DE2659903B2 - 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referred to as PCB compounds) since the 1930's, as mineral oil In certain applications these PCB connections have been replaced by the normal electrical ones insulating liquid in electrical devices.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 also known from DT-AS 1189170, 1261573 and 1106821, with the addition already in the latter 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 the expected 20 years. A capacitor filled with a suitable electrically insulating liquid is speaking impregnated is free of Coro up to at least twice the calculated stress na discharge. Becomes an electrically insulating fluid during operation of a growing bean subjected to stress, then you get to a point where partial breakdown occurs The voltage at which the capacitor suddenly breaks down to a corona discharge is called Coro initial voltage (CIV). This voltage depends on the speed with which de the voltage is applied. The different liquids are what their sensitivity to the rate of increase in voltage affects very different from each other. The corona discharge, but stops again after the voltage has been lowered. This corona extinction voltage (CEV) is not a fü every liquid has a fixed value but a function

2 » on the intensity of the corona voltage before the voltage drops. The best results are obtained when both the CIV value and the CEV value are as high as possible and as close together as possible.

r> The transformers and capacitors are made with the well-known electrically conductive liquids This requirement - even if they already contain stabilizing additives such as ketones - still not in the way we want and need today

jo measured fair.

The invention is therefore based on the object of creating an electrically insulating liquid, de ren values for the corona initial voltage and the corona extinction voltage are very high and special

Γι ders close together.

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

The invention suitable liquid Polyor ganosiloxane are composed mainly of SiO ₂ siloxane units of the formula R, and they may further also contain minor amounts of siloxane units de formulas R ₃ SiO _{1/2, RSiO? / 2} and SiO _4/2. Of particular interest are liquid polyorganosiloxanes of the formula RjSiO (R ₂ SiO) _x SiR ₃ . In the aforementioned 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, xylyl, benzyl, 2-phenethyl, 3-chloropropyl, 4-bromobutyl, 3,3,3-trifluoropropyl, dichlorophenyl or α, α, α-trifluorotolyl. The substituent R preferably contains 1 to 6 carbon atoms, with methyl, vinyl or phenyl being particularly preferred

«The electrically insulating liquid used according to the invention expediently contains more ah 50% liquid polyorganosiloxane, and this preferably makes 80 to 99.5% by weight of the erfindungsge measured the liquid used. These liquid buttocks

bo lyorganosiloxanes are well known and widely available in commerce widely available materials.

As nitro-substituted hydrocarbons, all of the nitroverbin mentioned are suitable in the present case fertilize, mononitro compounds with 1 to 10 ohms

_However, carbon atoms are particularly preferred. The liquids according to the invention can fer

Also contains small amounts of the usual additives such as hydrogen chloride scavengers and corrosion inhibitors

other conventional additives normally used in such fluids, provided that they do not adversely affect the mode of action of these liquids.

Except for capacitors and transformers, those used here can be electrically conductive 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 by weight and all viscosity values are at a temperature of 25 ° C measured unless otherwise stated.

example

An investigation method for assessing electrically insulating liquids is being developed, which should agree well with the test results obtained using test capacitors. The essential component of the device used for this experiment is a Biddle Corona detector with a manually operated Variac control. The test cell consists of a cylindrical glass container. The base of the cell is a ceramic-filled plastic and contains a stainless steel metal plate that is directly grounded. The cover of the container is a stainless steel plate which is connected to a high-voltage electrode that can be adjusted using a micrometer and at the end of which is a steel phonograph needle. The point of this needle is located 0.0635 cm above the grounded foot. The high voltage line connected to the electrode has a resistance of 1.67 X 10 ⁸ 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 the applied voltage is again at partial discharge potential. By discharge electricity is discharged again, whereupon the process is repeated. It comes to one as a result Very quick switching on and off of the current, 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 Voit per second. After determining the CIV value, slowly lower the voltage, until the partial cessation of the discharges leads to an elliptical display on the grid again sees. The point at which this occurs is also recorded and this is the corona extinction voltage " (CEV).

A number of electrically insulating liquids are produced, consisting essentially of a liquid trimethylsilyl endblocked polydimethylsiloxane with a viscosity of 50 cSt and made of various nitro-substituted Hydrocarbons exist in various amounts. These liquids will examined by the above-mentioned method. The special nitro-substituted ones used for this purpose Hydrocarbons, the amounts of them used (the remainder is the siloxane in each case) and the amounts involved The test results obtained are shown in the following 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 quantity CIV CEV

compound (% by weight) (in KV) (in KV)

A * no 0 15.6 14.8 B. Nitrobenzene 5 18.0 14.5 2.5 20.0 18.8 I. 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 ** = Saturated solution

Claims (2)

Patent claims: 1. Electrically insulating liquid, consisting of a liquid polyorganosiloxane and a small amount of a nitro-substituted aromatic hydrocarbon soluble in a siloxane, nitro-substituted aliphatic hydrocarbon, nitro-substituted cycloaliphatic Hydrocarbon or a mixture thereof according to patent P 2608397.6, characterized by a viscosity of 5 to 500 mnr / 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.