Method for judging lock by zero sequence voltage and current

A technology of zero-sequence voltage and zero-sequence current, applied in the field of line protection, to improve reliability and prevent malfunction

Active Publication Date: 2012-04-25
STATE GRID ZHEJIANG ELECTRIC POWER +1
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

However, if the zero-sequence current generated by the zero-sequence potential is in the same direction as the crossing zero-sequence current, it cannot be blocked by increasing the zero-sequence current threshold

Method used

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  • Method for judging lock by zero sequence voltage and current
  • Method for judging lock by zero sequence voltage and current
  • Method for judging lock by zero sequence voltage and current

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Embodiment Construction

[0015] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0016] Working steps of the present invention are:

[0017] The line protection device samples the voltage and current waveforms of the transformer, and calculates the magnitude of the fundamental zero-sequence voltage and zero-sequence current, which is recorded as: U 0 , I 0 ; If the protection device judges that the power grid is abnormal, and the zero-sequence power is judged to flow from the line to the bus, continue to judge at this time I 0 , U 0 Is it greater than the threshold value, namely:

[0018] I 0 > I 0zd

[0019] U 0 > U 0zd

[0020] in, I 0zd is the zero-sequence current threshold, U 0zd is the threshold value of the zero-sequence voltage. If the two inequalities hold simultaneously, the zero-sequence directional element is allowed to act; otherwise, the zero-sequence directional ...

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Abstract

The invention discloses a method for judging lock by zero sequence voltage and current, relating to a line protection method. In the existing line protection, in particular in weakly electrically and strongly magnetically connected double circuits, a mutual inductance electric potential is easy to cause longitudinal zero sequence direction protection misoperation. The technical scheme of the method disclosed by the invention comprises the following steps of: (1) sampling voltage and current wave forms of a mutual inductor by a line protecting device, and figuring out the sizes of zero sequence voltage and zero sequence current of a fundamental wave; and (2) when the line protecting device judges that a power grid is abnormal and zero sequence power flows from a line to a bus, allowing an element in a zero sequence direction to operate if the zero sequence voltage is larger than a zero sequence voltage threshold value and the zero sequence current is larger than a zero sequence current threshold value; otherwise, locking the elements in the zero sequence direction. Zero sequence current locking and zero sequence voltage locking conditions are added to protection in a longitudinal zero sequence direction, thus non-fault line longitudinal zero sequence direction protection misoperation caused by zero sequence mutual inductance can be prevented, and the reliability of longitudinal zero sequence direction protection in the weakly electrically and strongly magnetically connected double circuits is improved.

Description

technical field [0001] The invention relates to a line protection method. Background technique [0002] At present, longitudinal zero-sequence directional protection is widely used in domestic transmission lines with voltage levels of 220kV and above. With the rapid increase of double-circuit lines erected on the same pole and in the same corridor in the high-voltage power grid, the mutual inductance between lines seriously affects the correct action of line protection, especially in double-circuit lines with weak current and strong magnetic connections, the mutual inductance potential causes no fault lines The zero-sequence power flows from the line to the busbar at both ends, resulting in misoperation of the longitudinal zero-sequence direction protection. [0003] In order to improve this problem, the existing technology adopts the method of increasing the zero-sequence current threshold to avoid the maximum zero-sequence current value caused by mutual inductance, or use...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02H7/26H02H3/32
Inventor 方愉冬徐习东裘愉涛仇群辉王全
Owner STATE GRID ZHEJIANG ELECTRIC POWER
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