SU1464242A1 - Low-voltage transformer with damage protection unit - Google Patents

Abstract

The invention relates to electrical engineering and can be used to protect low-voltage power transformers from damage. The purpose of the invention is to increase the sensitivity of protection to winding circuits in a transformer. When a small fraction of turns in transformer 1 is closed, the value of the current in the primary winding 2 is not sufficient for the operation of fuse 4. The flow of short circuit current heats the transformer 1 and triggers the newly introduced thermal relay, which by its closing contact 6 shunts part of the primary winding 2, which causes the increase in the current in it and the operation of the fuse 4. The number of shunted coils is selected from the conditions of the precise operation of the fuse 4 and the limiting current of the primary winding 2 to permissible level 1 il. about

Description

The invention relates to electrical engineering and can be used to protect low-voltage power transformers from damage.

The purpose of the invention is to increase the sensitivity of protection to coil circuits in a transformer.

The drawing shows a schematic diagram of a low voltage transformer with a damage protection unit.

In the drawing are indicated: N; - the total number of turns of the primary winding of the transformer; \ w - the number of turns of the shunt part of the primary winding; 1 | - current of the primary winding of the transformer; 1sh - current of the shunted part of the primary winding.

Low-voltage transformer 1 contains primary 2 and secondary 3 windings. The protection unit, made in the form of a fuse 4, is included in the power supply circuit of the primary winding 2 of the transformer having an intermediate tap 5. Parallel to the part of the turns (Nu) of the primary winding 2, make contact 6 of the thermal relay located in the immediate vicinity of the transformer windings (magnetic core) 1. The secondary winding 3 of the transformer has conclusions for connection to the load 7.

The transformer operates as follows.

In case of internal damage or damage in the load circuit 7, accompanied by the occurrence, in terms of the primary winding 2, of a current exceeding the operating current Tsr of the fuse 4, the latter, by burning, disconnects the transformer 1 from the mains.

When a small part of the turns of the primary or secondary winding is closed, the increase in the current B in the fuse circuit is insignificant and insufficient for the operation of the latter. The current flow in the closed part of the turns causes the windings and the magnetic circuit of the transformer to heat up 1. At a certain elevated, but still safe for the transformer, temperature value, a thermal relay is activated, closing part of the primary winding 2 with its contact. At the same time, an increase in the current of the primary winding causes the fuse 4 to trip and shut off transformer 1.

The number of 6 turns (Nin) of the primary winding shunted by the contact should be selected so that when they are closed, the current 11 is greater than the trip current Ps? fuse, but did not exceed the maximum permissible current for this winding 11.1. The current in the shunt part of the winding 1sh should also not exceed 1y. Thus, the initial conditions for

Niu have VIEW 1 (1) 1 j s / I ι .ц (2) lllisdl.'l. (3)

When accepting Nui / N’i ^ 0.5 from the condition of equal ampeo-turns.

(N1 — Цш) = 1ш · N.u, (4) written for the primary winding, if the load current of the transformer is neglected, Im ^ Ii follows and condition (3) is automatically satisfied when condition (2) is fulfilled.

From conditions (1) and (2) with allowance for ¹ ~ ⁽⁵⁾

Ν. ¹ Ν, where 1p. - the value of the nominal primary current of the primary winding of the transformer, receive the following conditions for choosing the number of shunt turns:

^J NH / N.,>0.5;

1 - D '111' / 11 ep <Nui / N 1 1 --- \ / 11n / 1] D. (6)

Thus, by switching on in parallel a part of the turns of the primary winding of the transformer, made with an intermediate tap, and the make contact of the thermal relay, an increase in the sensitivity of protection to coil circuits in the transformer is provided. The given conditions for choosing the number of shunted turns allow, when shorted, to limit the current in the primary winding to a value safe for the transformer, but sufficient for the fuse to trip.

Claims (1)

Claim A low-voltage transformer with a damage protection unit containing primary and secondary windings having terminals for connecting to the mains and the load, respectively, the damage protection unit is made in the form of a fuse included in the primary winding power supply circuit, characterized in that, in order to increase the sensitivity of protection to coil circuits in the transformer, parallel to the part of the turns of its primary winding, made with an intermediate tap, the closing contact of the thermal relay located close proximity to the windings (magnetic) transformer, the number of revolutions Nm shunted determined by the conditions L III / N I / ^ 0.5 AND 1 D'1; II / 1 I cf ίζΝ III / N) 1 —D 11P / 11D> where Νι is the number of turns of the primary winding; Ιρι is the rated current of the primary winding; Iв ·? - fuse trip current; - permissible value of the primary current.