SU99722A1 - Device to protect the secondary winding of the current transformer - Google Patents

Description

In case of accidental opening of the secondary circuit of current transformers, when current flows through the primary circuit, the secondary winding, depending on the device parameters, causes a more or less significant increase in voltage, sometimes reaching tens of kilovolts.

This phenomenon is dangerous both for service personnel and for the integrity of the insulation of windings and devices.

The prior art devices for protecting the secondary winding of a current transformer against overvoltages, for example, using an arrester, have the disadvantage that they short the secondary winding at any increase in voltage across the circuit, including the flow through the primary circuit. short circuit, and do not, therefore, the difference between the short circuit mode in the high voltage circuit and the mode of opening of the secondary windings. In addition, the gaiter acts only once and requires for its replacement in the case of a device shutdown.

In the proposed device for the protection of the secondary winding of a current transformer against overvoltages

when the secondary circuit is broken, containing, similarly to known devices, the winding relay of which is connected in series in the secondary circuit about the circuit and which, if the loop is broken, draws the current transformer winding with its contacts, the required selectivity, i.e. all modes except open loop secondary mode.

This is achieved by supplying the relay with a differential current winding connected to the auxiliary winding on the current transformer and creating in all modes except the open-circuit secondary circuit, a magnetizing flux equal in magnitude, and for direct transmission of the first winding of the relay, which ensures the relay is locked in the indicated modes and triggered when the circuit is broken.

The drawing shows a circuit diagram of the device.

The winding 2 of relay 3 is connected in series with the secondary winding 1 of the current transformer. The current transformer is provided with an additional winding 4 formed by one or several turns (depending on the requirements of calculation). The differential winding 5 of the relay 3 is connected to the additional winding 4 of the transformer through a resistance 6, which is of such magnitude that the total resistance of the circuit consisting of windings 4 and 5 and resistance 6. is equal to the resistance of the main secondary winding / transformer. Under this condition, under any mode of operation of the current transformer, the currents in the circuits of both windings of relay 3 will be the same.

Both windings 2 and 5 of relay 3 act on the same movable element of the relay, controlling the closing and opening of contacts 7, which in the closed position close the main secondary winding 1 of the current transformer to resistance 8.

If it is necessary that a current flow through the o-winding 5, which is equal in magnitude only to the part of the current flowing through the winding 2, then the resistance 9 is connected in parallel with the latter.

In all modes, a mode with an open secondary circuit, the differentially operating winding 5 of the relay creates a magnetizing force equal in magnitude and opposite in direction to the magnetizing force generated by the winding 2, resulting in a relay B.YuKiruyutsya.

When the secondary circuit is broken, the equality of the magnetizing forces created by the coils 2 and 5 of the relay is disturbed, and the latter is triggered by the contact 7 of the transformer secondary winding 1 to the resistance 8.

The resistance value 8 is determined by the minimum values of the currents in the primary and secondary circuits of the current transformer. In separate

In such cases, this can lead to an unacceptably large drop in voltage in a closed secondary value. In order to avoid this, a special contactor can be used, which is excited via contact 7 from the direct current circuit and further operating according to the “stickiness” scheme. In this case, the secondary winding / transformer resistance circuit, 8 will not be reflected at the voltage at the open ends, and protection will ensure any minimum wiring at the secondary value after it is closed from the relay at any fraction of the nominal value of the primary current (provided sufficient sensitivity of the relay).

The device can be supplemented with contacts that include acoustic and light signals, as well as contacts that short-circuit the ballast resistor 6, which reduces the resistance value 5.

The subject will invent and

Device for protection of the secondary winding of a current transformer against overvoltages. Breaking a secondary circuit containing a relay, which is connected in series to the secondary circuit, and which breaks the current transformer winding with its contacts, in order to ensure reliable operation the protected transformer, the mentioned relay is supplied with a differentially operating winding connected to an additional winding on the current transformer and creating it in all modes except regikim with a closed secondary circuit, the magnetizing force equal in magnitude, and in the direction opposite to the magnetizing force of the first winding, which blocks the relay at the specified modes and unlocks it when the secondary circuit is broken.

Secondary CRP l load / e.

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