The greatest application has a way of test at which the cable line (rice 1-1 is completely disconnected. at high efficiency this way rather labor-consuming as process of test demands a serial conclusion of lines from work. Thus the normal mode of a network that conducts to increase in losses of energy in a network is broken and reliability of power supply of consumers decreases. Shutdown and the return inclusion of lines happens at a high voltage, i.e. it is necessary to ensure safety of the personnel which is carrying out these operations.
Except for direct mechanical damages, the weakened places and defects of C have the hidden character. In due time not revealed by tests they can develop with this or that speed under the influence of working tension. Thus perhaps final fracture of the C elements in the weakened place with transition of the line to the mode of short circuit and its shutdown with the corresponding violation of power supply of consumers.
The cable sample having defects at breakdown is recommended to be cut out and surveyed in stationary installations. It is necessary for the purpose of definition of the reasons of emergence of defect and development of the relevant activities excluding such defects. Results of inspection are made out by the relevant protocol and register in the C card. With factory defects the unsatisfactory condition of the equipment which is reported to manufacturer of a cable and fittings is formed.
It is made at metal trailer seals on lines of all tension, except lines to 1000 V with the grounded neutral, and on lines of 110 — 220 kV also at metal designs of cable wells and make-up points
The reasons of emergence of such weakened places are very various. They can arise at production of a cable and fittings at plant because of constructive shortcomings of a cable and fittings, at negligent laying of cable lines, at low-quality performance of installation works. The weakened places come to light in use C as over time aging of isolation of cables and corrosion of their metal covers is observed. The cable lines laid in an earth trench despite of additional protection in the form of a covering a brick and systematic supervision over a condition of the route of lines, are very subject to external mechanical damages which can arise during the laying and repair of other city underground constructions passing on the route C.
The scheme of measurement is carried out with use of special wires and clips for the purpose of an exception of influence of resistance of contacts on results. If the line has inserts of different sections, resistance of the line is given to one equivalent. At application of a bridge method it is necessary to have one uninjured vein or a vein with a transitional resistance, not less than by 100 times big the transitional resistance of other veins. Value of transitional resistance of the injured vein no more than 5000 Ohms. Single-phase and multiphase damages of steady character reliably are defined by method. At breaks of veins definition of a place of damage is made by measurement of capacity of the line by means of the bridge of alternating current. As a rule, universal cable Bridge R-334 which allows measurement on direct and alternating current is applied.
The second way of test is developed by the increased tension only for C of 6 kV now. Application of a way leads to reduction in cost of tests due to considerable reduction of number of switches in networks and reductions of the labor costs connected with production of tests. In this case the network site which is in the normal mode is subjected to test. As a rule, tests are carried out to the period of the minimum loading, with the prior notice of consumers of the tested network site.
Acceptance tests (), tests differ at capital (To) and flowing (T) repairs, and also between-repairs tests (M). For cable lines of city networks tests of P,K and M are characteristic. Thus tests To and M according to the accepted terminology carry names of the preventive tests (PT).
where L — line length; R1 and R2 — resistance of the resistor attached to the injured and uninjured veins respectively. Measurements are performed since both ends of the cable line. As an indicator of correctness of measurements the ratio serves