RU1797077C - Method of determination of short-circuit current - Google Patents

Abstract

The invention can be used to make devices for determining short-circuit currents in electrical installations of alternating voltage. The purpose of the invention is to improve measurement accuracy. The internal resistance of the electric network is determined by loading it with a known low-current rectifier load with measuring the constant component and the difference in the duration of the positive and negative voltage polarity of the network. From the measurements obtained, the active and reactive components of the internal resistance and the short circuit current at a given point in the network are determined. 1 ill.

Description

The invention relates to the field of electrical engineering and can be used for the manufacture of devices that can determine the short-circuit currents (TKZ) in electrical installations of alternating voltage.

To check the sensitivity of protective devices in electrical installations, it is necessary to know the TKZ, which are determined by the internal resistance of the source.

Known methods for determining T.K.Z. directly from the experience of short circuiting or by measuring the internal resistance of the source when it is de-energized. But these methods require de-energizing consumers, are rather laborious and insecure.

A known method for determining the short circuit current by measuring the internal resistance of a source using the principle of an equivalent generator. In this case, idle

the source voltage, the open circuit voltage Uxx is measured; in the external load connection mode, the voltage UH and the current N of the load are measured. The internal resistance of the source is determined by the formula:

7 .UXX-UH AU

Zn - ---- j ----- - -G--

Ihih

.(1)

However, this method has the following disadvantages: 1. Without taking into account the shear angle between UXx and formula (1), it gives an approximate value of the internal resistance of the source, but taking the shear angle into account greatly complicates the procedure for determining ZM.

2. Due to the voltage fluctuation of the DCCol in the network during the measurement process, which takes place in real conditions in real power installations, to obtain the correct measurements, which is possible with.

to C

3

3

XI XI

Fulfillment of the Di-Dikol condition, it is necessary to increase the external load current IH, which leads to an increase in the dimensions of devices based on this method.

3. In electric networks of high power with significant T.K.Z. an increase in n is also required to obtain sufficiently accurate measurements of Dee.

4. Significant load currents In, by. required by devices with this principle of operation, makes the measurement process unsafe, because in the event of a contact failure at the point of connection of the device to the network, an arc with overlap and K. to adjacent phases. in

The aim of the invention is to increase the accuracy of measuring the total internal resistance of an AC voltage source and to reduce the additional load current in the measured network. Using the proposed method for determining the internal resistances of electrical sources, it will be possible to create small-sized, simple, and safe-to-use devices that measure the following parameters of low-voltage alternating current networks under operating voltage:

1. internal resistance;

2. internal inductive reactance;

Short circuit parts;

4. quality of contact compounds;

5. the presence in the network of loads of a half-wave rectification scheme.

The goal is achieved in that:

Claims (3)

1. Consistently, a rectifier element (diode, transistor, etc.) is included in the circuit of the known low-current resistance of the device for measuring internal resistance, loading the measured network with a unipolar load current. 2. To determine the active resistance, the source of alternating voltage when connecting the load according to claim 1, measure the average value of the DC voltage for a period in the network and current. The active resistance of the source is determined by the formula: gee di wed 1 day network voltages fired. The inductance of the source is determined by the formula:. . hn gn tg cp "gn (r gnsh DT (3) 0 5 0 5 0 5 0 5 where p is the angle of the load; W-circular frequency. The main feature of the proposed method is that normally (without connecting a load with a current of one polarity) in industrial AC networks, the network voltage parameters measured in this method have the following values: Disc 0 and -W- and these parameters it does not depend on the load, network, and, therefore, it is not necessary to fix the network parameters in idle mode, load the network with loads that cause significant changes in voltage. The drawing shows an example diagram of a device based on the proposed method. The device consists of a load resistance 1 connected to the network through a rectifier element 2, an ammeter of the magnetoelectric system 3 and a switch 4. In parallel with this circuit, an average voltage meter AUcp is connected, consisting of an average voltage filter including active resistance 5 and capacitance b, and a voltmeter of the magnetoelectric system 7, and a meter for the difference in the duration of the polarity of the DT, consisting of upstream resistance 8, two on-board zener diodes 9, a voltmeter magneto system 10/ When the device is connected to the network with switch 4 open, both voltmeters 7 and 10 will normally (in the absence of a unipolar load) give zero readings. When the switch 4 is closed, the voltmeter 7 will measure the value, and the 1Q voltmeter - DiSr.st 0. In this case, the duration difference is determined by the formula: fifty A T (4) 3. In order to determine the inductive resistance of the AC voltage source when connecting the load according to p. 1, the difference in the time DT (angles) is measured  : t +. t and negative positive where Dis.st is the average value of the stabilized alternating voltage; UCT is the amplitude of the stabilized alternating voltage, From (2) and (3), the active Vi and reactive chi are determined. The resistance of the source (network), and the impedance will be equal to 2i f gi b hee When using amplifying semiconductor devices for measuring average values (constant components) SUMMARY OF THE INVENTION A method for determining a short-circuit current by measuring the total internal resistance, which is of an active-inductive nature, in AC power networks, which includes detecting a voltage change when an additional load is connected, which means, in order to To increase the measurement accuracy and reduce the additional load current in the measured network, a low-current rectifying load is created in the measurement unit and the active component of the internal resistance is determined by measuring this component of the mains voltage and the average value of the load current with the subsequent determination of the active component of the resistance, according to the formula Guy AUcp / icp, voltages provided that the variable component is suppressed; ranges of measurement of the internal resistances of the network and can dramatically increase. where AUcp is the constant component of the voltage in the network; icp is the average value of the load current, the inductive component of the resistance is determined by measuring the difference in the durations of the positive and negative voltage polarities of the network with the subsequent determination of the inductive component of the resistance, according to the formula . chi gn 2 ts f DT, where gn is the resistance of the additional load; f is the network frequency; L T is the difference in the duration of the positive and negative polarity of the voltage in the network. and the total internal resistance is determined by the formula: 2 And SGi + Chi.