SU1599814A1 - Apparatus for measuring asymmetry in three-phase electric mains - Google Patents

Abstract

The invention relates to electrical measurements and is intended to measure the power loss factor in three-phase networks with unbalanced loads. The application of the proposed device allows to increase the accuracy of measurements, as well as to take into account the effect of asymmetrical loads connected to the linear voltage, which expands the functionality of the device. This is ensured by the fact that the device is equipped with direct, reverse, and zero sequence current filters and units of reverse current and zero sequence current dividing into direct current, as well as two quadrants and a linear amplifier, which allows to realize the exact power loss increase function. 1 il.

Description

The invention relates to electrical measuring equipment and is intended to measure asymmetry in three-phase electric networks, in particular, to measure the ratio of the increase in active power loss in three-phase networks with current unbalance.

. The aim of the invention is to improve the accuracy and expand the functionality of the device.

The drawing shows a block diagram of the proposed device.

The device contains input sensors 1–3 of current, which are multiwinding current measuring transformers and are used to measure the instantaneous values of currents in a three-phase network. Current sensors 1-3 are connected to the inputs of filters of symmetrical component currents of reverse 4, direct 5 and zero 6 sequences connected to the corresponding inputs of reverse current 7 and zero 8 blocks of direct current, the outputs of which are connected to the inputs of quadrants 9 and 10. The output of the quadrant 9 is connected to one of the inputs of the adder 11 directly, and the output of the quadrant 10 is connected to another of the inputs of the adder 11 through a linear amplifier 12. The output of the adder 11 is connected to the indicating or self-recording device 13, Azan m which is judged on the value of the power loss.

The device allows you to implement the function

00

jKp 1 + ef KfiK

i

(I)

de K - magnification factor

power losses, showing how many times the active power losses in the network in the asymmetrical mode are greater than the corresponding losses in the equivalent symmetric mode;

 current unbalance factor, equal to the ratio of negative sequence current to direct current; Cc is the active resistance coefficient equal to the ratio of the active resistance of the zero sequence RO to the active resistance of the direct sequence R ,. The Kp value for the 0.33 kV line is determined by the expression

R

f (2)

where r and r

f active resistances of phase and neutral wires; K is the unbalance factor of the currents, which is equal to the ratio of the zero-sequence current to the direct current.

The coefficient of increase in power losses Кр, which is a multiplicity of increase in power losses when the currents in the network are asymmetrical, is equal to the ratio of power losses under an asymmetrical load to the power loss under a symmetrical mode, i.e

K - A1 - p UP.

, + llRi -I- loRo

,

 1 + ej +,

(3)

since Iz / Ii fr o / I (, and R, Ra.

In expression (3) I ,, I j, and IQ is the current, reverse, and zero sequence in the network; Rg is the resistance of the reverse sequence network.

Since the losses in are usually measured in terms of, then by a known value of Kp, the losses can be found with an equivalent symmetric mode. --- and thus mo1 kp

live life | estimated asymmetry damage

currents.

The device works as follows.

The signals from sensors 1 - 3 are fed to the input terminals of filters 4 - 6

symmetric components, the outputs of which receive signals proportional to the currents of the inverse, direct and zero sequences, which are fed to blocks 7 and 8 of the division. Block

7 division implements dividing the Negative Current by the direct current, and block 8 - dividing the zero sequence current by the direct current. The signal from block 7, proportional to the asymmetry factor of the currents j, through the quad 9 goes to the first input of the summing unit 11, and the signal c block 8, proportional to the imbalance coefficient of the currents K; ,through

the quad 10 is fed to the input of the linear amplifier 12, the gain of which is determined by the ratio RQ / R ,. The amplified signal from block 12 is fed to the second input of the adder

11, in which the addition occurs

signals and a signal proportional to 1 + 8i + appears, which is fed to measuring device 13 (indicating or self-recording), according to

indications of which judge loss of power.

The accuracy of the measurement is achieved by introducing into the filter device symmetric components DI and blocks of dividing the reverse and zero sequence currents of direct current, which allows, together with the square converter, to realize the exact function of the loss increase factor described by the expression for K.

Expansion of functionality is achieved by introducing blocks determining, i.e., a negative sequence current filter, a unit dividing this current into a direct and square converter, which allows this device to be used in networks with unbalanced loads, connected to line voltage ,, and three-phase four-wire networks.

In addition, the presence of filters of currents of symmetrical components excludes

51

the effect of phase asymmetry of currents on the accuracy of the device. The form m at la invented and

A device for measuring unbalance in three-phase power grids, containing three input current sensors installed on each phase, as well as an adder, a first dividing unit and a recording device, which, in order to increase accuracy and enhance functionality, it additionally introduces a second dividing unit, two quadrs, a linear amplifier, and three filters, respectively, direct, inverse, and zero sequences, first, second

four . 6

and the third inputs of which are connected respectively to the outputs of the first, second and third current sensors, and the outputs of the filters of the symmetrical components of the forward and reverse sequences are connected to the input of the first dividing unit, the output of which is connected to the first quad connected to the first input of the adder, and the outputs filters of symmetrical components of direct and zero-sequence current are connected to the input of the second dividing unit, the output of which is connected to the input of the second quadr, connected through linear amplification Tel a second input of the adder whose output is connected to the recording device.

Claims (1)

Claim A device for measuring the asymmetry in three-phase electrical and third inputs of which are connected respectively to the outputs of the first, second and third current sensors, and the outputs of the filters of the symmetrical components of the current of the forward and reverse sequences are connected to the input of the network containing three input current sensors installed on each phase, and also an adder, a first division unit and a recording device, characterized in that, in order to increase the accuracy and expand the functionality, an additional second division block, two quadrators, a linear amplifier and three filters, respectively, of direct, reverse and zero sequences, the first, second first division blocks, the output of which is connected to the first quadrator connected to the first input of the adder, and the outputs of the filters are symmetrical current components direct and zero sequences are connected to the input of the second division unit, the output of which is connected to the input of the second quadrator, connected through a linear amplifier to the second input of the adder, the output of which is connected to the register kntsemu device.