FIELD OF INVENTION:
[001] The present invention relates to, residual-current device (R.CD). The
5 present invention more particularly relates to a residual current device (RCD) with
pre trip current ,leakage indicating mechanism having an additional secondary
winding on current transformer.
BACKGROUND AND PRIOR ART:
10 [002] The prior art residual current devices work in the conventional manner
wherein they are sensitive to the differences between phase and neutral current.
They trip the circuit when the difference lies within a band, as per their timecurrent
operating characteristics.
15 [003] Tripping of protective devices during fault is essential, but it causes
inconvenience. Previous residual current circuit breakers did not forewarn the user
when leakage current in the premises crosses over a certain threshold. Very often
a sudden interruption of important processes, when the circuit breaker trips in case
. of fault, causes a loss of work and data. Which could have been avoided had the
20 . user got an intimation as soon as certain leakage threshold was crossed, as he
could have taken corrective maintenance actions.
[004] Publication No. CN103956709 (A) relates to a residual current trip with
remote alarm function, comprising means for detecting leakage state leakage
25 detection circuit, the leakage. detection circuit output by a threshold comparator
circuit a comparison circuit connected to the delay, the delay of the output
terminal of the comparator circuit trip driving circuit; leakage detection circuit, a
threshold comparing circuit, the delay circuits are used to provide a comparison of
the operating voltage and the leakage indication state 'indication circuit connected
30 to the power supply.
[0051 Publication No. W02014089637 (Al) relates to a circuit breaker that
includes a built in Residual Current Device (RCD) that can be adjusted to tlirn on
or off, or to operate at a range of currents, preferably, but not limited to IOmA,
30mA, 100mA, The present invention also seeks to provide a circuit breaker
5 which may have electrical parameters such as, but not limited to, power, current,
voltage, demand, freqilenc,~a long with status, pretrip alarm, and rcsidllal cl~rrent
remotely monitored. It also provides a power distribution system and method,
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which includes a controller to sense parameters of a load, and, in the event of
. 8 exceeding predetermined values, operate a circuit breaker. However, above type
I
10 of devices are limited to electronic type circuit breakers only. I
1
[006] Publication No. JPHO5 103426 (A) relates to a warning mechanism when
I
i
load current increases over a certain threshold. It provides a current monitor 1 section for outputting a first signal when detecting the current consumption
15 exceeds a predetermined threshold to monitir the current consumption, in
response to said first signal a warning indication unit for outputting the second
signal, the current-excess -corresponding apparatus characterized in that it is I
constituted by a warning notification unit that alerts the said second warning I
means which is provided in advance tjy receiving a signal. The warning notifying I
20 section gives warning to a user of an equipment by means of a buzzer or a lamp.
(0071 US Publication No. 20120146655 relates to a system for sensing leakage
current. The system for sensing leakage current includes one & more of the I
following features: (i) the' ability to automatically, and preferably on a I
25 programmable, periodic basis, perform a self-test of the critical system hardware I
and/or software used to measure and monitor leakage current; (ii) the ability to . I
permit an operator to set one or more leakage current levels, such as a warning
level and/or a critical level; (iii) the ability to visually display a.status indication
of one or more leakage current conditions, such as an actual RMS leakage current I
30 measurement, an indication of a normal (or acceptable) leakage current level, an I
indication of a warning (e.g., elevated but not critical) leakage current level, an
indication of a critical (c.g., an unacceptably, or near unacceptably, elevated)
leakage current level, an indication that a self-test has uncovered faulty hardware
andlor 'software; and (iv) the ability to dispatch notifications reporting the
presence of one or more of the aforementioned status indications (andlor a change
in such status), such as by way of the simple network management protocol
(SNMP), e-mail, and/or other electrnnic means. However, this invention is also
voltage dependent1 electronic type.
[0081 Publication, No. CN2042873 17 (U) relates to a three-phase smart meters
10 with leakage detection, the smart meter itself has a leakage detection function, so
the utility model in real time to detect whether there is leakage occurs, and.in a
timely alarm when there is leakage, thereby reducing the fire accident caused d~ie
to leakage, but also reduces the cost of household electricity. However, it gives a
warning alarm when it detects a leakage current above a certain threshold but does
15 not trip when leakage current exceeds danger level, i.e. it does not give protection,
only warning. Further it is electronic type and can be applied to three phase only.
[009] Publication No. CN 102 103 160 (A) relates to a method and the device for
monitoring and alarming the residual current, and the detection controller, a
20 leakage alarm and a false alarm caused by the conventional fixed alarm threshold
value can be avoided. However, it only gives a residual current monitoring alarm
I
method.
[00101 Publication No. CN201623456 (U) relates to an electro'nic circuit
25 arrangement for residual current operated relay. It is provided with a zero- I
sequence'transformer leakage detection signal, by sampling circuit output signal i
to the main CPU processing, the main CPU through calculation and processing 1
the data through the RS485 communication circuit, via the bus uploaded first bit 1
machine, leakage of infurrnaliur~ exlr-acted from the transformer through Icakagc
30 sampling circuit, conveyed to the main CPU, the main CPUl through calculation
and processing, control relay driver circuit.
I [0011] Thus, in vicw of the above prior arts, it is clear that devices available are
either voltage dependent, electronic type or limited to any one kind of phase only.
Moreover, prior art devices did not have the indicating mechanism as well as
tripping mechanism, to alert the user of future potential fault situations, when
5 leakage current reached above a specific limit but is below the trip threshold and
to trip the circ.uit when leakage current rises over fa.111tt. hreshold.
[0012] Thus, the present invention is directed to provide a residual currenl device
(RCD) with pre-trip current leakage indicating mechanism in addition to trip
10 mechanism independent of voltage. By having such a pre-trip indicator on
,residual current devices, user gets an indication and some potential fault situations
can be obviated by taking proper maintenance and corrective actions.
OBJECTS OF THE INVENTION:
15 100131 The principal objective of the present invention is to provide a residual
current device (RCD) with pre-trip current leakage indicating mechanism.
[0014] Another object of the present invention is to provide pre-trip leakage
indication on residual current devices in a simple and compact arrangement.
100151 Still another objective of the present invention is to provide a pre-trip
20 ind'icator to warn the user of possible leakage current sources, such as improper
connections, old wiring insulations, moisture and conductive dusts etc.
100161 Yet another object .of the present invention is to provide a pre-trip
indicator so that a corrective action and maintenance can be taken in advance;
much before current leakage rises to fault values and RCD trips the circuit.
25 100171 Another objective of the present invention is to provide a pre-trip indicator
which can be used for any type of circuit breaker- electromechanical or electronic,
voltage-dependent or voltage independent type.
(0018) Yet another objective of the present invention is to provide a pre-trip
indicator independent of voltage so it can operate without needing any complex
30 arrangements.
SUMMARY OF THE INVENTION:
[0019] The present invention provides a residual current device (RCD) with pretrip
current leakage indicating mechanism. The device senses when the leakage
current in circuit reaches a particular threshold and give a visual indication of the
5 same.
[0020] This serves as a pre-trip signal for the c.onsumer, before the leakage
current reaches to higher levels and the circuit breaker operates.
[0021] In a preferred embodiment of the present invention, a residual current
10 device (RCD) with pre-trip current leakage indicating mechanism is provided
where on the core of the current transformer, an additional secondary winding has
been wound, with number of turns as per the pre-determined threshold setting.
The pre-trip leakage indicator functionality in KCD alerts the user when current
leakage in the circuit's downstream of the protective device exceed a particular
15 threshold. Hence the consumer takes the corrective actions in advance, much
before the leakage current rises to fault values and circuit is disconnected by the
residual current device.
100221 In another embodiment of the present invention, when using any device,
20 indicator goes on, then that device can be checked for possible sources of current
leakage.
lo0231 In yet another embodiment of the present invention, when circuit in the
house, say the kitchen or washroom has leakage current above a certain limit, may
25 be because of moisture, or conductive dust, then the residual current device gives
intimation.
BRIEF DESCRIPTION OF THE DRAWINGS
100241 It is to be noted, however, that [he appended drawings illustrate only
30 typical embodiments of this invention and are therefore not to be considered for
PPO D E L H I 1 2 - 1 1 - - 2 0 1 % 17 12.2
limiting of its scope, for the invention may admit to other equally effective
embodiments.
[0025] Figure 1 shows pre-trip current leakage indicator arrangement for single
phase residual current devices according to the present ihvention; and
5 [0026] Figure 2 shows pre-trip current leakage indicator arrangement for three
phase residual current devices according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
100271 Accordingly the present invention provides a pre-trip current leakage
10 indicator on the residual current device. The device senses when the leakage
current in the circuit reaches a particular limit and give an indication. The
indicator according to the present invention is voltage independent and has a
simple and compact design.
15 100281 Referring to the fig. I, residual current circuit breakers 10 have a toroidal
core current transformer (CT) 1 I, through which a line (L) and a neutral (N) wire
pass. The line (L) and the neutral (N) form primary winding of the CT 1 I . There
is a secondary winding consists of N1 number of turns of a wire 12 wound around
the core of CT I 1. The secondary winding is connected to the controland tripping
20 mechanism 13. When the difference between line (L) and neutral (N) current is
non-zero, then voltage is induced in the secondary winding 12 of CT I I. When
this difference lies within the trip band of circuit breaker 10, the control .
mechanism gets actuated and it trips the circuit.
25 [0029] As explained above, the secondary winding 12 of the CT is connected to I
the control and tripping mechanism 13. The tripping mechanism used in the
present subject, mmattecr an be any known tripping mechanism 13, such as voltage
dependent and voltage independent known in the art. ~urther, in the proposed
circuit breaker, the energy uf fault current is used to trip circuit. When the leakage
30 current in circuit is beyond trip threshold, the output of the secondary winding 12
operates a magnetic relay which in turn actuates the tripping latch and mechanism,
thereby mechanically disconnect the circuit.
100301 In an arrangement according to the present invention, an additional
5 "secondary winding 14 with number of turns N2 has been wound ovef rhe core of
CT 11, wherein the number of turns N2 in the additional secondary winding 14 is
more than the number of 'turns N1 in the secondary winding 12 of C'I' 11 which 1s
- -1illkcd to tkc tripping mechanism 1-3. Thesecnnrlary winding 122s associated with- -
the fault tripping mechanism 13, whereas the additional secondary winding 14 is
10 associated with the pre-trip warning indication mechanism. The additional
secondary winding 14 is as per the pre-trip warning threshold. The number of
turns N2 on the additional winding 14 depends on different factors, such as
material of core CT, sensitivity of residual current device (i.e., 30 mA, 100 mA,
300 mA), and limit of threshold indication warning.
15
[0031] For example, the pre-trip warning threshold can be set say 50% of.RCD
sensitivity. The RCDs with the sensitivity of 30mA, 100mA or 300mA can be set
to have indication warning threshold at 50%, i.e., 15mA, 50mA or 150mA
respectively. Accordingly, the RCDs with different indication warning thresholds
20 can be manufactured by changing the number of turns in the additional winding
14.
[0032] The ends of the additional secondary winding 14 are connected to a LED
indicator 15 to indicate.the leakage of current if the leaked current is beyond the
pre-trip warning threshold. The LED indicator is one of a bulb (15), LED light
25 (1 5) or any other indicating device for indication.
100331 When there is a leakage in the circuit, vector sum of the line (L) and the
.neutral line (N) is non zero. If the circuit is three phase circuit, the vector sum of
R, Y, B, N current is non-zero. A magnetic flux is produced in the core of CT 1 1
30 due to leakage of current. By the transformer CT 11 acliur~, a voltage V2 is
I induced across the additional secondary winding N2.
5 Na= Number of turns of.primary winding, i.e., how many times L & N are wound
over the CT 1 1. In present explanation il is taken as 1.
Ia = 1,eakage current in primary coil
1 Q V2, I2 = Voltage induced and current in the additional winding
The turn ratio of Na & N2 is set such that when current Ia in primary coil is
equivalent to pre-trip warning threshold, the voltage V2 is just sufficient to, light
up the LED.
15
(00341 When the leakage current in the primary coil is more than the pre-trip
warning threshold, induced voltage in the additional secondary winding 14 is
sufficient to turn on the indication bulb 15. When the bulb glows, it gives a signal
to the user for the presence of leakage cu'rrent in the device. Accordingly, the user
20 can save the load 16 in advance from any possible'fault.
100351 For example, let the voltage required to turn on a certain LED 15 be 1.5V.
* Let the pre-trip warning threshold of given RCD be set at 50%, i.e. 150mA for an
RCD with sensitivity of 300mA. When 150mA leakage current is produced in the
25 circuit experimentally, and number of turns N2 are more than or equal to 'x', it is
observed that the secondary induced voltage is more than 1.5V, thus the LED
gives indication. Hence the number of turns N2 are chosen as 'x' which is as per
the pre-trip warning threshold of 150mA, being just sufficient to turn on the LED.
30 [0036] Above explained, indication mechanism is voltage independent as its
working is not dependent on the energy drawn from mains source voltage. It
would be unaffected by fluctuations in mains voltage. The indication mechanism
will work equally well even if load and supply side connections of the breaker are
invertcd. This ,is because the method of visual indication depends on detection of
35 . leakage current and is independent of the source polarity. Therefore, the pre-trip
leakage current warning mechanism according to the present invention is voltage
independent and is unaffected by line-load reversibility.
[0037] Similar to the single phase systems, the above explained arrangement can
5 also be used for three phase systems one example uf wliicl-I is as shown, in fig. 2.
The arrangement according to the present invention can be used for different types
of residual current devices like RCCB and KCBU. The preseril a1.1angemcnt can
be used in ull type of rcsidual current breakers where current transformers are
used. The present arrangement can also work in circuit breakers that have voltage
10 independent (electromechanical) or voltage dependent (electronic) tripping
methods.
100381 The advantage of the pre-trip leakage indicator is that it works as an
t
indicator for the consumer to know whether the .cumulative standing leakage is in
1 15 the premises are below the threshold limit or not. The leakage current in the
circuits may increase over the life of an electrical system due to various reasons,
e.g., aging of installation and the equipment connected to installation, degradation
of wiring insulation over time, presence of conductive dust and moisture, etc.
When the consumer has the indication of the residual current is above the set
20 threshold limit, corrective action and maintenance can, be taken in advance, much
before current leakage rises to fault values and RCD trips the circuit.
[0039] In this way, it is possible to avoid potential fault situations by correcting
the connections, old wiring insulations, moisture, and conductive dusts etc., which
25 may be the cause of the current leakage. In another application, if a faulty device
is used and it causes the indication to go on, the device can be identified and
repaired. Hence precautionary measures can be taken. Very often due to lack of
particular measuring instruments, user is not aware that leakage current in his
house/ building has increased over the time. This leakage current also means a
30 loss of energy. This way, the consumer car1 keep a chcck.
100401 Although the invention herein has been described with reference to
particular embodiments, it is to be under stood that these embodiments are merely
illustrative of the principles and applications of the present invention. Numerous
modifications and adaptations of the system of the present invention will be
5. apparent to those skilled in the art, and thus it is intended by the appcnded claims
to cover all such modifications and adaptations which fall within the true spirit
and scopeof this invention.

We claim:
1. A residual current device (RCD) (10) with' pre-trip current leakage
indicating mechanism comprising:
toroidal core current transformer (CT) (1 1);
a primary winding on the toroidal core CT (I I); and
an additional secondary winding (14) on the toroidal core CT (1 I),
wherein the additional secondary winding (14) is connected with a
indicator (I 5) to indicate the pre-trip current leakage.
10 2. The residual current device (RCD) (10) as claimed in claim 1, wherein the
toroidal core CT (1 1) further comprises a secondary winding (12) with N1 number
of turns to trip and control the RCD (1 0) using tripping mechanism (1 3).
3. .The residual current device (RCD) (10) as claimed in claim 1, wherein the
15 additional secondary winding (14) has number of turns N2 which is more than the
number of turns N1 in the secondary winding (12).
4. The residual current device (RCD) (10) as claimed in claim 1,' wherein the
number of turns N2 of the additional secondary winding (14) are as per pre-trip
20 warriing threshold.
5. The residual current device (RCD) (10) as claimed in claim 1 wherein
RCD (1 0) indicates the leakage of residual current:
when difference between line (L) and neutral (N) current is nonzero;
a voltage is induced across the additional secondary winding (14);
and
when the residual current is more than pre-trip warning threshold,
the induced voltage in the additional secondary winding (14) is sufficient
to turn on the indication bulb (1 5) giving a signal for presence of leakage
of the residual current.
I P 8 D E L H I 12-
6. The residual current device (RCD) (10) as claimed in claim 2, wherein the
secondary winding (12) consist N1 number of turns wound around the core of CT
(1 I), wherein the secondary winding (12) is connected to the control and tripping
mechanism (I 3).
5
7. The residual current device (RCD) (1 0) as claimed in claim 2, wherein
when difference between line (L) and neutral (N) current is nonzero,
a voltage is induced across the secondary winding (12) of CT (1 1);
and
10 when the difference lies within trip band of circuit breaker of the
RCD (I 0), the control and tripping mechanism (1 3) gets actuated and trips
the circuit.
8. The residual current device (RCD) (10) as claimed in claim 1, wherein the
15 pre-trip current leakage indicating mechanism is voltage independent and is
unaffected by line-load reversibility.
9. The residual current device (RCD) (10) as claimed in claim 1, wherein the
pre-trip current leakage indicating mechanism is used in any type of residual
20 current device, whether electromechanical or electronic.
10. The residual current device (RCD) (10) as claimed in claim 1, wherein the
pre-trip current leakage indicating mechanism is useful for single phase as well as
multiple phase systems.