GB1567519A - Electrical capacitor - Google Patents

Description

(54) AN ELECTRICAL CAPACITOR (71) We, LICENTIA PATENT VER WALTUNGS G.mb.H., of 1 Theodor Stern-Kai, 6 Frankfurt/Main 7(). Federal Republic of Germany, a German body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an electrical capacitor which is not impregnated and which is sheathed in plastics, the capacitor winding of which comprises insulating material foils which have been vapour deposited on one side with metal.

It is known to sheathe capacitor windings in plastics by means of injection moulding or casting. The sheathing serves as a protection against mechanical damage from outside, and against penetration by moisture or, in wet electrolyte capacitors, against leakage of the electrolyte. The sheathing is thus provided instead of a metal casing.

Capacitors for fairly high voltages, for pulse loads or fairly high power are incorporated in the usual manner into metal casings and are impregnated with a suitable impregnating means, e.g. mineral oils or chlorophenols etc. in order to avoid pockets of alr or air bubbles and thus to avoid the incidence of glow discharge or to displace it to higher voltages. In various cases, the impregnating means should have particular chemical compositions which release suitable substances when there is disruptive discharge in the capacitor winding, these substances should be non-reactive with the reaction products arising during disruptive discharge.

The present invention seeks to considerably lower the manufacturing costs of power capacitors as far as possible while retaining the electrical values and of saving on expensive method steps.

According to the invention, there is provided an electrical non-impregnated capacitor comprising a capacitor winding formed by insulating foil on one side of which a vapour deposited metal layer is formed and a plastics sheathing, surrounding the capacitor winding which shrinks during or after sheathing.

A two component product is suitable as a plastics, such as polyurethane, epoxy resins or polyester resins. Polypropylene is preferably used for the insulating material foil.

This may be vapour-deposited on one side with aluminium as a capacitor coating.

Previously the view was held that in order to manufacture capacitors for fairly high voltages and powers. an impregnating means could not be dispensed with and moreover no vapour-deposited layers could be used. Surprisingly however it has been found that this is possible if corresponding pressure is applied to the winding and that it is sufficient here to encapsulate or injection mould it with a suitable plastics producing a constant pressure exercised on the capacitor winding during hardening. In order to manufacture capacitors of fairly large power and high voltage in a manner known per se several capacitors in accordance with the invention may be connected in parallel and/or in series.As a result of this, a single winding size may be manufactured for all types of capacitor and these may be constructed purely in accordance with the invention or if necessary several uncast or cast capacitor windings may be cast together to form a capacitor module and these modules may be used as the basis for all capacitor sizes required. As a result, a dry power capacitor made up of windings encapsulated in plastics can be obtained whereby the individual elements or modules may be mass-produced in a simple manner, may be stored for any desired length of time and if necessary may be assembled and connected to form capacitors of the desired power and voltage.

The invention will now be described in greater detail, by way of example, with reference to the drawings in which: Figure I shows a capacitor in accordance with the invention from the side and in section Figure 2 shows the construction of individual layers; Figure 3 shows a capacitor module in accordance with the invention in plan view; Figure 4 shows the module from the side and in section; Figure 5 shows a power capacitor made up of several modules in accordance with the invention in a common casing as shown from the side and in section; Figure 6 shows a portion of the circuit of Figure 5; Figure 7 shows a circuit plan for singlephase alternating current, and Figures 8 and 9 each show a circuit plan for three-phase current.

A capacitor winding is designated 1 in Figure 1, said winding comprising insulating foils which have been coated with metal, by vapour-deposition, and wound up on to a hollow mandrel 2 of a winding whereby the coatings project alternately up to one edge or terminate before the edge, as is shown in enlarged view in Figure 2. One capacitor coating 3, terminating at the top, which is applied to the insulating foil 4. is contacted by a contact layer 5 which has been injection-moulded or pressed and is provided with a terminal part 6. The corresponding coating 7 of the insulating foil 8 extends as far as the lower face. is contacted there by means of an applied contact layer 9 and is provided with a terminal conductor 10 which passes through the hollow mandrel 2 to the upper face and extends beyond this latter.

In accordance with the invention the winding 1 is not impregnated and is encapsulated or injection-moulded in a plastics sheathing 11 whereby a plastics is used which exercises pressure on the capacitor winding 1 after age-hardening and/or cooling off. Preferably substances are used for the plastics sheathing which have a high heat resistance, a favourable coefficient of thermal conductivity. a high dielectric breakdown strength and low dielectric losses, so that a high voltage resistance and a high glow voltage are ensured. These substances are preferably the reaction product of the mixture of two components or thermosetting plastics. In order to produce a moderate pressure, polyurethane is used in an advantageous manner. in order to produce a medium pressure. it is advisable if epoxy resin is used and in order to produce a strong pressure a polyester resin is preferably used.Mixtures of the individual abovementioned substances are also possible. Furthermore, it may be advisable to add materials which ensure good heat conduction but which do not worsen the remaining features, at least not significantly, e.g. aluminium oxide or magnesium oxide powder or particles of a suitable size and form.

A module assembled in accordance with the invention into a fairly large construction unit from several encapsulated capacitor windings is shown in Figures 3 and 4. Thus several capacitor windings 1 of, for example, approximately 1 kVAR and 400 V alternating voltage are assembled to form a module at a spacing from each other and adjacent each other in a row and possibly several of these rows are arranged at a spacing one behind the other and are provided jointly with a plastics sheathing il.

In the embodiment, three rows are arranged in one plane and their upper or lower faces are each connected to a busbar 12, 13, 14, 15. 16, 17 respectively so that six connections are present which are designated for example U, V, W, X, Y, Z.

A continuous bore 18 or an opening is provided in the plastics core between four adjacent capacitor windings 1, through which opening the lower connections are passed upwards, in this case connections X, Y, Z.

The bores 18 at the same time serve for improved dissipation of heat and distribution of pressure of the pressure exercised on the windings 1 by the plastics sheathing 11.

Moreover. they may serve to connect several modules together by means of a fixing element 24, e.g. a rod, engaging through said modules, this may take place for example by means of screw connection and/or by fixing the module on a carrier or in a container. By stacking several of these modules and respective connection of the same terminals, a capacitor of high power may be obtained. This type of embodiment is shown in Figure 5.

In this embodiment in accordance with the invention six modules in accordance with Figures 3 and 4 are stacked one on top of each other by interposing spacers 19 and all of the terminals X, all Y etc. are joined together to lead wires 20 which pass out of the casing cover 21 of a casing 22. The spacers 19 preferably comprise spacing rings which are placed over the bores 18 and may rest on their edge (cf. the cut-away portion of Figure 5). It is advantageous if a narrowed part 23 engages in the bores 18.

In the plan view there are possibilities for connection in accordance with Figure 7 for single-phase alternating current. there are possibilities of connection for delta connection with three-phase current in accordance with Figure 8 and for star connection with three-phase current in accordance with Figure 9, as are already known per se for terminal boards in motors and transformers.

In order to increase the operating voltage in modules lying one on top of each other, the output of one module may be connected to the input of the following module. The container 22 which may comprise metal or plastics may be filled advantageously with a substance, preferably a liquid, which permits good dissipation of the heat from the heat loss arising in the modules. However a high value impregnating means need not be used as in previously used impregnated capacitor windings since this is not under such strong loading here.

By using these plastics blocks with cast capacitor windings therefore, the most varied of power capacitors may be manufactured with one and the same type. These may be manufactured as a mass-produced product and may be stored and may be assembled in a very short period of time depending on the task of the appropriate capacitor type as vaccum processes and impregnations are no longer necessary.

It has proved to be particularly favourable to use polypropylene foils vapour-deposited on one side with aluminium as insulating foils and capacitor coatings. Capacitors made from this material without impregnating means are known and are used as motor and illuminating capacitors, i.e. for voltages up to approximately 400 V alternating voltage. Fairly high voltages, particularly the required test voltage of over 1000 V cannot be carried by these capacitors. However it has been proved that when using an external pressure on the winding a test voltage of far above 1000 V may be achieved.

The glow voltage rises with the pressure under which the thin layers of air which cannot be completely avoided are located between the plastics foils as the result of the shrinking pressure of the plastics casing (plastics sheathing). The average free path length of the ionized gas molecules is reduced as is known with the pressure so that the collision ionization becomes less likely. In comparison to the previous power capacitors, the glow current of the MKP winding under pressure seems to have different importance and value. While with the impregnated metal foil power capacitors.

the glow current emanates from a few weak points in the system, for example chiefly from edge areas having an increased field strength, from flaws in the dielectric (plastics foil, paper foil) or from metal edges of the surface of the metal foils, the test results in the described MKP windings point to a more uniform and larger area glow current.

In other words while the glow current originates from a few quite limited local areas in impregnated foil capacitors, with MKP windings large areas are involved. As the current density is a decisive factor in damaging the dielectric (foil) a glow current of equal size may lead to damage in an impregnated metal foil capacitor, while the MKP winding does not exhibit any sort of damage. Thus power capacitors may also be implemented using a cheap nonimpregnated capacitor and the individual windings or modules may furthermore be used as previously as motor and illuminating capacitors as they are not more expensive in terms of price but may, if necessary, become even cheaper as a result of mass-production for use in power capacitors and as a result of the possibility of being able to omit the previously necessary metal shielding can.

In accordance with an advantageous further refinement of the invention it is advisable if each individual capacitor winding 1 is equipped with a heat detector as a safeguard against melting in the region of the upper face. It has been proved in surprising manner that a capacitor in accordance with the invention responds to heat detectors as a result of encapsulating with plastics despite the use of self-healing vapour-deposited metal coatings and polypropylene as a carrier.

This experimentally observed behaviour may be explained bv fairlv high conversion of energy in a MKP winding under high pressure. In fact. substantially wider disruptive discharge channels are observed here than for example in normal MP windings.

This resultant substantially larger conversion of energy is expressed in an external current which may cause a heat detector to respond in time to prevent melting.

Because of the good properties of the capacitors in accordance with the invention, such as there being no danger of explosion, lack of arcing. no leakage of impregnating fluid, said capacitor may be housed in a common switchbox together with other switching and control devices, above all such as an electronic reactive power controller. special air-type contactors and NH safety devices prior-connected to capacitors.

WHAT WE CLAIM IS: 1. An electrical non-impregnated capacitor comprising a capacitor winding formed by insulating oils on one side of which a vapour deposited metal layer is formed and a plastics sheathing. surrounding the capacitor winding which shrinks during or after sheathing.

2. A capacitor according to claim 1, wherein the insulating material foils comprise polypropylene.

3. A capacitor according to claim 1 or 2, wherein a plurality of capacitor windings are arranged at a spacing from each other in a row. the plastics sheating surrounding the entire row.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (23)

**WARNING** start of CLMS field may overlap end of DESC **. three-phase current in accordance with Figure 9, as are already known per se for terminal boards in motors and transformers. In order to increase the operating voltage in modules lying one on top of each other, the output of one module may be connected to the input of the following module. The container 22 which may comprise metal or plastics may be filled advantageously with a substance, preferably a liquid, which permits good dissipation of the heat from the heat loss arising in the modules. However a high value impregnating means need not be used as in previously used impregnated capacitor windings since this is not under such strong loading here. By using these plastics blocks with cast capacitor windings therefore, the most varied of power capacitors may be manufactured with one and the same type. These may be manufactured as a mass-produced product and may be stored and may be assembled in a very short period of time depending on the task of the appropriate capacitor type as vaccum processes and impregnations are no longer necessary. It has proved to be particularly favourable to use polypropylene foils vapour-deposited on one side with aluminium as insulating foils and capacitor coatings. Capacitors made from this material without impregnating means are known and are used as motor and illuminating capacitors, i.e. for voltages up to approximately 400 V alternating voltage. Fairly high voltages, particularly the required test voltage of over 1000 V cannot be carried by these capacitors. However it has been proved that when using an external pressure on the winding a test voltage of far above 1000 V may be achieved. The glow voltage rises with the pressure under which the thin layers of air which cannot be completely avoided are located between the plastics foils as the result of the shrinking pressure of the plastics casing (plastics sheathing). The average free path length of the ionized gas molecules is reduced as is known with the pressure so that the collision ionization becomes less likely. In comparison to the previous power capacitors, the glow current of the MKP winding under pressure seems to have different importance and value. While with the impregnated metal foil power capacitors. the glow current emanates from a few weak points in the system, for example chiefly from edge areas having an increased field strength, from flaws in the dielectric (plastics foil, paper foil) or from metal edges of the surface of the metal foils, the test results in the described MKP windings point to a more uniform and larger area glow current. In other words while the glow current originates from a few quite limited local areas in impregnated foil capacitors, with MKP windings large areas are involved. As the current density is a decisive factor in damaging the dielectric (foil) a glow current of equal size may lead to damage in an impregnated metal foil capacitor, while the MKP winding does not exhibit any sort of damage. Thus power capacitors may also be implemented using a cheap nonimpregnated capacitor and the individual windings or modules may furthermore be used as previously as motor and illuminating capacitors as they are not more expensive in terms of price but may, if necessary, become even cheaper as a result of mass-production for use in power capacitors and as a result of the possibility of being able to omit the previously necessary metal shielding can. In accordance with an advantageous further refinement of the invention it is advisable if each individual capacitor winding 1 is equipped with a heat detector as a safeguard against melting in the region of the upper face. It has been proved in surprising manner that a capacitor in accordance with the invention responds to heat detectors as a result of encapsulating with plastics despite the use of self-healing vapour-deposited metal coatings and polypropylene as a carrier. This experimentally observed behaviour may be explained bv fairlv high conversion of energy in a MKP winding under high pressure. In fact. substantially wider disruptive discharge channels are observed here than for example in normal MP windings. This resultant substantially larger conversion of energy is expressed in an external current which may cause a heat detector to respond in time to prevent melting. Because of the good properties of the capacitors in accordance with the invention, such as there being no danger of explosion, lack of arcing. no leakage of impregnating fluid, said capacitor may be housed in a common switchbox together with other switching and control devices, above all such as an electronic reactive power controller. special air-type contactors and NH safety devices prior-connected to capacitors. WHAT WE CLAIM IS:

1. An electrical non-impregnated capacitor comprising a capacitor winding formed by insulating oils on one side of which a vapour deposited metal layer is formed and a plastics sheathing. surrounding the capacitor winding which shrinks during or after sheathing.

2. A capacitor according to claim 1, wherein the insulating material foils comprise polypropylene.

3. A capacitor according to claim 1 or 2, wherein a plurality of capacitor windings are arranged at a spacing from each other in a row. the plastics sheating surrounding the entire row.

4. A capacitor according to claim 3,

wherein a plurality of rows are cast to form a module.

5. A capacitor according to claim 4, wherein the plastics sheathing material has bores running continuously parallel to the axis of and between the capacitor windings in a module containing a plurality of capacitor windings.

6. A capacitor according to claim 5, wherein the capacitor windings are provided with a contact layer at the end faces, with capacitor windings of a module, arranged in a row, the lower contact layers respectively and the upper contact layers of a row are connected together respectively by means of a busbar.

7. A capacitor according to claim 6, wherein each busbar is provided with a connector for providing connection thereto.

8. A capacitor according to claim 7, wherein the bores or a part of the bores serve as passages for the connectors.

9. A capacitor according to claim 7, wherein the connectors are provided in two rows of bores such that all of the inputs lie in one row and all outputs lie in the other row.

10. A capacitor according to claim 9.

wherein the terminals of one row are arranged in the series sequence I. II. III and the outputs are arranged in the other row in the series sequence III. I. II.

11. A capacitor according to any one of claims 4 to 10, wherein a plurality of modules are arranged at a spacing from each other one above each other by interposition of spacers.

12. A capacitor according to claim 11, when appendent directly or indirectly to claim 4, wherein the range spacers are provided in the region of the bores.

13. A capacitor according to claim 12.

wherein annular range spacers are provided around the bores.

14. A capacitor according to claim 13, wherein the annular range spacer has at least one extension one one side which engages in a bore.

15. A capacitor according to claim 5. or any claim appendent directly or indirectly thereto, wherein a fixing element passes through at least one bore.

16. A capacitor according to claim 15, wherein the fixing element serves to fix one module or the modules on one carrier or casing and/or to hold several modules together.

17. A capacitor according to claim 7. or any claim appendent directly or indirectly thereto. wherein the connectors serve to hold several modules together.

18. A capacitor according to claims 3. 4 to 17, wherein one or several modules are housed in a casing and the casing is filled with an insulating means.

19. A capacitor according to claim 18, wherein a liquid insulating means is provided.

20. A capacitor according to any one of claims 1 to 18, wherein the or each capacitor winding is sealed off with a melting protection device.

21. A capacitor according to claim 20, characterised in that the melting protection device is provided in the region of the upper face.

22. A capacitor according to any one of claims 1 to 21, characterised in that it is housed in a common switch panel together with an electronic reactive power controller, air-tight contactors and prior-connected NH safety devices.

23. An electrical capacitor substantially as described herein with reference to the drawings.