CN101726514B - Oil-immersed type transformer solid insulation moisture content assessment method based on return voltage - Google Patents

Oil-immersed type transformer solid insulation moisture content assessment method based on return voltage Download PDF

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CN101726514B
CN101726514B CN200910254424A CN200910254424A CN101726514B CN 101726514 B CN101726514 B CN 101726514B CN 200910254424 A CN200910254424 A CN 200910254424A CN 200910254424 A CN200910254424 A CN 200910254424A CN 101726514 B CN101726514 B CN 101726514B
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transformer
insulation
return voltage
moisture content
oil
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CN200910254424A
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CN101726514A (en
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于峥
张祥全
张冠军
杨双锁
魏建林
王世强
董明
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西北电网有限公司
西安交通大学
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Abstract

The invention discloses an oil-immersed type transformer solid insulation moisture content assessment method based on return voltage, comprising the following steps: 1) preparation work: the temperature of a transformer is lowered without forced oil circulation; an outgoing line terminal and a line of each winding sleeve are separated; and each phase of a high voltage winding and neutral points are in short circuit and grounded; 2) wire connection: each measured winding is in grounded insulation; 3) parameter configuration; 4) test end judgment: a polarized spectrum curve raises smoothly and then declines, when the peak value of the polarized spectrum curve appears, test is ended; when the tested polarized spectrum curve has serious jump or a plurality of peak values, the test is ended when the charging time Tc equals to 100s; 5) moisture content is judged according to a main time constant of the polarized spectrum curve; and 6) when the moisture content is less than 1%, the insulation state is good; when the moisture content ranges from 1% to 2.5%, the insulation state is general; and when the moisture content is higher than 2.5%, the insulation state is very poor. The invention can accurately assess brackish moisture content in insulation paper and judge the insulation and aging state of oil paper without suspended core and sampling and destroying the insulation material.

Description

Oil-immersed type transformer solid insulation moisture content assessment method based on return voltage

Technical field

The invention belongs to transformer insulation state diagnosis and life appraisal field, relate to a kind of appraisal procedure of the oil-immersed type transformer solid insulation based on return voltage.

Background technology

Transformer is the safety and stability of the operational reliability direct relation electric system of large oil immersed power transformer especially; Data shows according to statistics; The interruption of service of transformer is mainly caused by its insulation system fault, so its life-span is depended on paper oil insulation system aging state to a great extent.In the transformer operational process, paper oil insulation bears multiple external stress effects such as heat, electricity, machinery, chemistry for a long time, causes self insulation to descend gradually with mechanical property and also possibly cause transformer fault.Therefore, accurately diagnose the ageing state of paper oil insulation system, most important to the prediction transformer's life span, also be the prerequisite and the basis of realizing that transformer state is safeguarded.

Temperature, moisture, oxygen etc. all can quicken transformer insulated ager process; Wherein moisture is the product of solid insulation degradation with aging; Wear out as what the catalyzer accelerating solid insulated conversely again simultaneously, the harm that the existence of moisture simultaneously also can bring other significantly descends electric insulation intensity like moisture; The loss aggravation, the rate of ageing of quickening insulating board; Increase loss and leakage current, thereby make the transformer heating, running temperature raises, and reduces transformer serviceable life; The moisture distribution imbalance will cause that the partial discharge inception voltage in high field intensity zone reduces, and degree of discharge strengthens; The migration of small amount of moisture causes on the oilpaper interface oil flow electrification etc., and is therefore particularly serious to transformer insulated harm, need be strict controlled within the specialized range.Stipulate in the DL/T597-1996 power equipment preventive trial rules that for the 220kV transformer, its solid insulation moisture content must not surpass 3%, the 330kV transformer must not surpass 2%, and the 500kV transformer must not surpass 1%.

The test method of tradition diagnosis transformer oil paper insulation ageing state mainly contains furfural content analysis and the insulating paper degree of polymerization (DP) analysis etc. in dissolved gas analysis (DGA), Partial Discharge Detection (PD), the oil.These methods can both disclose and reflect transformer insulated ageing state from certain angle, can't the paper insulated water cut of reaction oil, if transformer makes moist, though obviously aging as yet, still be in non-health status, the maintenance of should in time stopping transport.Detection for water content in the solid insulation; That adopts at present has two kinds of methods: a kind of is from transformer, to extract oil sample; Adopt methods such as cassette titration, the way of distillation to measure micro-water content in the oil, the profile of equilibrium that in oilpaper, distributes based on moisture is estimated solid insulation moisture content then; Another kind is that direct suspended core is got pattern, adopts Ka Shi titration, weight method etc. to measure solid insulation moisture content.But preceding a kind of method error is too big; Because the power transformer water translocation is very complicated; Usually be present in the solid insulation up to the moisture more than 99%, only contain moisture in the oil, and there is the transport phenomena between oilpaper in moisture under different temperatures less than 1%; Need just can reach equilibrium state for a long time, so this method has significant limitation.Though a kind of method in back can directly obtain solid insulation moisture content, need the transformer suspended core is handled, complicated operation and have destructiveness, the regional difference that pattern is chosen can be brought the moisture estimation error equally, suitablely promotes employing at the scene.

When electric field action was on dielectric, can be observed two kinds of dielectric response phenomenons: electricity was led and is polarized.It is owing to charge carrier is that constantly moving of electronics and ion forms that electricity is led, and polarization is to form owing to dielectric inside macroscopical dipole moment occurs along direction of an electric field.The polarization process of medium is quite complicated, and it is inseparable with the wearing out of medium, deterioration and state such as make moist.Return voltage value after the return voltage method polarizes through the measurement insulating medium, and some corresponding characteristic quantities utilize the data that obtain to carry out analyzing and processing to judge the insulation status of paper oil insulation system again.

Its concrete operations are: at certain hour t 0To t 1In, a direct current step voltage is put on the medium, shown in accompanying drawing 1.The charging current of multilayered medium insulation system forms polarization current.This electric current can reduce in the whole polarization time gradually, drops to a more stable value always, and this value is by the dc conductivity decision of insulation system itself.Duration of charging t 1Later, through the amp gauge short circuit, discharge current can suddenly change and jump to decay gradually then on the negative value this moment with the medium insulation system.Be short-circuited to time t 2After, with medium insulation system open circuit and carry out voltage measurement.Gather owing to the remaining electric charge of depolarization can produce at the insulator two ends this moment, thereby form voltage difference.The return voltage tester can record the peak value of this return voltage and be recorded in the instrument, changes the duration of charging, can obtain corresponding return voltage peak value, with duration of charging T cThe coordinate points of being described with corresponding return voltage peak value couples together with curve, is the return voltage polarized spectrum curve of medium.Discharge and recharge the parameter that test can obtain reflecting the dielectric polorization characteristic of time constant through medium being carried out a series of differences, draw its polarized spectrum curve.

Summary of the invention

Could extract the insulation pattern to need transformer being carried out the suspended core processing in the transformer solid insulation moisture content assessment method; Running program is complicated and possibly destroy transformer insulated; And can bring the technical matters of the error of moisture assessment when the regional difference chosen of insulation pattern; The invention discloses a kind of oil-immersed type transformer solid insulation moisture content assessment method, comprise the steps: based on return voltage

1) transformer and return voltage tester are prepared: be connected with the transformer stoppage in transit and with the circuit disconnection; Keep sleeve pipe intact and be connected normally with transformer; Transformer oil paper insulation temperature is reduced to environment temperature; There is not forced oil-circulation; With transformer senior middle school low pressure winding each mutually and neutral point at sleeve pipe leading-out terminal place with copper bare wire short circuit and ground connection, 10-20 minute ground connection time; The return voltage tester is wanted reliable ground;

2) test connection carries out according to the instrument instructions, when the time allows, each winding insulation against ground of transformer is all measured;

3) the parameter setting comprises charging voltage U c, discharge and recharge time ratio T c/ T d, the maximum charge time T Cmax

4) measure sampling and need not artificial participation automatically; But because the increase in duration of charging; Every survey one data points of return voltage tester; The needed time is index law to be increased: when smoothly descending again after the level and smooth rising of institute's polarimetry spectral curve, after test lasts till that peak value appears in the polarized spectrum curve, promptly stop measuring; When institute polarimetry spectral curve jump serious, when a plurality of peak value perhaps occurring, T then cStop during=100s measuring;

5) data processing method does, in the duration of charging corresponding according to the return voltage peak value of institute's polarimetry spectral curve, promptly main time constant is judged water cut, and its computing formula is:

Lg τ CdIn=3.8268-0.8773m the formula

τ Cd---polarized spectrum curve master time constant, unit is s; M---water cut, %;

To test the gained data and bring the aforementioned calculation formula into, can obtain the water cut in the transformer solid insulation;

6) when water cut is lower than 1%, judge that transformer insulation state is good; When water cut equals 1%~2.5%, judge that transformer insulated situation is general, should be noted that observation; When water cut is higher than 2.5%, judge that transformer insulation state is very poor, need overhaul processing accordingly.

Said step 2) when the time is not abundant, preferentially measures the low pressure winding in to high pressure winding and ground insulation;

Setting concrete parameter in the said step 3) is: charging voltage U c=1000V discharges and recharges time ratio T c/ T d=2, the maximum charge time T Cmax=1000s;

The RVM5461 or the RVM5462 return voltage tester of Tettex company adopted in test.

The present invention is based on the oil-immersed type transformer solid insulation moisture content assessment method of return voltage; Can be at suspended core not, do not destroy insulating material; Assess the micro-water content in the insulating paper under the prerequisite that need not take a sample accurately; And analyze oil paper insulation ageing state with this, for the accurate transformer insulated performance of assessment provides reliable basis with the prediction residual life.This method not only can be used as the useful of present isolation diagnostic method and replenishes, and probably becomes the important tests means of transformer state diagnostic field in the future.

Description of drawings

Fig. 1: return voltage test philosophy figure

Fig. 2: the present invention assesses the operational flowchart of transformer solid insulation moisture content

Fig. 3: the present invention tests the test connection figure of transformer low voltage winding to the polarized spectrum curve of high pressure winding and ground insulation

Fig. 4: typical oil-filled transformer paper oil insulation polarized spectrum curve

Embodiment

Below in conjunction with accompanying drawing the present invention is further specified, what this instance adopted is the RVM5461 return voltage tester of Tettex company.

A kind of oil-immersed type transformer solid insulation moisture content assessment method based on return voltage comprises the steps:

1) transformer and return voltage tester are prepared: be connected with the transformer stoppage in transit and with the circuit disconnection; Keep sleeve pipe intact and be connected normally with transformer; Transformer oil paper insulation temperature is reduced to environment temperature; There is not forced oil-circulation; With transformer senior middle school low pressure winding each mutually and neutral point at sleeve pipe leading-out terminal place with copper bare wire short circuit and ground connection, at least 10 minutes ground connection time, perhaps 10~20 minutes; The return voltage tester is wanted reliable ground.

2) test connection carries out according to the instrument instructions; With the two-winding transformer is example; If measure the return voltage polarized spectrum curve of low pressure winding to high pressure winding and ground insulation; Then need to be connected with each phase short circuit of low pressure winding and with the red terminals of the test cable of return voltage tester, each is connected also ground connection with copper bare wire short circuit and with the black terminals of the test cable of return voltage tester mutually with the high pressure winding, and transformer case will keep ground connection.

If measure the return voltage polarized spectrum curve of high pressure winding to low pressure winding and ground insulation; Then need to be connected with each phase short circuit of high pressure winding and with the red terminals of the test cable of return voltage tester; Each is connected with copper bare wire short circuit and with the black terminals of return voltage tester test cable and ground connection mutually with the low pressure winding, and transformer case will keep ground connection.When the time allows, each winding insulation against ground of transformer is all measured; When the time is not abundant, preferentially measure the low pressure winding to high pressure winding and ground insulation.

3) the parameter setting comprises charging voltage U c=1000V discharges and recharges time ratio T c/ T d=2, the maximum charge time T Cmax=1000s.

4) measure sampling and need not artificial participation automatically; But because the increase in duration of charging; Every survey one data points of return voltage tester; The needed time is index law to be increased: when smoothly descending again after the level and smooth rising of institute's polarimetry spectral curve, after test lasts till that peak value appears in the polarized spectrum curve, promptly stop measuring; When institute polarimetry spectral curve jump serious, when a plurality of peak value perhaps occurring, T then cCan stop during=100s measuring.

5) data processing method does, in the duration of charging corresponding according to the return voltage peak value of institute's polarimetry spectral curve, promptly main time constant is judged water cut, and its computing formula is:

Lg τ CdIn=3.8268-0.8773m the formula

τ Cd---polarized spectrum curve master time constant, unit is s; M---water cut, %;

To test the gained data and bring the aforementioned calculation formula into, can obtain the water cut in the transformer solid insulation.

6) when water cut is lower than 1%, judge that transformer insulation state is good; When water cut equals 1%~2.5%, judge that transformer insulated situation is general, should be noted that observation; When water cut is higher than 2.5%, judge that transformer insulation state is very poor, need carry out corresponding maintenance and handle.

Fig. 1 is return voltage test philosophy figure in the prior art, also is the principle of institute of the present invention foundation.T among the figure 0-t 1Be the charging stage, t 1-t 2Be short circuit dischange stage, t 2Be open circuit and generation return voltage stage later on.Curve 1 is the charging voltage curve, and curve 2 is the polarization current curve that produces when medium is charged, the return voltage curve of the depolarization current curve that curve 3 produces during for short circuit, curve 4 generation during for open circuit.

Fig. 2 is the oil-immersed type transformer solid insulation moisture content assessment method FB(flow block) that the present invention is based on return voltage.

Fig. 3 tests the polarized spectrum curve test connection figure of transformer low voltage winding to high pressure winding and ground insulation in the prior art.This wiring diagram is based on the operation instruction of Tettex RVM5461 or RVM5462 return voltage tester.5 is the red terminals of return voltage tester test cable among the figure, and 6 is the black terminals of return voltage tester test cable, and these terminals keep ground connection always during test; 7 is the test cable of return voltage tester, and 8 is the return voltage tester, and 9 is the high pressure winding of tested transformer; 10 is the low pressure winding of transformer; 11 is bushing shell for transformer, and 12 is transformer case, and 13 is the transformer base.When measuring the low pressure winding to the return voltage polarized spectrum curve of high pressure winding and ground insulation; Need to be connected with low pressure winding 10 each phase short circuit and with the red terminals 5 of the test cable 7 of return voltage tester 8; Each is connected also ground connection with copper bare wire short circuit and with the black terminals 6 of the test cable 7 of return voltage tester 8 mutually with high pressure winding 9, and transformer case 12 will keep ground connection.

Fig. 4 adopts the present invention that certain transformer is carried out the polarized spectrum curve map that the return voltage test is obtained, and horizontal ordinate is duration of charging T c, ordinate is return voltage peak value U RmaxCan find out that the pairing duration of charging of maximal value in the return voltage peak value is 50s in this polarized spectrum curve, with m=50 substitution lg τ CdIn=3.8268-0.8773m the formula, can carry out the water cut assessment to this transformer.

With the two-winding transformer test is example:

Transformer stop transport and oily temperature drop to stationary value, the transformer leading-out terminal is untied, and with each winding with copper bare wire short circuit and ground connection 10 minutes.After return voltage tester ground connection and energized, shown in accompanying drawing 3, the return voltage tester is connected with the transformer corresponding windings, and notes keeping in touch good with the special test cable.Start is provided with parameter U c=1000V, T c/ T d=2, T Cmax=1000s presses testing button and begins to measure.Constantly note institute's polarimetry spectral curve, when peak value appears in the polarized spectrum curve, can interrupt measuring that derived data is analyzed, the estimation water cut is also finally judged its state of insulation.

Certain retired transformer model is SFL1-8000/110, and rated voltage is 110/10kV.Adopt in July, 2008 return voltage method of the present invention that this transformer low voltage winding is tested high pressure winding and ground insulation respectively, obtained its polarized spectrum curve.Institute's polarimetry spectral curve master time constant is 20s, and calculating its water cut in the substitution formula (1) is 2.89%, shows that this transformer insulation state is very poor, need carry out corresponding maintenance processing such as drying.And adopt model is that the water cut that the frequency domain spectra insulation diagnosis analyser of IDAX-206 is analyzed is 3.0%, and visible above-mentioned moisture evaluation method has higher accuracy, can be used for the moisture measurement of on-the-spot transformer.In addition, this test method also has non-destructive, easy and simple to handle, accuracy advantages of higher, very is convenient to the scene and promotes the use of.

Claims (4)

1. the oil-immersed type transformer solid insulation moisture content assessment method based on return voltage comprises the steps, it is characterized in that:
1) transformer and return voltage tester are prepared: be connected with the transformer stoppage in transit and with the circuit disconnection; Keep sleeve pipe intact and be connected normally with transformer; Transformer oil paper insulation temperature is reduced to environment temperature; There is not forced oil-circulation; With transformer senior middle school low pressure winding each mutually and neutral point at sleeve pipe leading-out terminal place with copper bare wire short circuit and ground connection, 10~20 minutes ground connection time; The return voltage tester is wanted reliable ground;
2) test connection carries out according to the instrument instructions, when the test duration allows, each winding insulation against ground of transformer is all measured;
3) the parameter setting of return voltage tester comprises charging voltage U c, discharge and recharge time ratio T c/ T d, the maximum charge time T Cmax
4) measure sampling and need not artificial participation automatically; But because the increase in duration of charging; Every survey one data points of return voltage tester; The needed time is index law to be increased: when smoothly descending again after the level and smooth rising of institute's polarimetry spectral curve, after test lasts till that peak value appears in the polarized spectrum curve, promptly stop measuring; When institute polarimetry spectral curve jump serious, when a plurality of peak value perhaps occurring, T then cStop during=100s measuring;
5) data processing method does, in the duration of charging corresponding according to the return voltage peak value of institute's polarimetry spectral curve, promptly main time constant is judged water cut, and its computing formula is:
Lg τ CdIn=3.8268-0.8773m the formula
τ Cd---polarized spectrum curve master time constant, unit is s; M---water cut, %;
To test the gained data and bring the aforementioned calculation formula into, can obtain the water cut in the transformer solid insulation;
6) when water cut is lower than 1%, judge that transformer insulation state is good; When water cut equals 1%~2.5%, judge that transformer insulated situation is general, should be noted that observation; When water cut is higher than 2.5%, judge that transformer insulation state is very poor, need overhaul processing accordingly.
2. the oil-immersed type transformer solid insulation moisture content assessment method based on return voltage according to claim 1 is characterized in that: when the test duration is not abundant, preferentially measure the low pressure winding to high pressure winding and ground insulation said step 2).
3. the oil-immersed type transformer solid insulation moisture content assessment method based on return voltage according to claim 1 is characterized in that: setting concrete parameter in the said step 3) is: charging voltage U c=1000V discharges and recharges time ratio T c/ T d=2, the maximum charge time T Cmax=1000s.
4. the oil-immersed type transformer solid insulation moisture content evaluation test method based on return voltage according to claim 1 is characterized in that: the RVM5461 or the RVM5462 return voltage tester of Tettex company adopted in test.
CN200910254424A 2009-12-22 2009-12-22 Oil-immersed type transformer solid insulation moisture content assessment method based on return voltage CN101726514B (en)

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Families Citing this family (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102998338B (en) * 2012-11-20 2015-04-22 中国电力科学研究院 Dielectric response characteristic-based insulation dampness diagnosis method for transformer oil paper
CN103063989A (en) * 2012-12-28 2013-04-24 四川电力科学研究院 Transformer oil paper insulation state testing device and control method based on return voltage method
CN104215669B (en) * 2014-09-15 2016-08-24 国家电网公司 The moisture measurement method of transformer insulating system
CN104714100B (en) * 2015-04-01 2018-08-07 国家电网公司 A kind of insulation measurement data processing method for analysis of moisture content
CN104793113A (en) * 2015-04-03 2015-07-22 国网重庆市电力公司电力科学研究院 Method and system for evaluating ageing states of main insulation systems of transformers
CN105223217A (en) * 2015-09-11 2016-01-06 云南电网有限责任公司电力科学研究院 The method that in detecting insulating oil, active sulfur compound exists in situation is there is based on oxygen
CN105116201B (en) * 2015-09-29 2018-07-20 广东电网有限责任公司佛山供电局 The measuring device and measuring method of return voltage parameter
CN106443129A (en) * 2016-09-26 2017-02-22 哈尔滨理工大学 Numerical computation method for recovery voltage of electrical equipment and insulating material
CN108061828A (en) * 2017-12-12 2018-05-22 青岛科技大学 Dielectric internal space-charge accumulated amount characterizing method
CN108387824B (en) * 2018-02-05 2020-06-09 三峡大学 Oiled paper insulation state evaluation method for improving return voltage measurement mode
CN108845074B (en) * 2018-04-18 2020-11-03 国网江西省电力有限公司电力科学研究院 State evaluation method for oil-immersed transformer
CN111458663A (en) * 2020-05-21 2020-07-28 福州大学 Oiled paper capacitive bushing moisture monitoring device and method based on air humidity sensing

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
董明 等.回复电压法在变压器故障诊断中的作用.《电网与水力发电进展》.2007,(第4期),21-25. *
许维宗 等.电力变压器油纸绝缘状态的诊断——回复电压法.《华中电力》.2007,第20卷(第4期),4-12. *

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