SU981909A1 - Device for checking current transformers - Google Patents

Description

(DEVICE FOR TESTING TRANSFORMERS

CURRENT

The invention relates to electrical measuring technology and can be used in the calibration and metrological certification of model and precision measuring transformers of sinusoidal current.

A device for checking current transformers is known, comprising a generator, a series-connected primary windings of a turnable and two auxiliary transformers, a zero indicator, two resistance boxes, an in-phase and integrating operational amplifiers, and a summing amplifier Cl.

A disadvantage of this device is the low accuracy of verification.

The closest to the proposed technical essence and the achieved result is a device for calibrating current transformers, containing a differential-zero comparison unit, consisting of a differential branch, in-phase and quadrature flow rates and a null indicator, ammeter and magnetic current comparator, connected to the resulting circuit Comparison unit 2.

However, the device is characterized by low calibration performance.

The purpose of the invention is to increase productivity.

This goal is achieved by the fact that a current transformer calibration device containing a comparison unit, consisting of a differential circuit of in-phase and quadrature rheord chords and a null indicator, as well as a magnetic current comparator, the resulting circuit of which is connected to the comparison unit, and an ammeter are additionally entered precision current transformer, the primary windings of which and the comparator are connected in series, the secondary winding of which is connected on one side to

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terminal for connecting an exemplary converter, and on the other through an ammeter and a resistor - to a comparison unit, as well as a compensation unit connected to the input parallel to the resistor, and to the output - parallel to the differential circuit of the reference unit, while the magnetic comparator input is connected to the bus current transformer.

The drawing shows a diagram of the device for calibration of current transformers.

The device contains a precision current transformer 1 connected to the sample converter side, a magnetic current comparator 2 connected with its own circuit from (3 sides of the inverter being turned to a differential-zero comparison unit 3. Comparator 2 primary windings of the comparator are connected in series with each other.

Comparison unit 3 has a differential circuit k, in-phase 5 and quadrature 6 reichords, a null indicator 7. The device contains an ammeter 8, a resistor 9 and a compensation unit 10 The secondary winding of the transformer 1 is connected to the comparison unit 3 through the ampremeter 8 and the source 9. Compensation the block-10 from the side of its input is connected in parallel to the resistor 9, and from the output side - parallel to the differential circuit. The unit 10 can be made, for example, from an isolating matching three-winding transformer, a resistance store, a capacitance store and a winding switch.

The comparator 2 and the precision transformer 1 have the same nominal conversion factors.

Current transformers are calibrated as follows.

Prior to direct measurements of the calibrated transformer errors, primary windings of the precision transformer 1 and comparator 2 pass the primary current 1. It is measured indirectly using an ammeter 8. The magnetic flux in the comparator magnetic circuit is balanced. After balancing the MDS of the comparator 2 through the differential circuit {will flow

its output current. The secondary current C of transformer 1 will flow along circuit 4 towards the output current of comparator 2 through ammeter 8, resistor 9 and reohords 5 and 6. Due to the fact that the current and angle errors of comparator 2 and transformer 1 are different, the differential current d1 flows through circuit k . The current In, the flow through the resistor 9, creates a voltage drop across it that feeds the input of the compensation unit 10, i.e. EMF appears at the output of this block. Equivalent to the resistance of the Zg circuit is equal to Zo l) where R "is the resistance of the differential circuit;

L h - complex error of the comparator.

Since the error Dx is, as a rule, 1-10 - 2-10-, the equivalent resistance of the ZQ circuit is many times smaller than all other resistances connected to it in parallel. Consequently, under the action of the EMF at the output of block 10, a current 1 flows through circuit k ,. As a rule, the I Р Ig regulation of the current in amplitude and phase by changing the parameters of the unit 10 compensates for the difference current I1. The moment of equilibrium is judged by the absence of a signal on the null indicator 7 at the zero position of the flow engines 5 and 6. At the moment of equilibrium, the reactor sum of the current I and the compensation current from block 10 is equal to the output current of comparator 2. The parameters of block 10 are fixed, at which this equality takes place.

Claims (2)

For direct measurements of the errors of the transformer to be tested, it is connected to the device instead of comparator 2. The fixed parameters, such as capacitance and resistance, are set at block 10 at the respective stores. The primary current I /) is passed through the primary windings of the transformers 1 and is measured indirectly with an ammeter 8. The secondary current of the transformed transformer flows through the differential circuit 4, and the vector sum of the current 1 and the compensation current caused by the fixed parameters of the 10 Since the resistances of the sections of the current circuits Ij and the compensation circuit, which are connected in series with the resistance, are many times greater than the resistance ZQ defined by formula (1), the replacement in comparative circuit 3 is measured by This transformer has practically no effect on the sum of T and compensation currents. This is due to the fact that the errors of a posed transformer and the errors of a precision transformer corrected by a magnetic comparator, i.e. the almost equal errors of the comparator are different; in the circuit k of the circuit- 3, a difference current ul occurs. The zero-indicator 7 shows a signal caused by unbalance of circuit 3. Current l1 is actually a measure of the difference between the errors of the comparator and the transformer under test. Since the current L I is a vector quantity, the difference in error is characterized by two components of current, proportional to the component of current l I, which is in phase with primary current 1 and angular, proportional to the component of current that falls in quadrature to current 1. The voltage drop from the current L1 on resistance R is balanced by voltage drops on the in-phase reich 5 which is powered by a current in-phase with the current I and on quadrature rheochord 6 that is fed by a current shifted by 90 ° relative to current I. Sign of the value of the drops rheochords voltage to alter the displacement of each slider rheochords in the positive or negative direction from zero then ki. Scales of rheochords are graded in current (in-phase) and angular (quadrature) errors. Produced readings on scales of rheochords. If the counts are 5-10, i.e. the requirement of a triple margin is met in terms of the accuracy of an exemplary measuring instrument as compared to a test one; they are assumed to be equal to the current and angular errors of the transformer to be tested without amending. At each next primary current value, the corresponding parameters of the compensation unit are determined. One after another, many and usually multi-range current transformers are calibrated one by one, with the inspection performed at -5 primary current values for each of the nominal conversion ratios, replacing the time-consuming, long-lasting and the required special skill of the comparator's magnetic flux compensation procedure - a simple and quick operation of setting the recorded parameters of the compensation block considerably speeds up the measurement process while maintaining high accuracy, the magnetic characteristic of the current comparator. Claims An apparatus for calibrating current transformers, comprising a comparison unit, consisting of a differential circuit of an in-phase and quadrature rheord and null indicator, as well as a magnetic current comparator, the resulting circuit of which is connected to the comparison unit, and an ammeter, different from in order to increase productivity, a precision current transformer is additionally introduced in it, the primary windings of which and the comparator are connected in series, the secondary winding which is connected on one side inen to the terminal for connecting an exemplary converter, and on the other through an ammeter and a resistor to a comparison unit, as well as a compensation unit connected to the input parallel to resistor 3 f output - parallel to the differential circuit of the comparison unit, while the magnetic comparator input is connected to the bus adjustable current transformer. : Sources of information taken into account during the examination 1. USSR author's certificate No. 702328, cl. G 01 R 35/01, 1979. 2.Gornshteyn G.L., Zakharov B.V., Peshkov G.M. Installation for calibration of laboratory current measuring transformers. - Measuring equipment, M., Publishing House of Standards, 1972, No. 1, p. 79-81.