CN111257794A - Transformer substation grounding device thermal stability checking method based on conduction test - Google Patents
Transformer substation grounding device thermal stability checking method based on conduction test Download PDFInfo
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Abstract
The invention discloses a method for checking the thermal stability of a transformer substation grounding device based on a conduction test. The method supplements a detailed solving method of key parameters, and obtains the shunt coefficient value of the grounding device in an actual measurement mode; and selecting an excavation point of the grounding device by using the conduction test result, and further obtaining the effective sectional area of the grounding device by means of excavation inspection. The invention improves the method for checking the thermal stability of the grounding device of the transformer substation in the prior art, provides a technical basis for whether the grounding device of the transformer substation needs to be subjected to capacity-increasing transformation or not, and ensures the safe and stable operation of the transformer substation.
Description
Technical Field
The invention belongs to the grounding technology in the field of electrical engineering, and particularly relates to a method for checking the thermal stability of a grounding device of a transformer substation based on a shunt coefficient and conduction test technology.
Background
Twenty-five key requirements for preventing power production accidents 14.1.4: and the thermal stability of the grounding device which is put into operation at the earlier stage is checked, and the grounding device which does not meet the requirement needs to be modified. The heat stability checking calculation is the key for the technical improvement of the grounding device and is an essential means for ensuring the safe and stable operation of the electrical equipment.
In the thermal stability verification of the grounding conductor (wire) of the existing transformer substation grounding device, the formula commonly applied at present is as follows:
in the formula: sgThe minimum cross-sectional area of the grounding device (specifically divided into a wiring body and a grounding wire), IgThe effective value of the maximum ground fault asymmetric current flowing through the grounding body; t is teC is the ground fault equivalent duration and the ground device material thermal stability factor. Wherein, IgThe shunt coefficient S of the grounding device is calculated when the short circuit occurs in or out of the stationf1Or Sf2(collectively referred to as the grounding device shunt factor S)f) Maximum grounding short-circuit current I when grounding short circuit occurs in transformer substationmaxAnd current I flowing through neutral point of electrical equipment when grounding short circuit occurs in transformer substationnIt is related.
Therefore, only the calculation parameter, namely the shunt coefficient S of the grounding device in the short circuit of the substation is accurately obtainedf1And the shunt coefficient S of the grounding device during short circuit outside the substationf2Maximum grounding short-circuit current I when grounding short circuit occurs in transformer substationmaxAnd when the grounding short circuit occurs in the transformer substation, the current I flowing through the equipment neutral pointnThe maximum earth fault asymmetric current effective value I flowing through the grounding body (wire) can be calculatedg. The requirement of the power system on the sectional area of the grounding device of the transformer substation can be obtained through calculation
Then, compare
And SgCan judge whether the thermal stability of the checked grounding device meets the actual operation requirement.
However, the above-described verification has the following problems:
1. the transformers of 220kV and below are mostly three-phase integrated equipment, the neutral point of the transformer is directly led out and grounded, while the neutral point of a single-phase main transformer with the voltage level of 500kV and above is led out phase by phase (called as a neutral point grounding wire independent section), and then the three phases are converged to form the neutral point (called as a neutral point grounding wire sharing section). When a three-phase short circuit occurs, the three-phase short circuit current value flows through the independent section of the neutral point grounding wire of the three-phase transformer, and only unbalanced current (theoretical value is zero) flows through the shared section of the neutral point grounding wire due to the symmetry of the three-phase short circuit current. When the three-phase short-circuit current at 500kV side of a 500kV transformer substation provided with a single-phase main transformer is larger than any asymmetrical earth fault current value, the maximum earth fault asymmetrical current effective value I flowing through an earth conductor (line)gIt cannot be used to check the neutral grounding line independent segment.
2. In the same transformer substation, the current values of two different positions with direct electrical connection in the same voltage class are the same when short-circuit faults occur, but the current values of the two different positions with direct electrical connection in the same voltage class are different from each other, and the short-circuit faults are removedThe action time of the movable protection device and the matching logic and the backup protection are different. In particular, formula
Medium and same grounding thermal stability coefficient C only
The product of (a) and (b) is the largest,
the square is the largest. Using only the maximum earth-fault asymmetric current effective value I flowing through the earth conductor (line)gThe calculation can only ensure the maximum current value and cannot completely ensure
The product of (d) is the largest and the check results will be biased accordingly.
3. Compared with an off-station short circuit, the in-station short circuit of the transformer substation has higher danger on safe operation and is easier to cause accidents. Thus, the maximum ground fault asymmetrical current effective value I of the ground conductorgThe calculation is more efficient in terms of intra-site shorts.
The short-circuit fault shunt coefficient comprises two definitions, namely a shunt coefficient S of the grounding devicefThe other is a ground wire shunt coefficient S'fAnd the sum of the two is 1. For a transformer substation with more inlet and outlet wires, statistical data show that the ground wire shunting capacity is up to 50%, and the ground wire shunting capacity of the transformer substation is not small. Therefore, the checking result of the thermal stability of the grounding device, which accurately accounts for the shunt coefficient, has more practical guiding value. However, the existing calculation process of the shunt coefficient has the problems of inaccurate calculation model, complex calculation process and large actual difference of engineering. Therefore, the intra-station short circuit shunt coefficient S cannot be accurately calculatedf1。
4. The earthing device is influenced by the pH value and the moisture content of soil, and oxides formed on the surface of the earthing device do not have good through-current capacity, namely the effective through-current sectional area of the earthing device is reduced. Therefore, for a substation that has been operating for a certain period of time, the impact of corrosion on the effective flow area of the earthing device must be taken into account.
In the related standards or regulations such as DL/T596 "preventive test regulations for power equipment", DL/T393 "state overhaul test regulations for power transmission and transformation equipment", excavation inspection requirements are provided in the form of "inspection items" or "routine tests", generally stipulated: 5-8 points can be selected according to the importance of electrical equipment and the safety of construction, and excavation inspection can be carried out along the grounding wire, and the excavation range can be enlarged if doubt. However, the standards and regulations only refer to the technical requirements of excavation inspection, and a judgment method convenient for technicians to excavate and select points is not provided. Particularly for old stations with grounding electrodes and grounding wire corrosion fracture conditions, if a targeted excavation point selection method is not available, the actual corrosion state of the grounding device is difficult to grasp due to improper point selection, and S in the formula (1) cannot be obtainedgThe exact value of (c).
Namely: the prior art of thermal stability checking of the grounding device of the transformer substation at present does not really consider the corrosion problem of laying a grounding electrode (wire) in a certain-age ground. In the prior art, although there are many methods for searching or evaluating corrosion of the grounding device, there is no method for selecting the excavation point position of the grounding device by using a conduction test, and there is no related method for applying the method to checking the thermal stability of the grounding device.
Disclosure of Invention
The invention provides a thermal stability checking calculation method of a substation grounding device based on a shunt coefficient and a conduction test technology, and aims to improve and improve the implementation process of checking while solving the problems in the prior art.
The object of the invention is thus achieved. The invention provides a method for checking the thermal stability of a transformer substation grounding device based on a conduction test, which comprises the following steps:
step 1, acquiring information required by thermal stability check calculation of a grounding device of a transformer substation;
the information required by the checking calculation of the substation grounding device comprises the following information: voltage grade, main wiring form, grounding device material, protection configuration mode, main protection sleeve number and main transformer neutral point grounding mode;
IΔ＝Imax-In
In the formula ImaxThe maximum grounding short-circuit current I is the maximum grounding short-circuit current when the grounding short-circuit occurs in the transformer substation under the maximum operation mode of the power systemnThe current flowing through the neutral point of the electrical equipment when the grounding short circuit occurs in the transformer substation;
maximum grounding short-circuit current I when grounding short circuit occurs in transformer substation under maximum operation mode of power systemmaxAnd current I flowing through neutral point of electrical equipment when grounding short circuit occurs in transformer substationnObtaining the load through a PSD-BPA load flow calculation program;
the method for selecting the fault position of the ground short circuit comprises the following steps: if a bus bar exists in the main wiring, selecting the bus bar to be short-circuited; if the main connection line is a bridge type connection line, selecting a position of a bridge breaker for short circuit; if the main wiring is in a unit wiring form, selecting a position of a breaker for short circuit;
For a transformer substation configured with two sets of quick-acting active protection and breaker failure protection:
te＝tm+tf+to
in the formula, tmThe main protection action time; t is tfThe time for the failure protection action; t is toThe circuit breaker open time;
for a substation configured with a set of quick-action active protection:
te＝to+tr
in the formula, trThe action time of the next-stage backup protection is obtained;
if the number of the next-stage backup protection devices is 2 or more than 2, selecting the maximum value of the action time of all the next-stage backup protection devices as the action time t of the next-stage backup protectionr；
Main protection actionTime tmTime t of malfunction protection actionfTime t of opening of circuit breakeroAnd the action time t of the back-up protection of the next stagerLooking up the data of the transformer substation;
step 4, determining the shunt coefficient S of the grounding device of the transformer substation through field testf1；
Sf1＝1-S′f1
Of formula (II) S'f1Carrying out on-site test and acquisition on a transformer substation ground wire shunt coefficient measured value through a transformer substation ground wire shunt test device with wireless transmission phase difference comparison;
Ijh＝IΔSf1
Specially, for the neutral point grounding wire independent section of the single-phase main transformer with the voltage class of 500kV or above, under the maximum operation mode of the power system, when the short circuit occurs in the transformer substation with the voltage class of 500kV or above, the three-phase symmetrical short-circuit current I(3)Greater than the difference of grounding short-circuit current IΔThen, the short-circuit current I for calibration is calculated according to the following formulajh：
Ijh＝I(3)Sf1
In the formula, three-phase symmetrical short-circuit current I when short circuit occurs in a transformer substation with voltage class of 500kV or above(3)Obtaining the load through a PSD-BPA load flow calculation program;
step 6, determining the required sectional area S of the grounding device of the transformer substation;
in the formula, C is the thermal stability coefficient of the grounding device of the transformer substation, and is obtained by consulting the national standard;
and 7, excavating and measuring on the spot by utilizing the conduction test to obtain the minimum sectional area S of the grounding device of the transformer substationg；
Selecting a main transformer grounding wire as a measurement datum point, sequentially carrying out grounding conduction test on the grounding wires of all the electrical equipment in the electrical interval according to a mode that the grounding wires of all the electrical equipment in the same electrical interval are far away from the test datum point A, searching abnormal points of a grounding device of the transformer substation, and taking the abnormal points as excavation inspection positions;
specifically, the method comprises the following steps:
step 7.1, determining a test reference point A;
selecting a neutral point of a main transformer or a grounding wire of a shell as a test reference point A, and checking and confirming that the electrical connection between the grounding wire and a main grounding grid is reliable by means of a grounding conduction test;
step 7.2, determining a test point and carrying out conduction test;
selecting n electrical equipment grounding wires at the same electrical interval in a checked transformer substation as test points, fixing the test reference points A according to the mode that the distances between the n test points and the test reference points A are from near to far, and then sequentially testing the resistance values between the n test points and the test reference points A; the resistance values between the test points and the test reference point A form a resistance value array R { R }1,R2,...,Rn}；
Recording any test point in the first n-1 test points as a test point j, wherein j is the serial number of the test point, and j is 1,2jThe resistance value between the test datum point A and the test point j is set;
7.3, setting an abnormal resistance index, and preliminarily judging the state of the grounding device;
set as Rj≥0.7Rj+1Then, the resistance value R is determinedjAn anomaly;
according to the index to the resistance value series R { R }1,R2,...,Rj,...,RnThe front n-1 resistance values in the resistor are judged one by one, if a certain resistance value RjSatisfy Rj≥0.7Rj+1Judging that the grounding device of the test point j is abnormal;
the judgment result is the following two conditions:
resistance value array R { R }1,R2,...,Rj,...,RnIf no abnormal resistance value appears, go to step7.4；
Resistance value array R { R }1,R2,...,Rj,...,RnIf abnormal resistance value appears, go to step 7.5;
and 7.4, randomly taking 3-5 positions in the transformer substation equipment area for excavation, polishing and measuring the effective sectional area of the grounding device at each excavation position, taking the average value of the effective sectional areas of the grounding devices at each excavation position, and recording the average value as the minimum sectional area S of the grounding device of the transformer substationg；
Step 7.5, excavating at the position of the abnormal test point obtained in the step 7.3, wherein the method specifically comprises the following two conditions:
if the number of the test points with abnormal resistance values is 1, excavating at the test point positions, polishing and measuring the effective sectional area of the grounding device at the excavation positions, and recording the effective sectional area of the grounding device as the minimum sectional area S of the grounding device of the transformer substationg；
If a plurality of test points with abnormal resistance values exist, excavating at the positions of the plurality of abnormal test points, polishing and measuring the effective sectional areas of the grounding devices at the plurality of excavation positions, and taking the smallest effective sectional area to record as the minimum sectional area S of the grounding device of the transformer substationg；
if SgIf the temperature is more than or equal to S, judging that the thermal stability of the grounding device of the transformer substation meets the current operation requirement;
if SgIf the temperature is less than S, the thermal stability of the grounding device of the transformer substation is judged not to meet the current operation requirement, and transformation is needed.
Preferably, the thermal stability factor C in step 6 is selected as follows:
for the materials of the steel, aluminum, copper and copper-coated steel grounding device, the thermal stability coefficient refers to the national standard;
the transformer substation grounding device adopts two or more materials, and selects a main material for checking;
when the thin copper is adopted to wrap the steel material, the grounding material is selected according to the thermal stability coefficient C of the steel material.
Preferably, the step 7.3 of determining that the grounding device of the test point j is abnormal includes:
the grounding wire and the grounding electrode of the jth test point are corroded, broken or connected in a virtual mode;
and corrosion, fracture or virtual connection exists between the grounding wire and the grounding electrode between the jth test point and the test reference point A.
Preferably, the conduction test in step 7.2 is performed according to DL/T475, and the current pole injection current of the conduction tester is set to be equal to or larger than 20A.
Preferably, the effective cross-sectional area of the grounding device in step 7.4 is, when the grounding device at the excavation position has two or more cross-sectional area specifications, the effective cross-sectional areas are respectively averaged according to the cross-sectional area specification types, and are sequentially recorded as Sg1、Sg2、Sg3A; 7.5 in the second case, the effective cross-sectional area of the grounding device is respectively minimum according to the type of the cross-sectional area specification when the grounding device at the excavation position has two or more cross-sectional area specifications, and the effective cross-sectional area is sequentially recorded as Sg1、Sg2、Sg3、...。
Compared with the prior art, the invention has the beneficial effects that:
1. the invention perfects the short-circuit current I for checkingjhShort circuit equivalent duration teAnd a specific determination method of key parameters such as the thermal stability coefficient C of the grounding device, improves a method for checking the thermal stability of the grounding device of the transformer substation, and provides a technical criterion for the safety and stability of the primary and secondary equipment of the transformer substation if the grounding device of the transformer substation needs to be subjected to capacity expansion transformation. The method specifically comprises the following steps:
1) short-circuit current I for checkingjh: aiming at the independent section of the neutral point grounding wire of the main transformer of 500kV or more, the influence of the special connection form of the independent section of the neutral point grounding wire of the main transformer of 500kV or more on checking is supplemented. The invention will flow through the maximum earth fault of the earth conductor (line)Effective value of asymmetric current IgChanged into a short-circuit current I for checkingjh。
2) Short-circuit position: any two electrically connected positions with the same voltage grade in the transformer substation have the same short-circuit current value after short circuit, but the equivalent short-circuit duration time teAction time t of middle and later stage backup protectionrValue, the maximum action time t of the next-stage backup protection is selected from the action times of the next-stage backup protection matched with the main protectionrThe value is obtained. It is necessary to determine the location of the short circuit and this location involves as much of the next level of backup protection in the substation as possible. Therefore, the invention provides a short circuit position determination method under different main wiring forms, and defines the equivalent duration time t of the short circuiteThe calculation of (2).
3) Equivalent duration of short circuit te: the invention comprehensively considers the short-circuit position and the short-circuit current I for checkingjhAnd short circuit equivalent duration teThe internal association relationship between the I and the I in the prior art is not changedg、teAs an independent parameter, but as an organic and related entity, selected at the time of checking
The maximum value of the voltage is calculated to ensure that the required sectional area value of the grounding device of the transformer substation is maximum.
4) Grounding device thermal stability coefficient C: the selection mode of the thermal stability coefficient C of the grounding device under the conditions that the grounding device of the transformer substation adopts two or more materials, the material of the grounding device adopts thin copper-coated steel grounding material and the like is supplemented.
2. The invention introduces the transformer substation grounding device ground wire shunt test device with wireless transmission phase difference comparison into the grounding device thermal stability checking and calculating method, and solves the problem of shunt coefficient S in the prior artf1The method has the advantages that the calculation model is not accurate enough, the calculation process is complex, and the actual engineering difference is large, so that the technical utility of checking the calculation result to guide the actual production is ensured.
3. According to the method, the corrosion condition of the grounding device is fully considered, the effective sectional area of the grounding device is obtained by utilizing an excavation measurement mode, and the accuracy of the verification calculation of the thermal stability of the grounding device of the transformer substation operating for a certain period of time by the verification method is enhanced.
4. The invention provides a grounding device excavation point selection method based on grounding conduction testing by utilizing a grounding device conduction testing test method according to electrical topological characteristics of electrical interval arrangement of a substation grounding device and the like. According to the method, new instrument equipment or software facilities do not need to be added, and testers can complete point selection work before excavation by using the grounding conduction tester; the judgment method is simple and easy to implement and is suitable for field use. In the conduction test, the current electrode injection current of the tester is required to be not less than 20A, so that the accuracy of the test result, namely the resistance value is improved.
5. The electrical equipment of the transformer substation is arranged one by one at intervals, the distance between A, B and C three-phase electrical equipment with the same electrical interval and the distance between adjacent electrical interval similar electrical equipment and the main transformer are basically consistent, so that the resistance values between A, B and C three phases can form transverse comparison, the resistance values between different electrical intervals similar electrical equipment can also form transverse comparison, and the comparison is convenient for test testers to find abnormal test results of conduction tests.
Drawings
Fig. 1 is a flowchart of an implementation of a method for checking thermal stability of a grounding device of a substation according to the present invention.
Fig. 2 is a flowchart of an implementation of step 7 of a thermal stability checking method for a substation grounding device according to the present invention.
Fig. 3 is a schematic diagram of the arrangement of the grounding devices at equal intervals and the testing thereof.
In fig. 3: 0-test reference point a, 1-ground line 1, 2-ground line 2, 3-ground line 3, 4-ground line 4, 5-ground line 5, 6-ground device grid; 7-ground line 1 ', 8-ground line 2 ', 9-ground line 3 ', 10-ground line 4 ', 11-ground line 5 '.
Detailed Description
Fig. 1 is a flowchart of an implementation of a method for checking thermal stability of a grounding device of a transformer substation according to the present invention; fig. 2 is a flowchart of an implementation of step 7 of a thermal stability checking method for a substation grounding device according to the present invention. As can be seen from the figure, the checking method of the invention comprises the following specific steps:
step 1, acquiring information required by thermal stability check calculation of a grounding device of a transformer substation;
the information required by the checking calculation of the substation grounding device comprises the following information: voltage grade, main wiring form, grounding device material, protection configuration mode, main protection sleeve number and main transformer neutral point grounding mode;
IΔ＝Imax-In
In the formula ImaxThe maximum grounding short-circuit current I is the maximum grounding short-circuit current when the grounding short-circuit occurs in the transformer substation under the maximum operation mode of the power systemnThe current flowing through the neutral point of the electrical equipment when the grounding short circuit occurs in the transformer substation; maximum grounding short-circuit current I when grounding short circuit occurs in transformer substation under maximum operation mode of power systemmaxAnd current I flowing through neutral point of electrical equipment when grounding short circuit occurs in transformer substationnObtaining the load through a PSD-BPA load flow calculation program;
the method for selecting the fault position of the ground short circuit comprises the following steps: if the main wiring has a bus bar, selecting the bus bar to be short-circuited; if the main connection line is a bridge type connection line, selecting a position of a bridge breaker for short circuit; if the main wiring is in a unit wiring form, selecting a position of a breaker for short circuit;
For a transformer substation configured with two sets of quick-acting active protection and breaker failure protection:
te＝tm+tf+to
in the formula, tmThe main protection action time; t is tfThe time for the failure protection action; t is toThe circuit breaker open time;
for a substation configured with a set of quick-action active protection:
te＝to+tr
in the formula, trThe action time of the back-up protection of the next level.
If the number of the next-stage backup protection devices is 2 or more than 2, selecting the maximum value of the action time of all the next-stage backup protection devices as the action time t of the next-stage backup protectionr。
Main protection action time tmTime t of malfunction protection actionfTime t of opening of circuit breakeroAnd the action time t of the back-up protection of the next stagerAnd looking up the data of the transformer substation.
Step 4, determining the shunt coefficient S of the grounding device of the transformer substation through field testf1。
Sf1＝1-S′f1
Of formula (II) S'f1And carrying out field test and acquisition on the measured value of the transformer substation ground wire shunt coefficient through a transformer substation ground wire shunt testing device with wireless transmission phase difference comparison.
Ijh＝IΔSf1
Specially, for the neutral point grounding wire independent section of the single-phase main transformer with the voltage class of 500kV or above, under the maximum operation mode of the power system, when the short circuit occurs in the transformer substation with the voltage class of 500kV or above, the three-phase symmetrical short-circuit current I(3)Greater than the difference of grounding short-circuit current IΔThen, the short-circuit current I for calibration is calculated according to the following formulajh。
Ijh＝I(3)Sf1
In the formula, three-phase symmetrical short-circuit current I when short circuit occurs in a transformer substation with voltage class of 500kV or above(3)And obtaining the power flow through a PSD-BPA power flow calculation program.
And 6, determining the required sectional area S of the grounding device of the transformer substation.
In the formula, C is the thermal stability coefficient of the grounding device of the transformer substation, and is obtained by consulting the national standard.
And 7, excavating and measuring on the spot by utilizing the conduction test to obtain the minimum sectional area S of the grounding device of the transformer substationg。
Selecting a main transformer grounding wire as a measurement datum point, sequentially carrying out grounding conduction test on the grounding wires of all the electrical equipment in the electrical interval according to a mode that the grounding wires of all the electrical equipment in the same electrical interval are far away from the measurement datum point A, searching abnormal points of a grounding device of the transformer substation, and using the abnormal points as excavation inspection positions.
Specifically, the method comprises the following steps:
and 7.1, determining a test datum point A.
And selecting a neutral point of the main transformer or a grounding wire of the shell as a test reference point A, and checking and confirming the reliable electrical connection between the grounding wire and the main grounding grid by virtue of a grounding conduction test.
And 7.2, determining the test point and carrying out conduction test.
Selecting n electrical equipment grounding wires at the same electrical interval in a checked transformer substation as test points, fixing the test reference points A according to the mode that the distances between the n test points and the test reference points A are from near to far, and then sequentially testing the resistance values between the n test points and the test reference points A; the resistance values between the test points and the test reference point A form a resistance value array R { R }1,R2,...,Rn}。
Recording any test point in the first n-1 test points as a test point j, wherein j is the serial number of the test point, and j is 1,2jThe resistance value between the reference point A and the test point j is tested.
7.3, setting an abnormal resistance index, and preliminarily judging the state of the grounding device;
set as Rj≥0.7Rj+1Then, the resistance value R is determinedjAnd (6) abnormal.
According to this fingerTarget resistance value array R { R }1,R2,...,Rj,...,RnThe front n-1 resistance values in the resistor are judged one by one, if a certain resistance value RjSatisfy Rj≥0.7Rj+1Then, it is determined that the grounding device of the test point j is abnormal.
The judgment result is the following two conditions:
resistance value array R { R }1,R2,...,Rj,...,RnIf no abnormal resistance value appears, go to step 7.4;
resistance value array R { R }1,R2,...,Rj,...,RnIf abnormal resistance value appears, go to step 7.5;
and 7.4, randomly taking 3-5 positions in the transformer substation equipment area for excavation, polishing and measuring the effective sectional area of the grounding device at each excavation position, taking the average value of the effective sectional areas of the grounding devices at each excavation position, and recording the average value as the minimum sectional area S of the grounding device of the transformer substationg。
Step 7.5, excavating at the position of the abnormal test point obtained in the step 7.3, wherein the method specifically comprises the following two conditions:
if the number of the test points with abnormal resistance values is 1, excavating at the test point positions, polishing and measuring the effective sectional area of the grounding device at the excavation positions, and recording the effective sectional area of the grounding device as the minimum sectional area S of the grounding device of the transformer substationg。
If a plurality of test points with abnormal resistance values exist, excavating at the positions of the plurality of abnormal test points, polishing and measuring the effective sectional areas of the grounding devices at the plurality of excavation positions, and taking the smallest effective sectional area to record as the minimum sectional area S of the grounding device of the transformer substationg。
If SgIf the thermal stability of the grounding device of the transformer substation meets the current operation requirement, judging that the thermal stability of the grounding device of the transformer substation meets the current operation requirement；
If SgIf the temperature is less than S, the thermal stability of the grounding device of the transformer substation is judged not to meet the current operation requirement, and transformation is needed.
In the above steps, the thermal stability factor C in step 6 is selected as follows:
for the grounding device material of steel, aluminum, copper and copper-coated steel, the thermal stability coefficient refers to the national standard;
the transformer substation grounding device adopts two or more materials, and selects a main material for checking;
when the thin copper is adopted to wrap the steel material, the grounding material is selected according to the thermal stability coefficient C of the steel material.
In the above step, the abnormality of the grounding device of the test point j in step 7.3 includes:
the grounding wire and the grounding electrode of the jth test point are corroded, broken or connected in a virtual mode;
and corrosion, fracture or virtual connection exists between the grounding wire and the grounding electrode between the jth test point and the test reference point A.
In the above steps, the conduction test in step 7.2 is performed according to DL/T475, and the current electrode injection current of the conduction test device is set to be not less than 20A.
In the above step, the effective cross-sectional area of the grounding device in step 7.4, when the grounding device at the excavation position has two or more cross-sectional area specifications, the effective cross-sectional areas are respectively averaged according to the cross-sectional area specification types, and are sequentially recorded as Sg1、Sg2、Sg3A; 7.5 in the second case, the effective cross-sectional area of the grounding device is respectively minimum according to the type of the cross-sectional area specification when the grounding device at the excavation position has two or more cross-sectional area specifications, and the effective cross-sectional area is sequentially recorded as Sg1、Sg2、Sg3、...。
Verification of the present invention is performed by way of example below.
Example 1, a 110kV substation was put into operation in 1989 in 8 months, a 110kV side main connection was in a single bus segment form, and two 110kV/10kV main terminals were configured in the substationThe transformer and the neutral point of the transformer are not grounded, and the 110kV outgoing line is 3 times. The bus is not provided with bus differential protection, the breaker is not provided with failure protection, and the protection mode adopts far backup protection. When the transformer substation is designed, round steel with the diameter of 10mm is adopted for both a grounding electrode and a grounding wire of the grounding device; in 2009, when the capacity of the grounding device is increased and modified, part of the grounding wire and the grounding electrode are changed into 120mm2The galvanized flat steel.
Step 1, obtaining information required by checking and calculating of a grounding device of a transformer substation.
Under the maximum operation mode of the power system and when a 110kV bus of a transformer substation is short-circuited, the maximum grounding short-circuit current I when grounding short-circuit occurs in the transformer substation is obtained through a PSD-BPA load flow calculation programmaxAnd current I flowing through neutral point of electrical equipment when grounding short circuit occurs in transformer substationnAnd calculating to obtain IΔIt was 6.19 kA.
For the substation configured with the next level of backup protection: t is te＝to+tr；
In the formula, trThe action time of the next-stage backup protection is obtained; if the number of the next-stage backup protection devices is 2 or more than 2, selecting the maximum value of the action time of all the next-stage backup protection devices as the action time t of the next-stage backup protectionr。
When a bus of the transformer substation is in a ground short circuit and a 110kV side circuit breaker fails, if a fault needs to be removed, the opposite side circuit breaker of the 110kV side circuit needs to be disconnected; namely, the distance II section of the power supply side line protects the override action to trip off the circuit breaker. The action time of the next-stage protection device is the larger value of 1.0s in the protection action time of the section II of the distance between the two loops of the station; therefore, the equivalent duration of the substation ground fault is: t is te≥to+tr＝1.0+0.04＝1.04(s)。
Step 4, determining the shunt coefficient S of the transformer substation through field testf1。
The transformer substation ground wire shunt test device for wireless transmission phase difference comparison is used for carrying out field test to obtain a short-circuit ground wire shunt coefficient S 'in the transformer substation'f135.01%, then Sf1＝1-S′f1Obtaining the grounding device shunt coefficient S of the grounding device of the transformer substation in short circuit as 64.99 percentf1。
And 6, determining the required sectional area S of the grounding device of the transformer substation.
The transformer substation grounding device uses steel, national standard GB/T50065 appendix E is consulted, and the thermal stability coefficient C is 70. Will Ijh＝4020(A)、teSubstituting 1.04(s) and 70 into the formula
In (1), S.apprxeq. 58.58 (mm) is obtained2)。
And 7, excavating and measuring on the spot by utilizing the conduction test to obtain the minimum sectional area S of the grounding device of the transformer substationg。
In example 1, the ground line of the main transformer No. 1 is selected as the test reference point a in conjunction with the arrangement of the electrical devices in the substation. The grounding wire of the No. 1 main transformer is reliably connected with the adjacent grounding wires, and the resistance values are all smaller than 0.05 omega, so that the grounding wire can be used as a test reference point A.
And sequentially carrying out ground conduction test on the ground wires of the electrical equipment in the electrical interval by using the ground conduction tester according to a mode that the distance between the ground wire of the electrical equipment in the same electrical interval and the test reference point A is from near to far.
In the test result, no abnormal value is found in the conduction test result of the transformer substation. Therefore, 4 positions are selected for excavation in the 110kV and 10kV equipment areas. After polishing measurement, the operation time of the round steel grounding body with the diameter of 10mm is long, and the average value of the effective sectional area of the round steel grounding body is 50mm2。120mm2The galvanized flat steel grounding wire has light corrosion degree and the average value of the effective sectional area is about 113mm2。
7.4, when the grounding device at the excavation position has two or more sectional area specifications, the effective sectional areas are respectively averaged according to the sectional area specification types and are sequentially recorded as Sg1、Sg2、Sg3、...。
Therefore, the average value of the effective sectional area of the round steel grounding body is recorded as the minimum sectional area S of the substation grounding deviceg1，Sg1＝50(mm2) (ii) a Recording the average value of the effective sectional area of the galvanized flat steel grounding wire as the minimum sectional area S of the substation grounding deviceg2，Sg2＝113(mm2)。
Sg1S, 10mm used in the original design stage2The round steel grounding wire and the grounding body can not meet the operation requirement of the transformer substation and need to be modified. Sg2And the mass is more than or equal to S, which indicates that the galvanized flat steel grounding wire meets the current operation requirement without modification.
Example 2, step 7 is illustrated using this example: by utilizing conduction test, excavation and field measurement are carried out to obtain the minimum sectional area S of the grounding device of the transformer substationg。
A certain 110kV transformer substation is built in 2001 and in 2003, the transformer substation is built comprehensively in 6 months, three 110kV main transformers are arranged in the substation, the 110kV inlet wire is 4-turn, the 35kV outlet wire is 12-turn, and the 10kV outlet wire is 8-turn. The original grounding wire is designed to be single and 160mm2Galvanized flat iron of standard. Fig. 3 is a schematic diagram of the arrangement of the grounding devices at equal intervals and the testing thereof.
Step 7.1, determining a test reference point A;
the grounding wire of the No. 1 main transformer shell is selected as a measurement reference point A (namely, a vertical grounding body 0 in the figure 3) of the grounding conduction test, and the resistance test values between the measurement reference point A and the adjacent grounding wires are all less than 0.05 omega by utilizing the conduction tester, so that the measurement reference point A is electrically and reliably connected and can be determined as the measurement reference point A.
Step 7.2, determining a test point and carrying out conduction test;
according to the 'grounding device electrical integrity' test requirement stated in DL/T475, sequentially carrying out a grounding conduction test on the grounding wires of the electrical equipment in the electrical interval in a mode that the grounding wires of the electrical equipment in the same electrical interval are far away from a test reference point A; the current pole injection current of the conduction tester is not less than 20A.
Specifically, the method comprises the following steps: according to the test method of the grounding conduction test, the grounding wire of the No. 1 main transformer housing is selected as the measurement reference point A of the conduction test, namely '0' in figure 3. The tested electrical intervals are two in total, namely 301 electrical intervals and 352 electrical intervals adjacent to the electrical intervals.
The ground wires of the 3011 disconnector, the 3012 disconnector, the 301 breaker, the 301 current transformer and the 3016 disconnector in the 301 electrical interval meet the position arrangement rule from "1" to "5" in fig. 3; namely: 3011 the ground line of the electrical equipment in the 301 electrical interval, such as a disconnector, meets the requirement from near to far from the measurement reference point a.
Similarly, the ground wires of the "3521 disconnector", "3522 disconnector", "352 breaker", "352 current transformer" and "3526 disconnector" in the 352 electrical interval also satisfy the position arrangement rule from "7" to "11" in fig. 3; namely: 3521 ground lines of electrical equipment in 352 electrical intervals such as disconnecting switches meet the requirement of being far from the measurement reference point a.
7.3, setting an abnormal resistance index, and preliminarily judging the state of the grounding device;
the ground conduction test results are: the resistance arrays for the conduction tests at 301 electrical intervals and 352 electrical intervals are, respectively, in units of: m omega;
R301＝{R1,R2,R3,R4,R5}＝{10.82,11.53,13.19,24.96,16.03}，
R352＝{R,1,R,2,R,3,R,4,R,5}＝{10.52,11.00,12.58,13.75,15.87}。
R301and R352The change in the value indicates that: as the distance between the test reference point and the test point increases, the resistance value of the test reference point generally shows an increasing trend. The trend conforms to the change logic.
However, R4Has a test value of 24.96 m.OMEGA.R5Has a test value of 16.03 m.OMEGA.R4≥0.7R5Judgment of R4An anomaly exists.
301 electrical intervals and adjacent 352 electrical intervals, the types and the number of the electrical equipment configured in the two electrical intervals are the same, and the arrangement mode and the electrical interval distance of each electrical equipment are also consistent, so that the distances from the main transformer to each electrical equipment in the two electrical intervals are basically consistent. Thus, lateral contrast can also be formed between electrical devices of the same type in different electrical compartments, e.g. R1And the group consisting of R and R,1，R4and the group consisting of R and R,4. Accordingly, R4Has a test value of 24.96m omega, greater than R,4test value of (2) 13.75m Ω. It is preliminarily determined 301 that corrosion or breakage of the grounding wire of the current transformer or the grounding electrode connected thereto exists in the electrical compartment.
Series of resistance values R301＝{R1,R2,R3,R4,R5An abnormal resistance value appears when the value is 10.82,11.53,13.19,24.96 and 16.03, and the process goes to step 7.5.
Step 7.5, excavating at the position of the abnormal test point obtained in the step 7.3, wherein the method specifically comprises the following two conditions:
excavation is performed along 301 the ground line of the electrically-spaced current transformer and the ground line of the 352 electrically-spaced current transformer, respectively.
The measurement finds that: the grounding wire of the 301 mutual inductor is seriously corroded in total, a plurality of openings appear on the edge of the metal, and the whole body presents a form of being about to break; the most serious corrosion part is 24.00mm wide and 3.1mm thick, and the effective cross section area is about 74.1mm2。
The grounding wire of the 352 mutual inductor is corroded to a certain degree, the most serious part of the grounding wire is 29.42mm wide and 4.5mm thick, and the effective sectional area is about 132.4mm2。R352The test result is not abnormal.
In summary, the ground line of the 301 transformer is the only abnormal point of the test, and 74.10mm of the ground line of the 301 transformer is recorded2For minimum sectional area S of transformer substation grounding deviceg。
Claims (5)
1. A method for checking the thermal stability of a transformer substation grounding device based on a conduction test is characterized by comprising the following steps:
step 1, acquiring information required by thermal stability check calculation of a grounding device of a transformer substation;
the information required by the checking calculation of the substation grounding device comprises the following information: voltage grade, main wiring form, grounding device material, protection configuration mode, main protection sleeve number and main transformer neutral point grounding mode;
step 2, determining the grounding short-circuit current difference I of the checked substation in the maximum operation mode of the power systemΔ；
IΔ＝Imax-In
In the formula ImaxThe maximum grounding short-circuit current I is the maximum grounding short-circuit current when the grounding short-circuit occurs in the transformer substation under the maximum operation mode of the power systemnThe current flowing through the neutral point of the electrical equipment when the grounding short circuit occurs in the transformer substation;
maximum grounding short-circuit current I when grounding short circuit occurs in transformer substation under maximum operation mode of power systemmaxAnd current I flowing through neutral point of electrical equipment when grounding short circuit occurs in transformer substationnObtaining the load through a PSD-BPA load flow calculation program;
the method for selecting the fault position of the ground short circuit comprises the following steps: if a bus bar exists in the main wiring, selecting the bus bar to be short-circuited; if the main connection line is a bridge type connection line, selecting a position of a bridge breaker for short circuit; if the main wiring is in a unit wiring form, selecting a position of a breaker for short circuit;
step 3, determining the equivalent duration time t of the short circuite；
For a transformer substation configured with two sets of quick-acting active protection and breaker failure protection:
te＝tm+tf+to
in the formula, tmThe main protection action time; t is tfThe time for the failure protection action; t is toThe circuit breaker open time;
for a substation configured with a set of quick-action active protection:
te＝to+tr
in the formula, trThe action time of the next-stage backup protection is obtained;
if the number of the next-stage backup protection devices is 2 or more than 2, selecting the maximum value of the action time of all the next-stage backup protection devices as the action time t of the next-stage backup protectionr；
Main protection action time tmTime t of malfunction protection actionfTime t of opening of circuit breakeroAnd the action time t of the back-up protection of the next stagerLooking up the data of the transformer substation;
step 4, determining the shunt coefficient S of the grounding device of the transformer substation through field testf1；
Sf1＝1-S′f1
Of formula (II) S'f1Carrying out on-site test and acquisition on a transformer substation ground wire shunt coefficient measured value through a transformer substation ground wire shunt test device with wireless transmission phase difference comparison;
step 5, determining the short-circuit current I for checkingjh；
Ijh＝IΔSf1
Specially, for the neutral point grounding wire independent section of the single-phase main transformer with the voltage class of 500kV or above, under the maximum operation mode of the power system, when the short circuit occurs in the transformer substation with the voltage class of 500kV or above, the three-phase symmetrical short-circuit current I(3)Greater than the difference of grounding short-circuit current IΔThen, the short-circuit current I for calibration is calculated according to the following formulajh：
Ijh＝I(3)Sf1
In the formula, three-phase symmetrical short-circuit current I (in the case of short circuit in a transformer substation of 500kV or higher voltage class3) Obtaining the load through a PSD-BPA load flow calculation program;
step 6, determining the required sectional area S of the grounding device of the transformer substation;
in the formula, C is the thermal stability coefficient of the grounding device of the transformer substation, and is obtained by consulting the national standard;
and 7, excavating and measuring on the spot by utilizing the conduction test to obtain the minimum sectional area S of the grounding device of the transformer substationg；
Selecting a main transformer grounding wire as a measurement datum point, sequentially carrying out grounding conduction test on the grounding wires of all the electrical equipment in the electrical interval according to a mode that the grounding wires of all the electrical equipment in the same electrical interval are far away from the test datum point A, searching abnormal points of a grounding device of the transformer substation, and taking the abnormal points as excavation inspection positions;
specifically, the method comprises the following steps:
step 7.1, determining a test reference point A;
selecting a neutral point of a main transformer or a grounding wire of a shell as a test reference point A, and checking and confirming that the electrical connection between the grounding wire and a main grounding grid is reliable by means of a grounding conduction test;
step 7.2, determining a test point and carrying out conduction test;
selecting n electrical equipment grounding wires at the same electrical interval in a checked transformer substation as test points, fixing the test reference points A according to the mode that the distances between the n test points and the test reference points A are from near to far, and then sequentially testing the resistance values between the n test points and the test reference points A; the resistance values between the test points and the test reference point A form a resistance value array R { R }1,R2,...,Rn}；
Recording any test point in the first n-1 test points as a test point j, wherein j is the serial number of the test point, and j is 1,2jThe resistance value between the test datum point A and the test point j is set;
7.3, setting an abnormal resistance index, and preliminarily judging the state of the grounding device;
set as Rj≥0.7Rj+1Then, the resistance value R is determinedjAn anomaly;
according to the index to the resistance value series R { R }1,R2,...,Rj,...,RnThe front n-1 resistance values in the resistor are judged one by one, if a certain resistance value RjSatisfy Rj≥0.7Rj+1Judging that the grounding device of the test point j is abnormal;
the judgment result is the following two conditions:
resistance value array R { R }1,R2,...,Rj,...,RnIf no abnormal resistance value appears, go to step 7.4;
resistance value array R { R }1,R2,...,Rj,...,RnIf abnormal resistance value appears, go to step 7.5;
and 7.4, randomly taking 3-5 positions in the transformer substation equipment area for excavation, polishing and measuring the effective sectional area of the grounding device at each excavation position, taking the average value of the effective sectional areas of the grounding devices at each excavation position, and recording the average value as the minimum sectional area S of the grounding device of the transformer substationg；
Step 7.5, excavating at the position of the abnormal test point obtained in the step 7.3, wherein the method specifically comprises the following two conditions:
if the number of the test points with abnormal resistance values is 1, excavating at the test point positions, polishing and measuring the effective sectional area of the grounding device at the excavation positions, and recording the effective sectional area of the grounding device as the minimum sectional area S of the grounding device of the transformer substationg；
If a plurality of test points with abnormal resistance values exist, excavating at the positions of the plurality of abnormal test points, polishing and measuring the effective sectional areas of the grounding devices at the plurality of excavation positions, and taking the smallest effective sectional area to record as the minimum sectional area S of the grounding device of the transformer substationg；
Step 8, comparing the required sectional area S of the grounding device of the transformer substation obtained in the step 6 with the minimum sectional area S of the grounding device of the transformer substation obtained in the step 7gJudgment changeWhether the thermal stability of the power station grounding device meets the current operation requirement:
if SgIf the temperature is more than or equal to S, judging that the thermal stability of the grounding device of the transformer substation meets the current operation requirement;
if SgIf the temperature is less than S, the thermal stability of the grounding device of the transformer substation is judged not to meet the current operation requirement, and transformation is needed.
2. The method for checking the thermal stability of the substation grounding device based on the conduction test is characterized in that the thermal stability coefficient C in the step 6 is selected as follows:
for the grounding device material of steel, aluminum, copper and copper-coated steel, the thermal stability coefficient refers to the national standard;
the transformer substation grounding device adopts two or more materials, and selects a main material for checking;
when the thin copper is adopted to wrap the steel material, the grounding material is selected according to the thermal stability coefficient C of the steel material.
3. The method for checking the thermal stability of the substation grounding device based on the conduction test according to claim 1, wherein the step 7.3 of checking the grounding device of the test point j for an abnormality comprises:
the grounding wire and the grounding electrode of the jth test point are corroded, broken or connected in a virtual mode;
and corrosion, fracture or virtual connection exists between the grounding wire and the grounding electrode between the jth test point and the test reference point A.
4. The method for checking the thermal stability of the substation grounding device based on the conduction test as claimed in claim 1, wherein the conduction test of step 7.2 is performed according to DL/T475, and the current pole injection current of the conduction test device is set to be not less than 20A.
5. The method for checking the thermal stability of the substation grounding device based on the conduction test according to claim 1, wherein the step 7.4 isWhen the grounding device at the excavation position has two or more sectional area specifications, the effective sectional areas are respectively averaged according to the sectional area specification types and are sequentially recorded as Sg1、Sg2、Sg3A; 7.5 in the second case, the effective cross-sectional area of the grounding device is respectively minimum according to the type of the cross-sectional area specification when the grounding device at the excavation position has two or more cross-sectional area specifications, and is sequentially recorded as Sg1、Sg2、Sg3、...。
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