WO2013167127A1

WO2013167127A1 - A fuse cap, a power meter base station, and a power metering system

Info

Publication number: WO2013167127A1
Application number: PCT/DK2012/050156
Authority: WO
Inventors: Søren Stig TVILSTED
Original assignee: CLEANFUSE ApS
Priority date: 2012-05-09
Filing date: 2012-05-09
Publication date: 2013-11-14

Abstract

A fuse cap (4) adapted for cooperation with a fuse base. The fuse cap (4) comprises current sensing means (28) for measuring the current though a fuse held in the fuse base by the fuse cap. The fuse cap (4) further comprises a first wireless communication means (13) and a built-in first power supply (11) adapted to harvest energy from the current flowing through the fuse held in the fuse base. A power metering system uses the fuse cap (4) in conjunction with a power meter base station adapted to be plugged into a wall socket.

Description

A fuse cap, a power meter base station, and a power metering system

The present invention relates to a system, a method and an appara- tus for monitoring electrical energy consumption, primarily but not exclusively in homes and private households.

Awareness of energy consumption appears to be growing. A lot of people wish to reduce the energy consumption of their households. Reducing energy consumption will benefit the environment and, if done properly, the long-term economy of the household. When it comes to electrical energy it is often not evident, what quantities of energy are used where. High power devices and appliances may consume a lot when they are used, but contribute only little to the overall energy consumption, whereas even a small continuous consumption may easily amount more to the overall energy consumption.

Using a powerful hairdryer shortly every weekday morning may still amount to less than the small standby power used by a television, when it is not in use, which may, in turn, still be less than what is consumed during the time it is switched on. This in turn depends on the ratio between on and off time of the television, which may differ in every household. The energy con- sumption is thus not very transparent to the consumers in the household. Consequently, there is not much awareness about the overall consumption pattern in a household.

If one wants to reduce energy consumption, it should be done in an economically rational way. If old equipment is to be replaced by new, the money should be spent where it provides the largest reduction for the money spent. This, however, necessitate that the energy consumption is transparent to the user. In this respect, changing the consumption pattern, such as learning to remember to switch off unused apparatuses, and understanding which apparatuses it makes more sense to switch off, is basically an economically free investment. This, however, is difficult given the lack of transparency and awareness. Power meters which can be inserted between the plug of a device and a wall socket in order to measure e.g. the momentary power consumption and energy consumption over time are well known, and generally work quite well if one wants to learn more about the energy consumption of an old refrig- erator or the like. Often, however, the user doesn't even posses this knowledge, and would not know where to start investigating, i.e. where to use the power meter. Also, there is the drawback that for some apparatuses, such as a built-in refrigerator, the plug and the associated wall socket might not be readily accessible. Other devices such as gas or oil furnaces, which may have built-in pumps, electronics etc., or electrical water heaters, may not even be connected to the electrical installation via plug and socket, but directly, leaving no place to interpose the power meter for the ordinary consumer.

Often, however, the consumer is not really interested in the consumption of the individual device, but more in the overall pattern. E.g. does laundry consume a lot, does cooking consume a lot, do the children's TVs, game consoles, stereos etc. consume a lot?

In this respect it has been suggested to place power meters in conjunction with the fuse holders in the fuse panel. One such system is disclosed in Swedish patent SE-C-532819. In this patent a current sensor is arranged in the cap which holds the fuse in the fuse base of the fuse holder. A cable is drawn from the cap to an external power calculation box, from which it is transmitted to a display. More caps may be connected to the same power calculation box. This thus allows the monitoring of the power and energy consumption of each individual fuse group.

The system presented in SE-C-53281 9, however, still has a few drawbacks. One is that wires have to be drawn from the current sensors in the caps to the power calculation box, which, in turn, means that the power calculation box should be located close to the fuse panel in order to avoid having to draw long cables, e.g. through walls, if there is little space around the fuse box. The system of SE-C-532819 does not lend itself to retrofitting of an existing system. For one there may not be sufficient room for the power calculation box in the vicinity of the fuse panel. Moreover, the power supply is difficult in the sense that it may require an electrician. Though fuse panels in Sweden may differ on this point, in most countries no power outlet is provided in conjunction with the fuse panel. The power calculation box can thus not just be plugged in, but needs an electrician to connect it to suitable wires in the fuse panel. The consumer thus cannot just replace the existing caps for the caps of SE-C-532819 and plug in the cables in the calculation box and connect it to the mains.

Based on this prior art it is the object of the invention to provide a system where the power through a fuse can be measured without necessitat- ing cable and installation work to be performed at the fuse panel.

According to a first aspect of the invention this is achieved in a fuse cap adapted for cooperation with a fuse base, said fuse cap comprising current sensing means for measuring the current through a fuse held in the fuse base by the fuse cap, characterized in that said fuse cap further comprises wireless communication means for transmitting current measurements to a remote evaluation system, and in that said fuse cap comprises a built-in first power supply adapted to harvest energy from the current flowing through the fuse held in the fuse base. Thereby any additional wiring is avoided. All the user has to do is to replace the existing fuse caps with fuse caps according to the invention and set up the remote power meter base station, which in turn may involve nothing else than plugging it into the nearest wall socket to the fuse panel.

Thus, according to a second aspect of the invention there is provided a power meter base station adapted to be plugged into an electrical wall socket and comprising voltage measuring means allowing local voltage measurements based on the voltage delivered by said wall socket, characterized in that the power meter base station comprises wireless communication means adapted to wirelessly receive measurement information based on current measurements performed in a remote location.

Experience has shown that if a wall socket is used which is not too far away from the fuse panel, the phase and voltage value measured can be assumed to correspond to the phase and voltage values that would be meas- ured for the entire group at the fuse where the current is measured. This will evidently not be an exact match but accuracy suffices.

According to a third aspect of the invention the present invention comprises a power metering system comprising a fuse cap according to the first aspect of the invention and a power meter base station according to the second aspect of the invention. Thereby a complete system readily installed by an end user is provided.

According to a preferred embodiment of the first aspect of the invention, the fuse cap comprises timing means for the current measurements. This allows precise timing of measurements and in particular synchronisation of the voltage measurements, which are made at a remote location by e.g. the power meter base station according to the second aspect of the invention. Precise timing is necessary for precise calculation of the power, and may also be used for determining whether the fuse cap is inserted in the same phase as the one to which the power meter base station according to the second aspect of the invention is connected.

Preferably, according to a further preferred embodiment of the first aspect of the invention, the wireless communication means is adapted to receive information for the control of the timing means. This allows the already present wireless communication means to be used for two-way communication.

According to another embodiment of the first aspect of the invention, the fuse cap comprises a first microprocessor. This allows control of the timing and measurement while still coping with the power restraints from the built-in first supply. The first microprocessor also allows the calculation and storage of power values or even integration of these over time to energy values, which may then periodically be transmitted to the power meter base station according to the second aspect of the invention. This periodical transmission, in turn, reduces power consumption as the transmitter need only be switched on for short periods.

According to a preferred embodiment of the second aspect of the invention, the power meter base station comprises an estimator for estimating the voltage of other phases than that of the wall socket into which the power meter base station is plugged. This allows one and the same power meter base station to be used for all installed fuse caps according to the invention, even if these are inserted in another phase.

According to a further embodiment of the second aspect of the invention, the wireless communication means is adapted for transmitting timing information to a remote current measuring device. This allows simultaneous current and voltage measurements to be made so as to calculate power correctly. Moreover, this allows the time keeping means in the fuse cap to be made relatively cheap and simple, because a precise time base need not be kept over long time spans.

According to another embodiment of the second aspect of the invention, the wireless communication means is adapted for transmitting voltage information to a remote current measuring device. This allows precise power calculations to be made in the fuse cap according to the first aspect of the invention.

The invention will now be described in greater detail based on non- limiting exemplary embodiments and with reference to the drawings on which:

Fig. 1 shows a diagram of an electrical installation in which the inven- tion is installed,

Fig. 2 shows a simplified diagram of an embodiment of the built-in first power supply of the cap,

Fig. 3 shows a block diagram of the electronics of in a schematically shown fuse cap according to the invention,

Fig. 4 shows a block diagram of the power meter base station according to the invention, and

Fig. 5 shows a more detailed diagram an embodiment of the built-in first power supply.

In Fig. 1 a simple schematic diagram of an electrical installation is shown. In Fig. 1 the letters a, b and c have been appended to the general reference numerals of items in order to inter alia associate items relating to the same electrical circuit and to distinguish between otherwise identical items. The installation has three phases R, S and T connected to an electricity meter 1 . The installation, however, is only two-phased, phase S not being connected. The installation comprises three fuses 2a, 2b, 2c, arranged in fuse bases 3a, 3b, 3c, and held by caps 4a, 4b, 4c according to the invention. As can be seen, fuses 2b and 2c are arranged in two branches of the same phase R whereas the fuse 2a is arranged in the sole branch of the phase T. A load illustrated as a lamp 5a is supplied via the fuse 2a. Similarly, lamps 5b and 5c are supplied via fuses 2b and 2c in the two branches of the phase R. Lamps 5a, 5b, 5c are all illustrated without terminals to illustrate that they may not be accessed by a watt meter, whereas a further lamp 6 illustrated with terminal such as the plug and socket of a wall outlet could be. In parallel with the lamps 5c and 6 the power meter base station 7 of the invention is connected to the fuse 2c via terminals 8, in particular a socket in a wall outlet. The fuse caps 4a, 4b, 4c are all according to the invention and contain at least one electronics part 9a, 9b, 9c. Evidently, in an actual installation not all fuse caps in the installation need be according to the invention. However, as will be clear from the description further below, the measurements are likely to be incorrect if not all fuses of the same phase are equipped with fuse caps according to the invention.

As will be described later in conjunction with Fig. 3, the at least one electronics part 9 of the fuse cap 4 according to the invention may, comprise sub-parts, or components, e.g. as sub-assemblies or modules, or it may integrate all the electronics necessary. The skilled person will know that the distinction may only be conceptual for definition and understanding. In the follow- ing description, the at least one electronics part 9 is exemplified by three general components.

Thus, the electronics part 9 comprises at least a built-in first power supply (energy harvester) 1 1 , a measurement device and a wireless communications means 13. The electronics part also comprises a first microproces- sor 14 controlling inter alia the taking of the measurements, the timing thereof the communication of the measurements via the wireless communication means 13. This communication, as illustrated by the double zig-zag arrows 10a, 10b, 10c in Fig 1 , is a two-way communication adapted for relatively short-range communication with the power meter base station 7. The communication could use a standard, such as ZigBee®, Z-Wave, Wireless M-bus, SimpliciTI™, Bluetooth®, WiFi or it could be proprietary. SimpliciTI™ is cur- rently preferred.

The built-in first power supply is specially developed for the very difficult constraints of the fuse cap 4. Not only is space very limited, but there is no access to a ground wire. Basically, a traditional fuse cap is just a short length, e.g. 3 cm to 4 cm, of conductor arranged in a cylindrical insulator. Ide- ally, there is no voltage over a conductor, and hence a power supply cannot be coupled in parallel therewith. It could be possible to incorporate an inductive coupling to the conductor of the fuse cap 4, but this does not seem viable as an inductive coupling means will tend to be spacious.

Instead, as illustrated in Fig. 2, the preferred embodiment of the built- in first power supply 1 1 according to the invention utilises a voltage drop over a controllable resistance 17 such as a Field Effect Transistor (FET) inserted in series with the conductor of the fuse cap and thus in series with the circuit in which the power and/or energy consumption is to be measured. Fig. 2 is a simplified illustration for explanatory purposes. The voltage drop over the con- trollable resistance 17 connected between the conductors 16 and 19 on the input side of the built-in first power 1 1 is used to charge a storage means such as a storage capacitor 18 arranged in parallel with the controllable resistance 17, where the storage capacitor 18, in turn, delivers power to the output side 20 of the built-in first power supply 1 1. When the controllable resistor 17 has a high resistance there will be a substantially higher voltage drop than if it has a low resistance, i.e. if a FET is conducting. This voltage will depend on the charging state of the storage capacitor, which is charged with rectified current diverted to the through a rectifying diode 21 , when the resistance of the controllable resistance 17 is high. As the storage capacitor 18 charges, the capacitor voltage rises. This capacitor voltage is compared with a reference voltage on the input 22 of a comparator 23. The reference voltage could e.g. be provided by a Zener diode 24. When the capacitor voltage rises, the output of the comparator will reduce the resistance of the controllable resistance 17, e.g. turning a FET on, thus reducing the voltage drop over the controlled resistance 17. The storage capacitor 18 will then discharge into any load connected to the output 20 of the built-in first power supply 1 1 until the capacitor voltage approaches the reference voltage and the comparator increases the resistance of the controllable resistance 17, upon which the whole process repeats. This process needs no external control as it repeats itself automatically depending on the current drawn by the load connected to the output 20. Alternatively, however, rather than a free-running uncontrolled circuit, a fixed frequency control of the charge/discharge cycle could be used. Having a fixed frequency aids in noise filtering, but comes at the expense of more complicated power supply circuitry.

Based on Fig. 2, the actual power supply circuitry may be devised in various ways, which are all within the reach of the skilled person. A more de- tailed example is shown in Fig. 5, in which corresponding reference numerals are used for corresponding components. As can be seen the controllable resistance 17 in Fig. 5 comprises two FETs 17' arranged symmetrically on either side of the measuring resistance 44. The FETs 17' are controlled by an operational amplifier 23 coupled as a comparator. When current is drawn from the output 20, the storage capacitor 18 is discharged and the voltage over the storage capacitor 18 drops. The comparator compares the voltage over the storage capacitor 18 with a reference value determined by the Zener diode 24. When the voltage drops below the reference value, the comparator output goes low, and the FETs 17' stop conducting. Since the storage capaci- tor 18 is arranged in parallel with the FETs 17', it is charged through one of the recitifying diodes 21 arranged in series with the storage capacitor 18. Which one depends on whether the AC is in the negative or positive part of the AC cycle, but having two recitifying diodes 21 allows power to be harvested during both half periods of the AC cycle. In the illustrated example the charging period will be very short, as there is no current limiting resistor in series with the storage capacitor 18. Consequently, the reduced supply voltage for the consumers 5a-5c, 6 caused by the increased voltage drop over the FETs 17 during the charging of the storage capacitor 18 will be transient and not disturb these consumers 5a-5c, 6. Though the currently preferred embodiment illustrated in Fig. 5 uses two FETs it may also be possible to use only one, thus keeping component costs down and reducing the overall cost for the fuse cap 4 according to the invention.

In respect of Fig. 5 it should be noted that even though parts appear to be connected to ground, this is local floating ground within the fuse cap 4, and not actual ground, as the very essence of the power supply according to the invention is to harvest energy where no actual ground or Zero is available. As far as Fig. 5 goes, the horizontal ground lines just indicate that these points are connected together and at essentially same potential.

In Fig. 3 a fuse cap 4 according to the invention is schematically shown. The fuse cap 4 has a threaded but otherwise generally cylindrical conductor 25, in which a fuse 2 (shown only schematically in Fig. 1 ) is re- ceived so as to conductively engage one or more contacts 26 matching the typically annular bottom terminal of a NEOZED or DIAZED fuse, in which an indicator is located in the central hole of the annulus. The invention, however, is not limited to fuse caps for these types of fuses, but may be adapted by the skilled person to other types of fuses.

The fuse cap 4 has a housing 27 made of an insulating material, which similarly to conventional fuse caps may be adapted for gripping when screwing the fuse cap 4 into the fuse base 3 (shown only schematically in Fig 1 ).

The built-in first power supply 1 1 is inserted between and electrically in series with the cylindrical conductor 25 and the contacts 26 so as also to be connected in series with the fuse 1 in the circuit in which the power is to be measured. In Fig. 3 the current measuring device comprises a current sensing device 28 with a measuring resistance 44 (shown in Fig. 5 only) which is also connected in series with the built-in first power supply 1 1 . If other current sensing devices 28 are used, such as e.g. a Hall sensor, the built-in first power supply 1 1 could be connected directly between the cylindrical conductor 25 and the contacts 26. The built-in first power supply 1 1 supplies electri- cal energy to all those parts of the electronics of the fuse cap 4 in need thereof, such as, but not limited to, a first microprocessor 14, an A/D converter 30 forming part of the current measuring device, first digital memory 31 , such as RAM, wireless communication means 13. Wires or leads to these parts are not illustrated. The skilled person will realise that these parts may be more or less integrated than illustrated in the schematic block diagram of fig. 3. E.g. the first microprocessor 14 could include some or all of the first digital memory 31 . Likewise, as can be seen in Fig. 5, the current sensing device 28 may include an amplifier 45 and other amplifying circuitry so as to amplify the voltage detected over the measuring resistance 44, and representing the current through it, before it is supplied as an input signal to the A/D converter 30.

The first microprocessor 14 controls the current measurements. The current measurements are performed using an A/D converter 30 converting the voltage over the measuring resistance (not shown) or the output from a Hall sensor to a digital value. The A/D converter 30 preferably has a high resolution of e.g.16 bit. This resolution is appropriate to cover the necessary measuring range of current from approximately 10 mA to e.g. the rated 16 A, i.e. from small stand by currents of approximately 3 W to full rated consumption of an appliance such as a washing machine, a tumble drier or electrical heating panels of more than 3.5 kW, which all have to be measured with sufficient precision to yield a useful result.

The measurements are preferably performed at a high sampling rate, e.g. of 6 kilosamples/second or more in order to measure even a current with several harmonics precisely, e.g. such as a current to a dimmer or to a switch mode power supply of a computer or the like. The timing of the measurement is controlled by the first microprocessor 14 in order to match the current measurements performed by the A/D converter 30 with the voltage measurements performed in the power meter unit. If measurements are out of sync, the momentary values of power, as calculated by the product momentary cur- rent and momentary voltage, will be wrong yielding a wrong power value.

The synchronisation may be controlled via signals received at regular intervals, such as once per second, with the wireless communication means 13. Making the synchronisation only at regular intervals keeps the power consumption of the wireless communication means 13 down, as the transmitter circuits may be kept switched off most of the time. If the synchronisation intervals are kept suitably short, e.g. a second or less, keeping time in the inter- vals between synchronisation points may be performed by quite simple oscillation means, avoiding inter alia the cost of an oscillator crystal, and thus keeping the price of the fuse cap 4 down.

Likewise the receiver of the wireless communication means 13 may be kept switched off most of the time if data is kept in the first digital memory 31 and only transmitted to the power meter base station 7 at regular intervals, e.g. also once a second. The data transmitted could be the raw current measurement for further processing in the power meter base station, e.g. the calculation of momentary power and integration thereof over time to energy consumption. It may, however, also be possible to perform these calculations directly in the first microprocessor 14, provided that the first microprocessor 14 has the necessary information about voltage. Such information could also be received with the wireless communication means 13 and stored in the first digital memory 31 . Where to make the calculations is largely a matter of choice, as it may in some occasions be more suitable to perform them in the power meter base station 7, which also includes digital data processing means, e.g. a second microprocessor 38, second digital memory 41 , etc. to be described further below in conjunction with Fig. 4. In this respect it should be noted that when used for similar items in different parts of the system the terms first and second are used merely for distinguishing similar items found is different places in the system. No ranking or priority is intended to be implied. Likewise when the term second is used in description of an item in one part of the system, it does not imply that this part of the system includes a first part, only that he overall system may.

If the power calculations, as it is currently preferred, are performed by the first microprocessor 14 in the fuse cap 4, the synchronization information matching voltage with the current measurements is, however, not sufficient for the calculation of power. The reason is that in practice the voltage over the load deviates from the nominal voltage depending on the load because of the impedances in the net. Because the loads of the circuit form a voltage divider with the impedances of the net, which are in practice constant, the voltage drop over the loads in the circuit will decrease with increasing load. Thus for a higher current, such as full rated 16 A, the voltage will be lower than for a stand by current of a few mA.

As will be explained below in connection with the general description of the power meter base station 7, the power meter base station 7 is inter alia adapted to take this into account.

The power meter base station 7 is shown as a block diagram in Fig.

4. The power meter base station 7 comprises a flexible electrical cord 33 with a plug 34 adapted to be plugged into a wall socket, preferably as close to the fuse panel as possible, or as close as it is practical or convenient. If the fuse panel comprises a wall socket this would be ideal, but alternatively it could be on the other side of the wall holding the fuse panel or farther away on the same side. In any case the location of the socket would constitute a remote location as compared to the points in the fuse caps 4 where the current measurements are performed. The ground wire 35 and the phase wire are connected to a second power supply 37, which supplies all relevant parts of the power meter base station 7. These parts may include but are not limited to a second microprocessor 38, second wireless communication means 39, voltage sensing means 40, second digital memory 41 , such as RAM and/or mass storage such as a hard drive, a display 42 and a zero-transition detector 43. Supply wires or leads to these parts are not illustrated. The size of the power meter base station 7 will depend on how many of the the above parts are included. If no mass storage and no display 42 is included, the power meter base station 7 may simply be a small unit with a housing comprising an integrated plug, adapted to be held by the socket itself. This would obviate the need for a cord and a support, such as a shelf, for the power meter base sta- tion 7. The skilled person will realise that the included parts may be more or less integrated than illustrated in the schematic block diagram of Fig. 4. For instance the zero-transition detector 43 could form part of or be integrated with the voltage sensing device 40. The zero-transition device detects when the A/C voltage crosses zero and supplies this information to the second microprocessor 38 as a reference. The voltage sensing device 40 is preferably an A/D converter controlled by the second microprocessor 38. The second microprocessor 38 controls the measurements performed by the voltage sensing device 40, so as to sample the voltage at suitable intervals, e.g. at a sample rate of 6 kilosamples/second. Based on the voltage samples and the current samples measured in the fuse cap 4, the momentary power may be calculated. This may be done in more or less direct ways, depending on where which parts of the calculation is performed, be it in the fuse cap 4, as suggested above, or in the power meter base station 7. Referring now also to Fig. 1 for exemplification, if the power calculation is performed in the power meter base station 7 is based on current measurement information received from the second wireless communication means 32 in a fuse cap 4b, 4c by means of the wireless communication means 39, where the fuse cap 4b, 4c is in the same phase as the one into which the power meter base station 7 is plugged, the power may be calculated directly. The voltage resulting from all the currents through all the fuse caps 4b, 4c of this phase is measured directly and can be multiplied by the values of the respective currents. If the calculation is performed in the fuse caps 4b, 4c the resulting voltage has to be communicated to all the fuse caps 4b, 4c at appropriate intervals, e.g. concurrent with the transmission of the synchronisation information. The wireless communication between the power meter base station 7 and the fuse caps 4a, 4b, 4c may use time division in addition to the preferred protocol so that communication between all fuse caps and the power meter base station does not take place concurrently but e.g. in a time slot assigned to each of them, thus minimizing the risk that they disturb each other's communication. If a proprietory protocol is used, or if otherwise possible, frequency multiplexing could also be used so as to avoid the fuse caps 4a, 4b, 4c from disturbing each other's communication.

However, if the fuse cap 4a is in another phase than the one into which the power meter base station 7 is plugged, the situation is not so easy because the phase voltage measurable by the power meter base station 7 is not linked to the current consumption measured by the fuse cap 4a, because the current consumption is in another phase. Experience, however, has shown that it can relatively safely be assumed that symmetry exists in the electrical grid, in particular from the local distribution transformer to the fuse panel. Thus the impedances of the net, as illustrated by the equivalent impedances Z_R, ZS and Z_T in Fig 1 , can be assumed to be identical, meaning that at least appoximately Z_R, = Z_S = Z_T.

Having identified which fuse caps 4b, 4c belong to the phase into which the power meter base station 7 is plugged, the impedance Z_R may be derived by comparing voltage measured by the power meter base station 7 and the fuse cap 4b, 4c in a series of test measurements. This value of Z_R may then be stored in the second digital memory 41 of the power meter base station 7. If calculation takes place in the fuse caps 4 then the value of Z_R is transmitted to the fuse caps 4 and possibly stored locally in the first digital memory 31 in the fuse cap 4. Assuming, however, that Z_R=Z_S=Z_T the value of Z_R may also be used in fuse cap 4a as a substitute for Z_T, or in the corresponding calculation in the power meter base station 7 if the power calculation is performed there. Rather than calculating the impedance Z_R, Z_S or Z_T it is also possible to tabulate voltage versus current and possibly interpolate between the values in order to use these values for compensation. Such values could be store in the second digital memory 41 and/or the first digital memory 31 as the need may dictate.

Performing the calculation for other phases, the phase difference should also be taken into account. However, by comparison between a power value calculated from current measured in one phase and voltages phase shifted corresponding to all three respective phases will relatively clearly reveal which one yields the higher power output and which phase shift corresponds to the phase in which the fuse cap 4 is inserted.

The calculated power values and/or the integrated energy consumption may be displayed continuously on a display 42, but it may evidently also be stored in the second digital memory 41 for selective display or it may be transmitted to an additional device (not shown) such as a remote computer for post processing, remote display, data logging etc. This could be through transmission via the second wireless communication means 39, already present for communication with the fuse caps 4, using a standard, such as Zig- Bee®, Z-Wave, Wireless M-bus, SimpliciTI™, Bluetooth®, WiFi or it could be proprietary. It could also be through cabled connection such as Ethernet or the like.

Claims

P A T E N T C L A I M S

1 . A fuse cap adapted for cooperation with a fuse base, said fuse cap comprising current sensing means for measuring the current though a fuse held in the fuse base by the fuse cap,

c h a r a c t e r i z e d in that said fuse cap further comprises a first wireless communication means,

and in that said fuse cap comprises a built-in first power supply adapted to harvest energy from the current flowing through the fuse held in the fuse base.

2. A fuse cap according to claim 1 , wherein the fuse cap comprises timing means for the current measurements.

3. A fuse cap according to claim 2, wherein said first wireless communication means is adapted to receive information for the control of the timing means.

4. A fuse cap according to any one of the preceding claims wherein said fuse cap comprises a first microprocessor.

5. A fuse cap according to claim 4, wherein the first microprocessor is adapted to calculate power values.

6. A power meter base station adapted to be plugged into an electri- cal wall socket and comprising voltage measuring means allowing local voltage measurements based on the voltage delivered by said wall socket, c h a r a c t e r i z e d in that the power meter base station comprises second wireless communication means adapted to wirelessly receive measurement information based on current measurements performed in a remote lo- cation.

7. A power meter base station according to claim 6, comprising an estimator for estimating the voltage of other phases than that of the wall socket into which the power meter base station is plugged.

8. A power meter base station according to claim 6, wherein the sec- ond wireless communication means is adapted for transmitting timing information to a remote current measuring device.

9. A power meter according to claim 6, wherein the second wireless communication means is adapted for transmitting voltage information to a remote current measuring device.

10. A power metering system comprising a fuse cap according to any one of claims 1 to 5 and a power meter base station according to any one of claims 6 to 8.

1 1 . A power supply adapted for being inserted in series with a first load, said power supply comprising

a controllable resistance,

a means for controlling said controllable resistance,

an energy storage means, arranged in parallel with said controllable resistance,

wherein said means for controlling said controllable resistance is adapted to temporarily increase the resistance value of said controllable resistance, so as to divert current to said energy storage means, and to de- crease the resistance value of said controllable resistance so as to allow current to be supplied from said energy storage means to a second load.

12. A power supply according to claim 1 1 , wherein a rectifier is connected in series with said energy storage means, and in parallel with said controllable resistance.

13. A power supply according to claim 1 1 or 12, wherein said controllable resistance comprises a transistor.

14. A power supply according to any one of claims 1 1 to 13, wherein said means for controlling said controllable resistance comprises a comparator monitoring the voltage over said energy storage means.

15. A power supply according to any one of claims 1 1 to 14, wherein said energy storage means comprises a capacitor.