SU1677662A1 - Device for measuring electric mains insulation resistance - Google Patents

Abstract

The invention relates to electrical measuring technique and can be used to calculate the active and capacitive components of the insulation resistance of a two-wire DC network. The purpose of the invention is the extension of functionality - is achieved by further determining the network capacity. The device contains a shunt resistor 1, the first capacitor 2, the first voltage-to-voltage converter 3, the first electronic switch 4, the second electronic switch 5, the second capacitor 6, the switch 7, the second resistor 8, the second voltage converter 9 to the code, the control unit 10, the computing unit 11. 1 or

Description

The invention relates to electrical engineering and can be used in automatic systems for measuring the insulation and capacitance of DC networks at power facilities for various purposes.

The purpose of the invention is the expansion of functionality by measuring the capacitive component of the network resistance.

The drawing shows a block diagram of a device.

The device contains a shunt resistor 1, a reference capacitor 2, a first voltage to code converter 3, electronic keys 4 and 5, a second capacitor 6. a key 7, a second resistor 8, a second voltage to code converter 9, a control unit 10 ,. calculating unit 11. The shunt resistor 1 and the reference capacitor 2 are connected in series and form a measuring circuit connected at one end to the housing. The second end of the measuring circuit is switched by electronic keys 4 and 5 at the poles of the measured network. The second capacitor 6 is connected by a key 7 between the negative pole and the housing. The second resistor 8, the resistance of which is equal to the resistance of the shunt resistor 1, is connected between the poles of the measured network.

The device is working! in the following way.

Electronic keys 4 and 5 alternately switch the measuring circuit to the poles of the measured network. With each switching, the voltage-to-code converter 3 measures the value of the current flowing through the measuring circuit. According to the measured values of the currents, the computing unit 11 determines the first algebraic difference of the currents. Converter 3 voltage to code measures the current 1 ₀ . Then, the key 7 connecting the capacitor 6 is closed, and the process of alternating switching to the poles of the measured network is repeated, measuring the currents flowing through the measuring circuit and determining the second current difference, after which the computing unit 11 implements the relations given in the formulas _R = _AMLlzJ2L_ (Io + Iz) (Ιο +)) c ₌ (L ° _- 'ύ (' ο +12) r '2 Ιο (Ιι -Ι2) °' where Ίο is the absolute value of the current equal to the ratio of the voltage of the measured network to the resistance of the shunt resistor ;

h is the first algebraic current difference;

1d is the second algebraic current difference;

Ro - resistance of the shunt resistor:

Co is the capacity of the first reference capacitor. *

Then the circuit returns to the measurement mode 10 of the first algebraic current difference. To implement this mode of operation, the following signals should be generated at the device outputs:

- the pulse duration must be 15 not less than the sum of the counting time of voltage converters 3 and 9 to the code and the time required to read the code corresponding to the measured current from voltage converters 3 and 9 to the code by computing unit 11;

- a negative front should be formed earlier than a positive front (this is necessary to exclude the state when both keys are closed and the measured network is shorted by them).

The control pulses must be formed by voltage converters 3 and 9 into a code that satisfy the following requirements: pulses must be of a duration of at least 2 μs; a positive front should be formed earlier than a negative one.

Thus, a measurement mode of the first algebraic difference 35 'of the currents is formed. Computing unit 11 reads information about the measured currents from voltage converters 3 and 9 into a code by the output signal generated from the moment the data is ready. To implement the measurement mode 40 of the second algebraic difference, at the end of the measurement cycle of the first algebraic difference, a low level should be generated at the output of the control unit, causing the key 45 to close. 7. Since the key 7 has a speed significantly lower than the electronic keys 4 and 5. to complete short circuit key 7 at the outputs of the control unit must be set low. After the key 7 is closed at these outputs, the same signals must be generated as for the mode for determining the first algebraic difference, after which a high logic level must be generated at the output of the control unit 10, which causes the key 7 to open. Until the outputs are fully open control unit 10 is kept low, after opening, the circuit should repeat the measurement cycle. The calculation of the desired values by the formulas is performed in the computing unit 11. In the device, in addition, a measurement mode of only the active component of the insulation resistance is implemented, using 5 known capacitive components. To do this, it is necessary to implement the definition of only the first algebraic difference of currents, and then return the circuit to its original state.

Claims (1)

Claim A device for measuring the insulation resistance of electric networks, containing a shunt resistor, two electronic keys connected to the corresponding terminals for connection to a controlled network, a control unit, a voltage-to-code converter and a computing unit connected in series, 20 a common input of keys is connected to the voltage converter-to-code input, control inputs of keys, voltage to code converter and computing unit are connected to the output of the control unit, characterized in that, in order to expand functional capabilities, it is equipped with a first and second capacitors, a second voltage to code converter, a second resistor, a third key, the first output of which is connected in series through the second capacitor to the grounded terminal 10 of the shunt resistor, the other terminal of which is connected through the reference capacitor to the second terminals of the electronic keys, the second resistor is connected to the corresponding terminals for connecting 15 to the monitored network, and the third output to the first input of the second voltage converter one, and the first voltage to code converter is connected by the first input to the third terminal of the shunt resistor, the output of the second voltage converter to code is connected to the second input of the computing unit, and the input to the corresponding output of the control unit,