CN104635107A - Small-current grounding fault line selection system and line selection method - Google Patents

Abstract

A line selection system for small current grounding faults, including zero-sequence current transformers installed on each feeder, voltage transformers installed on the busbar, grounding transformers connected to the busbars, and neutral points on the high-voltage side of the grounding transformers connected to the ground. The grounding loop between them, and the grounding line selection device, the grounding loop is connected in series with a grounding resistor and a contactor for controlling the on-off of the loop, and the grounding line selection device is connected with the zero-sequence current transformer, voltage transformer and The contactor connection is used to control the conduction of the ground loop when the voltage transformer detects the zero-sequence voltage, and then judge the fault line according to the current data collected by the zero-sequence current transformer.

Description

A small current ground fault line selection system and line selection method

technical field

The invention relates to a grounding fault line selection system and a line selection method of a small current grounding system.

Background technique

For the 10KV neutral point ungrounded distribution network, when a line is single-phase grounded, its main characteristics: the magnitude of the zero-sequence current on the non-fault line is equal to the ground capacitance current of the line itself, and the direction flows from the bus to the line ; The magnitude of the zero-sequence current on the fault line is equal to the sum of the capacitance currents of all non-fault lines to ground, and the direction flows from the line to the bus. At present, it is usually only possible to use the difference of the above-mentioned zero-sequence current, and use the zero-sequence power direction method or the zero-sequence current amplitude comparison method to realize the grounding line selection of the microcomputer. Due to the small number of single-phase grounding faults in the neutral point ungrounded system, the fault characteristics are not obvious, and are affected by many factors such as the grid structure, fault nature, zero-sequence current transformer accuracy, etc., the accuracy of grounding line selection is not high, generally not More than 70%.

Contents of the invention

The object of the present invention is to provide a high-accuracy line selection system and method for small current grounding faults in view of the deficiencies in the prior art.

The purpose of the present invention is achieved through the following technical solutions:

A small-current ground fault line selection system is used for ground fault line selection of a neutral point ungrounded distribution network. The distribution network includes a substation bus and several feeders connected to the bus respectively. The line system includes the zero-sequence current transformer installed on each feeder, the voltage transformer installed on the busbar, the grounding transformer connected to the busbar, the grounding loop connected between the neutral point of the high-voltage side of the grounding transformer and the earth, and the grounding transformer. A line selection device, the grounding circuit is connected in series with a grounding resistor and a contactor for controlling the circuit on and off, and the grounding line selection device is respectively connected with a zero-sequence current transformer, a voltage transformer and a contactor for When the transformer detects the zero-sequence voltage, the ground loop is controlled to conduct, and then the fault line is judged according to the current data collected by the zero-sequence current transformer.

Further, the resistance value of the grounding resistor used in the 10KV neutral point ungrounded distribution network is 130-140Ω.

A line selection method for a small current ground fault line selection system, characterized in that it includes the following steps:

(1) When a single-phase ground fault occurs, the voltage transformer detects the zero-sequence voltage and feeds it back to the grounding line selection device. When the zero-sequence voltage exceeds the preset value, the grounding line selection device controls the contactor to close and the grounding resistance is switched on Use and disconnect after 1-2 seconds;

(2), during the time when the grounding resistance is put into use, each zero-sequence current transformer collects the zero-sequence current of each feeder and feeds it back to the grounding line selection device, and the grounding line selection device compares the zero-sequence current of each feeder line, wherein, If the zero-sequence current has a large sudden change or has a significant increase in resistive current, it is determined to be a ground fault line.

The present invention has following beneficial effects:

In the initial stage of distribution network operation, there are fewer lines, fewer cables, and a smaller system. Usually, the neutral point is not grounded (there is no need to install arc suppression coils). In this neutral point ungrounded system, the present invention accurately realizes the grounding line selection by instantaneously inputting the grounding resistance. In theory, the line selection accuracy rate for stable single-phase grounding faults can be as high as 100%, and The accuracy of line selection can also be greatly improved.

When the distribution network develops or the proportion of cables is relatively large, and the single-phase ground fault capacitive current exceeds the prescribed value (10A for overhead line system or 30A for full cable system), the neutral point of the system adopts the arc suppression coil grounding method. At this time, the resistors and other equipment installed in the early stage can still be used, which will not cause waste of equipment investment. When a single-phase ground fault occurs, after the inductive current of the arc suppression coil compensates the capacitive current at the ground fault point, if the fault still does not disappear, it is judged as a permanent ground fault. , Accurately realize the grounding line selection, and better solve the problem of low accuracy of grounding line selection in the resonance grounding (neutral point is grounded through the arc suppression coil) system.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Fig. 1 is a structural schematic diagram of the present invention.

Detailed ways

Referring to Figure 1, the small current ground fault line selection system is used for ground fault line selection of a 10KV neutral point ungrounded distribution network, which includes a bus 1 and several feeders 2 connected to the bus 1 respectively.

A line selection system for small current grounding faults, including zero-sequence current transformers 4 installed on each feeder 2, voltage transformers 5 installed on the bus 1, grounding transformers 6 connected to the bus 1, grounding transformers 6 connected to the The grounding loop 7 between the neutral point of the high-voltage side (Z-type wiring) and the earth, and the grounding line selection device 3, the grounding loop 7 is connected in series with a grounding resistor 71 with a resistance value of 135Ω and a vacuum contact for controlling the on-off of the loop. device 72, the grounding line selection device 3 is respectively connected with the zero-sequence current transformer 4, the voltage transformer 5 and the vacuum contactor 72, and is used to control the grounding circuit 7 to conduct when the voltage transformer 5 detects the zero-sequence voltage, and then The fault line is judged according to the current data collected by the zero-sequence current transformer 4 .

The line selection method of the above-mentioned small current ground fault line selection system includes the following steps:

(1) When a single-phase ground fault occurs, the voltage transformer 5 detects the zero-sequence voltage and feeds it back to the grounding line selection device 3. When the zero-sequence voltage exceeds the preset value, such as the secondary side 25V, the grounding line selection device 3 Control the closing of the vacuum contactor 72 to put the grounding resistor 71 into use and disconnect it after about 1 second;

(2), in the short time when the grounding resistance 71 is put into use, each zero-sequence current transformer 4 collects the zero-sequence current of each feeder and feeds back to the grounding line selection device 3, and the grounding line selection device 3 is to the zero-sequence current of each feeder 2 The current is compared horizontally and vertically. Among them, if the zero-sequence current has a large mutation amount or has a significant increase in resistive current, it is determined to be a ground fault line.

The above is only a preferred embodiment of the present invention, so it cannot limit the scope of the present invention, that is, equivalent changes and modifications made according to the patent scope of the present invention and the content of the specification should still belong to the present invention covered by the patent.

Claims (3)

1. a small current grounding failure wire selection system, for the earth fault line selection of isolated neutral power distribution network, this power distribution network comprises some feeder lines of substation bus bar and difference connection bus, it is characterized in that: described grounding failure wire selection system comprises the zero sequence current mutual inductor be arranged on each feeder line, be arranged on the voltage transformer (VT) on bus, the grounding transformer be connected with bus, be connected to the ground loop between grounding transformer high-pressure side neutral point and the earth, and line-selected earthing device, described ground loop is serially connected with stake resistance and the contactor for control loop break-make, described line-selected earthing device respectively with zero sequence current mutual inductor, voltage transformer (VT) is connected with contactor, for when voltage transformer (VT) detects residual voltage, control described ground loop conducting, then according to the current data failure judgement circuit that zero sequence current mutual inductor gathers.

2. a kind of small current grounding failure wire selection system according to claim 1, is characterized in that: be 130-140 Ω for the resistance of stake resistance described in 10KV isolated neutral power distribution network.

3. a selection method for small current grounding failure wire selection system, is characterized in that: comprise the steps:

(1), when generation singlephase earth fault, voltage transformer (VT) detects residual voltage and feeds back to line-selected earthing device, and when residual voltage exceedes preset value, line-selected earthing device control contactor closes a floodgate and stake resistance come into operation and disconnects after 1-2 second;

(2), within the time that stake resistance comes into operation, line-selected earthing device gathers the zero-sequence current of each feeder line by zero sequence current mutual inductor, the zero-sequence current of each feeder line is compared, wherein, zero-sequence current has compared with macromutation amount or has obvious current in resistance property increment, be then judged to be earth fault line.