SU1513563A1 - Device for differential protection with braking - Google Patents

Abstract

The invention relates to electrical engineering and is intended for relay protection of generators, buses, transformers. The purpose of the invention is to increase the sensitivity of the device. The goal is achieved by the fact that the device uses two types of braking: for external damage - braking with arithmetic sum of shoulder currents, with internal and external with low frequency flowing currents - braking with arithmetic difference and geometric sum of arm currents. The transition from one type of braking to another is carried out automatically depending on the signal level of the external harmonics at the control input of the threshold element and the level of the differential current signal at the input of the threshold element. 2 Il.

Description

The invention relates to electrical engineering, in particular to relay protection, and can be used to protect electrical installation buses, generators, transformers and other electrical equipment.

The aim of the invention is to increase the sensitivity.

Figure 1 shows a block diagram of a device for differential protection with braking; in fig. 2 - dependences of the differential signal and the level of higher harmonics on the total error of current transformers (CT).

The device contains TT 1-3, the secondary windings of which are connected to the inputs of transducers 4-6 current-to-voltage, the outputs of which are connected to driver 7 of differential

a signal consisting of a series-connected adder 8 and a former 9 module, the formers 1012 brake circuit module, the outputs of which are connected to a former 13 of the brake signal, made in the form of an adder. To the entrance of the shaper

13 is also connected to the output of the inverter 14, whose input is connected via switch 15 to output 7. To the output of adder 8, a differential signal form control block 16 is connected, consisting of successively connected high-pass filter 17, module 18, and a threshold element. 19, the signal from output 7 being fed to the input of the threshold element 19, and the signal from the output of the module maker 18 is the threshold signal. Output threshold

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The Boro element 19 is connected to the control input of the key 15. The output of the imaging unit 13 is connected to the brake input of the reacting body 20, to the working input of which a signal is output from output 7 proportional to the differential current (Id).

The device works as follows.

The currents of the shoulders, taken from the secondary windings of TT 1-3 of the same phase, are transformed into proportional voltage with the help of 4-6 current-to-voltage converters. By the adder 8, the instantaneous values of the signals are summed. The sum (rectified by the differential current) rectified by shaper 9 module is applied to the working input of the reacting body 20 and acts in the direction of operation. The signal from the output of adder 8 is also fed to the input of block 16. Here, using a high-pass filter, a signal proportional to the level of high harmonics (G) is extracted. This signal is then rectified and multiplied by a constant factor (a) in the imaging unit 18. The signal from the output of modulator 18 (and C, where) is used as a variable threshold level of threshold element 19 and is compared in it with the differential signal (id) entering the input of threshold element 19 from output 7. The output signal of threshold element 19 appears when the condition that occurs with a short circuit outside the protected area. The signals from the outputs of the inverters 4-6 current - voltage through the formers 10-12 of the brake circuit module are fed to the inputs of the braking signal generator 13, to the input of which through the switch 15 also supplies a differential signal proportional to the geometric sum of shoulder currents Thus, at the output of the imaging unit 13, a brake signal is formed, which is either projectively either the arithmetic sum or the difference between the arithmetic and geometrical sum of the TOROB shoulders (depending on the position of the key 15), and is applied to the brake hydrochloric input react ordinating body 20, brake signal proportional to the difference of the arithmetic and geometric sum shoulders currents for faults within the protected zone

decreases dramatically, since in this case the differential signal (geometric sum) is high. However, the considered braking in the case of an external short-circuit is able to provide a build-up of protection only with small levels of TT error. Therefore, when operating TTs with significant errors, it is advisable to apply a brake signal proportional to the arithmetic sum of shoulder currents. It provides defensive protection in case of external short circuits, but it also remains in case of internal short circuits, which is undesirable because it reduces the sensitivity of the protection. Such braking should work only for tuning from external short circuits.

The transition from one type of braking to another is carried out as follows.

Claims (2)

To form a control signal, a variable threshold level is used, equal to G. The dependences II and G (mean values) on the total error () TT and for external and internal short circuits are shown in FIG. 2. Lines a and S illustrate the change in the differential signal (with external and internal short-circuits, respectively). The dependences of the level of higher harmonics F () with external and internal short circuits practically coincide and in Figure 2 are shown with one line & . Line g corresponds to the dependence a G () and is a variable threshold level, since it is located between lines a and 5 (when calibrating the axis of ordinates of FIG. 2, the voltage corresponding to the rated current of the protected object is taken as the basis, the figures correspond to the multiplicity short circuit current 1.0, with other multiplicities, the relative position of the lines does not change). Thus, it is possible to identify the location of a short circuit (inside or outside the protected area} within a wide range of possible TT errors with an accuracy sufficient to control the braking. In the case of an internal short circuit, braking is undesirable. A brake signal proportional to the difference of the arithmetic and geometric sum of the currents shoulders, dramatically reduces braking in case of an internal short-circuit.This corresponds to the area located above the threshold level (U.aG) .In external short-circuit conditions, the area below the threshold level () is a reasonable transition. for braking by the arithmetic sum of shoulder currents, which provide reliable deflection of protection in this mode, since it is possible to set the maximum braking coefficient. Such an embodiment of the device for differential protection with braking eliminates the inconsistency in providing selectivity and sensitivity, makes it possible to significantly increase the sensitivity protection, in which, depending on the degree of saturation of the CT and the location of the short circuit, automatically (due to the operation of the block 16 controlling the shape ialnogo signal and the key 15) is used to select the corresponding conductive braking signal supplied to the reacting body 20. The claims Device for differential protection with braking, containing current sensors designed to be installed at the ends of the protected object, the secondary windings of which through Q 5 0 five transformed current - voltage is connected to the inputs of the differential signal formation unit and through the drivers of the brake circuit module to the inputs of the brake signal formation unit, the first output of the unit that generates the differential signal is connected to the first input of the differential form control unit, and its second output is the working input of the control of its organ, the output of which is the output of the device, the output of the differential signal shape control unit is connected to the control input of the key element, differing In order to increase the sensitivity, an inverter was additionally introduced, connected to the second output of the differential signal generation unit. the control input of the differential signal shape control unit and, through a key element, the inverter input, the output of which is connected to the auxiliary input of the brake signal formation unit, the output of which is connected to the brake input of the reacting element. Off figure 1 u, (. 0.6. 0.9 / g 0.5 0.3 o20W60 ig.2 / N 80