Talking about the General Maintenance Method of Low Voltage Cable
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Determining the number of the core wire 1. Low low voltage cable type selected cable type and length of the core 2. Determine the number of cables and low voltage cables 3. Select the cable length is determined <br> <br> main low-voltage cable core cross sections of the primary core cross sections Must meet the following conditions:
1) During normal operation, the actual temperature of the cable core should not exceed the long-term allowable temperature of the cable, so it should be ensured that the maximum long-term operating current flowing through the cable must not exceed its allowable continuous current;
2) During normal operation, ensure that the terminal voltage of all motors of the power supply network is in the range of 95% to 105% of the rated voltage, and that individual special far-end motor terminals are allowed to shift by 8% to 10%; 3) The distance is far and the power is large. The motor should be guaranteed to start normally under heavy load conditions, and ensure that its starter has enough suction voltage.
4) The selected cable cross-section must meet the mechanical strength requirements. When the cross-section of the main core wire of the low-voltage cable is selected according to the above conditions, the branch cable is generally selected according to the minimum cross section of the mechanical strength, and after confirming the allowable continuous current, it can be determined. When selecting the main cable of the trunk cable, if the cable of the trunk cable is not long, the primary current shall be selected according to the allowable continuous current of the cable; when the trunk cable is longer, the primary voltage shall be selected according to the normal allowable voltage loss.
General maintenance of low-voltage cables 1. Inspection line inspection: The cable line should be regularly inspected on the entire line, including: whether there is excavation marks on the cable trench and nearby ground, whether the soil layer covered by the groove surface is normal, and whether the trees are planted. And piling, whether to stack heavy objects, with or without excretions such as acid and alkali, whether the roads and building facilities passed by cable circuits are being overhauled and repaired.
2. Operation check: The cable line should be checked regularly for operation, including:
(1) Measurement of voltage and current: The voltage must not exceed 15% of the rated voltage of the cable, and the current must not exceed the design specification.
(2) Cable temperature check: Generally estimate the temperature of the inner core wire through the cable jacket temperature, the estimated empirical formula is: cable core temperature = skin temperature +15 ~ 12 degrees Celsius (3) insulation performance test: power cable below 1KV, Applying 1KV megger measurement, the insulation resistance per km of cable (ambient temperature 20 degrees Celsius) must not be lower than 50 megohms.
(4) Withstand voltage test: Generally, 4 to 5 times the DC voltage of the rated voltage of the cable, continuous voltage for 5 minutes for pressure test (not commonly used).