Electrically insulating oil composition, and oil-impregnated electrical equipment

Abstract

It is an object to provide an electrically insulating oil composition that can maintain dielectric breakdown voltage high in a wide temperature range of ?50? C. to 65? C., and can suppress a decrease in dielectric breakdown voltage even in the case of use at high temperature for a long time, and there is provided an electrically insulating oil composition comprising 1,1-diphenylethane and benzyltoluene, wherein the proportion of a para isomer in the benzyltoluene is 45% by mass or more based on a total amount of the benzyltoluene.

Claims

1. An electrically insulating oil composition comprising: 1,1-diphenylethane; and benzyltoluene, wherein the proportion of a para isomer in the benzyltoluene is 50% by mass or more based on a total amount of the benzyltoluene, such that a decrease in dielectric breakdown voltage of the electrically insulating oil composition is suppressed during its use between 50? C. and 80? C. for 1,000 hours or more.

2. The electrically insulating oil composition according to claim 1, wherein a total content of the 1,1-diphenylethane and the benzyltoluene is 80% by mass or more based on a total amount of the electrically insulating oil composition.

3. The electrically insulating oil composition according to claim 1, further comprising 0.01 to 1.0% by mass of an epoxy compound based on the total amount of the electrically insulating oil composition.

4. The electrically insulating oil composition according to claim 1, wherein a chlorine component is 50 ppm by mass or less.

5. Oil-impregnated electrical equipment impregnated with the electrically insulating oil composition according to claim 1.

6. The oil-impregnated electrical equipment according to claim 5, being an oil-impregnated capacitor using a polypropylene film at least in part as a dielectric.

Description

DESCRIPTION OF EMBODIMENTS

(1) The present invention will be described in detail below in accordance with preferred embodiments thereof.

(2) An electrically insulating oil composition according to this embodiment comprises a diarylalkane mixture in which 1,1-diphenylethane and benzyltoluene are blended, and the proportion of the para isomer in the above benzyltoluene is 45% by mass or more based on the total amount of the benzyltoluene.

(3) The methods for obtaining 1,1-diphenylethane and benzyltoluene are not particularly limited, and commercial products may be used, or 1,1-diphenylethane and benzyltoluene may be produced by oneself. For the benzyltoluene, the production method may be adjusted so that the proportion of the para isomer is in the above range, or isomers may be separately produced and mixed in the desired proportion.

(4) The proportion of the para isomer in the benzyltoluene is 45% by mass or more based on the total amount of the benzyltoluene (the total amount of all isomers), and is preferably 50% by mass or more, more preferably 52% by mass or more, and further preferably 55% by mass or more from the viewpoint of still further suppressing a decrease in dielectric breakdown voltage in the case of use at high temperature for a long time. On the other hand, from the viewpoint of improving performance at low temperature and performance at high temperature in good balance, the proportion of the para isomer in the benzyltoluene is preferably 80% by mass or less, more preferably 75% by mass or less, and further preferably 70% by mass or less based on the total amount of the benzyltoluene.

(5) The proportions of isomers other than the para isomer in the benzyltoluene are not particularly limited, but from the viewpoint of the suppression of a decrease in insulation performance due to crystallization and a decrease in fluidity (an increase in viscosity) at low temperature, the proportion of a meta isomer is preferably 5% by mass or more, more preferably 8% by mass or more, based on the total amount of the benzyltoluene.

(6) The ratio (1,1-DPE/BT) of the 1,1-diphenylethane (1,1-DPE) to the benzyltoluene (BT) in the electrically insulating oil composition is not particularly limited but is preferably 0.50 or more, more preferably 0.55 or more, and further preferably 0.58 or more in terms of a mass ratio from the viewpoint of further improving performance at low temperature. In addition, the above ratio is preferably 2.5 or less, more preferably 2.2 or less, further preferably 2.0 or less, and particularly preferably 1.3 or less in terms of a mass ratio from the viewpoint of sufficiently increasing the concentration of p-BT in the electrically insulating oil composition and further improving dielectric breakdown voltage at high temperature

(7) In addition, the content of p-BT in the electrically insulating oil composition is not particularly limited but is preferably 13% by mass or more, more preferably 15% by mass or more, further preferably 18% by mass or more, and particularly preferably 20% by mass or more based on the total amount of the electrically insulating oil composition from the viewpoint of still further suppressing a decrease in dielectric breakdown voltage in the case of use at high temperature for a long time. On the other hand, from the viewpoint of improving performance at low temperature and performance at high temperature in good balance, the content of p-BT in the electrically insulating oil composition is preferably 50% by mass or less, more preferably 45% by mass or less, based on the total amount of the electrically insulating oil composition.

(8) The electrically insulating oil composition can contain components other than 1,1-diphenylethane and benzyltoluene, but the total content of the 1,1-diphenylethane and the benzyltoluene is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more based on the total amount of the electrically insulating oil composition. By setting the total content of the 1,1-diphenylethane and the benzyltoluene in the above range, dielectric breakdown voltage in a wide temperature range can be maintained higher.

(9) The electrically insulating oil composition may comprise other hydrocarbons such as bicyclic aromatic compounds such as alkylbenzenes having 12 to 18 carbon atoms, cycloalkylbenzenes, 1,2-diphenylethane, and diphenylmethane, and polycyclic aromatic compounds such as alkylnaphthalenes, in addition to 1,1-diphenylethane and benzyltoluene.

(10) Benzyltoluene is usually produced by reacting benzyl chloride and toluene, and therefore a chlorine component is included in the electrically insulating oil composition. But, it is found that the chlorine component deteriorates the performance of the electrically insulating oil composition. Therefore, the chlorine component in the electrically insulating oil composition is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, and further preferably 10 ppm by mass or less. By suppressing the content of the chlorine component in the above range, deterioration in the performance of the electrically insulating oil composition can be suppressed. In the electrically insulating oil composition, a polar substance that adversely affects the performance of the electrically insulating oil composition is removed by performing white clay treatment, but organochlorine components are difficult to remove by white clay treatment, and therefore it is desired to decrease chlorine concentration at the benzyltoluene production stage.

(11) In the electrically insulating oil composition, the dielectric dissipation factor increases by containing a polar substance such as water, and the insulating properties decrease when the dielectric dissipation factor is high, and therefore the performance as the electrically insulating oil composition deteriorates. In order to avoid these, when the electrically insulating oil composition is brought into contact with activated clay to remove the polar substance such as water, the dielectric dissipation factor reduces, and the performance as the electrically insulating oil composition improves. The activated clay used at this time is not particularly limited. The shape of the activated clay is not particularly limited, but a molded body is preferred from a practical viewpoint. The chlorine component cannot always be removed with activated clay, and therefore preferably an epoxy compound is added as a chlorine-trapping agent (chlorine-capturing agent). This epoxy compound is removed to some extent by being brought into contact with activated clay, and therefore it is desired to add the epoxy compound after the electrically insulating oil composition is white clay-treated.

(12) Examples of the epoxy compound include alicyclic epoxy compounds such as 3,4-epoxycyclohexylmethyl(3,4-epoxycyclohexane) carboxylate, vinylcyclohexene diepoxide, and 3,4-epoxy-6-methylcyclohexylmethyl(3,4-epoxy-6-methylhexane) carboxylate, and bisphenol A diglycidyl ether type epoxy compounds such as phenol novolac type epoxy compounds and ortho-cresol novolac type epoxy compounds. The amount of the epoxy compound added is preferably 0.01 to 1.0% by mass, more preferably 0.3 to 0.8% by mass, based on the total amount of the electrically insulating oil composition. When the amount added is less than 0.01% by mass, there is a tendency that the effect of trapping the chlorine component is not sufficiently exhibited, and when the amount added exceeds 1.0% by mass, there is a tendency that the electrical characteristics of the electrically insulating oil composition decrease, dielectric loss occurs inside a capacitor to generate heat and impair the performance of the capacitor.

(13) The electrically insulating oil composition in this embodiment is preferably used in oil-impregnated electrical equipment and preferably used particularly for impregnating an oil-impregnated capacitor using a plastic film in at least part of an insulating material or a dielectric material.

(14) As the plastic film, in addition to polyester films, polyvinylidene fluoride films, and the like, polyolefin films such as polypropylene films and polyethylene films, and the like can be used, and among them, polyolefin films are preferred. Particularly preferred polyolefin films are polypropylene films.

(15) An oil-impregnated capacitor preferred in this embodiment is produced by winding metal foils such as aluminum as conductors and a plastic film as the above insulating material or dielectric material together with another material such as insulating paper as necessary, and impregnating the electrically insulating oil composition by a conventional method. Alternatively, the oil-impregnated capacitor is also produced by winding a metal-vapor-deposited plastic film (metallized film) in which metal layers as conductors such as aluminum or zinc are formed on a plastic film as the above insulating material or dielectric material by a method such as vapor deposition, together with a plastic film or insulating paper as necessary, and impregnating the electrically insulating oil composition by a conventional method.

EXAMPLES

(16) The present invention will be more specifically described below by Examples, but the present invention is not limited to these Examples.

Example 1

(17) As shown in Table 1, an electrically insulating oil composition comprising 35% by mass of 1,1-diphenylethane (1,1-DPE) and 60% by mass of benzyltoluene (BT) was prepared. Here, the 1,1-DPE was blended as a DPE fraction in which the effective component concentration (1,1-DPE concentration) was 85% by mass or more, and components other than the 1,1-DPE included in the DPE fraction are shown as other components in Table 1. In addition, the content of the other components shown in Table 1 is an amount also including 0.65% by mass of an epoxy compound described later. For the benzyltoluene, one in which benzyltoluene produced by replicating a reference production example described in Japanese Examined Patent Publication No. H8-8008 was precisely separated into isomers by distillation and then the isomer ratio was set at 3% by mass of the ortho form (o-BT), 51% by mass of the meta form (m-BT), and 46% by mass of the para form (p-BT) by the mixing of the fractions was used. In addition, bicyclic aromatic compounds such as diphenylmethane and 1,2-diphenylethane other than 1,1-diphenylethane and benzyltoluene, polycyclic aromatic compounds such as alkylnaphthalenes, alkylbenzenes having 12 to 18 carbon atoms, and cycloalkylbenzenes are included in the other components. The unit of a numerical value in Table 1 is ppm by mass for a chlorine component and % by mass for all of others.

Examples 2 to 12 and Comparative Examples 1 to 6

(18) The electrically insulating oil compositions of Examples 2 to 12 and Comparative Examples 1 to 6 were prepared as in Example 1 except that the 1,1-DPE content, the BT content, the content of other components, and the BT isomer ratio were changed to values shown in Table 1. The BT isomer ratio was adjusted by changing the mixing proportion of the isomers of benzyltoluene produced as in Example 1.

Comparative Examples 7 and 8

(19) The electrically insulating oil compositions of Comparative Examples 7 and 8 were prepared as in Example 1 except that instead of 1,1-DPE, phenylxylylethane (PXE) was used in an amount shown in Table 1, and the BT content, the content of other components, and the BT isomer ratio were changed to values shown in Table 1. The BT isomer ratio was adjusted by changing the mixing proportion of the isomers of benzyltoluene produced as in Example 1.

(20) TABLE-US-00001 TABLE 1 Composition of electrically insulating oil composition Isomer ratio Other components (including 1,1-DPE + Chlorine in BT 1,1-DPE PXE BT epoxy compound) BT component o-BT m-BT p-BT Example 1 35 60 5 95 1 or less 3 51 46 Example 2 44 50 6 94 1 or less 3 51 46 Example 3 52 40 8 92 1 or less 3 51 46 Example 4 66 30 4 96 1 or less 3 51 46 Example 5 35 60 5 95 31 42 6 52 Example 6 44 50 6 94 26 42 6 52 Example 7 52 40 8 92 21 42 6 52 Example 8 66 30 4 96 16 42 6 52 Example 9 35 60 5 95 8 12 19 69 Example 10 44 50 6 94 7 12 19 69 Example 11 52 40 8 92 6 12 19 69 Example 12 66 30 4 96 4 12 19 69 Comparative Example 1 66 30 4 96 15 10 50 40 Comparative Example 2 66 30 4 96 8 7 63 30 Comparative Example 3 66 30 4 96 3 22 42 36 Comparative Example 4 52 40 8 92 18 38 42 20 Comparative Example 5 35 60 5 95 5 28 70 2 Comparative Example 6 35 60 5 95 55 65 27 8 Comparative Example 7 37 60 3 60 8 12 19 69 Comparative Example 8 56 40 4 40 6 12 19 69

(21) <Test A: Evaluation of Test Oil by Model Capacitor>

(22) The capacitor used in the test was as follows. As the dielectric, one in which two inflation method polypropylene films manufactured by Shin-Etsu Film Co., Ltd. having a thickness of 12.7 ?m (weight method) were stacked was used, and as the electrodes, aluminum foils were used. By winding and laminating these according to a conventional method, a model capacitor element for oil impregnation was fabricated.

(23) This element has a capacitance of 0.2 to 0.3 ?F. This element was placed in a can made of tinplate. The can was formed in a flexible structure so as to be able to adapt sufficiently when the insulator shrinks at low temperature. In addition, the ends of the electrodes were in a state of being slit as they were and not folded. As a method for making connections from the electrodes to a terminal, as in a method used for a high frequency capacitor, a structure was made in which winding is performed in a structure in which one ends of the electrodes are each protruded from the polypropylene films, and the protruded portions were spot-welded together to a lead wire.

(24) The can type capacitor prepared in this manner was vacuum-dried according to a conventional method, and then impregnated with a test oil (the electrically insulating oil compositions of Examples 1 to 12 and Comparative Examples 1 to 8) and sealed under the same vacuum. In the impregnation, the test oil was used after being previously treated with activated clay. In other words, 10% by mass of activated white clay Galleonite #036 manufactured by Mizusawa Industrial Chemicals, Ltd. was added to the test oil (one before the addition of the following epoxy compound), and was stirred at a liquid temperature of 25? C. for 30 minutes and then filtered. After the filtration, an epoxy compound (alicyclic epoxy compound, trade name: CELLOXIDE 2021P, manufactured by Daicel Chemical Industries, Ltd.) as a chlorine-capturing agent was added so as to be 0.65% by mass based on the total amount of the electrically insulating oil composition, and the obtained electrically insulating oil composition was used for impregnation as the test oil.

(25) Next, in order to make the impregnation condition inside the capacitor uniform for stabilization, heat treatment was performed in a thermostat at 80? C. for 2 days and nights. Then, the capacitor was allowed to stand at room temperature for 5 days, then voltage application treatment was performed at AC 1270 V (corresponding to 50 V/?m) in a thermostat at 30? C. for 16 hours, and then the capacitor was subjected to the test. This is referred to as preliminary voltage application.

(26) Next, alternating voltage was applied to each of these oil-impregnated capacitors at predetermined temperatures by a predetermined voltage application method, and from the voltage and time at which the capacitor suffered dielectric breakdown, dielectric breakdown voltage was obtained by the following formula (1). The predetermined temperatures were ?50? C. and 80? C. On the high temperature side, actually performance at 65? C. was required, but in this test, evaluation was performed at 80? C., which was a more severe condition. The predetermined voltage application method is a method of increasing the applied voltage stepwise from a potential gradient of 50 v/?m at the rate of 10 v/?m every 24 hours. The results are shown in Table 2.
Dielectric Breakdown Voltage (v/?m)=V+S?(T/1440)(1)

(27) wherein V, S, and T represent applied voltage (v/?m) at the time of dielectric breakdown, increased voltage (v/?m) for every 24 hours, and elapsed time (minutes) until dielectric breakdown after applied voltage increase, respectively.

(28) <Test B: Durability Test>

(29) Those in which the same capacitors as the capacitors subjected to the test A were fabricated, and treatment until the preliminary voltage application was carried out were prepared. A potential gradient of 90% of the dielectric breakdown voltage at 80? C. obtained in the test A was applied to each of these model capacitors at 60? C. for 1000 hours. For one that suffered dielectric breakdown before 1000 hours was reached, the time is shown, and for one in which breakdown did not occur until 1000 hours, from the stage, a dielectric breakdown test similar to the test A was carried out at 80? C., and the performance evaluation of the capacitor after voltage application at 60? C. for a long time (durability test) was carried out. In addition, a performance decrease rate was obtained by the following formula (2). The results are shown in Table 2.
Performance Decrease Rate (%)={(80? C. dielectric breakdown voltage in the test A?80? C. dielectric breakdown voltage after 1000 hours in the test B)/80? C. dielectric breakdown voltage in the test A}?100(2)

(30) TABLE-US-00002 TABLE 2 Test B: durability test Test A (dielectric Endur- Dielectric Performance breakdown voltage) ance breakdown decrease ?50? C. 80? C. time voltage rate (v/?m) (v/?m) (hour) (v/?m) (%) Example 1 101 168 1000 159 5 Example 2 100 150 1000 144 4 Example 3 95 148 1000 140 5 Example 4 82 139 1000 133 4 Example 5 95 168 1000 165 2 Example 6 90 155 1000 150 3 Example 7 87 154 1000 152 1 Example 8 85 144 1000 141 2 Example 9 99 173 1000 170 2 Example 10 97 166 1000 163 2 Example 11 96 159 1000 157 1 Example 12 90 155 1000 152 2 Comparative 92 158 1000 128 19 Example 1 Comparative 95 155 560 Example 2 Comparative 90 156 721 Example 3 Comparative 92 148 522 Example 4 Comparative 98 142 319 Example 5 Comparative 78 140 401 Example 6 Comparative 88 153 1000 125 18 Example 7 Comparative 81 147 753 Example 8

(31) As seen from the results shown in Table 2, in the Examples, good results were obtained in both the test A and the test B. Thus, it was confirmed that the electrically insulating oil compositions of the Examples were high performance electrically insulating oil compositions not only having high performance at low temperature but having high durability also in a high temperature region. On the other hand, in Comparative Examples 1 and 7, the performance decrease rate after 1000 hours was large in the test B, and in Comparative Examples 2 to 6 and 8, dielectric breakdown occurred within 1000 hours in the test B. In addition, when the polypropylene film exposed on the capacitor element surface was observed for the model capacitor after the test B was carried out, wrinkles on the film surface indicating the volume expansion of the polypropylene film were significant in Comparative Examples 1 to 8, and on the other hand, in Examples 1 to 12, their number and the extent of the wrinkles were small.

INDUSTRIAL APPLICABILITY

(32) The electrically insulating oil composition of the present invention not only has necessary performance in a low temperature region, but has excellent electrical characteristics also in a high temperature region by suppressing the swelling properties of a polypropylene film, and is practically extremely useful as use for capacitor impregnation, and the like.