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The current flowing through the insulator consists of an internal current and a surface current. Internal resistance changes depending on the purity of the substance, and surface resistance
Depends on the surface condition. As the temperature rises, both internal resistance and surface resistance decrease. Start applying voltage to the table below The internal resistance and surface resistance (both at room temperature) measured after 1 min are shown. The current at this time is the conduction current Not only does it contain the amount of charge stored in the insulator. This value is the resistance value obtained from the current in the equilibrium state.Much bigger. The strength of the insulation rupture is the value obtained at commercial frequency for a 1-3 mm plate-shaped sample. |
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| Quality | Internal resistance ρ/Ω･m |
Surface resistance (Humidity 50-60%) R/Ω |
Dielectric breakdown strength F/106 V･m-1 |
|
|---|---|---|---|---|
| mica (Molding) | 1013 | 5x1013 | － | |
| Crow (quartz) | > 1016 | 3x1012 | 20-40 | |
| Crow (soda) | 109 － 1011 | 1010 － 1012 | － | |
| Crow (Pyrex) | 1012 | － | － | |
| Rubber (Chloroprene) | 1010 － 1011 | － | 10－15 | |
| Rubber (silicone) | 1012 － 1013 | － | 5-25 | |
| Rubber (Natural) | 1013 － 1015 | － | 20-30 | |
| insulation (Mine) oil | 1011 － 1015 | － | － | |
| Ceramics | ||||
| alumina | 109 － 1012 | － | 10-16 | |
| Steatite | 1011 － 1013 | － | 8-14 | |
| Feldspar porcelain (Base material) | 1010 － 1012 | 109 | 10－15 | |
| Feldspar porcelain (With glaze) | 1010 － 1012 | 1011 | － | |
| marble | 107 － 109 | 109 | － | |
| paraffin | 1013 － 1017 | 1015 | 8－12 | |
| Palas Chicks | ||||
| acrylic | > 1013 | > 1014 | ||
| Epoxy | 1012 － 1013 | 3x107 － > 1014 | 16－22 | |
| PVC (Soft) | 5x106 － 5x1012 | > 1014 | 10－30 | |
| PVC (Hard) | 5x1012 － 1013 | 1012 － 1015 | 17－50 | |
| Teflon | 1015 － 1019 | 4x1012 － 1017 | 20 | |
| Nylon | 108 － 1013 | 1011 － 1015 | 15－20 | |
| polyethylene | > 1014 | － | 18－28 | |
| polystyrene | 1015 － 1019 | > 1014 | 20－30 | |
| sulfur | 1014 － 1015 | 7x1015 | － | |
| References: "Chronological Scientific Tables" (National Astronomical Observatory of Japan, 2000 edition) Physical / Chemical Electrical / Magnetic Properties 65 (489) Quoted from insulating materials. | ||||