GB2043971A - Voltage regulators - Google Patents

Abstract

A mains voltage regulator comprises a transformer having a primary winding (6) for energisation from the mains supply, and a secondary winding (7) for permanent connection in series with the load (1) supplied from the mains. When a requirement for regulation of the supply voltage is detected by supply voltage sensor (2), a switch (8) connected across the primary winding is opened. The effect of the transformer on the voltage supplied is neutralised by closing the switch to short out the primary when no requirement for regulation is indicated. <IMAGE>

Description

SPECIFICATIÓN Voltage regulators The present invention relates to voltage regulators and in particular to voltage regulators which may be used to compensate for variations in the voltage delivered to premises from a power main.

In many countries of the world the voltage supplied via the local utility company mains power distribution network varies widely about the rated voltage. This can cause equipment connected to the main to become inoperative with potentially disasterous consequences.

Voltage regulators are known in which a transformer primary is connected across the mains supply and the transformer secondary is connected in series with the load current path supplied from the regulator. Such a regulator can compensate for fairly wide voltage variations of for example 25%. The regulator is not required to operate however when the mains supply voltage is at or close to the rated voltage and therefore replay contacts are provided to short out the transformer secondary and to disconnected the transformer primary when regulation is not required. The problem with such an arrangement is that the contacts which are connected in parallel with the transformer secondary so as to short out this winding when voltage regulation is not required are required to switch the main load current passing from the regulator to the premises being served.This current can be very large, for example sixty amps or more, and therefore the contacts which switch the load current are prone to failure after repeated operation.

It is an object of the present invention to obviate or mitigate the problems associated with the known mains voltage regulators described above.

According to the present invention, there is provided a mains voltage regulator comprising a transformer having a primary winding for energisation from the mains supply, and a secondary winding for permanent connection in series with the load current path supplied from the mains, means for sensing the supplied voltage, means for indicating a requirement for regulation of the supplied voltage, and a switch connected across the primary winding, whereby the effect of the transformer on the voltage supplied may be neutralised by closing the said switch to short out the primary when no requirement for regulation is indicated.

Preferably further switches are provided for effectively reversing the connection of the primary to the supplied voltage so that the supplied voltage may be either increased or decreased by the voltage developed across the secondary.

The various switches may be either solid state or electromagnetic or a combination of the two.

The degree of voltage regulation may be adjusted either by providing a series of voltage regulators or by providing a plurality of tappings to the primary and switches to select the tapping to be energised to match the required voltage regulation.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic circuit diagram of an example of a voltage regulator in accordance with the prior art; and Fig. 2 is a schematic circuit diagram of an embodiment of the invention.

Referring to Fig. 1, a load 1 is shown supplied from the mains live L and neutral N. The voltage supplied is sensed by a circuit 2 which controls contacts 3 and 4 in response to the sensed voltage. A voltage regulator in the form of a transformer 5 is provided to compensate for variations in the voltage supplied. The transformer 5 has a primary winding 6 energised from the mains supply when switch 4 is closed and a secondary winding 7 connected in parallel with switch 3.

When the voltage supplied is within a predetermined range extending on either side of the nominal mains voltage, the circuit 2 maintains contacts 3 closed and contacts 4 open. If the supplied voltage falls below the predetermined range, contacts 4 close and contacts 3 open. The energised primary 6 then generates a voltage across the secondary 7 which is added to the voltage supplied, and the voltage across the load is thus increased.

The problem with the circuit of Fig. 1 is that, when contacts 3 are opened to enable regulation of the voltage applied to the load 1, the current being supplied to the load may be large and arcing can result. Therefore unless the contacts are designed to withstand such arcing, and this requires complex and expensive contact structures, the contacts will fail after repeated operation.

Referring now to Fig. 2, the problems associated with the prior art are overcome by dispensing with the contacts which have to switch load currents.

Components shown in Fig. 2 which correspond exactly to components of Fig. 1 carry like reference numerals and will not be described.

In place of the contacts 3 of Fig. 1, the invention provides contacts 8 in parallel with the primary 6 which may be closed to neutralize the effect of the transformer on the voltage supplied to the load 1. When regulation is required, contacts 4 are closed and contacts 8 are open.

The primary is then energised and the transformer operates in exactly the same way as that described in Fig. 1. When no regulation is required, contacts 4 are opened, thereby de energising primary 6. The effects of the transformer are neutralized by closing contacts 8 to short out winding 6. A voltage drop will occur across the-secondary 7 but this will be very low, for example one volt, and can therefore be discounted.

To enable the mains voltage to be either increased or decreased, ganged switches 9 and 10 enable the phase of the mains as applied to the primary 6 to be reversed. Furthermore, the degree of regulation may be controlled by selecting alternative primary winding taps (not shown), by suitable switching circuits.

The various switches may be solid state such as thyristors or electromagnetic as desired. None of the switches are required to switch large currents as was the case with the prior art.

Claims (4)

1. A mains voltage regulator comprising a transformer having a primary winding for energisation from the mains supply, and a secondary winding for permanent connection in series with the load current path supplied from the mains, means for sensing the supplied voltage, means for indicating a requirement for regulation of the supplied voltage, and a switch connected across the primary winding, whereby the effect of the transformer on the voltage supplied may be neutralised by closing the said switch to short out the primary when no requirement for regulation is indicated.

2. A mains voltage regulator according to claim 1, wherein further switches are provided for effectively reversing the connection of the primary to the supplied voltage so that the supplied voltage may be either increased or decreased by the voltage developed across the secondary.

3. A mains voltage regulator according to claim 1 or 2, comprising a plurality of tappings to the primary and switches to select the tapping to be energised to match the required voltage regulation.

4. A mains voltage regulator substantially as hereinbefore described with reference to the accompanying drawings.