DE2659903C3 - Electrically insulating liquid - Google Patents

Description

Many electrical devices need an electrically insulating liquid as Isolation medium. This liquid has a significantly higher breakdown resistance than Air. Replaces the existing between conductors in an electrical device or apparatus Air through such a liquid, then the breakdown voltage of the electrical Increase device. The ever increasing refinement of electrical equipment leads to that the various electrical devices are operated at increasingly higher voltages. This means that the electrically insulating liquids used in such devices always are subject to increasing loads. Because of these problems must of course better such liquids are sought.

With the exception of certain special uses, the polychlorinated are biphenyl compounds (commonly referred to as PCB compounds) since the 1930's, as mineral oil In certain applications these PCB connections have been replaced by the normal electrical ones insulating liquid in electrical devices. As electrically insulating liquids were various other liquids have also been proposed, including some polysiloxanes. For this purpose, for example, US-PS 2,377,689 and 3,838,056 and GB-PS 899 658 and 899661 referenced. The use of polyorganosiloxanes as an electrically insulating liquid is distant / also from DE-AS 1189170, 1261573 as well 1 106821 known, with the addition of ketones as a stabilizer for the organopolysiloxane is described. Recently was found that the PCB compounds have a negative impact on the environment and it is therefore used worldwide searched for a suitable replacement for these compounds.

For example, a corona or partial discharge is an essential factor that can lead to destruction and failure of capacitors and other amperage correction devices. A capacitor operated at corona voltage only lasts a few minutes or hours instead of it

waited 20 years, A capacitor that comes with a

suitable electrically insulating liquid

• is impregnated to speak · is up to at least that

Twice the calculated stress free of coro-

na discharge. Becomes an electrically insulating liquid subjected to increasing stress during operation, then you come up to one Point at which partial strike-through occurs. The voltage at which the capacitor suddenly increases

ίο a corona discharge breaks through is called the corona initial voltage (CIV). This voltage depends on the speed at which the voltage is applied. The different liquids are, in terms of their sensitivity to the rate of voltage increase, very different from each other. However, the corona discharge stops again after the voltage has been reduced. This corona extinction voltage (CEV) is not a fixed value for every liquid, but a '; function on the intensity of the corona voltage before the decrease in the Tension. The best results are obtained when both the CIV value and the CEV value are as close as possible are high and as close together as possible.

The transformers and capacitors are made with the well-known electrically conductive liquids However, this requirement - even if they already contain stabilizing additives such as ketones - still applies not in the way desired and required today

jo measured fair.

The invention is therefore based on the object of creating an electrically insulating liquid whose Values for the initial corona voltage and the corona extinction voltage are very high and particularly

j ^r ] ders are close together.

This object is achieved by the invention specified in the claim.

The liquid polyorganosiloxanes suitable according to the invention are composed predominantly of siloxane _{units of the formula R 2} SiO, and they can also contain smaller amounts of siloxane units of the formulas R ₃ SiO ₁ ^, RSiO ₂ and SiO ₄ ^. Liquid polyorganosiloxanes of the formula RjSiO (R ₂ SiO) ^ SiR ₃ are of particular interest. In the proposed

mentioned formulas, the substituents R are preferably hydrocarbon or halogenated hydrocarbon radicals. Examples of suitable substituents R are methyl, ethyl, propyl, butyl, hexyl, decyl, dodecyl, octadecyl, vinyl, allyl, cyclohexyl, phenyl,

-, ο Xenyl, Tolyl, XyIyI, Benzyl, 2-Phenäthyt, 3-Chlorpropyl, 4-Bromobutyl, 3,3,3-Trifluopropyl, Dichlorphenyl or α, α, α-Trifluortolyl. The substituent R preferably contains 1 to 6 carbon atoms, methyl, vinyl or phenyl being particularly preferred.

The electrically insulating liquid used according to the invention advantageously contains more than 50% liquid polyorganosiloxane, and this preferably makes up 80 to 99.5% by weight of that according to the invention used liquid. These liquid po-

(, o lyorganosiloxanes are well known and in trade worldwide available materials.

In the present case, all of the nitro compounds listed are suitable as nitro-substituted hydrocarbons, However, mononitro compounds having 1 to 10 carbon atoms are particularly preferred. The liquids according to the invention can also contain small amounts of customary additives such as hydrogen chloride scavengers, corrosion inhibitors and

other conventional additives normally used in such fluids, as long as these do not adversely affect the mode of action of these liquids,

Except for capacitors and transformers, the electrically living ones used here can be used Liquids are also beneficial for other electrical devices such as electrical cables, rectifiers, Electromagnets, switches, fuses and circuit breakers and also as coolants and isolators for electrically isolating devices such as transmitters, receivers, rewind coils, sound buoys or toys are used. The methods of using the electrically insulating Liquids in these different types of applications (for example, where they are used as a liquid reservoir or used as impregnating agents) are known to the person skilled in the art.

The invention is further illustrated by the following example. All parts and percentages contained therein are based on weight and all viscosity values are at a temperature of 25 ° C measured unless otherwise stated.

example

An examination method for assessing electrically insulating liquids is being developed, which should agree well with the test results obtained using test capacitors receives. The essential component of the device used for this experiment is a Biddle corona detector with a manually operated variac control. The trial is best from a cylindrical glass container. The base of the cell is a plastic filled with ceramic and contains a metal plate made of stainless steel that is directly earthed. The cover of the container is a Stainless steel plate connected to a high-voltage electrode that can be adjusted using a micrometer at the end of which is a steel phonograph needle. The point of this needle is Placed 0.0635 cm above the grounded foot. In the high voltage line connected to the electrode there is a resistance of 1.67 X 10 "ohms. This resistor is used to limit the current.

During the experiment, a few cubic centimeters of the liquid to be examined will be in the container given, which is then provided with the cover. With increasing tension, it comes to a partial discharge between the tip of the electrode and the grounded plate. This discharges electricity, the applied voltage decreasing to below the discharge voltage. Will no electricity dissipated, then there is the applied voltage again to partial discharge potential, current is discharged again through discharge, whereupon the Process repeated. As a result, ej-

The electricity is switched on and off very quickly, which means that there is never a total breakdown of the liquid can occur.

During operation, the applied voltage is slowly increased. The partial discharges that occur are observed one on the oscilloscope of the corona detector. The point at which the elliptical display on the grid is flooded by discharges and at which from the cell there is a constantly audible crack is applied as the initial corona voltage (CIV). The rate of increase in the applied Voltage may be a few hundred volts per second. After determining the CIV value, the voltage is slowly lowered until the partial cessation of the discharge

-M gen again an elliptical display on the grid sees. The point at which this occurs is also recorded and this is the corona extinction voltage ' (CEV).

A series of electrically insulating fluids is

2 '> liquids which essentially consist of a liquid trimethylsilyl endblocked polydimethylsiloxane with a viscosity of 50 cSt and of various nitro-substituted hydrocarbons in various amounts. These liquids are examined according to the above-mentioned method. The special nitro-substituted hydrocarbons used for this purpose, those used

'fviciigeir (the remainder is - in each case the siloxane) and the test results obtained are based on the following

»> From the table. A number with a (+) after it means that the attempt is aborted at this point and the actual value is something is greater than the specified value.

Nitro lot CIV CEV link (Wt .-%) (in KV) (in KV) A * no 0 15.6 14.8 B. Nitrobenzene 5 13.0 14.5 2.5 20.0 18.8 1 19.2 17.6 C. 2-nitropropane 10 19.8 17.0 5 18.4 17.6 2.5 20.0 + 18.0 1 20.0 + 19.0 D. o-nitrotoluene 1 19th 18th E ** o-nitrodi- <1 18th 16.4 phenylamine ♦ - comparison · * - Ocsaturated solution

Claims (2)

Claims; 1, electrically insulating liquid, consisting of a liquid polyorganosiloxane and a small amount of a siloxane-soluble nitro-substituted aromatic hydrocarbon, nitro-substituted aliphatic hydrocarbon, nitro-substituted cycloaliphatic hydrocarbon or a mixture thereof according to patent 2608397, characterized by a viscosity of 5 to 500mm ^s / s at 25 ° C and a content of 0.5 to 20 percent by weight of the nitro-substituted hydrocarbon. 2. Use of the electrically insulating liquid according to claim 1 for the insulation of Transformers and capacitors.