SU48798A1 - Device for detecting grounding in cables - Google Patents

Description

Small cable networks, powered by generators or transformers, the neutral of which is not grounded, are quite numerous. These networks include, for example, the station's own consumption network. Grounding one of the cores of the cable of such a network, if left unnoticed, may develop into an accident. There are several ways to detect damaged cables. One of the devices for this purpose, which provides for damage signaling, consists of a Ferranti-type transformer, which is worn on a controlled cable and connected to a reactive power relay. In case of grounding of one of the conductors and the occurrence of grounding current, the geometric sum of the currents in the cable will cease to be equal to zero, and the secondary winding of the transformer generates a current that will trigger the relay. A disadvantage of this device is the presence of a sinus relay, which is a complex imported device.

The purpose of the present invention is to replace a sine-wave relay with a conventional active power relay. For this, a large resistance is introduced into the secondary circuit of the transformer, for example, in the form of a tube amplifier. Due to this inclusion, the amplified secondary current appears in quadrature with the primary current, which allows the use of

with the same effect active power relay.

In the attached drawing of FIG. 1 shows a schematic diagram of the proposed device, and FIG. Option 2: Grounding the cable sheath to eliminate stray currents.

The cable I, which received a short circuit to earth (Fig. 1), is equipped with a Farranti transformer 2 transformer, whose toric winding 3 is closed to a rectifier and an amplifier 5. The amplifier feeds power from the windings of an RS-6 wattmeter, the second winding is connected to transformer 7. Funnel The cable is grounded by a conductor 4 passing inside the frame 2 to compensate for the effect of parasitic currents in the cable jacket.

In contrast to the normal operation of any current transformer operating with a secondary winding closed for low resistance, in the proposed device the Ferranti transformer operates as if with an open secondary winding using only magnetizing current. The voltage from the transformer is applied to the grid of the lamp of the first stage of the two-stage amplifier. The variable component of the anode current of the second stage amplifier will be in phase with the voltage applied to the grid of the first stage. Thus, the amplified ground current will be shifted relative to the primary

 The voltage used to power the relay 6 is the „zero voltage, obtained by one of the known methods from a voltage transformer. Since the zero voltage is shifted when it is shorted to earth with respect to the zero current, the zero current after the amplifier will be in phase with zero voltage. This makes it possible to use as ground relays not sinus wattmeter imported high sensitivity relays, but simple coarse active cosine wattmeters with a zero in the middle or wattmeter cosine relays.

To eliminate the interfering influence of stray alternating currents flowing into the ground through grounding at the funnel, the grounding wire of the cable funnel,

as shown in FIG. 1, is missed inside the transformer frame, or in FIG. The grounding of the cable sheaths is made below the Ferranti transformer.

The subject matter of the invention. A device for detecting grounding in cables from a current transformer, the primary winding of which is the cable under test, and the secondary winding is closed to an indicator or relay triggered when the cable is grounded when the geometric sum of the currents in it is different from zero

Quadrature m / "DU- °" "; P j;, ° the sum of the currents in the cable and the voltage on the secondary winding of the transformer last closed on most active resistance, for example, on the input resistance of the lamp amplifier.

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