SU754494A1 - Change-over switch of transformer being adjustable under load - Google Patents

Description

The invention relates to transformer and can be used for transformers with stepwise voltage regulation under load.

Known switching devices of transformers with RPN, in which resistors are used to protect against circulating currents in the switching circuit of the transformer branches. In the known devices containing a current-limiting resistor, the contactor is provided with contacts connected in a bridge circuit, in one of which diagonals the moving contacts of the voter are included. The current limiting resistor is connected in series with the contacts of the selector in one diagonal of the bridge, and the current interrupter is connected in the other diagonal [1].

A disadvantage of the known switch is the insufficient resource of the moving contacts.

The closest in technical essence to the present invention is a device for limiting the circulating current in a switch for an adjustable transformer, containing several arcuate contacts located around the circumference, lying 2

in the same plane and connected to the tapings of the transformer winding. A triple movable contact slides along these contacts, connected to the supply wire and rotated around the central geometric axis of the switch. The three contacts of the moving triple contact mechanically form one whole. In the known switch, the circulation current is limited by means of two bridge active resistances connected between the outermost contacts and the contact ring of the feed wire. In this switch, the value of the circulating current in the “bridge” position is determined by the emf value of the control stage and the resistance value of the two resistors. In this case, one of the extreme contacts switches the current equal to the difference between the load current and the circulation current, and the second one - the current equal to the sum of the load current and the circulation current. The average contact switches the current equal to the load current [2].

A disadvantage of the known device is the rapid wear of the contacts. The main factors affecting the wear of contacts, other than mechanical, are 757594

the rank of the switching current and the magnitude of the recovering voltage at the contacts. Switching unequal currents leads to uneven contact wear and premature failure of the switching device.

The purpose of the invention is to increase the resource by reducing the electrical contact of the switch.

This goal is achieved by the fact that in the switch of a transformer regulated under load, containing an adjusting winding, fixed contacts located around the circumference, a triple moving contact, two current-limiting resistors connected in series with extreme moving contacts and a current lead, between the moving contacts and their common connection point three alternating current EMF sources are connected in series, while the EMF source in the middle contact circuit is connected in accordance with the control winding, and the other two are opposite, the lead wire is connected to the middle moving contact.

FIG. Figure 1 shows schematically, in a single-phase version, the adjustable side of a transformer and the interconnection of a circulating current limiting device with it in normal mode and in the process of switching from one tap to another.

The device contains an unregulated winding 1, an adjustable winding 2, fixed contacts 3 switches, movable, mechanically forming a single whole, contacts 4, current-limiting resistors 5, sources 6 EMF, lead wire 7. Sources EMF can be made in the form of three separate windings, wound on an adjustable transformer magnetic circuit. In this case, the number of turns of each of the three additional windings should be equal to one-fourth of the number of turns of the control stage of the transformer's control winding. Separate transformers with the corresponding secondary voltage can also be used as sources of EMF. In this case, it is possible to use both three double-winding transformers, and one transformer with three secondary windings.

The device works as follows.

In the normal long-term mode (Fig. 1a, h) the lead-through wire 7 is connected through the movable and fixed contacts of the switch directly to the tap of the transformer, the current through the windings of the sources of EMF does not leak and there are no additional losses. In the process of switching when closing the lower movable contact 4 with a stationary (Fig. 16) in the resulting circuit, the total emf of two sources, equal to half the emf of the control stage, acts. The circulation current caused by it is limited to the nominal active current-limiting resistance 5, included in the lower arm of the bridge. In this position, a current flowing through the middle moving contact is equal to the difference between the load current and the circulation current, which is zero at the nominal load of the transformer. Through the bottom of the movable contact in this position flows a circulation current equal to the rated current of the transformer.

When the average moving contact is opened with a fixed one (Fig. 1c), a current that does not exceed the nominal value is switched. This current is zero at the rated load of the transformer and the rated value at idle. In this position, the same current-limiting resistance as in known devices is connected in series with the load.

When the upper moving contact 4 is closed with the next tap-off (Fig. 1e), the total emf of the control stage and two sources, equal to half of the emf of the control stage, also act in the resulting circuit. The circulation current caused by it is limited by two current-limiting resistances and is equal to half the nominal value. In this case, a current flowing through the upper movable contact is equal to the sum of half the load current and the circulation current, i.e. The maximum value of this current can reach the rated value (at rated load of the transformer). A differential current of half the load current and the circulation current flows through the lower moving contact.

When opening the lower movable contact 4 (Fig. 1 <?) The current is switched, the maximum value of which is half the nominal.

With the closure of the average moving contact 4 with the next tap-off (Fig. 1g) in the resulting circuit, the total emf of the two sources is equal to zero, since in this circuit the equal emf is switched on. In this case, no current flows through the upper moving contact, and a current equal to the load current flows through the middle contact.

When the upper contact 4 is opened (Fig. 1h), a current of almost zero is switched.

When switching back from position z to position a, only the sequence of switching of currents by moving contacts changes.

In the process of closing the contacts, the maximum potential difference between them,

those. the magnitude of the recovery voltage can reach only half of the EMF

steps of regulation.

five

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Thus, in the switching process, none of the three moving contacts commutes a current exceeding the nominal value of the load current, and on one of them the value of the recovering voltage does not exceed half of the EMF of the control level.

The electrical wear of the switch contacts with the proposed device for limiting circulation currents with a transformer load close to the nominal value decreases by almost an order of magnitude. ^ten

Claims (1)

Claim Switch ₁₅ controlled by HA Booting transformer comprising adjusting winding, fixed contacts disposed in a circle, triple movable contact, the two current-limiting resistor in series with the extreme movable contacts and the collector wire, characterized in that in order to increase the service life by decreasing elektroiznosa contacts of the switch, between the moving contacts and their common connection point, are connected in series three sources of alternating current EMF, while the source E DS in the circuit of the middle contact is included in accordance with the adjustment winding, and the other two are opposite, the lead wire is connected to the middle movable contact.