Technical field
[0001] The invention relates to the method of overvoltage protection of direct-current electrical
circuits with currents even in tens of amperes, especially of photovoltaic sources
of electric current, at which in the device for overvoltage protection the current
path is cut off in the place (X) of intentional cutting off the current path.
[0002] The invention relates to the device for overvoltage protection of direct-current
electrical circuits with currents even in tens of amperes, especially of photovoltaic
sources of electric current, which comprises the contacts (00) for connection of electric
conductors of protected circuit, between the contacts (00) the current path is arranged
with at least one varistor (1), between the varistor (1) and one contact (00) there
is created a point (X) of intentional cutting off the current path with soldered joint
of surface of fixed element of current path and surface of moving element of current
path, to the point (X) of intentional cutting off the current path there is assigned
thermal initiated cut-out mechanism (3) with spring-loaded moving action member, which
applies a force (F) towards the moving element of the current path in direction parallel
with plane of the soldered joint of surface of the fixed element of current path and
surface of moving element of current path.
Background art
[0003] It is generally known, that upon disconnecting the current path in direct current
electrical circuits the electric arc occurs in a situation, when the basic conditions
of minimum electric voltage between the disconnected parts of the current path and
minimum values of electric current in the point of disconnecting are met. If these
conditions are not met, the electric arc is not created between the parts of current
path being disconnected.
[0004] The document
DE 10 2007 015 933 (analogy of
DE 20 2007 018 507) discloses the device for overvoltage protection of photovoltaic sources of direct-current
electrical circuits, which comprises between the terminals for connection to protected
circuit an inserted switched discharger and cutting-off discharger. Parallel to both
dischargers between the terminals for connection to protected circuit there is connected
a non-linear resistance element, which in the represented example of embodiment is
formed of a pair of varistors. The device further comprises a control circuit working
as a co-ordinating and supervising unit and comprising a number of further parts.
[0005] The disadvantage of this arrangement is a considerable complexity and price of the
device, as the device requires installation of a number of parts, including the complex
and costly control circuit.
[0006] From
EP 2 132 752,
WO 2006/120522,
PCT/IB2010/000528,
W02007/017736 and further documents there are known the devices for overvoltage protection, which
use varistors as non-linear resistance elements. These devices are built-in into a
unified box installed on a standard unified installation slat. Inner space of the
box usable for mounting of all necessary elements is considerably restricted. The
box comprises contacts for connection to protected electrical circuit. Between contacts
in the box there is arranged the current path, in which at least one varistor or a
group of parallel connected varistors is connected. Contacts of varistor are flat,
while one contact of varistor is electrically conductively coupled with one contact
of the device for overvoltage protection, and the second contact of varistor is on
its surface connected by means of a solder with opposite surface of the first end
of flexible electrically conductive means, through which a point of intentional cutting
off the current path is created. The flexible electrically conductive means is with
its second end electrically conductively coupled with second contact of the device
for overvoltage protection. To the first end of the flexible electrically conductive
means the spring-loaded moving element is assigned, which to the first end of the
electrically conductive means develops a force F in direction parallel with solder
connected surfaces of the second contact of varistor and the first end of flexible
electrically conductive means. Due to ageing of varistor the value of relatively small
values of electric current running through varistor and the current path increases,
thus even through the point of intentional cutting off the current path. Then due
to overvoltage a short-circuit of varistor occurs, as a result of which through varistor
and also through current path, thus through the point of intentional cutting off the
current path, the short-circuit current having values often of tens of amperes is
flowing. Due to flowing of electric current and spreading of heat from varistor the
parts of current path in the point of intentional cutting off the current path are
being warmed and solder connecting the second contact of varistor and the first end
of flexible electrically conductive means is molten, this soldered joint loses its
strength and the first end of flexible electrically conductive means is by action
of the spring loaded moving element pushed off in a sliding movement on surface of
the second contact of varistor and in direction being parallel with surface of the
second varistor contact up to the space outside contact with the second varistor contact,
and the current path is cut off. At usage of this solution in circuits with alternate
voltage at this cutting off the current path, at which the moving disconnected part
of current path is gradually accelerated to a final speed for cutting off, while still
for a certain time, when the first end of flexible electrically conductive element
in a sliding manner already moves for the purpose of cutting off, there still flows
electric current between the second contact of varistor and the first end of flexible
electrically conductive means, which is caused by presence of a molten solder between
non-moving second contact of varistor and the moving first end of flexible electrically
conductive means, no electric arc is induced between the disconnected parts of current
path not even at short-circuit of varistor due to overvoltage, which is caused first
of all by a speed with which the first moving end of flexible electrically conductive
means moves in a moment of disconnecting the current path, when the insulation strength
of an air gap increases very rapidly. From movement of spring loaded moving element
also an optical and possibly remote status signalling of device for overvoltage protection
is derived. Nevertheless at usage of this solution in direct-current electrical circuits
at short circuit of varistor due to overvoltage, when short-circuit current in tens
of amperes is flowing, an uncontrolled electric arc occurs at these devices, which
is not permissible according to the safety regulations. In experiments it was verified,
that at these devices an uncontrolled electric arc does not occur at values of electric
current in units of amperes, which does not meet requirements of practice.
[0007] Known is also device for overvoltage protection, which comprises the current path
with point of intentional cutting off, which is performed as a change-over switch
of the current path between the branch with varistor and the short-circuit branch
with a fuse cut-out, when in initial status the current path is lead through the branch
with varistor. If in the point of intentional cutting off the current path is disconnected,
between the parts of current path being disconnected an electric arc develops, and
simultaneously the moving section of the current path being disconnected moves into
a contact with the free end of the short-circuit branch with the fuse cut-out, then
after connection of moving part of the current path being disconnected with free end
of the short-circuit branch with fuse cut-out the varistor is in a short circuit,
the above mentioned electric arc switches off and through melting the fuse cut-out
electric current is cut off.
[0008] The goal of the invention is to remove or at least minimise shortcomings of the background
art at direct-current electrical circuits, especially at photovoltaic sources of electric
current, at which in case of a short circuit of varistor the flowing currents achieve
the values of even tens of amperes.
Principle of the invention
[0009] The goal of the invention has been achieved through the method of overvoltage protection
of direct-current electrical circuits with currents even in tens of amperes, especially
of photovoltaic sources of electric current, whose principle consists in that during
cutting off the current path in the point (X) between the current path elements being
disconnected the value of electric current is limited, through which occurrence of
uncontrolled electric arc between the current path parts being disconnected is suppressed.
[0010] Principle of the device for overvoltage protection of direct-current electrical circuits
with currents even in tens of amperes, especially of photovoltaic sources of electric
current, consists in that to the point (X) of intentional cutting off the current
path the capacitor is assigned in parallel manner.
[0011] This invention enables in simple and price affordable means to realise a safe cutting
off the current path in the device for overvoltage protection of direct-current electrical
circuits with currents even in tens of amperes, especially of photovoltaic sources
of electric current, this both at values of current under 10 A even above 10 A, which
meets the requirements of praxis and requirements of the draft (DRAFT) of the norm
prEN 50539-11. Another advantage is that only for a short time of heating the current
path in a point "X" the electric current flows through the device for overvoltage
protection and the protected circuit e.g. the photovoltaic source of electric current
after cutting off the current path is fully functional. Another advantage is, that
it is not necessary to insert into the current path of the device for overvoltage
protection a fuse for direct current as it is in the background art, because the fuse
for direct current including the holder is relatively expensive, so that the invention
enables besides also to reduce price of the device for overvoltage protection. Another
advantage is that the capacitor for the whole service life of the device for overvoltage
protection without voltage, through which its voltage loadability for the whole period
of service life of the device for overvoltage protection is preserved. Voltage on
the capacitor is acting only from the moment of cutting off the current path in the
point X till the moment the varistor insertion is replaced.
[0012] Advantageous embodiments of the invention, especially the structure of the current
path of the device for overvoltage protection are described in description of exemplary
embodiments and are the subject of patent claims.
Description of the drawing
[0013] The invention is schematically represented in the drawing where the Fig. 1 shows
a ground plan of one device for overvoltage protection, the Fig. 1a an example of
another arrangement of the device for overvoltage protection, the Fig. 2 exemplary
embodiment of the point X of intentional cutting off the current path of the device
for overvoltage protection with parallel assigned capacitor, the Fig. 3a to 3d an
exemplary embodiment of the point X with parallel assigned capacitor and a temporary
serial resistance and the individual phases of concurrence of these elements and the
Fig. 4 a time course of electric voltage and of electric current at the method according
to the invention.
Examples of embodiment
[0014] The method of overvoltage protection of direct-current electrical circuits with currents
even in tens of amperes, especially of photovoltaic sources of electric current, consists
in that the current path is cut off in a place of intentional cutting off the current
path, at the same time at this cutting off the conditions unfavourable for occurrence
of uncontrolled electric arc are created, so that in the moment when between the current
path elements being disconnected a nonzero interval is created, value of electric
current in the point of cutting off is limited, by which occurrence of uncontrolled
electric arc between the current path elements being disconnected is prevented. The
value of electric current in the point of cutting off is limited due to increase of
voltage through rerouting the flow of electric current to parallel current path formed
of capacitor (condenser or a group of condensers). The capacitor at moment of creation
of the nonzero interval between the current path elements being disconnected represents
only a minor electric resistance, because the voltage on capacitor corresponds to
the status before creation of the nonzero interval between the current path elements
being disconnected and it is being increased in dependence on capacity of the capacitor
and the value of current. Speed of mutual shifting away the current path elements
being disconnected is so high, that the breakdown strength of air gap between the
mutually shifting away elements of the current path being disconnected increases quicker
than voltage on the capacitor, which increases due to charging the capacitor by a
incoming electric charge from the rerouting flow of electric current, and this voltage
grows up to the height of maximum voltage of the source of the direct-current electric
current.
[0015] Such behaviour of the device for overvoltage protection may be achieved by a suitable
structure of the device for overvoltage protection with respective dimensioning of
individual elements.
[0016] Exemplary embodiment of the device for overvoltage protection of direct-current electrical
circuits with currents even in tens of amperes, especially of photovoltaic sources
of electric current, comprises the box
0, in which individual functional elements of the device for overvoltage protection
are built-in. The device for overvoltage protection comprises contacts
00 for connection of electric conductors of protected circuit. Between the contacts
00 there is in the box
0 arranged the current path, in which as a protective element at least one non-linear
resistance element is integrated, for example varistor
1 or a group of parallel integrated varistors
1.
[0017] In the current path the point
X of intentional cutting off the current path is arranged. The point
X in the represented example of embodiment is performed in the contact place of the
upper surface of the lower electrode
10 of varistor
1 and of the lower surface of the first end of flexible electric conductor
11. Both these contact surfaces are connected by means of solder
12. Function of cutting off the current path in the point
X is realised by means of thermal initiated cut-out mechanism
3, which is assigned to the point
X, and which in the represented example of embodiment is formed of a spring loaded moving
action member, which on the flexible electric conductor
11 develops the force
F in direction parallel with upper surface of the lower electrode
10 of varistor
1 and with lower surface of the first end of the flexible electric conductor
11. The force
F is either developed directly in direction parallel with upper surface of the lower
electrode
10 of varistor
1 and with lower surface of the first end of flexible electric conductor
11 or it acts in this direction, e.g. thanks to production deviations etc., as a component
of totally acting force. The force
F after melting the solder
12 as a result of increased temperature of varistor pushes off the first end of flexible
electric conductor
11 from the lower electrode
10 of varistor
1 by a shearing action on the molten solder
12, i.e. by sliding motion of the first end of flexible electric conductor
11 on the lower electrode
10 of varistor
1, so that the first end of flexible electric conductor
11 at the moment of creation of nonzero interval between it and the lower electrode
10 of varistor
1 already develops a relatively high speed. Solder
12 is molten and the thermal initiated cut-out mechanism
3 is initiated by means of a heat, which is partly developed by a non-linear resistance
element (varistor
1) integrated in the current path, and which is also developed by passage of electric
current through the current path.
[0018] Thermal initiated cut-out mechanism
3 is coupled with means for optical and/or remote signalling of status of the device
for overvoltage protection. For optical signalling of status of the device for overvoltage
protection the device is provided with swing lever
4, which is coupled with thermal initiated cut-out mechanism
3.
[0019] In the Fig. 2 to the current path of the device for overvoltage protection in vicinity
of the point
X there is assigned the parallel current path
15 with the capacitor
16. The capacitor
16 is in parallel manner to the current path through the point
X connected between the lower electrode
10 of varistor
1 and the non-moving section of the flexible electric conductor
11 only after the first end of the flexible electric conductor
11.
[0020] In the Fig. 3a to 3d to the current path of the device for overvoltage protection
in vicinity of the point
X there are assigned the parallel current path
15 with the capacitor
16 and the serial temporary resistance element
P, which since the moment of beginning of the sliding disconnecting movement of the
first end of flexible electric conductor
11 has a longer time of electric current conduction than is the conduction time of electric
current through the current path through the point
X since the moment of beginning of the sliding disconnecting movement of the first
end of flexible electric conductor
11, when the sliding disconnecting movement is started after melting of the solder
12 through action of the force
F. At the end of the lower electrode
10 of varistor
1 distant from the first end of the flexible electric conductor
11 there is electrically in a conductive manner attached the auxiliary electric conductor
13, which has distinctly higher electric resistance, than the lower electrode
10 of varistor
1 and a flexible electric conductor
11 have, e.g. it is formed of a strip made of stainless steel of a small thickness.
The auxiliary electric conductor
13 runs along the lower surface of the lower electrode
10 of varistor
1 up to a free space in distance
A from the edge of the lower electrode
10 of varistor
1, where it finishes with a contact edge
130 situated in a free space behind the first end of flexible electric conductor
11 outside the contact with flexible electric conductor
11. At the same time the distance
A is smaller than the length of the first end of flexible electric conductor
11. Between the auxiliary electric conductor
13 and the lower electrode
10 of varistor
1 there is, with exception of the place of connection of the auxiliary electric conductor
13 to the lower electrode
10 of varistor
1, situated electric insulation
14, e.g. insulation foil. Capacitor
16 is parallel to the current path through the point
X connected between the lower electrode
10 of varistor
1 and the non-moving section of the flexible electric conductor
11 still after the first end of flexible electric conductor
11.
[0021] The Fig. 3a represents full functioning status of the device for overvoltage protection
without occurrence of a failure status. Solder
12 is in a solid status and holds the first end of flexible electric conductor
11 and the lower electrode
10 of varistor
1 together. The capacitor
16 shows voltage U
0.
[0022] The Fig. 3b represents the status when solder
12 has already been molten and the spring-loaded moving action member of thermal initiated
cut-out mechanism
3 has already begun to push off the first end of flexible electric conductor
11 in direction of actioning the force
F parallel with surface of the lower electrode
10 of varistor
1. The first end of the flexible electric conductor
11 moves in gradually increasing speed, at the same time it is still in electric contact
with the lower electrode
10 of varistor
1 and it newly has entered into electric contact with contact edge
130 of auxiliary electric conductor
13. The capacitor
16 shows voltage U
01.
[0023] The Fig. 3c represents status when the spring-loaded moving action member of thermal
initiated cut-out mechanism
3 has already pushed off the first end of the flexible electric conductor
11 in a still increasing speed parallel with surface of the lower electrode
10 of varistor
1 totally outside electric contact with lower electrode
10 of varistor
1, nevertheless the first end of flexible electric conductor
11 remains in electric contact with contact edge
130 of auxiliary electric conductor
13. The capacitor
16 shows voltage U
2. The Fig. 3d represents status of total cutting off the current path of the device
for overvoltage protection in the point
X, when the spring-loaded moving action member of thermal initiated cut-out mechanism
3 has pushed off the first end of the flexible electric conductor
11 totally outside electric contact with contact edge
130 of the auxiliary electric conductor
13. The capacitor
16 shows voltage U
3.
[0024] Function of the device according to the Fig. 2 is so that, once overvoltage occurs,
this is eliminated by passage of electric current through varistor
1, which is thus being warmed by which also the lower electrode
10 of varistor
1 becomes warm. Once the lower electrode
10 of varistor
1 reaches the temperature for melting the solder
12, this becomes molten and releases motion of the spring-loaded moving action member
of the thermal initiated cut-out mechanism
3 in direction parallel with surface of the lower electrode
10 of varistor
1. The spring-loaded moving action member starts gradually with increasing speed in
sliding manner to shift the first end of the flexible electric conductor
11 on surface of the lower electrode
10 of varistor
1, while thanks to molten solder
12, electric current still passes between the first end of flexible electric conductor
11 and the lower electrode
10 of varistor
1. Once the nonzero interval occurs between the first end of the flexible electric conductor
11 and the lower electrode
10 of varistor
1, voltage between the first end of flexible electric conductor
11 and lower electrode
10 of varistor
1 is increased, by which the flowing electric current re-routes into parallel current
path
15 with capacitor
16, which in this moment represents only minor electric resistance, because the voltage
on capacitor
16 corresponds to status before occurrence of the nonzero interval between the current
path elements being disconnected and it is increased depending on capacity of the
capacitor
16 and value of the current. Thanks to sliding motion of the first end of the flexible
electric conductor
11 on surface of the lower electrode
10 of varistor
1, this first end of flexible electric conductor
11 at the moment of creation of the mentioned nonzero interval reaches still a sufficient
speed of its motion, so that at its further shifting away from the lower electrode
10 of varistor
1 the interval being created increases, and with it also its breakdown strength quicker
than the voltage is increased on capacitor
16, which (voltage on the capacitor
16) increases due to charging the capacitor
16 by the incoming electric charge from the re-routed flow of electric current. This
voltage on capacitor
16 increases till the value of maximum voltage of the source of electric direct-current.
At this arrangement there will not be even at values of electric current in tens of
amperes occurrence of uncontrolled electric arc between the current path elements
being disconnected at the point
X of intentional cutting off the current path. Under the term "uncontrolled" electric
arc it is understood a longer lasting electric arc. Experimentally it was proven,
that upon cutting off the direct-current in values of tens of amperes using the device
according to the invention being submitted, there was occurrence of only a sparkle
between the first end of flexible electric conductor
11 and the lower electrode
10 of varistor
1 at the moment of creation of the nonzero interval between the first end of the flexible
electric conductor
11 and the lower electrode
10 of varistor
1. No uncontrolled electric arc was created.
[0025] Function of the device according to the Fig. 3a to 3d is following. The device is
fully functional, see the Fig. 3a, no electric current flows through the varistor
1. There is no movement of individual elements of the current path. Once overvoltage
occurs, this is eliminated by passage of electric current through the varistor
1, which is warmed this way, by which also the lower electrode
10 of varistoru
1 becomes warm. Once the lower electrode
10 of varistor
1 warms to the temperature for melting the solder
12, this gets molten and releases motion of the spring loaded moving action member of
thermal initiated cut-out mechanism
3 in direction parallel with surface of the lower electrode
10 of varistor
1. The spring loaded moving action member starts gradually in an increasing speed to
shift the first end of flexible electric conductor
11 on surface of the lower electrode
10 of varistor
1, at the same time thanks to the molten solder
12 between the mutually moving elements of the current path, i.e. between the first
end of the flexible electric conductor
11 and the lower electrode
10 of varistor
1 electric current is still passing. Consequently the first end of the flexible electric
conductor
11 touches the contact edge
130 of auxiliary electric conductor
13, while the first end of flexible electric conductor
11 is still in electrically conductive contact with the lower electrode
10 of varistor
1, as it is represented in the Fig. 3b. Through creation of electrically conductive
contact between the first end of the flexible electric conductor
11 and the contact edge
130 of auxiliary electric conductor
13 upon preservation of electrically conductive contact between the first end of flexible
electric conductor
11 and the lower electrode
10 of varistor
1 , there occurs jump increase of electric resistance of current path at the point
X, which results in that the flow of electric current is re-routed via capacitor
16, which is being charged, the voltage U
01 ≥ U
0 and through the current path through the point
X only fraction of original value of electric current is flowing. By further shifting
the first end of the flexible electric conductor
11, the Fig. 3c, electrically conductive connection of the first end of the flexible
electric conductor
11 and of the lower electrode
10 of varistor
1 is cancelled, so that the point
X is disconnected, most of electric current flows through capacitor
16, which is being charged, the voltage U
2 > U
01 ≥ U
0, but simultaneously the voltage is U
2 < U
arc (arc voltage), so that there is no uncontrolled electric arc between the elements
of current path being disconnected in the point
X. By further shifting the first end of the flexible electric conductor
11, the Fig. 3d, also electrically conductive connection of the first end of flexible
electric conductor
11 and of contact edge
130 of auxiliary electric conductor
13 is cancelled, while the moving first end of the flexible electric conductor
11 shows such speed of its motion, that the insulation strength of air gap between the
first end of flexible electric conductor
11 and the contact edge
130 of auxiliary electric conductor
13 increases quickly and no uncontrolled electric arc occurs. It is obvious, that at
embodiment according to the Fig. 3a to 3d the total resistance of the current path
is increased, by which redistribution of current between the current path in the point
X and the parallel current path
15 with the capacitor
16 is increased.
[0026] As it is seen from the Fig. 4, through the method and the device according to this
invention an effective restriction of conditions necessary for creation of (uncontrolled)
electric arc between the elements of current path being disconnected is achieved,
as at increase of voltage there is significant drop in value of electric current.
Industrial applicability
[0027] The invention is applicable at overvoltage protection of direct current electric
circuits with currents even in tens of amperes, especially of photovoltaic sources
of direct current.
1. Method of overvoltage protection of direct-current electrical circuits with currents
even in tens of amperes, especially of photovoltaic sources of electric current, at
which in the device for overvoltage protection the current path in the point (X) of
intentional cutting off the current path is disconnected, characterised in that, during cutting off the current path in the point (X) between the current path elements
being disconnected the value of electric current is limited, through which occurrence
of uncontrolled electric arc between the current path parts being disconnected is
suppressed.
2. The method according to the claim 1, characterised in that, the value of electric current between the current path elements being disconnected
is limited by rerouting the flow of electric current through the parallel assigned
capacitor (16).
3. The method according to the claim 1, characterised in that, between the current path elements being disconnected during cutting off the interval
is created at least at such a speed, at which an increase of breakdown strength of
air gap between the current path parts being disconnected is greater than the increase
of voltage on the capacitor (16).
4. The method according to the claim 2, characterised in that, during cutting off the current path in the point (X) the serial temporary resistance
element (P) is connected, by which redistribution of flow of electric current between
the current path elements being disconnected and capacitor (16) is increased.
5. The device for overvoltage protection of direct current electric circuits with currents
even in tens of amperes, especially of photovoltaic sources of electric current, which
comprises contacts (00) for connection of electric conductors of protected circuit,
between the contacts (00) there is arranged the current path with at least one varistor
(1), between the varistor (1) and one contact (00) there is created the point (X)
of intentional cutting off the current path with soldered joint of surface of the
fixed element of the current path and of surface of moving element of current path,
to the point (X) of intentional cutting off the current path there is assigned thermal
initiated cut-out mechanism (3) with spring-loaded moving action member, which applies
a force (F) towards the moving element of the current path in direction parallel with
plane of the soldered joint of surface of the fixed element of current path and of
surface of moving element of current path, characterised in that, to the point (X) of intentional cutting off the current path the capacitor (16)
is assigned in parallel manner.
6. The device according to the claim 5, characterised in that, the capacitor (16) is parallel to the current path connected between the lower electrode
(10) of varistor (1) and the non-moving section of the flexible electric conductor
(11) after the first end of the flexible electric conductor (11).
7. The device according to the claim 5, characterised in that, to the point (X) of intentional cutting off the current path there is assigned the
temporary serial resistance (P).
8. The device according to the claim 7, characterised in that, the temporary serial resistance (P) is formed of auxiliary electric conductor (13),
which at one of its ends is electrically in a conductive manner connected with lower
electrode (10) of varistor (1), and on its second end it is provided with contact
edge (130) situated in the distance (A) from lower electrode (10) of varistor (1)
in a free space after the first end of the flexible electric conductor (11) outside
the contact with flexible electric conductor (11), at the same time the distance (A)
is smaller than the length of the first end of the flexible electric conductor (11).
9. The device according to the claim 8, characterised in that, the auxiliary electric conductor (13) is formed of a steel strip made of stainless
steel of a small thickness.
10. The device according to any of the claims 8 or 9, characterised in that, between the auxiliary electric conductor (13) and the lower electrode (10) of varistor
(1) there is, with exception of the place of connection of the auxiliary electric
conductor 13 to the lower electrode 10 of varistor 1, situated electric insulation (14).