GAS INSULATED SWITCHGEAR

Abstract: Gas insulated switchgear comprises at least one inter­ rupter (12, 14, 16) disposed at an end of the region to be protected, at least one arc detector 30 disposed for detecting an arc within a vessel 32 in which an electrically insulating gas is filled, the vessel being within the region to be protected, and a fault detector (50) for detecting a fault. A control device (10) actuates the interrupter only when the fault detector detects the fault and also the arc detector detects the arc. The vessel (32) is preferably a housing of a said interrupter.

Description: BACKGROUND OF THE INVENTION This invention relates to a gas insulated switchgear and in particular to a protective system therefor. Fig. 4 illustrates a conventional gas insulated switchgear. In the figure, the broken lines designate a gas insulating vessel. When a fault condition occurs in a gas insulated bus bar 2, current transformers 4, 6 and 8 detect abnormal currents in the same phase. These abnormal currents are supplied to a control circuit 10, which causes the interrupters 12, 14 and 16 to be tripped to protect the bus bar 2. On the other hand, when a fault condition occurs outside of the region to be protected for example, at a transmission line 24 in the air outside of bushings 18, not all of the current transformers 4, 6 and 8 detect the abnormal current in the same phase. Therefore, the control circuit 10 determines that the fault condition occurs outside of the region to be protected and does not protect the bus bar 2. However, there are the following problems in the conventional protecting system. Since there is some error in the current transformer and the voltage transformer in a control circuit, it is impossible to determine whether the fault is within the region to be protected or the fault is outside of the region to be protected when the fault current is low and within the range of the error. Therefore, the conventional system is disadvantageous in that it is activated even when the fault is outside of the region to be protected or that it fails to achieve interrupting operation even when the fault occurs within the region to be protected. FR-A-1413925 discloses a gas-insulated device protected by an earthing device triggered by the arc, in particular by the gas pressure rise when an arc occurs, in order to provide a more rapid response. This does not improve fault discrimination. DE-A264442 discloses a system for protecting a switch installation against the effect of an internal arc by detecting the arc, in order to improve and in particular accelerate the response to the fault. This system also does not provide for enhanced discrimination. This invention has as its object the provision of a protective device in which fault discrimination is enhanced and which achieves a high reliability. According to the present invention, there is provided a gas insulated switchgear having at least one interrupter disposed at an end of a region to be protected, fault detecting means for detecting a fault, and at least one arc detector means disposed for detecting an arc within a vessel which is filled with an electrically insulating gas, said vessel being within the region to be protected, characterised in that control means are arranged for actuating said interrupter only when said fault detecting means detects the fault and said arc detecting means detects the arc. When a fault occurs, irrespective of whether it is inside or outside of the region to be protected, the fault detecting means detects the fault. When the fault is within the region to be protected, the arc detecting means detects the arc. The control means interrupts the interrupter on the basis of the outputs from both detectors. On the other hand, if a fault occurs outside of the region to be protected, the arc detecting means does not provide a detection output, so that the interrupter does not interrupted. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more readily apparent from the following detailed description of the preferred embodiment of the invention taken in conjunction with the accompanying drawings, in which: Fig. 1 is an electrical diagram showing one embodiment of the present invention; Fig. 2 is a cross sectional view showing the state in which a photoelectric detector element is installed; Fig. 3 is a view showing an electrical diagram of the control circuit; and Fig. 4 is a view showing a conventional gas insulated switchgear. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 illustrates one embodiment of the present invention. In this embodiment, a voltage transformer 50 is used as a fault detecting means. Within the vessel in the region to be protected, photoelectric detector elements 30a - 30u which are arc detecting means are provided. Fig. 2 illustrates the manner in which the photoelectric detector element 30a is mounted to the vessel 32 of the interrupter 12. When a fault occurs and an electric arc is generated inside of the interrupter 12, the photoelectric detector element 30a provides an output. This output is supplied to a control circuit 10 shown in Fig. 1. A simplified circuit diagram of the control circuit 10 is shown in Fig. 3. When a voltage drop is detected at the voltage transformer, a contact 34 closes. When a detection output is provided from any one of the photoelectric detector elements 30a - 30u, the contact 36 is also closed. Therefore, the coil 38 is energized and the interrupters 12, 14 and 16 are tripped open. When a fault occurs outside of the region to be protected such as on the transmission line 24, no output is provided from either of the photoelectric detector elements 30a - 30u, so that the contact 36 is held open. Therefore, in this case, an operation in which all of the circuit interrupters interrupt is not effected. The contact 36 is closed even when a very small arc which does not result in a fault is generated. However, in this case, since an abnormal current is not detected at the voltage transformer 50, the contact 34 is kept open. That is, no unnecessary interrupting operation is effected. While a photoelectric detector element is used as an arc detecting means in the above embodiment, an element which detects vibration or pressure change generated by the arc may also be used. Also, as another embodiment, an element for detecting a zero-phase current may be employed as the fault detecting means. According to the present invention, an occurrence of a fault is detected by a fault detecting means and the determination of whether the fault is outside of the region to be protected or inside of the region to be protected is made by an arc detecting means. Therefore, the following advantages are provided. Firstly, an accurate determination of whether the fault is outside of the region to be protected or inside of the region to be protected can be made without errors even when the fault current is small as in the case of an ineffective grounding system. Secondly, since an arc detecting means is provided between the interrupter and the current transformer protection can be provided with respect to this region which has heretofore been a blind spot. Thirdly, as a result of eliminating the above blind spot, the need to provide the interrupter and current transformer in a proximate relationship is eliminated. That is, the degree of freedom in deciding the mounting position of the current transformer is increased, enabling the gas insulated switchgear to be reduced in size and made at lower cost.

Claims: A gas insulated switchgear having at least one interrupter (12, 14, 16) disposed at an end of a region to be protected, fault detecting means (50) for detecting a fault, and at least one arc detector means (30) disposed for detecting an arc within a vessel (32) which is filled with an electrically insulating gas, said vessel being within the region to be protected, characterised in that control means (10) are arranged for actuating said interrupter only when said fault detecting means (50) detects the fault and said arc detecting means (30) detects the arc. A gas insulated switchgear as claimed in claim 1, wherein said arc detecting means (30) detects the light of the arc. A gas insulated switchgear as claimed in claim 1, wherein said arc detecting means (30) detects the vibration or the pressure change resulting from the arc. Gas insulated switchgear as claimed in claim 1 in which a said arc-detecting means (30) is placed between the interrupter and the fault-detecting means (50).

Inventors: YAMAUCHI, TAKAO C/O ITAMI WORKS MITSUBISHI DENKI
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1986
Main classification: H02B13
IPC codes: H02H7, H02H5, H02H1, H02B13