Patent Description:
To limit the destruction effect of an arc fault inside a switchgear or other equipment, it is desirable to limit the arc destruction duration by establishing a fast and stable current path from the conductor on potential to ground potential or between the phases if available, that the arc fault current is commutated to an arc mitigation device and the arc fault is distinguished. Currently, all active arc mitigation devices are trigger and powered from separate electronics and the required energy is provided from a capacitor or another energy storage. In addition, the device requires an auxiliary power supply. To get the information to trigger the arc mitigation device there must be an optical sensor (for example an optical eye or glass fibre) and in addition information regarding the fault current status is required, requiring for example a current transformer, sensor or reed contact(s).

<CIT> relates to a switchgear with a switching device, driven by propellant chemical charge or fast acting switch, with means for current or fault current detection and optical sensor means for arc fault light or arc fault light detection.

<CIT> relates to an arrangement for protecting systems and persons, comprising a switching element which can be triggered by detecting an arc fault, where the electrical energy for triggering the switching element results exclusively from the electrical energy of the accidental arc that occurs.

This does not always lead to the most effective and required arc mitigation.

Therefore, it would be advantageous to have an improved technique for providing energy for arc mitigation in low-, medium- and high- voltage switchgears.

In an aspect, there is provided an arc mitigation apparatus for a low-, medium-, or high-voltage switchgear, the arc mitigation apparatus comprising:.

The arc mitigation device is configured to be mounted to a low-, medium-, or high voltage switchgear. The arc mitigation device when activated is configured to stop or limit current flow within at least one part of the low-, medium-, or high- voltage switchgear. The solar-cell is configured to be located within a compartment of the low-, medium-, or high- voltage switchgear. The solar-cell is configured to cause the arc mitigation device to activate due to radiation from an electrical arc fault of the switchgear impinging upon the solar-cell.

In an example, the solar-cell is configured generate a current over a threshold current level to cause the arc mitigation device to activate due to the radiation from the electrical arc of the switchgear impinging upon the solar-cell.

In an example, the solar-cell is configured such that radiation impinging upon the solar-cell below a threshold intensity level is not sufficient to cause the arc mitigation device to activate.

In an example, the solar-cell is configured to directly activate the arc mitigation device due to the radiation from the electrical arc of the switchgear impinging upon the solar-cell.

In an example, the solar-cell is configured to generate a current over a threshold current level to directly activate the arc mitigation device due to the radiation from the electrical arc fault of the switchgear impinging upon the solar-cell.

In an example, the arc mitigation apparatus comprises a merging unit. The merging unit is located within or associated with the arc mitigation device. The merging unit is configured such that when activated the merging unit is configured to activate the arc mitigation device. The solar-cell is configured to activate the merging unit due to the radiation from the electrical arc fault of the switchgear impinging upon the solar-cell.

In an example, the merging unit comprises a stored energy unit (will be charged from solar-cell in case of a fault) and wherein activation of the merging unit is configured to release energy from the stored energy unit (threshold value) to activate the arc mitigation device.

In an example, the stored energy unit supplies the trigger (activation) energy to the micro gas generator or a pressurized gas container or one or more springs.

In an example, the arc mitigation device when activated (triggerd) is configured to make a connection between the life parts (bus-bar on potential) and/or to ground potential.

In an example, the arc mitigation device is an Ultra-Fast-Earthing-Switch "UFES" or an other fast acting device.

In an example, the radiation from the electrical arc fault of the switchgear impinging upon the solar-cell is configured within the merging unit to trip a circuit breaker of the low-, medium- or high- voltage switchgear.

In an example, the arc mitigation apparatus comprises a magnetic core memory configured to store arc fault location information initiated by the provided solar-cell current to be used the remanence of the iron core.

In an example, the arc mitigation apparatus comprises an arc fault indication device within the merging unit.

In an example, the arc fault indication device is a single use arc fault indication device, the arc fault indication device comprises a magnetic powder.

The above aspect and examples will become apparent from and be elucidated with reference to the embodiments described hereinafter.

<FIG> relate to an arc mitigation apparatus for a low-, medium-, or high- voltage switchgear.

In an example the mitigation apparatus, for a low-, medium-, or high- voltage switchgear, comprises an arc mitigation device <NUM>, and a solar-cell <NUM>. The arc mitigation device is configured to be mounted to a low-, medium-, or high- voltage switchgear. The arc mitigation device when activated (triggered) is configured to stop or limit current flow within at least one part of the low-, medium-, or high- voltage switchgear. The solar-cell is configured to be located within a compartment of the low-, medium-, or high- voltage switchgear, or circuit. The solar-cell is configured to cause the arc mitigation device to activate due to radiation from an electrical arc fault of the switchgear impinging upon the solar-cell.

In an example, the solar-cell is configured generate a current <NUM> over a threshold current level to activate the arc mitigation device due to the radiation from the electrical arc fault of the switchgear impinging upon the solar-cell.

In an example, the solar-cell is configured to directly activate the arc mitigation device due to the radiation from the electrical arc fault of the switchgear impinging upon the solar-cell.

In an example, the solar-cell is configured generate a current <NUM> over a threshold current level to directly activate the arc mitigation device due to the radiation from the electrical arc fault of the switchgear impinging upon the solar-cell.

In an example, the merging unit comprises a stored energy unit (will be charged from solar-cell in case of a fault) and activation of the merging unit is configured to release energy from the stored energy unit to activate the arc mitigation device. Here a simple analoge electronic circuit can be applied.

In an example, the stored energy unit activate a micro gas generator or a pressurized gas container or one / more springs.

In an example, the arc mitigation device when activated is configured to make a connection between the life part of the switchgear phases or to the circuit ground potential.

In an example, a signal from the solar-cell due to the radiation from the electrical arc fault of the switchgear impinging upon the solar-cell is configured within the merging unit to trip optionally an upstream circuit breaker of the low-, medium- or high- voltage switchgear.

Continuing with the figures, the arc mitigation apparatus for a low-, medium-, or high-voltage switchgear is further described with respect to specific embodiments.

The inventors realised they could develop an arc mitigation apparatus that only uses a solar-cell to obtain the light and the fault arc current information to make a reliable trip by the production of enough energy from the solar-cell, only in the situation when such fault mitigation is required, in order to activate any arc mitigation device.

It was realised that in the case of an arc fault, the light produced that can be considered to be "Light and "Current" information" can be utilized to trigger an arc mitigation device without any monitoring of arc fault current. It was realised that in the case of an arc fault the light emission is strong enough that the solar-cell will produce enough energy (around <NUM> times more than provide by typically given strong sunshine impinging) which exceeds a given threshold value to inititate activation of the arc mitigation device. At the same time, standard light, ambient light or flashlight cannot produce, via the solar-cell, enough energy to trip the mitigation device. The sunshine light converted energy from the solar-cell will be leaded directly to earth to avoid energy loading in storage.

Thus, currently the detection of an internal arc fault inside a switchgear / circuit is done by means of an optical arc flash sensor, which triggers an external power supplied electronic device with a charged capacitor to actuate the active primary arc mitigation device, and this is linked with determination of a current threshold value.

However, now with the new apparatus developed by the inventors, there is no need to detect both the current and the light together because the arc fault itself is used to generate enough power to trigger the active arc mitigation device. The new technique using a solar-cell triggers and powers the mitigation device within less than <NUM>-<NUM> in the situation of arc fault currents above typical values of 2kA.

The new technique provides for extremely short operation time of the primary arc mitigation devices within less than <NUM>-<NUM> in the case of fault arc currents above 2kA current, in conjunction with the rapid and reliable detection of the fault, leads to the arc fault being extinguished almost immediately after it arises.

A solar-cell such as a monocrystalline-Si unit (or other solar-cell) can be selected, based on fast and durable analogue technology, to provide for a reliable, robust, and fast function.

Thus the new technique provides for threshold tripping only in the case of an arc fault. All other light sources (sunlight, lamps or flash) do not provide enough energy to the solar-cell to provide enough power to trip the arc mitigation device. With this selective technique an unwanted operation of the arc mitigation device will be avoided.

The solar-cell monitors the switchgear (the circuit) on a continuous and autonomous basis without being influenced by these external light sources. Along with the arc mitigation device, this approach ensures continuous, complete equipment and personnel protection all the time, even during maintenance operations.

Since the standard switchgears are designed as internal arc-proof solutions, in line with the standard, the new manner of providing arc elimination by means of arc mitigation devices and a solar cell, that can provide a highest possible level of protection to persons, to the circuit and to the equipment in case of an internal arc event in switchgears or electrical circuits, is recognized by the Standard IEC <NUM>-<NUM>.

The following provides details on an operational sequence of the new technique utilizing self-powered solar-cell, that in the situation case of an internal arc fault event provides a trigger element for arc mitigation devices in an intrinsically robust and simple manner:.

The long-term operational reliability of state-of-the art solar-cells are well known. In switchgear application these solar-cell will be installed inside switchgear compartments or in or outdoor circuits which are protected from the environmental impacts. That leads to an expected lifetime of more than <NUM> years.

The selectivity between the arc mitigation devices in a "complex" switchgear configuration with respect to the solar-cell in different compartments is possible.

EMC/EMI related complications are very much reduced, because of the higher operational energy requirement of the arc mitigation device.

The arc detection by means of solar-cell is able to activate the mitigation device within less than <NUM> at the time the arc fault current is present, and the UFES (arc mitigation device) operates within < <NUM> milliseconds. Therefore, the arc fault is eliminated within less than <NUM> (arc-fault current > 2kA).

As detailed above, the new arc mitigation apparatus for a low voltage, medium voltage, or high voltage switchgear detect and eliminates the arc fault in low- and medium- and high- voltage switchgear. The technique is simple and flexible and can be adapted to different switchgear configurations, and ensures personnel safety and faster repair of the switchgear in the case of an internal arc fault.

The new apparatus can be part of newly built switchgear, but can also be retrofitted to already installed switchgears arrangements.

It is also to be noted that reference to switchgear is mentioned, but the new apparatus can be utilized for example in converters (DC-grid) as well.

<FIG> shows an arc mitigation apparatus for a low voltage, medium voltage, or high voltage switchgear according to the invention. An arc fault produces light that falls on the solar-cell <NUM> and the current flow <NUM> produced from the solar-cell via the merging unit <NUM> or directly from the solar-cell <NUM> to the arc mitigation device <NUM> triggers the arc mitigation device to operate.

The following relates to specific features:.

It is also to be noted that UFES status monitoring and diagnosis function can be utilized to find the fault location. This can be implemented by using magnetic-core memory technology, as shown in <FIG>, where Im and Ul are current are potential respectively.

This technology offers the following features:.

Claim 1:
An arc mitigation apparatus for a low voltage, medium voltage, or high voltage switchgear, the arc mitigation apparatus comprising:
- an arc mitigation device (<NUM>); and
- a solar cell (<NUM>);
wherein the arc mitigation device is configured to be mounted to a low voltage, medium voltage, or high voltage switchgear;
wherein the arc mitigation device when activated is configured to stop or limit current flow within at least one part of the low voltage, medium voltage, or high voltage switchgear;
wherein the solar cell is configured to be located within a compartment of the low voltage, medium voltage, or high voltage switchgear; and
wherein the solar cell is configured to cause the arc mitigation device to activate due to radiation from an electrical arc fault of the switchgear impinging upon the solar cell.