HIGH- VOLTAGE EQUIPMENT

FIELD OF THE INVENTION

The present invention relates to an arc mitigation trigger apparatus for a low -, medium -, or high- voltage eqipment.

BACKGROUND OF THE INVENTION

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).

EP2624272B1 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.

This does not always lead to the most effective and required arc mitigation. 2

There is a need to address this issues.

SUMMARY OF THE INVENTION

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

The object of the present invention is solved with the subject matter of the independent claims, wherein further embodiments are incorporated in the dependent claims.

In an aspect, there is provided an arc mitigation apparatus for a low-, medium-, or high- voltage switchgear, the arc mitigation apparatus comprising: an arc mitigation device; and a solar-cell;

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. - 3 - ln 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. - 4 -

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.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be described in the following with reference to the following drawing:

Fig. 1 shows an example of an arc mitigation apparatus for a low-, medium-, or high- voltage switchgear;

Fig. 2 shows an example of a magnetic core memory; and

Fig. 3 shows an example of a single use arc fault location indication device with magnetic powder, shown before and after detection of an arc fault.

DETAILED DESCRIPTION OF EMBODIMENTS

Figs. 1-3 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 10, and a solar-cell 40. 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. - 5 -

In an example, the solar-cell is configured generate a current 20 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 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 fault of the switchgear impinging upon the solar-cell.

In an example, the solar-cell is configured generate a current 20 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 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. 6 ln an example, the arc mitigation device is an Ultra-Fast-Earthing-Switch “UFES” or an other fast acting device.

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.

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.

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 5 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 - 7 - 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 4-5ms 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 2-3ms 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 62271-200. 8

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 primary arc fault energy is converted to the actuation energy by the solar cell, and therefore this does not need any auxiliary supply.

• The solar cell when exposed to light produced due to an arc fault current the energy output is about factor 5 higher than the current that the solar-cell can produce with maximum ambient light.

• The arc mitigation device can be for example an Ultra-Fast-Earthing-Switch (UFES) for low-, medium- voltage application, and the arc fault can be eliminated in less than 5ms in the situation when the arc current will be above 2kA. In the situation when arc currents are lower than this, an operation time of less than 50ms is achievable and arc fault mitigation can be done within that time period. o It is to be noted that normally currents below 2kA are handled by present protection systems in switchgear.

• A trip signal can if necessary be sent to the upstream breaker to interrupt the fault current.

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 35 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 3ms at the time the arc fault current is present, and the UFES (arc mitigation - 9 - device) operates within < 2 milliseconds. Therefore, the arc fault is eliminated within less than 5ms (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. 1 shows an example of an arc mitigation apparatus for a low voltage, medium voltage, or high voltage switchgear. An arc fault produces light that falls on the solar cell 40 and the current flow 20 produced from the solar-cell via the merging unit 30 or directly from the solar-cell 40 to the arc mitigation device 10 triggers the arc mitigation device to operate.

The following relates to specific features:

Fault location signalling

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. 2, where l _m and Ui are current are potential respectively.

This technology offers the following features:

• Magnetic core memory to store the information arc fault location.

1. Storing the fault location by using of a single magnetic core to latch the ON” state with the fault current information.

2. Reading of the core status with and external device by resetting to OFF” state. 10

Fault location indication based on magnetic field

• Solar-cell cable generated based on coil winding magnetic field and supported by steel core, to trigger the magnetic powder.

• This can be a single use device (security label) to indicate the arc fault location.

• The magnetic powder detects by optical indication the arc fault with a magnetic field of about 50 mT and it is immediately visible, as shown in Fig. 3.

• The information can be even provided from a fast acting bistable relays.

• This part can be placed on the outside as well as on the inside at the switchgear.

Tripping power management

Solar panel loop supervision

• The supervision of solar panel circuit can be done via a pilot impulse.

• Powered if needed by a long-life “lithium” battery that enables with the entire system to operate independently from the auxiliary voltage.

PSE trip circuit supervision

• The supervision of the activation circuit is checked by a pilot impulse.

• Powered if needed by a long-life “lithium” battery that enables with the entire system to operate independently from the auxiliary voltage.

Activation power supervision

In the case of an arc fault the availability of minimum needed activation energy can be monitored.

• The current from the solar-cell will feed the capacitor storing the activation energy.

• In case the threshold value is reached, the energy of the capacitor is used to operate the mitigation device.

• The occurrence of ambient light or flash will not lead to an operation of the mitigation device because the charging current is filtered with a characteristic that even long-duration lightning cannot operate the mitigation device.