DE2335692B2 - Dielectric fluid - Google Patents

Description

The dielectric liquid known from the aforementioned Swiss patent does contain no balanced organic esters, but she asked not the favorable properties that would actually be desired,

The object of the invention is to improve the aforementioned dielectric liquid to the effect that that it has properties that are as good as those from Environmental considerations no longer desirable chlorinated diphenyl compounds.

This object is achieved in that the proportion of the ester is 20 to 95% by weight and that the liquid is additionally between 5 and 80% by weight of at least one non-halogenated aromatic hydrocarbon or ether with 1 to 2 which is soluble in the ester Contains rings and a loss factor of less than 10% at 10O ⁰ C.

This novel mixture of certain types of esters and certain types of hydrocarbons or ether not only gives a dielectric fluid with very good properties, it is present mainly biodegradable and therefore no longer poses an environmental hazard. The electrical properties such as electrical strength, loss factor, dielectric constant and corona behavior are those comparable to TCDP. It can also be cleaned to obtain a low loss factor. If corona phenomena occur, no persistent bubbles generated. The preferred dielectric fluids are TCDP in terms of preservation. The service life of a capacitor is even superior, which is important for thermal stability and inertness speaks against the capacitor components Finally, the dielectric fluids according to the invention are also cheaper than TCDP and in conjunction with the The same dielectric materials can be used as are used for capacitors containing TCDP.

The invention is explained in more detail below using exemplary embodiments in conjunction with the drawing explained

It shows

F i g. 1 is a perspective view of a partially unwound film-Z-paper-film capacitor roll with a section on an enlarged scale; and

FIG. 2 shows the winding of FIG. 2 in a perspective and partially broken away view. 1 after introduction in a capacitor case.

In Fig. 1, two layers of metal foil 1 and 2 are wound with paper layers 3 and plastic foil 4. The plastic foil is preferably made of polypropylene, so that the capacitor can be operated with high reactive power per unit volume due to its high electrical strength and its low dissipation factor. In addition, as a result of the use of the dielectric liquid according to the invention, its functioning is not impaired even under extreme operating conditions. It is also possible to use other plastic films such as high-density polyethylene. With the metal foils 1 and 2 conductors 5 ω and 6 are connected. The capacitor winding 7 is inserted into a cup 8, see FIG. 2, and impregnated with a dielectric liquid 9. The conductors 5 and 6 are with connections !! 10 or 11 connected.

The dielectric liquids according to the invention b5 contain about 2 "to 95% (all percentages given herein relate to weight, if not otherwise indicated) of an organic ester and about 5-80% of an aromatic hydrocarbon or ether, the dielectric fluids with the best properties contain between 75 and 90% of the organic ester and between 10 to 25% of the aromatic hydrocarbon or ether,

The organic ester is liquid in the entire temperature range from -20 ⁰ C to 150 ⁰ C and has a dissipation factor of less than 10% at 100 ⁰ C. It preferably contains a benzene ring, since aromatic substances have better corona resistance and better thermal stability. Either the acid part or the base part of the ester can be aromatic. Phthalic esters appear to have better properties than other esters, and in particular, diisononyl phthalate (hereinafter referred to as "DINP") has excellent properties. Other suitable esters are

Dibutyl adipate, diethyl adipate, Nozzleodecyl adipate, ethyl benzoate, n-butyl benzoate, isopropyl benzoate Isobutyl benzoate, n-propyl benzate Ethyl caproate ethyl caprylate, Methyl caprylate, diethyl malonate, Dimethyl malonate dietary hydroxalate, Dibutyl phthalate, diallyl phthalate Dimethyl phthalate, dioctyl phthalate Diethyl succinate, butyl valerianate etc.

Mixtures of suitable esters can be formed to meet the temperature requirements and can also be used where the individual esters do not meet the temperature requirements would correspond.

The aromatic hydrocarbon or the aromatic ether is a compound that is soluble in the ester and has one or two rings and a loss factor of less than 10% at 100 ⁰ Q. It is said to have low vapor pressures, since compounds with a low boiling point are difficult to handle and evaporate in a condenser. The boiling point is preferably above 140 ⁰ C compounds having two rings are preferable, since they have boiling points above 140 ° C. Diphenyte oxide (hereinafter referred to as "DPO") is preferred because it has excellent electrical properties and does not soften the polypropylene film or react with it in capacitors. Other suitable aromatic hydrocarbons or ethers are acenaphthene, anisole, benzene, ethylbenzene, propylbenzene, cumene, cymene, Diphenyl, diphenylmethane, durol, fluorene, indene, mesitylene, naphthalene, phenotol, styrene, toluene, xylene, etc. Mixtures of aromatic hydrocarbons and / or ethers can also be used

The dielectric liquid also preferably contains between 0.5 and 5% (of the ester plus hydrocarbon or ether) of an antioxidant. The antioxidant is a free radical inhibitor that is soluble in the solution of the ester and the hydrocarbon or ether. It helps to keep the loss factor low over a long period of time, both for the liquid itself and for the liquid even if they are present in a capacitor. The preferred amount of antioxidant is between 0.1 and 3%, and a preferred antioxidant is di-tert-butyl paracresol (hereinafter referred to as "DTBPC") for which has been shown to work very well Other suitable antioxidants contain phenols with the following structure:

OH

wherein the R groups are typically hydrogen or alkyls. Also, other known antioxidants can be used that reduce the loss factor of the dielectric fluid do not: increase significantly. Mixtures of antioxidants also come in Consideration

The dielectric liquid also preferably contains between 0.1 and 3% (of the ester plus hydrocarbon or ether) of the corona resistance increasing additive to increase the resilience of the

in dielectric fluid versus the impact Increase the corona by decreasing the time it takes to recover from a corona evoking Overvoltage is needed. This additive is a compound that reacts with hydrogen and these takes up under charge conditions, while in the solution of the ester and the aromatic ether or Hydrocarbon is soluble. It probably works in such a way that hydrogen is absorbed by the Corona formation occurs, so that the formation of bubbles is reduced. A preferred additive is /? - methylanthraquinone, which is easy to handle and stable is. Other suitable additives are azobenzene, anthraquinone and other substances that contain hydrogen take up. Mixtures of such additives can also be used.

The invention is explained in more detail below on the basis of practical exemplary embodiments:

example

A mixture of 80% DINP and 20% DPO was made and various of its properties were compared with those of TCDP and mineral oil:

Characteristic

80% DINP -20% DPO

TCDP

mineral oil

Electrical Strength (kV) - ASTM 01816 Dielectric constant at 100 C Heat loss factor (%) at 100 C Viscosity (Pa.s) at 20 C Ignition point (C) Solidification point (C) Vapor pressure at 50 C (mbar)

48 40 35 3.7 4.9 2.2 0.4 0.2 <0.05 34.8 x 10 "' 64.5 · 10 ³ 18.4 ■ 10 " ³ 160 670 150 <-40 <-40 <-40 0.23 0.02 0.067

The above values show that the DINP / DPO mixture has satisfactory properties for the Capacitor manufacture (i.e. a sufficiently low viscosity and a sufficiently low vapor pressure and a sufficiently high ignition point) and a Capacitor performance like that in Connection with the following examples is shown in more detail. Because the ignition point is the same as for mineral oil, similar precautions must be taken as for mineral oil.

example

Small Prüfkondensatoren were prepared, each comprising a winding of a flattened roll of webs of about 6 - 10 ~ ⁶ m thick aluminum foil, about 12 x 10 ~ ^ ⁶ m thick polypropylene film, about 13 ■ 10 ^-6 m thick paper a density of 0.7, about 12 ^ · 10- ⁶ m thick polypropylene film, about 0.6 - 10- ^e m thick aluminum foil, about 12.5 x 10- ⁶ m thick polypropylene film, approximately 13 x 10 - ⁶ m thick paper and approx. 12 - 10 m thick polypropylene film. These wraps had a height of about 7.5 cm, a width of about 5 cm and a thickness of 10 mm, with one Capacity of about 0.3 μΡ. Some capacitors were impregnated with DINP, some with 80% DINP and 20% DPO. The treatment was carried out accordingly generally known and applied processes. The dielectric liquid was used for impregnation Vacuum is added, pressurized to atmospheric pressure and then the cycle of several times Vacuum and pressurization repeated The units impregnated with 80% DINP and 20% DPO were subjected to fewer impregnation cycles than the units impregnated with DINP.

Example 3

There were capacitors as in Example 2 with 80% DINP and 20% DPO and treated with TCDP. The table below shows the results of these Capacitors carried out dielectric studies and also contains extrapolated values for with Mineral oil impregnated capacitors.

23 7th characteristic 35 692 8th TCDP mineral oil liquid Dielectric 80% DINP 3.1 2.6 Average dielectric constant (t'r) Temp. C - 20% DPO 0.05 low Power factor (%) at operating voltage 2.9 0.08 25th 0.04 3200 2600 Corona inception voltage (V) 85 0.06 2600 600 Corona erasing voltage (V) 125 2700 1900 **) - Mininiuni corona inception voltage (V) 25th 2100 25th 2500 *) 1600 **) - Minimun-corona release tension -40 & about that 1600 *) -40 & about that

·) At -40 ( **) at -20 C

The table above shows that the capacitors impregnated with DINP-DPO have dielectric constants and had power factors similar to those of TCDP impregnated capacitors are comparable. It also shows that mineral oil is a relatively poor impregnating agent for such Capacitors because it has a low corona erasing voltage and therefore a dielectric coolant results, which is only lower average.

Example 4

The corona values for capacitors treated according to Example 2 were used in conjunction with different dielectric liquids measured. The results thereby obtained are shown below Table compiled.

Dielectric fluid Zoit (min) until the extinction of the
Corona at 1600 V after a
6 sec overvoltage of 430OV
(Shunt) Corona-
Threshold voltage Corona-
Erase voltage 530OV
(Line) _ TCDP <i U 3200 2600 30% DINP - 20% DPO with 0.15% DTBPC > 20 4th 2600 2100 80% DINP - 20% DPO with 2%> methyl
anthraquinone 3.5; 5 - 2800 2300 80% DINP - 20% DPO with 1% azobenzene
and 0.15% DTBPC 4; 12th > 30; 30th 2600 2000 80% DINP - 20% biphenyl > 30 > 40 3000 2000 80% DINP - 20% naphthalene > 40 - 2400 1900 80% diethylhexyl phthalate - 20% DPO with
0.2% DTBPC 6; 12th 6th 2400 1800 80% diisodecyl adipate - 20% DPO 25th > 30 3100 2600 DINP > 27 2700 1700

The above investigation can be particularly hard in view of the 6 see sustained overvoltage be considered. The overvoltages of 5300 or 4300 V are the highest values when using Power capacitors in series or parallel connection for dielectrics of this composition are expected can be, whereby they only for a fraction of an alternating voltage period (<· / «see) would occur. This investigation shows with

60 large safety margin if a certain dielectric recovered from the impact of such surges The table shows that the addition of DPO to DINP increases the corona resistance considerably The antioxidant DTBPC had no other effect, but a hydrogen acceptor improved as / J Methylanthraquinone or azobenzene the properties even further.

example

It were made with different dielectric fluids Impregnated test capacitors tested according to Example 2 for their service life by they have been aged at 1600 V at 125 ° C. The end of The service life of the condenser was considered to have been reached when the heat loss factor was reduced to a

Value increased at which it was in a large power capacitor thermal runaway can occur. The table below gives the results again, where "relative service life" is the ratio of the service life of the capacitor in relation to The service life of a capacitor impregnated with TCDP is:

Dielectric fluid

Relative
lifespan
at 125 C.

80% DINP - 20% DPO
80% DINP - 20% DPO with
0.15% DTBPC
80% DINP - 20% DPO with
0.26% DTBPC

'J / 0 L / liTi /.,I/OL/I \ J

50% DINP - 50% DPO

0.8 1.7

2.1

0.8
1.1

The above values show that the dielectric liquids according to the invention are particularly good impregnating agents for film-paper capacitors and for capacitors made entirely of paper, and that dielectric liquids according to the invention which contain an antioxidant give capacitors impregnated therewith a far longer life than it is the case with capacitors impregnated with TCDP. The data show that a 150 kVA power capacitor (with a hot spot of 85 ^° C. occurring 10% of the time) can be expected to operate for at least about 40 years if the dielectric fluid has 80 DINP and 20% DPO Represents 0.26% DTBPC.

Example 6

There were capacitors with a capacity of 0.8 μΡ with two layers of 10 · 10 ~ ⁶ m thick paper

made with a density of 0.9 between aluminum foil. The capacitors were made with 80% DINP and 20% DPO impregnated. The power factors were 0.26% at 85 ° C and 0.38% at 125 ° C determined when a voltage of 440 V. The corona threshold voltages were above 800 V. These capacitors could be used as lighting ballast, for starting the motor, for commutators and Low voltage power factor corrections are used.

Example 7

There were 1 l amounts of 80% DINP and 20% DPO 80% DINP-20% DPO prepared with 0.15% DTBPC antioxidant. Both liquids were exposed to ambient air at 100 ° C. After four days it was Heat loss factor of the antioxidant-free liquid increased by more than 10%. Against it the heat loss factor of the liquid containing the antioxidant was only down after two weeks increased less than 1%.

Examples

Capacitor sections were made according to Example 5 using 0.15% DTBPC, some with tinned copper conductors and some with aluminum conductors, and these capacitor sections were then inserted into steel cans as shown in FIG. These capacitors were operated at a voltage of 1600 V at a temperature of 115 ⁰ C. Both embodiments had the same operational stability, that is, the copper did not lead to any adverse effects. Copper catalyzes the breakdown of organic substances with a large percentage of hydrogen, such as in this impregnating agent, but it can be assumed that this effect was inhibited by the antioxidant.

1 sheet of drawings

Claims (13)

Claims; 1 »Dielectric fluid containing a non-halogenated organic ester which is liquid between -20 ^e C and 150 ° C and has a loss factor of less than 10% at 100 ⁰ C, characterized in that the proportion of the ester is 20 to 95 wt .-% and that the liquid additionally contains between 5 and 80% by weight of at least one non-halogenated aromatic hydrocarbon or ether which is soluble in the ester and has 1 to 2 rings and a loss factor of less than 10% at 100.degree 2. Dielectric fluid according to claim 1, i>. characterized in that the ester in an amount of 75 to 90 wt .-% and the aromatic Hydrocarbon or ether is contained in an amount between 10 to 25% by weight 3. Dielectric fluid according to claim 1 or 2, characterized in that the ester is a is an aromatic ester 4. Dielectric liquid according to claim 3, characterized in that the aromatic ester is a phthalic acid ester 5. Dielectric fluid according to claim 4, characterized in that the aromatic ester Is dsononyl phthalate 6. A dielectric fluid according to any of claims 1-5, characterized in that the aromatic hydrocarbon or ether has two rings and fcuien boiling point above 140 ⁰ C. 7. Dielectric liquid according to claim 6, characterized in that the aromatic ether is a diphenyl oxide 8. Dielectric fluid according to any one of claims 1-7, characterized in that it between 0.05 and 5% by weight, based on the ester plus aromatic hydrocarbon or ether, an antioxidant contained in the solution of the ester and the aromatic hydrocarbon or ether is soluble 9. Dielectric fluid according to claim 8, characterized in that the antioxidant in an amount between 0.1 to 03% by weight, based on " on the ester plus the aromatic hydrocarbon or ether. 10. Dielectric liquid according to any one of claims 1-9, characterized in that the aromatic hydrocarbon or ether is contained in such an amount between 5 and 25% by weight 11. Dielectric fluid according to claim 8, 9 or 10, characterized in that the antioxidant is di-tert-butyl paracresol 12. Dielectric liquid according to any one of claims 1-11, characterized in that it 03 to 3 wt. <%, Based on the ester plus the aromatic hydrocarbon, or ether, containing a hydrogen acceptor that is in solution of the ester and the aromatic hydrocarbon or ether is soluble. 13. Dielectric fluid according to claim 12, characterized in that the hydrogen acceptor is methyl anthraquinone. 65 The invention relates to a dielectric liquid containing a non-halogenated organic ister which is liquid between -2q ° C and 150 "C and a dissipation factor of less than 10% at JOO C has ⁹ Such a dielectric liquid has already become known from CH-PS 375449. How on Page 1, lines 62 to 67 of this publication, is used as an impregnating agent for an electrical Condenser an aromatic'ester of phthalic acid (z, B, Dioctylphthalat) is used Dielectric liquids are not only used in capacitors, but also in transformers, Coaxial cables, as well as other electrical arrangements, are used to keep gases away from the insulating area of the Keep equipment away and thus create insulation with a higher dielectric strength. In addition to the high electrical strength, the dielectric fluid also has additional properties Requirements, in particular it should be inexpensive and preferably fire-resistant. You should too Can be easily cleaned in order to achieve a low conductivity and thus a good dissipation factor. at When used in capacitors, it should also have a high dielectric constant and be able to to impregnate the dielectric interfaces of the capacitor coil. In addition, it must have good corona properties, especially when used in Capacitors. In order to obtain good corona properties, a high corona threshold voltage is as well a high corona quenching voltage is necessary, the former being the voltage at which the applied voltage increased until the onset of the corona and then decreased again until it goes out becomes (erase voltage). Stronger corona phenomena, which can occur sporadically during operation, should be also lead to no permanent damage such as permanent blisters, because z. B. Bubbles to a considerable extent Reduction of the threshold voltage as well as the extinguishing voltage can lead. The dielectric Liquid should have good electrical properties even at high temperatures and in the vicinity of the dielectric and metallic components of the arrangement maintained. You should not have too great a volatility, since such volatile liquids only difficult to handle and evaporate quickly during operation. Also, the liquid should be at low levels Do not solidify temperatures, as it cracks when solidified and therefore has electrical strength forfeited. Because of their good compromise between the three desired properties mentioned, chlorinated diphenyl compounds such as trichlorodiphenyl are used (hereinafter referred to as "TCDP") used commercially as dielectric fluids If dielectric liquids are used in large quantities, there is always a risk that they will accidentally spilled or leaked. However, many of the chlorinated compounds are not readily biodegradable, persist for a long time, and can persist thereby accumulate in the food chain. It is therefore desirable to use chlorinated diphenyls as dielectric Avoid liquids or apply such extensive precautionary measures that their use becomes costly. Because of the problems of environmental protection which have recently become very significant Thus the object is to find a satisfactory replacement for the above-mentioned halogenated dielectric Find liquids.