Transformer differential protection uses case study by accident

Domestic 35kv reachs preface to change below in electric place, the protection that uses generally is formed in order to divide vertical relay. Its biggest characteristic is loop is formed 2 simple, intuitionistic palpability, economy, reliable. When power system malfunctions, can accompany electric current dash forward add, phasic difference horn produces change between voltage light and electric current and voltage, the protection device that these basic characteristics made all sorts of different principles [1] . As transformer advocate vertical couplet differential of protection (abbreviation differential) protection, performance factor is in from beginning to end 50% one 60% wander, the stability of the safety of this pair of transformer and system moves very adverse. Cause " the reason is unidentified " transformer is incorrect the movement is many sided, design research, make, installation is debugged and move safeguard a branch to have more or less responsibility, although real work is medium,each relevant production manufacturer are improving a technology ceaselessly to raise behavioral dependability, but transformer differential uses example by accident still amount to is not little [2] . The purpose of the article depends on sum up his experience and discussing with communication of person of the same trade, run a level to raise transformer differential protector jointly and try hard. The case study that 2 differential protection uses by accident 2.

1 excitation current causes transformer differential to protect the characteristic that uses transformer excitation current by accident is normal moving circumstance next its values are very little, do not exceed transformer commonly of rated electric current 3% one 5% , transformer job is in the linear of magnetic flux paragraph OS, if pursue 1. Core is not saturated, its guide magnetism leads μ relatively very big, the excitation inductance of transformer winding is very big also. When producing exterior short circuit, because voltage drops, excitation electric current is smaller, because this is opposite below these circumstances,the influence of excitation electric current need not consider commonly [3] . Graph the relation curve Fig of =f(I) of 1 　 Φ and U=f(I) .

1Functionof Φ =f(I)andu=f(I) restores when the voltage after transformer airdrop or breakdown are excised when, because the magnetic flux in transformer core is urgent leap is great, make core instant saturated, guide magnetism rate is close to relatively 1, transformer winding inductance is reduced, accompany the excitation current with occurrence very great numerical value, what the bag contains very large part is aperiodic heft and heft of Gao Cixie wave, give priority to with 2 harmonic, the 6 ～ that its numerical value can achieve rated electric current 8 times above, the excitation current of occurrence fastigium appearance, if pursue 2, in attenuation of current of initiative instant excitation very fast, to general medium or small transformer, via 0.

After 5~1s, its value does not exceed 0 of rated electric current.

25~0.

5 times, the attenuation rate of current of large transformer excitation is slower, want 2~3s to afore-mentioned values damply, already the capacity of transformer is jumped over damply greatly more slow, at the same time excitation current weaveform appears discontinuous, have discontinuous part, this electric current flows into differential relay, the likelihood causes protector to be moved by accident [4] . The excitation current of surge electric current and transformer is same, had shed transformer a side only, in gate closes in transformer airdrop or excising the voltage of exterior short circuit to resume a course, all excitation current will flow into differential loop, certainly will causes the misoperation that transformer differential protects. And while a transformer generates excitation current, surge electricity still can produce in the transformer that with its paralell connection runs, surge electric current also will flow into differential loop entirely, cause transformer differential to protect misoperation [5] . Can come through the following measure differentiate excitation current: ① uses the differential relay that possesses fast saturation core, ② differentiates the weaveform of short-circuit current and excitation current, ③ uses harmonic apply the brake 2 times, comparing of apply the brake is 15%~20% commonly, ④ uses the differential relay of undee and symmetrical principle. Among them ① basically applies to groovy electromagnetism relay type differential protection; ② and ④ basically are used at personal computer transformer to protect, but taller to the requirement of hardware, through differentiating weaveform the feature can come true, this is the most essential settlement the method of excitation current problem [6] . Additional, in advocate change when differential protects place to choose with voltaic transformer, divide outside should choosing the transformer of D class core that contains air gap, still should increase voltaic transformer to change appropriately than, in order to reduce short-circuit current multiple, can weaken excitation current effectively so, reduce the lopsided electric current of the generation in differential loop, heighten the sensitivity that differential protects. This pair prevents the breakdown outside groove guard, especially the most serious three-phase gold belong to sexual short circuit and bring about advocate change differential protects misoperation particularly effective [7] . 2.

2 times loop breaks 2CT the CT loop wiring of the relay of differential of electromagnetism type transformer that the line causes transformer differential protection to use a convention by accident, the option that must carry pair of CT wiring forms above all undertakes external " phasic compensation " , eliminate transformer wiring group not to differ phasic difference and differential protect the electric current of tall, low-pressure side that cause loop is lopsided electric current. The transformer of the Y/dll wiring that exemple as usual uses, as a result of triangular side electric current phasic lead of samer than astral form side phase current 300, must the CT2 of side of transformer star form second side is received triangularly, and the CT of triangular side receives astral form, the CT2 that will flow into differential relay thereby second electric current is phasic and corrective come over. Differential of personal computer transformer protects a root to occupy Y, the phase shift that D commutation produces undertakes interior " phasic compensation " computation, for example, for wiring simple, aleatoric wiring group is other transformer second loop can use its CT2 whole heavenly body join, its are phasic compensation can come true by the software of protector interior, and the choice that need not resemble traditional differential protection relying on CT wiring means in that way undertakes external " phasic compensation " , the compensation of this kind of software is to use symmetrical heft law to undertake " matrix alternates " computation gets [8] . Of the behavioral electric current that transformer differential protects whole calm, want to consider the element of the following respects and impact commonly: L) should escape the influence of the transformer excitation current when the voltage after transformer airdrop and exterior breakdown restores, rectify calm formula Idz=KkIe, kk reliable coefficient is taken 1.

3~1.

5, ie rated electric current; 2) should escape transformer the biggest lopsided electric current that causes in transformer protection when exterior breakdown, rectify calm formula Idz=KkIbp, kk reliable coefficient is taken 1.

3, ibp is lopsided electric current; 3) should hide the influence of the differential electric current that when transformer differential protects loop line 2 times, causes in differential loop, rectify calm formula Idz=KkIe. Kk reliable coefficient is taken 1.

3, ie rated electric current. 3 kinds of maximum regard above as the differential movement electric current of transformer. Electric current rectified the movement that electromagnetism transformer differential protects to consider the 3rd surely, second loop of differential loop CT2 breaks a line to won't be moved by accident, protection of transistor transformer differential and the behavioral electric current that differential of personal computer transformer protects press transformer commonly the 25% one 50% considerations of rated electric current, its protect a function to come true with logic, protect fast, delicacy than electromagnetism transformer differential, and behavioral electric current is whole decide lesserly. Because of this CT2 in differential loop second when winding a string, if do not take step, transformer differential protects meeting misoperation. CT breaks the feature with the most apparent thread is electric current drops, in personal computer protection, want to have reasonable judgement only, solve voltaic transformer not hard 2 times protection of differential of the transformer when loop breaks a string uses an issue by accident. If some side electric current satisfies following condition to consider as CT to break a string at the same time, only one photograph or two-phase electric current are 0, other two-phase or one phase current is as equal as starting electric current, the choppy quantity of breakdown phase current (drop) the calm value that gives more than, can judge a CT to break a string. After differentiate gives CT to break a string, can be when normal load closedown differential, prevent transformer differential to protect misoperation [5] . 2.

The differential protection that the breakdown outside 3 areas causes moves by accident [difference of generation of the breakdown outside 9] area flows to basically have below a few kinds of reasons: The rated electric current of each side when ① transformer moves normally is abhorrent; ② is contained when transformer a side when articulatory head adjusts, voltage happening change produces lopsided electricity; Transformer of ③ electric current (error of TA) itself existence; The error that ④ TA different type causes; ⑤ harmonic and aperiodic the heft influence to different type TA; ⑥ does not cause each side electric current with the load of the type phasic happening deviation; Be based on the consideration of afore-mentioned elements, want to remove the combined influence of these lopsided heft when rectifying the differential that decides transformer to be worth surely, its movement electric current is in commonly (0.

3~0.

5)In(In is) of rated electric current. Produce the breakdown outside serious area when transformer, two side can produce bigger difference to flow, exceed differential doorsill value possibly below following case: ① short-circuit current is bigger, model of each side transformer is abhorrent, especially a side with big short-circuit current uses P class transformer (the voltaic transformer that does not take transient character) , and a side with small short-circuit current uses TPY class transformer (the voltaic transformer that takes transient character) ; ② is contained in short-circuit current bigger aperiodic heft and harmonic heft; ③ breakdown excises the instant, as a result of the existence of remanence, what size differs arise to restore sexual current when voltage restores; If ④ characteristic load allows gender or perceptual and laden existence, cause each side short-circuit current is phasic produce deflection, produce bigger difference to flow; For many times the accident makes clear, transformer produces the breakdown outside the area, the time in the breakdown outside producing a division paragraph, differential protection won't be moved by accident commonly, in the twinkling differential that excises breakdown protection is moved by accident instead, analyse according to the collection wave of to a few typical accident, discovery protects behavioral point to all fall in curve of differential scale apply the brake (apply the brake of scale of two paragraphs of broken line) those who do not have character of apply the brake is horizontal less than of the first inflection point, namely difference shedding is more than doorsill value, restraint current is less than electric current of the first inflection point (inflection point electric current is (0.

9~1.

0)In) , if the graph shows C 4 times to nod (the Id in the graph is differential electric current, ir is restraint current; K1, k2, k3 is) of coefficient of proportionality. The graph folds Fig of apply the brake of line type scale two paragraphs 4.

4Theproportionalrestraintoftwosegments records wave data analysis and movable mould experiment to emulate to the spot, all knowable inevitability of existence of act of the protection below this kind of circumstance. When breakdown, short-circuit current is bigger, contain aperiodic heft and harmonic heft, the lopsided weight that arises during breakdown is greater (the likelihood is more than differential movement doorsill to be worth) , but restraint current is bigger, behavioral point drops in blame motion division, if pursue,4 show B drop. In the instant that excises breakdown, the level of transient heft attenuation of two side TA is different, difference shedding is right now bigger still, and restraint current is reduced, the C that behavioral point moves is nodded, differential protection is moved by accident, the curve of scale apply the brake that installs by this principle is protected cannot apply the brake. To prevent differential of the breakdown outside the area protection is moved by accident, can begin from the following respects: When ① is undertaking protection is worth computation surely, protection decides a value to should not be too low, rectify commonly be in surely 0.

4In or above; Two side TA chooses ② as far as possible of same type, can be P class or TPY class transformer together, effect of transformer of use TPY class is better; ③ .

Raise the sampling precision of hardware and computational accuracy; ④ installs advanced new principle protection. Because our country is most,what power system station of the place all uses with TA is P class, some places use TPY level in high-pressured side, low-pressure side uses P level, affect the lopsided sex of two side TA badly. Protection is worth a requirement to rectify surely be in surely (0.

3~0.

Extremely specific place rectifies 5)In to be in surely 0.

2In, the doorsill that decide a value is too low. As the development of computer standard, protector hardware level rises ceaselessly, of a variety of principles apply integratedly, sampling precision and computational accuracy also are rising. Besides, also can begin from the software of the work out, 3 last words are used by accident to what protection causes when the breakdown outside avoid an area is excised in recent years, the application of personal computer protector is increasingly wide, but transformer advocate of protection using an account by accident still is many sided. The article gives the technical staff that cannot find transformer differential protection to use an account by accident to offer a few train of thought only, we are debugged in installation only do each link work in the process fine, according to examine byelaw and concerned regulations regulation, father to pass groups of whole tests, take corresponding step actively, be the dependability that can raise transformer differential to protect, can avoid completely perhaps advocate the misoperation that changes to be protected in the differential in moving. CNC Milling