CN109031044B - Small-current single-phase grounding automatic line selection method for dispatching-end transformer substation - Google Patents

Abstract

The invention discloses a low-current single-phase grounding automatic line selection method of a dispatching-end transformer substation, which comprises the following steps: judging whether one of the following three conditions is satisfied: zero sequence voltage 3U0>15V; alternatively, the phase voltage (U ₁ ，U ₂ )>7kV and U3<5kV; alternatively, the bus bar is grounded and the calculation cycle=2 is continued; if one of the voltages is met, storing the bus voltage, recording the running state of the line, and recording the line load and zero sequence current in the fault state; the running line comparison satisfies: IN0 failure-IN 0 initial +.0, MAX (I _NO Failure) and MAX (I _N0 failure-I _N0 Initial) or MAX (2 gamma I _N0 failure-I _N0 Initial), outputting the line ID, sending out an alarm instruction, and ending. The invention has the advantages that: when a single-phase grounding occurs in the system, a grounding fault line is rapidly and accurately determined, so that the accident handling efficiency is improved, and the power supply stability of a power grid is improved; the power supply reliability of the power consumer is ensured, and the comprehensive economic loss caused by power failure or unqualified power quality is reduced.

Description

An automatic line selection method for small current single-phase grounding in dispatching end substation

Technical field

The invention relates to an automatic line selection method for small current single-phase grounding in a dispatching end substation.

Background technique

With the continuous development of the power grid, the safe operation of the power grid has become the focus of attention. Any failure of the power system will inevitably lead to inestimable losses. How to accurately process the obtained information and troubleshoot in a timely manner has become the key to the stable operation of the power system. location. In addition, people have put forward higher requirements for the safe operation of the power grid and the reliability of power supply. When the power system fails, workers need to be able to accurately locate and restore the stable operation of the power grid as quickly as possible.

In my country, most of the 6-35kV medium-voltage distribution network systems adopt a neutral point non-direct grounding method, which is called a small current grounding system. This grounding method is helpful to improve power supply reliability. The probability of single-phase ground faults in distribution networks accounts for approximately 80% of the total faults. In a small current grounding system, single-phase grounding poses little threat to the power grid and can continue to operate for 1 to 2 hours. With the development of power grid construction, distribution network transmission lines are getting longer and longer, and more and more cables are used, which increases the ground capacitance of the lines. If only the neutral point is not grounded, the short-circuit current at the fault point will increase, which is not conducive to arc extinguishing and poses a greater threat to the equipment insulation. Therefore, the neutral point wiring methods of my country's distribution network system include: the neutral point is not grounded, the neutral point is grounded through a small resistance, and the neutral point is grounded through an arc suppression coil. The connection of arc suppression coils and resistors reduces the current during a one-way ground fault, and also weakens the sensitivity and selectivity of using this amount of information to select fault line devices, affecting the reliability of power supply. The existing single-phase ground fault line selection methods for small current grounding systems, whether based on transient quantities or steady-state quantities, are affected by CT imbalance, number of outgoing circuits, line length, system operation mode and transition impedance. This makes us more eager to demand new line selection methods, thereby improving the accuracy of line selection accuracy.

At this stage, in a small current grounding system, when a single-phase ground fault occurs, the main processing method at the control end is to test the outlet lines of the corresponding abnormal voltage bus. According to the grounding line selection table, follow the principle of "pull one, send one" and proceed one by one to determine the faulty line. This process will inevitably cause discontinuity in power supply to power users and multiple repeated operations of power equipment switches. And it is greatly affected by factors such as the proficiency of personnel, the smoothness of open3000 system operation, and the smoothness of information channels.

The original low-current single-phase grounding line selection device on the substation site was very inconvenient due to the unattended substation and centralized dispatch monitoring. The zero-sequence current was visible at the time of single-phase ground fault and the parameters were fine-tuned. The accuracy of the grounding line selection was compromised. lower and lower.

With the development of society and economy, people have higher requirements for uninterrupted power supply. How to quickly and accurately determine the faulty line when a single-phase grounding occurs in the system can speed up the elimination of line faults, improve operational reliability, and reduce the risk of faults. Comprehensive economic losses caused by power outages play a very important role in ensuring continuous power supply for power users.

Contents of the invention

The purpose of the present invention is to provide an automatic line selection method for low current single-phase grounding in a dispatching end substation, which can effectively solve the current problem of being unable to quickly and accurately determine a faulty line when a small current single-phase grounding is present in the dispatching end substation.

In order to solve the above technical problems, the present invention is realized through the following technical solutions: a small current single-phase grounding automatic line selection method in a dispatching end substation, including the following steps:

A. Determine whether one of the following three conditions is met: zero sequence voltage 3U ₀ >15V; or, phase voltage (U ₁ , U ₂ ) > 7kV and U3 <5kV; or, busbar grounding action, and continuous calculation period = 2 ;

B1. If the result of step A is that one of the three conditions is met, store the bus voltage (U _a , U _b , U _c , 3U ₀ ), record the line operating status, the line load _ILN in the fault state, and the line load at the time of the fault. Zero sequence current I _{N0 fault} , enter step C1;

C1. The operating line is relatively satisfied: I _{N0 fault} - I _{N0 initialization} ≠ 0, MAX (I _{NO fault} ) and MAX (I _{N0 fault} - I _{N0 initialization} ), otherwise MAX (2×I _{N0 fault} - _{I N0 initialization} ), output Line ID, issue an alarm command, end, where _{IN0 fault} is the zero-sequence current of the line at the time of the fault, _{IN0 initial} refers to the initial zero-sequence current of the line before the fault;

B2. If the result of step A does not meet one of the three conditions, determine whether the ground fault duration is greater than or equal to 3. If yes, perform the second operation; if not, proceed to step C2;

C2. Determine whether the duration period of the ground fault changes to 0, and the circuit breaker 1 of the operating line changes to 0; if so, the output line ID is consistent with the circuit breaker change operating line, indicating the fault line, and the zero sequence current I _{N0 of the non-fault operating line is initial} Change to I _{N0 fault} value, and then end; if not, store the initial operating line zero sequence current I N0 _initialized by I _{N0 fault} if one of the three conditions of step A is not met and the _IN0 fault has not been filled in, and end.

Preferably, in step B2, if the ground fault continues to be greater than or equal to 3, the second operation step is:

B2-1. Determine whether there is a running circuit breaker and the circuit breaker 1 changes to 0. If not, end; if yes, go to the next step;

B2-2, storage bus voltage (U _a , U _b , U _c , 3U ₀ ), line operating status, line load I _LN2 and zero sequence current I _N0 fault 2 in fault state;

B2-3. Determine whether it is an arc suppression coil. If so, the operating line is relatively satisfied: I _{N0 fault 2} - I _{N0 initial} ≠ 0, MAX (I _{N0 fault 2} - I _{N0 fault} ), output the line ID, issue an alarm command, and end ; If not, the operating line satisfies: I _{N0 fault 2} - I _{N0 initial} ≠ 0, MAX (I _{NO fault 2} ) and MAX (I _{N0 fault 2} - I _{N0 fault} ), otherwise, output the line ID and issue an alarm command, Finish.

Compared with the prior art, the advantages of the present invention are:

1) When a single-phase grounding occurs in the system, quickly and accurately determine the ground fault line, improve the efficiency of accident handling, and improve the stability of the power grid;

2) Ensure the reliability of power supply for power users and reduce comprehensive economic losses caused by power outages or substandard power quality.

Description of drawings

Figure 1 is a flow chart of a method of automatic line selection for small current single-phase grounding in a dispatching end substation according to the present invention;

Figure 2 is a flow chart of the second operation in the present invention.

Detailed ways

Embodiments of the invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and are not to be construed as limiting the present invention.

Referring to Figure 1, an embodiment of an automatic line selection method for low current single-phase grounding in a dispatching end substation of the present invention is shown. An automatic line selection method for low current single-phase grounding in a dispatching end substation includes the following steps:

A. Determine whether one of the following three conditions is met: zero sequence voltage 3U ₀ >15V; or, phase voltage (U ₁ , U ₂ ) > 7kV and U3 <5kV; or, busbar grounding action, and continuous calculation period = 2 ;

B1. If the result of step A is that one of the three conditions is met, store the bus voltage (U _a , U _b , U _c , 3U ₀ ), record the line operating status, the line load _ILN in the fault state, and the line load at the time of the fault. Zero sequence current I _{N0 fault} , enter step C1;

C1. The operating line is relatively satisfied: I _{N0 fault} - I _{N0 initialization} ≠ 0, MAX (I _{NO fault} ) and MAX (I _{N0 fault} - I _{N0 initialization} ), otherwise MAX (2×I _{N0 fault} - _{I N0 initialization} ), output Line ID, issue alarm command, end, where I _{N0 initial} refers to the initial zero sequence current of the line before the fault;

B2. If the result of step A does not meet one of the three conditions, determine whether the ground fault duration is greater than or equal to 3. If yes, perform the second operation; if not, proceed to step C2;

C2. Determine whether the duration period of the ground fault changes to 0, and the circuit breaker 1 of the operating line changes to 0; if so, the output line ID is consistent with the circuit breaker change operating line, indicating the fault line, and the zero sequence current I _{N0 of the non-fault operating line is initial} Change to I _{N0 fault} value, and then end; if not, store the initial operating line zero sequence current I N0 _initialized by I _{N0 fault} if one of the three conditions of step A is not met and the _IN0 fault has not been filled in, and end.

As shown in Figure 2, in step B2, if the ground fault continues to be greater than or equal to 3, the second operation step is:

B2-1. Determine whether there is a running circuit breaker and the circuit breaker 1 changes to 0. If not, end; if yes, go to the next step;

B2-2. Store bus voltage (U _a , U _b , U _c , 3U ₀ ), line operating status, line load I _LN2 and zero sequence current I _{N0 fault 2} under fault status;

B2-3. Determine whether it is an arc suppression coil. If so, the operating line is relatively satisfied: I _{N0 fault 2} - I _{N0 initial} ≠ 0, MAX (I _{N0 fault 2} - I _{N0 fault} ), output the line ID, issue an alarm command, and end ; If not, the operating line satisfies: I _{N0 fault 2} - I _{N0 initial} ≠ 0, MAX (I _{NO fault 2} ) and MAX (I _{N0 fault 2} - I _{N0 fault} ), otherwise, output the line ID and issue an alarm command, Finish.

The small and medium current grounding system of the present invention refers to a three-phase system in which the neutral point is not grounded or is grounded through an arc suppression coil and high impedance, also known as the neutral point indirect grounding system. When a ground fault occurs in a certain phase, since a short circuit cannot be formed, the ground fault current is often much smaller than the load current, so this system is called a "small current grounding system". The zero-sequence current, line operating status, and load of the distribution network lines at the unattended substation site are collected through the substation measurement and control device and sent to the dispatching end. The dispatching end deploys an automatic line selection system to utilize the line operating status, zero-sequence current Steady-state size, distinguish whether arc suppression coil is configured, compare the running zero-sequence current value of the line with historical ground faults of other lines on the same bus, horizontally compare the zero-sequence current value of the running line with this ground fault, automatically select the faulty line, and send an alarm through the alarm method It reminds the dispatcher to pay attention and visualizes the real-time value and historical curve of the zero-sequence current value of the fault line, providing a new method for automatic line selection of single-phase ground faults in small current grounding systems at the control end, and improving single-phase ground fault line selection in small current grounding systems. accuracy and speed.

Using the original substation automation system, the 10 kV bus voltage data (Ua, Ub, Uc, 3U0) of the unattended substation site, distribution network equipment operation data (measurement data such as P, Q, I, 3I ₀ , etc., location Status such as circuit breaker, isolating switch, grounding switch, etc.), arc suppression coil equipment operating data (measurement data such as compensation inductor current I, capacitor current I, neutral point current I, etc.), position status such as circuit breaker, isolating switch, etc. ), bus single-phase grounding alarm information, etc. are collected through the substation measurement and control device and sent to the dispatching end SCADA system. The dispatching end deploys an automatic line selection system to interface with the SCADA system to track bus voltage data (Ua, Ub, Uc, 3U0 ), using three methods: 3U0 is greater than 15V, or two of the three-phase voltages are greater than 7kV and the other phase is less than 5kV, or the bus is grounded, as the start judgment conditions, both calculation cycles comply with one of the three methods , to determine the occurrence of a single-phase ground fault, conduct a comprehensive correlation analysis on the zero-sequence current value after each operating feeder fault and the line operating zero-sequence current value at the time of historical ground faults on other lines on the same bus, and provide the ground fault line according to the likelihood. Alarm, push SCADA system alarms and optical words to remind dispatchers to pay attention, realize automatic fault line selection, and visualize the real-time zero sequence current value and historical curve of the fault line through the SCADA system, which can effectively improve the accuracy of distribution network line selection. and rapidity.

The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention. among.

Claims (1)

1. A small-current single-phase grounding automatic line selection method of a dispatching-end transformer substation is characterized by comprising the following steps of:

the method comprises the following steps:

A. judging whether one of the following three conditions is satisfied: zero sequence voltage 3U ₀ >15V; alternatively, the phase voltage (U ₁ ，U ₂ )>7kV and U3<5kV; alternatively, the bus bar is grounded and the calculation cycle=2 is continued; if the condition is met, executing the B1, and if the condition is not met, executing the B2;

b1, storage bus voltage (U) _a 、U _b 、U _c 、3U ₀ ) Recording the running state of the line and the line load I under the fault state _LN Zero sequence current I of line at fault moment _{N0 failure} Step C1 is entered;

and C1, comparing and satisfying the operation line: i _{N0 failure} -I _{N0 initial} ≠0，MAX(I _{NO fault} ) And MAX (I) _{N0 failure} -I _{N0 initial} ) Otherwise MAX (2×I) _{N0 failure} -I _{N0 initial} ) Outputting a line ID, sending out an alarm instruction and ending; wherein I is _{N0 initial} The initial zero sequence current of the line before failure;

b2, judging whether the ground fault duration is greater than or equal to 3, if so, performing a second operation step B2-1 to B2-3; if not, entering a step C2;

b2-1, judging whether the running line breaker 1 is changed to 0, if not, ending; if yes, entering the next step;

b2-2, storage bus voltage (U) _a 、U _b 、U _c 、3U ₀ ) Line running state, line load I under fault state _LN2 Zero sequence current I _{N0 failure 2} ；

B2-3, judging whether an arc suppression coil exists or not, and if so, comparing the running lines to meet the following conditions: i _{N0 failure 2} -I _{N0 initial} ≠0，MAX(I _{N0 failure 2} -I _{N0 failure} ) Outputting a line ID, sending out an alarm instruction and ending; if not, the run line comparison satisfies: i _{N0 failure 2} -I _{N0 initial} ≠0，MAX(I _{NO fault 2} ) And MAX (I) _{N0 failure 2} -I _{N0 failure} ) Outputting a line ID, sending out an alarm instruction and ending;

c2, judging whether the earth fault duration period is changed to 0, and the operating circuit breaker 1 is changed to 0; if yes, the output line ID is consistent with the circuit breaker change operation line, a fault line is marked, and the zero sequence current I of the non-fault operation line is marked _{N0 initial} Change to I _{N0 failure} The value, then end; if not, storing the data which does not meet one of the three conditions in the step A and is not filled with I _{N0 failure} Give I _{N0 initial} Zero sequence current I of the running line of (2) _{N0 initial} And (5) ending.