Patent Description:
Fortunately, flash-overs inside medium or high voltage switchgear happen rarely, but they do occur for a number of different reasons. The consequences for personnel, equipment and process may then be devastating.

Switchgear failure through for example cable end box or busbar failure, causes a rapid expansion of air, gases and, in the case of oil filled switchgear, liquid. To mitigate this, the expanded air, gases and liquid is vented out of an overpressure relief flap within the switchgear. At the same time a switchgear circuit breaker is tripped, to make the switchgear safe.

Currently Ith limiters (also called microswitches) are installed on the overpressure relieve flap. In case of an electrical arc or flash-over, the air pressure inside the panel rapidly increases and opens the flap as discussed above. A microswitch operates with the flap, changing the system status to OFF and at the same time providing a tripping signal for a circuit breaker. However, there are sources of vibrations during flap travel or movement, which interrupts the tripping signal.

Thus in the current design (a microswitch / Ith limiter) is attached to flap, and vibrations are transmitted to the mobile or moveable contact of the Ith limiter microswitch during flap operation. This leads to interruption of the tripping signal. The sources of vibrations are:.

<CIT> describes that the tripping device has a switch, which is operated by a pressure. The electrical signal of a converter is provided with an operating element. The operating element is impinged with a given control movement by a mobile element. An electrical switching arrangement with an electrical switching device is also described.

Attempting to mitigate vibrations through tightening of the microswitch actuator can be problematic. This is because the reaction time of the Ith limiter microswitch depends on its setting. Tightening of the microswitch actuator can lead to a reduction in reaction time.

There is a need to provide for an improved way of providing a trip signal during an electrical arc event or flash-over for a medium or high voltage switchgear.

Therefore, it would be advantageous to have improved means for providing a trip signal during an electrical arc event or flash-over for a medium or high voltage switchgear.

In a first aspect, there is provided an overpressure relief flap apparatus for a medium or high voltage switchgear as defined in appended claim <NUM>. In a second aspect, there is provided an overpressure relief flap apparatus for a medium or high voltage switchgear as defined in appended claim <NUM>.

In an embodiment of the application, there is provided an overpressure relief flap apparatus for a medium or high voltage switchgear. The apparatus comprises:.

The lever is attached to an overpressure relief flap of a compartment of a switchgear. The microswitch is mounted to a frame of the compartment of the switchgear. When activated the microswitch is configured to transmit a trip signal to a circuit breaker of the switchgear. The lever is configured to activate the switch when the overpressure relief flap opens.

In other words, a new overpressure relief flap apparatus design uses a microswitch or limiter embedded in a metal housing and a lever operating it. The Limiter (microswitch) is installed on the panel frame, whilst the lever is installed on the overpressure relieve flap. Vibrations are then not transmitted to the limiter during flap operation.

In this way the effect of vibrations that can affect the tripping time signal are suppressed, because they are not transferred to the microswitch or limiter. In this manner, because vibrations are suppressed that would otherwise be transferred to a moveable or mobile contact of a microswitch or limiter, and uninterrupted trigger signal for a circuit breaker is provided in the situation when there is an electrical arc.

Thus, during opening of the overpressure relief flap, for example during the first <NUM> of an electrical arc, the effect of vibrations that can affect the signal transmitted by the microswitch are mitigated and the overall reaction time of the apparatus in tripping a circuit breaker is improved.

Faster set-up and testing of the circuit breaker trip system, due to operation of an overpressure relief flap, is also provided. Additionally, the new design is significantly cheaper than previous designs.

The trip signal as well as being used to trip the circuit breaker can be used for other purposes, such as being used to indicate that there has been an event leading to opening of the overpressure relief flap.

In an example, an overtravel distance of the microswitch is less than <NUM>.

Thus, a contact of the microswitch moves a distance after which it activates (termed pretravel) and can then move a further distance known as the overtravel distance and this distance is kept to a minimum whilst still ensuring that switching operation takes place, thereby providing a short bouncing time and reducing the effect of vibrations.

A microswitch having a contact with a small overtravel distance ensures that one can easily and correctly set up the limiter microswitch.

In an example, the overtravel distance of the microswitch is approximately <NUM>.

In an example, the microswitch is mounted to the frame of the compartment via at least one damping component.

In an example, the at least one damping component comprises at least one ethylene propylene diene monomer (EPDM) rubber.

In other words, the microswitch is mounted or inserted to or into the frame of a compartment of a switchgear and is isolated from the frame/chassis by EPDM rubbers. In an example, the microswitch is located within a case, and the microswitch is spaced from at least one wall of the case by the at least one damping component. The case is attached to the frame of the compartment of the switchgear.

In an example, wherein the case comprises metal.

In an example, the lever comprises metal.

In an example, the lever comprises one or more slotted mounted holes, oriented such that the lever can be moveably repositioned closer to or further away from the microswitch.

In this manner. The position of the lever can be easily adjusted with respect to the microswitch, thereby making set-up easier.

In accordance with the second embodiment of the invention, the lever is configured to enable a user to operate the lever by hand to activate the microswitch with the lever when the overpressure relief flap is in a closed position.

In accordance with the first embodiment of the invention, the lever is configured to enable a user to operate the lever by hand to bend the lever to activate the microswitch with the lever when the overpressure relief flap is in a closed position.

In accordance with the second embodiment of the invention, a force required by the user to activate the microswitch by hand with the lever when the overpressure relief flap is closed is less than 20N.

In this manner, the overpressure relief flap apparatus can be efficiently tested to ensure integrity of the protection function.

In a second aspect, there is provided a medium or high voltage switchgear comprising an overpressure relief flap apparatus according to the first aspect.

In an example, the switchgear comprises a circuit breaker. The circuit breaker is configured to be tripped upon receipt of the trip signal transmitted from the microswitch of the overpressure relief flap apparatus.

<FIG> show examples of an overpressure relief flap apparatus for a medium or high voltage switchgear.

These figures show an overpressure relief flap apparatus for a medium or high voltage switchgear. The apparatus comprises a lever <NUM>, and a microswitch <NUM>. The lever is shown in detail in <FIG> and the microswitch is shown along with other components in detail in <FIG>. The lever is attached to an overpressure relief flap of a compartment of a switchgear, as shown in <FIG>. The overpressure relief flap is not shown in full detail in <FIG> for reasons of clarity. The microswitch is mounted to a frame of the compartment of the switchgear, as shown in <FIG>. The full compartment is not shown in <FIG> again for reasons of clarity, but it is clear that these components are positioned such that when the overpressure relief flap opens, the lever contacts the microswitch to activate it. When activated the microswitch is configured to transmit a trip signal to a circuit breaker of the switchgear. The circuit breaker is not shown. The lever is configured to activate the switch when the overpressure relief flap opens.

According to an example, an overtravel distance of the microswitch is less than <NUM>.

According to an example, the overtravel distance of the microswitch is approximately <NUM>.

According to an example, the microswitch is mounted to the frame of the compartment via at least one damping component <NUM>.

According to an example, the at least one damping component comprises at least one ethylene propylene diene monomer (EPDM) rubber.

According to an example, the microswitch is located within a case <NUM>. The microswitch is spaced from at least one wall of the case by the at least one damping component. The case is attached to the frame of the compartment of the switchgear.

According to an example, the case comprises metal.

According to an example, the lever comprises metal.

In an example, the metal is stainless steel. In an example, the metal is stainless steel <NUM>.

According to an example, the lever comprises one or more slotted mounted holes. These are located in a base of the lever, and are oriented such that the lever can be moveably repositioned closer to or further away from the microswitch.

According to a second embodiment of the invention the lever is configured to enable a user to activate the microswitch with the lever when the overpressure relief flap is in a closed position.

According to a first embodiment of the invention, the lever is configured to bend to enable the user to activate the microswitch with the lever when the overpressure relief flap is in a closed position.

According to a second embodiment of the invention, a force required by the user to activate the microswitch with the lever when the overpressure relief flap is closed is less than 20N.

In an example, an arm part of the lever is connected to the base part of the lever that is attached to the overpressure relief flap. The arm part extend away from the base part at an angle. In the example the angle is <NUM> degrees, and can be other angles. In an example, the lever is attached to the overpressure relief flap via the base part, and the arm part is angled toward the microswitch location.

As discussed, in this way a medium or high voltage switchgear can have an overpressure relief flap apparatus as discussed above, and provides for improved way trip signal during an electrical arc event or flash-over for a medium or high voltage switchgear that can be used to trip a circuit breaker for example.

According to an example, the switchgear comprises a circuit breaker, and wherein the circuit breaker is configured to be tripped upon receipt of the trip signal transmitted from the microswitch of the overpressure relief flap apparatus.

Continuing with the figures, <FIG> and explaining details of a specific embodiment a microswitch <NUM> is used. This is a miniature Crouzet <NUM> Wide contact gap microswitch that is resistant to vibrations. The microswitch is inserted in the metal case <NUM> and isolated by EPDM rubbers <NUM> from the chassis of the case. The case is itself mounted to a frame of a compartment of a medium voltage or high voltage adjacent to an overpressure relief flap, and thus the microswitch in addition to being resistant to vibrations is made more resistant to the effects of vibrations caused through mounting on the frame of the compartment and vibrationally isolating it through the use of damping EPDM rubbers. A lever <NUM> is used to operate the microswitch, and this is installed on the overpressure relieve flap itself. For fast setting and testing of the tripping function, the lever is made from stainless spring steel <NUM> and can be operated by hand to activate the microswitch with a force (F < 20N). <FIG> shows specific details of how the microswitch is located to the case, and it is clear how the case can then be mounted to the frame of the switchgear compartment. <FIG> then shows specific details of the lever, again showing how it can be mounted to the overpressure relief flap and where slotted mounting slots provide adjustment means.

During an electrical arc, rapidly raised pressure (<<NUM>) cause the overpressure relieve flap to open upon which the lever is installed, and leading to operation of the microswitch. Electrical signal delivered to a protection circuit, trip a switchgear circuit breaker. This design suppresses vibrations transferred to the microswitch mobile or moveable contact during opening of the flap i.e. first <NUM> of electrical arc and therefore speeds up reaction time. <FIG> shows an example of the trip signal for the new overpressure relief flap apparatus termed "NEW TRIP" against that for an existing trip signal shown as "OLD TRIP". This shows how vibrations that affect the previous device have been mitigated in the new overpressure relief flap apparatus described here.

It is to be noted that the measured total tripping time of new overpressure relief flap apparatus (limiter), with respect to initiation of a short-circuit current (measured in CB compartment) is <NUM>, including the opening time of the flap and a maximum opening time of the circuit breaker (<NUM>). The requirement is less or equal to <NUM>, which has been met.

<FIG> serves to explain the problems caused by vibrations in existing systems, showing debouncing of the mobile contact of a microswitch during switching. Vibrations of the mobile contact slow the coil response on a voltage step unit, and thus prolong charging time. This so-called debouncing of mobile contact previously caused several voltage interruptions as shown in <FIG>, where interruptions of a duration <NUM> and longer, cause current drop in the charging characteristic (see. events <NUM> and <NUM>), and to an interrupted trigger signal. The new overpressure relief flap apparatus described here overcomes these issues.

Claim 1:
An overpressure relief flap apparatus for a medium or high voltage switchgear, the apparatus comprising:
- a lever (<NUM>); and
- a microswitch (<NUM>);
wherein, the lever is attached to an overpressure relief flap of a compartment of a switchgear;
wherein, the microswitch is mounted to a frame of the compartment of the switchgear;
wherein, when activated the microswitch is configured to transmit a trip signal to a circuit breaker of the switchgear;
wherein, the lever is configured to activate the switch when the overpressure relief flap opens; and
characterised in that the lever is configured to enable a user to operate the lever by hand to bend the lever to activate the microswitch with the lever when the overpressure relief flap is in a closed position.