Present solutions in primary distribution realise the supply of all the CBs, the <BR> <BR> protections and other accessories, such as heating resistors, lamps, etc. , through one or more auxiliary supply connections. The supply circuit in the switchboard, particularly for primary distribution applications, is always dependent from an external storage unit, typically one or more batteries providing 1 lOV DC power supply. Such an external storage unit ensures reliability of system operation in case of loss of the electric power source, which is usually derived from the MV busbar.

The supply circuit within the switchboard is then usually split according to the functionality in several independent circuits: - supply of protection devices, - supply of opening circuit and shunt opening releases, - supply of closing circuit and shunt closing releases, - supply of spring charging motors (typically AC), - supply of other AC loads, resistors, lamps for internal illumination, plugs for power supply availability at each bay Each circuit is protected by LV circuit breakers at bay level, in the secondary equipment compartment, as shown in Figure 1.

In the case of a standard distribution CB having a mechanical operating mechanism, most of secondary functions are delegated to external control equipment. A standard distribution CB requires external auxiliary supply only to allow automatic recharge of the operating mechanism spring. For such systems, it is possible to implement a remote control for supplying the release coils; also

an automatic auxiliary undervoltage functions can possibly be implemented.

Self supply solutions have also been developed for secondary distribution applications, where the auxiliary supply in some cases is not at all available. In such cases, the current sensors provides the energy required for the CB operation when the current is equal or higher than 20% of rated value at least on one phase. The energy obtained through the current sensor enables the supply of a protection device, such as a microprocessor based over-current release. Then the protection device, based on the protection settings and according to the measured current, supplies the opening solenoid which directly acts on the mechanical operating mechanism. The energy required to open the circuit breaker is stored in the spring mechanism, and in the absence of an auxiliary supply system the recharge of the operating spring is carried out manually. The operating mechanism can store for unlimited time up to three operations, i. e. the conventional open-close-open (O-C-O) cycle. This solution is applied to most of the conventionally operated mechanically systems available in the market.

Magnetically actuated switching devices behaves differently from mechanically operated ones, in that they need a system for storing electric power. In case of loss of the auxiliary supply, the electrical storage of operation energy in a capacitor leads to a limited time of operation availability. After loss of the supply, the self-discharge processes of the capacitor and the energy consumption from the various electronic devices drains energy from the storage. When the lower operating voltage is reached, the switch must either be locked or automatically open according to the customer requirement.

This is critical in the event of a loss of auxiliary supply, as the supply requires a start-up time to charge-up the storage at power restoration levels. In such a case the protection functions could be not operative during the re-supply event, which normally takes a time period in the range of 10-30 s.

The above described solutions have some relevant limitations.

For the self-supplied mechanical operated mechanism, the protection device on-

board is supplied only in case of current greater than 20% of the nominal value.

With this concept it is not possible to supply an integrated communication device, giving the possibility to remotely manage and monitor the switching device, unless there is enough current flowing in the device, thus making the solution unreliable.

For the magnetic actuated switching device, it is not possible to avoid the need of the auxiliary supply connection, and in case of loss of it, after some time, the operation will not be anymore possible. Also, at the return of the auxiliary supply a certain time has to be allowed before the full functionality of the circuit breaker is back.

In general, all the systems known in the art, require a highly reliable auxiliary supply with corresponding relevant cost.

Goal of the invention is to realise a primary or secondary distribution switchboard and/or switching device with a self supply system, which allows to sustain the auxiliary supply system in case of loss of the main secondary equipment supply.

According to the present invention, it is possible to even avoid any auxiliary supply, relying only to the self-supply source of power. This is particularly useful in secondary distribution switchgear, where adding an auxiliary supply circuit is often considered as a useless nuisance, and the customers are unwilling to pay the related costs.

The system of the present invention is based on the integration, within the switching device or switchboard, of a suitable device able to drain the needed power from the medium voltage power network. The power thus obtained, is used in order to increase the functionality of the switching device or switchboard.

This can be done either by using a traditional power transformer already available for metering or measurement, or by a suitable device.

This power source drain device can be used to supply the electronic on-board

the device, in such a way to make available power for communication purposes as well as for remote control, measurements, monitoring, and so on.

Moreover, in case of magnetic actuated switching devices, the power can be used to charge, even almost instantaneously the capacitor bank, in order to provide immediate availability of the switching devices for protective open operation; this is particularly important during re-insertion after a period of black-out where both auxiliary supply and MV supply has been absent for a certain time. In addition to that, the power can be used to keep the capacitor bank charged.

Self-supply enables the switching device or switchboard to higher availability in case of presence of the auxiliary supply.

For primary distribution substations, it gives the possibility to have a device to drain power from MV network. It is therefore possible to under-dimension, or even completely eliminate, the UPS system, which is usually installed within the auxiliary supply equipment, with related purchasing and maintenance costs.

For secondary distribution substations, where often the auxiliary supply is absent due to cost-related reasons, a self supply system allows for a better integration of mechanical operated switching device in a modern control system, even in case of low value of flowing current, when the current transformer does not give enough power to supply an electronic device in economical way.

The concentrated self-supply architecture according to the present invention is modular and can be built up on four different levels: - single input auxiliary supply to electronic devices with 110V DC auxiliary supply by an external UPS at substation level. A schematic representation is given in Figure 2, which relates to standard solution with no self-supply installed; - redundant supply architecture by one centralized converter for the whole switchboard, supplied by an external UPS and by the self supply system, e. g. a busbar VT. A schematic representation is given in Figure 3;

- redundant supply by one centralized converter to substitute the substation UPS; in such a case the lower functionality under emergency conditions is compensated by system savings. A schematic representation is given in Figure 4; - redundant concentrated/distributed supply, with or without a substation UPS, with total redundancy; any of one single fault in the distribution network does not affect the behavior of the complete system. A schematic representation is given in Figure 5.

The auxiliary supply bus is distributed to all the single input electronic devices from a central converter, supplied by both the auxiliary and the busbar/incoming Voltage Transformers. This solution has a number of advantages: higher availability, since in case of loss of auxiliary supply it is still operative; a central converter can accept different voltage ranges; the external possible UPS function can be eliminated or under dimensioned.

The self supply function integrated into the switchboard can require a service panel to house centralized converter and voltage transformers for power drain from MV; or whenever possible the self supply capability can be obtained using Voltage Transformers, which are located at busbar level or in correspondence in-coming feeders.

Operating principle, solutions and relevant advantages are described in attached figures.

In case of a self-supply function integrated in the switching device, a suitable device is used to drain the needed power from the medium voltage distribution network. This device can be based on a capacitor which, acting as a current source generator, provides the switching unit with the electrical power needed.

Such a system is described in Figure 6. The capacitor can be either added to the switching device pole or even integrated within it.

Since the size of the capacitor is limited by the available volume, a mutual inductance can be used in order to"amplify"the current drained from the capacitor. In this way by correctly dimensioning the capacitor and the mutual inductance, it is possible to have the desired electrical power in such a way to satisfy all needs of the switching device. This solution is described in Figure 7.

With the system of the present invention, it is possible to supply the switching unit with a low cost and reliable solution.