Patent Description:
Circuit breakers and switches in switchgears, such as ring main units, are operated by drives comprising spring type mechanisms, magnetic or pneumatic actuators etc. or a combination thereof. During energizing and operation of the drive, several different mechanical parts move and their surfaces slide against each other at high speed or they stay in contact with each other during energy storage. To prevent wear of the mechanical contact surfaces and to provide low friction during movement, the parts are conventionally lubricated with grease.

Grease lubricated drives need maintenance in form of re-greasing or replacement in certain time intervals as the lifetime of the grease is limited compared to the <NUM>-<NUM> years of lifetime of the switchgears. Moreover, the right type of grease needs to be chosen, depending on the climate conditions of the place where the switchgear is positioned when operating. Additionally, grease is only useful within a limited temperature range. In case of aged grease or wrong type of grease there is an increased risk for failure of the drive mechanism which prevents the switching operation of the switchgear.

As an alternative to metal drives, there are polymer drives available for low energy switching applications, but they face fatigue and low/high temperature operation strength related issues.

The all polymer drives are used for low energy applications and still have to scale up when higher currents and voltages are involved during switching. The fatigue curve (SN diagram) for polymers (for e.g. epoxy) shows much lower strength even at <NUM><NUM> cycles, which is the operating requirement for M2 qualification in a switchgear certification. There are some inherent limitations (material deterioration) of polymer drives when exposed to outdoor environment. There is also much more change in structural properties compared to metals at ambient temperatures of -<NUM> or below and of <NUM> and above, limiting the usefulness of polymer drives.

Document <CIT> discloses a device according to the preamble of claim <NUM>.

It is an objective of the present invention to provide an improved drive for an electrical switch, with reduced maintenance need compared to greased metal drives, and with improved strength and temperature resistance compared to polymer drives.

Proposed is a metal drive which may be regarded as a hybrid drive, in which a core of at least one of the parts of the drive is metal to provide strength, while at least one surface of the part is coated with a polymer material to provide protection against the ambient environment and improved performance. The moving, e.g. sliding and/or rolling, parts of the drive may be at least partly coated with the polymer coating discussed herein, while some other surfaces may be coated by e.g. a combination of polymer and/or metallic coating providing resistance against material degradation of the core metallic structure of the drive parts. An idea is to combine the strengths of metal and polymer drives in a hybrid drive, where the core is made up of metal (having relatively high strength and durability) and a surface is polymer-based providing lower friction and reduced maintenance need. Wear and corrosion resistance may be provided over the entire life-time of the drive and in different environmental conditions such as moderate, arctic or tropic climates.

According to an aspect of the present invention, there is provided a metal drive according to claim <NUM>.

According to another aspect of the present invention, there is provided a switchgear comprising an embodiment of the metal drive of the present disclosure, and comprising the electrical switch.

By means of the polymer coating, a dry lubricant is provided, reducing or eliminating the need for lubrication maintenance during the lifetime of the drive, while maintaining the advantages of a metal drive over a polymer drive by means of the metal cores of the drive parts.

<FIG> illustrates a switchgear <NUM> comprising a drive <NUM> for operating an electrical switch of the switchgear. The drive may be actuated in any conventional way, e.g. spring, magnetically or pneumatically actuated. The drive <NUM> comprises a plurality of parts <NUM> which are arranged to move in relation to each other during operation of the drive. The drive <NUM> is a metal drive, implying that at least the core <NUM> of each of the parts is of a metallic material. Two parts <NUM> which are arranged to move in relation to, and in contact with, each other each comprises a contact surface <NUM> for making contact with the corresponding contact surface <NUM> of the other part <NUM>. At least one contact surface <NUM> of at least one part <NUM> of the drive <NUM> has a polymer coating <NUM> of a polymer material <NUM>. The polymer coating is arranged to act as a dry lubricant. That the contact surface <NUM> has a polymer coating <NUM> implies that the contact surface is (at least partly) provided by the polymer coating, since the polymer coating <NUM> provides an outermost surface of the part <NUM>, which then becomes the contact surface <NUM>. In some embodiments, the coated part <NUM> is coated only where it is arranged to contact another part <NUM> of the drive <NUM>. Alternatively, in some other embodiments, the coated part <NUM> is coated also on other surfaces, the metal core <NUM> being partly or fully enclosed by the polymer coating <NUM>.

The polymer coating <NUM> is applied directly on a metallic material <NUM> of the part <NUM>. Typically, the metallic material <NUM> is of the metal core <NUM>, implying that the polymer coating is applied directly onto the metal core, without any intermediate layer, but in some embodiments, the metallic material <NUM> may be provided by intermediate layer <NUM> provided between the metal core <NUM> and the polymer coating <NUM>, e.g. e.g. an anti-corrosion layer such as a nickel containing layer. Metallic anti-corrosion nickel layers are conventionally used.

In the example of <FIG>, two parts <NUM> of the drive <NUM> are shown, a first part 2a and a second part 2b. The first part 2a comprises a first contact surface 3a arranged to move (as indicated by the downward pointing arrow in the figure) in relation to, and in contact with, a second contact surface 3b of the second part 2b. Each of the first and second parts 2a and 2b comprises a metal core 4a and 4b. The first contact surface 3a has a dry lubricant polymer coating <NUM> of a polymer material <NUM> applied directly on a metallic material <NUM>, e.g. of the metal core 4a or of a metallic intermediate layer <NUM>.

Often, the second contact surface 3b is metallic, e.g. of the metal core 4b or of a metallic coating <NUM>. However, in some embodiments, also the second contact surface 3b has a dry lubricant polymer coating <NUM> of a polymer material <NUM> applied directly on a metallic material <NUM>. The polymer material of the second contact surface according to the invention is different than, the polymer material of the first contact surface. Typically, the tribological properties when the two contact surfaces 3a and 3b move in contact with each other are improved when surface materials are different rather than the same, why it is preferred that the polymer coating <NUM> of the second contact surface 3b is of a different polymer material <NUM> than the polymer coating <NUM> of the first contact surface 3a. It is envisioned that it may in some applications be preferred with the second contact surface being of a polymer material <NUM> rather than being metallic, e.g. for improved tribological properties or reduced heat formation when the first and second contact surfaces move in contact with each other.

The drive <NUM> may have any number of parts <NUM> and any number of pairs of contact surfaces <NUM> arranged move in relation to, and in contact with, each other. In any of these pairs, at least one of the contact surfaces <NUM> may be provided by a polymer coating <NUM> as discussed herein. In case there is more than one pair of contact surfaces in the drive which are provided with a polymer coating <NUM>, the polymer material <NUM> may be the same for all coatings <NUM>, e.g. for simplifying the manufacture of the drive <NUM>, or the polymer material <NUM> of at least one of the coatings <NUM> may be different from at least one other of the coatings <NUM>. The use of different materials <NUM> allows the material <NUM> to be selected depending on the particular requirements on each contact surface, e.g. depending on the pressure, movement and/or temperature the contact surface is intended for.

Thus, in some embodiments of the present invention, wherein the drive <NUM> further comprises a third part <NUM> and a fourth part <NUM>, the third part comprising a third contact surface <NUM> arranged to move in relation to, and in contact with, a fourth contact surface <NUM> of the fourth part. Similar to the first contact surface, the third contact surface has a dry lubricant polymer coating <NUM> of a polymer material <NUM> applied directly on a metallic material <NUM>. In some embodiments, similar to the discussion about the first and second contact surfaces, also the fourth contact surface <NUM> has a dry lubricant polymer coating <NUM> of a polymer material <NUM> applied directly on a metallic material <NUM>, the polymer material of the fourth contact surface being the same as or different than, preferably different than, the polymer material of the third contact surface. As discussed above, the polymer material <NUM> of the third contact surface <NUM> is the same or different than, preferably different than, the polymer material <NUM> of the first contact surface 3a. Depending on the contact pressure and sliding speed of each mechanical contact in the drive <NUM>, a combination of different coating materials <NUM> can be used within the same drive <NUM>.

The polymer material <NUM> of any polymer coating <NUM> in the drive <NUM> may be any suitable polymer material. Since the drive is not involved in the conduction of an electrical current, that being handled by the switch of the switchgear, the polymer material does not have to be electrically conducting, and typically is electrically insulating though electrically conducting materials are not excluded.

The polymer material <NUM> may conveniently be or comprise a thermoplastic material or a thermosetting material, optionally comprising a filler material as an additive.

Examples of suitable thermoplastic materials <NUM> includes thermoplastic materials comprising or consisting of polyaryletherketones (PAEK), for instance polyether ether ketone (PEEK) or polyetherketone (PEK); fluoropolymers, for instance polytetrafluoroethylene (PTFE); ultrahigh molecular weight poly ethylene (UHWPE); polyamides (PA); polyimides (PI); and/or polyoxymethylen (POM). Preferably the polymer material comprises or consists of PEAK and/or PTFE.

Examples of suitable thermosetting materials <NUM> includes thermosetting materials comprising or consisting of an epoxy and/or phenolic varnish, preferably an epoxy varnish.

Examples of suitable filler additive includes a filler comprising or consisting of graphite, molybdenum disulphide (MoS<NUM>), tungsten disulphide (WS<NUM>) and/or PTFE, preferably MoS<NUM> and/or PTFE. A specific example of suitable polymer material <NUM> comprising a filler is an epoxy varnish comprising a MoS<NUM> and/or PTFE filler.

In some embodiments of the present invention, any or all polymer coating(s) <NUM> in the drive <NUM> has a thickness within the range of <NUM>-<NUM>, preferably within the range of <NUM>-<NUM>. The coating <NUM> may be applied to the part <NUM> using an automated coating process, e.g. including spray coating, drum coating or powder coating, depending on the polymer material <NUM> used.

In some embodiments of the present invention, the first contact surface 3a is arranged to move in relation to the second contact surface 3b by sliding or rolling, e.g. by sliding against the second contact surface. The same could apply for any further contact surface pairs in the drive <NUM>. Examples of rolling contact may be in a ball bearing, e.g. where at least one of the balls is coated with the polymer material <NUM>. Other examples of parts <NUM> include e.g. a spring actuator, or any part <NUM> arranged to be moved by an actuator e.g. a spring, magnetic or pneumatic actuator, in the drive <NUM>.

In some embodiments of the present invention, any of the respective metal cores <NUM> of the drive <NUM>, e.g. the metal core 4a of the first part 2a and/or the metal core 4b of the second part 2b are of made of steel. Steel can provide the strength and durability desired for the drive <NUM>. In case the part <NUM> is in the form of, or part of, a spring, the core <NUM> may be made of a spring steel.

<FIG> illustrates a switchgear <NUM> comprising an electrical switch <NUM> for switching an electrical current I having the voltage U. The switchgear <NUM> thus comprises the drive <NUM> discussed above, as well as the switch <NUM> (and possibly further switches <NUM>). The switchgear <NUM> may be any switchgear configured for breaking or switching a current I by means of the at least one switch <NUM>. The switchgear <NUM> may e.g. be configured for breaking or switching a current I having a voltage within the medium voltage range, e.g. within the range of <NUM>-<NUM> kV.

Claim 1:
A metal drive (<NUM>) for operating an electrical switch (<NUM>) of a switchgear (<NUM>), the drive comprising at least a first part (2a) and a second part (2b), the first part comprising a first contact surface (3a) arranged to move in relation to, and in contact with, a second contact surface (3b) of the second part;
wherein each of the first and second parts comprises a metal core (4a, 4b);
characterised in that
the first contact surface (3a) has a dry lubricant polymer coating (<NUM>) of a polymer material (<NUM>) applied directly on a metallic material (<NUM>); and
wherein also the second contact surface (3b) has a dry lubricant polymer coating (<NUM>) of a polymer material (<NUM>) applied directly on a metallic material (<NUM>), the polymer material of the second contact surface being different than the polymer material (<NUM>) of the first contact surface (3a).