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Single-phase ground line selection method with function of accuracy improvement for small-current grounding system

A low-current grounding and single-phase grounding technology, applied in the direction of the fault location, can solve problems such as unobvious fault characteristics, complex and changeable fault conditions in the small-current grounding system, and difficult line selection with high accuracy, so as to achieve small impact, The effect of strong resistance to excessive resistance and high line selection accuracy

Active Publication Date: 2016-03-23
TIANJIN UNIV +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Due to the complex and changeable fault conditions of the small current grounding system, the fault characteristics, especially the fault characteristics of the neutral point through the arc suppression coil grounding system, are not obvious, and each method has its scope of application and limitations, so as to achieve high accuracy line selection is difficult

Method used

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  • Single-phase ground line selection method with function of accuracy improvement for small-current grounding system
  • Single-phase ground line selection method with function of accuracy improvement for small-current grounding system
  • Single-phase ground line selection method with function of accuracy improvement for small-current grounding system

Examples

Experimental program
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Effect test

example 1

[0024] Ungrounded neutral system with figure 1 Take the structure diagram shown as an example, the model in the figure contains 5 outgoing lines L 1 ~ L 5 , where L 1 , L 2 For overhead lines, the lengths are 20km and 6km respectively; L 3 , L 4 is the cable, the lengths are 10km and 3km respectively; L 5It is a mixed line of overhead cables, the cable part is close to the busbar, the length is 5km, and the length of the overhead line is 7km. The parameters of overhead lines and cable lines are shown in Tables 1 and 2. All loads adopt "Three-phaseSeriesRLCLoad", the neutral point is not grounded, and the power factor is 0.8.

[0025] Table 1 Overhead Line Parameters

[0026] phase sequence

Resistance (Ω / km)

Capacitance (μF / km)

Inductance (mH / km)

Positive sequence

0.17

0.061

7.600

zero sequence

0.23

0.038

34.400

[0027] Table 2 Cable Line Parameters

[0028] phase sequence

Resistance (Ω / km...

example 2

[0041] The neutral point is connected to the high-impedance grounding system with image 3 The structure diagram shown is an example. The number of outgoing lines, line parameters, and loads of the system are the same as those of the neutral point ungrounded system. The neutral point grounding resistance generally follows the neutral point current I R =1~1.5I C to choose, I C It is the capacitive current to the ground of the system. According to the simulation model and line parameters, the neutral point resistance is 200Ω.

[0042] The fault location is selected at the 2km distance from the busbar of the third outgoing line, the A phase is grounded through a 5000 ohm resistor, and the fault phase angle is 0°. The line selection results are shown in Table 5.

[0043] Table 5 Fault line selection results of the neutral point through the high-impedance grounding system (L 3 / 5000€ / 0°)

[0044]

[0045] It can be seen from Table 5 that due to the large grounding resistanc...

example 3

[0047] The neutral point is grounded by the arc suppression coil Figure 5 Take the structure diagram shown as an example, the number of outgoing lines, line parameters, and loads of the system are the same as those of the neutral point ungrounded system, the compensation degree of the arc suppression coil is 5%, and the distributed capacitance C of the system to ground is obtained from the line parameters Σ , and then calculate the arc suppression coil equivalent inductance L=1 / 1.05*1 / (3ω 2 C Σ ) = 0.6554H. The active loss of the arc suppression coil is 3% of the inductive loss, R L =0.03ωL=6.1767Ω.

[0048] The fault location is selected at the 2km distance from the busbar of the 3rd outgoing line, the A phase is grounded through a 50 ohm resistor, and the fault phase angle is 45°. The line selection results are shown in Table 6.

[0049] Table 6 Results of fault line selection of neutral point via high-impedance grounding system (L 3 / 50Ω / 45°)

[0050]

[0051] No...

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Abstract

The invention relates to a single-phase ground line selection method with the function of accuracy improvement for a small-current grounding system. The method comprises: (1), whether a fault occurs is monitored; if so, a fault line section algorithm is started; (2), Fourier transform is carried out on sampling data of a zero-sequence voltage and a zero-sequence current in a fifth cycle after fault occurrence and amplitudes and phase angles of the zero-sequence voltage and zero-sequence current fundamental waves of all paths of outgoing lines are obtained; and if a neutral point passes through an arc suppression ground system, amplitudes and phase angles of harmonic waves are calculated for five times; (3), amplitude-comparing-method fault measurement is constructed; (4), a phase-comparing-method fault measurement is constructed; (5), initial-half-wave-method fault measurement is constructed; (6), wavelet-analytical-method fault measurement is constructed; and (7), a serial number of a line with the largest fault measurement is found out under each criterion; if the serial numbers are identical, the line is a fault line and a line selection result is outputted, and the line selection is completed; and if the serial numbers are different, a multi-criterion fusion method based on a D-S evidence theory is started. With the method, accuracy of the fault line selection algorithm is improved effectively.

Description

technical field [0001] The invention belongs to the technical field of relay protection and power distribution network. It is a single-phase grounding line selection method for small current grounding systems with high accuracy. Background technique [0002] my country's medium and low voltage distribution network is generally a small current grounding system, including the neutral point ungrounded system, the neutral point through the high resistance grounding system and the neutral point through the arc suppression coil grounding system. After a single-phase ground fault occurs in the low-current grounding system, the line voltage is still symmetrical and does not affect the power supply to users. The regulations stipulate that it can run for 1 to 2 hours with a fault, and the power supply reliability is high. [0003] After a single-phase ground fault occurs in a low-current grounding system, the voltage of the non-faulted phase rises, which will pose a threat to the ins...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R31/08
Inventor 李永丽宋金钊刘勇
Owner TIANJIN UNIV
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