SU805467A1 - Device for braking differential protection of transformer by the second harmonic of differential current - Google Patents

Description

(54) DEVICE FOR DIFFERENTIAL BRAKING. PROTECTION OF THE SECOND HARMONIC DIFFERENTIAL CURRENT TRANSFORMER

The invention relates to electrical engineering, in particular, to a relay protection technique and can be used to brake the differential protection of transformers or autotransformers with the second harmonic of the differential current.

Devices for braking differential protection are known, which contain an intermediate current transformer, the primary winding of which is included in the through current circuit of the protected transformer, and the secondary winding is connected via a rectifier to the input of the protective agent J

The closest to the proposed technical entity is an apparatus for braking the differential protection of a transformer with the second harmonic of the differential current, containing a transreactor, the primary winding of which is connected to the differential protection circuit, as well. the secondary winding is through a second harmonic filter, a rectifier with a smoothing capacitor at the output and a series-connected resistor connected to the brake input of the reactive protection body 2.

However, with short circuits accompanied by saturation of the current transformers installed on the protected object, the second current harmonic appears in the differential circuit, therefore the sensitivity of the protection containing this device for braking is reduced.

The aim of the invention is to increase the sensitivity of protection to short-circuits, accompanied by saturation of current transformers installed on the protected object.

Claims (2)

This goal is achieved in that a device for braking the differential protection of a transformer with a second harmonic of a differential current contains a transformer whose primary winding is connected to a differential protection circuit and the secondary winding through a second harmonic filter, a rectifier with a smoothing capacitor at the output and a series-connected resistor are connected to the brake input of the reactive body of protection / additionally introduced voltage limiting element, which is connected in parallel to the smooth ayuschemu capacitor. FIG. 1 shows a device diagram / in FIG. 2 - brake characteristics of the known and proposed device. The device contains a transformer 1 with a primary winding 2 connected to a differential protection circuit (not shown), with secondary coils 3 and 4, a reactive protection unit 5, a second harmonic filter, a regulator 7, a smoothing condenser. 8, limiting voltage element 9 (for example, Zener diode), resistor 10, brake input 11 of the reactive protection body. FIG. Figure 2 shows the deceleration characteristic 12 of this device and the deceleration characteristic brake 13. The ordinate axis in FIG. the multiplicity of the primary short-circuit current is plotted against the rated current of the protected transformer, and on the e-axis; bddc is the current error from the current transformer installed on the protected object. The device works in the following way. In the event of a short circuit, accompanied by the saturation of current transformers installed on the protected object, the differential current flowing through the primary winding 2 of transformer 1 induces proportional voltages 3 and 4 on the secondary windings. The signal from the winding 3 is fed to the working input of the reacting protection body 5, and the signal from the winding 4 to the brake input 11 of the specified organ through the second harmonic filter 6, the rectifier .7 and the resistor 10 / and this signal is smoothed by the capacitor 8 and is limited by the magnitude of the limiting-pitch element 8 .. The limitation of the brake signal leads to a change in the braking characteristic of the protection. The protection containing the known braking device is buried even with a relatively small current error of about 20% (feature 13 in FIG. 2). The protection containing this device for braking is deepened when the current transformers are saturated less (characteristic 12 in Fig. 2). Thus, when used in the differential protection of this device for braking, the sensitivity of the protection to short-circuits, accompanied by the saturation of current transformers installed on the object to be protected, is increased. Claims Device for braking the differential protection of a transformer with a second harmonic of a differential current, containing a transreactor, the primary winding of which is connected to a differential protection circuit, and the secondary winding through a second harmonic filter, a rectifier with a smoothing capacitor at the output and a series-connected resistor connected to the brake input of the reactant protection, characterized in that, in order to increase the sensitivity of the protection to short circuits, which are accompanied by current transformers installed on the protected object. It is additionally introduced with a voltage limiting element, which is connected in parallel to the smoothing capacitor. Sources of information taken into account in the examination 1. Fedoseev A. m. Relein protection of electrical systems. M., Energy, 1976, p. 323 fig. 6 and 12a, 2.Dmitrenko A.M. Differential protection of transformers and autotransformers, t Electricity, No. 2, 1975, p. 4, fig. four. m