The present invention relates mainly to a method for improving the
electric protection in electric systems according to the preamble of claim 1.
All electric systems require an electric energy source to operate.
Many electric systems take electric energy from external supply electric mains.
These electric mains can be of alternating current or of direct current (civil,
industrial, telephonic, TNV, etc.). In these cases, it becomes useful the use of
line automatic mechanical breakers fundamentally for two technical reasons: for
having access to the circuits of the electric system, for example, for maintenance
without risks for personnel, and for protecting both the electric mains and the
users in case a failure or an accidental contact could cause electrocutions, overheating
Therefore, the use of such mechanical breakers is much widespread
also because of the electric safety standards in force at the national and at the
international level, that, for many electric systems, require their use.
In many cases, the breaker (that constitutes the general electric
protection device of the electric system) comprises a magneto-thermal breaker device
in combination with a differential current breaker; alternatively, it may consists
of a relay or of a contactor driven by line current or of another automatic protection
device. The intervention time of a device of these types depends on the current
intensity that flows through it and on its own intrinsic speed characteristic (delay,
semidelay, fast, etc.). By way of example, in the attached Fig.4 it is shown the
intervention characteristic of a magneto-thermal breaker on a Cartesian plane in
which in the ordinate, with logarithmic scale, is written the intervention time
of the breaker in seconds, and in the abscissa, with linear scale, is written the
ratio between the breaker current and the nominal current; the breaker considered
has a nominal current of 25 Ampere and the two curves in the figure represent respectively
the minimum and maximum intervention time of the breaker in relation to a constant
current flowing through it; this characteristic has intrinsic uncertainties (for
small currents, medium currents and large currents) that depend on factors hardly
predictable by the user of the breaker.
Through the general protection device several user electric units
are usually power supplied; these are usually provided with their own local electric
protection devices such as fuses, restorable fuses, PTC resistors, relays, magneto-thermal
breakers (with nominal current lower than the one of the general protection device),
or other similar devices.
Some examples of such a situation are:
- a telecommunication exchange in which the supply mains are of direct current
and the user units are the boards performing the different functions in the exchange;
- a house in which the supply mains are the public ones for civil use at 230V
and 50Hz alternating current and the user units are, for example, the different
electric household appliances;
- an automated industrial plant in which the supply mains are the public ones
for industrial use and the user units are the different machines.
Both the general protection device of the electric system and the
local protection devices of the user electric units have intervention characteristics
that are much variable and hardly predictable with extreme precision. This is due
to the fact that they are electric devices essentially based on thermal and/or magnetic
and/or mechanical effects; therefore, a precise co-ordinated protection through
such devices is hard to be obtained. Moreover, for these reasons, there could happen
undesired interventions of the general protection device, for example, in the following
- one of the user units gives rise to a temporary current overconsumption situation
without being in failure;
- one of the user units is in failure but the local protection device does not
intervene or intervenes too late;
- in the supply mains there happens a common mode or differential mode voltage
in these cases, in fact, these are either temporary anomalies in the
power supplied to a user unit or to the whole system, or permanent anomalies of
only one user unit, so the permanent interruption in the power supplied to the whole
system is a protection measure effective but exaggerated.
In case of an undesired intervention of the general protection device,
all the user units remain without power and the service that the electric system
(telephone exchange, house, industrial plant) provides is completely interrupted.
The restoration of the service requires, in general, the physical
intervention of an operator in order to restore/reset manually the general protection
The cost caused by the undesired intervention of the general protection
device may be, in certain cases, very high because it requires the physical intervention
of an operator and because of the long interruption of the service that it implies.
Patent US 5.581,433, discloses an electronic breaker to be connected
to an active computer bus; the breaker is designed so that, as soon as the output
current exceeds a fault current level, a capacitor begins to charge and the output
current is limited to a maximum current level; once the voltage across the capacitor
reaches a predetermined value, a temporary interruption in the output power is performed;
the cycle repeats uritil the fault disappears. Such functionality is especially
useful for limiting in-rush currents (like when a device is connected to an active
bus) but is not adapted to deal with situations like (permanent) short circuits;
in fact, in this case, the cycle would repeat forever and the load would be highly
Object of the present invention is to overcome the drawbacks of the
known art and, particularly, to provide a method for improving the electric protection
of electric systems protected by traditional breaker devices trying to avoid all
the unnecessary interventions (therefore undesired) and trying to assure all necessary
interventions (therefore desired), and that can be implemented in an easy and economic
This object is substantially achieved through the method having the
functionalities set out in independent claim 1; further advantageous features of
the method according to the present invention are set out in the dependent claims.
The basic idea of the present method is to prevent the intervention
of the breaker device and the consequent permanent power interruption, and to perform
a temporary power interruption of a predetermined duration in such a way that eventual
temporary anomalies may end and/or exhaust.
According to further aspects, the present invention relates also to
an electric circuit, a protection system, a power supply system and an electric
system having the features set out respectively in claims 13, 20, 26 and 27, that
implement such method.
The invention will become clearer from the following description to
be considered in conjunction with the accompanying drawings, that must be considered
not in a restrictive sense but only in a descriptive sense, wherein:
- Fig. 1 shows the block diagram of an electric system according to the present
- Fig. 2 shows the block diagram of an electric circuit according to the present
- Fig. 3 shows a mixed block and schematic diagram of an electric circuit according
to the present invention;
- Fig. 4 shows the intervention characteristic of a traditional magneto-thermal
- Fig. 5 shows the waveform of the supply current of an electric system in different
- Fig. 6 shows the waveform of the supply current of an electric system according
to the present invention when a first failure happens; and
- Fig. 7 shows the waveform of the supply current of an electric system according
to the present invention when a second failure happens.
It has to specified that the waveforms of Fig.5, Fig.6 and Fig.7 have
to be considered purely as schematic helps for a better comprehension of the description,
and their absolute and relative dimensions are neither representative nor binding.
With reference to Fig.1, an electric system SYS, according to the
present invention, is provided with at least an own supply input IS to be connected
to external supply electrical mains RA and comprises :
- at least one user electric unit provided with at least an own supply input,
- a protection system PR connected to the supply input IS of system SYS and to
the supply input of the unit and adapted to distribute power internally to system
SYS in an electrically protected way.
System SYS of Fig.1 comprises three units U1, U2, U3, each of them
is provided with an own supply input I1, I2, 13.
The peculiarity of protection system PR, according to the present
invention, mainly consists in a particular electric circuit CKT, according to the
present invention, comprised in system PR.
Protection system PR is provided with a supply input IP and at least
one supply output; in the example of Fig.1, system PR is provided with three supply
outputs O1, O2, O3.
System PR, according to the present invention, essentially comprises:
- an automatic breaker device MT, for example a magneto-thermal breaker, having
an input IM connected to input IP of system PR and an output OM,
- an electric circuit CKT, according to the present invention, having an input
IC connected to output OM of breaker device MT, and an output OC connected to the
output of system PR.
In the example of Fig.1, output OC is connected to all outputs O1,
O2, O3 of system PR that are connected in parallel to each other.
It is important to notice that, in the example of Fig.1, the above
mentioned connections are not direct connections but indirect connections because
of the presence of further circuit elements FS1,FS2,FS3,CB1,CB2.CB3 that will be
The supply current of system SYS that flows from mains RA towards
system SYS depends on the consumption of units U1, U2, U3, not considering, for
simplicity, the current consumption of device MT and of circuit CKT; in normal conditions,
the supply current of system SYS is lower than the nominal current "In" of device
MT; but there may be anomalous cases where this does not happen.
In Fig.5 there is shown the possible waveform of the supply current
of system SYS in six different anomalous cases:
- case A: current exceeds a little the nominal value "In" for a short time;
- case B: current exceeds a little the nominal value "In" for a long time;
- case C: current exceeds a lot the nominal value "In" for a short time;
- case D: current exceeds a lot the nominal value "In" for a long time;
- case E: current exceeds the nominal value "In" and continues to increase quickly;
- case F: current exceeds the nominal value "In" and continues to increase slowly.
In the absence of any protection device and of circuit CKT, cases
A and B would not have negative effects on system SYS, case C would have a negative
effect on system SYS damaging it slightly, case D would have a negative effect on
system SYS damaging it seriously, cases E and F would surely have a negative effect
on system SYS and it would be damaged irreparably.
In the presence of an appropriate breaker device MT having, for example,
the characteristic shown in Fig.4, it may be assumed that there is an intervention
of device MT in cases D, E, F; in case C, because the current pulse is very short,
the intervention of device MT is not sure. In conclusion, in cases A and B there
is no intervention and this is desired, in cases E and F there is an intervention
and this is desired, in case C there is no intervention but system SYS is not adequately
protected, in case D there is an intervention but this is an exaggerated measure
because the current transient would be limited in time.
The method according to the present invention improves the electric
protection provided to an electric system by an automatic breaker device; such protection
consists in performing a permanent (save manual or pseudo-manual restoration) interruption
in the power supplied to the user units of the electric system when predetermined
electric situations are reached.
With reference (not restrictively) to Fig.1 and Fig.6, the method
according to the present invention comprises the steps of :
wherein the temporary interruption is of a predetermined duration "Tb".
- a) performing a monitoring of the power supplied to system SYS at least when
the current supplied to system SYS is greater than a predetermined first value "In",
- b) performing a temporary interruption in the power supplied to the unit (U1,
U2, U3) through an electric circuit (CKT), distinct from the automatic breaker device,
starting before said electric situations are reached so that the intervention of
the automatic breaker device is prevented;
In this way, automatic breaker device MT does not intervene and, therefore,
its (manual or pseudo-manual) restoration is not required.
Ideally, the temporary interruption should start just before the intervention
of device MT, for example some milliseconds or even less; practical reasons advise
to use safety margins because it is absolutely not easy to estimate with extreme
precision the intervention instant of device MT; in practice, the start of every
temporary interruption is determined on the basis of past history and, logically,
not on the basis of future history; so it is not possible to precisely determine
how in advance each interruption starts with respect to the corresponding intervention
of device MT.
Naturally, the type of supply power monitoring to be performed (instant
current, average current, rms current, peak current, instant voltage, average voltage,
rms voltage, peak voltage, instant electric power, average electric power, peak
electric power, ...) depends on the type of electric situations that lead to the
intervention of the breaker device used.
For the sake of completeness, it has to be added that the intervention
of the breaker device may be influenced by environment parameters such as: temperature,
humidity, atmospheric pressure.
According to the type of breaker device, the monitoring may be more
or less extended in time; in certain cases, the monitoring may be permanent; it
is common practice to perform the monitoring by sampling.
After such temporary interruption, it is possible to provide simply
for the further step of :
- c) restoring power to user electric units U1, U2, U3.
More sophisticated but more complicated to implement strategies may
provide for restoring supply power, for example, with a limited supply voltage value
or with a supply current limitation.
After such restoration, the supply current of system SYS can become
normal again or, in any case, falling within non-dangerous limits, as shown in Fig.6
with waveform H; actually, waveform H includes a slight exceeding of threshold "In"
for a short time period.
Alternatively, after such restoration, there can happen again another
anomaly in the supply current of system SYS, as shown in Fig.7. The method according
to the present invention may then advantageously provide that steps a), b), c) be
repeated for a predetermined number of times; in other words, a certain number of
trials are performed in the hope that the problem be solved by itself; in the example
of Fig.7, there are performed three temporary interruptions Tb1, Tb2, Tb3 and thereafter
the current has become normal according to waveform N. In the case of repetitions,
complex strategies may provide that the duration of the temporary interruption be
different from trial to trial, for example, increasing or decreasing.
Notwithstanding the temporary interruption or the eventual repeated
temporary interruptions, the supply current may anyway not return within non-dangerous
limits, that is to say that such predetermined electric situations may anyway be
reached again; in this case, the method may advantageously provide that a permanent
interruption in the power supplied to user units U1, U2, U3 be performed.
The easiest way to obtain this is to leave the automatic breaker device
MT to intervene. There may be also provided to facilitate the intervention of device
MT through crow-bar devices, as will be better described hereafter.
Alternatively there may be provided that this permanent interruption
be performed by the same device that has the task to perform the temporary interruption;
in this case, it would seem that device MT has no longer utility: this is not true;
in fact, its presence may be on one hand required by safety standards and on the
other hand recommended as further protection in case of non-action of the normal
By what described till now, it is possible to avoid undesired interventions
of the automatic breaker device while guaranteeing electric protection to the electric
There are cases anyway, as the one indicated with letter C in Fig.5,
in which automatic breaker device MT may not be able to intervene even if system
SYS may run the risk of being damaged to a more or less serious degree.
A very frequent situation is that a very high supply current peak
may damage system SYS: in the example of Fig.5, higher than a certain value "Im".
To face this case, the method according to the present invention may
advantageously provide that the supply. current of system SYS be limited to a predetermined
value during the operation of the system; in the case of Fig.5 such value is "Im".
The waveform of the supply current shown in Fig.7 corresponds to a
case in which both a current limitation and a temporary interruption repetition
have been performed, in particular a triple repetition: during a first section K
of the waveform limiting the current for a relatively long time interval has been
necessary, during a second section L of the waveform limiting the current for a
shorter time interval has been necessary, during a third section M of the waveform
no limitation has been necessary to be performed. It has to be noticed that it would
be a good thing to limit as much as possible the time intervals during which a forced
limitation of the supply current is performed because this leads to a corresponding
limitation of the supply voltage and therefore to an anomalous power supplying to
the user units.
A basic parameter of the method according to the present invention
is the current value above which it is necessary to monitor the power supplied to
the system; the most natural choice is that this value corresponds substantially
to the value of the nominal current of automatic breaker device MT. It is also possible
to make more conservative choices, for example: 50% or 80% of the nominal value.
Another basic element of the method according to the present invention
is the electric situations that cause intervention of automatic breaker device MT
and that must be prevented; in the simplest case, but perhaps the most realistic,
these depend on the characteristics of device MT itself: in many practical cases,
such electric situations are functions at least of the intensity and the duration
of the current flowing through the device; naturally, it is possible to think of
breakers with programmable intervention. As already said, it is necessary to keep
in mind that the breaker device intervention may be influenced also by environment
parameters such as: temperature, humidity, atmospheric pressure.
An important parameter of the method according to the present invention
is the duration "Tb" of the temporary interruption or interruptions; a good compromise
choice is that such duration be in the order of the second; in any case, the choice
should be made case by case on the basis of the frequency, the duration and the
entity of the various anomalies in the power supplying that may happen and also
on the basis of the down time acceptable for system SYS; similar considerations
are valid also for the number of interruption repetitions.
Another important parameter of the method according to the present
invention is the current limitation value; this choice depends on the characteristics
of the automatic breaker device; for sure, the current limitation value will be
a multiple (not necessarily an integer) of the nominal current of automatic breaker
device MT; the value of the current limitation shall be chosen in such a way as
to assure a reliable response by device MT; in the case of the device corresponding
to the characteristic of Fig.4, a reasonable choice is, for example, between five
and eight times the nominal current. It has to be noticed that it would be a good
thing to limit, as much as possible, the time during which a supply current limitation
is performed because this leads to a corresponding reduction in the supply voltage
and therefore, during the limitation time, the user units of the electric system
are power supplied in an anomalous way (out of their constructive specifications).
In the method according to the present invention it is necessary to
take a basic decision: when to start the power supply temporary interruption. This
implies to estimate when the electric situations that lead to the intervention of
the automatic breaker device are next to be reached.
A good implementation of the method must provide for a conservative
estimate; that is to say, the estimate must be made in such a way that it would
be really unlikely that the breaker intervenes before the start of the temporary
A good implementation of the method must also imply an estimate relatively
simple to be made in terms of computation.
A very good implementation of the method should make an estimate that
takes into account also environment situations important for the specific breaker
device used; such an estimate implies the detection also of these environment parameters.
If a physical-mathematical accurate model of the breaker device would
be available, the mentioned estimate could be made in a very precise way; unfortunately
this happens very seldom.
A first good compromise implementation consists in that the start
time of said temporary interruption of step b) corresponds to the time when a certain
predetermined value is exceeded by the time integral of the difference between the
current supplied to the system obtained through the monitoring of step a), and the
nominal current of the automatic breaker device, the integral being computed starting
from the time when the current supplied to the system exceeds such nominal value;
with reference to Fig.6, such integral corresponds to the area delimited on the
upper side by waveform section G and on the lower side by horizontal straight line
The mentioned value must be determined typically at least on the basis
of the automatic breaker device characteristic. In the following there will described
some possible good choices making reference to Fig.4 and Fig.6.
A first very conservative choice consists in determining the peak
value of the current within section G, using such peak value to estimate the corresponding
minimum intervention time using the lower curve in Fig.4 and thereafter making the
product of them; if, for example, during an operation phase of the electric system
the peak within waveform G is 75 Ampere, i.e. three times the nominal current of
device MT, the corresponding minimum intervention time is about 0,2 seconds, and
the mentioned value will be equal to (75-25)*0,2=10; in this case, the mentioned
"predetermined value" depends not only on the characteristic of the device but also
on the course of the current in the system and therefore it has to be updated instant
A second choice similar to the first one but less conservative consists
in considering the average value of the current within section G instead of the
peak value; also in this case, the mentioned "predetermined value" depends not only
on the characteristic of the device but also on the course of the current in the
system and therefore it has to be updated instant by instant.
A second good compromise implementation consists in that the start
time of said temporary interruption of step b) corresponds to the time when a certain
predetermined value is exceeded by the time integral of the difference squared between
the current supplied to the system obtained through the monitoring of step a), and
the nominal current of the automatic breaker device, the integral being computed
starting from the time when the current supplied to the system exceeds such nominal
The mentioned value of the second implementation can be determined
with methodologies and considerations similar to the value of the first implementation.
For sure, further good compromise implementations based on different
simplified models of the breaker device, may be provided.
The method according to the present invention requires circuitries
and electric and electronic systems in order to be implemented; these constitute
further aspects of the present invention. It is better to clarify that during the
implementation phase of the method according to the present invention it is advisable
to consider appropriate safety margins in the parameter choice, in the measurement
estimate, and in the use of the device characteristics.
With reference (not restrictively) to Fig.2 and Fig.3, electric circuit
CKT, according to the present invention, is provided with a supply input IC and
a supply output OC; input IC is adapted to be connected to an output OM of an automatic
breaker device MT; output OC is adapted to be connected to a supply input of a user
electric unit (in the example of Fig.2, output OC is connected in parallel to all
the supply inputs I1,I2,I3 of the three user units U1,U2,U3 of electric system SYS);
circuit CKT is adapted to carry out the method according to the present invention
and, to this purpose, it comprises :
- detection means DET for detecting at least the current flowing at supply output
OC of electric circuit CKT,
- conduction means SW for connecting in a controlled way supply input IC and supply
output OC of electric circuit CKT, and
- control means CNT connected to detection means DET and to conduction means SW,
and adapted to control said conduction means SW in relation to at least the current
detected by detection means DET.
It is clear that the implementation of the method is mainly entrusted
to control means CNT, while conduction means SW will have the task to perform the
temporary interruption and the restoration of the power.
In the example of Fig.2, supply input IC is provided with an own positive
terminal IC+ and an own negative terminal IC- and supply output OC is provided with
an own positive terminal OC+ and an own negative terminal OC-, conduction means
SW operate only on the positive line while the negative line is constituted by a
permanent direct connection at very low resistance, detection means DET operate
only on the positive line.
Examples of implementation different from the one of Fig.2 may provide
that the conduction means operate both on the positive line and on the negative
line, or, in systems with alternating current supply, on one or on both lines or
on the ground, or, in three phase systems, on all phase lines and on the common
line. Examples of implementation different from the one of Fig.2, may provide that
the detection means operate on the negative line, or, in systems with alternating
current supply, on one of the lines or on the ground, or, in three phase systems,
on one of the phase line or on the common line; moreover, the detection means may
be adapted to detect current in more than one conductor at the same time or in temporal
Current detection can be made, in case of direct current supply, through
a resistive shunt or a Hall-effect sensor, or, in case of alternating current supply,
through an ammeter transformer or a compensated coil/choke.
The electric circuit according to the present invention may provide
that the detection means be further adapted to detect other supply quantities at
supply output OC of the electric circuit, for example, supply voltage at output
OC; in this case, the control means are adapted to control the conduction means
further in relation to these other detected supply quantities.
According to their simplest embodiment, conduction means SW consists
of an ON/OFF controlled switch as, for example, a relay; if it is necessary to operate
on more lines, the number of controlled switches in consequence increases.
In order to obtain a more accurate conduction control, it is necessary
that conduction means SW comprises at least a conduction path having a resistance
of a controlled value for connecting input IC to output OC.
In order to obtain the advantageous effect of supply current limitation,
it is advantageous to use conduction means SW with controlled resistance conduction
path and control means CNT able to control them in such a way as to limit the current
flowing between input IC and output OC.
Means SW can be easily realised, for example, through one or more
transistors; in case of alternating current supply, it is possible to use two transistors
connected in such a way that their main conduction paths be opposed.
As the method according to the present invention provides for complicated
computation, it is advantageous that the said control means CNT comprises essentially
a programmed and/or programmable type intelligent unit UI. Such unit UI may comprise
a microprocessor and some memory or, alternatively, a microcontroller.
In case that circuit CKT is provided with an intelligent unit UI,
this last may control means SW and may also enable the remote control and/or monitor
of circuit CKT. Examples of control may be the programming of unit UI itself in
terms of method parameters; monitor may refer to both supply quantities and performed
In the example Fig.2 and Fig.3, unit UI exchanges information with
a remote control and monitor unit UCM internal to electric system SYS; it is then
the task of unit UCM to exchange management information with a remote manager RMT
where e.g. a human operator acts.
In Fig.3 it is shown a mixed block and schematic electric diagram
of a particular embodiment of the electric circuit according to the present invention:
four MOSFET type transistors Q1, Q2, Q3, Q4 connected in parallel to each other
constitute essentially conduction means SW; the network comprising resistors R13,
R18 and capacitor C5 constitutes essentially detection means DET; each MOSFET type
transistor is connected to a self-protection circuitry with appropriate filters
(transistor Q1 is connected to transistor Q5, to resistors R1, R2, R3, R14 and to
capacitors C1, C7); control means CNT consists of an amplifier AMP directly connected
to the current detection network, an analog-to-digital converter ADC connected to
the output of amplifier AMP, an intelligent unit UI connected to the output of converter
ADC, a power supply block BA connected to input IC and to unit UI for providing
supply power to it, and a driving block BP connected to an output of unit UI and
to the control terminals of transistors Q1,Q2,Q3,Q4.
An electric circuit CKT according to the present invention may be
used and applied into a protection system.
With reference (not restrictively) to Fig.1, protection system PR,
according to the present invention, is provided with a supply input IP and at least
one supply output; in the example of Fig.1, system PR is provided with three supply
outputs O1,O2,O3, one for each of the user units U1,U2,U3 of electric system SYS.
System PR comprises :
- an automatic breaker device MT having an input IM connected to input IP of system
PR and an output OM,
- an electric circuit CKT according to the present invention having an input IC
connected to output OM of device MT, and an output OC connected to the output of
in the example of Fig.1, output OC of device MT is connected in parallel
to all the three outputs O1, O2, O3 of system PR.
Actually, it is very likely and advantageous that system PR be provided
with more supply outputs, all connected in parallel to the output of circuit CKT.
In case of a plurality of outputs, in protection system PR each output
O1, O2, O3 may advantageously be provided with an own local electric protection
device FS1, FS2, FS3; local protection electric devices FS1, FS2, FS3 are advantageously
co-ordinated, to the possible extent, with device MT. The purpose of all this is
that local protection devices FS1, FS2, FS3 intervene in case of failures or anomalies
and that they do this before general protection device MT; in any case, before any
of these interventions it would be good that electric circuit CKT according to the
present invention acts in order to avoid undesired interventions.
In addition to local protection devices FS1, FS2, FS3 it is advantageous
to provide an own controlled local crow-bar device CB1, CB2, CB3 for each of outputs
O1, O2, O3 of system PR, that is able to cause the intervention of the corresponding
local electric protection device FS1, FS2, FS3; in practice, if through an appropriate
detection of the supply quantities, it is possible to determine that one of the
user units connected to the outputs of protection system PR is irreparably faulty
and out of order, it is possible to control the closing of the corresponding crow-bar
device and to obtain the intervention of the corresponding local protection device
or (if it is necessary) of the general electric protection device; such failure
or bad operation may then be signalled to the remote and/or local operator.
In order to improve the performances of protection system PR, it is
possible to advantageously provide further a thermal compensation device CT for
the characteristics of the breaker device MT.
.Finally, protection system PR according to the present invention
may advantageously comprises a remote control and/or monitor unit UCM; the control
may refer, for example, to circuit CKT and to crow-bar devices CB1, CB2, CB3; monitor
may refer to the various supply quantities and to protection system PR history and
A protection system according to the present invention may be used
and applied e.g. into a power supply system for electronic equipments.
A protection system according to the present invention may be used
and applied into electric systems.
With reference (not restrictively) to Fig.1, electric system SYS according
to the present invention is provided with at least an own supply input IS to be
connected to external supply electrical mains RA and comprises :
- at least one user electric unit provided with at least an own supply input,
- a protection system PR according to the present invention, connected to supply
input IS of system SYS and to the supply input of the or each unit and adapted to
distribute power internally to system SYS in an electrically protected way;
in the example of Fig.1, user electric units U1, U2, U3 are three.
The circuitries and the systems described above require calibration:
method parameters have to be set on the basis of the user units, of the automatic
breaker device i.e. of the general protection device and of the eventual local protection
devices and also of the type and frequency of the failures and of the disturbances.
Such calibration may be made manually by the installer or the user;
alternatively, such calibration may be made in an automatic or pseudo-automatic
In case of an intelligent unit UI, it is possible to perform a sort
The self-learning operation consists in detecting all characteristic
parameters of automatic breaker MT through a test on itself instead of setting them
on the basis of its characteristics provided by the manufacturer.
Such operation must be performed during the installation phase and
when loads are not applied, i.e. when user units are not connected; an operator
must be present in order to restore/reset the breaker; the overall duration of such
operation must be of the order of the minute.
The self-learning operation can be summarised as follows:
- downstream of breaker MT only an appropriate test equipment is connected;
- the breaker is restored/reset manually by the operator;
- the self-learning procedure is started on the test equipment;
- the test equipment automatically applies at the breaker output loads in such
a way as to cause flowing currents with a step-by-step increasing width and duration;
- in those cases when there happens an intervention of the breaker, the quantities
are memorised that led to the intervention and it is required through an appropriate
signalling to restore/reset the breaker;
- when the test is complete all data memorised during the preceding step are transferred
in an appropriate way to unit UI of circuit CKT according to the present invention
through a serial connection or of another type.
In other words, the self-learning operation builds up point by point
the intervention curve of the breaker under test. It is important to keep in mind
that such curve has been derived in particular conditions (for example of temperature,
of humidity) and may be extremely appropriate to apply safety margins; this may
be done by the test equipment or by intelligent unit UI.
Once the self-learning operation is over, unit UI and the corresponding
circuit CKT can be used; obviously, what is left is to connect the user units to
circuit CKT and then to supply power to breaker MT.