A single-phase ground fault detection and indication method and device for a small current ground distribution network

Abstract

The distribution network in China and other countries mainly adopts the small current grounding method. Most of the faults in the small current grounded distribution network are single-phase high-resistance ground faults. The transient capacitive current signals generated during the fault process have low amplitude and short duration, making fault detection difficult, and there is a lack of effective fault detection and indicating equipment. The invention discloses a fault detection and indication method and feeder monitoring unit equipment for a small current grounded distribution network. The feeder monitoring unit is powered by a power-taking device with power control, uses a capacitive voltage sensor to collect voltage signals, and an electronic current sensor to collect current signals. After detecting a suspected ground fault, wirelessly triggers the other two phases synchronously. Communication mode transfers data. After collecting the data of the three-phase feeder monitoring units of multiple points on the platform software of the system master station, the ground fault detection is performed according to the calculated zero-sequence voltage and zero-sequence current, and the fault signal is sent to the feeder monitoring unit before the fault point on the fault phase Carry out fault indication.

Description

technical field [0001] The present invention generally relates to the fault detection and indication of feeder automation part in power distribution automation, especially the method and equipment for single-phase grounding fault detection and indication of small current grounding distribution network. Background technique [0002] In the power system, the power comes from the power plant, and is transmitted to the load side through the high-voltage or ultra-high-voltage transmission network, and then the power is distributed to users of different voltage levels by the network with a lower voltage level, which mainly plays the role of power distribution in the power grid. The network is called the distribution network, referred to as the distribution network. In the power system, the distribution network is a short board that affects the reliability of power supply for users. The investment in the distribution network is relatively insufficient, and the level of automation ...

AI Technical Summary

Problems solved by technology

[0005] However, after a single-phase ground fault occurs, the single-phase ground fault point must be found as soon as possible to eliminate the fault.

Otherwise, the overvoltage generated by the ground fault can cause power system accidents such as cable explosion, voltage transformer PT burnout, and busbar burnout.

At the same time, if the grounding line is operated as a normal line for a long time, it will bring great hidden dangers to the safety of local residents and livestock.

In 2010, long-term operation of single-phase high-resistance grounding of power distribution overhead lines occurred in Hechi City, Guangxi, resulting in personal electric shock and death

[0020] (3) The zero-sequence reactive power of the fault line is negative;

[0021] (4) The zero-sequence active power of the fault line is large;

[0022] (5) The 5th harmonic current of the faulty line is large and reversed with that of the non-faulty line;

[0023] (6) The negative sequence current of the fault line is large

Therefore, the actual CT usually has an angle error and a change error on the phase, which causes the three-phase CT to be unbalanced, and there is an unbalanced current in the zero-sequence current obtained by superimposing the three-phase CT, and there is an error with the actual zero-sequence current, which affects the line selection result

In addition, the traditional measurement CT has a magnetic core, and the excitation characteristics of the magnetic core are nonlinear, which affects the current linearity from small current to large current; and when the current of the magnetic core is large, magnetic saturation will occur, which will lead to CT saturation. In practical applications, CT saturation often occurs in medium and low voltage power grids. At this time, the correct zero-sequence current cannot be obtained for line selection; the magnetic core has energy storage links and hysteresis links, which makes the CT transient characteristics not good. It is difficult to follow the sudden change of current, and it is difficult to accurately capture weak transient signals

[0031] (2) The location of the ground fault cannot be accurately located

[0038] (2) Signal sources and other equipment require additional investment and construction, and power outages are required during construction;

[0039] (3) For common grounding faults with a grounding resistance of more than 800 ohms, it is impossible to generate a large enough coded signal current to activate the fault indicator, and it is impossible to detect high-resistance grounding faults;

[0040] (4) Unable to detect instantaneous ground fault

[0044] (1) A switch needs to be installed, and there must be a CT and PT inside the switch, and the investment in the switch and FTU is huge;

[0045] (2) It is difficult to capture small current transient signals when measuring CT, and high current will be saturated. When three-phase superposition generates zero sequence, it will cause large errors due to three-phase imbalance, and it is difficult to detect high-impedance grounding;

[0046] (3) PT has a ferromagnetic resonance problem;

[0047] (4) The installation of switches and FTU requires line power outage construction;

[0048] (5) Only the section between the switches can be located, and more accurate positioning cannot be achieved;

[0049] (6) It is very difficult to provide power to FTU on the overhead line, which affects its installation and normal operation

[0050] At present, the small current grounding system, especially the neutral point through the arc suppression coil grounding system, lacks effective ground fault detection methods and equipment, and cannot quickly detect the ground fault and indicate the grounding position

Many power supply departments are still using manual investigation methods such as pulling wires to locate ground faults. These methods have a low degree of automation, are difficult to implement, and have low efficiency. They cannot meet the requirements of the power system to continue to improve the reliability of power supply. one of the main difficulties of sex

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