SU739447A1 - Method of measuring ratio of high voltage divider - Google Patents

Description

The invention relates to a high voltage measuring technique, can be used to measure the division ratio of high voltage dividers on alternating current and direct current. Known methods for measuring the division ratio of high-voltage voltage dividers are based on a comparison of the measured voltage high-voltage divider with low-voltage reference cells, for example, exemplary low-voltage voltage dividers included in auxiliary voltage circuit 1, for example. ways - low accuracy of measurement of alternating current. Closest to the proposed method of measuring the division ratio of a high-voltage voltage divider, which consists in changing the resistance of the low-voltage arm of the voltage divider, measuring the currents (voltage) flowing through the divider corresponding to each value of the specified resistance, followed by the division division factor This method is of low accuracy, especially when measuring on alternating current, due to the influence of leakage currents. In addition, the applicability of the known DC method is limited by voltage (10-50) due to the increased requirements for the accuracy of current (voltage) measurement. The aim of the invention is to improve the measurement accuracy of direct and alternating current with an operating voltage of up to and more. This goal is achieved by measuring the division ratio of a high-voltage voltage divider by varying the parameters of its low-voltage arm according to the invention, with the low-voltage shoulder disconnected from the grounding point, measuring the ratio of the currents flowing through the high-voltage divider arm, and the leakage conductor to the low-voltage output divider , to the current flowing through the exemplary conductivity measures connected to the divider pin, then the ratio of the current flowing through the heights is measured a voltage divider arm, to the current flowing through exemplary conductivity measures connected in parallel to a grounded low-voltage divider arm, and the result is calculated from

formula:

P1.;) O

a deviation from the unit of the first measured ratio;

m is a numerical value defining the deviation from the unit of the second measured ratio;

o conductivity of exemplary measures when measuring the first otnoshenii;

ZO2. conductivity of exemplary measures when measuring the second ratio.

Fig, 1 shows a diagram of the device, the best way. FIG. Figures 2–4 show a measurable divider having Y and Vj shoulders, and under high operating voltage, and low-voltage standard measures, capacitance and resistance Y, some device for comparing the DCT current, leakage conductivity U of the low-voltage divider output to the screen (t. e. to earth), grounded through a current comparison device.

The essence of the method consists in measuring two ratios: the ratio of the current difference 1 flowing through the high-voltage arm of the divider in the absence of low-voltage reference measures Ud (Fig. 2) and the leakage current 1, from the low-voltage output of the divider to the screen (Fig. 3), to the current If through the low-voltage reference measures of the voltage regulator connected to the output of the ungrounded; 5elite, and measuring the ratio of current 1 (Fig. 1) to the current Xd through the low-voltage reference elements1, connects 1 "to the output of the grounded divider.

To increase the accuracy, the measurement process can be constructed in such a way that it is not the ratios themselves that are determined, but only their deviations from unity. Therefore, we present:

 (one)

, 01

I

(2)

P, M--., Current values °

i. (, jk: bL

 .

l h ol

i,

Substituting (3) in (1) and (2), we find:

(four)

i 01

whence the division factor of the divider

(five)

K-, .- rriVlei-.

In principle, it is possible to measure the direct currents 1, 1, 1 1, ..., and then determine the division ratio of the divider in accordance with formulas (1), (2), (4) and (5). However, this will lead to a loss of accuracy, so all operations in accordance with formulas (1) and (2) must be carried out in the device itself comparison, TSI currents (including separation of the integer part, i.e. unit) from the relationship. For this, a certain auxiliary current 1 (Figs 2, 3, 4) is proportional to the voltage on the certified divider, which serves to establish (memorize) the value of current 1 (Fig. 2).

Balancing the current through the high-voltage divider arm with the auxiliary current disconnected from the grounding point of the low-voltage shoulder

(6)

where C is a coefficient of proportionality.

Then, after connecting to the output of the divider low-voltage model measures of capacitance and resistance and balancing the current through them, the difference between the set value of the auxiliary current and the leakage current of the output of the divider on its screen, we have (Fig.3):

, (7)

tw.

Balancing the previously established auxiliary current with current through low-voltage measures of capacitance and resistance with a grounded low-voltage arm, we find (Fig. 3):

(, . (eight)

Equalities (6), (7) and (8) lead to expressions (4) and (5). The auxiliary current only serves to memorize the current 1 |, so knowledge of the exact values of the parameters of the auxiliary current circuit is not required. It is only necessary that they have sufficient short-term stability over a period of time between three balances.

As follows from (4), the method is fundamentally free from the influence of parasitic conductivity on the ground when measuring the parameters of the high-voltage divider arm. When measuring the total conductivity of the divider, this parasitic parameter is automatically taken into account. The ability to measure from a separately high-voltage arm is important for the manufacture and fitting of high-voltage dividers and is an additional advantage of the method. FIG. 1 shows an example of the implementation of the method on alternating current. The diagram shows the measured high-voltage voltage divider (resistor and capacitor), a current comparator 2 with close inductive coupling, low-voltage reference circuits 3, 4, and a three-position switch 5, zero pointer b, the auxiliary converter 7 from high to low voltage for supply the auxiliary circuit, element 8 and 9, used to balance the circuit with an auxiliary current. The device works as follows. The switch 5 is set to the first position. In this case, the high voltage arm 10 is connected to earth through the winding 11 of the constant arms of the comparator 2, the low voltage arm 12 is disconnected from the ground point, and the output divider screen 13 is grounded through the winding 14. The divider 1 is supplied with its working high voltage the elements 8 and 9. Then re; switch 3 is switched to the second position, in which the low-voltage arm 12 remains ungrounded, the output screen 13 is still grounded through the comparator 2, and low-voltage reference measures 3 and 4 are connected to the output of divider 1, for the second time, the device is balanced by changing the number of turns of the decade windings 1.5 and 16. with parator 2. After this, switch 3 is set to the third position, when low-voltage arm 12 of the divider is connected to ground point, output screen 13 is grounded besides comparator 2, and s 3 and 4 remain. connected to the output of the divider. With the same values of elements 8 and 9, the device is balanced by changing the number of turns of the decade windings 15 and 16. The condition of the first equilibrium is of the form; . where is the conductivity of the high voltage arm 10; the conversion ratio of high voltage to low auxiliary, converter 7; -conductivity of the circuit composed by elements 8, 9; - the number of turns of the winding 17; n is the number of turns of the winding 11; Second equilibration yields: IV i P: otVV} l. . -l .9оН «о (10 RQ, GO -: resistor where d is the resistance and capacitance, respectively, of the elements 3,4; R d - the number of the included turns of the decade windings 15 and 16 of the comparators; so that n2. n, where the number of turns of the winding is 14. Then from (9) and (10) it follows: (11) Expressions (9) and (10) are obtained without taking into account the resistance of the comparator, since at the moment of equilibrium it is practically equal to ohmic resistance, windings and very little.; Third equilibrium condition: (.) - jujCoC i-tv) 4 .. new values of numbers where p and g are included s decadal turns of windings 15 and 16 of the comparator; conductivity of the low voltage arm 12. Equating the expressions (9) and (12), we obtain: (11) and (13) we find the complex division factor of the certified divider:,. , Nlj, (juCoq. FV p - tA C-oC | a oL JL% jaup. Where dL i IbndLlР) are the readings on the scale of the device, respectively, at the second and third balances. Close-inductive current comparators have very high accuracy and sensitivity. Using multi-decade comparators, low-voltage reference capacitance and constant-value resistance measures can be used, which can also be adjusted with high accuracy. Therefore, the measurement error on the continuous voltage can be small. At a constant voltage, the comparison of currents with a sufficiently high accuracy can be made using current compensators or comparators, for example, thermoelectric. When the atom is earthed, a low-voltage output of the divider through the input of the current comparison device is not required at the first and second equilibration, since at a constant voltage only the insulation resistance matters, which generally exceeds the resistance of measures 3 and 4.

In order to be safe, in case of a breakdown of the measured object and high voltage in the measuring circuit when an accidental rupture occurs in it, it is necessary to provide usual protective measures, for example, by means of arresters.

To verify the calculated data, a model of a device that implements the method was collected and experimentally investigated. Studies have confirmed the advantages of the method, its high sensitivity and accuracy. The layout of the device confidently responded to the sixth sign of low-voltage standard measures of capacitance and resistance, with a high-voltage-to-voltage ratio of these measures equal to one thousand.

The average result of a series of ten measurements of the division factor of the divider (while preserving the ratios of voltages and currents corresponding to the working state), the upper arm of which formed non-reactive sample resistance coils of type P361 class 0.02, did not go beyond the class of coils and amounted to 0.015% .

When the mains voltage fluctuated, when the auxiliary current circuit was powered by the low voltage winding of a high-voltage transformer, the high voltage of which was measured by a 15 kV divider from a cast microdrive-based resistor, the deviation of the readings did not exceed one thousandth of a percent.

The degree of insensitivity of the device layout to parasitic conductivities on the ground when measuring the resistance of the high-voltage arm of the divider was determined by artificially introducing a leakage capacitance of more than 0.3 microfarads, in actual conditions it is practically not encountered. The deviation of the readings from the average series of measurements with the natural leakage capacity did not exceed 0.015%.

The accuracy of measuring VDN by the method is high and is determined by practically exemplary low-voltage measures of capacitance and resistance of a constant value, that pbie can always be measured. drive with high precision. In this case, an auxiliary converter can be used, for example, a high-voltage voltage transformer (its low-voltage winding), supplying a certified separator, or an auxiliary high-voltage voltage divider, exact values8

nor is the division coefficient of which knowledge is required. Elements 8 and 9 of the auxiliary circuit may be ungraded.

The described method eliminates the influence of leakage resistance on the measurement result of the parameters of the high voltage arm of the voltage divider. This is achieved by grounding the low voltage output terminal of the VDN at the first two balances and grounding through the input of the current comparison device, whose input resistance is very small.

The ability to determine the resistance of the high-voltage arm of the VDN and the high accuracy at the same time allows this method to be used to adjust and adjust the dividers during their manufacture.

The method can be implemented kick on alternating or constant voltage. In this case, it is possible to certify a high-voltage voltage divider of any design at their working high voltage without the need for special precision adjustable low-voltage voltage dividers. Certificated dividers can be both capacitive and resistor nature.

Improving the accuracy and reliability of certification, eliminating the need for. exemplary VDN and in special precision adjustable low-voltage voltage dividers, the possibility of testing VDN of any design at alternating and constant voltage, the ability to control VDN arms in their manufacture show that the invention has great technical and economic efficiency. The implementation of the proposed method will facilitate widespread, accurate measurements at high voltages, will allow measuring devices to be cheap, transportable, significantly improve the measurement accuracy and the upper limit of the voltages at which measurements can be made, as well as improve the accuracy of energy metering that will give a significant economic effect.

Claims (1)

Invention Formula A method for measuring the division ratio of a high voltage voltage divider by varying the parameters of its low voltage arm, and with V in order to improve accuracy, when the low voltage arm is disconnected from the ground point, the current difference flowing through the high voltage arm of the divider, and leakage conductance on