CN1512524A - Changing current ratio of 10KV and higher high-voltage current transformer under live condition - Google Patents

Abstract

A current mutual-inductor used in measurement in power system is that its no-load voltage ratio is matched based on the load current, if its variation exceeds the tolerant value, the ratio should be converted to meet the needs of measurement and protection which should be done when power cuts or the current ratio conversion should be done with three conditions when power is on, 1. more than three current ratioes, 2. the error compensation method to the current mutual-inductor should be improved 3. the secondary coil is led to a connection terminal of a switch cabinet or an end box to get the necessary ratio if only altering wiring of the terminal.

Description

10KV and above high-tension current inductor change the electrorheological ratio under no cut-off condition

Technical field: the current transformer electric measurement equipment that in electric power system, is absolutely necessary, current transformer divide measure and protection with two big classes.This paper focuses on Verification of Measuring Current Transformer.

Background technology: the current transformer in being suitable for has strict demand technically except electric pressure, accuracy and secondary rated capacity etc., a rated current determined that tighter regulation is arranged too: according to regulation among the power industry standard DL/T448-2000 of the People's Republic of China (PRC) " electric power meter technical management rules ", determining of current transformer rated primary current, should guarantee that it reaches about 60% of rated value at normal operating actual loading electric current, should be not less than 30% at least.

But be difficult to the requirement in the assurance afore mentioned rules in actual use, especially to the individual line subscriber in the transformer station, because of being produced the influence of season, market supply and demand variation and electricity consumer production development etc., user's power load fluctuation alters a great deal.Power supply department guarantees the correct and electric equipment protection action message of metering for the variation that adapts to power load and the increase of electricity consumer power consumption, needs the current transformer of replacing respective electrical rheology ratio in time.When transposing 10kV and above high-tension current inductor, must carry out under the power failure condition, electric personnel can more change jobs under the reliable situation of safety measure.And the user not only will bear transposing current transformer expense, also will bear and answer economic loss brought by power failure.

For this reason, I am through years of researches and test, and having invented a kind of is a kind of new Technological improvement plan in the method that does not need the current ratio of transposing current transformer under the power failure condition, can solve the insurmountable always difficult problem of electric power system.

Summary of the invention: the present invention mainly improves aspects such as the internal structure of current transformer and external cablings.

One, analyze from the current transformer principle:

The structure of current transformer is very similar with power transformer; mainly form by iron core, winding and secondary winding etc.; a umber of turn of different is current transformer seldom; a windings in series is in test line during use; and the secondary winding number of turn is more, is serially connected in the loop of measuring instrument, protective device.

The effect of current transformer is the electric current that differs in size in the supply line with different electric pressures, by the primary winding of current transformer.According to different current ratios, obtain the unified rated current of a 5A or 1A from the Current Transformer Secondary coil.A rated current I ₁N and secondary rated current I ₂The ratio of n claims rated transformation ratio, represents with Kn.

$\mathrm{Kn}=\frac{I_{1}n}{I_{2}n}--\left(1\right)$

Current transformer is not having under the situation of loss, and primary side current is all sensed secondary side, promptly

E ₁I ₁＝E ₂I ₂ (2)

E in the formula ₁And E ₂Respectively expression once with the induced potential of secondary coil;

I ₁, I ₂Represent once respectively and secondary current.

Learn that from electromagnetic induction principle the induced potential and the number of turn of coil are directly proportional.

$\frac{E_1}{E_2}=\frac{W_1}{W_2}--\left(3\right)$

W in the formula ₁And W ₂Represent respectively current transformer once with the number of turn of secondary coil.

Can be with formula (3) substitution formula (2) in the hope of the corresponding relation of the current ratio when not having error and the number of turn.

$K=\frac{I_1}{I_2}=\frac{W_2}{W_1}--\left(4\right)$

K is a current ratio in the formula.

Current transformer once, secondary current size with once, the secondary coil number of turn is inversely proportional to, and is that current transformer calculates the fundamental formular of current ratio K value.Can obtain current ratio or calculate once the number of turn with secondary coil from formula (4), the product of electric current and coil turn claims number of ampere turns.According to above-mentioned principle,, just can obtain multiple required electrorheological ratio as long as increase and reduce current transformer once or the number of turn of secondary coil.

Two, current transformer wants to change current ratio under no cut-off condition, must possess following three conditions:

1, current ratio more than three should be arranged at least.Present power supply department and the user current transformer that all adopts single ratio-changeable and divide metering to protect two groups of different no-load voltage ratios, but respectively on iron core separately, see accompanying drawing 1 common metering and protective current transformer, schematic diagram.

Below we with metering with being example: as a primary winding is that 3 circles, secondary coil are that current transformer, the no-load voltage ratio of 360 circles is 600/5.In order to reach the current ratio more than 3,

Need improve the primary current instrument transformer.

1) former primary winding 3 circles are constant.

2) divide 3 groups of coilings with secondary coil 360 circles, every group of coil is 120 circles, adopts tapped drawing, and sees that accompanying drawing 2 improves the tapped polytropic ratio current transformer schematic diagram in back.

2, must the error compensating method of current transformer be improved in order under charged condition, to change current ratio.The intrinsic error of current transformer mainly is made up of exciting curent, core material quality and core structure etc.In order to improve the current transformer accuracy, manufactory adopts compensatory approach to reduce the error of current transformer.The compensation of tapped polytropic ratio current transformer all between first section S1 and S2 of secondary coil, is mainly considered the error that the exciting curent loss causes,, can be guaranteed basically the error of other two groups of no-load voltage ratios as long as error compensation that will this section is controlled well.But this current transformer needs the continuous earth point of the secondary circuit of turn-off current instrument transformer when changing wiring, see accompanying drawing 3 traditional compensation current transformer winding diagrams.According to DL408-91 " electrical safe working order " regulation is unallowed.If make wiring from bottom to top into, be S4 → S3 → S2 → S1, removing 600/5A can guarantee in the permitted maximum range, other no-load voltage ratio all can be seriously overproof, especially 200/5A shelves time error maximum between S4-S3, so need do necessary improvement to the error compensation of current transformer, compensation of error is focused between S4 and the S3, just original traditional compensation method is opposite.So not only can under the situation of the continuous earth point that does not disconnect secondary circuit, change current ratio, and wiring is seen the different current ratio winding diagrams of the tapped current transformer of accompanying drawing 4 phase three-wire threes also than original convenience, much simple and direct.

Can ask and the current ratio of above three kinds of wiring by formula (4).

Fig. 4 (a) $K=\frac{W_2}{W_1}=\frac{120}{3}=\frac{200}{5}$

Its current ratio is 200/5.

Fig. 4 (b) $K=\frac{W_2}{W_1}=\frac{240}{3}=\frac{400}{5}$

Its current ratio is 400/5.

Fig. 4 (c) $K=\frac{W_2}{W_1}=\frac{360}{3}=\frac{600}{5}$

Its current ratio is 600/5.

By above-mentioned three kinds of wiring, can obtain 200/5,400/5 and 600/5 current ratio respectively, certain size according to actual primary current, can select 100/5,200/5,300/5 and 400/5,800/5,1200/5 and many winding currents instrument transformer of other no-load voltage ratios for use, though but this current transformer has multiple current ratio, change electrorheological than the time still need could change power-off condition under, change the condition of electrorheological ratio but possessed not have a power failure.

3, most critical must change traditional mode of connection, the head and tail tap S1～S4 of 3 coils of Current Transformer Secondary is guided on the binding post of switch cubicle or terminal box, just can obtain required current ratio as long as change the wiring of terminal, see the tapped current transformer terminal connection diagram of accompanying drawing 5 phase three-wire threes.

But when changing wiring, should notice that the Current Transformer Secondary coil can not open a way.

Operating current transformer, the load that its secondary side connect are the current coil of electric energy meter, and impedance is very little, are in short-circuit condition substantially.Like this, because the result of the mutual degaussing of magnetic flux that magnetic flux that the secondary electricity produces and primary current produce makes the magnetic flux density in the iron core can maintain reduced levels.At this moment, the secondary voltage of current transformer is also very low.In service behind second open circuit, the electric current of primary side is still constant, and secondary current equals zero, and then the degaussing magnetic flux of secondary current generation also disappears.Like this, primary current all becomes exciting current, makes the iron core of current transformer saturated suddenly, and magnetic flux density increases.Because unshakable in one's determination is seriously saturated, the secondary side of current transformer will produce the high pressure of thousands of volts.Peaked wave has appearred in induced potential, two minor insulation is constituted a threat to, and jeopardize equipment and personal safety.

So when the wiring of conversion current ratio, on terminal, must have one group of winding at least, with can change wiring behind short-circuit line or the short-circuit piece short circuit, wait finish wiring check errorless after, short-circuit line or short-circuit piece could be removed, just can normal operation input.

Description of drawings: accompanying drawing 1 common metering and protective current transformer, schematic diagram.

Accompanying drawing 2 improves the tapped polytropic ratio current transformer schematic diagram in back.

Accompanying drawing 3 traditional compensation current transformer winding diagrams.

The different current ratio winding diagrams of the tapped current transformer of accompanying drawing 4 phase three-wire threes.

The tapped current transformer terminal connection diagram of accompanying drawing 5 phase three-wire threes.

Embodiment: when needing the change electrorheological to compare when the line load bigger variation of generation, need only on terminal board with short-circuit piece or short-circuit line general one group of current mutual inductor coil short circuit wherein, in current terminal outlet side, change wiring as required and just can obtain required electrorheological ratio.Deng finish wiring check errorless after, short-circuit line or short-circuit piece are removed, just can normal operation input.

On July 18th, 2002

Claims (1)

1. At the electrorheological ratio of change high-tension current inductor that do not have a power failure, it is a kind of safe, new solution simply and easily, can improve the utilance of current transformer, the economic loss that minimizing needs power failure to bring because of transposing electrorheological ratio, prolong the life cycle of current transformer, generally according to enterprise in the recent period, mid-term or production development at a specified future date and electricity consumption situation, make rational planning for, can accomplish that 5 ∽ need not change current transformer in 10 years.Power plant, power supply enterprise and big-and-middle-sized industrial and mining enterprises etc. have been solved, the technical barrier that when transposing high-tension current inductor no-load voltage ratio, must under the power failure condition, carry out.

   This technology is applied widely, and is especially obvious for instrument transformer manufacturer economic benefit.For the intellectual property that makes oneself is inviolable, ask this patent of invention to be protected at home.

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