systems are interconnected by a high-speed current-limiting circuit breaker configured with a single-phase rectifier bridge circuit and a DC reactor for each phase, The present invention relates to a device for quickly detecting a system failure in order to make a high-speed current limiting circuit device function effectively.

[0002]

2. Description of the Related Art When performing interconnection operation between the two systems, a circuit breaker such as a mechanical circuit breaker or a thyristor circuit breaker is conventionally installed at an interconnection point, and a CT (current transformer) is used. From the detected interconnection current, an overcurrent relay
The circuit breaker is configured to be opened when an increase in the interconnection current exceeding a predetermined amount due to a failure is detected. In addition, the voltage of the private power generation system is detected by PT (voltage transformer),
When the detection result is equal to or less than a predetermined value, the undervoltage relay may detect a failure and open the circuit breaker.

However, in the undervoltage relay for detecting a drop in AC voltage, for example, theoretically, a half cycle is required for failure detection.
It takes 0 msec, and therefore, it is difficult for the overcurrent relay and the undervoltage relay to detect a failure within about several msec required by the high-speed current limiting interrupter to which the present invention is applied.

On the other hand, an instantaneous value type overcurrent relay is mentioned as a relay which can detect a failure more quickly than the overcurrent relay or the undervoltage relay.

[0005]

However, the conventional relay does not consider the current limiting effect, and the current limiting effect reduces the difference between the fault current and the rated current so that fault detection becomes impossible. It may be.

For example, in a private power generation system, the short-circuit current does not fall below five times the rated current. Therefore, empirically, the fault detection level is set to about 1.5 times the rated energizing current in consideration of the margin for preventing malfunction.

On the other hand, the fault current is limited to, for example, １ ／ by the current limiting function. Further, in order to take measures against an instantaneous voltage drop, it is necessary to detect, for example, a voltage drop of 50% of the rated voltage. Therefore, the fault detection must be performed based on the fault current of 1/4 level. For this reason, in order to prevent the current limiting function and the instantaneous voltage drop, in the high-speed current limiting interrupter, it is necessary to set the failure detection level to about 5/4 = 1.25 times the rated energizing current. is there.

Here, if a failure is not determined up to one time of the rated energizing current, and it is determined that a failure has occurred at a time exceeding one time, as shown in FIG. The time t until the current having the amplitude of 1.25 times the rated current exceeds the determination threshold is 50 Hz, and t = sin ⁻¹ (1 / 1.25) × １．２1000 / (50 × 2 × π) )｝ = 2.95 (msec). At 60 Hz, it is 2.46 msec.

Therefore, the detection time is an ideal detection time (2 m) which can protect the generator of the private power generation system.
sec), there is a problem that, depending on the failure occurrence timing, the cutoff of the first phase may not be in time for the cutoff of the first phase, and the cutoff of the first phase may be in the next cycle.

[0010] In the case of the detection by the CT,
There is an output corresponding to the rated current, and when this differential value is used, the rise is quicker, but at the same time, the noise also increases, so that there is a problem that the S / N at the time of occurrence of a fault becomes worse.

An object of the present invention is to provide a system fault current detecting device capable of detecting a system fault quickly and accurately.

[0012]

According to a first aspect of the present invention, there is provided a system fault current detecting apparatus in which a current limiting DC reactor is connected between DC terminals of a single-phase rectifying bridge circuit for each phase. A system fault current detection device applied to a system in which a high-speed current limiter is used for interconnection between systems, and a detection unit that detects a terminal voltage of the DC reactor, and a detection result of the detection unit. And a determining means for determining that a failure has occurred in the system when is greater than or equal to a predetermined value.

According to the above configuration, a DC current flows through the DC reactor. Therefore, since ω = 0, the terminal voltage of the DC reactor is 0 (V _DCL = L (di)
_DCL / dt) ≒ 0). When a fault occurs and the AC current i _{fault has} a peak value equal to or greater than the DC current i _DCL that has been flowing in the DC reactor, the charging current of the DC reactor having a transient change flows into the DC reactor, and the DC current A voltage proportional to the differential value of the current is generated between the terminals of the reactor (V _DCL = L (di
_fault / dt)).

As shown in FIG. 3, this terminal-to-terminal voltage shows a very steep rise as soon as i _fault > i _DCL . When i _fault ≤i _DCL , almost no voltage is generated. That is, it is not only very effective in detecting in a short time, but also has a feature that a failure can be detected with high sensitivity, and the detecting means detects this inter-terminal voltage,
When the set value is equal to or more than a predetermined set value, the judging means judges a system failure, and cuts off a thyristor constituting the single-phase rectification bridge circuit or a circuit breaker interposed between the single-phase rectification bridge circuit and the system. I do.

Therefore, the fault current can be detected quickly and accurately, and when a thyristor is used in at least one arm of the single-phase rectifier bridge circuit, the first phase can be cut off quickly. , All phases can be disconnected within one cycle. As a result, the function of suppressing the instantaneous voltage drop by the high-speed current limiter can be effectively used.

Further, in the system fault current detecting apparatus according to the present invention, the detecting means is a search coil for detecting a magnetic field of the DC reactor.

According to the above configuration, an expensive DC voltage transformer (DCPT) is usually used to detect the voltage between terminals of the DC reactor, whereas the DC reactor usually used is an air core. By utilizing a coil, a search coil having relatively good sensitivity is inserted at the center of the air-core coil, and a voltage proportional to the terminal voltage of the DC reactor is detected from the output terminal voltage. .

Therefore, it is economical, and the insulation of the air-core coil having the system potential from the search coil having the substantially ground potential can be easily secured.

Further, the system fault current detecting device according to the third aspect of the present invention is further provided with a primary delay circuit for extracting only a system frequency component from an output of the search coil.

According to the above configuration, since the primary delay circuit extracts only the system frequency component from the output of the search coil, the primary delay circuit is caused by the rush current generated by the input of the static capacitor used for the phase adjustment or the like. Overvoltage near the fourth harmonic can be suppressed, and only a system failure can be accurately detected.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
The following is a description based on FIGS. 1 to 7.

First, an example of a high-speed current limiting circuit to which the present invention is applied will be described with reference to FIG. The high-speed current limiting device 1 shown in FIG. 6 has been proposed by the present applicant in Japanese Patent Application Laid-Open No. 9-285012. This high-speed current limiting device 1 is provided with a single-phase rectifier bridge circuit and a DC reactor, is installed at a connection point between two systems, and quickly disconnects and suppresses a voltage drop due to a failure. To achieve.

In the commercial power supply system, the commercial power supply line 2 drawn into the customer is connected to the power receiving bus 4 via the circuit breaker 3. Many power distribution lines 5 connected to a general load are connected to the power receiving bus 4. In the private power generation system, a private power generation device 7 is connected to the private power generating bus 6 via a circuit breaker 8, and the private power generation capacity is 60 to 70, for example.
The distribution line 9 to the important load which occupies% is connected. The power receiving bus 4 and the self-generated bus 6 are connected to each other by the high-speed current-limiting circuit device 1.

The high-speed current limiting device 1 is interposed in a bus connecting line 10 connecting the buses 4 and 6, and is composed of a pair of thyristors TH1 and TH2, which are rectifying switching elements, and a pair of diodes D1 and D2. Rectifier bridge circuit, a DC reactor L, and a circuit breaker 11. One of the pair of AC terminals AC1 and AC2 connected to the bus connecting line 10 is connected to the pair of thyristors TH1 and TH2, and the other is connected to a pair of diodes D1 and D2 (FIG. 6
In the example, the thyristors TH1, TH2 are connected to the AC terminal AC1.
Are connected, and diodes D1 and D2 are connected to AC terminal AC2). On the other hand, DC terminals DC1, DC1
A DC reactor L is connected between C2.

The single-phase rectifier bridge circuit may be composed entirely of diodes, or may be composed entirely of thyristors. If the thyristor is provided on at least one arm (either one of the AC terminals AC1 and AC2), the circuit breaker 11 may be omitted.

The high-speed current-limiting device 1 constructed as described above
In the steady state, the gates of the thyristors TH1 and TH2 are driven, the thyristors TH1 and TH2 are turned on, and a current flows through a path indicated by reference numeral i1 or i2. Therefore, by selecting the current decay time constant of the DC reactor L to be at least 2.5 times the system frequency cycle, the current i _DCL flowing through the DC reactor L becomes a DC current having a substantially constant level, and the terminal of the DC reactor L The inter-voltage is 0 (V _DCL = L (di _DCL / dt) ≒ 0).

On the other hand, for example, it is assumed that the above-described failure occurs in the power receiving bus 4 as indicated by reference numeral 12 and an overcurrent i _fault flows from the self-generated bus 6 to the power receiving bus 4. Then, as soon as the peak value of the overcurrent i _fault exceeds the level of the DC current i _DCL that has been flowing through the DC reactor L, the DC current L is supplied to the DC reactor L by an AC current that attempts to charge the DC reactor L. Flows, and a voltage proportional to the differential value of the overcurrent i _fault is generated between the terminals of the DC reactor L (V _DCL = L (di _fault
/ Dt)).

Therefore, between the AC terminals AC1 and AC2,
A voltage equal to the terminal voltage V _DCL of the DC reactor L is generated. That is, an apparent impedance appears between the AC terminals AC1 and AC2, and a current-limiting action for suppressing a current flowing from the self-generated bus 6 to the power receiving bus 4 via the bus connecting line 10 is realized. be able to. While the current limiting operation is being performed, the gates of the thyristors TH1 and TH2 are blocked by the output from the AND gate 30 of the system fault current detection device 21 described later, the circuit breaker 11 is opened, and the self-generated bus 6 At a high speed and reliably from the power receiving bus 4 to suppress an instantaneous voltage drop due to an overload of the private power generator 7.

FIG. 1 is a block diagram showing an electrical configuration of a system fault current detecting device 21 according to one embodiment of the present invention. A search coil 22 is arranged in the DC reactor L composed of an air-core coil as shown in FIG. 2, and a voltage is applied to the search coil 22 by a magnetic field variation due to a variation in current flowing through the air-core coil. In the event of a system failure, the induced voltage is, for example, as shown in FIG.
It becomes as shown by. The voltage induced in the search coil 22 is input to an amplifier 25 via a detection circuit 23 and a Zener diode 24 for preventing overvoltage. The detection circuit 23 includes resistors R1 and R2 and a capacitor C.
The following delay circuit is used to select a constant as described below to convert a 50 Hz or 60 Hz system fundamental wave into
It has a function of separating from a frequency component near the fourth harmonic which is dominant to a transient phenomenon which occurs when a static capacitor described later is turned on.

The output of the amplifier 25 is supplied to the full-wave rectifier circuit 2
At 6, the peak value of the pulsation of the system frequency component is detected and output to the adder 27. The adder 27
After a predetermined bias voltage from the bias power supply 28 is added to the peak value, the result is output to the comparator 29. The comparator 29 performs level discrimination of the output voltage of the adder 27 with a predetermined threshold voltage, and when the output voltage is equal to or higher than the threshold voltage,
A high-level failure determination output is output to one input of the AND gate 30. The other input of the AND gate 30 includes:
During normal operation, a high-level output is input from the detecting means 31 such as a relay.

Accordingly, when an output indicating a system failure is input from the comparator 29 in the normal operation state from the AND gate 30, an output for reporting the failure is derived, and the outputs of the thyristors TH1 and TH2 are output. Gate is blocked.

In the system fault current detecting device 21 configured as described above, the DC reactor L
As shown by the outer diameter a1 = 500 (mm) and the inner diameter a2 =
270 (mm), the axial length b = 375 (mm), the rated current of the DC reactor is 300 (A) DC, the center magnetic field of the coil is 0.15 (T), and As shown in FIG. 3, assuming that the changing current of the DC reactor L due to the fault is about 8000 (Apeak), first, the changing magnetic field amplitude ΔB generated by the changing current is ΔB = 0.15 × (8000/2) / 300 = 2 (T) (1)

The voltage Vs induced in the search coil 22 by the fluctuating magnetic field is as follows: When the magnetic flux is φ, the number of turns of the search coil 22 is n, and the system frequency is f, Vs = n (δφ / δt) = 2πf · nφ = 2πf · n · SΔB = 2π × 50 × 2 × nS = 628.32 × nS (2) Here, S is the area of the search coil 22 (m ² )
It is. Also, the approximation is made at f = 50 (Hz).

On the other hand, the signal level to the subsequent circuit is
Vs = 100 (Vpeak) is sufficient,
Assuming that the diameter of the search coil 22 is, for example, 50 (mm), S = (π / 4 × 0.05 ² ) = 0.001963 (m ² ) (3), and the number of turns n is n = 100 / ( 628.32 × 0.001963) = 81 (turns) (4)

Such a search coil can be realized by, for example, about １ ／ of the inner diameter of 270 mm of the DC reactor L. As shown in FIG. Even if the coil 22 is arranged, there is no need to particularly insulate the search coil 22 having a substantially ground potential with respect to the DC reactor L having a system potential.
The change in the system fault current can be detected with an inexpensive configuration.

The search coil 22 is not limited to the center of the DC reactor L as long as the current flowing through the DC reactor L can be detected with good sensitivity. Good.

The search coil 22 configured as described above
, The inductance of the DC reactor L is 10 m
With respect to H, the mutual inductance is about 0.317 mH.

In accordance with this, the resistance values of the resistors R1 and R2 in the detection circuit 23 are selected to be about 2.5 kΩ, and the charging capacity of the capacitor C is selected to be about 1 μF. Here, the equivalent circuit of the resistors R1 and R2 and the capacitor C can be represented by a coefficient unit and a primary delay circuit as shown in FIG. 5, and the delay time (= C · R1 · R2 / (R1 + R2)) is 1.25 ms
ec, for example, when the system frequency is 50 (Hz), the 4.1 harmonic (= {R2 / (R1 + R2)})
・ ｛1 / [1 + S ・ C ・ R1 ・ R2 / R1 + R
2)]｝) attenuates to 19%. In this way, the detection circuit 23 is configured to pass a component of the system frequency of about 50 Hz or 60 Hz, and particularly to greatly attenuate the vicinity of the fourth harmonic.

On the other hand, in order to suppress an overcurrent at the time of turning on the power, a static capacitor (= 1 / ωC) of 6 is added to the static capacitor which is put into the power system for phase adjustment.
% Of the series inductance is connected, and the 4.1th-order (= (100/6) ^1/2 ) harmonic is generated by turning on the static capacitor. This harmonic component is removed by the coefficient unit and the first-order delay circuit as described above.

FIG. 7 shows the gate-off time, the cut-off completion time, and the gate-off time in a configuration in which a thyristor is used in at least one arm of a single-phase rectifier circuit, such as the high-speed current limiting circuit device 1 shown in FIG. Shows the relationship. The example of FIG. 7 is an example in which the power factor is 1 and the failure occurrence phase is 0 ° in a three-phase short-circuit failure in which the time required to shut off all phases is the longest. In FIG. 7, for example, in the B phase, if the gate is turned off by 8.5 msec after the occurrence of the failure, the shutoff can be completed by 13.3 msec after the failure time, and in the C phase, it can be completed up to 5.7 msec. , The shutoff can be completed by 10.5 msec.

On the other hand, regarding the phase A, if the gate is turned off by 2.9 msec after the occurrence of the failure, the shutoff can be completed by 16.2 msec after the occurrence of the failure. ,
The time at which the shutoff can be completed next is the time when 23 msec has elapsed from the occurrence of a failure in the next cycle. Therefore, in order to complete the shutoff of the thyristors of all phases within one cycle from the occurrence of the failure, the time until the shutoff of the thyristor of the first phase is 2.9 msec.
It must be set within c.

Therefore, in the fault detection configuration using CT and PT as described in the section of the prior art, it is difficult to detect a fault within a required time, and the instantaneous voltage drop caused by the high-speed current limiter 1 is reduced. While the suppression function cannot be used effectively, there is a possibility that the voltage drop such that the important load cannot operate on the self-generated bus 6 side may be caused. In the detection device 21,
Failure detection can be performed at a high speed within 2.9 msec. In this way, the high-speed cutoff function of the high-speed current limiting cutoff device 1 can be effectively exerted, and the faulty system can be quickly disconnected.

In the configuration of the fault detection using CT,
In the steady state, an output corresponding to the steady-state rated current is derived, whereas in the system fault current detection device 21 of the present invention, the output in the steady state is 0, and high detection sensitivity can be obtained. In this regard, if the differential value of the CT output is used,
Although the rising of the detection waveform becomes steep and the detection sensitivity can be increased, the noise also increases and the S / N deteriorates. On the other hand, in the system fault current detection device 21 of the present invention, such a problem is caused. There is no problem, and no malfunction is caused when the static capacitor is normally turned on. Only a system failure can be accurately detected, and the reliability can be greatly improved.

Further, an expensive DC voltage transformer (DCPT) is usually used to detect the voltage between the terminals of the DC reactor L. On the other hand, in the system fault current detecting device 21 of the present invention, Utilizing that a normally used DC reactor is an air-core coil, a search coil 22 having relatively good sensitivity is inserted at the center of the air-core coil. Since the voltage between the terminals of the reactor is detected, it is economical, and the insulation of the air-core coil having the system potential from the search coil 22 having substantially the ground potential can be easily secured.

It should be noted that the breaking of the circuit breaker 11 requires about two to three cycles as described above. If the single-phase rectifying bridge circuit is composed of only diodes, the circuit breaker 11 must be closed until the circuit breaker 11 is broken. Although the system cannot be disconnected between the systems, fault detection can be performed at high speed, and the present invention can be effectively used in such a configuration. In addition, the present invention is not limited to the high-speed current limiting circuit breaker 1 configured by connecting the current limiting DC reactor L between the DC terminals of the above-described single-phase rectification bridge circuit, but includes the DC reactor L. It can also be applied to the detection of a failure in a power circuit having another configuration.

[0046]

As described above, the system fault current detecting device according to the first aspect of the present invention is configured by connecting a current limiting DC reactor between DC terminals of a single-phase rectifying bridge circuit for each phase. In detecting a fault current in a system that is connected with a high-speed current-limiting circuit device, a DC current flows between terminals of the DC reactor, and a voltage between the terminals of the DC reactor is substantially zero. When a failure occurs, the current flowing through the DC reactor has a frequency component, and a system failure is determined by utilizing the rapid increase in the inter-terminal voltage.

Therefore, the fault current can be detected at high speed and accurately, and when a thyristor is used in at least one arm of the single-phase rectifier bridge circuit, the first current can be quickly detected.
Phases can be cut off, and disconnection can be made within one cycle of all phases.

Further, in the system fault current detecting apparatus according to the second aspect of the present invention, as described above, the detecting means is a search coil for detecting the magnetic field of the DC reactor.

Therefore, the search coil having relatively good sensitivity can be arranged at the center of the air-core coil used for the DC reactor, and the earth potential of the system-potential air-core coil is almost equal to the ground potential. Can be easily secured with the search coil.

Further, the system fault current detecting device according to the third aspect of the present invention further includes a primary delay circuit for extracting only a system frequency component from the output of the search coil as described above.

Therefore, it is possible to suppress an overvoltage in the vicinity of the fourth harmonic generated by turning on a static capacitor used for phase adjustment or the like, and it is possible to accurately detect only a system failure.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of a system fault current detection device according to an embodiment of the present invention.

FIG. 2 is a simplified perspective view for explaining an installation state of a search coil in a DC reactor in the system fault current detection device shown in FIG.

FIG. 3 is a graph showing a voltage between terminals of a DC reactor when a system failure occurs.

FIG. 4 is a simplified axial cross-sectional view for explaining a configuration of a DC reactor.

FIG. 5 is an equivalent circuit diagram of a detection circuit in the system fault current detection device shown in FIG.

FIG. 6 is a single-phase connection diagram for explaining a high-speed current limiting circuit breaker to which the present invention is applied.

FIG. 7 is a graph showing a relationship between a gate-off time from the occurrence of a failure and a cut-off completion time in the high-speed current limiting cut-off device shown in FIG. 6;

FIG. 8 is a graph for explaining a failure detection time by a conventional relay when a high-speed current-limiting device is used for interconnection between systems.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High-speed current limiting circuit breaker 2 Commercial power line 3, 8, 11 Circuit breaker 4 Power receiving bus 5, 9 Distribution line 6 Self-generated bus 7 Private power generator 10 Bus connecting line 21 System fault current detector 22 Search coil (detection means) Reference Signs List 23 detection circuit (primary delay circuit) 24 Zener diode 26 full-wave rectifier circuit 29 comparator AC1, AC2 AC terminal D1, D2 diode DC1, DC2 DC terminal L DC reactor TH1, TH2 thyristor

Claims (3)

[Claims] 1. A system in which a high-speed current-limiting device configured by connecting a current-limiting DC reactor between DC terminals of a single-phase rectifying bridge circuit for each phase is used for interconnection between the systems. A system fault current detection device to be applied, wherein a detection unit for detecting a voltage between terminals of the DC reactor, and a fault has occurred in a system when a detection result of the detection unit is equal to or greater than a predetermined value. And a judging means for judging. 2. The system fault current detecting device according to claim 1, wherein said detecting means is a search coil for detecting a magnetic field of said DC reactor. 3. The system fault current detecting device according to claim 1, further comprising a primary delay circuit for extracting only a system frequency component from an output of said detecting means.