GB2115244A - Power supply means comprising impedance device for saving energy - Google Patents

Abstract

A first coil 20 is installed in a power line leading from an A.C. source to a load 14. A second coil 24 is inductively coupled to the first, and connected so that the induced EMF acts to increase the load current. Thus the current drawn from the source is reduced owing to the inductive load 20, but the energy lost thereby is largely recovered by the second coil. The assembly thus acts as a nearly lossless impedance. The first coil may have a plurality of taps 30 so that its inductance is variable. Thus fluorescent lights can be run with a voltage adjusted to be just sufficient to preserve ionisation, whereby much power is saved for a very small loss in illumination. The load 14 may alternatively be an incandescent lamp or an electric motor. <IMAGE>

Description

SPECIFICATION Power supply means comprising impedance device for saving energy The present invention relates to an electrical power supply arrangement which employs impedance to reduce the energy consumption. It particularly relates to an arrangement suitable for supplying power to electric discharge lights.

In one aspect the present invention provides a power supply means for connection between a source of A.C. or rectified A.C. power and a load, the means comprising first and second coils which are mutually inductively coupled, the first coil being in series with a power supply line to the load and the second coil being arranged to feed current induced therein to the load. The coils may be provided by a transformer, and at least the first said coil may have a plurality of selectable tappings for the series connection.

In another aspect the invention provides a method of operating an electrical device, comprising supplying the device with an A.C. or rectified A.C. power supply via a series-connected coil which is inductively coupled to a second coil, whereby a secondary voltage is induced in the second oil; and feeding the current produced by the induced voltage to the load.

It is, of course, well known to use a dropping resistor to limit the power supply to a load. However, this is very wasteful of energy, and is suitable only for low-power systems. The use of an inductive impedance would be less costly in terms of energy, but would still tend to dissipate a substantial amount.

Broadly, the present invention arises from the realisation that it is possible to use an inductive impedance coupled to a further coil which can be arranged effectively to "pick-up much of the energy dissipated by the impedance, and return it to the load circuit. Thus, in effect, an almost-lossless impedance is achieved. Such a device may be of wide utility, not restricted to its use in a simple mains power supply line.

Some preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Fig. lisa schematic circuit diagram showing a first embodiment of a power supply means according to the invention; Fig. 2 is a schematic circuit diagram showing a second embodiment; and Fig. 3 is a graph for use in explaining the application of the present invention to powering electric discharge lights.

The power supply means shown in Fig. 1 has a pair of power lines 10, 12 for connecting a load 14to the live and neutral terminals 16, 18 (respectively) of an AC mains source. The primary coil 20 of a transformer 22 is connected in series in the live line 10. The secondary coil 24 of the transformer 22 is connected across the live and neutral lines 10, 12, the connection to the live line 10 being between the live terminal 16 and the primary coil 20. Thus a circuit is formed containing the primary coil 20, the load 14, and the secondary coil 24. The coils are so connected that the voltage induced in the secondary coil acts to increase the current through the load.

The power supply means shown in Fig. 2 is very similar to the embodiment shown in Fig. 1, the only difference being that the transformer 22 is a variable transformer, having a plurality of taps 30 on the primary coil.

The operation of each of the illustrated embodiments will now be described, with reference to the Fig. 2 embodiment. To simplify the discussion, a power factor of unity will be assumed.

The voltage V5 of the A.C. mains source produces in the power lines 10,12 adjacent the terminals 16, 18 a current I,. The (alternating) current passing through the primary coil 20 of the transformer 22 induces a voltage in the secondary coil 24, which in turn causes a current Icto flow in the branch of the circuit containing the secondary coil. The current la and lc are additive, giving a larger current lb flowing through the primary coil 20 and the load 14. This current produces a voltage drop VL across the load 14.

Thus, the secondary coil 24 can be regarded as saving energy which would otherwise be merely wasted by the primary coil 20, and using it to supplement the current through the load so that a load current lb is created from a lesser current la drawn from the power source.

The power taken from the supply is given by Ps = Vs Ia I, volt-amps The power in the load is given by PL = V,.lb volt-amps In an ideal system Ps woul be equal to PL.

However, in real systems a small amount of energy is dissipated by the transformer system, so that PL is somewhat less than Ps. But by choosing the components properly, this loss can be kept quite low. For example, actual experiments gave the following results.

(A) In the absence of any current-reducing means, a supply voltage (Vs) of 240V led to a current through a load of 722 nA. Thus, Pus = Pal = 173.28 volt-amps.

(B) The embodiment shown in Fig. 2 was used, with the same supply and load as in example (A) above. The current drawn from the supply was found to be la = 597 mA. Thus, Pus = 143.28 volt-amps.

The reduction in power drawn from the supply is thus 30.00 volt-amps, i.e. 17.36%.

It was further found that lb = 647 mA; and VL = 217 volts.

Thus, PL = 140.40 volt-amps.

Power loss = Ps-PL = 2.88 volt-amps = 2.01% of power supplied.

Thus, the power supply to the load has been reduced by over 17% at a cost of only about 2% - an The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

efficiency of 98%. Efficiencies of the order of 94-98% can generally be expected - i.e. the high efficiencies achievable by transformers.

It can be calculated that if a similar reduction in load power PL were to be achieved using a simple inductive impedance, the reduction in the power Ps drawn from the source would be less than 10% (as compared with the saving of greater than 17% achieved in the present example). Still better results could be achieved by using a transformer designed especially for use under particular conditions.

The use of a variable transformer, as shown in Fig.

3, enables different degrees of power reduction to be achieved. The illustrated embodiments each employ a transformer whose primary coil is in the power supply line. Of course a transformer could be used the other way round (so that coils 20 and 24 would be the secondary and primary coils respectively). But this is not at present preferred, since it tends to yield a lesser efficiency and to require a larger transformer.

An energy-saving power supply means embodying the present invention can of course be used for many different types of load. However, it may be especially useful for a load comprising one or more electric discharge lights, such as fluorescent lights.

In general, such lights are run with a greater power dissipation than is necessary to maintain ionisation.

The excessive power is largely wasted as heat. Fig. 3 is a graph showing schematically the effect that varying the voltage across the load has on the power consumption (line 40), and the effective illumination (broken line 42). Thus, as the voltage is reduced from the normal value, the power consumption falls smoothly until a cricital voltage value is reached, at which it falls very rapidly before resuming a gradual descent. The sudden fall corresponding to the loss of the ionised condition of the gas in the discharge light which is requires for its normal operation. It can be seen that the effective illumination hardly falls at all over a range of several tens of volts, and suddenly falls to zero when normal ionisation is lost.Thus, the gap 44 between the power and illumination lines in the initial region of the graph indicates a saving in power which is potentially achievable for very little loss in effective illumination. It is thus potentially very worthwhile to use power supply means embodying the present invention to operate electric discharge lights in a voltage region where the gap 42 is substantial. If a system such as that shown in Fig. 2 is used, with a variable transformer, a suitable operating voltage can be chosen such that there is no danger of losing ionisation.

This form of power control can be very simple and effective. The apparatus can be cheap and reliable.

There are no elaborate electronic devices, and the operating principle is simple. it is applicable to a wide range of devices operated by A.C. current. Of course, when it is used with (e.g. motors or incandescent lights its function is to give a reduced output, with an almost equal reduction in input. In contrast, its special utility with discharge lights is to reduce the input without substantially reducing the output.

Claims (9)

1. A power supply means for connection between a source of A.C. or rectified A.C. power and a load, the means comprising first and second coils which are mutually inductively coupled, the first coil being in series with the power supply line to the load and the second coil being arranged to feed current induced therein to the load.

2. A power supply means according to claim 1 wherein the second coil is connected between (a) the power supply line leading to the first coil; and (b) the line for connecting the end of the load remote from the first coil to the power source.

3. A power supply means according to claim 1 or claim 2 wherein the coils are provided by a transformer.

4. A power supply means according to any preceding claim wherein the effective inductance of at least one of said coils is selectively variable.

5. A power supply means according to claim 4 wherein at least one of said coils has a plurality of selectable tappings for varying its inductance.

6. A power supply means substantially as described herein with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawing.

7. A method of operating an electrical device, comprising supplying the device with an A.C. or rectified A.C. power supply via a series-connected coil which is inductively coupled to a second coil, whereby a secondary voltage is induced in the second coil; and feeding the current produced by the induced voltage to the load.

8. A method according to claim 7 wherein the electrical device comprises one or more discharge lights.

9. A method of operating an electrical device substantially as herein described with reference to Fig. 1, Fig. 2, or either of these together with Fig. 3 of the accompanying drawing.