DD285698A7 - CIRCUIT FOR THE REALIZATION OF FOREIGNABLE LOSS FACTOR ASSEMBLY - Google Patents

Abstract

The invention relates to a circuit for implementing veraenderbarer Verlustfaktormassverkoerungen. Starting from the various causes of the loss factor of capacitors, the loss factors attainable with commercially available film and ceramic capacitors and with condensed or inert gas-filled capacitors and the disadvantages of using these capacitors as loss factor mass components, a passive circuit for variable loss factor mass ratios is given and in two circuit variants described. The object of the invention is to provide variable loss factor mass distributions, which are distinguished by the fact that both large and very small loss factor values can be represented with commercially available capacitors. Here, the representation of smaller loss factors than the Eigenverlustfaktorwerte of the capacitors used to realize. This object is achieved in that two commercially available capacitors are supplemented by a variable resistor to form a T-circuit, that by balancing this resistance, the relatively large loss factor of the capacitors preventing the realization of small loss factor values can be neglected for a very small loss factor value, which is larger Value is compensated that to realize larger loss factor values, the value of a constant resistance level via a transformer, which is connected in series or parallel to said T-circuit, is transformed down or up and that the desired loss factor values can be adjusted by changing the transformation ratio of the transformer , For the calculation of the loss factor, or for the dimensioning of the circuit, the numerical knowledge of the internal loss factors of the capacitors is not required.

Description

tanö, = ω C r. (3)

For fixed frequencies, one of the two resistors (parallel or series resistor) can be converted into an equivalent resistor (series or parallel resistor). Depending on expediency, therefore, the entire

Due to the various causes of the loss factor of capacitors and the associated associated dependence on the material of the dielectric and the electrodes, commercially available film and ceramic capacitors depending on the capacity and frequency loss factor values in the range of 1CT ³ to 10 ^{-4 are} achieved. Only in exceptional cases loss factor values of some 10 ~ ⁶ can be realized with these capacitors. Loss factors <10 ~ ⁶ , on the other hand, can only be achieved with condensing gas-filled capacitors, which have a rather large volume due to their low relative dielectric constant.

If commercially available Follien- or Normalalluftkondensatoren be used as dissipation factor, they deliver at a given frequency only a single loss factor value. To expand the application possibilities, it is customary to realize by parallel or series connection of constant resistances to the capacitor, at a nominal capacitance several loss factor points. Here, according to the relationships (2) or (3), a resistance value is required for each operating frequency and each loss factor rating. This results in the realization of various loss factor values, possibly at several Metfrequenzen, very quickly to a plurality of resistors, which must be individually adjusted to achieve predetermined loss factor values. It should be noted that the Eigenverlustfaktorwerte the capacitors used in the Widerstaridsabgleich with and that falls below these Eigenverlustfaktorwerte is not possible. For the realization of low loss factor values, air or gas-filled capacitors are therefore always required. The production of variable loss factor standards of the current state of the art is very labor intensive, especially when a wide dissipation factor range is to be realized. So far, only individual copies of such loss factor standard have been produced in the laboratory. An industrial production was carried out at most exceptionally and in very small numbers.

In addition to the possibilities already mentioned for the realization of loss factor standard embodiments, the series connection of two capacitors to a loss factor normal is known from high-voltage technology (Barz, J.-U .: Low-Voltage Measurable Loss Factor Standard for High Voltages: Wirtschaftspatent, DD PS 217038, GO1R 27/26) , By a suitable capacitive subdivision is achieved in this circuit that the normal operating at high voltage normal at low voltage can be measured with less expensive measurement method. The loss factor of this standard is determined by the structure of the circuit and by the parameters of the capacitors. Falling below the specified loss factor value is not possible. The representation of low loss factor value can therefore also be achieved only by the use of air- or gas-filled capacitors, which, as already shown, always have a fairly large volume. A realization of various loss factor values is not provided with the ar be given circuit. This is only possible if the circuit is extended according to the known prior art with the laborious disadvantages already explained by parallel or series connection of resistors to the capacitors.

According to the current state of the art, the exact measurement of the capacitance and the loss factor of capacitors are predominantly bridge circuits, which are used in a wide variety of circuit variants, such as, for B. the measuring bridge to Schering, the Giebe-Zickner bridge (Blechschmidt, E .: Precision measurements of inductors and time constants, VEB Verlag Technik Berlin, Volume 11955, pp. 81-97) and circuits from other patents, such as "arrangement and Measurement of the capacitance and dielectric losses of grounded samples, especially at high voltage "(Business Patent, DD PS 757167, GO1R 27/26) and" Circuitry for loss factor measurement of capacitors "(commercial patent, DD PS 233765, GO1R 27/26) known , used. The adjustment of these measuring bridges is carried out according to the zero balance method or according to the compensation principle. When using highly sensitive zero indicators, which are already industrially produced according to the current state of the art, the resolution and the measurement uncertainty of these measuring bridges is determined predominantly by the ability to balance and the stability of the components of the measuring bridges.

The introduction of inductive dividers into the bridge measuring technique has brought about a significant improvement in the resolution and the reproducibility due to the extraordinary stability of the parameters of these dividers and, associated with this, a noticeable reduction in the measurement uncertainty. Therefore, for the precision measurement of capacitors in the low-voltage range, only inductive divider bridges, which are increasingly being produced by the rapid development of electronic computing technology as semi-automatic or automatic measuring bridges, are used. During the measurement, the capacitance and the dissipation factor of the capacitor to be measured are always derived from the corresponding magnitude of a comparison capacitor, just as in the case of the bridge circuits already presented. This property of the reduction of the sizes of the measurement object to known sizes of a comparison standard is common to all bridge circuits. This results in the necessity that for exact measurements, or for the calibration of measuring bridges always material measures with known technical parameters must be present. Thus, the ongoing development of low-loss dielectric materials, insulating materials and cables has in recent years led to increased demands on the loss factor measurement, both in the measurement and representation of the loss factor, and in the preservation and propagation of the loss factor using loss factor measures. As a result, there has been an increasing demand in the national economy for variable loss factor standard embodiments with which an easy and fast calibration of automatic measuring bridges can be carried out.

A very suitable for the precision measurement of the capacitance and the loss factor of capacitors inductive Teilermeßbrücke based on the principle of Thomsonmeßbrücke (Eckardt, H., Hornemann, D .: Development of loss factor measuring for the low voltage range Metrologische Abhandlungen, Berlin 51985 2, p 151 , Fig. 2). In addition to the inductive voltage dividers for the main bridge and the Thomson branch, this measuring bridge also contains an inductive voltage divider in Wagner's auxiliary branch for eliminating the earth capacitance within the bridge. This ensures that after the balance of the measuring bridge, the capacity and the loss factor of the capacitor to be measured, taking into account the capacity and the loss factor of the reference standard, from the division ratio of the main divider and the setting of an RC element, which is a measure of the difference between the loss factor of the specimen and the loss factor of the normal, can be calculated. To carry out the measurement while the capacitor to be measured in the branch 1 and the comparison standard in the branch 2 of the bridge is to be switched. Here, the loss factor of the reference standard must be selected so that it is smaller than the loss factor of the specimen. In addition, the shield of the device under test and the reference standard must be connected to the central earth point of the bridge. With the most careful construction of the measuring bridge and the use of highly stable components in the measuring bridge, the measurement uncertainty of this bridge is mainly determined by the knowledge of the capacity and the loss factor of the reference standard. Thus, there is a need for loss factor measurements with known and stable technical parameters to always be present for exact loss factor measurements.

Object of the invention

The object of the invention is to provide a passive circuit, can be realized with the variable loss factorals, which are characterized in that both large and very small loss factor values can be represented with commercially available and inexpensive capacitors. In this case, for a given number of loss factor values and operating frequencies, the required number of resistors, as compared to solutions according to the known prior art, substantially reduced and the time required to balance the individual loss factor values are significantly reduced. At the same time, the quality of the loss factor standard should satisfy high demands.

-3- 285 698 Presentation of the Essence of the Invention

The object of the invention is to create prerequisites to the invention, that is with commercially available capacitors whose internal loss factor> 10 ~ ^4, switchable Verlustfaktormaßverkörperungen can be realized, the loss factor values in the range: s 1 x 10 ^"B set and to 1, the low The aim is to ensure the temporal constancy of the loss factor values over a longer period of time (years), as well as to reduce the number of required components and circuit engineering work compared to known solutions According to the invention, the object is achieved in that the relatively large and the realization of small loss factor values preventing self-loss factor of commercially available capacitors to a very small (<10 " ⁶ ) and thus negligible for the representation of larger loss factor values negligible value. For this purpose, two constant capacitors C connected in series are supplemented by a resistor Ri to form a T circuit. By balancing said resistance is achieved that the total loss factor of this circuit is almost zero. To realize the larger loss factor values, the value of a constant resistance R _{2 is} transformed down or up via a transformer connected in series or parallel to this T-circuit. By changing the resistance ratio ü with corresponding taps of the total winding of the transformer, the desired loss factor values can be set. The calculation of the transmission ratio required in each case is very simple since it is determined only by the desired loss factor value itself, the operating frequency, the capacitance values of the two capacitors and by the resistance to be transformed. Taking into account the self-loss factors of the two capacitors C is not necessary because of the compensation carried out. Furthermore, by using a transformer for resistance transformation and selecting a high-quality constant resistance for R _2, the stability of the individual loss factor values can be guaranteed over long periods of time. For the adjustment of the loss factor standard embodiments, it is only necessary, as a function of the intrinsic loss factor of the capacitors C, to adjust the resistance R ₁ . As a result, the compensation work is significantly reduced compared to known technical solutions.

embodiments

The invention will be explained in more detail below with reference to two exemplary embodiments. According to the invention, two capacitors of the same nominal capacitance C and approximately the same loss factor value tanö with a variable resistor R ₁ and a transformer, to the total winding W _{2 of} the resistor R _{2 is} connected, connected together to form a T-circuit. The total winding of the transformer has a plurality of taps, so that to set different loss factor values, the partial winding Wi to be changed ^b . <Inn. In order to realize the variable loss factor standard, the described circuit according to FIG. 1 is installed in a corresponding housing for electrical shielding, the base of the resistor R _{1 is} connected to the housing and the housing is earthed. Thus, the circuit described represents a loss factor standard in circuit C _12. That is, the capacitance C ₁₂ , whose loss factor can be varied by varying the number of turns W ₁ , acts between terminals 1 and 2, while between terminals 1 and 0 and 2 and 0 the earth capacities C ₁₀ and C ₂ O and their loss factors tanö ₁₀ and tanö ^ are effective

 To calculate the aforementioned capacitances and loss factors, the T-circuit of FIG. 1 must have the conductance values

⁽⁶⁾

be converted into their equivalent n-circuit according to the figure 2. Here, it is assumed that the T-circuit consisting of the two capacitances C and the resistor R ₁ , by adjusting said resistance, is set so that the capacitance acting between points 1 and 2 has a loss factor of zero and that the self-loss factor the capacitors C max. 10 ~ ³ . After execution of the star-delta transformation, the following relationships thus result for the conductance values of the equivalent circuit according to FIG. 2:

vt .- "c," (, "5," ₊ j, -ο, α ,, ψ + «-»>

and

\ Λ _ .. _. .. 2 (üCtan5 (1 + jtanö) ...

Y ₂ O = coC _M | tanö _2O + j) = ^(9> The relationships for the individual elements of the n-equivalent circuit are the following

With

such as

Ctanötanö _{) 2}

1 + (tanö | ₂ - tanö) ² with

₍₁₂ ,

tanö and

tanö ₁₂ (tanö ₁₂ - tan5)

(13)

CtanÖ (tanö - tanö ₁₂ )

With

tang »« (15)

tanö tanö _l2

valid. Between terminals 1 and 2 of the overall circuit thus acts as Eq. (10) shows a capacity for which approximately the equation

C ₁₂ = - | - (16)

applies. The loss factor acting between said clamps can be determined according to Eq. (11) can be calculated very easily, whereby for selected loss factors, a quick sizing of the circuit is possible. The analysis of equations (12) to (15) shows that very small capacitances with a loss factor significantly greater than one are effective between terminals 1 and 0 or 2 and 0 respectively. This means that between the mentioned terminals outweighs the influence of ohmic resistors.

The circuit shown in FIG. 1 can be advantageously used in those capacitance and frequency ranges in which the contact and winding resistances present between points 2 and 2 'do not cause any impermissible errors. In the area in which said resistances lead to non-negligible errors, the circuit shown in Figure 3 is applicable. According to the invention here, the total winding Wi of the transformer is connected in parallel to the T-circuit, again consisting of two capacitors, with the capacitance value C and the loss factor tanö and the variable resistor Ri. The total winding of the transformer also has several taps here, so that the partial winding W ₂ , at which the resistor R _{2 is} connected, can be changed to set different loss factor values. According to Figure 3, as shown above, the entire circuit must be electrically shielded and the resistor R ₁ connected to ground.

To calculate the capacitance acting between terminals 1 and 2 and their loss factor, the circuit must also be converted to its equivalent n-equivalent circuit according to FIG. In the conversion is also assumed here that the T-circuit consisting of the two capacitors C and the resistor R ₁ is adjusted so that this part of the circuit has a loss factor of zero and that the intrinsic loss factor of the capacitors s 10 ~ ³ , Starting from the GIn. (4) to (6), the following equations result for the conductance values of the n-equivalent circuit according to FIG. 2:

ΫΪ2 = ü) C _{) 2} (tanöu + j) = ü> Ctan ³ ö + - ^ - + j - , (17)

Yio = (uCio (tan5, o + j) = coCtanö (1 + jtanö) (18)

and

Y ₂ O = <uC _M (tanöjo + j) = (üCtanö {1 + jtanö). (19) As a result, for the elements of the equivalent circuit, the relationships

C ₁₂ = - | ", (20)

tanö, ₂ =, (21)

C ₁₀ = CtBn ² O, (22)

tanöio = -, (23)

tano

C _M = Ctan ² 5, (24)

tanö ₂₀ = T 'f ²⁵ )

Tanoé

valid. Thus, in the circuit of Figure 3, the between-terminals 1 and 2 acting capacity and loss factor are very easy to calculate and thus to dimension the circuit very quickly, while between the terminals 1 and 0 and 2 and 0 also predominantly ohmic Resistors are effective

 The circuit shown in Figure 3 is particularly suitable in those capacity and frequency range in which the loss factor is mainly caused by series losses.

Claims (2)

Circuit for implementing variable loss factor standards, consisting of two series-connected lossy capacitors, a transformer with variable transmission ratio and ohmic resistances, characterized in that - That the two series-connected capacitors having the capacitance rating (C) and the loss factor value (tanö) are connected together with a variable resistor (R ₁ ) to a T-circuit, wherein dia loss factor values (tanö) of the two capacitors (C ) are compensated by the variable resistor (R ₁ ) to approximately zero, and - That in a conventional manner the value of a constant resistance R ₂ via the transformer, which is connected in series or in parallel to said T-circuit down according to the value to be set of the loss factor or the basal or highly transformed · *. For this 2 pages drawings Field of application of the invention Oils invention relates to a passive circuit for implementing variable loss factor, which is characterized in that both very low and large loss factor values can be displayed in a circuit with commercially available capacitors. They are used in the field of electrical measuring technology for the representation and preservation of the loss factor as well as for the examination of loss factor measuring instruments for the production of dielectric materials and insulating materials, in the manufacture of capacitors and in the cable industry. Characteristic of the known state of the art The losses of capacitors always consist of two components, the parallel and the series losses together. The series losses are caused by the ohmic resistance of the supply lines to the electrodes, the ohmic resistances in the electrodes themselves and by eddy currents in the supply lines and electrodes. The influence of insulation resistance and dielectric or absorption is summarized in the parallel losses. In the equivalent circuit diagram, the parallel losses as effective resistance R parallel to the capacitance C and the series losses as resistance r in series with this parallel circuit have been shown. For the total loss factor thus the relationship applies tanö = tan5 _R + tans, (D