CN1037392C - Transformer differential protection of wave mode symmetrical method - Google Patents

Abstract

The present invention relates to transformer differential protection of a wave shape symmetrical method, which is a control system which adopts a wave shape symmetrical method for protecting a transformer. The present invention is mainly applied to the field of the protection of a power transformer and is mainly composed of alternating current transformation, analog-to-digital conversion, a central control unit, a man-machine conversation part, switching quantity input, an outlet, signals and a warning part. The alternating current transformation is used for transforming current and voltage signals into low voltage signals; the signals are transformed into frequency modulation pulses through the analog-to-digital conversion; finally, the frequency modulation pulses are transmitted into a counter of the central control unit. The central control unit adopts a control program for symmetrically comparing wave shapes of the signals; control signals are outputted for protecting the transformer.

Description

The waveform symmetry method of transformer differential protection

The present invention is a kind of control system that adopts the waveform symmetry method that transformer is protected, and belongs to the technical field of relay protection of power system and automation.

The current transformer differential protection that uses in electric power system; interval angle principle and second harmonic principle are arranged; the differential method with analog circuit of interval angle principle can realize; difficult realization of method with microcomputer or digital circuit; the interval angle principle is relatively poor to transformer remanent magnetism adaptive capacity, is applicable to the situation of transformer remanent magnetism less than 0.6 times of maximum magnetic flux.The differential quilt of second harmonic principle uses in a large number but has a defective.When no-load transformer close a floodgate break down or the external fault excision after break down, tripping can take place second harmonic principle transformer differential protection or deferred action can not instantaneous excision fault.

Proposed several algorithms abroad voltage braking principle equivalent circuit principle has been arranged; magnetic flux braking principle etc.; but all be theoretical research or experimental stage; really be not used in the field of power system control in the system; though use microcomputer technology in large quantities, to the very imperfect product of transformer microcomputer protection.

The objective of the invention is to reach the difficulty that interval angle principle protection microcomputer is difficult to realize, adopt microcomputer technology, a kind of waveform symmetry method of transformer differential protection is provided for solving the current defective of in system, using second harmonic principle transformer differential to protect existence.

The present invention is a kind of by system computer-controlled, that employing waveform symmetry method is carried out transformer differential protection; on complete machine structure, the present invention mainly comprises exchange conversion 1, analog-to-digital conversion 2, centralized control unit 3, human-computer dialogue part 4, switching value input 5, outlet, signal, alarm part 6.Exchange conversion is the acquisition port of controlling object signal, with primary current and voltage become can with the ac voltage signal of the low-voltage of microcomputer interface, send into the analog to digital conversion part, to be transformed into frequency modulation on pulse through the voltage-to-frequency converter of analog to digital conversion part through electric current, the voltage signal of conversion, then this pulse signal be sent into the counter of centralized control unit.Centralized control unit is " CPU " more than one structure, with " 8032 " and extend out chip such as " RAM, EPROM " counter and form microsystem, finishes following steps:

1. each analog quantity (having become frequency modulation on pulse) of acquired signal is counted sampling.

2. the switching value to transformer monitors.

3. the data of gathering are calculated, analyze, judged,, start exit relay if internal fault is sent switching value.

4. with human-computer dialogue module exchange message, the computing information of necessity can be sent the message pick-up that personnel adjust.

Human-computer dialogue partly uses " 8031 " and necessary peripheral hardware chip to form, and finishes human-computer dialogue and communicate by letter with work " CPU ", and the switching value input is that the quantity of state with primary equipment becomes weak electric signal, sends into respectively " CPU " through the photoelectricity isolation.Outlet, signal, alarm this three parts, be respectively three group relaies, the switching value that " CPU " sends starts some relays, sends node behind the relay excitation and gives control loop or signal circuit, with the excision transformer, finally finishes the protection to transformer.

Aspect the collection and processing and control in real time of signal; the present invention adopts the waveform symmetry method and has designed a kind of computer processing, to reach the signal of gathering is analyzed, and judges; make at last and whether excise the transformer order, protect transformer and electric power system effectively.

The waveform symmetry principle is differential, and it is differential that data are carried out complete all Fu Shi filtering realizations, difference internal fault and outer fault.Make symmetry with the data of preceding half-wave in the week with the data pointwise of back half-wave and relatively distinguish magnetizing inrush current and fault current.For fault current is that sinusoidal quantity adds the direct current transient state component, through differential handle the back with regard to elimination DC component become cosine component, the preceding half-wave of cosine function and back half-wave be symmetrical fully Cos (wt+ α)=-(wt+ α+π) establishes a certain moment instantaneous value I to Cos _I180Spend later instantaneous value I _I+180=Ij, then I _i=-I _I+180If formula: $\left|\frac{I_i+I_{i+180}}{I_i-I_{i+180}}\right|\≤A$ Wherein the span of A is 2.5～4, sets up all the time for this formula of fault component.

The magnetizing inrush current of transformer is the electric current that the instantaneous value by transformer remanent magnetism and switching angle causes.The magnetizing inrush current characteristic is made a simple analysis whether after the CPU computing, can differentiate internal fault exactly,, start exit relay transformer is excised from system if internal fault is sent switching value.

Behind the programming start, at first carry out initialization, carry out electric current, voltage sample then and promptly gather through analog-to-digital electric current, voltage signal; Then the data of gathering being made differential handles; Handle the filtering of laggard line number word; Whether be internal fault, if external fault then withdraws from, if internal fault, then the laggard row of counter O reset is further judged with the ratio braking method if differentiating; Preceding half cycle data and the data based relational expression of second half with signal: $\left|\frac{I_i+I_{i+180}}{I_i-I_{i+180}}\right|\≤A$ Pointwise compares, and judgement is internal fault or shoves, if asymmetric, then program is skipped counter and added 1 step and carry out the judgement whether a weekly data relatively finishes, if symmetry, then counter adds automatically and carries out the judgement whether a weekly data relatively finishes after 1; Return the comparison of descend a bit again after then pushing away a bit down if more do not finish,, then carry out counter values whether greater than the judgement of all sampled points of 0.6 sesquialter as if relatively finishing; Then be fault current if satisfy condition, start exit relay excision transformer then; Otherwise for shoving, program withdraws to digital filtering.

The invention has the advantages that:

Power transformer is the key link of electric power system, himself be worth very expensive, claimed can any fault of fast and reliable ground excision.The realization of waveform symmetry method tranformer protection; realize the digital intelligentization of tranformer protection, improved automaticity, accomplished that transformer breaks down in any case can both move reliably rapidly; guarantee system stability, the damage control after transformer is broken down is in the degree of minimum.

Waveform symmetry principle feature in theory is very obvious, and superfluous nargin relatively is big, so reliable in action is stronger than the antijamming capability of interval angle principle and second harmonic principle.

Fig. 1 is the structural representation of computer control system of the present invention.

Fig. 2 is the structured flowchart of centralized control unit among Fig. 1.

Fig. 3 is the control flow chart of computer control system work among the present invention.

Embodiment of the present invention are as follows:

Exchange conversion 1 usefulness small transformer becomes primary current and voltage signal into ac voltage signal less than 5V, so that and microcomputer interface.Analog-to-digital conversion 2 adopts voltage-to-frequency converters, electric current, voltage signal is become frequency modulation on pulse send into counter 3-1 in the centralized control unit 3.Centralized control unit 3 adopts multi-CPU structure, and CPU card is the integrated chip of " 8032 " with model and extends out chips composition computer systems such as RAM, EPROM counter.4 of human-computer dialogue parts are formed a microsystem with " 8031 " single-chip microcomputer and necessary peripheral cell separately, finish human-computer dialogue and and work CPU communication.Switching value input 5 quantity of states with primary equipment become weak electric signal, isolate through photoelectricity and send into CPU.Outlet, signal, alarm part 6 are the relay group, and the control signal of relay is from CPU, and the switching value of sending as CPU starts certain relay, send node behind the relay excitation and give control loop or signal circuit, with the excision Working transformer.

Aspect software, mainly be the applied waveforms symmetry approach, according to relational expression: $\left|\frac{I_i+I_{i+180}}{I_i-I_{i+180}}\right|\≤A$ Wherein the numerical value of A is a certain determined value in 2.5～4, makes symmetry relatively with preceding half cycle data and the pointwise of second half data, be symmetry when satisfying " relational expression ", otherwise be asymmetric, and be fault if 60 percent point satisfies symmetric condition, otherwise for shoving.

Claims (3)

1. the waveform symmetry method of a transformer differential protection is characterized in that having adopted the waveform symmetry method that the transformer signal is discerned and by computer control, its controlled step is:

Start-up system work is also carried out initialization;

Gather through analog-to-digital electric current, voltage signal;

Electric current, the voltage signal gathered are made differential to be handled;

The signal that differential is handled carries out digital filtering;

Whether be internal fault, if external fault then withdraws from, if internal fault is then further judged at the laggard row of counter O reset with the ratio braking method if differentiating;

Preceding half cycle data and the data based relational expression of second half with signal: $\left|\frac{I_i+I_{i+180}}{I_i-I_{i+180}}\right|\≤A$ Pointwise compares, and judgement is internal fault or shoves;

If asymmetric, then program is skipped counter and is added 1 step and carry out the judgement whether a weekly data relatively finishes;

If symmetry, then counter adds automatically and carries out the judgement whether a weekly data relatively finishes after 1;

Return the comparison of descending a bit again after then pushing away a bit down if more do not finish;

If relatively finish, then carry out counter values whether greater than the judgement of 0.6 sesquialter week sampled point;

Then be fault current if satisfy condition, start exit relay excision transformer then, otherwise for shoving, program withdraw to digital filtering.

According to claim 1 described and the waveform symmetry method of transformer differential protection, it is characterized in that the preceding half cycle and the pointwise of second half data of signal are made symmetry relatively, should satisfy relational expression: $\left|\frac{I_i{+I}_{i+180}}{I_i-I_{i+180}}\right|\≤A$ Wherein the span of A is 2.5～4.

3. the waveform symmetry method of transformer differential protection according to claim 1 and 2; it is characterized in that on hardware configuration, comprising exchange conversion (1); analog-to-digital conversion (2); centralized control unit (3); human-computer dialogue part (4); switching value input (5); outlet; signal; alarm part (6); the output of exchange conversion (1) connects analog-to-digital conversion (2); the output of analog-to-digital conversion (2) connects the counter (3-1) of centralized control unit (3); the interface of centralized control unit (3) is imported (5) with human-computer dialogue part (4) and switching value respectively; outlet; signal; alarm (6) is suitable mutually to be connect, and centralized control unit (3) adopts many " CPU " structure.

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