SU756317A1 - Device for measuring symmetrical components of forward and inverse sequencies of multiphase voltage system - Google Patents

Description

The invention relates to the field of _изм electrical measuring equipment and can be used to create devices for monitoring the asymmetry of a multiphase network, as well as in protection schemes for multiphase devices and systems.

A device for measuring the voltage of the reverse sequence, containing a voltmeter, transformers, rectifier bridges with smoothing filters and a three-input functional converter of the root-mean-square value, is known [1]. The device does not exclude completely the influence of deviations of the frequency and non-sinusoidality of the system under study on. yarns. The use of an indirect measurement method places high demands on the error of the blocks used for the calculation.

A device is known for measuring the asymmetry of a multiphase network, for example, a three-phase device, containing a series of phase number transformer connected to the network, a multiphase rectifier, a frequency-selection filter, and an indicator [2 \. However, such a device does not exclude the error of the transformer number

2

phases arising from variations in the frequency of the mains supply.

To eliminate the influence of the non-sinusoidal voltage of the network on the measurement accuracy at the output of a multi-phase rectifier, a selective filter is connected through an isolating capacitor, which selects only the second voltage harmonic. This introduces an error, since the reverse sequence voltage is proportional to the amplitude, variable non-sinusoidal component at the output of a multiphase rectifier in the absence of higher harmonic voltages of the network under study.

The purpose of the invention is to improve the accuracy of measurements.

The goal is achieved by the fact that the device for measuring the symmetrical components of the forward and reverse sequences of a multiphase voltage system, containing a phase number converter, a frequency-selective filter, a multiphase rectifier and voltage indicators of the forward and reverse sequences, is equipped with series-connected variable-amplifier power amplifier '75

Is the voltage applied to the rectifier and the alternating voltage converter to a constant voltage level of the variable component _? as well as the unit measuring the DC component of the rectified voltage. Moreover, the inputs of the band-pass frequency-selective filter are connected to the device inputs, the outputs through series-connected phase number converter and multiphase rectifier - to the inputs of the Power amplifier and the constant component measuring unit of the rectified ¹ voltage, and the voltage indicators of the forward and reverse sequences rectified voltage and AC voltage to constant voltage converter according to the amplitude level, respectively.

The drawing shows a block diagram of a measuring device containing a band-pass frequency-selective filter 1, a potentiometric, a phase converter 2) a multi-phase rectifier 3; a wideband amplifier 4 of the power of the variable component of the rectified voltage, an alternating voltage converter 5 to a constant level of amplitude value, a negative sequence voltage indicator 6, a constant component measuring unit 7 of the rectified voltage and a direct sequence voltage indicator · 8.

The use of a potentiometric phase converter allows to reduce the error with frequency deviations and fluctuations, as well as reduce the size of the device.

The variable component of the multi-phase rectified voltage is fed to the input of a broadband power amplifier, which almost does not distort the waveform. An AC / DC converter is connected to the output of the power amplifier according to the amplitude value of the variable component. The output voltage of the summation unit, proportional to the voltage of the negative sequence, is fed to the measuring device. To measure the voltage of the direct sequence to the output of the multiphase rectifier bridge, a block is connected that contains a filter of the constant component of the voltage, the value of which is proportional to the voltage of the direct sequence.

The device makes it possible to virtually eliminate the influence of the non-sinusoidality of oscillations and frequency deviations of the studied network on the measurement accuracy, as well as to reduce the power consumed by the measurement circuits.

Claims (1)

Claim A device for measuring the symmetrical components of the forward and reverse sequences of a multiphase voltage system, which contains a phase number converter, a frequency-selective filter, a multiphase rectifier, and voltage indicators of the forward and reverse sequences, characterized in that it is equipped with a series-connected amplifier the power of the variable component of the rectified voltage and the AC-to-DC converter by the amplitude level The variable component as well as the DC component of the rectified voltage, the inputs of the band-pass frequency filter are connected to the device inputs, the outputs through the series-connected phase number converter and the multi-phase rectifier are connected to the inputs of the power amplifier and the DC component of the rectified voltage, and the indicators the voltage of the direct and inverse sequences are connected to the outputs of the block measuring the constant component of the rectified voltage Ia and AC inverter in a constant level of amplitude value respectively.