JP2012039711A - Ground fault detector of double-fed synchronous machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a single line to ground fault in a field circuit of a double-fed synchronous machine for sure by using a simple structure.SOLUTION: A double-fed synchronous machine 1, which is constructed in such a way that AC excitation current having a frequency (slip frequency) equivalent to the difference between a system frequency and rotating speed of a rotor is supplied from an AC excitation unit 5 to a rotor coil, comprises a simulated neutral point circuit formed via a high resistor 9 branching from a field circuit which connects the rotor coil and the AC excitation unit 5, a resistance grounding circuit which grounds a neutral point 10 of the simulated neutral point circuit to earth via a resistor 11, and a ground fault detector 12 which, when a single line to ground fault occurs in the field circuit including the rotor coil and the AC excitation unit 5, detects a ground fault current flowing in the resistance grounding circuit, thereby detecting a ground fault of the field circuit.

Description

The present invention relates to a ground fault detection device for a double-feed synchronous machine in which a primary (stator) side is connected to a power system and a secondary (rotor) side is connected to a variable frequency power converter, and in particular, 1 of a field circuit. The present invention relates to a wire ground fault detection device.

The field circuit of the conventional double-fed synchronous machine is applied with a high voltage and is ungrounded. Therefore, the neutral point of the rotor of the double-fed synchronous machine is extracted when detecting a one-wire ground fault. A high resistance grounding circuit was constructed. A current monitoring circuit is provided in the ground circuit, and since a ground fault occurs due to the occurrence of a ground fault, the current value is monitored.
In addition, for example, as described in Patent Document 1, a method has been proposed in which a capacitor neutral phase of a DC potential portion between an inverter and a converter of an exciter is drawn out and a current flowing between the ground is measured.

JP-A-8-168166

  In the conventional method in which the neutral point of the rotor is pulled out and the resistance is grounded, it is necessary to install a slip ring for pulling out the neutral point, which increases the cost of the double-feed synchronous machine.

  The technique disclosed in Patent Document 1 is a method of extracting a grounded resistance circuit from a neutral phase between a converter and an inverter and detecting a ground fault. In this method, the capacitance of a generator with respect to the ground is determined. In comparison, the capacitance of the inverter and converter is absolutely small, so the generator rotor shows a stable potential with respect to the ground during normal operation with no ground fault. The ground potential of the sex phase always shows a fluctuating behavior, and the difference from the fluctuation at the time of the occurrence of the ground fault accident is difficult to clearly show, so there is a problem that it is difficult to accurately detect the ground fault accident .

The present invention was made to solve the above problems, and without drawing out the neutral point of the double-feed synchronous machine, the one-line ground fault of the AC field circuit, with a simple configuration, An object of the present invention is to obtain a ground fault detection device for a double-fed synchronous machine that can be reliably detected.

  A ground fault detection device for a double-feed synchronous machine according to the present invention has a stator winding connected to an electric power system, and a rotor winding connected to an AC exciter composed of a variable frequency power converter. In the double-feed synchronous machine configured to supply an AC excitation current having a frequency (slip frequency) corresponding to a difference from a rotation speed of the rotor to the rotor winding from the AC excitation device, the rotation A simulated neutral point circuit branched from the field circuit connecting the child winding and the power converter and grounded via the resistor and the neutral point of the simulated neutral point circuit grounded via the resistor A resistance grounding circuit, and a ground fault current flowing in the resistance grounding circuit is detected when a one-line ground fault occurs in the field circuit including the rotor winding and the power converter. It has a ground fault detector that detects the ground fault of the magnetic circuit. That.

  According to the ground fault detection device of the double-feed synchronous machine of the present invention, since the ground fault detection circuit is branched from the AC field circuit, the circuit can be configured at low cost, and the constant voltage Since the fluctuation is small, a one-line ground fault of the field circuit can be reliably detected.

  The above-described and other objects, features, and effects of the present invention will become more apparent from the detailed description and the drawings in the following embodiments.

It is a circuit block diagram which shows Embodiment 1 of this invention. It is a circuit block diagram which shows Embodiment 2 of this invention. It is a figure which shows the input-output waveform example to the 1st-order lag filter of Embodiment 2 of this invention. It is a circuit block diagram which shows Embodiment 3 of this invention. It is a block of the slip frequency component removal calculating part in Embodiment 3 of this invention. It is a figure which shows the waveform of each part of the slip frequency component removal calculating part in Embodiment 3 of this invention. It is a circuit block diagram which shows Embodiment 4 of this invention. It is a figure which shows the input-output waveform of the peak hold circuit in Embodiment 4 of this invention. It is a circuit block diagram which shows Embodiment 5 of this invention. It is a circuit block diagram which shows Embodiment 6 of this invention. It is a circuit block diagram which shows Embodiment 7 of this invention. It is a circuit block diagram which shows Embodiment 8 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol shall show the same or an equivalent part.
Embodiment 1 FIG.
FIG. 1 is an overall schematic circuit configuration diagram of a ground fault detection device for a double-feed synchronous machine according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a double-feed synchronous machine, and its stator winding The line is connected to the power system 4 through the parallel circuit breaker 2 and the main transformer 3. The AC excitation device 5 composed of a variable frequency power converter is fed from the bus between the parallel circuit breaker 2 and the main transformer 3 via the excitation transformer 6 and the excitation circuit breaker 7, and the system frequency An AC excitation current having a frequency (that is, slip frequency) corresponding to the difference in rotational speed of the rotor of the double-feed synchronous machine 1 is supplied to the rotor winding of the double-feed synchronous machine 1.

  Reference numeral 8 denotes a ground fault detection circuit which constitutes a main part of the present invention. The ground fault detection circuit is branched from an AC field circuit (hereinafter also simply referred to as a field circuit) for connecting the double-feed synchronous machine 1 and the AC excitation device 5 to the A simulated neutral point circuit is formed via a resistor 9, and the simulated neutral point 10 is grounded via a resistor 11 and a ground fault detection relay circuit 12 which is a ground fault detector. Reference numeral 13 denotes a one-wire ground fault (example) in the field circuit. A loop through which a ground fault current flows is defined as a ground fault current circuit 14.

Next, the operation will be described.
When no ground fault occurs, the voltage at the simulated neutral point 10 is 0 V, and no ground fault current flows through the ground fault detection relay circuit 12 that is a ground fault detector.
When a ground fault occurs in the field circuit, a ground fault current flows along the ground fault current circuit 14 that loops the resistor 9, the resistor 11, the ground fault detection relay circuit 12, and the ground fault point 13. By recognizing the ground fault current by the ground fault detection relay circuit 12, a one-line ground fault of the AC field circuit including the rotor winding and the variable frequency power converter is detected.

  As described above, according to the ground fault detection device for a double-feed synchronous machine according to Embodiment 1 of the present invention, the stator winding is connected to the power system 4, and the rotor winding is a variable frequency power converter. An AC excitation current having a frequency (slip frequency) corresponding to the difference between the system frequency and the rotational speed of the rotor is a double-feed synchronous machine 1 connected to an AC excitation device 5 comprising: In the dual-feed synchronous machine configured to be supplied to the rotor winding from the field circuit connecting the rotor winding and the power converter, the simulation is formed via the resistor 9 A neutral point circuit, a resistance grounding circuit for grounding the neutral point 10 of the simulated neutral point circuit via a resistor 11, and a field including the rotor winding and the power converter provided in the resistance grounding circuit When a one-wire ground fault occurs in the magnetic circuit, the ground fault current flowing in this resistance ground circuit is detected. In addition, since the ground fault detector 12 for detecting the ground fault of the field circuit is provided, it is not necessary to draw out the neutral point of the rotor winding of the double-feed synchronous machine 1, and an inexpensive ground fault detection device is provided. Can be configured. In addition, since there is little voltage fluctuation at all times, it is possible to obtain a highly reliable ground fault detection device for a double-fed synchronous machine that reliably detects a ground fault current that flows when a ground fault occurs.

Embodiment 2. FIG.
A second embodiment of the present invention will be described with reference to FIGS.
The ground fault detection device for a double-feed synchronous machine according to Embodiment 2 of the present invention shows an example of a specific configuration of a ground fault detector. In FIG. 2, a ground fault detection relay that is a ground fault detector. The circuit 12 has a circuit configuration in which a voltage signal is extracted from both ends of the resistor 15 and the voltage signal is input to the ground fault determination unit 17 through the first-order lag filter 16. In addition, in order to force a current to flow through the resistance grounding circuit when a ground fault occurs, a DC power supply is configured by a rectifier circuit 20 from an external AC power supply 18 via a transformer 19.
FIG. 3 shows an example of an input signal waveform to the first-order lag filter 16 and an example of an output signal waveform.

Next, the operation of the second embodiment will be described.
When a ground fault occurs in the field circuit, a DC ground fault current corresponding to the ground fault resistance is caused to flow by applying a DC voltage generated by the rectifier circuit 20 to the resistance ground circuit.
However, the excitation current that the AC excitation device 5 flows is a low-frequency current of several Hz due to the slip frequency, and the ground-fault current that flows through the ground-fault detection relay circuit 12 when a ground fault occurs also includes a slip-frequency component. For this reason, the ground fault signal taken out from both ends of the resistor 15 is a signal in which the slip frequency component is superimposed on the direct current as shown in FIG.
The ground fault determination unit 17 is provided with a filter 16 in order to determine the level of the ground fault current including the slip frequency component. This filter 16 has a first-order lag function, and as shown in FIG. 3, it can remove the slip frequency component and extract only the DC ground fault current component due to the DC voltage application. The output of the first-order lag filter 16 is input to the ground fault determination unit 17, and the ground fault determination unit 17 determines the level to detect a one-line ground fault.

As described above, according to the second embodiment of the present invention, the ground fault detector 12 includes the external AC power source 18 and the rectifier 20 for supplying the DC component superimposed on the ground fault current to the resistance ground circuit. A DC power supply unit, a first-order lag filter 16 for removing a slip frequency component included in the ground-fault current, and a ground-fault determination unit 17 that determines an output level of the first-order lag filter 16 and detects a ground fault. Therefore, it is possible to remove the slip frequency component contained in the ground fault current, which is a feature of the double-fed synchronous machine, and to obtain a circuit for reliably determining the ground fault by simply applying an inexpensive circuit called a first-order lag. Can do.
Further, since a ground fault current is forcibly applied by applying a DC power source, the presence or absence of a ground fault can be confirmed by applying the DC power source even when the double-feed synchronous machine is stopped.

Embodiment 3 FIG.
A third embodiment of the present invention will be described with reference to FIGS. 4, 5, and 6. FIG.
In the second embodiment, the first-order lag filter 16 is used to remove the slip frequency component in the ground fault detector 12. However, in the third embodiment, as shown in FIGS. 4 and 5, the ground fault detection is performed. In this device, a slip frequency component removal calculating unit 21 is provided in place of the first-order lag filter to obtain the same effect.

FIG. 5 shows a calculation block of the slip frequency component removal calculation unit 21.
As shown in FIG. 5, the slip frequency component removal calculation unit 21 includes a differentiation circuit 23 to which a ground fault voltage signal 22 converted from a ground fault current by a resistor 15 is input, and an output (that is, a calculation result) of the differentiation circuit 23. ) And the ground fault voltage signal 22 is input, and the subtractor 24 subtracts the calculation result of the differentiation circuit 23 from the ground fault voltage signal 22 and outputs it as the ground fault determination signal 25. Has been.
The ground fault determination unit 17 performs ground fault determination using the ground fault determination signal 25 from the slip frequency component removal calculation unit 21.
FIG. 6 shows an example of the input and output signal waveforms of the slip frequency component removal calculating unit 21 and an output waveform example of the differentiating circuit 23.

  According to the third embodiment of the present invention configured as described above, when the ground fault voltage signal 22 passes through the differentiating circuit 23, the slip frequency component included in the ground fault voltage component is converted to the fluctuation amount of the ground fault voltage signal 22. Output as. By subtracting this from the ground fault voltage signal 22 by the subtractor 24, the slip frequency component can be removed. As a result, the ground fault determination signal 25 has only a DC component, and the ground fault determination unit 17 can recognize the occurrence of the ground fault.

  In the third embodiment, since the differential circuit is used to remove the slip frequency component, the circuit is slightly more complicated than the first-order lag filter of the second embodiment. Therefore, it is an effective means when no time delay is given to the ground fault determination.

Embodiment 4 FIG.
Embodiment 4 of the present invention will be described with reference to FIGS.
The fourth embodiment of the present invention eliminates the slip frequency component included in the ground fault current in the ground fault detector, so that the first-order lag filter 16 and the slip frequency component removal calculating unit 21 in the second and third embodiments described above. Instead, a peak hold circuit 26 is provided.
Other configurations are the same as those in the second and third embodiments, and a description thereof will be omitted.
FIG. 8 shows an input signal and an output signal to the peak hold circuit 26.

Next, the operation of the fourth embodiment will be described.
In order to hold the peak value of the slip frequency component, the peak hold circuit 26 sends the peak value of the slip frequency to the ground fault determination unit 17 as a DC signal.
In the fourth embodiment, since the peak hold circuit 26 is used, the ground fault is determined by a large signal as compared with the signal after the removal of the slip frequency component according to the second and third embodiments. It operates with a ground fault resistance higher than the actual ground fault. For the purpose of protecting the double-feed synchronous machine, detection is possible at an early stage, which is effective when the circuit is applied for the purpose of preventing a ground fault. Further, the peak hold circuit has an advantage that the time delay is smaller than that of the first-order lag filter 16 of the second embodiment.

Embodiment 5 FIG.
Embodiment 5 of the present invention will be described with reference to FIG.
FIG. 9 shows the ground fault detection circuit 8 of FIG. 1 taken out. The invention of the fifth embodiment deals with a case where the disconnection 28 occurs in any of the ground fault detection circuit units. An arrester 27 is connected in parallel with the ground fault detector 12 between the resistor 11 of the ground circuit and the ground fault detection relay circuit 12 which is a ground fault detector.

Next, the operation of the fifth embodiment will be described.
When the disconnection 28 occurs while the ground fault 13 is generated, or when the ground fault 13 occurs when the disconnection 28 is generated, the ground circuit voltage of the ground fault detection relay circuit 12 is several kV. Therefore, the voltage similarly rises to several kV. Therefore, it is necessary to use a high voltage specification so that the equipment connected to the ground fault detection relay circuit 12 is not broken. However, if all the devices have high voltage specifications, the cost increases. Therefore, by installing the arrester 27, the voltage applied to the ground fault detection relay circuit 12 is suppressed and the breakdown voltage specification level of the devices is lowered.
In addition, since the arrester 27 is installed, even if a disconnection occurs, a low-cost device with a reduced withstand voltage specification can be applied to the ground fault detection relay circuit 12.

Embodiment 6 FIG.
A sixth embodiment of the present invention will be described with reference to FIG.
The sixth embodiment of the present invention is a modification of the fifth embodiment, and is provided with an overvoltage detection function and a contactor in place of the arrester 27 in the fifth embodiment.
In FIG. 10, an overvoltage detector 29 for detecting an overvoltage applied to the ground fault detection relay circuit 12 is connected between the resistor 11 of the resistance ground circuit and the ground fault detection relay circuit 12 which is a ground fault detector. 30 is connected between the resistor 11 and the branch to the overvoltage detector 29.

Next, the operation of the sixth embodiment will be described.
In the fifth embodiment, the overvoltage is suppressed by the arrester 27. However, in this sixth embodiment, when the overvoltage is detected by the overvoltage detector 29, the contactor 30 is opened to open the ground fault as a ground fault detector. Since the detection relay circuit 12 can be disconnected from the resistance grounding circuit and an overvoltage can be prevented from being applied to the ground fault detection relay circuit 12, the device can be prevented from being broken by the overvoltage.
When the arrester of the fifth embodiment is applied, the voltage suppression effect is high, but it may be difficult to obtain necessary characteristics. In this case, the circuit using the overvoltage detector 29 and the contactor 30 is effective.

Embodiment 7. FIG.
A seventh embodiment of the present invention will be described with reference to FIG.
In the seventh embodiment of the present invention, as shown in FIG. 11, a ground fault detection relay circuit 31 having the same circuit and function is connected in parallel with the ground fault detection relay circuit 12.

  In the seventh embodiment configured as described above, when a disconnection and a ground fault occur at the same time as in the fifth and sixth embodiments, in order to prevent a high voltage from being applied to the ground fault detection relay circuit 12, When the ground fault detection relay circuit 31 is connected and a ground fault occurs, the operation signals of the ground fault detection relay circuits 12 and 31 are operated by the OR circuit.

  Note that the method of providing the ground fault detection relay circuits 12 and 31 utilizes the fact that disconnection rarely occurs in two circuits at the same time, and combines the cost and reliability with the fifth and sixth embodiments. Judgment is made and the best method is selected.

Embodiment 8 FIG.
An eighth embodiment of the present invention will be described with reference to FIG.
In the eighth embodiment of the present invention, as shown in FIG. 12, the ground fault detector 12 is included in the output of the rectifier 32 that rectifies the ground fault voltage signal extracted from both ends of the resistor 15 and the rectifier circuit 32. Ripple removal, for example, a ripple removal circuit 33 composed of a CR circuit or the like using a resistor R and a capacitor C, and a DC signal converted into a direct current by this ripple removal circuit are input to detect and detect a one-wire ground fault A ground fault determination unit 17 is provided.

Next, the operation of the eighth embodiment will be described.
The ground fault current flowing through the resistor 15 is an AC signal having a slip frequency. In order to determine the ground fault, the ground fault voltage signal taken out from both ends of the resistor 15 is rectified through the rectifier circuit 32.
In order to remove the ripple included in the rectified signal, a DC signal is passed to the ground fault determination unit 17 via a ripple removal circuit 33 configured by a CR circuit using a resistor R and a capacitor C.

  According to the ground fault detection device of the eighth embodiment, since the rectifier circuit 32 is applied to the voltage signal drawn from both ends of the resistor 15, the transformer 19 applied in the second, third, and fourth embodiments is not necessary. However, since the DC power supply is not forcibly applied, monitoring is performed only during operation.

1 double-feed synchronous machine, 4 power system, 5 AC exciter, 8 ground fault detection circuit,
9, 11 resistance, 10 simulated neutral point, 12 ground fault detector (ground fault detection relay circuit),
13 ground fault point, 14 ground fault current circuit, 15 resistance, 16 first order lag filter,
17 ground fault determination unit, 18 AC power supply, 19 transformer, 20, 32 rectifier circuit,
21 slip frequency component elimination operation unit, 22 ground fault voltage signal, 23 differentiation circuit,
24 subtractor, 25 ground fault determination signal, 26 peak hold circuit,
27 Arrester, 28 Disconnection, 29 Overvoltage detector, 30 Contactor,
31 Ground fault detector (ground fault detection relay circuit), 33 Ripple elimination circuit

Claims (8)

The stator winding is connected to the power system, the rotor winding is connected to an AC exciter consisting of a variable frequency power converter, and the frequency (slip frequency) corresponding to the difference between the system frequency and the rotational speed of the rotor. In a double-feed synchronous machine configured to supply an AC excitation current having a current to the rotor winding from the AC excitation device,
A simulated neutral point circuit branched from a field circuit connecting the rotor winding and the power converter and formed via a resistor, and a neutral point of the simulated neutral point circuit via a resistor When a one-wire ground fault occurs in the field circuit including the rotor winding and the power converter, the ground fault current flowing in the resistance ground circuit is detected. A ground fault detection device for a double-feed synchronous machine comprising a ground fault detector for detecting a ground fault in the field circuit.   The ground fault detector includes a DC power supply unit including a rectifier for supplying a DC component superimposed on a ground fault current to the resistance grounding circuit, and a primary delay for removing a slip frequency component included in the ground fault current. 2. The ground fault detection device for a double-feed synchronous machine according to claim 1, further comprising a filter and a ground fault determination unit that determines an output level of the first-order lag filter and detects a one-line ground fault.   The ground fault detector includes a DC power supply unit including a rectifier for supplying a DC component superimposed on a ground fault current to the resistance ground circuit, and a slip frequency for removing a slip frequency component included in the ground fault current. A component removal calculation unit, and a ground fault determination unit that detects an output level of the slip frequency component removal calculation unit and detects a one-wire ground fault, and the slip frequency component removal calculation unit converts the ground fault current into a voltage signal. A differential circuit that calculates the slip frequency component by inputting the converted ground fault voltage signal, and outputs only the DC component of the ground fault voltage signal by subtracting the calculation result of the differential circuit from the ground fault voltage signal before differentiation. The ground fault detection apparatus for a double-fed synchronous machine according to claim 1, further comprising a subtractor that performs the operation.   The ground fault detector has a DC power source composed of a rectifier for supplying a DC component superimposed on a ground fault current to the resistance grounding circuit, and holds a peak value of a slip frequency component included in the ground fault current. The double-feed synchronous machine according to claim 1, further comprising: a peak hold circuit that outputs a signal; and a ground fault determination unit that determines a peak value of the peak hold circuit and detects a one-wire ground fault. Ground fault detection device.   5. The ground fault detection device for a double-feed synchronous machine according to claim 1, wherein an arrester is provided in parallel with the ground fault detector of the resistance grounding circuit.   An overvoltage detector for detecting an overvoltage applied to the ground fault detector between a resistance of the resistance ground circuit and the ground fault detector, and when the overvoltage detector detects an overvoltage, the circuit is opened to detect the ground fault. The ground fault detection device for a double-feed synchronous machine according to any one of claims 1 to 4, further comprising a contactor for separating the device from the resistance ground circuit.   5. The ground fault detection device for a double-feed synchronous machine according to claim 1, wherein voltage rise due to disconnection is prevented by duplexing the ground fault detection circuit.   The ground fault detector includes a rectifier circuit that rectifies a ground fault voltage signal obtained by converting a ground fault current into a voltage signal, a ripple elimination circuit that removes a ripple included in the output of the rectifier circuit, and a ripple elimination circuit. The ground fault detection apparatus of the double feeding synchronous machine of Claim 1 provided with the ground fault determination part which determines the level of the direct current signal of this and detects a 1 line ground fault.

Images