RU2258993C2 - Phase-failure protective device for three-phase load - Google Patents

Abstract

FIELD: electrical engineering; electric drives.

SUBSTANCE: proposed device has three delta-connected primary windings of current transformer inserted in series with neutral point of load. Transformer secondary winding is connected to relay. Novelty is use of protective disconnecting device for the purpose.

EFFECT: simplified design, enhanced reliability.

1 cl, 3 dwg

Description

The invention relates to the field of electrical engineering and can be used, in particular, in an electric drive.

The closest in technical essence and the achieved results is a device [1], containing a current transformer, the primary winding of which is included in the load circuit, and the secondary is connected to the relay. The disadvantage of this device is the complexity due to the need to use three current transformers.

The aim of the invention is to simplify.

This goal is achieved due to the fact that the current transformer is additionally equipped with two primary windings, and these three windings are connected in a triangle, the terminals of the vertices of which are connected to the terminal terminals of the loads.

An additional difference is that a three-phase residual current device is used as a current transformer and relay.

Figure 1 and 2 presents a diagram of devices.

The load 1 ends of the conclusions connected to the primary windings 2 of the current transformer. The windings 2 are located on a common magnetic circuit 3 and are connected in a triangle. The secondary winding 4 of the transformer is connected to relay 5.

Figure 2, the current transformer contains in the circuit of the primary windings 2 contacts 6 of the relay 5. In addition, the relay contains a drive 7 with a trip mechanism. All nodes, marked with numbers 2-6, form the so-called residual current device (RCD).

The device operates as follows.

In normal mode, currents flow through all three phases of load 1. These currents are evenly distributed between the windings 2 of the current transformer. In the secondary winding 4, there is no current, and relay 5 is not turned on. When one of the phases of the network or load breaks, current flows through all three windings. The equivalent circuit of the winding circuits is shown in Fig.3. As you can see, due to the presence of contact resistance of the contacts in the circuit of the two windings, the current distribution between the parallel circuits will not be correlated as 2: 1. An imbalance of currents and magneto-driving forces of the current transformer will appear. A current will appear in winding 4, and relay 5 will trip, signaling a malfunction.

In Fig.2, the flow of processes is similar. But when relay 5 is activated, contacts 6 open and load 1 is disconnected from the network. Manual drive 7 is used to turn on the RCD.

Thus, the protection function is implemented by a minimum number of transformers and relays, which increases reliability and simplifies the device.

Sourse of information

1. Kolesnikov EB Three-phase motor protection device from emergency mode. USSR copyright certificate No. 1098059. Published "Bulletin of inventions" 1984, No. 22.

Claims (1)

A device for protecting a three-phase load from phase failure, containing a current transformer, the primary winding of which is included in the load circuit, and the secondary is connected to a relay, characterized in that the current transformer is equipped with two additional primary windings, and these three windings are connected in a triangle, the ends of the vertices of which connected to the terminal outputs of the loads, and when the above relay is activated, the contacts open and the load is disconnected from the network.

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