AU2003262614A1

AU2003262614A1 - Electric switch power supply

Info

Publication number: AU2003262614A1
Application number: AU2003262614A
Authority: AU
Inventors: Martti Sairanen; Olli Salonen
Original assignee: Lexel Finland Oy AB
Current assignee: Schneider Electric Industries SAS
Priority date: 2002-09-23
Filing date: 2003-09-23
Publication date: 2004-04-08
Anticipated expiration: 2023-09-23
Also published as: RU2005111544A; FI113502B; WO2004027807A1; NO20052005L; CN1685458A; AU2003262614B2; CN100372039C; EP1547110A1; PL375739A1; RU2316074C2; FI20021692A0; PL206414B1; NO328490B1

Description

WO 2004/027807 PCT/FI2003/000692 1 Electric switch power supply The invention relates to a method for realizing power supply to an electric switch according to the preamble of claim 1. The invention also relates to a power supply arrangement for an electric switch according to the preamble of claim 2. In the present application, an electric switch is an electromechanical switch, such as a relay switch, a semiconductor switch and/or a combination thereof, for instance a relay switch and a semiconductor switch coupled in parallel, such as a triac. This kind of electric switches are used for switching on and off electric appliances, particularly lighting fixtures, to be connected to an alternating-current supply, such as AC mains, and they are controlled for example by a timer, a twilight switch or a motion sensor. Electromechanical switches, such as a relay switch, are suited to be used with all types of loads, both resistive, capacitive and inductive loads. When in parallel with a relay switch, there is arranged a semiconductor switch, such as a triac, the load currents can be raised with all load types so that they are equal to the rated current of the relay switch. The appliances, i.e. the loads to which the AC current supply is adjusted/controlled through the electric switch are realized so that there is brought in both a network phase advance, i.e. a phase voltage/electric current wire and a zero wire, i.e. earth. Now the electric supply to the electric switch control unit and possibly also to the electric switch itself is arranged directly at the mains supply, i.e. between the electric and zero wire. However, it is pointed out that a mains zero wire is not always available. This is the case for instance in interior wire installations, in wall power sockets meant for switches, in which power sockets a zero wire is not provided. In that case the zero wire must be installed afterwards, in case the electric supply to the electric switch and to the control unit thereof is realized in the conventional way. The problem with an electric switch where only the electric wire can be used for electric supply is that in order to function, the control unit of the electric switch, and often also the electric switch itself need electric power both when the electric switch is off, i.e. conductive, and when the electric switch is on, i.e. non-conductive. Because only the phase advance passes via the electric switch, there is no reference potential, such as earth potential, in order to create a voltage difference and in order to arrange power supply to the electric switch and to its control unit on the basis of it.

WO 2004/027807 PCT/FI2003/000692 2 In the prior art there is known, from the US patent publication US-4,713,598, a relay switch, where the power supply to the amplifier of the PIR sensor connected to the control of said relay switch is realized without a zero wire, by utilizing an electric wire only. Now the relay switch serves as a so-called twin wire switch. The relay switch is connected to the AC mains in series with the load and with the primary winding of the current transformer. When the relay switch is off, i.e. it is conductive, the alternating voltage of the primary winding of the current transformer is rectified, and the obtained result is the direct voltage required by the amplifier power supply. When the relay switch is on and current cannot pass through the switch, the voltage effective over the switch is rectified, and the operating voltage required by the amplifier is created thereof. When the relay switch is off and the load current passes through the switch, the voltage drop over the primary winding of the current transformer is slight in comparison with the load voltage prevailing over the load. Typically the voltage drop is of the order of 1% of the load voltage. The voltage drop prevailing over the primary winding is transformed in the current transformer to a high secondary voltage over the secondary winding, which secondary voltage is completely or partly rectified by a diode, in connection of which diode there is arranged, as a voltage directing filter, a bypass capacitor, and over which diode there is obtained a rectified voltage for the amplifier. By way of example, the number of turns for the primary and secondary windings W1, W2 of the current transformer may be W1 = 45 and W2 = 2000, when the load is 60 W. In addition, the primary winding also includes several intermediate taps, in which case the turns ratio can be adjusted to suit the load. The problem is that in structure and measures, and particularly as regards the number of turns, the current transformer takes up a lot of space. This type of current transformer is cumbersome to fit in limited installation spaces, for example in the installation boxes of electric switches or similar electric appliances. Yet another problem is that the size of the load to be coupled in series with a current transformer is restricted. Generally current transformers are designed for small loads, such as for a load of 60 W only, as in the example given in the above mentioned US patent publication. If a similar transformer is used with larger loads, its physical size grows immensely. The object of the invention is to eliminate the drawbacks connected to the above described electric switch power supply. Another object of the invention is to realize WO 2004/027807 PCT/FI2003/000692 3 a new electric switch power supply that is particularly suited for providing power supply for a switch that is fitted in an installation box of an electric installation system, particularly in a mortise mounted installation box. The method according to the invention for realizing an electric switch power supply is characterized by what is set forth in claim 1. The switch power supply arrangement according to the invention is characterized by what is set forth in claim 2. The dependent claims represent preferred embodiments of the power supply arrangement according to the invention. In a method according to the invention, in order to realize an electric switch power supply, the switch is arranged in the current path between an AC current source, advantageously an AC current mains, and the load in order to interrupt and allow power supply, and the switch also is arranged in series with the primary circuit of the current transformer, and the power required by the control unit of the switch and possibly by the switch itself is taken over the switch, when the switch is on, and from the secondary circuit of the current transformer through the rectifier, when the switch is off and power is being supplied in the load. According to the invention, the current transformer is arranged to function so that it is saturated at each half-cycle of the mains current, and the saturation peaks of the secondary voltage of the secondary circuit of the current transformer are rectified in order to obtain direct current power when the switch is off. An advantage of the invention is that a current transformer operating in the saturation range can be realized in a small size. The number of wire turns of the current transformer can be maintained low, particularly the number of turns of the primary winding, in which case also the dimensions of the current transformer are made distinctly smaller than in conventional transformer structures. This is particularly important when the electric switch, the current transformer and an auxiliary control unit must be fitted in a small space, particularly in an electric installation box. Another advantage of the invention is that one current transformer can be used in a wide load power range, such as 25 W - 3,7 kW. In this case, the load currents may be within the range 100 mA - 16A. The invention is described in more detail below with reference to the appended drawings, where WO 2004/027807 PCT/FI2003/000692 4 figure 1 describes the principle of an electric switch where the power supply according to the invention is applied; figure 2 describes the principle of another electric switch and of the power supply according to the invention; figure 3 is a schematical illustration of a practical application of the power supply into an electric switch according to the invention; and figures 4A and 4B illustrate the curve forms of the secondary voltages of the current transformer with two different loads. Like numbers for like parts are used in the drawings. The invention relates to the power supply arrangement of an electrically controlled electric switch 1, such as an electromechanical switch and/or a semiconductor switch, when only one wire, i.e. the electric wire is arranged to pass through the switch. The electric switch 1 is arranged in the current path, such as in an electric wire J, between an AC current source E, preferably one phase in an AC current mains, and the load L, as is illustrated in figures 1 and 2. By means of the electric switch 1, the power supply from the AC current source E to the load L is cut or interrupted and respectively enabled depending on the position of the switch, on a and respectively off k. The electric switch 1 is set in the on and off positions by means of the control unit 2. The functional command to the control unit 2 is most advantageously given from outside said unit (cf. arrow in figures 1 and 2). The power supply arrangement of the electric switch 1 comprises a current transformer 3, a rectifier 4 and a constant voltage source 5. The primary circuit W1 of the current transformer 3 is arranged in series with the electric switch 1. The electric power required by the electric switch 1 and its control unit 2 is arranged to be taken from the constant voltage source 5 over the electric switch 1, when the switch is on a and power supply is cut off, and from the secondary circuit W2 of the current transformer 3 via the rectifier 4, when the switch is off k and AC current from the AC current source E is fed in the load L. According to the invention, the current transformer 3 is arranged to function so that it is saturated at each half-cycle of the mains current.

WO 2004/027807 PCT/FI2003/000692 5 In a conventional, ideal current transformer, the ratio of the currents of the primary and secondary circuits is reversely proportional to the ratio of the winding turns of the primary and secondary circuits. In practice, the size of the magnetizing current causes differences in the current ratio. In order to keep the ratio of the primary and secondary circuits in control as accurately as possible, the distortion caused by the magnetizing current must be minimized, i.e. the volume of the magnetizing current must be kept as small as possible. The larger the magnetizing inductance, the smaller is the magnetizing current. The volume of the magnetizing inductance is affected by the number of winding turns, the size of the transformer and the employed core material. Generally the magnetizing current of a conventional current transformer is designed to be less than 3% of the current value to be measured. The value of the secondary voltage U of a conventional current transformer is designed to be left under the value of the threshold voltage Uk = 1V, because a high secondary voltage would increase the value of the magnetizing current i: Uk = Lx (di /dt) <> di = (dt x U) / L ,where L = the inductance of the current transformer. For this reason, the secondary winding of the current transformer is connected to a load resistor with a low impedance, and by means of said resistor, the value of the secondary voltage U is restricted to a desired voltage value. In a power supply according to the invention, the current transformer 3 is arranged to be saturated, as was already mentioned above. In that case the secondary voltages U are not restricted, as in a conventional current transformer, and the number of winding layers is arranged to be low. Both of said conditions raise the value of the magnetizing current so high that the transformer is saturated. The chosen core material for the current transformer 3 is a material with a high permeability P. These materials are, among others, pure iron (P = 180,000) and some alloys of iron and nickel, such as 78 Permalloy (P=100,000). One of the commercially available materials that are suited to be employed as core material is NANOPERMT. The saturation flux density of this material is 1.2 T, and is maximum permeability is 80,000. The number of wire turns in the primary winding W1 of the current transformer 3 is arranged to be smaller than or equal to 10. In addition, the transversal area of the primary winding wire is arranged to be at least 0.75 mm 2 in order to allow the current transformer to process large currents, such as for instance 10 A. Then number of turns in the secondary winding W2 of the current WO 2004/027807 PCT/FI2003/000692 6 transformer 3 is arranged to be larger than or equal to 200. It is also advantageous that the core of the current transformer 3 is realized by means of a toroid ring. Let us now calculate, as an illustrative example, what is the maximum value of the sinusoidal secondary voltage U of the secondary winding W2 by which the current transformer 3 is not saturated. The maximum flux linkage of the current transformer is: Amax = N x A, x B, where N = the number of turns in the winding 300

A

c = the transversal area of the toroid ring 0.24 x 10-6 m 2 Bs = the saturation flux density of the toroid material 1.2 T 2max: 8,64 x 10 -3 Vs On the other hand, the flux linkage can also be calculated from the integral of the sinusoidal secondary voltage: 0 ? / Umax sin ot dt = 2xUmax/0 Umax = peak value of the secondary voltage and 0) = angular frequency 2if Now the obtained value for the flux linkage must be = kmax i.e. 2xUmax / 0) = 1max a Umax = kmax Rf = 8,64 x 10 -3 Vs x 3,14 x 50 Hz = 1,36 V As is apparent from figures 4A and 4B to be dealt with below, with a minimum load of the current transformer 3, the peak value of the secondary voltage is at least 9V, which is clearly higher than the above obtained calculatory maximum value 1.36 V of the sinusoidal secondary voltage. Consequently, the transformer 3 is saturated with the given initial values. Another power supply arrangement for an electric switch 1 according to the invention is illustrated in figure 2. In this case, the electric switch 1 comprises, as the switch element proper, a relay switch 11, particularly a bistable relay switch. A bistable relay switch needs electric power only when its mode is changed from conductive to non-conductive or vice versa. Thus, from the point of view of power consumption, it is an economical switch element. In this embodiment, the secondary WO 2004/027807 PCT/FI2003/000692 7 winding W2 of the current transformer 3 comprises two windings W2a, W2b, which are connected in series. The number of rectifiers, most advantageously full-wave rectifiers, is two, 4a, 4b. The input of the first rectifier 4a is only connected over the first winding W2a, whereas the input of the second rectifier is connected over both secondary windings W2a, W2b. The constant voltage source 5 includes two capacitors C1, C2, the first capacitor C1 of which is connected to the output of the first rectifier 4a, and the second capacitor C2 is connected to the output of the second rectifier 4b. The alternating-current supply E, such as one phase of the current mains, is brought through the relay switch 11 of the electric switch to the load L, and via the load to the zero of the mains, so that there is formed a circuit that can be switched off and respectively on by means of the relay switch. When the relay switch 11 of the electric switch is on, i.e. it is non-conductive, it represents a high impedance. Now the necessary electric power functionally required by the elements of the electric switch is generated by means of a small current passing through the load L. For this purpose, the alternating voltage source 5 includes a voltage drop circuit 51 that is connected over the relay switch 11 and over the primary winding W1 of the current transformer 3. In the voltage drop circuit 51, the prevailing mains voltage E is transformed into a suitable low functional voltage. Now the capacitors C1 and C2 are charged by said functional voltage. From the first capacitor Cl there is supplied power to the control unit 2 of the electric switch. In the capacitor C2, there is only charged the energy required for changing the mode of the relay switch 11. When the relay switch 11 is in a stabile mode, the capacitor C2 is only charged by its own, very low leakage current. From the control unit 2 of the electric switch, there is sent a control command for switching the relay switch 11 on, i.e. into conductive mode, by a suitable control pulse. The control unit 2 in turn is controlled for instance by an external sensor, such as a PIR, or by a timer. In conductive mode, the relay switch 11 has a low impedance. When the relay switch 11 is on, load current starts to proceed through the relay switch 11, and the voltage prevailing over the electric switch drops to nearly zero. The voltage of the capacitor C2 drops down to a lower level than before, because the relay switch 11 consumes control power. The voltage of the capacitor Cl begins to drop, because the control unit 2 charges it all the time. Simultaneously as the load current begins to proceed through the relay switch, the current transformer 3 begins to function. Because the secondary windings W2a and W2b of the current transformer 3 are connected in series, the voltage of the WO 2004/027807 PCT/FI2003/000692 8 capacitor C2 is set essentially on the same level as the voltage sum obtained from the secondary windings (subtracted by the voltage losses of the full-wave rectifier 4b) and respectively the voltage of the capacitor C1 is set on the level of the voltage obtained from the first secondary winding W2 (subtracted by the voltage losses of the full-wave rectifier 4a). In the course of time there is achieved a voltage balance where the leakage current of the capacitor C2 is equal to the charging current obtained from the current transformer 3. Now the voltage of the capacitor C2 remains sufficiently high in order to be able to turn the relay switch 11 of the electric switch off. The voltage of the capacitor C1 remains on a level that is sufficient for maintaining the operation of the electric switch. From the control unit 2, there is again sent a control command in order to switch off the relay switch 11 by a suitable control pulse. The control unit 2 in turn is controlled externally, in similar fashion as above, when switching the relay switch 11 on. Now the passage of the load current is cut off. The mains voltage is again effective over the electric switch. The voltage level of the capacitor C2 may slightly drop, but the capacitors are immediately started to be charged through the voltage drop circuit 51. The voltage level of the capacitor Cl is maintained by charging in similar fashion. A third power supply arrangement of an electric switch 1 according to the invention is illustrated in figure 3. In this case, the electric switch comprises, as the switch components proper, a relay switch 11, particularly a bistable relay switch, and in parallel with it, a two-way semiconductor switch 12, in this embodiment a triac. As for the rest, the electric switch of figure 3 and its power supply correspond to the electric switch of figure 2 and its power supply. The semiconductor switch 12 is arranged to be conductive when the contacts of the relay switch 11 are switched off and on. Thus the contacts of the relay switch 11 are prevented from spiking. By means of a semiconductor switch 12, there can also be realized a so-called zero point switch. This means that the electric power of the load is switched on and off always at the zero point of the mains voltage. The advantage of this arrangement is that it makes it possible by the electric switch to switch and control all types of loads: resistive, capacitive and inductive loads. In principle, the electric switch and its power supply illustrated in figure 3 function in the same way as those illustrated above in the embodiment of figure 2, and here we refer to the functional description given above. The electric switch of figure 3 is illustrated as an example of a few preferred embodiments for the connection circuits of the capacitors Cl, C2 and for the voltage drop circuit 51. The control unit 2 also WO 2004/027807 PCT/FI2003/000692 9 is illustrated as two circuit units: the control unit 2a proper, and the power supply unit 2b of the switch-components 11, 12. In this embodiment, the control unit also is controlled by control signals obtained from a passive infrared sensor PIR. The voltage drop circuit 51 comprises a third capacitor C3, a resistor R1 and a zener diode Z1. The connection circuits of the first and second capacitor C1, C2 comprise a first and respectively a second diode Dl 1, D2. The capacitors Cl 1, C2 are connected over the outputs of respective rectifiers 4a, 4b. The diode D1, D2 is connected in the opposite direction, and the cathode terminal is connected to the voltage terminal of the capacitor C1, C2. The anode terminals of the diodes Dl, D2 are connected to each other and further to the cathode terminal of the zener diode Z1, which in turn is connected in series, via the provided resistor and the third capacitor C3 in between the load L and the switch 11. The anode terminal of the zener diode Z1 is connected to the alternating voltage source, i.e. to the phase advance. The voltage terminal of the first capacitor C1 is connected to the control unit 2, particularly to the control unit 2a proper, in order to provide for its power supply. The voltage terminal of the second capacitor C2 also is connected to the control unit 2, particularly to the power supply unit 2b. When the relay switch 11 of the electric switch 1 is on, the electric power of the control unit 2 is generated by means of the load L and the capacitor C3 of the voltage drop circuit 51, the resistor R1 and the zener diode Z1. Now the capacitors C1 and C2 are charged to the voltage potential restricted by the zener diode Z1 (subtracted by the threshold voltage of the diodes D1 and D2). When from the control unit of the electric switch 1, there is given a control command to switch the relay switch 11 on, the control unit 2 first sends a control pulse (duration roughly 40 ms) to the semiconductor switch 12, and somewhat later (after about 10 ms) to the relay switch 11. Now the load current begins to pass through the switches 11, 12. When from the control unit of the electric switch 1 there is sent a control command to switch the relay switch 11 off, the control unit 2 sends a control pulse (duration roughly 40 ms) to the semiconductor switch 12, and somewhat later (after about 10 ms) the relay switch 11 is switched off. Not the passage of load current is interrupted, and the mains potential is again effective over the electric switch 1. The charging of the capacitor C2 is started through the capacitor C3 and resistor R1 of the voltage drop circuit 51, until the zener diode Z 1 restricts the rise of the voltage. The voltage of the capacitor C1 rises up to the same potential.

WO 2004/027807 PCT/FI2003/000692 10 The number of the wire turns in the primary winding of the current transformer 3 is of the order 10 or even less. The minimum numbers of wire turns in the first and second secondary winding W2a, W2b are of the order 200, advantageously within the range 200 - 400. Figure 4A illustrates the secondary voltage pulses of the current transformer 3 of the electric switch according to figure 3, as measured by an oscilloscope, when the employed load L is a 25 W incandescent bulb. The first secondary voltage Ul is measured over the first secondary winding W2a. The second secondary voltage U2 is measured over both secondary windings W2a and W2b. According to the measurements, the maximum voltage values of the saturation peak of the secondary voltages Ul, U2 are 9 V and respectively 14 V. Figure 4B illustrates respective secondary voltages Ul, U2, when the employed load is a 100 W incandescent bulb. With a larger load current, the duration of the saturation peak KP of the secondary voltage Ul, U2 is shortened, but respectively the voltage level is raised. Now the maximum voltage values of the saturation peak KP of the secondary voltages Ul, U2 are, according to the measurements, 18 V and respectively 30 V. In the most advantageous embodiment of the invention, the electric switch 1 and its power supply arrangement is meant to be installed in a wall box, particularly in a mortise mounted wall box with a limited space for the elements of the electric switch. The current transformer 3 of an electric switch 1 was built on a toroid ring with an outer diameter of 20 mm. The employed material for the ring was

NANOPERM

T M -material (manufacturer: MAGNETEC GmbH). Let us now give a list of the number of turns of the windings of the current transformer 3 and of the employed wires: Wl: 6turns 0,75 un 2 insulated wire W2a: 300 turns 0 0.18 mm copper W2b 200 turns 0 0.18 mm copper On the basis of performed tests, the electric switch functions without defects with the desired load currents 100 mA - 10 A. The invention is not restricted to the above described preferred embodiment only, but many modifications are possible within the scope of the inventive idea defined in the claims.

Claims

1. A method for realizing power supply to an electric switch (1), where the switch is arranged in the current path (J), between an AC current source (E), preferably an AC current mains, and a load (L) in order to interrupt and enable power supply, which switch also is arranged in series with the primary circuit (W1) of a current transformer (3), so that the electric power required by the control unit (2) of the switch and possibly of the switch itself is taken over the switch when the switch is on (a), and from the secondary circuit (W2) of the current transformer via a rectifier (4), when the switch is off and power is fed to the load (L), characterized in that the current transformer (3) is arranged to function so that it is saturated at each half-cycle of the mains current, and that the saturation peaks (KP) of the secondary voltage (W2; W2a, W2b) of the secondary circuit of the current transformer are rectified in order to obtain direct electric power, when the switch (1) is off(k).

2. A power supply arrangement for an electric switch (1), where the switch is arranged in the current path (J) between an AC current source and a load (L) in order to interrupt and enable power supply, which switch also is arranged in series with the primary circuit (W1) of a current transformer (3), and where the electric power required by the control unit (2) of the switch and possibly of the switch itself is arranged to be taken over the switch when the switch is on (a) and power supply to the load is interrupted, and from the secondary circuit (W2) of the current transformer via a rectifier (4), when the switch is off and power is fed in the load (L), characterized in that the current transformer (3) is arranged to function so that it is saturated at each half-cycle of the mains current, and that the saturation peaks (KP) of the secondary voltage of the secondary circuit (W2; W2a, W2b) of the current transformer are fed into a rectifier (4; 4a, 4b) in order to obtain direct electric power, when the switch (1) is off (k).

3. A power supply arrangement for a switch accordingto claim 2, characterized in that the core material of the current transformer (3) is a material with a high permeability.

4. A power supply arrangement for a switch according to claim 3, characterized in that the core material of the current transformer (3) is NANOPERMTM. WO 2004/027807 PCT/FI2003/000692 12

5. A power supply arrangement for a switch according to claim 3 or 4, characterized in that the number of wire turns in the primary winding (W1) of the current transformer (3) is equal to or smaller than 10.

6. A power supply arrangement for a switch according to claim 5, characterized in that the transversal area of the wire of the primary winding (W1) of the current transformer is at least 0.75 mm 2

7. A power supply arrangement for a switch according to any of the preceding claims, characterized in that the core of the current transformer (3) is realized by means of a toroid ring.

8. A switch power supply arrangement according to any of the preceding claims, characterized in that the number of wire turns of the secondary winding (W2; W2a, W2b) of the current transformer (3) is larger than or equal to 200.

9. A switch power supply arrangement according to any of the preceding claims, characterized in that the current transformer (3) includes two secondary windings (W2a, W2b), through which the power supply is arranged on one hand to the control unit (2) of the switch (1) and on the other hand to the switch itself (11, 12).