The present invention relates to an automatic reset device
particularly for residual current-operated circuit breakers and the like. More particularly,
the invention relates to a device that allows to reset automatically a residual
current-operated circuit breaker following its release, after checking the correct
operation of the system.
As is known, residual current-operated circuit breakers
are normally provided in home and industrial systems in order to prevent a fault
current from causing danger to users and to the loads connected to the electric
line.
Essentially, the residual current-operated circuit breaker,
when it detects the fault current, disconnects the line, accordingly interrupting
the supply of power to the load or loads arranged downstream.
After the release of the residual current-operated circuit
breaker, and once the correct operating conditions of the system have been restored,
the residual current-operated circuit breaker must be reset.
The operating conditions often restore themselves spontaneously,
because the fault is of a transient type caused by overvoltages.
Such reset normally occurs manually by acting on an appropriately
provided reset lever.
However, if the user performs the reset after an opening
or release of the residual current-operated circuit breaker, he cannot be sure that
the fault has been removed. Therefore, when the user performs the reset, a subsequent
closely spaced release of the residual current-operated circuit breaker can occur,
because the problem has not been solved correctly.
US-4,979,070
, which is considered to represent the closest prior art, discloses an
automatic reset circuit for a Ground Fault Circuit Interrupter by means of which
circuits are monitored after tripping of the GFCI and the GFCI is automatically
reset when no fault conditions are detected.
It provides an automatic reset device particularly for
residual current-operated circuit breakers and the like that allows to check the
correct operation and status of the system before resetting the residual current-operated
circuit breaker.
The prior art may provide an automatic reset device particularly
for residual current-operated circuit breakers that provides the user with assurance
of continuity of service by reclosing the residual current-operated circuit breaker
after temporary faults, after checking the status of the system before performing
the actual reset.
An object of the present invention is to provide an automatic
reset device that is capable of checking the correct connection of the device itself
to the system.
Another object of the present invention is to provide an
automatic reset device that is highly reliable, relatively simple to provide and
at competitive costs.
This aim and these and other objects that will become better
apparent hereinafter are achieved by an automatic reset device as claimed in the
appended claims.
Further characteristics and advantages of the invention
will become better apparent from the description of a preferred but not exclusive
embodiment of the reset device according to the present invention, illustrated by
way of non-limiting example in the accompanying drawings, wherein:
- Figure 1 is a general circuit diagram of the device according to the present
invention;
- Figure 2 is a block diagram of the reset device according to the present invention;
and
- Figure 3 is a circuit diagram of the reset device according to the present invention.
With reference to the figures cited above, the reset device
according to the present invention, associated with a residual current-operated
circuit breaker, includes a control means 1, which is conveniently connected to
a residual current-operated circuit breaker 2 by virtue of connections 3 and 4,
which connect the control means 1 downstream of the residual current-operated circuit
breaker 2 and upstream of a load 5 on one side and upstream of the residual current-operated
circuit breaker 2 by virtue of connections 6 and 7 on the other side, so as to bypass
the residual current-operated circuit breaker, without any connection to the ground
system.
Figure 1 and the other figures show the electrical line
with the phase 8 and the neutral 9.
The control means 1, conveniently constituted by a control
board, is therefore interposed between the electrical line and the residual current-operated
circuit breaker 2 and between the residual current-operated circuit breaker 2 and
the load 5, accordingly constituting a bypass of the residual current-operated circuit
breaker.
An actuation means 10, suitable to actuate the resetting
of the residual current-operated circuit breaker 2, is connected to the control
board 1 and powered by the line 8, 9 by virtue of the connection of the control
board 1 to the line.
In detail, the control means 1 includes a control unit
15, which is connected to a power supply means 16 so as to derive a control voltage
that is equal to half the mains supply voltage of the device. The power supply means
furthermore includes a power supply 17 for the control unit.
The device furthermore has a circuit for detecting the
presence and value of the power supply voltage, designated by the reference numeral
18, which is connected to the control unit 15 and sends to the control unit a response
signal 19 related to the presence and value of the supply voltage.
A circuit 20 for checking the cables connected to the system,
electrically separated from the remaining circuit, is furthermore connected to the
control unit 15 in order to verify the correct connection of the cables, i.e., verify
that the reset device is correctly connected to the system.
The circuit 20 receives in input a signal 21 requesting
a check of the connection of the cables and sends in output to the control unit
15 a signal 22 that indicates the outcome of the cable check.
The device according to the invention furthermore includes
a circuit 23 for detecting the leakage current of the connected system; this detection
occurs by virtue of a unidirectional pulsed voltage derived from the mains voltage,
which is closed, in case of fault, on the mains by virtue of the ground; finally,
the device includes a circuit 24 for protection against electrical shocks during
the system verification cycle.
The control unit 15 sends an actuation signal 25 to the
thermal actuator 10 in order to activate the reset device.
With reference to the figures cited above, the operation
of the reset device according to the present invention is as follows.
The control means 1 is supplied with power by the closure
of a contact 30 exclusively after release of the associated residual current-operated
circuit breaker, which opens the contacts 2 and removes power from the system.
The control means closes immediately a relay 31, connecting
the system to be verified to the previously described measurement circuits.
The control unit 15 sends a signal requesting a check of
the cables 21 to the control circuit 20, which checks the connection of the cables,
verifying that there is an impedance between test points A and B. This verification
indicates correct connection of the device to the system before continuing the test
sequence. An impedance value exceeding a preset value prevents the reset device
from continuing the sequence.
At this point, the control unit 15 verifies, by virtue
of the circuit 23, the possible presence of an earth leakage current, and if the
earth leakage current exceeds a preset threshold it blocks the automatic reclosure
of the device.
If one of the two verifications described above fails,
the device reports the anomaly by switching on a LED with a steady light.
If the entire first step ends with a positive outcome,
the control unit provides power to the thermal actuator 10 in order to reset the
device. Such thermal actuator is a hot-wax actuator, which resets the associated
residual current-operated circuit breaker, accordingly supplying power to the system
connected thereto.
If the residual current-operated circuit breaker trips
a second time within a preset time, the reset device does not attempt a second reset
and remains in a blocked status, which is indicated by the fixed lighting of the
above cited LED, until the associated circuit breaker is reset manually.
Substantially, the automatic reset device according to
the present invention allows to check both the connection of the reset device and
any occurring leakage current before being able to actually actuate the automatic
reset of the residual current-operated circuit breaker.
In practice it has been found that the device according
to the present invention fully achieves the intended aim and objects, since it allows
to perform, prior to an automatic reset operation, a series of checks on the device
and on the system in order to perform a reset if the conditions are such as to ensure
subsequent correct operation of the system.
The device thus conceived is susceptible of numerous modifications
and variations, all of which are within the scope of the claims.
In practice, the materials used, as well as the contingent
shapes and dimensions, may be any according to the requirements and the state of
the art.
