CN106841890B - A Fault Diagnosis Method Based on Grounding Current in Cross Interconnection Box - Google Patents

Abstract

A method for diagnosing faults in a cross-interconnected box based on grounding current, including a data acquisition unit, a current coefficient K calculation unit, an unbalance coefficient J calculation unit, and a diagnostic parameter K and J comprehensive acquisition fault type unit. The data acquisition unit is composed of a ground current acquisition unit, a ground current band-pass filter unit, and an information recording unit. The current coefficient K calculation unit is composed of a current data information storage unit and a current coefficient calculation unit. The unbalance coefficient J calculation unit is composed of a current coefficient storage unit and a calculation unbalance coefficient unit. The diagnostic parameter K, J comprehensive acquisition fault type unit is composed of a parameter table unit composed of diagnostic parameters K, J normal working condition value and fault value, and a comprehensive judgment specific fault type unit. A method for diagnosing faults in a cross-connection box based on grounding current in the present invention realizes the purpose of effectively diagnosing three typical faults in the cross-connection box, has little external interference, low cost, and can be better applied to lines of different voltage levels and can be popularized to multi-circuit long lines.

Description

A fault diagnosis method for cross-connection boxes based on ground current

Technical Field

The invention relates to the field of fault detection in a cross-connected grounding line of a power cable metal sheath, in particular to a fault diagnosis method in a cross-connected box based on grounding current.

Background Art

With the acceleration of my country's urbanization construction, the negative demand for electricity has increased sharply. More and more power cable lines are laid in underground power grids, and the cable lines are becoming longer and longer. In order to effectively reduce the sheath circulation current, long cable lines currently use a cross-interconnected grounding system.

Cross-connection boxes in the line are prone to natural or human factors that cause failures. According to statistics on failure cases in Guangzhou, each year, failures in cross-connection boxes account for more than half of the total number of cross-connection line failures, such as wiring errors in the cross-connection box, coaxial cable breakage, water ingress in the box, etc. After such failures occur, the equivalent circuit of the entire cross-connection section changes, resulting in abnormal grounding current flowing to the earth through the metal sheath. If measures are not taken in time, serious accidents may occur. For example, a 110kV single-core cable line under the jurisdiction of a power supply station failed two years after it was put into operation. The cable line was then checked and it was found that the sheath protector in the cross-connection box at 520m in the main cable corridor was broken down and burned, and the fault point was broken down and the surrounding area was severely burned. Subsequent analysis showed that the main protection configured for this cable line: current limiting speed break; back protection: composite voltage overcurrent. According to operating experience and failure cases, traditional protection has failed to effectively avoid accidents in advance, and usually can only take corresponding protection actions for faults.

As the incidence of such faults increases, fault diagnosis is increasingly widely used in the system, and more and more research is being conducted on diagnostic technology. Currently, more research focuses on online monitoring systems. By online monitoring of circulating currents, induced voltages, etc., a set of measures have been proposed to grasp the operation of the entire cross-connected line. However, the size of the circulating current is affected by factors such as grounding resistance, load current, and laying methods. The reliability of the online monitoring device is unstable and susceptible to external interference. The installation of the entire line is slightly complicated, and the line cost is relatively high. Therefore, it is of great significance to study a set of diagnostic methods that can avoid interference from the external environment, eliminate the impact of changes in different working conditions, and reduce line costs.

Summary of the invention

The purpose of the present invention is to provide a fault diagnosis method in a cross-connection box based on ground current, which achieves the purpose of effectively diagnosing three typical faults in the cross-connection box, has little external interference, low cost, can be well applied to lines of different voltage levels, and can be extended to multi-circuit long lines.

The technical solution adopted by the present invention is:

A fault diagnosis method in a cross-connected box based on grounding current includes a data acquisition unit, a current coefficient K calculation unit, an unbalance coefficient J calculation unit, and a fault type acquisition unit for comprehensive diagnosis parameters K and J.

The data acquisition unit consists of a ground current acquisition unit, a ground current bandpass filtering unit, and an information recording unit.

The current coefficient K calculation unit is composed of a current data information storage unit and a current coefficient calculation unit.

The unbalance coefficient J calculation unit is composed of a current coefficient storage unit and an unbalance coefficient calculation unit.

The diagnostic parameters K, J comprehensive acquisition fault type unit is composed of a parameter table unit composed of the normal operating value and fault value of the diagnostic parameters K, J, and a comprehensive evaluation unit for the specific fault type.

The diagnostic steps are as follows:

Step 1: The grounding current acquisition unit collects the grounding current information on the grounding line, and the grounding current bandpass filter unit is responsible for filtering out other harmonic components, leaving only the fundamental component; the information recording unit records the specific line information and three-phase current data information; Step 2: The current data information storage unit receives the current data from the information recording unit; the current coefficient calculation unit calculates the current coefficient; the current coefficient calculation formula is K _AB = _IA / _IB , K _BC = _IB / _IC , K _CA = _IC / _IA , _IA , _IB , _IC are the fundamental wave values of the three-phase grounding current;

Step 3: In addition to receiving the three current coefficients obtained from the current coefficient calculation unit, the current coefficient storage unit can also input the standard current coefficient K _standard (K _standard = 1) and the unbalance coefficient J _standard (J _standard = 0) in advance. The unbalance coefficient calculation unit calculates the unbalance coefficient. The unbalance coefficient calculation formula is J _AB = (K _AB - K _standard ) / K _standard , J _BC = (K _BC - K _standard ) / K _standard , J _CA = (K _CA - K _standard ) / K _standard ; the standard value is the reference value, which is equivalent to the collected data calculated and compared with this standard value.

Step 4: In addition to receiving the three current coefficients obtained from the current coefficient calculation unit, the current coefficient storage unit can also input the standard current coefficient K _standard (K _standard = 1) and the unbalance coefficient J _standard (J _standard = 0) in advance, and the unbalance coefficient calculation unit 3.2 calculates the unbalance coefficient;

Step 5: The parameter table unit consisting of the normal operating value and fault value of the diagnostic parameters K and J integrates the diagnostic parameters K and J obtained by the current coefficient calculation unit and the unbalance coefficient calculation unit, as well as the K and J values under normal conditions, and compares the normal value with the fault value to evaluate and compare the diagnostic parameters;

Step 6: Integrate the normal values and fault values of the diagnostic parameters K and J to form a parameter table, and judge the fault type;

Step 7: Obtain the specific fault type based on the specific fault situation.

The present invention discloses a fault diagnosis method for a cross-connection box based on grounding current. The fault type is determined by directly measuring the grounding current on the direct grounding wires at both ends of the cross-connection line. The diagnostic parameters proposed by the diagnostic method can avoid the influence caused by changes in factors such as load current and grounding resistance. The diagnostic method is simple, highly operable, and highly accurate. It can be extended to long lines and avoids the problems of large external interference and high cost of traditional online monitoring. The method has strong practical engineering guidance significance.

The present invention provides a fault diagnosis method in a cross-connection box based on ground current, which achieves the purpose of effectively diagnosing three typical faults in the cross-connection box, has little external interference, low cost, can be well applied to lines of different voltage levels, and can be extended to multi-circuit long lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the process of the present invention.

FIG. 2 is a design diagram of a double-circuit 110 kV line in an embodiment.

DETAILED DESCRIPTION

The principle of the present invention is: directly measure the grounding current on the direct grounding wires at both ends of the cross-interconnected lines, calculate the two evaluation parameters of the current coefficient and the unbalance coefficient proposed in the diagnosis method, and the diagnostic parameters effectively avoid the influence of different working conditions such as load current and grounding resistance on the evaluation accuracy. The calculation results are compared with the normal working condition values, and finally the specific fault type is comprehensively evaluated.

A method for diagnosing faults in a cross-connected box based on grounding current includes a data acquisition unit 1, a current coefficient K calculation unit 2, an unbalance coefficient J calculation unit 3, and a fault type acquisition unit 4 for comprehensively obtaining diagnosis parameters K and J.

The data acquisition unit 1 is composed of a ground current acquisition unit 1.1, a ground current bandpass filter unit 1.2, and an information recording unit 1.3. The ground current acquisition unit 1.1 is composed of a zero-sequence current transformer of model LZCT2-10, the ground current bandpass filter unit 1.2 is composed of a Pasternack radio frequency low-pass filter, and the information recording unit 1.3, i.e., an information storage unit, is composed of a data storage module of model ZLKCFM100.

The current coefficient K calculation unit 2 is composed of a current data information storage unit 2.1 and a current coefficient calculation unit 2.2. The current data information storage unit 2.1 is composed of a data storage module of model ZLKCFM100, and the current coefficient calculation unit 2.2 is an Excel spreadsheet built into the computer for processing current data.

The unbalance coefficient J calculation unit 3 is composed of a current coefficient storage unit 3.1 and an unbalance coefficient calculation unit 3.2. The current coefficient storage unit 3.1 is composed of the same data storage module as the information recording unit 1.3, model ZLKCFM100, and the unbalance coefficient calculation unit 3.2 is an Excel spreadsheet built into the computer for processing current data.

The diagnostic parameter K, J comprehensive acquisition fault type unit 4 is composed of a parameter table unit 4.1 composed of the normal working condition value and fault value of the diagnostic parameter K, J, and a comprehensive evaluation unit 4.2 for specific fault type. The parameter table unit 4.1 composed of the normal working condition value and fault value of the diagnostic parameter K, J is composed of a data storage module, model ZLKCFM100, and the comprehensive evaluation unit 4.2 for specific fault type can be written by Simulink data size comparison module, compare the calculated value of the measured data with the standard value, and judge the fault type.

As shown in FIG1 , a method for diagnosing faults in a cross-connection box based on ground current includes the following steps:

The ground current acquisition unit 1.1 in B1 acquires the ground current information on the ground wire.

The ground current bandpass filter unit 1.2 in B2 is responsible for filtering out other harmonic components, leaving only the fundamental component and the information recording unit 1.3 recording specific line information and three-phase current data information.

In B3, the current data information storage unit 2.1 receives the current data from the information recording unit 1.3 and the current coefficient calculation unit 2.2 calculates the current coefficient.

In addition to receiving the three current coefficients obtained from the current coefficient calculation unit 2.2, the current coefficient storage unit 3.1 in B4 can also input the standard current coefficient _Kstandard ( _Kstandard =1) and the unbalance coefficient _Jstandard ( _Jstandard =0) in advance, and the unbalance coefficient calculation unit 3.2 calculates the unbalance coefficient.

The parameter table unit 4.1 consisting of the normal operating value and fault value of the diagnostic parameters K and J in B5 integrates the diagnostic parameters K and J obtained by the current coefficient calculation unit 2.2 and the unbalance coefficient calculation unit 3.2, as well as the K and J values under normal conditions, and compares the normal values with the fault values to evaluate and compare the diagnostic parameters.

B6 integrates the normal values and fault values of the diagnostic parameters K and J to form a parameter table, and judges the fault type.

In B7, the specific fault type is obtained according to the specific fault situation.

Step B1: The ground current acquisition unit 1.1 acquires the ground current information on the ground line; the ground current bandpass filter unit 1.2 is responsible for filtering out other harmonic components and leaving only the fundamental component; the information recording unit 1.3 records the specific line information and three-phase current data information.

Step B2: the current data information storage unit 2.1 receives the current data from the information recording unit 1.3; the current coefficient calculation unit 2.2 calculates the current coefficient, and the current coefficient calculation formula is K _AB = _IA / _IB , K _BC = _IB / _IC , K _CA = _IC / _IA , where I _A , I _B , and I _C are the fundamental wave values of the three-phase grounding current.

In step B3, in addition to receiving the three current coefficients obtained from the current coefficient calculation unit 2.2, the current coefficient storage unit 3.1 can also input _the standard current coefficient Kstandard ( _Kstandard =1) in advance; the unbalance coefficient calculation unit 3.2 calculates the unbalance coefficient J, and the unbalance coefficient calculation formula is _JAB =( _KAB - _Kstandard )/ _Kstandard , _JBC =( _KBC - _Kstandard )/ _Kstandard , _JCA =( _KCA - _Kstandard )/ _Kstandard .

In step B4, in addition to receiving the three current coefficients obtained from the current coefficient calculation unit 2.2, the current coefficient storage unit 3.1 can also input the standard current coefficient _Kstandard ( _Kstandard =1) and the unbalance coefficient _Jstandard ( _Jstandard =0) in advance, and the unbalance coefficient calculation unit 3.2 calculates the unbalance coefficient.

The parameter table unit 4.1 consisting of the normal operating value and fault value of the diagnostic parameters K and J in B5 integrates the diagnostic parameters K and J obtained by the current coefficient calculation unit 2.2 and the unbalance coefficient calculation unit 3.2, as well as the K and J values under normal conditions, and compares the normal values with the fault values to evaluate and compare the diagnostic parameters.

B6 integrates the normal values and fault values of the diagnostic parameters K and J to form a parameter table and judges the fault type.

B7 obtains the specific fault type according to the specific fault situation.

Table 1

It can be seen from Table 1 that the current coefficient K can effectively identify the coaxial cable break fault and determine the fault phase, and the current coefficient of the fault phase is 0; the transposition failure shows that the three-phase current coefficients are quite different, the two-phase current coefficients are small and less than 1, and the one-phase current coefficient is large, greater than 2; the box is flooded, and the current coefficients are all around 1, and the difference between the three current coefficients of the one-box water inflow fault is larger than that of the two-box water inflow fault. In view of the fact that the current coefficient may not be able to effectively and finely distinguish the water inflow of the cross-connected box, the unbalanced coefficient is proposed to diagnose the fault type based on the K standard. It can be found from the unbalanced coefficient J in Table 1 that the J of the one-box water inflow is greater than the two-box water inflow, and the J values are quite different. The unbalanced coefficient can effectively and finely distinguish the water inflow in the cross-connected box. The established evaluation criteria can judge the three types of faults in the box.

The following is an example of a double-circuit 110kV line actually operated by a power supply bureau, and the line situation is shown in Figure 2. Combined with the above specific implementation steps 1-7, it is described in detail.

The entire line is as follows: Four cross-connection boxes are installed in the middle part, and both ends of the line are directly grounded. The grounding current of the four cross-connection boxes in the A1, A2, A3, and A4 joint wells is monitored by the PMS status monitoring unit. Table 2 gives some monitoring data.

Table 2 Measured ground current

The entire southern region continued to experience heavy rainfall in May, and various regions were severely affected. The on-duty personnel of the transmission line status monitoring center found an alarm in the online monitoring device of the cable sheath circulation in the A3 well of the 110kV line through the PMS status monitoring unit. After field investigation, it was found that most of the interconnection boxes in the well had been submerged in water, and there were obvious rust marks on the outside of the box, while other wells were in normal condition. A clamp meter was used to monitor the grounding wire current at both ends of the faulty line in the field, and the data is shown in Table 3.

Table 3 Measured ground current

It can be seen from Table 2 and Table 3 that under normal working conditions, the current is basically maintained at about 5A, and the current coefficient and the unbalance coefficient are 1 and 0 respectively. Once a fault occurs in the box, such as a box completely filled with water in this example, the three current coefficients are all about 1, and the unbalance coefficients are all above 20%, and the unbalance coefficients are quite different. The diagnostic method based on the current coefficient and the unbalance coefficient as the criteria proposed by the present invention can timely judge the fault through the head end grounding current.

Claims (1)

1. A fault diagnosis method in a cross-connection box based on grounding current is characterized in that: the system comprises a data acquisition unit (1), a current coefficient K calculation unit (2), an unbalance coefficient J calculation unit (3) and a diagnosis parameter K, J comprehensive fault type acquisition unit (4); the data acquisition unit (1) consists of a grounding current acquisition unit (1.1), a grounding current band-pass filtering unit (1.2) and an information recording unit (1.3); the current coefficient K calculating unit (2) consists of a current data information storage unit (2.1) and a current coefficient calculating unit (2.2); the unbalance coefficient J calculating unit (3) consists of a current coefficient storage unit (3.1) and an unbalance coefficient calculating unit (3.2); the diagnosis parameter K, J comprehensive acquisition fault type unit (4) consists of a parameter table unit (4.1) consisting of normal working condition values and fault values of diagnosis parameters K, J and a comprehensive judgment specific fault type unit (4.2);

the diagnosis steps are as follows:

step 1: the grounding current acquisition unit (1.1) acquires grounding current information on a grounding wire, and the grounding current band-pass filtering unit (1.2) is used for filtering other harmonic components and only leaving fundamental components; an information recording unit (1.3) records specific line information and three-phase current data information;

step 2: the current data information storage unit (2.1) receives the current data from the information recording unit (1.3); a current coefficient calculating unit (2.2) calculates a current coefficient; the current coefficient calculation formula is K _AB =I _A /I _B 、K _BC =I _B /I _C 、K _CA =I _C /I _A ，I _A 、I _B 、I _C The three-phase grounding current fundamental wave value;

step 3: the current coefficient storage unit (3.1) can receive three current coefficients obtained from the current coefficient calculation unit (2.2) and input a standard current coefficient K in advance _{Standard of} And unbalance coefficient J _{Standard of} The unbalance coefficient calculating unit (3.2) calculates the unbalance coefficient, and the unbalance coefficient calculating formula is J _AB =（K _AB -K _{Standard of} ）/K _{Standard of} 、J _BC =（K _BC -K _{Standard of} ）/K _{Standard of} 、J _CA =（K _CA -K _{Standard of} ）/K _{Standard of} ；

Step 4: the parameter table unit (4.1) consisting of the normal working condition value and the fault value of the diagnosis parameter K, J integrates the diagnosis parameter K, J obtained by the current coefficient calculating unit (2.2) and the unbalance coefficient calculating unit (3.2) and the K, J value under the normal condition, and the normal value is compared with the fault value to evaluate and compare the diagnosis parameters;

step 5: integrating to form a parameter table composed of normal values and fault values of the diagnosis parameters K, J, and judging the fault type;

step 6: and obtaining the specific fault type according to the specific fault condition.

Images