CS259717B1 - Apparatus for measuring and registering a short-circuit current - Google Patents

Abstract

The device concerns the measurement and registration of the short-circuit current surge in the distribution network to determine the power stress of the equipment of the power system by short-circuit currents, e.g. transformers, generators, reactors, etc. The device in its main part consists of three two-way rectifiers for individual phases, R, S, T, analog memory, electronic switch, digital registration unit and control unit. Its operation consists in continuously measuring the peak current value in phases R, S, T, of which the highest, corresponding to the short-circuit current surge, is transferred from the analog memory via the electronic switch to the digital registration unit in the event of a short-circuit fault. The data is converted into permanent registration in digital form by means of the control unit either at the start of the command voltage to switch off the circuit breaker, or at the command of an internal comparison circuit set to a certain overcurrent level. The device is supplemented with a phase resolution unit with a short-circuit current surge, a calibration source for calibration and an optical signaling circuit.

Description

The invention relates to a device for measuring and registering a short-circuit shock current in a distribution network for detecting the short-circuit current loads of the power systems of a power system.

Short-circuit currents arising from disturbances - in the distribution network - are stressed by power-current equipment in the power system. For example, in transformers, generators, compensators, reactors, a short-circuit current induces a mechanical shock that breaks the mechanical cohesion of the windings. The decisive factor for assessing the mechanical effects of short-circuit currents is the dynamic short-circuit current I _km , which, according to ČSN 38 0411, is defined as the peak value of the first amplitude of the short-circuit current when the largest possible DC component exists.

The current state of short-circuit failure registration in the power supply networks in the CSSR consists of the use of Osciloperturbograph, ie a recording device with an electromechanical recording system, adapted for recording fast events, which will capture the overall time course of short-circuit currents or overcurrents on registration paper.

A disadvantage of this short-circuit current detection device is the insufficient recording size, so that when reading the short-circuit short-circuit current 1 _km , large errors would occur. Oscilloperturbograph oscillates cannot practically be used to determine 1 _km . Even the devices according to the invention No. 172 203/1978 installed on power transformer units in the 400 kV-and 220 kV upstream network do not allow the determination of short-circuit surge current, as they only register overcurrent credits exceeding the set current levels of 2 Ifm, 4 lim and 6 µm.

Also, the sets of measured values of the operating status of the power network, often processed by the station or central computer, do not contain dynamic short-circuit current data. Knowledge of the absolute magnitude of the current surges, in particular the knowledge of the magnitude of the short-circuit current, is thus important for diagnosing the mechanical stresses of the power systems of the power system to assess the reliability of the gait and their service life.

Measuring and registration of the impactor _to the short circuit current I "allows a device for measuring the impact a- register circuit current according to the present invention.

Its essence is that it consists of three two-way rectifiers to which an analog-memory is connected, the output of which is connected via an electronic switch to a digital registration unit. The apparatus according to the invention further comprises a phase resolution unit connected to an analogue memory, a calibration source connected to the inputs of the two-way rectifiers, an optical signaling circuit connected to the digital registration unit and a control unit to which the electronic switch is connected. registration, unit-phase resolution -and optical signaling circuit. The main advantages of the device according to the invention are that the amplitude of the short-circuit current is measured with sufficient sensitivity and this value is stored in the digital registration unit for any time. The value of the inrush short-circuit current can be read out at any time on the digital display after the fault has ended.

The device according to the invention meets the following criteria:

- capturing the amplitude of the short-circuit current with both possibilities of short-circuit current unbalance, ie the DC component of positive or negative polarity;

- continuous measurement of the peak value of the short-circuit current separated in all phases R, S, T;

- registration of the first peak value of the short-circuit current in digital form without time limitation of the data retention period;

- the resolution of the phase whose surge short-circuit current is registered;

- digital output of measured data in direct BGD code for the possibility of - connection to a printer, event. computer (via interface) for further data processing;

—- optical signaling of the fault-induced recording;

- verification of the correct functioning of the device and its calibration by an installed calibration source generating a calibration pulse of 5 V, 1 ms;

- easy handling, easy reading of results, resistance to parasitic influences in the substation.

An exemplary embodiment of the device according to the invention is schematically depicted in FIG. Showing a block diagram of a device for measuring and registering a short-circuit current.

The device consists of three two-way rectifiers 1, an analogue memory 2, an electric switch 3, a digital registration unit 4, a control unit 5, a phase resolution unit 6, a calibration source 7 and an optical signaling circuit 8.

The operation of the device consists in continuously measuring the peak value of the current in phases R, S, T, the highest of which is stored for some time in analogue memory 2. Explosion depends on the discharge constant of the memory capacitor circuit of analogue memory 2, which is chosen to be as high as possible (in the order of tens of seconds).

The conversion of the data into permanent registration in digital form is performed either to the command voltage current, eg from protections (overcurrent, distance) to circuit breaker opening, or to the command of an internal comparator circuit set to a certain overcurrent level (1, 2 _µm ). The command voltage is triggered by the control circuit in the control unit 5 which, via the trigger circuits, ensures that the data from the analog: memory 2 is written to the digital registration unit 4.

The input of the two-way rectifiers 1 is supplied with a signal from the individual phases R, S, T supplying a heavy-current device, eg a power transformer. This signal in the form of a voltage is obtained from the load (load) of the current transformer to supply the current circuits of the protections (overcurrent, distance) Two-way rectifier: 1 AC voltage - proportional to current - rectifies linearly.

Two-way rectification ensures that maximum current amplitude is captured when the short-circuit current is unbalanced. The rectified, unfiltered voltage from the outputs of the two-way rectifiers 1 is fed to analog current amplitude memory 2, in which the highest amplitude selected from all three phases is continuously captured. The analog current amplitude memory 2 comprises a memory capacitor with charging and decoupling electronic circuits, guaranteeing a short charging time constant (approx. 50 µs) for the memory capacitor and a load discharge constant (approx. 20 s).

The DC voltage at the output of the analog memory 2, proportional to the highest amplitude of the short-circuit current, is connected by means of an electronic switch 3 to the digital registration unit 4. In the case of a functional sample of the device according to the invention, this is realized by a panel digital device M1 T240, product of the company ZPA Brno. Another digital meter with external control of the measuring cycle can be used.

Keying of the electronic switch 3 and writing to the memory of the digital registration unit 4 is performed by the control unit 5. This control unit 5 also controls the opening of the input to the logic circuits of the phase resolution unit 6. The phase resolution units of the β phase resolution by LEDs indicate in which phase the highest amplitude of the short-circuit current has been registered. In this case, it is assumed that for a given analog memory 2 connection there is a positive voltage (positive voltage pulse) at the output of the circuit belonging to one of the phases R, S, T which last charges the memory capacitor to the highest peak value.

The other outputs corresponding to the remaining phases with a lower short-circuit current value have a negative level. This logic network is used to capture this state, with R — S circuits for each phase and NAND gates connected to achieve the desired function. The input to the logic circuits of the phase resolution unit 6 is gated by the control unit 5. When a fault occurs (i.e., when a command voltage is triggered or a comparator circuit is applied), the signal path from the analog memory 2 to the phase resolution unit 6 is included, thus retaining the last fault state in the logical network, i.e. indicating the phase in short circuit current of the highest value.

Content Management Unit 5 is an Internal Comparison Circuit, Control R — S Circuits, and Triggered Mortarable Flip-Flops that Control the Function of Electronic Switch 3. You control the operation of the measurement cycle of Digital Registration Unit 4 (overwriting new short-circuit current values from the Digital Registration Unit 4), gate the input to the Θ phase resolution unit and control the operation of the optical signaling circuit 8.

The control R — S circuit is activated by the command voltage from the OP input to the command voltage connection, or by an internal comparator, acting on its “Set” input. When activated, the electronic switch 3 (for 1 s) is opened, the data from analogue memory 2 is transcribed to> the digital registration unit 4 (in 100 ms), the signal is blocked to the phase resolution unit 6 and the optical signaling circuit 8 starts. the last one until the control R — S circuit is turned back to the “wait state.” This is done manually via the RO input for manual control (ie the logic zero level is applied to the “Reset” R-S input).

By resetting to the "waiting state", the device is again ready to register a new value of the short-circuit current. The optical signaling circuit 8 controls the intermittent on and off of the digital registration unit 4 display. It is designed as an astable flip-flop with rectangular oscillations with a frequency of approximately 1 Hz. The circuit oscillates and the display turns on and off when the control unit R-S of the control unit 5 has been activated, ie when the value of the short-circuit current has been written.

The calibration source 7 generates a one-time manually triggered calibration pulse with a stabilized amplitude of 5 V and a duration of 1 ms. The impulse can be applied individually via a switch to the inputs of two-way rectifiers 1 of phases R, S, T. It is used to verify the correct function and to calibrate the equipment.

The device according to the invention is intended for measuring and registering a short-circuit current in a power distribution system. The data in digital form at the output of the digital registration unit 4 can be used as input data for the station computers in the substations of the master system for further processing.

Furthermore, the device can be used to measure the starting currents of an asynchronous motor, current surges during the operation of electric furnaces, etc. In general, the device allows to measure and register the peak value of single current or voltage pulses with a duration greater than 500 μβ.

Claims (3)

1. Equipment for the measurement and registration of surge short-circuit current in the electricity grid, consisting of three two-way rectifiers, an analogue memory, an electronic switch, a digital registration unit, a control unit, a phase resolution unit, a calibration source and an optical signaling circuit; the outputs of the two-way rectifier (1j) are connected to an analog memory input (2), while its output is connected via an electronic switch (3) to a digital registration unit (4) to which an optical signaling circuit (8j) is also connected. Device according to claim 1, characterized in that a phase resolution notation (6) is connected to the analogue memory (2) and an electronic switch (3), a digital registration unit (4), a unit (6) are connected to the control unit (5). ) phase resolution and circuit (8j optical signaling). Device according to Claims 1 and 2, characterized in that each of the three two-way rectifiers (1) for each phase (R), (S), (T) is equipped with an input (SP) for> proportional current signals and an input (KT) of the calibrating pulse to which the power supply (7) is connected, while the control unit (5) has an input (RO) for manual control and an input (UP) for connecting the command voltage.