|Title of Invention||
A RESISTOR HAVING A HOLLOW INSULATING BODY
|Abstract||The present invention proposes an improved resistor comprising of an electrically conductive material encased within a hollow insulating body having insulating and heat absorbing conditions surrounding the said electrically conductive material within the said body, the two ends of the said electrically conductive material protruding from the said body.|
|Full Text||FORM 2
THE PATENTS ACT. 1970 (39 OF 1970)
[SECTION 10, RULE 13
"IMPROVED RESISTOR HAVING A
SIEMENS LIMITED, AN INDIAN COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956 HAVING ITS REGISTERED OFFICE AT
130, PANDURANG BUDHKAR MARG, WORLI, MUMBAI 400 018, MAHARASHTRA STATE, INDIA.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES AND
ASCERTAINS THE NATURE OF THIS INVENTION AND THE MANNER
IN WHICH IT IS TO BE PERFORMED:-
This invention relates to an improved resistor.
The resistors are used in electric circuits to limit the current flowing through the circuit.
The various types of resistors known in the prior art are -
(a) Wire wound Resistors:
These comprise of heating alloy wire / strip wound over a ceramic tube. The cross section of the said heating alloy wire / strip, its length and the material of the heating alloy depend upon the ohmic value and the wattage rating to be assigned to the resistor. Such heating alloy wire / strip are either Silicone coated or Enamel coated.
In another embodiment of wire wound resistors, the said heating alloy wire / strip wound on a ceramic tube as stated above is eneased in a ceramic or Aluminum body and its axial leads are sealed.
(b) Wire Resistors:
These comprise of a heating alloy wire / strip whose cross seiption, length and material depend upon the ohmic value of the resistor. It is Goated by
in insulating material such as Poly Vinyl Chloride (PVC) or Poly Terra luroethyIene (PTFE) or impregnated and varnished glass sleeve or combination of these materials.
These are widely employed in contemporary switches used for switching capacitor banks.
However, when the above referred resistors carry the overload current for a longer duration or for a duration higher than their destruction time, under certain extreme operating conditions, they catch fire damaging the device / machine / panel as also sometimes the property or life or both. This also results into breaking of the circuit, which is not the desired use of the resistor. This limits the application of such resistors. The resistors known in the prior art also cannot be directly mounted on the associated electric circuitry and are required to be either screwed or soldered on the circuit board / plate or are required to be stud mounted thereon. Further, the end leads of the resistor remain in an open/" live condition making them prone to shock.
This invention therefore proposes an improved resistor wherein the aforesaid defects of the resistors known in the prior art have been overcome and there is provided a resistor having a higher overload current withstanding capacity in small dimensions or volume and it Gan be directly mounted on the
associated electrical circuitry. Its end leads are not exposed and are therefore not prone to shocks.
Accordingly this invention provides an improved resistor comprising of an electrically conductive material encased within an insulating body having heat absorbing conditions surrounding the said electrically conductive material within the said body.
More particularly, the present invention comprises of (i) an electrically conductive material (ii) encased within a hollow insulating body (iii) having insulating and heat absorbing conditions surrounding the said electrically conductive material within the said body, (iv) the two ends of the said electrically conductive material protruding from the said body.
The said protruding ends of the said electrically conductive material are made into a rigid construction so as to facilitate easy mounting of the resistor on the associated electrical circuitry.
The said protruding ends are preferably insulated between the points of protrusion from the insulating body and the points of connection to the associated electrical circuitry. The points of protrusion of the aforesaid ends are also preferably insulated.
In another preferable embodiment, the electrically conductive material may be a heating alloy Still further, the said heating alloy may be in the form of a wire or strip.
The invention is now described with reference to the drawings accompanying the provisional specification wherein same numerals are used to denote the same parts. The drawings however, are only illustrative and in no way limit the scope of the invention. The said drawings show only one of the preferred embodiments of the improved resistor according to this invention.
In the said drawings: -
Figure 1 shows an exploded view of the improved resistor in a disassembled condition.
Figure 2(a) shows the top view of the improved resistor.
Figure 2(b) shows the isometric view of the improved resistor.
Figure 2(c) shows the front view of the improved resistor.
igure 2(d) shows the sectional view of the improved resistor along line A-A shown in Figure 2(c).
Figure 3 shows the improved resistor mounted on the contactor.
Figure 4 shows the exploded view of both the sides of the
improved resistor in a dissembled condition
of the provisional specification and figure 4 of the complete
Referring to Figures 1 and 2| the electrically conductive material (P-l) is specification, housed in an insulating body (P-2) made of materials e.g. ceramic / porcelain / sheet moulding compound (SMC) / Dough moulding compound (DMC) etc. The insulating body may be of circular cross section (tube) or rectangular or square or any other cross section. The said electrically conductive material (P-1) is secured or connected electrically (soldered, crimped, riveted, brazed, etc.) to a conductive outer cap (P-4) on both the ends of the said insulating body. However, in one of the preferred embodiment, the said electrically conductive material (P-l) is secured or connected electrically (soldered, crimped, riveted, brazed, etc.) to an intermediate cap (P-3) on both the ends of the insulating body. Thereafter, the conductive outer cap (P-4) is fitted over the intermediate cap on both the ends of the said insulating body.
As shown in Figure 2(d), the said insulating body (P-2) is left unfilled (vacuum) or filled with either air / sand / bitumen / araldite or any other suitable insulating resin or medium (P-7), wherein the medium is used to absorb the heat in itself.
An insulated conductive metallic piece / wire (ie, rigid end) (P-5) bent straight / curved in desired shape is connected electrically either directly to the
conductive outer cap (P-4) or via an intermediate metallic piece like wire lug (P-6). Alternatively, the insulated conductive metallic piece / wire (P-5) can be kept flexible. In turn, the wire lug (P-6) is connected electrically to the said conductive outer cap (P-4). Thereafter, the conductive metallic piece / wire (P-5) is crimped or connected otherwise to the said wire lug (P-6) on both the ends.
Sometimes, in one of the preferred executions, the conductive metallic piece / wire (P-5) comprises of a bare conductor (P-10), which in turn is insulated by heat shrinkable sleeve (P-11).
The solid end connection / lug (P-8) is connected firmly (by way of
crimping, soldering, or otherwise) to the conductive metallic piece / wire (P-5). This makes it possible to connect the resistor onto the said associated electrical circuitry easily.
An insulating outer cap (P-9) made up of rubber / plastic / elastomer or any such insulating material is provided on both the ends.
It should be appreciated that the improved resistor embodied herein, and as described in greater details, have universal applications in places wherever conventional resistors are used.
However, for the purpose of specific illustration, a preferred embodiment of this invention is described in connection with one particular application, namely, in functioning as a charging current limiting element in a capacitor-switching device.
Such a switch comprising of a contactor designed for switching capacitor bank of 15-kVAr rating was selected as shown in Figure 3. The contactor has a set of leading contacts and a charging current limiting resistor in series with them. The other set of contacts close after a short time delay and short the pre-charging resistors within a very short period of time. Thus the pre-charging resistors are only short time rated and generally dissipate much more than their rated wattage rating for a very small duration" typically of 3 milliseconds. However, under extreme operating conditions these resistors will be required to carry the current for longer duration (2 -3 seconds) and thus are required to dissipate the higher wattage as compared to their rated capacity.
The innovation will now be explained by way of the exemplifications as below:
Experiment 1 - A commercially available silicone coated resistor of 3 ohms having a length of 54 mm with a diameter of 10 mm and rated by the manufacturer at 15 Watts, was selected for use on 15 kVAr capacitor bank. The rated current of the capacitor bank is 21A at 415V system voltage.
fn extreme conditions of operations, this resistor is required to carry this 21 A current for longer duration. The contactor was made to chatter (an abnormal condition of operation) and the resistor was made to carry the rated capacitor current. The wattage dissipated by the resistor was calculated as
P = I2R - (21)2 * 3 = 1323 Watt
This wattage is 1323/15 = 88 times the claimed rated wattage of the resistor.
The time for the catastrophic failure under such conditions as described above was noted and varied between few tens of milliseconds to less than 1 second. The mode of failure noticed was melting of the resistor and a flame of the coating was observed. The flame needed to be extinguished to avoid its spread and damage to the other surrounding equipment.
Experiment 2 - In the same test set-up, the improved resistor, as described in the construction above, with comparable dimensions to silicone coated resistor selected in Experiment 1 was tested.
The representative improved resistor was made using a ceramic tube of 50mm length and 12,5 mm diameter and the said heating alloy wire / strip of 0.6 mm diameter of FeCrAl alloy wire. It should be noted that the choice of dimensions and material chosen is specific to this experiment only, for the purpose of demonstrating the function of the innovation. The resistor was constructed as per the construction as described in this innovation.
This resistor was mounted on the contactor (Figure 3) and similar abnormal operating conditions were simulated as in Experiment 1 and the resistor was made to carry 21 A current for longer duration or till failure.
It was observed that the resistor could withstand such higher wattage pulses for 2-3 seconds without any destruction. The number of such pulses was applied to the same unit repeatedly to establish consistency.
When the test was carried up to the failure by extending the period of
passage of the current for longer duration, the failure observed was in the form
of breakage/only. No flame was observed. as it was arrested there by
providing safety and awoding damage to the surraunding
Hence it can be concluded mat the improved resistor has much higher short time withstand capacity (2-3 times) than that of the presently commercially available resistors for same or similar dimensions and volume.
It can be seen from the Figure 3 that the unique construction makes it easily possible to assemble or disassemble the resistor on the switch (contactor) compared to commercially available silicone coated or ceramic coated or aluminum housed resistors. It can be seen that the leads also support and hold the resistor. Thus the resistor can be thought of as a plug, in simple analogy, which can be directly and easily mounted on to the associated circuitry and can be tightened. Moreover, at the fault condition, only the insulating body breaks open, thus leaving the resistor as it is, thereby not breaking the circuit.
(i) The improved resistor has higher thermal overload withstand capacity in smaller volume than that of the presently commercially available resistors. This is achieved by way of selection of the material for the element, and also the high temperature withstand capacity of the sand or any such suitable filling material and also the high temperature withstand capacity of the enclosure such as ceramic tube. These factors
are utilised to obtain the higher overload withstand capacity of the improved resistor.
(ii) The unique construction makes it easily possible to assemble or disassemble the improved resistor electrically to any other electrical device (like contactor or terminal block, etc,) without the need of soldered securements, separate fastening elements or threaded members.
(iii) The above mentioned leads can be so designed and proportioned, so as to hold and support the device and also the means of effecting the external circuit connections thereto.
as rebber, plastic, elastomer,provided on both the ends (iv) Further, the outer cap (P-9) of insulating material such, makes it
possible to mount the devices, in close arrangement, even touching each
other, from electrical safety point
1. An improved resistor comprising of an electrically conductive material
encased within an insulating body having heat absorbing conditions
surrounding the said electrically conductive material within the said
1. A resistor having a hollow insulating body comprising of a conventional electrically conductive material encased within said hollow insulating body, said hollow insulating body either filled with sand or air or bitumen or araldite or other insulating medium or any combination thereof or vacuum is maintained in said hollow insulating body.
2. A resistor as claimed in Claim 1 wherein the two ends of the said electrically conductive material protrude from said hollow insulating body.
3. A resistor as claimed in Claim 2 wherein the said protruding ends of the said electrically conductive material are rigid.
4. A resistor as claimed in Claim 2 wherein the said protruding ends of the said electrically conductive material are flexible.
5. A resistor as claimed in Claim 3 or 4 wherein the said one or both ends are insulated.
6. A resistor as claimed in Claim 1, wherein the said electrically conductive material is an alloy.
7. , A resistor as claimed in Claim 1, wherein the said electrically
conductive material is in the form of a wire or strip.
8. A resistor as claimed in any of the aforesaid claims, wherein an insulating covering is fitted on one or both the ends of the said hollow insulating body.
9. A resistor as claimed in any of the aforesaid claims as substantially described herein with reference to the drawings accompanying the provisional specification and complete specification.
Dated this 5th day of March 2003.
The Controller of Patents, The Patent Office, Mumbai 400 013.
S-1/D/PATENT/SIEMENS IMPROVE RESISTOR CS
|Indian Patent Application Number||239/MUM/2002|
|PG Journal Number||13/2008|
|Date of Filing||11-Mar-2002|
|Name of Patentee||SIEMENS LIMITED|
|Applicant Address||130, PANDURANG BUDHKAR MARG, WORLI, MUMBAI-400 018.|
|PCT International Classification Number||H01C1/08, H01C1/028|
|PCT International Application Number||N/A|
|PCT International Filing date|