Low-voltage, medium-voltage, or high-voltage power receiving/distributing equipment is an equipment system essential as a social infrastructure of power supply-demand for buildings, factories, and the like, and safety and reliability thereof are sufficiently considered for, as well as the manufacturers, the overall range including installation work and operation maintenance. However, although in very rare cases, the insulation function for the electric path might be lost due to, for example, device damage by unexpected entry of a small animal or a foreign material, insulation deterioration due to aging, great earthquake beyond the assumptions, whereby fault such as ground fault or short circuit can occur.
In particular, in internal short circuit fault of a closing device such as a switchgear, a large-current arc occurs to cause a plasma state at about 10,000 to 20,000 degrees Celsius in the vicinity of the arc. Thus, metals and insulating materials around there are partially evaporated and an insulating gas such as air around the arc instantaneously expands to make an extremely high pressure inside the device. In the case of providing a pressure releasing device for a switchgear or the like, the high-pressure insulating gas together with the evaporated metal gas and insulating material decomposed gas is pressure-released at once in a safe direction to outside of the device in about 10 milliseconds, thereby preventing breakage of the switchgear.
Thereafter, the large-current arc is continuously generated as long as the fault continues, so that the surrounding metals such as conductors and a housing are further melted and evaporated, whereby damages to the device and the like are expanded. Even in the case where the inside of the switchgear is partitioned per electric path section by metallic shielding plates as in a metal-clad switchgear, if the fault arc continues for a long time, the range of the damaged section and the damaged switchgear expands due to deformation, melting, or the like of the metal partition wall, resulting in significant damage.
Normally, the design is made such that a power circuit breaker provided for protecting each electric path eliminates such fault in the power receiving/distributing system. However, it takes at least about 100 milliseconds or longer from detection of the fault until the fault electric path is separated from a power supply by operation of the circuit breaker and the arc fault in the equipment device is eliminated. Therefore, during this period, the device in which the fault occurs is damaged to such a great extent that the device can hardly be used again, and a long period is needed for recovering the power receiving/distributing system. During this period, power cannot be supplied. In addition, the recovery requires huge cost.
Therefore, in order to suppress the damage to a minimum level and minimize the equipment recovery period after the fault, it is effective to shorten the arc fault continuation period.
Patent Document 1 describes that fault current is detoured to flow to the ground via a ground current-conduction circuit having a much lower impedance than an arc circuit in an extremely short time of several milliseconds after occurrence of arc fault, thereby eliminating, in an extremely short time, the arc at the part where the fault occurs, and discloses a system to which this configuration is applied.
Non-Patent Document 1 is a product catalog of the invention of the above Patent Document 1, and also describes the details of the application.
According to the Non-Patent Document 1, fault current is conducted so as to detour to a ground circuit in an extremely short time of several milliseconds after occurrence of the fault, thereby eliminating the arc at the fault part. As a result, arc energy injected to the insulating air space and metals such as conductors, insulating materials, and a housing at the fault part can be minimized. Therefore, damage due to arc to the part where the fault occurs becomes extremely small, and depending on the magnitude of the arc current, the damage can be suppressed to such an extent that the equipment can be operated almost as it is after the fault and the cause of the fault have been eliminated.
In these prior art documents, a high-speed closing device (in Non-Patent Document 1, primary switching unit) which is a main device of an arc eliminator (fault arc elimination device) is a device that closes to ground fault current upon arc fault in an extremely short time of 1.5 milliseconds. This device can be individually installed while being mounted on a stationary-type or drawer-type truck between the ground and three-phase electric paths having low voltage, medium voltage, or high voltage in the device such as a switchgear, and is provided at a free space of the switchgear or, as necessary, provided by extending a specific electric path and enlarging the switchgear.
The high-speed closing device mounted on a drawer-type truck can be easily installed by removing a circuit breaker such as a preparatory circuit breaker for a line that is not normally used, and inserting the drawer-type truck on which the high-speed closing device is mounted, into the circuit breaker compartment. However, in order to apply this method, it is necessary to replace the preparatory line with the arc eliminator function, and as a result, the redundancy as the power receiving/distributing equipment is deteriorated. In addition, this high-speed closing device is configured to weld a contact when conducting the fault current, thereby performing fault current conduction until the power-supply-side circuit breaker on the fault electric path is interrupted. Therefore, the high-speed closing device is to be replaced after one operation.