JP2009195062A - Protection device for ac coil and power system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC coil protection device which can accurately detect abnormal voltage caused by the deterioration of the AC coil connected to a power system and can prevent damages to the AC coil, and to provide a power system equipped with the same. <P>SOLUTION: The protection device is equipped with a pickup transformer 4 which is connected between the terminals of an AC coil 3 connected to a power system for supplying power from a system power source 1 to a load 10 and detects voltage between the terminals of the AC coil 3; a current transformer 2 which is connected in series with the AC coil 3 and detects system current; a phase shifter 12 for putting the output voltage of the pickup transformer 4 and the output voltage of the current transformer 2 into phase with each other; and a calculation controller (7, 8, 9, 10) which finds a difference between the two output voltages in phase with each other and, when the difference is larger than a predetermined value, controls to separate the AC coil 3 from the power system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a protection device and an electric power system for an AC coil in which an AC current flows as a steady current, such as a reactor, a transformer, or a current limiting coil connected to an electric power system.

  A coil formed by winding a suitable number of turns of a conducting wire has a wide range of applications as equipment. Depending on the form of current flowing in the coil, it can be divided into AC application and DC application, and the typical application destination of AC application is the power system. Such devices include reactors, transformers or current limiting coils.

In such devices, a rated current value is usually determined, and it is required that the device can be operated without abnormality for a predetermined period of time when energization is less than the rated current value. However, even at a current lower than the normal operating rated current, there is a possibility that the conductor is partially deteriorated for some reason inside the coil device. This may be due to factors such as aging of the conductor and surrounding insulating material. In that case, if the current is continuously supplied to the coil device, the heat may be partially concentrated, and the coil may be burnt out or fatally deteriorated. In order to avoid this state, it is necessary to quickly disconnect the coil from the system so that no current flows (see Patent Documents 1 and 2).
JP-A-4-229015 JP-A-6-153379

  In an AC coil in which an alternating current flows as a steady current, if an abnormal voltage is generated in the coil winding part due to deterioration of the wire material partially or entirely during operation at a normal rated current or lower, heat concentrates only on the deteriorated part. This can cause fatal deterioration and burnout of the coil. Therefore, it is necessary to quickly detect abnormal voltage due to such partial deterioration and stop the coil, and in the case of coil equipment connected to the power system, disconnect it from the power transmission / distribution system and switch to another system. There was a problem that it was necessary to continue power transmission and distribution to the load.

  There are many problems in detecting such partial deterioration of an AC coil. Since the coil is an AC coil connected to the power system, the coil itself is at a high voltage potential, and partial deterioration or the like generated in the coil from the high voltage application unit is detected. The abnormal voltage level such as partial deterioration may be a very low voltage on the order of microvolts, and it is necessary to insulate and transmit a signal from a high voltage potential to a low voltage potential close to the ground level. In addition, the AC coil has an inductance of at least 100 μH level as an inductance. Accordingly, an inductive voltage of several tens to thousands times the abnormality detection voltage value is constantly generated at both ends of the AC coil during operation. Further, when an accident occurs in the system, there is a problem in that a voltage of the order of kV is generated at least at both ends of the AC coil, and the generated voltage is applied as an overvoltage to the AC coil detector input section.

  Therefore, an object of the present invention is to provide an AC coil protection device and a power system that can accurately detect abnormal voltage due to deterioration of an AC coil connected to a power system and prevent damage to the AC coil. .

  In order to solve the above problems, an AC coil protection device of the present invention is connected between terminals of an AC coil connected to a power system that supplies power from a system power source to a load, and is generated between the terminals of the AC coil. A pickup transformer for detecting a voltage; a current transformer connected in series with the AC coil for detecting a system current; a phase shifter for matching the phase of the output voltage of the pickup transformer and the phase of the output voltage of the current transformer; And an arithmetic and control unit that obtains a difference between the two output voltages having the same phase and performs control to disconnect the AC coil from the power system when the difference is larger than a predetermined value.

  The power system of the present invention includes an AC coil connected to a power system that supplies power from a system power source to a load, a protection device for the AC coil, and a system power source when the AC coil is disconnected from the power system. A bypass circuit that supplies power to a load and a switch that is controlled by the arithmetic and control unit and switches between the power system and the Pibus circuit are provided.

  ADVANTAGE OF THE INVENTION According to this invention, the abnormal voltage by deterioration of the alternating current coil connected to the electric power grid | system can be detected correctly, and damage to an alternating current coil can be prevented.

Hereinafter, four embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
(Constitution)
As shown in FIG. 1, a grid power current is supplied from a grid power source 1 to an AC coil 3 via a CT (current transformer) 2. The AC coil 3 is generally composed of a copper wire or an aluminum wire, but when it is composed of a superconducting wire, the AC coil 3 is sufficiently cooled by a refrigerant so that it can be superconducting. The primary side of the pickup transformer 4 is connected to both ends of the AC coil 3.

  One of the secondary sides of the pickup transformer 4 is Y-connected in each of the three phases, and the middle point is input to the inverting input side of the differential amplifier 7 via the input resistor 6. The other secondary side of the pickup transformer 4 is connected to one side of the secondary variable resistor 5 of CT2. The other end of the secondary variable resistor 5 is connected to one side of CT2 and functions as a secondary burden resistor of CT2. The variable terminals Ra, Sa, Ta of the secondary variable resistor 5 are connected to a Y-connected resistor group 11.

  There is a difference of 90 degrees between the inductive voltage generated at both ends of the AC coil 3 and the voltage phase of the CT2 secondary side. Therefore, the Y-connected resistor group 11 has a midpoint output voltage advanced by 90 degrees by the phase shifter 12 so as to be in phase with the secondary side Y-connected midpoint signal of the pickup transformer 4. The in-phase signal and the secondary Y-connection midpoint signal of the pickup transformer 4 are input to the inverting input and the non-inverting input of the differential amplifier 7 respectively. Further, the voltage balance is performed by adjusting the secondary variable resistor 5 of CT2.

  The output voltage of the differential amplifier 7 is input to the voltage comparison circuit 9. The comparison voltage is set by the setting device 8. The output of the voltage comparison circuit 9 is output to the control sequence circuit 13 to control the opening / closing of the circuit breakers 13, 14, 15. The differential amplifier 7, the setting device 8, the voltage comparison circuit 9, and the control sequence circuit 13 constitute an arithmetic control device.

(Function)
In a normal state, electric power is supplied from the grid power source 1 to the consumer important load 10 through the AC coil 3 via the CT 2. As the AC coil 3, a reactor is assumed, but the same applies to a transformer and a current-limiting coil. The secondary side Y-connection midpoint voltage of the pickup transformer 4 and the Y-connection resistance group 11 midpoint voltage supplied from CT2 are 90 degrees out of phase, but a phase shifter 12 for phase adjustment that corrects this. The inverting input and the in-phase input are input to the differential amplifier 7 in the same phase as the pickup transformer 4 via the. If the voltage level is the same, the output voltage of the differential amplifier 7 is below a certain reference value (approximately 0 V). Further, even when the current balance of each phase is lost due to the state of the load, voltage fluctuations at the same rate are received, so that the voltage generated between the midpoints is maintained at 0V.

  If any one of the AC coils 3 generates an abnormal voltage due to partial deterioration, only one phase of the pickup transformer 4 provided for every three phases causes a voltage change. When the balance is lost and an output voltage appears in the differential amplifier 7 and a voltage higher than the voltage set by the setting device 8 is output, an abnormal voltage generation signal is output from the voltage comparison circuit 9. Based on the abnormal voltage generation signal, the control sequence circuit 13 operates to open the circuit breakers 14 and 15 and disconnect the AC coil 3 from the system current. Further, by closing the circuit breaker 16, a bypass circuit is formed and power supply to the consumer important load 10 is continued.

(effect)
According to the present embodiment, it is possible to detect an abnormal voltage generation signal on which a high voltage is superimposed even in a normal operation state to protect the AC coil 3 from failure and to continue supplying power to the consumer important load 10.

(Second Embodiment)
As shown in FIG. 2, the present embodiment includes a high voltage reed relay 17 that disconnects the pickup transformer 4 from the AC coil 3 when an event occurs in which a high voltage is applied to both ends of the AC coil 3 due to a system fault or the like. A system voltage waveform monitoring device 18 that operates the high-voltage reed relay 17 when the voltage waveform of the power system is monitored and the accident voltage waveform is recognized is provided.

  When a short circuit accident occurs in the power system, the input circuit of the protection device cannot withstand an overvoltage of several kV applied to both ends of the AC coil 3 even in terms of the voltage withstand capability and is destroyed. This can be avoided by quickly disconnecting the pickup transformer 4 by the high voltage reed relay 17.

(Third embodiment)
In this embodiment, as shown in FIG. 3, the phase adjusting capacitor 19 is connected to the secondary variable resistor 5 of CT2 in place of the phase shifter 12 shown in FIGS. It is. Other configurations are the same as those in FIG. 1 or FIG.
According to the present embodiment, since the phase adjusting capacitor 19 is used instead of the phase shifter 12 constituted by a semiconductor IC circuit or the like, the circuit is simplified.

(Fourth embodiment)
In this embodiment, as shown in FIG. 4, a signal switching device 20, a state inspection device 21, a constant current power source 22 and a microvolt voltage measuring instrument 23 are added to the configuration shown in FIGS. .

  After the AC coil 3 is partially deteriorated due to a reversible factor such as insufficient cooling and is disconnected from the power transmission system by a series of sequence operations, the cooling condition of the AC coil 3 is restored to a temperature at which the AC coil 3 can recover and be energized. At that time, the pickup transformer 4 circuit normally connected by the signal switching device 20 is switched and connected to the state inspection device 21, a direct current is applied to the AC coil 3 from the constant current power supply 22, and both ends of the AC coil 3 at that time The voltage is measured by the microvolt voltage measuring device 23 to evaluate whether or not it can be energized. If it is satisfactory, a signal is sent to the control sequence circuit 13 to return the AC coil 3 to the power transmission system.

  According to the present embodiment, by providing the signal switching device 20, the voltage across the AC coil 3 is measured by the microvolt voltage measuring device 23, and when it is determined that energization is possible, the AC coil 3 is used as a power system. Can be recharged.

The connection diagram which shows the structure of the protection apparatus of the alternating current coil of 1st Embodiment of this invention, and an electric power system. The connection diagram which shows the structure of the protection apparatus of the alternating current coil of the 2nd Embodiment of this invention, and an electric power system. The connection diagram which shows the structure of the principal part of the protection apparatus of the alternating current coil of the 3rd Embodiment of this invention, and an electric power system. The connection diagram which shows the structure of the principal part of the protection apparatus of the alternating current coil of the 4th Embodiment of this invention, and an electric power system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... System | strain power source, 2 ... CT, 3 ... AC coil, 4 ... Pickup transformer, 5 ... Secondary side variable resistance, 6 ... Input resistance, 7 ... Differential amplifier, 8 ... Setting device, 9 ... Voltage comparison circuit, DESCRIPTION OF SYMBOLS 10 ... Consumer important load, 11 ... Y connection resistance group, 12 ... Phase shifter, 13 ... Control sequence circuit, 14, 15, 16 ... Circuit breaker, 17 ... High voltage reed relay, 18 ... System voltage waveform monitoring apparatus , 19: phase adjusting capacitor, 20: signal switching device, 21: condition inspection device, 22: constant current power source, 23: microvolt voltage measuring instrument.

Claims (8)

  A pickup transformer connected between terminals of an AC coil connected to a power system for supplying power from a system power source to a load and detecting a voltage generated between the terminals of the AC coil, and a system connected in series with the AC coil A current transformer for detecting current; a phase shifter for matching the phase of the output voltage of the pickup transformer and the phase of the output voltage of the current transformer; and obtaining the difference between the two output voltages in the same phase. An AC coil protection device, comprising: an arithmetic and control unit that performs control to disconnect the AC coil from the power system when is greater than a predetermined value.   The arithmetic and control unit includes: a differential amplifier that obtains and amplifies the difference; a comparison circuit that compares an output value of the differential amplifier with a predetermined value; and an output of the comparison circuit that receives the output of the AC coil from a power system 2. The AC coil protection device according to claim 1, further comprising a control sequence circuit that is separated from the AC coil protection circuit. 3.   2. The protection device for an AC coil according to claim 1, further comprising a high-voltage reed relay that disconnects the pickup transformer from the AC coil when a voltage corresponding to a system voltage is generated in the AC coil.   4. The AC coil protection device according to claim 3, further comprising a system voltage waveform monitoring device that operates the high voltage reed relay when the voltage waveform of the power system is monitored and an accident voltage waveform is recognized.   2. The protection device for an AC coil according to claim 1, further comprising a phase adjusting capacitor connected to a secondary side of the current transformer instead of the phase shifter.   A state inspection device for inspecting the state of the alternating current coil by passing a direct current through the alternating current coil disconnected from the power system, and a signal switching device for switching the connection of the terminal of the alternating current coil to the pickup transformer or the state inspection device; 2. The protection device for an AC coil according to claim 1, wherein, when it is determined that the AC coil can be energized, the arithmetic control unit performs control to re-insert the AC coil into a power system.   An AC coil connected to a power system that supplies power to a load from a system power source, the AC coil protection device according to any one of claims 1 to 6, and when the AC coil is disconnected from the power system A power system comprising: a bypass circuit that supplies power from a system power source to a load; and a switch that is controlled by the arithmetic control device and switches between the power system and the Pibus circuit.   8. A power system according to claim 7, wherein a superconducting conductor is used for the conductor of the AC coil.

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