CONTROL SYSTEM FOR ELECTRICAL LIGHTING

Abstract: A control system for lighting a bank of fluorescent lamps, includes input terminals (10, 11) for mains voltage and output terminals (20, 21) to which the bank of lamps is connected. A transformer (T1) provides a reduced voltage (216V) as compared with the mains supply voltage (240V). The transformer (T2) provides a supplementary voltage (24V). Upon start up of the circuit, a control circuit (CC) operates contact (A1) to energise the transformer (T2) so that terminals (20, 21) receive both the reduced voltage from (T1) and the supplementary voltage from (T2) (i.e. 240V) which is sufficient to strike the fluorescent lamps. The control circuit (CC), after a predetermined delay e.g. 15 seconds, switches (A1) to disconnect the supplementary voltage from (T2). The lamps then continue to operate on the reduced voltage (216V) thereby reducing the power consumed by the lamps.

Description: - 1 - CONTROL SYSTEM FOR ELECTRICAL LIGHTING FIELD OF THE INVENTION This invention relates to a control system for electrical lighting, having particular but not exclusive application to fluorescent lighting configurations in large office blocks for example. BACKGROUND TO THE INVENTION With the cost of electricity being an important factor in operating lighting systems, especially on a large scale, there is a need to seek ways of reducing power consumption , to provide improved economy. This is especially true of the fluorescent lighting configurations found in large office blocks and other industrial premises. It has been found possible to reduce the voltage supply to lights without producing a noticeable drop in light output and it has been proposed to achieve this by means of a transformer in order to give a power reduction to the system. With fluorescent lamps, in order to ensure reliable striking on switching on, it - 2 - is however necessary to provide the full rated mains voltage at the time of switch on. To achieve this, it would in theory be possible to provide a transformed output during normal running of the lamps, but at start up, the transformer would be switched out and full mains voltage directly applied to the lamps. A major problem with such a configuration, especially with banks of lamps, is the power surge that is generated. A lOkva transformer for a bank of up to 200 lamps when switched, could generate a surge of the order of 400 amps, which among other tfiings ' would rapidly degrade the switching contacts employed and be unreliable in use, r SUMMARY OF THE INVENTION The present invention is concerned with power reduction without the drawbacks mentioned. According to the invention there is provided a control system for lighting comprising, means for providing a reduced voltage below normal mains voltage for the lighting to provide a reduced power output during operation thereof, means for providing a supplementary voltage when initially operating the lighting to - 3 - increment the reduced voltage to a value appoximating to normal mains voltage and means for thereafter removing the supplementary voltage. The means for providing a reduced voltage may comprise means providing a first transformer winding and the means for providing the supplementary voltage may comprise means providing a second transformer winding. Conveniently, the reduced voltage is provided by a first transformer and the supplementary voltage is provided by a second transformer^ Alternatively " , said voltage providing means may both be provided in the same transformer. The means for removing the supplementary voltage preferably includes timer means for removing the voltage after a predetermined period. The timer means may be triggered by current sensing means which senses current demand in the lighting system associated with switching on of the lamps. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully understood, embodiments thereof will now be described - 4. - by way of example with reference to the accompanying drawings wherein: Figure 1 is a block diagram of an embodiment of the invention; Figure 2 is a circuit diagram of a first example of a control system of the invention according to the embodiment of Figure 1; Figure 3 is a circuit diagram of a second example of a control system of the invention according to the embodiment of Figure 1; Figure _4 is a block diagram of a control circuit CC shown in Figure 3; Figure 5 illustrates wave forms developed in the r detector circuit of Figure 4; and Figure 6 is a block diagram of another embodiment of a control system according to the invention. DETAILED DESCRIPTION The first embodiment of the invention described with reference to Figure 1, comprises a control system for supplying electrical power to fluorescent lamps, the supply being switched between a level approximating to mains voltage at turn on of the lamps, to a reduced - 5 - voltage level which does not produce a noticeable drop in illumination but which provides a substantial improvement in economy. The system is described for use with a UK mains supply at 240 volts but it will be readily appreciated that the system can be adapted for use with other mains voltage supplies e.g. 110 volts. Mains voltage at full rating, i.e. 240 volts is provided at terminals 10, 11 and an Output for supply to a bank of fluorescent lamps (not shown) is provided at terminals 20, 21. A first transformer Tl in the form of an auto-transformer has winding tappings Wl, W2 connected across the mains voltage supply terminals 10, 11. The transformer Tl also has an output tapping W3 which provides a voltage less than mains voltage e.g. 216 volts which is supplied to the output terminals 20, 21. A second, step-down transformer T2 has its primary winding tappings W4, W5 connectible to the mains supply terminals 10, 11 through a changeover switch _ contact Al. The secondary winding tappings W6, W7 are connected in series with output terminals 20 and the tapping W3. A control circuit CC, shown schematically - 6 - in Figure 1, controls operation of changeover contact Al. In a first position of Al the transformer T2 is connected to provide a voltage in its secondary which increments the reduced voltage produced by transformer Tl, so as to provide an output voltage at terminals 20, 21 which closely approximates full mains voltage. When the control circuit CC operates changeover switch Al away from the position shown in Figure 1, the terminals W4, W5 of the primary of T2 are effectively short circuited such that T2 no longer produces the supplementary voltage and also does not impede current flow from Tl to the output terminals 20, 21. As will be desribed in more detail hereinafter, the control circuit CC is so arranged that upon start-up of the lamps, switch Al is in the position shown in Figure 1 so that a voltage approximating to mains voltage is produced at terminals 20, 21, to enable switch on of the lamps. A short period thereafter, e.g. fifteen seconds, the control circuit CC switches Al to the other position so as to disable operation of transformer T2 and thereby reduce the voltage supplied to the lamps by approximately 10% of normal mains voltage. _ 7 _ A more detailed example of the arrangement of Figure 1 will now be described with reference to Figure 2 in which the function of the control circuit CC is performed by a timer. Like parts to those in Figure I have- een given the same reference numbers. Thus the mains supply voltage is supplied through terminals 10, 11 to the transformer Tl via normally closed contacts CB1 and CB2 of a circuit . breaker CB. The tapped output W3 of Tl is fed through the secondary winding of T2 and thence through normally closed contact CB3 of circuit breaker CB. Th*e contact Al which controls operation of transformer T2, is operated by contactor coil A, which has a further contact A2 that switches power to a neon LI to signify when "mains-boost" is being provided by transformer T2. The primary winding of transformer T2 has capacitors Cll and C12 connected to the live and neutral rails respectively to suppress switching transients produced by operation of contact Al. Operation of the contactor A is controlled by a relay 22 having a control coil C, a timer module 22a and an actuator switch 22b of known - 8 - configuration. The coil C controls operation of changeover contact Cl, which in the position shown in Figure 2 supplies current to the contactor A and in its other position energises neon L2 that indicates that the system is running in "economy mode". A further relay B is provided which operates contact Bl that switches power to a contactor having a coil D which operates contact Dl. Also, the relay B operates contact B2 in order to switch voltage to neon L3. The control system shown operates as follows. When it is desired to operate the lamps, power is initially connected to 'the terminals 10, 11 by switching circuits (not shown) . The user will then actuate switch 22b which causes the relay to be released for a period .determined by the timer module 22b so that contact Cl moves into the position shown in Figure 2. Consequently, the "economy mode" neon L2 is switched off. Contactor coil A is energised and its contacts Al and A2 are moved into the positions shown in the Figure. The closure of A2 causes "mains boost" neon LI to be illuminated. The _ 9 - - . switching of Al causes the primary of transformer T2 to " be connected across the mains .rails. This allows the supplementary voltage from transformer T2 together with the output from transformer Tl to be applied to the fluorescent lamps connected to terminals 20, 21. The output from transformer Tl is typically 216 volts and transformer T2 provides a supplementary voltage of approximately 24 volts to give a full 240 volts mains requirement. The timer module 22a is set to give sufficient time for the lamps to strike using their associated starters, before timing out (e.g. 15 seconds) . Thereafter, the relay 22 is actuated to cause contact Cl to move to the alternative position to that shown in Figure 2, so that contactor coil A is de-energised, causing contact Al to move to the alternative position so that the primary winding of T2 is disconnected from terminal 10 and effectively short circuited to prevent any unwanted power losses. Contact A2 switches off neon LI. Capacitors Cll, C12 suppress any unwanted spikes resulting from switching of Al. With contact Al in this position, no supplementary voltage is produced by the secondary of T2 and the output at terminals 20 - 10 - and 21 is provided solely by the transformer Tl i.e. 216 volts. As the output is taken through the secondary of transformer T2, the transformer is wound so as to provide a low impedance path to minimise losses. The system will provide power at this reduced voltage continuously thereafter to give the desired saving in power consumption. Should the system become overloaded, the circuit breaker CB having a rating of say 50 amps will actuate causing contacts CB1 - CB3 to open. This isolates transformer Tl from the input and output terminals 10, 11 and 20, 21 and will effectively isolate transformer T2. Opening of CB1 and CB2 will also de-energise relay B so that contacts Bl and B2 will close. Neon L3 will light due to the closure of B2 so as to signify the overload condition. The closure of contact Bl causes contactor D to energise which closes contact Dl thereby providing a direct connection between terminals 10 and 20, bypassing the control system to prevent damage thereto and to permit the system to continue to operate. Should the overload be due to a fault - 11 - condition, fuses (not shown) associated- with the lamps would blow in the normal way. Neons L4, L5 indicate when the primary and secondary sides of the transformer Tl are energised; both neons will be actuated in normal operation of the circuit. It will appreciated that other values for the reduced and supplementary voltages could be selected. However with the values used in the example described with reference to Figure 2, it has been found that with a wattmeter fitted, tests have indicated a saving in the region of 20% of the power consumed for a negligible loss in light output. By switching only the supplementary power in the manner described, it has been possible to reduce dramatically the power rating of the contact (Al) needed. For example a 20 kva system can be handled with a contact rating of only 10 amps without the deterioration associated with switching large loads. - 12 - Referring now to Figure 3, another example of the arrangement of Figure 1 is described in more detail. In the circuit of Figure 3, the control circuit CC comprises a circuit arrangement 23 which utilises a current sensor 24 that senses pulses in current supplied through the output terminal 20. It has been appreciated that when the lamps are switched on, there is an initial current surge. The detector 24 comprises a transformer coil formed around the lead to terminal 20, which has induced therein a current pulse in response to the current surge, produced by switch on of the lamps. " The induced current pulse is used to trigger circuit 23 so as to cause operation of a low voltage relay C which actuates Cl and hence Al in the manner previously described, in order to provide to output terminal 20 - a voltage approximating to mains voltage, which comprises the reduced voltage from transformer Tl together with the supplemental voltage from transformer T2. After a predetermined period defined by a timer in circuit 23, the supplementary voltage from transformer T2 is switched off. The details of the control circuit 23 will now be described in more detail w th reference to Figure 4. Mains input from terminals 10, 11 is applied to lines 25, 26, the waveform being shown in Figure 5A, and hence to an Integrated power supply circuit 27 which produces a 24 volts supply for the coil of relay C. The current sensing transformer 24 is connected to an integrated current sensing circuit 28 which is adapted to produce an output pulse on line 29 when the current transformer 24 detects that the current ' supplied through output terminal 20 (Figure 3) rises by more than a predetermined amount, over a predetermined current range. For example, the circuit 28 may be arranged to detect rapid current rises in excess of of 2.5 amps over a range of 0 to 80 amps. The circuit does not respond to a fall in current so as to avoid spurious triggering. ' An output pulse on line 29 triggers an integrated circuit programmable timer 30 which produces on line 31 a logical "1" output for the duration of its timing period, shown in Figure 5C. This period controls the duration for which the supplementary voltage from transformer T2 is supplied. A control logic circuit 32 is provided with a time base signal derived by a zero crossing detector circuit 33 which produces a pulse for each zero crossing of the ac mains supply, as shown in Figure 5B. The logic circuit 32 thus switches current through the coil of relay C for a - 14 - period shown in Figure 5D and defined by a predetermined number of half cycles of the ac wave form (as detected by detector 33) during which the timer 30 provides its logical "1" output. Referring again to Figure 3, when coil C is energised, contact Cl causes contactor A to be energised so that contact Al assumes the position shown in Figure 3 thereby producing an output voltage at terminals 20, 21 comprising both the reduced voltage from Tl and the supplementary voltage from T-2-. A-t- the end of the time period, coil C is de-energised and the supplementary voltage from transformer T2 is disconnected. In practice, the mains supply voltage may vary substantially and reductions of 10% or more may occur during periods of peak demand. This reduction may itself reduce the value of the voltage produced by transformer Tl to a level at which a noticeable reduction in light emission from the lamps may occur or, in the case of fluorescent lamps, .may result in them becoming extinguished. This problem is overcome by the arrangement shown in Figure 4. An under-voltage sensing circuit 34 is connected to the supply rails 25, 26 to detect when the mains supply voltage falls below - 15 - a predetermined level. When such a fall is detected, an output is provided on line 35 to the timer circuit 30 so as to cause it to produce a logical "1" output on line 31. The timer 30 will continue to produce this output until the input on line 35 is removed. As a result, the relay C is operated in response to the fall in voltage and consequently when such a low voltage condition occurs, the output at terminal 20 (Figure 3) is boosted with the supplementary voltage from transformer T2 for the duration of the abnormally low supply voltage condition. It will be appreciated that the arrangement described with reference to Figures 3 to 5 has the advantage. that the supplementary voltage from transformer T2 is supplied automatically according to demand upon switch on of the lamps, with the advantage that it is not necessary to switch the lamps at the control circuit itself, as in the arrangement of Figure 2. Thus, the circuit of Figure 3 can be used with advantage for large banks of lamps as utilised in offices, shops and other industrial situations. - 16 - Whilst the previously described embodiments concern single phase ac supplies, it will readily be appreciated that the invention can also be applied to multiphase e.g. three phase supplies. A supplementary voltage may be applied through a respective transformer to each of the phases of a multiphase supply under the control of a respective circuit such as circuit 23. Alternatively, a single control circuit may be used to control injection of the supplementary voltage into all of the phases. Whilst in the circuit of Figure 3, a single current sensor 24 is provided, where the environment is noisy for example, it may be of benefit to have more than one r - such current transformer e.g. one at the input and one at the- output of the system and to include an arrangement to determine whether the surge is coming up stream or downstream. If upstream this can be taken as coming from the lights. If downstream it can be taken as spurious and ignored to avoid unwanted switching into the full voltage load. - 17 - The invention also has application to controlling lamps individually. Referring now to Figure 6, this illustrates a control system for use with a single lamp e.g. a street lamp. As previously, a 240 volt mains supply voltage is applied to terminals 10, 11 and output terminals 20, 21 supply power to a single lamp. An on-off switch SW, which may be under the control, of a timer or photocell (not shown) switches the main supply to an auto-transformer T to having the ends of its winding Wl, W2 connected to the terminals 10, 11. The transformer T also has an intermediate tapping W3 which in use produces a voltage of e.g. 216 volts. The switched ac supply is also fed to a delay circuit 36 of any convenient design and thence to the coil of a relay E having a changeover contact El. When the coil E is unenergised, contact El assumes the position shown in Figure 6 but when the coil is energised, the contact El is moved into electrical connection with intermediate tapping W3. Thus when switch SW is closed, the terminals 20, 21 initially receive a voltage comprising the transformer voltage developed between W2 and W3 and also a supplemental voltage comprising the voltage developed - 18 - between W3 and Wl. This closely approximates to the mains voltage of 240 volts. After a predetermined time e.g. 15 seconds, delay circuit 36 times out and consequently coil E is energised so that contact El is pulled into connection with tapping W3 with the result that the terminal 20 receives only 'the reduced voltage of 216 volts developed between the tappings W2, W3 i.e. the supplementary voltage developed between Wl and W3 is removed. This arrangement has the advantage in comparison with the . previously discussed prior proposals that the transformer T remains continuously energised and only a part of its windings are connected and disconnected for start up of the lamps. In the prior proposals, a transformer was, in its . entirety, connected and disconnected through the mains. It will therefore be appreciated that the arrangement of Figure 6 has the advantage that the required current handling capacity of contacts El is reduced substantially in comparison with the prior proposals.

Claims: - 19 - CLAIMS 1. . A control system for lighting comprising, means for providing a reduced voltage below normal mains voltage for the lighting to provide reduced power during operation thereof, means for providing a supplementary voltage when initially operating the lighting to increment the reduced voltage to a value approximating to normal mains voltage; and means for thereafter removing, the supplementary voltage. 2. A system according to claim 1, wherein the means for providing a reduced voltage comprises means providing a first transformer winding, and the means for providing the supplementary voltage comprises means providing a second transformer winding for providing this voltage in combination with the reduced voltage to a value susbstantially that of the mains voltage. 3. A system as claimed in claim 1 or 2, wherein said means for providing the reduced voltage comprises a first transformer and the means for providing the - 20 - supplementary voltage comprises a second transformer having a primary winding to receive the mains voltage and a second winding that produces the supplementary voltage. 4. A system as claimed in claim 3, wherein said secondary winding of the second transformer is connected so as to provide a series connection with the first transformer. 5. A system as claimed in claim 3 or 4, wherein the secondary winding of the second transformer is configured to provide a low impedance path when it is not providing the supplementary voltage. 6. A system as claimed in any preceding claim wherein the means for removing the supplementary voltage includes timer means for removing this voltage after a predetermined period. 7. A system as claimed in claim 6, wherein the removing means includes a relay operable by the timer means. - 21 - 8. A system as claimed in claim 7, wherein the removing means includes a contactor operable by the relay. 9. A system as claimed in any preceding claim wherein cut-out means are provided to disconnect the . control, system from the lighting so as to prevent overload and possible damage to the system when a rated load is exceeded. 10. A system as claimed in claim 9, wherein the cut¬ out means includes a switching arrangement to by-pass the control system and maintain a mains supply to the lighting. 11. A system as . claimed in any preceding claim wherein indicator means are provided to show operational status. 12. Apparatus as claimed in any preceding claim including sensor means for detecting initial operation of the lighting to effect the provision of the supplementary voltage. - 22 - 13. A system as claimed in claim 12 wherein said sensor means includes at least one sensor for detecting a current surge associated with initial operation of the lighting. 14. A system as claimed in claim 12 or 13 including a control circuit responsive to the sensor means and arranged to provide an output signal only in response to an increase in current in said surge. 15. Apparatus as claimed in any preceding claim including sensor means responsive to the applied mains voltage for providing said supplementary voltage when said mains vpltage drops below a predetermined level. 16. A system as claimed in claims 12, 13, or 14 including a first and a second said sensor.

Inventors: FINCH DAVID ALAN, LAWRENCE JOHN ARTHUR, FINCH, DAVID, ALAN, LAWRENCE, JOHN, ARTHUR
Applicants: FINCH DAVID ALAN, LAWRENCE JOHN ARTHUR, FINCH, DAVID, ALAN, LAWRENCE, JOHN, ARTHUR
Application year: 1987
Main classification: H05B41
IPC codes: H05B41