SU1490697A1 - Device for differential protection of electrical installations - Google Patents

Abstract

The invention relates to electrical engineering, namely, relay protection, and is intended for differential protection of an electrical installation. The purpose of the invention is to increase reliability and sensitivity with overloaded current transformers. The goal is achieved by the fact that the device for differential protection is triggered when the signal from the output of working unit 5 is greater than the signal of the brake unit 8. 2 Il

Description

figure 1

314

The invention relates to power engineering and is intended for the implementation of the differential current protection of busbars of power stations and substations, generators, transformers, engines.

The purpose of the invention is to increase the reliability and sensitivity of the differential protection under overloaded current transformers.

FIG. 1 shows a block diagram of the device; in fig. 2 - voltage and current diagrams.

The device consists of current sensors 1, connected at the ends of the protected object 2, transreactor 3, loaded on active resistance 4, operating signal generation unit 5, which contains rectifier 6 connected in series, and smoothing circuit 7, brake inhibitor forming unit 8, which starts connected rectifying diode 9, delayed link 10, analog multiplier 11, integrator 12, block 13 of sampling and storage, as well as differentiating link 14, shaper outputs are connected to block 15 connected with the threshold authority 16.

The device works as follows.

The working signal shaping unit generates a signal proportional to the average value of the derivative of the differential current. The voltage at the output of the brake signal formation unit is proportional to the autocorrelation function of the derivative of the differential current, i.e.

differential

and K i i (t); 0 in

output time lag

t) d

Where

the delayed link 10 compared to the input; i and the derivative of the differential current; K - coefficient. The delayed link provides a delay of the harmonic signal at the angle of el.

The brake signal generation unit calculates the autocorrelation characteristic at the input signal ramp-up. At the moment of the transition of this curve, through its maximum value, the derivative becomes negative and the sampling and storage unit 18 goes into storage mode.

and does not respond to the input signal.

In the event of internal damage in the differential circuit, a practically sinusoidal current iq flows. The aperiodic component of the short-circuit current is filtered out by the trans-reactor 3, so the voltage at the output of the trans-reactor 3 is also a sinusoidal function (Fig. 2a).

The signals at the outputs of the delayed link 10, analog multiplier 11 and integrator 12, respectively

0

five

0

five

0

five

0

and

ten

one

and

and

 k / i (u) t - tf);

 K / i (Wt) X i (wt - tf) /;

  i () i (wt -if) / dt.

The signal at the output of the sampling and storage unit with a positive derivative of the input repeats the input signal. cash L i. works in sampling mode. At the moment of in sign change, the input signal is memorized, which takes the maximum value at this moment.

This signal remains unchanged in the absence of a positive signal at the control input of the sampling and storage unit. The signal at the output of block 5, the formation of

signal s i - in turns out to be more

about

signal at the output of the brake signal formation unit (). At the same time, a signal appears at the output of the comparator unit 15, which leads to the triggering of the threshold organ 16 with a small delay (2-3 ms).

With external damage, the current in the differential circuit appears only when the magnetic core of the current transformer itself is loaded, and the current form is non-sinusoidal. Therefore, the area under the differential current curve decreases, and therefore the average value of the current decreases. Front edge

ABOUT

increases more steeply (as the rise time decreases), so the autocorrelation function exceeds the mean value, i.e. Consequently, there is no signal at the output of the comparison unit 15 and the threshold organ 16 does not work.

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Claims (1)

SUMMARY OF THE INVENTION A device for differential protection of an electrical installation, comprising current sensors for installation at the ends of the protected object, the secondary windings of which are connected according to the circuit for current circulation, the output of which is equipped with a transformer loaded with active resistance, the inputs of the brake units connected in parallel and connected to the secondary winding of the transreactor are connected working signals, the outputs of which are connected to the inputs of the comparison unit, connected in series with the threshold element, the output of the latter is I output device, characterized in that, in order to increase reliability and sensitivity in the congested current transformers, the braking signal generating unit ^{5 is} arranged in series-connected diode vtstse ,; delayed link, analog multiplier, integrator, sampling and storage unit, the output of the latter is the output of the brake unit, differentiating link, the input of which is connected to the cathode of the diode, and the output with the control input of the sampling and storage unit, _{15 the} second input of the analog multiplier is also connected to the cathode of the diode whose anode is the input of the brake unit.