Abstract
The mutual induction between the phase wires of the different overhead lines which situate close to each other cause unbalanced redistribution of currents in the line wires. This leads to emergence of the outof-balance zero sequence current which affects negatively on the sensitivity of the zero-sequence current protection. It is impossible to estimate such out-ofbalance current by the means of the typical calculation programs for short circuit currents. This paper describes the method of “virtual” lines for an extra correction of the values of zero-sequence currents during the current ground faults happening in the overhead lines 110-220 kV. There is an example of using this method for three parallel overhead lines 220 kV passing close to each other.
Highlights
In the multiended overhead lines 110-220 kV which include multiwire overhead parallel line (OHPL) and OHPL with single or several branches there is a problem of taking in account the zero-sequence current while adjusting sensitive stages of zero-sequence current protection[1]
This problem exists because of the high out-of-balance currents in the lines as much as in normal operating conditions and during the remote asymmetrical shortcircuits which happen by the reason of mutual induction between phase wires of one line or two separate lines
To consider the influence of the mutual induction of the triple-circuit transmission line on the phase currents flowing in it while fault regime the part of a network represented in the Fig. 1 has been taken for analysis
Summary
In the multiended overhead lines 110-220 kV which include multiwire overhead parallel line (OHPL) and OHPL with single or several branches there is a problem of taking in account the zero-sequence current while adjusting sensitive stages of zero-sequence current protection[1]. This problem exists because of the high out-of-balance currents in the lines as much as in normal operating conditions and during the remote asymmetrical shortcircuits which happen by the reason of mutual induction between phase wires of one line or two separate lines. The zero-consequence out-of-balance currents result the great difference between the real and calculated short-circuit currents of single-phase short circuits while using typical calculation programs [4].there is a requirement to accept set points of protection with a large safety factor to exclude non- selective operation, but sensitivity of protection is reduced
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