SU1670733A1 - Device for current protection of ac electrical plant - Google Patents

Abstract

The invention relates to electrical engineering, in particular to relay protection of electrical installations against short-circuit currents. The purpose of the invention is to increase the reliability of work. The goal is achieved by connecting series-connected square pulse shapers and integrators to the outputs of the phase-turn link whose voltage at the output is shifted relative to each other by an angle of 90 degrees electrical degrees at the main frequency of the monitored signal. 3 il.

Description

The invention relates to electrical engineering, in particular to relay protection of electric power systems, and can be used as measuring organs of current line protection, transformers, generators and other elements.

The purpose of the invention is to increase the reliability of operation achieved by reducing the error and stability of operation at saturation of measuring current transformers, improving performance and reducing the time to return to the initial state.

Figure 1 shows the structural diagram of the device: figure 2 - timing diagrams of the device when the current is less than the setpoint current (figure 2, a) and when the current is greater than the current setpoint (figure 2.6); Fig. 3 shows the characteristic that determines the response current 1cp as a function of the current error f of the current transformers.

The device (Fig. 1) contains a current sensor 1, for a setpoint sensor 2, a phase shifter 3, consisting, for example, of a series-connected resistor 4 and a capacitor 5 with a grounded midpoint, square drivers 6.7, integrators 8.9, the adder 10, the threshold element 11 and the output element 12.

The phasic link can be performed by other schemes both on passive elements and using active elements.

A square pulse shaper in the general case may include an amplifier-limiter, frequency filters, and the shaper itself.

In the absence of current, the voltage at the output of the phase-turn link is zero, and the formers of the rectangular pulses, the integrators and the adder have a maximum negative value.

Consider the operation of the device under the following conditions 151usr (figure 2, a) and l lycip (figure 2,6). On figa.b

Yo

ABOUT

vj

WITH

with

Ca.

solid lines show the time diagrams corresponding to the steady-state process, and dashed lines show the initial short-circuit period.

In the first case (lЈl Iyer), the time of exceeding the set value by a signal (± UV) is equal to the time of exceeding (for a signal with a mains frequency (fc– 50 Hz, this corresponds to 0.005 s). Phase-turn link 3 causes the voltage Ue and U to be shifted by an angle equal to l / 2 (in this case another phase shift is possible.) In this case, the pulses exceeding one signal (Ue) coincide with the pulses not exceeding the other signal (U) and, therefore, at the output of the integrators 8 and 9, the maxima and minima of The summation of the signals Ua and Ug gives the output Open voltage is zero, not exceeding the trigger voltage of the threshold element 11.

When the condition is fulfilled (1 time to exceed the time not to exceed, which leads to the fact that the average voltage at the outputs of the integrators 8.9 has a constant component of a positive sign and, as a result, the same can be noted for the adder 10. Voltage at the output of the accumulator, Uyu exceeds the response voltage Ucp of the threshold element 11 and it triggers, which causes the appearance of a signal at the output of the output element.

The magnitude of the voltage fluctuations at the output of the adder 10 is less than the voltage fluctuations of the integrators 8.9, which makes it possible to reduce the return coefficient of the threshold organ 11 and, as a result, reduce the time for the measuring organ to return to its initial state after the conditions for triggering have disappeared. The return coefficient of this measuring unit can reach a value.

Consider the work of the measuring body in the initial period of the fault.

The appearance of positive pulses at the outputs of the formers 6 and g leads to a change in the output signals Ui and U g of integrators 8.9. In the first case, the voltage (Fig. 2.a) the voltage at the output of the adder g 10 does not reach the response voltage, and in the second case (Fig. 2,6), the voltage U io reaches the operation voltage.

The response time of the considered measuring unit (IO) is less susceptible to the inclusion phase. This position is confirmed by the diagrams on

-

Fig.2.6, when comparing them, for the measurement body in question with two integration channels and one integration channel. The trigger level of a single-channel IO threshold organ corresponds to

Ucpo voltage. In the first case, with well. left turn-on time

The IO with one channel is equal to the time of failure of tsi of the considered IO. At other phases of switching on, for example, / 2, which corresponds to the voltage Us, the response time t $ 3 is longer than the response time tsl.

5 The tripping voltage UCp is (0.1-0.2) Ucpo, which can be determined

Ucpo ivyhmaks lt / f.

where tn is the time of exceeding the specified level and equal to a quarter of the period of the frequency of the protected network; m is the time constant of integrator RS-chains 8.9; On the output of 5, the maximum value of the voltage at the output of the rectangular pulse shaper is 6.7,

The characteristic depicted in FIG. 3 illustrates a smaller dependency.

0 current of operation of this device (curve a) in comparison with the IO with one integration channel (curve /). At the same time, frequency (bandpass) filters were included in the composition of both EUT, and their absence results in

5 to an even greater difference between the characteristics. The tests also confirm the greater stability of the two-channel IO as compared to the one-channel IO, which is expressed in the constancy of the output signal as compared to the pulse signal of the latter.

Thus, introducing the phase-shifting link, the second integration integrator, the adder, in conjunction with other elements, I0 allows you to increase the reliability of its operation both by increasing the speed (reducing the response time and return), and improving the stability of operation during

0 saturation current measuring transformers.

Claims (1)

The device for current protection of an alternating current electrically operated electric generator 5 comprising a current sensor, to the secondary winding of which the setpoint adjuster inputs are connected in series with the first rectangular pulse shaper and the first integrator, the successively connected threshold element and output element of the last one The output of the device, characterized in that, in order to increase the reliability of operation, a phase-rotation link is additionally introduced; atel pulses, the second integrator and an adder, wherein the outputs the setpoint adjuster is connected to the entrances of the phaeo-rotary link, the first and second outputs of which are connected to the inputs of the first and second rectangular pulse shapers, respectively, the output of the first integrator is connected to the second input of the adder, the output of the adder is connected to the input of the threshold element. -Up Us Us uscpo U-, b u " Wow PTF  r - / and /, ii  Uio hc  Uh 1.0