IEEE 1234:2007 pdf free download

IEEE 1234:2007 pdf free download.IEEE Guide for Fault-Locating Techniques on Shielded Power Cable Systems.
5.2.1 Safety consideration
Network cable systems require mention of several additional sally ISsLIeS, since the secondaries of transformers are tied to a common bus. With transformer primaries connected in a delta configuration, a primary cable could be energized via a closed network protector due to a faulty master relay within the protector. To avoid backfeeding of transformer primaries and cable, all network protectors must be locked in the open position before connecting fault-locating equipment. After verifying the status of all protectors, the primary cables must be checked for voltage and must be grounded.
5.2.2 Fault-locating parameters
In network distribution, fault-locating efforts often will require more than one fault-locating method. In a specific network, to select the right tool, the following factors should be considered and weighed:
a) The overall circuit length. number of branches, and the number of connected transformers will determine the effectiveness of a fault-locating method. For efficient fault locating with TDR techniques, more than one access point should be available in each network circuit. As a general rule, one access point for every three to four branches is desirable,
b) l)irect access to the defective cable is necessary for effective use of TDR. surge and bum arc reflection, surge (current) pulse. and voltage decay techniques. An impedance mismatch between test equipment and test object will limit or prevent the use of TDR techniques.
c) The total lumped capacitance oF the cable system limits the effective use of surge generators. When using a surge arc reflection method, a surge generator with internal capacitor of 10 times the cable capacitance is necessary. Burn arc reflection with an ac or dc burn set capable of maintaining an arc current of 4 A to S A is also very effective in locating a faulted cable section with a TDR.
d) The type of cable insulation restricts the use of burning and dc lest voltages. Oil-paper insulated cables often are subjected to burning in order to reduce the fault resistance for ease of identification. Burning of solid dielectrics usually does not result in a reduced fault resistance. More importantly, burning of cables with solid dielectric insulation for relatively short periods of time may lead to explosions: if the insulation ignites, manhole or duct fires can destroy unfaulted and energized cables in the vicinity of the fault. in general. burning should only be applied to paper insulated cables or cables submerged in water. Burning of cable faults should always be monitored with a TDR, thus minimizing burning time and possible damage.
e) Transformer primai connections must be considered when selecting a cable fault-locating method in situations where the cables cannot be isolated. Many network circuits LItiiizc delta- connected transformer primaries, which are permanently connected to the cables. All phases are tied together, causing unwanted paths and reflection points for TDR-type fault-locating equipment. A grounded. unfaulted phase will eliminate the use of fault-locating methods using dc equipment. Grounded wye-connected transformer primaries also will preclude the use of dc fault-locating equipment.
0 Whenever possible, the fault resistance should be measured using an insulation resistance tester/obmmeter combination.