SU1069055A1 - Method of releaving inrush of current of transformer magnetization - Google Patents

Abstract

A METHOD FOR DETECTING THE CURRENT OF MAGNETIZATION OF THE TRANSFORMER, which consists in determining the rate of current change over time, which is only due to the fact that, with the aim of increasing reliability and sensitivity, the transition times of the rate of current change through the zero value are measured, and the time intervals between adjacent transitions and the points are measured magnetizing current inrush if these durations differ from the half-period duration of the sawn frequency. about: oh ate

Description

The invention relates to a technique of relay protection of power systems, in particular, to the current protection of a transformer.

A known method of fixing the turn-on current of a power transformer at idle, according to which the current is twice differentiated according to the times, the current maximum time is calculated, the ratio of the second current derivative to its value is calculated for this moment, compared with the preset setting and judged about the desired mode, if found the relationship exceeds the setpoint C.

However, the method is difficult to implement.

The closest to the proposed technical entity is the method according to which the current is differentiated over time, sets the control level, measures the pause duration in the module of the first derivative at this level, compares it with the setpoint, and records the inrush current of the transformer if the pause duration exceeds setting C21. .

To reliably tune the differential relay using this method, the Conrol level at which psuzes are formed must be greater than the maximum amplitude of the negative current half-wave when transforming a unipolar inrush current by magnetizing current transformers. This requirement significantly degrades the sensitivity of the method. The method is not reliable enough, as it allows a failure at internal short circuit currents. large multiplicity due to the occurrence of long pauses in the signal, which forces to enter non-differential relays; dependent elements of the current cutoff, complicate it. Depending on the set level of control and the design mode, the setpoint may vary: within 1-2.5 times, which requires an increased range of adjustment of the setpoint and complicates the device implementing this method.

The aim of the invention is to increase the reliability and sensitivity of the method. I.

To achieve this goal, it is necessary to determine the inrush time of the transformer, fixing the moment of transition of the change in current time to zero, measure the time interval between adjacent sources and determine the inrush current in case of , if these durations are different from the half-period duration of the power frequency.

This method is based on the fact that for a short-circuit current. the intervals of the moment of change of the sign of the first derivative are strictly regular and equal to half the period of the industrial frequency; you're a protected electrical installation. For a surge of magnetizing current of any kind, the regularity of time intervals is violated, durations of less and more than half a period of industrial frequency alternate, which makes it possible to ascertain the inrush current of a power transformer.

FIG. 1 shows a functional diagram of a device implementing this method for detecting a surge of magnetizing current; in fig. 2 — oscillograms of signals at characteristic points for various modes (2 a, b — internal short circuit with a current of ordinary and large frequency ratio; 2 c — aperiodic inrush of magnetizing current with saturated current transformers; 2d periodic inrush of current and magnetization.

A device that implements this method contains a sensor 1 of the derivative of current over time, for example, a transreactor, a driver of 2 pulses, coinciding with transitions of the curve of the derivative of current through zero, a one-shot 3, a key 4, and an expander of 5 pulses.

The current sensor 1 performs the operation of differentiating the current, (curve b, FIG. 2), the former 2 determines the sign of the first derivative and. fixes the moments of its change, respectively, forming pulses, coinciding with transitions of the curve of the derivative of the current through the zero value (curve 7, figure 2). The key 4 performs the operation of comparing the interval / time arriving at its sample (setpoints b — measured by pulses of the one-vibrator 3 (curve 8, FIG. 2) and the actual time interval measured by shaper 2.

If the durations of the compared intervals coincide, the key 4 is opened at the moment of appearance of the pulse: at the output of the imaging unit 2, which is passed to the input of the expander 5 pulses and the latter is triggered (curve 9, figure 2). The single-vibration 3 is triggered by the puller of the -2. If they follow at intervals of less than half a period, the time-delayed one-time delay is reset before switching, and the counting starts again.

In the internal short-circuit modes. with a current of ordinary (Fig. 2a) or of a large multiplicity, transfused-immobilized saturated current transformers (ig.2b, the derivative module accepts various things;

Claims (1)

METHOD FOR DETECTING THE TRANSFORMER MAGNETIZATION THROWING CURRENT, which consists in determining the rate of change of current over time, characterized in that, in order to increase reliability and sensitivity, the moments of transition of the rate of change of current through a zero value are recorded, time intervals between adjacent junctions are measured and a current surge is detected magnetization if these durations differ from the duration of a half-period of industrial frequency. Figure 1 SU., „1069055