FR2707811A1 - Electronic trip device for power disconnectors. - Google Patents

Abstract

The invention relates to an electronic tripping device for power disconnectors, in particular a tripping device with automatic measurement field switching for the detected conduction currents (I1; I2; I3). A transducer is used, which converts the output current (Ia) of the current transformers (21; 22; 23) into a measurement voltage (Um), an apparent power resistor (51) with at least two partial resistors ( 511; 512). Using a voltage comparator (53) sweeping the measurement voltage (Um) and a downstream control element (54) it is possible to obtain that in each measurement field the output current (Ia) passes through another combination of the partial resistors (511; 512) and a corresponding value of the scale factor is used for the evaluation of the A / D conversion.

Description

I

  ELECTRONIC TRIGGERING DEVICE

FOR POWER DISCONNECTORS

  The invention relates to an electronic trip device for a power disconnector - or circuit breaker - comprising: - at least one current transformer (21; 22; 23) connected to a line (L1, L2, L3) of a circuit alternating current, the line (L1; L2; L3) being connected to a pole (11; 12; 13) corresponding to the power disconnector, - an electro-mechanical tripping mechanism (2) for opening the poles (11; 12; 13) of the power disconnector in the event of the conduction current (Il; I2; I3) passing below or beyond specified setting values (El; E2; Ek), - a signal transformer connected to at least one of the current transformers (21; 22; 23) for converting the output current Ia of the current transformer (21; 22; 23) into a corresponding measurement voltage (Um), - downstream means for sampling and maintaining the measurement voltage (Unm) for a previously defined number of samplings, - downstream means for A / D conversion of the sampled measurement voltage, with an additional input

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  (522) for the modification of the scale factor with respect to current units per bit, - a downstream microcomputer for determining the effective value of the conduction current (II; I2; I3) taking account of the factor d ladder, as well as an output circuit (1) for actuation of the trigger mechanism. The invention relates in particular to a device for

  automatic measurement field switching trip.

  Patent EP 179 017 A2 discloses such a device with at least one transformer or current connected to a line of an alternating current circuit, the line being connected to a corresponding pole of the power disconnector, as well as to a mechanism. electro-mechanical trip device for opening the poles of the power disconnector when passing above and below the specified setting values of the conduction current, and with a signal transformer connected to the current transformer to transform the current output from the current transformer to a corresponding measurement voltage. In addition, a sampling and holding circuit for repetitive sampling and maintaining of the measurement voltage for a determined number of samples is provided, to which are connected downstream of the analog / digital conversion means (conversion A / N), a microcomputer for calculating the effective value of the conduction current and an output circuit for actuating the triggering mechanism on the basis of a previously determined value of the conduction current. The problem with such tripping devices consists in the fact that, taking into account the measurement accuracy required within the measurement field of the conduction current extending from the smallest nominal current adjustable up to the largest adjustable overcurrent, they normally require high quality A / D converters with high resolution or word length (usually 10 or 12

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  bit trigger), these high resolution and word length leading, with increasing conduction currents, to very high measurement accuracy but not usable, and the computational load in the microcomputer increases. To avoid this drawback, the known triggering device comprises a switching device connected to the microcomputer for the automatic change of the scale factor of the A / D conversion with a resolution of 8 bits, in order to divide a given measurement field of the current. conduction with respect to current units per bit of the microcomputer in a first field, lower, and a second field, upper. This circuit generates in particular a reference voltage which can be switched between at least two values and consisting essentially of two operational amplifiers coupled on the output side, one of which is supplied on the input side, via a voltage divider network. , by a variable voltage signal supplied by the microcomputer, and the other by a fixed voltage, via another voltage divider network, so that the voltage at the connection point on the output side of the amplifiers operational changes according to the variable voltage signal and acts as a reference voltage modifying the scale after being driven

  up to the means intended for A / D conversion.

  The disadvantage of this state of the art is as follows: At each A / D conversion the microcomputer must recognize whether the existing scale factor corresponds or not to the measurement field corresponding to the conduction current currently sampled. In the second case, after switching the reference voltage, repeat the

  A / D conversion with the correct scale factor, i.e.

  in other words, for a measurement field switching an additional step is required respectively, requiring additional processing time for the A / D conversion and for the processing by the microcomputer. It should also be taken into account that the switching of the

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  reference, which is the most sensitive input variable for A / D conversion, can cause disturbances and thus measurement errors. This also requires a relatively large device for switching the reference voltage, comprising two operational amplifiers, four precision resistors and two diodes. The transformation of the output current supplied by the current transformer inside the wide measurement field into a corresponding measurement voltage also requires the use of precision resistors with high load capacity. The energy to be dissipated on the precision resistance of the transducer becomes all the more important because, for the self-energizing triggering device, each of the current transformers must supply, even for single-phase operation in the field. of the smallest adjustable nominal current, sufficient electrical energy which, finally, in the case of very high conduction currents, must be dissipated as thermal energy via the signal transformer. This high thermal energy in turn requires the use of expensive or little available electronic components, which must be designed for

high ambient temperatures.

  In a switching device known from the document DE 37 24 97 Ai, the magnitude of a voltage is checked on the cursor of a potentiometer using a hysteresis comparator, then a switch is controlled as a function of this value. . If the sampled voltage is located in a first, lower adjustment field, it is brought to an A / D converter via an amplifier and the switch located in its first switching position; if the sampled voltage is in a second, upper adjustment field, it is brought to the A / D converter directly via the switch located in its second switching position. To do this, the comparator output voltage is used as the control voltage for the switch and the A / D converter. The high colts and in particular for the use for the measurement of the current, the high dissipated power are disadvantages, since on the one hand, for the application of permanent current on the two fields of adjustment, a resistance of precision designed for large dissipated powers, and on the other hand the switching device would be too expensive due to the number of components necessary for carrying out the

field switching.

  An object of the invention is therefore to avoid the drawbacks mentioned above by an improved measurement field switching using standard means.

for A / D conversion.

  From an electronic triggering device of the type mentioned above, the objective is achieved according to the invention thanks to a device characterized in that: - the signal transformer is a load resistor (51) comprising at least two partial resistances (511,

512),

  - one of the partial resistors (511) is connected to the inputs of a hyteresis voltage comparator (53), the output signal of which changes suddenly when its input voltages pass above or below limit or threshold values, - the output (533) of the voltage comparator (53) is connected to the additional input (522) of the A / D conversion means and to the microcomputer, and - the output (533) of the comparator voltage (53) is also connected to the input (541) of a control element (54) causing non-application or application of the output current (Ia) of the current transformer (21; 22; 23 ) to corresponding partial resistors (511; 512) after an abrupt change in the output signal of the voltage comparator (53) to cause an increase or a decrease in the scale, one (511) of the partial resistors (511; 512) being under permanent load. By realizing the signal transformer in the form of a load resistance comprising several partial resistances and their respective connections with a voltage comparator and a control element, this is obtained with simple means, while maintaining the advantages of the prior art, on the one hand, because the voltage comparator is located upstream, each A / D conversion is carried out from the start in the measurement field corresponding to the sampled conduction current, and that, on the other hand, a high portion or low of the load resistance is charged by the output current of the current transformer, depending on whether the output current is assigned to the lower or higher measurement field. In any case, the current flow is not interrupted. Because the load resistance participates with different resistance values in the different measurement fields, the thermal energy to be dissipated is kept relatively low, which eliminates

  the disadvantages associated with thermal energy.

  The hysteresis of the voltage comparator prevents the going -

  generally troublesome feedback between two neighboring measurement fields, when the magnitude of the conduction current lies on the common field border, and makes the use of precision components unnecessary for the voltage comparator and for the control element. Interference switching of a reference voltage for A / D conversion is also suppressed. The entire measurement field for the conduction current must be divided appropriately and as necessary into at least

two partial measurement fields.

  Other advantageous developments of the invention are

  explained in the claims. The cyclic link of

  several current transformers belonging to a power disconnector with a common load resistance and therefore with common downstream means,

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  reduces expenses for these high precision or high integration components to a minimum. The use of a suitable microcontroller, already available on the market, brings an ingenious simplification. An additional INHIBIT control output on the voltage comparator prevents erroneous measurements during measurement field switching. The division of the load resistance into two partial resistors provides a solution requiring particularly simple and few means concerning the load resistance itself as well as at the level of the voltage comparator, the control element and the means for the A / D conversion. The effective or efficient value of the conduction current, which is decisive for the tripping behavior of the tripping device, can be determined by the microcomputer, either by calculating the quadratic value

  average either by using an appropriate memorized table.

  The invention is explained in more detail below with the aid of an exemplary embodiment which reveals other details and advantages in the accompanying drawings: FIG. 1 is a block diagram of an electronic trip device according to the invention; fig. 2 is a detailed representation according to fig. 1; fig. 3 is a diagram of characteristic quantities as a function of the output current of the

intensity transformer.

  In fig. 1 is shown in diagram form a three-phase alternating current line to be protected with poles 11, 12, 13 of a power disconnector located on the different lines L1, L2, L3. Another essential component of the power disconnector is an electronic trip device 10. On the output side, the trip device 10 includes a thyristor switch 1, which under certain conditions, in particular in the event of a set value being exceeded, by at minus one of the conduction currents Il, I2, I3 on the

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  line concerned L1, L2 or L3, supplies energy to an electro-mechanical tripping mechanism 2 via a measurement and supply line 3, which causes the poles 11 to 13 to open. example, the triggering mechanism 2 is produced in the form of a triggering electromagnet. On each of the lines L1, L2, L3 is mounted a transformer

  intensity 21, 22, 23 in series with the poles 11, 12, 13.

  The transformed conduction currents passing through the secondary windings of the intensity transformers 21, 22, 23 are brought to a switching device 4 in which these currents undergo full-wave rectification, then transmitted in successive cycles to the measurement and measurement line. power supply 3 in the form of output current Ia as a function of successive control signals S1, S2, S3 on the input side. Such a switching device is described in detail in document DE 40 16 075 C2. In normal operation of the power disconnector the thyristor 1 is open and all of the output current Ia arrives in a processing unit 5. By leaving the processing unit 5, the output current Ia feeds an electrical supply unit 6 used to supply power to the electronic trip device 10. Adjustment values El, E2 to Ek are entered into the processing unit by adjustment elements 7. The adjustment elements 7 are suitable means for specifying the values of setting El, E2 to Ek, for example switches or potentiometers. In the processing unit 5 the values of the output current Ia are processed in chronological order. This results in usable quantities of the conduction currents Il, I2, I3, in particular their effective values. If at least one of the usable quantities of the conduction currents I2, I2, I3 exceeds one of the corresponding setting values El, E2 to Ek, a trigger signal is sent on the control input of the switch to thyristor 1, depending on the importance of this setting value, with or without a more or less long delay, via the trigger line 8, which causes the opening of the poles 11, 12, 13 -and consequently the triggering of the holding lock (not shown) of the power disconnector. In fig. 2 shows in detail the processing unit 5. The output current Ia is converted in a load resistor 51 into an appropriate measurement voltage Unm. The measurement voltage Unm arrives at a signal input 521 of a commercial microcontroller 52. The microcontroller 52 comprises, arranged downstream of means for sampling and maintaining the measurement voltage Unm, means for A / D conversion of the measurement voltage sampled and maintained as well as a

  microcomputer. In addition to various control tasks (p.

  ex. cyclic transmission of the control signals Si, S2, S3), the microcomputer ensures the constitution of usable quantities (in particular of effective values) of the conduction currents Il, I2, I3 from the digitized measurement voltage. In the microcomputer of the microcontroller, the exploitable quantities are also compared with the specified adjustment values El to Ek, in order to emit a signal if necessary.

  trigger on the trigger line 8.

  The load resistor 51 is divided into two partial resistors 511 and 512, the base 515 of which is connected to the common ground of the processing unit 5. Parallel to the first partial resistance 511 are arranged the two inputs 531 and 532 of a hysteresis voltage comparator 53, the non-inverting input 531 being connected to the high point 513 and the inversense input 532 to the common point

  or of connection 514 of the partial resistors 511 and 512.

  Parallel to the second partial resistance 512 is arranged the output of a control element 54, more precisely the drain-source interval of a field effect transistor. In parallel with, at the output 533 of the voltage comparator 53 is disposed a voltage divider

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  55. The voltage divider 55 comprises two ordinary resistors 551 and 552 and is connected, by its intermediate socket 553, to the control electrode 541 of the control element 54, that is to say, to the door of the field effect transistor. If the measurement voltage Um has not yet exceeded the upper limit value of the voltage comparator 53, its output 533 is at

  low level. Thus the control element 54 remains non

  conductor and the second partial resistance 512 is fully effective. This results in a certain factor when converting the output current signals Ia into the measurement voltage Um. If the measurement voltage Um exceeds the upper limit value of the voltage comparator 53, its output 533 is at the HIGH level, which makes the control element 54 conductive and the second partial resistance 512 is short-circuited. In the upper measurement field, the conversion of the signals is carried out with a lower factor as well as with a lower energy consumption at the resistance of 51. The proportion of conversion factors in the higher measurement fields and lower results from the ratio between the first partial resistance 511 and the sum of the two partial resistors 511 and 512. The output 533 returns to the LOW level only if the measurement voltage Um remains below the lower limit value of the voltage comparator 53, which again makes the control element 54 non-conductive, the conversion of the signals continuing with the highest factor. In the same ratio, the measurement signal Um is available at the signal input 521 within a lower measurement field with a sufficiently large resolution in voltage units per current unit of the conduction currents LI, L2, L3 and, correlatively within a higher measurement field with a lower resolution but still sufficient for the

further processing.

  il 2707811 In each measurement field, the condition necessary to maintain the operation of the electronic trip device 10 is fulfilled, namely the flow of the secondary currents of the current transformers 21, 22, 23 and the flow of the output current Ia are not interrupted. The measurement fields are limited by the limit values of the voltage comparator 53 and overlap in the area between the limit values, which ensures a passage that is sufficiently free of disturbances.

  between the measurement fields, thanks to this hysteresis.

  Thanks to this signal conversion, for low output currents Ia with a high factor and for strong output currents Ia with a low factor, the following A / D conversion requires only resolution by simple means, at know a resolution of generally 8 bits. In order to be able to take into account the entire measurement field, the result of the A / D conversion is subject to a scale factor. This scale factor takes two values and is a function of the current measurement field. The scale factor values are in inverse proportion to the signal conversion factors in the two measurement fields. The scale factor is generated in the microcontroller 52, which has for this purpose an additional input 522 connected to the output 533 of the voltage comparator 53. A LOW level at the output 533 causes in the microcontroller 52 the lower value and a level HIGH

  the higher value of the scale factor.

  In fig. 3 are shown qualitatively the evolution of the measurement voltage Um (fig. 3a) and of the resolution of the A / D conversion per unit of current (fig. 3b) as a function of the output current Ia. For this representation, it has been assumed that the output current Ia passes from the lower measurement field to the upper measurement field and vice versa. The pace of the representation of the resolution corresponds to the inverse of that of the precision since the capture of the conduction currents Il, I2, I3 until the

formation of digitized values.

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  The microcontroller 52 is controlled by an output of

  INHIBIT 534 command of the voltage comparator 53 (fig. 2) until the process of switching from one measurement field to the other as well as the transients are completed.

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Claims (10)

  1. Electronic trip device for power disconnector, comprising: - at least one current transformer (21; 22; 23) connected to a line (L1, L2, L3) of an alternating current circuit, the line ( L1; L2; L3) being connected to a pole (11; 12; 13) corresponding to the power disconnector, - an electro-mechanical tripping mechanism (2) for opening the poles (11; 12; 13) of the disconnector power in case of conduction current flow (Il; I2; I3), below or beyond the specified setting values (Et; E2; ... Ek), - a signal transformer connected to at least the one of the current transformers (21; 22; 23) for converting the output current (Ia) of the current transformer (21; 22; 23) into a corresponding measurement voltage (Un), means downstream for sampling and maintaining the measurement voltage (Um) for a previously defined number of samplings, - downstream means for conversion n A / D of the sampled measurement voltage, with an additional input (522) for modifying the scale factor in relation to current units per bit, - a downstream microcomputer for determining the actual value of the current conduction (It; I2; I3) taking into account the scale factor, as well as an output circuit (1) for actuation of the trigger mechanism (2), characterized in that - the signal transformer is a load resistor (51) comprising at least two partial resistors (511, 512), - one of the partial resistors (511) is connected to the inputs of a hysteresis voltage comparator (53), the output signal of which changes suddenly in the event of passage of its input voltages beyond or below limit or threshold values, the output (533) of the voltage comparator (53) is connected to the additional input (522) of the A / D conversion means and to the microcomputer, and - the output (533) of the voltage comparator (53) is also connected to the input (541) of a control element (54) causing the non-application or application of the output current (Ia ) from the current transformer (21; 22; 23) to corresponding partial resistances (511; 512) after an abrupt change in the output signal of the voltage comparator (53) to cause an increase or a decrease in the scale, one (511) of the partial resistors (511; 512) being under constantly charging.   2. Electronic trip device according to claim 1, characterized in that the output currents of several intensity transformers (21; 22; 23) connected to different blades (11; 12; 13) of the power disconnector are connected by time cycles at the load resistance (51). -   3. Electronic trip device according to the   claims 1 or 2, characterized in that the means   of sampling and maintenance, the A / D conversion means and the microcomputer are components of a microcontroller (52).   4. Electronic trip device according to   one of claims 1 to 3, characterized in that the   voltage comparator (53) is provided with an INHIBIT control output (534), connected to a corresponding input of the microcomputer.   5. Electronic trip device according to   one of claims 1 to 4, characterized in that the 94 08738 04.11.94 2707811   load resistor (51) includes two resistors   partial (511; 512) connected in series.   6. Electronic trip device according to claim 5, characterized in that a first input (531) of the voltage comparator (53) is connected to the high point (513) and a second input (532), inverse of the first input (531), at the connection point (514) of partial resistances (511; 512).   7. electronic trip device according to claim 5 or 6, characterized in that the control element (54) is a transistor switch, the control electrode (541) is connected to the output (533) of the comparator tension (53) via a   voltage divider (55), and the path of which   electrodes on the output side is arranged between the connection point (514) and the base (515) of the partial resistors (511; 512).   8. Electronic trip device according to claim 7, characterized in that the element of   control (54) is a field effect transistor.   9. Electronic trip device according to one   claims 1 to 8, characterized in that the values   digital measurement signals generated by the A / D conversion means from the measurement voltage (Um) are processed by the microcomputer to calculate a mean square value. 10. Electronic trip device according to   one of claims 1 to 8, characterized in that the   digital measurement values generated by the A / D conversion means from the measurement voltage (Um) serve as the address for a table with quadratic square current values stored in the microcomputer.