|Title of Invention||
A DEVICE FOR USE WITH AN A.C.EARTH LEAKAGE CIRCUIT BREAKER PROVIDED WITH A.D.C. LOAD
|Abstract||A device for Use with an a.c. earth leakage circuit breaker provided for a d.c. load, said device comprising a current balance sensor provided for the phase and neutral lines of the a.c.power source, for Sensing the PUlsating d.c. ~ar~h leakage at the said load; a control unit incorporating a trigger circuit acting as an electronic switch, the trigger circuit being connected to ~he said sensor, such that the said sensor is capable of Sensing the d.c. imbalance crea~ed by d.c. earth leakage oCCUrring a~ the said load and ~o ac~uate the trigger circuit to close and create an a.c. imbalance in the said lines so as to trip the circuit breaker.|
This Invention relates to a device for use with an a-c earth leakage circuit breaker provided with a d.c. load.
Circuit breakers which are used for a.c. loads for tripping the circuit and cutting off power supply, whenever an earth leakage-current occurs, as a result of a fault, including human electrocution taking place, are usually termed ELCB (earth leakage circuit breaker) or RCCB (residual current circuit breaker)• The ELCB or RCCB type of circuit breakers are highly sensitive and react rapidly to trip the circuit whenever current— leakage occurs either in the a.c. load or In the power supply 1Ines and thus in cases of human beings being subject to electric shock 1ives are saved by the sensitivity and rapidi ty in action of these circuit breakers-
The circuit breakers, ELCB or RCCB type, however, have this drawback, namely, that they do not react to a d.c current-leakage fault occurring tn a d-c. load connected to an a.c. power supply through a rectifier. For instance, a television set which requires a d.c- power supply for operation has a
built-in rectifier which is connected to an a.c. power supply. Now, if the known ELCB or RCCB is connected in the power mupply circuit, while it will operate in the event of a.c- leakage occurring, it will not react in the event of . d.c. leakage occurring at the d.c, load as, for instance, in the case of some one being electrocuted by d.c. This is so because the known ELCB or RCCB, by very nature of its construction, i« unable to react to d.c leakage-
The term "circuit breaker" or earth break circuid breaker
in this specification is intended to mean and include circuit breakers of the ELCB or RCCB type refferred to above and other like circuit breakers-
Having regard to the foregoing drawback of the
known circuit breaker, it i© an object ai this
invention to propose a device which when connected
to such circuit breaker, render© the same not only
operable (in the known way) for a.c.
leakage, but also operable, in accordance wi th this invention, for d.c. leakage.
In the known circuit breaker a toroidal core current balance transformer (CBT) is provided and
the phase and neutral lines of the power supply are passed through the core of the CBT and theae 1ines form the primary of the CBT, A winding provided on and around the core itself forms the secondary of the CBT,
In the known circult breaker, occurrence of a.c imbalance (corresponding to a.c. earth leakage) is sensed by the CBT and this results in the tripping of the power supply.
However, when there is a d-c- load included in the load circuit, a d.c- earth leakage fault producing
a pulsating d.c- does not result in the tripping. It is only if the device proposed herein is incorporated in the circuit of the known circuit breaker that the tripping circuit will be activated even in the case of a d.c. earth leakage occurring, because the said device senses the d.c. earth leakage and creates an a-c. Imbalance to which the known circuit breaker reacts.
Various other features. of this invention wl 11 be apparent from the following further description
thereof given hereunder.
According to this invention, the device for use with an a.c circuit breaker provided for a d.c-load, comprises a current balance sensor provided for the phase and neutral line© of the a-c. power source, for sensing the pulsating d.c-. earth leakage at the said load; a control unit incorporating a trigger circuit acting as an electronic switch, the trigger circuit for being connected to the said sensor, such that on a d.c. earth leakage occurring at the said load, the d.c. imbalance is sensed by the sensor to actuate the trigger circuit to close and create an a.c-imbalance in the said lines and thus trip the said circuit breaker.
This invention will now be described with reference to the accompanying drawings, which illustrate, by way of example,
in Fig. I an embodiment of the proposed device connected to the circuit of the known circuit breaker (single phase power supply)
in Fig.2 an embodiment of the proposed device connected to the circuit of the known circuit
breaker (three phase power supply)
in Fi9.3 the asaembly of the device (single phase power supply)
In Fig.4 the assembly of the device (three phase power supply)
Referring to the accompanying drawings, the embodiment comprises a sensor coil S (CBT) whose output terminals T T are connected to the input of the eltctronic trigger circuit F comprised in the control unit A. The trigger circuit acts as an electronic switch in the normally open state-
The d.c- load is indicated by L.
As soon as a d.c earth leakage occurs at the d-c. load L. a pulsating d.c- is reflected in the phase line P of the power supply lines* This pulsating d.c. is sensed by the CBT . Since the CBT is connected to the trigger circuit, the normally open switch is triggered to close-
The terminals D D of the switch F are connected to the phase and neutral lines P N of the power supply at E E (or to phase and earth) such that.
on the said switch closing, the points E E are short-circuited to create an a.c. imbalance in the said lines. The known circuit breaker B then react© to the a.c imbalance in the known way to trip the circuit and cut off power supply to the load.
To avoid a dead short between points E E the trigger F comprises a current limiting impedance, to limit the current to safe values*
In the, embodiment discussed, the said swi tch comprises a BCR switching circuit.
In the embodiment i1lustrated, as an optional feature, the control unit comprises an over voltage monitoring circuit connected to the trigger circuit such that whenever over voltage conditions occur, the sensor actuates the trigger circuit to trip the circuit breaker and protect the connected load.
The trigger circuit has setting means for setting the operative level of the said circuit to values of earth leakage above a predetermined value, so that where the earth leakaop current.
negligible, tripping in avoided.
An advantage of the device proposed herein is that where the circuit breaker is already on the market or with the user, the device proposed herein can be connected thereto in the manner described hereinabove, to entend its operation to d-c. loads as well
Alternatively, the device can be made a part of
the known circuit breaker, at the stage of
manufacture Itself. In such a case, only one
current balance sensor will be required.
The terms and expressions in th is specification are of description and not of limitation, this invention not being limited to the embodiment described and illustrated by way of example, but it is understood that various other embodiments of the device proposed herein are possible without departing from the scope and ambit of this invention.
1 A device for use with an a.c earth leakage circuit breaker provided for a d.c. load, said device comprising a a current balance .sensor provided for the phase and neutral lines of the a.c. power source, for sensing the pulsating d.c. earth leakage at the said load, a control unit incorporating a trigger circuit acting as an electronic switch, the trigger circuit for being connected to the said sensor, such that on a d.c• earth leakage occurring at the said load, the d.c. imbalance is, sensed by the sensor to actuate the trigger circuit to close and create an a..c • imbalance in the said lines and thus trip the said circuit breaker.
2.A device as claimed in Claim 1 wherein the said switch comprise a SCR switching circuit.
3.A device as claimed in Claim 1 or Claim 2 wherein the said switch incorporates a current limiting impedance.
4.A device as claimed in any one of the preceding Claims wherein the control unit comprises a high
voltage monitoring circuit connected to the trigger circuit.
5.A device as claimed in any one of the preceding Claims wherein the trigger circuit has setting means for setting the operative level of the said circuit to values of earth leakage current above a predetermined value.
6.A device for use with an a.c earth leakage circuit breaker provided for a d.c. load substantially as herein described with reference to and as illustrated in, the accompanying drawings.
|Indian Patent Application Number||2197/MAS/1998|
|PG Journal Number||27/2007|
|Date of Filing||01-Oct-1998|
|Name of Patentee||ARULANANDASAMY JOSEPH STEPHEN|
|Applicant Address||166 DEVELOPED PLOT ESTATE , PERUNGUDI,CHENNAI 600 096.|
|PCT International Classification Number||H02H3/16|
|PCT International Application Number||N/A|
|PCT International Filing date|