CH635942A5 - Device used for testing instrument transformers for the automatic determination of the absolute-value error and the phase displacement angle of a current or voltage transformer - Google Patents

Description

635 942 2

PATENT CLAIMS. KNx, nnm. ln_.

1. Device for testing transducers for er a n, sses •% serious arsmd.

automatic determination of the amount error and the misalignment ",,

a current or voltage converter in three error range 7; Pnifeinrjchtung according to claim 1, characterized

stage according to the differential method, in which the test specimen with 5 daf'm case, unequal nominal translations of the test specimen is connected to a normal transformer in such a way that the resistance of the vector and normal voltage transformers (N0) em balancing resistance of the vectorial difference of the secondary currents of the test object (Ra) with the differential voltage (u Ä) between normal chip

and the normal current transformer or the secondary voltages voltage transformer (Ny) and the device under test (P), whereby the device under test and the normal voltage converter using the output current of the balancing resistor (Ra)

dung which feeds from the secondary current of the normal current transformer through io ler-compensated current transformer (T6)

Subsequent connection of a reference current transformer or that of the voltage transformer (T7) which also has the unequal nominal

Secondary voltage of the standard voltage converter is impressed by Nachzun® compensating correction current (j K). Circuit of a reference voltage converter derived Refe.

limit voltage of the amount errors and the misalignment after loading

Application and phase in two independent digital applications. 15

Pointing devices are displayed, characterized in that the invention relates to the testing of measuring transformers, the switching of the three error range levels by means of a device for automatically determining the amount-adjustable, error-compensated current transformer (T5, T6) and the error angle of a current or voltage wall -follows, whose secondary winding (WF) can be switched decadically, ^ ers ^ re 'error range levels (low error level equals that the sinusoidal reference voltage (îfR) is a digital 90 ° - 20 level small error; middle error level is equal to the middle switching stage that these two square-wave voltages (first error, high error level is equal to high error level), one of which is in phase with the reference voltage (uR) using the differential method, in which the device under test is connected to a Nordes reference current transformer (T,) or the Reference voltage derarj is interconnected that from the vekto converter (T3) and one around 90 ° is phase-shifted, and the difference between the secondary currents of the test object and that by means of these square-wave voltages, two follow-hold current transformers or the secondary voltages of the test amplifier (S / Hu S / H2) are controlled, so that the lm§s of the normal voltage transformer using the time of approximation from the ratio of the secondary currents to the secondary currents of the normal current transformer by means of secondary voltages or voltages of the normal transformers (NJ; N „) and the fcha! TunS of a reference current transformer or the differential voltage (uA) and the reference voltage of the normal voltage transformer derived from the Se device under test (P) by subsequent

° s ~ \. 30 circuit of a reference voltage converter derived reference voltage (u R) the voltage error and the error angle are available as the reference voltage, the magnitude error and the error angle according to the loading voltage value, which are two independent and independent digital independent digital voltmeters (DV1; DV2) m be shown to trigger pointing devices.

predefined cycle sequence are displayed. Test facilities working according to the differential method

2. Test device according to claim 1, characterized 35 are designed such that the device under test with a normal converter that compensates for the quotient from the differential SQ before the input of the difference between the vectorial difference of the reference voltage (u A ) and the reference voltage (u R) that form the secondary variables of both converters, the errors are arranged in relation to the Se quotient generator (Q) two structurally identical low-pass filters (TFl5 secondary variable of the normal converter according to magnitude and phase difference-TF2). Reference determined and displayed as an amount error and misalignment

3. Test device according to claim 1, characterized thereby 40. The advantage of the differential method lies in the fact that the digital 90 ° switching can be achieved with a low level of measurement uncertainty due to a phase locked, since the influence of the to-loop circuit and the exclusive-and / or-linkages of the components used is formed only by second order fung. on the error display. (Compare A. Keller: «Modern

4. Test device according to claim 1, characterized in transducer measuring device according to the difference method », net that in the case of the current transformer test, the difference span 45 ETZ-A, Vol. 74 (1953) 105-109).

voltage (u.) by a three-winding residual current transformer ^ "..,,. . ,,,.

(T2) is formed, the primary windings (P1; P2) of which are based on the task, one suitable for both the normal current transformer (N,) and the test object (P) Jtrom- aIs ^ voltage transformer measurements. To design the test device of the type mentioned at the outset,

that the determination and display of the current or voltage

5. Test device according to claim 1, characterized 50 and the error angle occurs completely automatically. In particular, that in the case of the voltage transformer test, the differences should not be taken into account when reading the measurement values in any measurement clothing (u A) by switching the secondary circuits of the rich conversion factors. Normal voltage converter (NTj) and the test object (P) is formed. According to the invention, this object is achieved by

. . 55 that the switching of the three error range levels by means of a

6 Test device according to claim 1, characterized in that adjustable, error-compensated current transformer takes place, such that, in the event of unequal testing of the test object, its secondary winding can be switched decadically, that the P) and normal current transformer (Nj) Gera differential current transformer sinusoidal reference voltage is a digital 90 ° circuit thus (T2) two-error compensated current transformers (T4, T5) excited; that these ^ square-wave voltages are generated, of which are switched, that to correct the primary flooding of the 60 one in phase with the reference voltage of the reference current current transformer (T5) m the current transformer (T4) from the second converter or the reference voltage converter and one um 90 ° därstrom (12x) of the test object (P) a correction current (1K) is phase-shifted, and that by means of this rectangle and in the second primary voltages acting as a correction winding two sequence holding amplifiers are controlled, so winding (WK) des Current transformer (T5) is fed in and that at the time of actuation from the ratio of that of this correction current (1K) is optionally passed through various 65 secondary currents or voltages of the normal transformers and windings of the current transformer (T5), the differential voltage and Reference number of turns of these windings are chosen so that all voltage, the voltage error and the misalignment l are available as span integer percentages of the nominal value, which are divided into two independent

3rd

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dependent digital voltmeters are displayed in a trigger cycle of a predetermined cycle sequence.

In a further development of the invention, it is advantageous if, in the case of unequal nominal translations of the test object and normal current transformer, the residual current transformer is followed by two error-compensated current transformers, if a correction current is derived from the secondary current of the test object to correct the primary flow of the one downstream current transformer in the other downstream current transformer is fed into the second primary winding (correction winding) of the other downstream current transformer, and if this correction current is optionally passed through different windings of the other downstream current transformer, the number of turns of these windings being selected such that all integer percentages of the ratio

K,

ses

■ Nx

K,

Are 100% adjustable.

■ Nn

It is also advantageous if, in the case of unequal nominal translations of the device under test and the standard voltage converter, a balancing resistor is acted upon by the differential voltage between the standard voltage converter and the device under test, the output current of the balancing resistor feeding a fault-compensated current converter, which also uses a voltage converter to compensate for the correction current that compensates for the uneven nominal translation is imprinted.

Such test devices offer the considerable advantage that, while maintaining the favorable properties of a converter test device according to the differential method, in particular high accuracy, measurement transducers with different nominal ratios can be measured against one another. The field of application of the test device according to the invention is thus significantly expanded compared to known devices of this type.

Further details and advantages of the invention are explained in more detail using exemplary embodiments with reference to the drawing. 1 and 2 represent basic circuits for which protection is not claimed, but which serve to better explain the invention shown in FIGS. 3 and 4.

In detail show:

1 shows a circuit arrangement for testing current transformers according to the differential method (basic circuit);

2 shows a section of a circuit arrangement for testing voltage converters according to the differential method (basic circuit);

3 shows a circuit arrangement according to the invention for testing current transformers with different nominal ratios;

Fig. 4 shows a detail of a circuit arrangement according to the invention for testing voltage converters with different nominal ratios.

As shown in Fig. 1, the basic circuit for testing current transformers is constructed as follows:

A reference current transformer Tj is connected to the secondary circuit of a normal current transformer Nj, and a load resistor RB is connected to its secondary side. The first primary winding Pi of a three-winding differential current transformer T2 is connected in series with the primary winding of the reference current transformer Tj, the second primary winding P2 of which is connected to the secondary side of the test object P.

A differential resistor R is connected to the secondary winding of the differential current transformer T2. The non-grounded pole of the differential resistor R is connected to the input of an electronic divider or quotient generator Q via a low-pass filter TFj. Likewise, the ungrounded pole of the load resistor RB is connected to the input of the quotient generator Q via a further low-pass filter TF2 and a rectifier G. The output of the quotient generator Q is connected to the inputs of two sequence holding amplifiers S / Hx and S / H2, the outputs of which are led to two separate, triggered digital voltmeters DVj and DV2.

s At the output of the low-pass filter TF2, a digital 9Ö ° circuit is connected via a square-wave converter RU, the outputs of which control the two sequence holding amplifiers S / Hj and S / H2.

The mode of operation of the circuit arrangement according to FIG. 10 is as follows:

With the help of the residual current transformer T2, the secondary current T2x of the test object P and the secondary current T2n of the normal current transformer Nj become the residual current 7 —T -> •

15 - A ~~! 2x 12n formed, which generates the differential voltage u A as a voltage drop across the resistor RA. The number of turns of the differential current transformer T2 and the size of the differential resistor RA 20 are chosen so that the differential voltage has the value

-A V2

if the test object P has an absolute value error of the final value of the selected measuring range, i.e. F; = 0.2%, 2% or 20% and the secondary current is equal to the nominal current.

The nominal ratio of the reference current transformer Tx and the size of its burden resistor RB are chosen such that the reference voltage u R the value at a secondary current equal to the nominal current

- V

35

Has.

An electronic vector meter determines the error of the device under test by determining the current error from the complex differential voltage H a and the reference voltage u R

40

_ Reûâ Hr and the misalignment as

45

ô. =

In the "R

100%

• 3438 '

determined.

The ratio uA / uR is formed using the electronic divider Q. Since it is a two-quadrant divider, it is not the reference voltage uR that is fed to it as the denominator voltage, but rather the rectifying value luRl. The output voltage u D of the divider Q results

55

10-Ua I URI

The AC voltage u D has the same phase position as u Ä, but its amplitude is no longer dependent on the set test 60 point, but only on the percentage error of the test object. If the measuring device is set to the error measuring range «2%» and the current transformer has a current error of 1%, this voltage has an effective value of

V.

65

Amount error determination

If the device under test does not have a misalignment, but only a current error, the voltage u A and therefore also u D has none

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Phase shift with respect to the voltage u R. The shear of the second signal with the same phase position, the double tel value ûD is therefore a measure of the current error F ;. Has a span measuring frequency. With the help of an “exclusive-or” gate

The nominal value ûD = 1.5 V corresponds to a current tester, for example, the square wave signal is doubled in frequency and the error of Fj = 0.5% if the measuring range «2%» is selected. SIG signal obtained a third square wave voltage (jH) that

In this case, the peak value ûD coincides with the frequency 5 that has the same frequency as the reference voltage, compared to the telwert ûR of the reference voltage. however, this lags by 90 °.

If the device under test also has a misalignment, as shown in FIG. 2, the basic circuit for voltage

there is a phase shift between u D and u R. In this converter test structured as follows: _

Trap is no longer proportional to the current error, but to determine the differential voltage u A, the seconds

the instantaneous value uF of the voltage uD that is temporally with 10 windings of the normal voltage converter Nu and the test

ûR coincides. ~~ lings P connected in a differential circuit. In the

This point in time is determined in a simple manner by the secondary circuit of the normal voltage converter Nu being a reference that the positive peak value of ÎTR is switched on with respect to the zero crossing voltage converter T3. Otherwise, the course of the positive flank of u R lags by 90 °. A digital circuit as characterized by the separation points u, v in FIG.

Switching signal (jH in Fig. 1), which continues by 90 ° compared to the zero 15 net. .

passage of the positive flank of R is controlled. In the case of absolute value from the end value of the selected measuring range

a follow-hold amplifier (S / H,) in such a way that its balance, i.e. ^ Fu = 0.2%, 2% or 20%, and secondary voltages r «. j. i a • • a_ of the size of the nominal voltage result for the reference

output voltage for a period of about 300 ms that Am- -, f '^

maintains the value of the amplitude uF, the u n at the time point of uR (t) - ûn, n ìì r and the differential voltage u a the same

Yiolfe values as for current transformer measurement.

In the case of unequal nominal translations of the test object P and determination of the incorrect angle of the normal current transformer Nj, the test device for the current

The error angle determination is carried out analogously to the error converter test according to FIG. 3 to train.

Mood. The instant of the instantaneous value sampling of ÛD, 5 brings the secondary circuit of the test object P em elec-

the zero crossing of the positive edge of u R. ~ current transformer error-compensated current transformer ^ is now switched on, '. "J". ~ „S ,, -R ... ~ whose primary winding with the second primary winding P2 of the Em digital switching signal (H m Fig. 1), which has no phase shift in series with u R three-winding differential current transformer T2, controls a second sequence is. Furthermore, the secondary winding of the differential current wall holding amplifier (S / H2). Its output voltage for jers <j ~ 2 with the primary winding of a further error-compensated-about 300 ms is equal to that instantaneous value that u D connected to the 30 sjerte current transformer T5. The error-compensated time uR (t) = 0 had. Current transformer T5 has two primary windings WA and WK as well as two secondary winding measured value displays • lungs W £ and WF on a common iron core. The secondary windings are Wt and WF

The error voltage uF and the error angle voltage u6, which are connected to one another via an amplifier V, while the second primary winding WK is available to the secondary winding of the error value after each measurement value sample for about 300 ms as DC voltage, during this time compensated current transformer T4 connected. To each of a digital voltmeter DV! or DV2 for the magnitude second secondary winding WF, the differential resistance RA error display and for the error angle display are measured and connected, to which the voltage u A drops. The verbin-shown. The command to take over the measured value for the digital voltage point between WF and RA is then possibly via meter is derived from the digital switching signal «jH», so the low-pass filter TFj is connected to the input of the quotient that connects the measuring voltage within the same period q.

distance of 90 determined error voltages uF and Uj The mode of operation of the circuit arrangement according to FIG. 3 at the same time from the digital voltmeters DVj, DV2 jst f0igen (each:

be taken over. ^ The error formulas explained earlier only apply under the

The measured value is taken over automatically assuming the same nominal translations of the test object and a distance of approximately 300 ms. The time of the measurement sample normal converter. If the nominal gear ratios of both converter units can alternatively be different due to an external switching command (KNx 4 = KNn), the following applies: From which can be determined. This operating mode of the converter measuring device component TF and the imaginary component T5 of the device is advantageous if, in cooperation with a 5Q residual current 7A, neither the current error nor the process computer can operate an automatic converter test station. Part is included that was caused by the unequal nominal translations and not by the error of the test object. Digital 90 circuit This component can be compensated for, for example, if the

The two digital switching signals «H» and «jH» are 5S number of turns of the reference voltage u R from the secondary current 72 of the device under test P with the aid of a phase-rigid reflective winding of the differential current transformer T2 (Fig. 1), the DC-loop PLL (Phase Locked Loop) won. With this is changed speaking. Because of the low number of turns, square-wave signals can be generated that have the same winding (6 turns for 72N = 5 A), which means that they have the same frequency and phase position as the Si- Mö supplied to them, but the adjustment cannot be carried out with sufficient precision, gna voltage , and at the same time signals which have an integer 6Q A very fine level compensation of different nominal multiples of this frequency and which is set against this is achieved by the circuit according to FIG. 3. In Fig. Signal voltage have no phase shift. The function x, the differential voltage is obtained by the fact that this circuit is also in a wide range fre- «...„ -v “

auen7unabhäneiff Dinerenzstrom 1A a voltage drop across the burden resistor

RA of the differential current transformer T2 generated. Since in this case the test device according to the invention was chosen to drive the residual current transformer because of the very large frequency range from 10 Hz to 75 Hz. If the PLL circuit load were to have an error that is too great, the diffusion generates two signals, one of which (H) of the same limit resistance RA is instead on the secondary side of a frequency and phase position as the reference voltage, while electronically error-compensated current transformers T5 (Fig. 3)

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orderly. The primary winding WA of the current transformer T5 is obtained from the secondary voltage u 2x of the device under test. Otherwise, the residual current flows through 7A. The error of this gene is the correction circuit according to FIG. 4, as is the circuit of the current transformer, even with small values of 7 A and large values according to FIG. 3.

Values for RA very low, since no corresponding magnetic induction 5 sttom influence the measurement value display of the converter measurement in the converter core is required to generate the voltage harmonic components in the test voltage or in the test case Ra, but only one by the factor of two different ways. On the one hand they falsify the reference voltage u R, and on the other hand they lead to a v ■ - reduced part of the same, where v the gain has a large harmonic component in the residual current 7A, since the wf transmission behavior of the device under test and normal converter for the amplifier V (v = 500) and wF and v / 1 the number of turns of 10 different frequencies is not the same and the top windings WF and WI (wF = 5 or 50 or 500, wt = vibration components therefore do not mean-3000 when forming the difference). compensate each other. So that this does not result in a false display

The error determination is now made possible by the fact that, in FIG. 1, between the differential current transformer T2 and the secondary current T2x of the device under test, a correction current 7K and the divider Q is a low-pass filter TF! switched, which is derived, which has a damping of more than 50 dB for frequencies> 150 Hz in a second primary winding WK of 15, so current transformer T5 is fed in that the voltage supplied to the divider Q is only higher than the secondary current T5 a stream of greatness! results. If the correction contains vibrations with a negligibly small amplitude. Since the output voltage of this low-pass filter depends very much on the measurement frequency in terms of magnitude and phase position, the reference voltage u R is also changed in the same way in terms of magnitude and phase position with the aid of a low-pass filter TF2 connected upstream of the rectifier G. The synchronization between the two identical low-pass filters TFt and TF2 is so good between 15 Hz and 65 Hz that the ratio u J u R, which is a measure of the error of the test object, is in this

,, ^ .... Frequency range is falsified by less than 0.1%,

d.h12x assumes the value of the secondary current that the testing device according to the invention distinguishes itself from

Test with the same nominal ratio as the normal converter would have known test devices of this type by the following. The advantages of i'A are then:

7'p 7'6 The determination and display of current or voltage

F; == ■ 100% and ô; = y ~ - ■ 3438 'missing and wrong angles occurs completely automatically. When reading

■ In the small measuring range, conversion factors must be taken into account. The reading is between

By choosing the corresponding number of turns in 1% - 15 Hz and 65 Hz see frequency independent. Not only

Levels, preferably in the range of 60 to 120% adjustable dje error display, but also the error angle display is without

Correction winding WK, the effects of the conversion are valid for all frequencies. The various translations according to the invention in the area of the test facility combined combine the advantages of the differential method.

rens with the possibility of using different nominal translations, especially when testing voltage transformers. The feature of the invention is thus to compensate in steps of 0.01. In addition to very good measuring accuracy, the KonektuistromTK can be used in a wide range of applications, preferably via correction switches, and can be used in a very wide range of applications. Just like the T5 current transformer. This is calculated from the ratio of the nominal gear ratios known from the previously known hand-held transformer measurement ratio The present test device is suitable not only for the current set to the switch on the front panel of the measuring device, but also for voltage transformer measurements, correction is independent of the set test point, since self-aligning measurement devices were previously only for

^ ... . Current or voltage converter measurements are known. Because of where I a a s auc i K are proportional to the test current. built-in low-pass filter, the influence of harmonics,

When testing voltage transformers, the correction is either contained in the test voltage or in the test current

Circuit also effective. As shown in FIG. 4, the differences or which are caused by the transfer behavior of the test specimen reference voltage u ^ with the help of a resistor first in one is eliminated, so that they affect the measured value.

Differential current I A implemented, the winding WA of the fault display have no influence.

compensated current transformer T6 flows through. The current î K required for the correction is in this case suitable with the aid of a 55 of current or voltage transformers of any kind and / or additional voltage converter T7 and a resistor RK voltage levels.

flow the value

7 -7 ^ Kn * "i ìk-i2x (1- -)

»• Nn has, will

7 / _-r KNx - 2x ~ Ì2x '-TT-l ^ -Nn c

4 sheets of drawings