US2421241A - Liquid-quenched switch - Google Patents

Description

May 27, 1947. F. M. CLARK LIQUID-QUENCHED SWITCH Filed Aug. 9, 1944 CONTAINS L/ um ALKYL 5575/? OF ILIPHAT/C AC/D gmsuu no A Inventor": Frank M. Clark,

, Hus Attorney.

Patented May 27, 1947 LIQUID-QUENCHED SWITCH Frank M. Clark, Plttsfleld, Mass.,

assiguor to General Electric Company, a corporation of New York Application August 9, 1944, Serial No. 548,6! 8

Claims. (Cl. 200-150) The present invention relates to liquidquenched make-and-break electrical devices, such as commonly known by the term oil-filled" circuit breakers, contactors, cut-outs and the like.

Petroleum oil has most commonly been emplayed as the quenching liquid in such devices. However, petroleum oil is partially decomposed when subjected to contact with an electric are or spark. As a consequence of the decomposition, carbon is set free and gas is evolved. The carbon remains in suspension in the oil and the gas escapes. The gradual accumulation of carbon in the liquid is troublesome and may lead to failures and breakdowns. The carbon tends to become deposited on the surfaces of the switch mechanism and interfere with its proper functioning. Electric short circuits may occur and, in general, electrical creepage effects reduce the emciency of the apparatus. When the circuit interrupter or contactor operates in a sealed container, excessive pressure caused by the accumulation of gas therein may be dangerous. Attempts made heretofore to provide an improved arcquenching liquid have not been successful.

The present invention is based on the discovery that the undesirable results obtained with petroleum oil, that is, the formation of carbon and its tendency to settle on the insulating and the contacting parts of the mechanism, are reduced or entirely eliminated when electric arcs are quenched by an alkyl ester of an organic acid. In other words, when properly chosen liquid organic esters are subjected to the electric are as in a contactor or switch, they evolve greatly reduced quantities of carbon and gas. The carbon formed is in such physical state that it has substantially no tendency to settle. Properly selected liquid-quenching agents in devices em-v bodying my invention produce only about 10 per cent of the amount of carbon normally formed under the same degree of use in mineral oil.

on a bearing 1. A circuit conductor 8 has been indicated for carrying current to the contact I. The contact I is brought into engagement with the contact 2 by a magnet (not shown) which is connected to a lever arm 9 whereby the movable contact is operated. The contact 2 is fixedly supported on a conductive bracket i0. when the operating magnet is deenergized, the contacts I and 2 are disengaged by gravity. The arcing contacts I, 2 may comprise copper, silver or other suitable metal and may be confined, as shown, between shields II, I! consisting of insulating material. The enclosing housing 4 is supported by a hanger I3 from a fixed bracket I4. As switches of the liquid-quenched type are well 1 known in the electrical field, the structural feattures of the device need not be described in The accompanying drawing shows conventionally an electric contactor embodying my invention.

As shown in the drawing, the contact-making and breaking electrodes I, 2 are mounted on a suitable support 3 consisting of insulating material within a tank or housing I containing a body 5 of quenching liquid. The contact I is yleldably supported on anarm 6 which is movably pivoted greater detail.

The arc-quenching liquid 5 indicated in the drawing comprises one or more alkyl esters of organic acids from 2 to 18 carbon atoms, as for example the esters of stearic and oleic acids (CnHasCOOI-I and CnHsaCOOH, respectively). The alkyl radicals associated with these acids contain preferably one to five carbon atoms and comprise the methyl, ethyl, propyl, butyl and amyl groups. The chosen ester should be insoluble in water, or substantially so, as otherwise it may pick up water with accompanying depreciation of insulating properties.

Illustrative of acid radicals which I have found of utility in accordance with my invention are the following: stearic, oleic, oxalic, ricinolelc, lauric, lactic, tartaric, sebacic, c, citric, propionic, caprylic and caproic acid. 7

Specific illustrations of alkyl esters suitable for the purposes of my invention are the following: butyl ricinoleate, glycol diricinoleate, 2-butoxyethanol, C4Ho-O-CHa-CHa-OH, ricinoleate, 2- methoxyethanol ricinoleate, glycol dioleate, butyl oleate, amyl oleate, methyl oleate, butyl stearate, methyl stearate, butyl laurate,"ethyl laurate, butyl tartrate, dibutyl sebacate, 2-ethyl hexyl sebacate, ethyl citrate, butyl citrate, Z-butoxyethanol citrate, butyl lactate, 2-ethoxyethanol acetate, ethyl levulinate, butyl oxalate, amyl oxalate, ethyl hydroxy propionate, butyl caproate and butyl caprylate. It will be observed that the alcoholic radicals of short chain length are combined with acid radicals of longer chain length and vice versa.

Alihousih all oi llJJ ester compositions of my invention are character ed by substantially no carbon deposition on cont: ting or dielectric surfaces, thereby insuring freedom from electrical deterioration in use, and although all are characterized by a high and stable dielectric strength despite the most severe arcing in service use, it is nevertheless possible to classify dielectric ester compositions which are suitable for arc-quenching purposes as forming two distinct groups on the basis of the amount of carbon formed under identical conditions of arcing.

In the first group are the methyl, ethyl, propyl, butyl or amyl esters of the monocarboxylio acids such as:

Stearic (CuHasCOOH) Oleic (CmHzaCOOH) Laurie CnHaCOOI-I) Acetic (CHaCOOH) Propionic (CzHsCOOH) Caproic (CsHu-COOH) Caprylic (CrHm-COOH) Oxalic acid (COOHCOOH) Ricinoleic acid (C17H32(OH) COOH) Hydroxy propionic acid CH3CHOHCOOH Sebacic acid (CHz)a-(COOH)2 Citric acid (COOH)-C(OH) (CH2COOH) Lactic acid (CH:)-CH(OH)-COOH Hydroxy isobutyric acid (CH3) 2-C(OH)COOH Levulinic acid CH3CO-(CH2) 2COOH Esters derived from the first group of acids are characterized as follows on the basis of gas and carbon formation as compared to equivalent arc-.

ing in the mineral oil normally used in contactors and switches (mineral oil=l).

Per cent Gas formed 50-60 Carbon formed 20-50 Carbon settling 0 Esters derived from the acids of the second group are characterized as follows on the basis of gas and carbon formation as compared to equivalent arcing in the mineral oil normally used in contactors and switches (mineral oil=100).

- Per cent Gas formed 25-40 Carbon formed -20 Carbon settling 0 It is not necessary that the alkyl esters should be used singly. It is possible, and even preferable in order to obtain the desired physical properties, such as a low freezing point, which is necessary for certain out-oi-doors locations, to mix esters of diflerent chemical formulation. Illustrative of such mixtures are compositions of ethyl and butyl citrate. A solution composed 01' equal proportions by weight or these esters has a freezing point of 40 C. When subjected to the electric arc such a blend or solution evolves about advantageous.

40 per cent as much gas as does the usual switch mineral oil and forms only about 16 per cent as much carbon which shows substantially no tendency to settle.

In like manner, the benefits of this invention may be obtained by blending alkyl esters with mineral oil. In general, the advantages thereby obtained are in proportion to the amount of ester composition present. For example, in a liquid composition consisting of 50 parts by weight each of dibutyl sebacate and the usual switch or contactor oil, the gas and-carbon formed on arcing is about one-half that normally expected from the mineral oil itself. Surprisingly, substantially no carbon settles from such solution after having been subjected to arcing and the behavior practically duplicates the non-settling characteristic already described in connection with a quenching medium consisting of dibutyl sebacate.

The advantages of my invention can be illus-' trated with reference to the five types 01' organic esters which have been round to be particularly These include butyl lactate, butyl sebacate and butyl oxalate, and ethyl hvdroxy isobutyrate. Butyl lactate and ethyl hydroiw isobutyrate represent esters derived from hydroxy monocarboxylic acids (propionic and butyric). Butyl oxalate represents an ester derived from a polycarboxylic acid (oxalic acid). Butyl sebacate represents an ester derived from a polycarbonlic acid. A mixture of equal parts by weight or ethyl and butyl citrate, and esters derived from a polycarboxylic hydroxy acid (citric acid) is an advantageous arc-quenching medium.

The following results obtained with an electrical contactor arranged to operate at 250 volts breaking a. current of 2V; amperes 24 times a minute for three hours illustrate the advantages of my invention. At the end of this period of operation examination was made of the carbon formed and the rate 01' carbon settling. To do this, the arced liquid was well mixed and 50 milliliters were taken for examination. The amount of carbon was gravimetricfl-lly determined. Samples of the creed liquid were then set aside in tall cylinders at 25 C. for five hours and the amount or carbon which had settled from the top 50 per cent or the liquid was determined. The results obtained are listed below. In this tabulation, the relative amount of carbon, carbon settling and gas formed in mineral switch 011 is given as Carbon formed Mineral switch oil 100 Butyl sebacate 16 Butyl lactate 11 Ethyl hydroxy isobutyrate 13 Ethyl and butyl citrate 16 Butyl oxalate 12 Carbon settled in five hours Mineral switch 011 100 Butyl sebacate 0 Butyl lactate 0 Ethyl hydroxy isobutyrate 0 Ethyl and butyl citrate 0 Butyl oxalate 0 Gas formed I Mineral switch oil 100 Butyl sebacate 18 Butyl lactate 40 Ethyl hydroxy isobutyrate 40 Ethyl and butyl citrate 17 Butyl oxalate 17' As already stated, the liquid esters of the monocarboxylic acids are suitable for the purposes or my invention. When tested as described in the foregoing paragraphs, the esters of oleic and of stearic acid such as methyl stearate, amyl oleate and butyl laurate give the following advantageous results:

- Carbon lormed In general, an arc-quenching liquid should have a viscosity not exceeding about 150 seconds Saybolt Universal at 37.8 C. (100 F). The characteristics of several typical ester compositions used in combination with contactors and liquidfilled electrical switching devices in accordance with my inventon are:

S in bo? Dec t Fire Pour Gravit Universal 15.5 Secogrds at Point Pomt Butyl sebacate. 940 46 20s -10 Aznyl oxalate 970 56 126 -n Amy] oleaie.. .862 47 -12 Butyl laurate 855 39 165 -13 Butyl stearate 858 48 208 2!) What I claim as new and desire to secure by Letters Patent 01 the United States is:

1. An electric circuit-interrupter containing separable electric contacts and an arc-quenching liquid operatively associated with said contacts, said liquid consisting of a substantially water-insoluble alkyl ester of aliphatic acid in which the organic acid radical contains from two to eighteen carbon atoms, and the ester alkyl radical contains one to five carbon atoms.

2. An electric circuit interrupter comprising make-and-break contacts and a water-insoluble liquid-quenching medium, the active agent of said medium consisting exclusively of an alkyl compound or an aliphatic acid containing from two to eighteen carbon atoms and being ch'osen from a group consisting of monocarboxylic acids, carboxylic acids containing respectively a hydroxy or ketone group and carboxylic acids containing a p urality of carboxy groups.

3, An electric circuit-mterrupter containing separable arcing contacts and an arc-quenching liquid enveloping said contacts, said liquid consisting of mineral oil and a water-insoluble alkyl ester in which the alkyl radical contains one to five carbon atoms and the acid radical contains 2 to 18 carbon atoms.

4. An electric circuit-interrupter containing separable arcing contacts and an arc-quenching liquid. enveloping said contacts, said liquid consisting exclusively of an alkyl ester of hydroxy monocarboxylic acid, the ester alkyl radical of which contains one to five carbon atoms and the acid radical of which contains two to eighteen carbon atoms, said ester having a viscosity not exceeding 150 seconds Saybolt at 37.8 C.

5. An electric circuit-interrupter containing separable arcing contacts and an arc-quenching liquid enveloping said contacts, said liquid consisting of an alkyl ester of polycarboxylic acid, the ester alkyl radical of which contains one to live carbon atoms and the acid radical of which contains two to eighteen carbon atoms, said ester having a viscosity not exceeding 150 seconds Saybolt at 37.8 C.

6. An electric circuit-interrupter containing separable arcing contacts and an arc-quenching liquid enveloping saidcontacts, said liquid consisting of mineral oil and dibutyl sebacate.

'I. An electric circuit-interrupter containing separable arcing contacts and an arc-quenching liquid enveloping said contacts, said liquid consisting oi! substantially equal parts by weight of mineral oil and dibutyl sebacate.

8. An electric circuit-interrupter containing separable arcing contacts and an arc-quenching liquid enveloping said contacts, said liquid consisting exclusively of alkyl ester of citric acid, the alkyl radical 01 said ester containing one to five carbon atoms.

9. An electric circuit-interrupter containing separable arcing contacts and an arc-quenching liquid enveloping said contacts, said liquid consisting exclusively of a mixture of'equai parts by weight of ethyl and butyl citrate.

10. Anelectric circuit-interrupter containing separable arcing contacts and an arc-quenching liquid enveloping said contacts, said liquid consisting of dibutyl sebacate.

. FRANK M. CLARK.

REFERENCES CITED FOREIGN PATENTS Country Date Number Germany Oct. 24, 1939

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