FR2536598A1 - Electrical capacitor block with inductive surge current stage - Google Patents

Abstract

An electrical capacitor block has a group of cylindrical capacitor elements; three in the case of three phase applications, with interconnecting inductive windings on the outer surface. The capacitor assembly is located within a thin walled metal tube that is in contact with the windings. The windings are arranged with a primary coil and a secondary winding that operates as a short circuit winding to produce considerable attenuation of any current surge condition. The attenuation of such surge transients during switch on results in an enhanced operational life. (First major country equivalent to ES8308652)

Description

 The invention relates to a block comprising one or more electric capacitors in a metal case of cylindrical shape.

 The use of capacitors in industry is well known, in particular for correcting the power factor in installations or on electrical devices which are highly inductive. We know that, in this application, when a capacitor is connected directly to the mains, it absorbs a high intensity current for a very short time (duration of steady state establishment), after which it adopts normal function .

 In the case of metallized film capacitors, the strong transient currents thus produced during the lifetime of the capacitor may damage the seal between the internal metal frame and the metal sprayed on the head of the capacitor.

 To keep this transient current within admissible limits, it is known to mount a choke or shock coil in series with the winding of the capacitor. In order for it to act effectively at high transient frequencies at the time of connection (of the order of kHz), this coil does not have a ferromagnetic core.

 The inductive shock coil is normally placed apart from the capacitor box and even outside the case or other container (made of metal or another material) in which the capacitor is placed.

 This arrangement, although it is functionally valid, naturally has drawbacks with regard to the wiring work and the bulk.

 One of the objects of the invention is to provide a block of capacitors where the respective shock coils are combined with the shells of the capacitors and are arranged inside the common shoemaker of the block.

 The invention aims at the same time to considerably increase the efficiency of the coils, by increasing the advantages drawn from normal shock coils.

 Girlfriend industrial installations' generally use three-phase current, the rest of this memo will relate to a block with three capacitors, one for each phase, which are placed in a common box, although a block according to the invention may include any other number of capacitors and coils.

 According to the invention, each shock coil consists of a winding which is formed - by an operation which is easy to perform and which is held in place on the case of the capacitor concerned. In other words, the winding is coaxial with the capacitor and its turns are very close to the common shoemaker, generally cylindrical, which covers the assembly. This outer shoemaker is a metal cylinder according to a preferred embodiment.

 In addition to the important advantages of a simpler production, a reduction in the overall size and a much more convenient positioning of the coils, this arrangement according to the invention provides a very marked improvement in the performance of the whole because of the following.

 The arrangement of the shock coil around the capacitor and near the metal tube forming the common boot creates a magnetic coupling between the winding forming the coil and the metal wall of the tube, which acts as a secondary winding formed by a single coil short-circuit> which greatly reduces the quality factor- (Q) of the shock coil. Therefore, during the establishment time, ot circulates a current of high overcurrent, an important resistance is formed which absorbs most of the energy likely to be dissipated by resistance during this transient regime of connection to the source current. The part represented by the head contacts of the capacitor in the total resistance and the heating of these contacts are thus greatly reduced.

 Following this establishment regime, the phenomenon described has only a negligible effect and the block, now operating at industrial frequency, works practically as pure capacity.

 The electrical effect described and claimed by the invention could also be obtained by placing the coils not on the capacitors but between them, although always so as to establish a magnetic coupling with the tube forming the common box or with the coils. capacitors.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows of a nonlimiting exemplary embodiment, as well as from the appended drawings, in which
- Figure 1 is a perspective view of a three-phase capacitor block and equipped with shock windings according to the invention, each arranged between a capacitor and the metal case of the assembly, boltier which is shown separately so that the interior layout is better visible;
- Figure 2 is an axial section on a larger scale of this block in the assembled state.

 As can be seen in the drawings, a block according to the invention comprises a series of capacitors or elements 1, which are three in number in three-phase applications, in the outputs of each of which is connected an inductive winding 2 arranged concentrically around of the capacitor 1 concerned.

The windings 2 are also very close to the internal wall 3 of the casing or of the common boot 4 when the capacitors are placed therein. The case 4 is made of a metal tube according to a preferred embodiment
With this arrangement, each of the windings 2 forms the primary winding of a coil whose secondary is short-circuited and is formed by the bolt-holder 4 which envelops the assembly,
As described in the above; thus obtaining, at the establishment regime, very advantageous effects as to the longevity of the block, in addition to the fact that it is very compact, the invention also reducing the space requirement and the wiring work.

 According to other embodiments, not shown, the shock winding 2 of each capacitor 1 is electromagnetically coupled to a short-circuited metal secondary in the form of a sheet, a disc, a washer or the like.

Claims (3)

R E V E N D I C A T I O N S 1. Block comprising one or more electric capacitors to correct the power factor, in particular of the type comprising shock windings connected in series with each of the block capacitors, characterized in that each shock winding (2) is electromagnetically coupled to a secondary metal circuit in short circuit, the winding (2) being formed of a series of turns arranged coaxially on the body or the shell of the capacitor and near the internal surface (3) of the envelope or the metal shell (4) of cylindrical shape which covers the assembly. 2. Block according to claim 1, wherein the secondary circuit is formed by the wall of the common metal shoemaker (4) of the block. 3. Block according to claim 1, wherein the secondary circuit is formed by a sheet, a disc, a washer or the like.