SU1751689A1 - Device for measuring resistance of incoming transmission lines of dc mains - Google Patents

Abstract

The invention relates to a measurement technique, in particular to a technique for measuring the active resistance of direct-current lines that are under voltage. The aim of the invention is to increase the convenience of measuring the resistance of the power line of the direct current network from the source to the consumer by connecting only from the side of the consumer. The device includes a resistor, keys, bridge, zener diode, shunt, amplifier, integrating element, repeater, switch, recorder, drivers. A feature of the invention is the introduction of an additional key, a switch control unit, as well as the implementation of sensors in the form of a zener diode and a shunt, respectively. 1 il.

Description

The invention relates to a measurement technique, in particular to measurements of the active resistance of direct-current lines, which are under voltage.

The aim of the invention is to increase the convenience of measurement by making it possible to measure the resistance of the power line of the direct current network from the source to the consumer when connected only from the side of the consumer.

The drawing shows the electrical circuit of the device for measuring the resistance of the power line of the direct current network, which is under voltage.

A device for measuring the resistance of the power line of the direct current network, which is under voltage, includes a load resistor 1, a thyristor switch 2 of the control unit 3 with the time element 4, a voltage sensor b made in the form of a bridge with a zener diode 6, a current sensor 7, made in the form of a measuring shunt; a scaling amplifier 8; an integrating element 9 for storing measured values; a key 10 at a field-effect transistor; a voltage follower 11; a switch 12; an indicator 13; a voltage driver 14 and a driver l 15 current.

Voltage sensor 5 is connected to the measured line by one bridge diagonal and to bridge inputs of the second diagonal bridge 8, the output of which is connected to the input of the transistor control key 10. The output of key 10 is connected to the input of the memory element containing the integrating element 9 and voltage follower 11 on the op amp. The output of the voltage follower through the switch 12 is connected to the indicator 13.

The channel for measuring the current increment is similarly assembled;

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00 Oh

an amplifier which is connected to the current output of the current sensor 7.

Parallel to the voltage sensor 5, a circuit is turned on consisting of a thyristor switch 2, a load resistor 1 and a current sensor 7,

The control unit includes a starting circuit consisting of elements C2, R3, VS1, VD1. VD2, R6, Sz, which provides the closing of the power thyristor switch 2 with the button SB1 with the time specified by the capacitance of the Sz and the resistor R6. Through the disconnecting contacts of the button SB1, a capacitor C1 is connected, which through the closing contacts is connected to a divider on resistors R4 and R5, the common point of which is connected to the control electrode of the thyristor switch 2.

In the circuit of the resistor 1 key 2 included current relay KA. The closing contact of this relay is connected by one pole to the positive wire of the network, and the other to the time delay element consisting of the resistor R7 and the capacitor C4, to which the relay KL is connected. The contacts of the KL relay are connected by one pole to the control electrodes of the field-effect transistors 10, and by others to the negative poles of the sources.

A device for measuring the resistance of the power line of the direct current network, which is under voltage, works as follows

After connecting the device to the line with an adjustable resistor R of the bridge while pressing the SB2 button, the voltage across the bridge diagonal, controlled by the indicator 13, is reduced to zero. Then the control unit is turned on, which briefly opens the switch 2 by connecting the load resistor 1. The current in the resistor D I causes an additional voltage drop in the supply line of the circuit Di, The magnitudes of the current increment and voltage are remembered and then read by the indicating device. The current in the load resistor 1 is fixed using a current sensor 7 and a current driver 15, including a scale amplifier 8, a transistor switch 10, an integrating element 9 and a voltage follower 11,

The resistance of a portion of a circuit is defined as the difference of resistance measured at its beginning and end.

For part of the circuit with ohmic resistance R on the basis of Ohm's law

R

(one)

where U is the voltage of the circuit;

I is the current in the circuit,

if the voltage increments D U, then the current receives a certain increment D I, then

R-U + AU, 2)

K I + D W

from where IR + D | R U-tAU. (3)

Since, then U + YY,

R-AU (l

)

Thus, the ohmic resistance of the circuit can be determined by the ratio of the voltage increment in this area to the current increment in it.

If it is required to find the resistance of the line from the source to the measuring point, then, provided that the voltage on the source buses is constant, the increment in the voltage drop in the line from the current increment in it is equal to the change in voltage at the measurement point:

A UnnH UvtcT-UHarp: Rni iH lHarp, (5)

Dulin Uist Unagr Rlin (1Nagr + D I), (6)

where D Ulin is the voltage drop in the line before turning on the ballast resistor;

D Ulin - voltage drop in the line after switching on the ballast resistor;

Uist is the voltage source (battery), taken constant;

Unag Voltage on load resistance;

Unagr - voltage at the load after connecting the ballast resistor;

Rlin - line resistance;

1 nagr - load current in the circuit;

DI is the increment of the current in the line due to the parallel connection to the load of the ballast resistor.

Since the decrease in voltage at the load due to an increase in the voltage drop in the line is a negligible value, the decrease in the load current in this case can be neglected.

And Ulin Dulin inagr-Unagr Rlin -Rlin (1Nagr + D 1) -Rlin D1.

from where

o - D Ulin - Doolin Doolin

NlinDPDT

To ensure that the voltage on the tires remains constant before and after the current increment in the line, the device provides for simultaneous measurement and memorization of the voltage increments and the current at the measuring point. For this, a load resistor is connected in parallel with the load,

Агagr- (7)

To prevent overloading of the load resistor 1. it is connected to the line briefly (on the order of 1 s), and the magnitude of the resulting voltage drop increment is memorized by a memory element made in the form of an integrating circuit with a small time constant. This makes it possible to measure the results with a measuring instrument for a longer period of time sufficient to clearly fix the measurements.

The proposed device makes it possible to measure the resistance of a laser from 0.010 to 10 ohms with an accuracy of the order of 1%, which makes it possible to estimate the heating and the state of the contacts of the measured line.

Claims (3)

1. A device for measuring the resistance of the power line of a direct current network, which is under voltage, contains a load resistor, the input of which is the first terminal for connecting the measured power line of the direct current network, a current sensor connected in series, a current shaping unit, the input of which is connected to the current output of the current sensor, a voltage sensor and a voltage shaping unit connected in series, an indicator, characterized in that, in order to increase the convenience of measurement by providing air the ability to measure the resistance of the power line of the direct current network from the source to the consumer when connected only by the consumer, a bridge is used as a voltage sensor from the arms of which is formed a zener diode, the first diagonal of which is the output of the sensor and connected to the power line of the direct current network, the second diagonal of which is the output of the voltage sensor. A measuring shunt is used as a current sensor, a thyristor switch is inputted, the input of which is connected to the output of a current sensor, a control unit, The first and second inputs of which are connected respectively to the first and second terminals for connecting the measured supply line of the direct current network, and the first, second and third control outputs of which are connected to the control inputs of the thyristor switch, respectively, of the current and voltage generation units, a switch, the first and second inputs of which are connected to the outputs of the current and voltage drivers, respectively, and the output is connected to the recorder's input. 2. Device pop. 1, characterized in that the current driver (voltage) contains a scaling amplifier, the input of which is the input of the current driver (voltage), the output of which is connected in series with the key. an integrating element and a pseudovator, the output of which is the output of the current driver (voltage). 3. The device according to claim 2. that is, so that the key of the current driver (voltage) is made on the field-effect transistor.