SU1755208A1 - Device for compensating errors of three-phase three-wire transformer meters - Google Patents

Abstract

Use: compensation of the error of the active component of the current, the load in the secondary circuit of the voltage transformer. The essence of the invention: the device comprises a voltage transformer (1), an electricity meter (2), three capacitors (1C, 2C, ES). 1-1С-2С-2, 1-ЗС-2, 1-2С. 3 il.

Description

This invention relates to electrical engineering and can be used to measure energy consumption.

 Devices for measuring energy consumption in three-phase networks are known, in which the meters are connected through current transformers and voltage transformers (TH).

The disadvantage of these devices is that the systematic errors of the instrument transformers lead to undercounting of electricity.

The closest to the present invention is a device for measuring energy consumption, in which, in order to reduce the undercounting of electricity due to the errors of voltage transformers, capacitors with a capacity of 1-1.5 microfarads are connected in parallel with the windings of the active energy meter voltage.

The disadvantage of this device is that it only compensates for the error in the metering of electricity, which is caused by the voltage drop in the resistance of the voltage from the inductive component of its load current, and at the same time the error from the active component of this current remains.

The aim of the invention is to improve the accuracy of measurement, energy consumption due to the compensation of errors in accounting, caused by the systematic errors of the voltage supplying electric meters,

This goal is achieved in that the error compensation device for three-phase three-wire power meters of a transformer switch-on device contains first and second capacitors, the first terminals of the first and second capacitors connected to the first and second terminals of the voltage transformer secondary, the third terminal of which is connected to the combined second terminals of the first and a second capacitor, a third capacitor is inserted, connected by the first lead to the first lead of the first capacitor, and the second to the first at the conclusion of the second capacitor, wherein the magnitude of said capacitors are selected from the ratios:

I hear about

00

(cozy

K-X -siny) R tg p v

where C is the capacitance of capacitors, f;

I - phase load current TH, A;

R and X, respectively, the active and inductive resistances of TH, reduced to its secondary side, Ohm;

U is the secondary linear voltage TH, B; r i

(o is the angular frequency; p is the average value of the load angle of consumers,

y is the angle between the phase voltage and the load current TH.

FIG. 1 shows the circuit diagram of the device (on the secondary side of the ТН 1 the load of the ТН 2 and capacitors 1C, 2С and ЗС are included); in fig. 2 is a vector diagram of the currents TN before and after switching on the compensating capacitors (U is the phase voltage, I and IK are the load currents of the TC, respectively, before and after switching on the compensating capacitors, I is the current in the TC from the compensating capacitors, ui0 is the phase angles of the currents) and 1 TO); in fig. 3 - vector diagrams of currents and voltages of TH in modes before (a) and after (b) connecting compensating capacitors. (1a and p are, respectively, active and reactive components of load current 1; TN0; respectively, load angles TH in the modes before and after switching on the compensating capacitors; Ui is the primary voltage; K is the rated transformer ratio of the transformers; n is the load current of consumers, p is the angle of the load current of consumers, the angular error TH, R and X are respectively the phase active and inductive resistances of the windings TH, reduced to the low voltage side.

The device works as follows.

Capacitive currents of capacitors included in the circuit (Fig. 1) create a longitudinal and transverse voltage drop across the resistance of the voltage transformer. A longitudinal voltage drop changes the voltage error of the voltage across the voltage, and the transverse voltage drop changes the angular error. The capacitance value of the capacitors is chosen such that the additional errors in the electricity metering, caused by the voltage errors of the voltage generator and the angular error, become equal in magnitude and opposite in sign and thus compensate each other.

ten

15

20

We derive a formula that implements these conditions.

The error in the metering of electricity from the use of voltage transformers DE is expressed by the formula (L3):

A3 (-100Aptgp + Au)% (2)

where the angular error is TN in radians;

Au is the relative error of the HP by the magnitude of the voltage in%.

To derive formula (1), we transform formula (2) so that, instead of the angular error D0, it contains a transverse voltage drop in TH A Up in%, and instead of Di, a longitudinal voltage drop Aiav%.

A positive value of the longitudinal voltage drop causes a decrease in the secondary voltage and, consequently, a negative error in the magnitude of the voltage.

25

(3)

The positive value of the lateral voltage drop, as can be seen from FIG. 3, leads to a negative angular error. Du angle in radians can be represented as

Doo

 AU

100

(four)

Substituting expressions (3) and (4) into formula 2, we get:

A e AUp tg (p - A Ua. (5)

From the vector diagram of FIG. 3 (b)

(Rcosy0-Xslny0), (6)

DC, J | p (Xcosy0 + Rslny0), (7)

where UV phase voltage.

Substituting (7) and (6) into expression (5), we get:

DE p (X cos yo + R sin y0) x U}

 tgp -ttr (R cos uo -X sin uo) -cr {(X + R tan p) sin yo - (R - X tan p) cos yo.

(eight)

Accuracy D provided that

(X + Rtgp) sin y0 (R-Xtg y) cos y0 (9) From here

To compensate for this error, a device consisting of three capacitors connected as shown in FIG. 1. Each capacitor with capacitance

y0 - arctg

R - X tg p

(ten)

X + R tg p

With such an angle of loading, the y0TN does not introduce errors into the metering of electricity.

To create a mode in which the current TF will lead the voltage at the angle of the EUT, it is necessary for the capacitors C to create a capacitive current c, which, according to the vector diagram of FIG. 2 equals

These capacitors create in the windings of the TN currents

lc Icosytg wq- isin y. (eleven)

This current is created by capacitors C, 20 v3 100 31 F1.88, connected to linear voltages of 1.02 A s

(12)

From expressions 10, 11 and 12 we get

HЈ igf-H- (i

g --P rme. TN type NTMI-b operates in accuracy class 1.0 with phase load

0.86e J6 ° CA.

 1.47 v1121 2 ° (- 0.76 + j 1.26)% Error in electricity metering,

The resistance of the transformer unit transformed to VT due to this drop (according to the formula winding 5) is equal to

, 83 e1 3U ° (0.71 + JQ.43) ohms.

40

Weighted average load of consumers whose meters are powered Resulting error in accounting

from this TN # 25.8 ° electricity after switching on the compensation. In this mode, the error in the accounting of the steering capacitors is equal to the electric power, due to the error 45. St mi TN from the currents of its load is equal to (according to

formula 8)

The proposed device is completely

compensates for errors in electricity metering due to errors in the voltage transformer 50.

DE DES +, 36 + 1,

 + Rtgp) slny- (R - X tg (p) cos y%

 loo / vf 0-434-0 711925 80 x sin (- 60 °) - (0.71 - 0.43 tg 25.8 °) x cos (-60 °) -1.36%

(ten)

WITH

I

Yu

0.86

G- 100 314

cos (-60 °)

xu71.-0.43tt, 25.8 °

043 + 0.71 tg 25.8 ° 1.88-.

These capacitors create in the windings of the TN currents

The voltage drop from this current on the resistance of TN

L ,, 1001 Z 100 2 yq-17 di - 100A / 3 3fz

 .o, 83e) 31-20

 1.47 v1121 2 ° (- 0.76 + j 1.26)% Error in electricity metering,

due to this fall (according to formula 5) is equal to

40

NPP AUptgy) - D1) and 126tg25.8 ° - (0, 76) 1.36%

Resultant error

capacitors equals

DE DES +, 36 + 1,

Claims (1)

The invention The device for compensating errors of three-phase three-wire transformer switching meters, containing the first and second capacitors, the first terminals of the first and second capacitors connected to the first and second terminals of the transformer secondary winding voltage, the third output of which is connected to the combined second terminals of the first and second capacitors, characterized in that, in order to improve the accuracy, a third capacitor is connected to the device, connected first to the first output of the first capacitor, and the second to the first output of the second capacitor, moreover, the capacity of these capacitors C are determined by the ratio f - TJ5 (No. FIG 2 0 where I is the phase load current of the voltage transformer, A; R, X are the active and inductive resistances of a transformer on a yarn, respectively, reduced to its secondary side, Ohm; U is the secondary linear voltage, V;  angular frequency; y is the angle between the phase voltage and the load current I; ip is the weighted average of the load angle of consumers whose meters are connected to this voltage transformer. / „ /, X °; ; Fig 3