FORM 2
THE PATENTS ACT, 1970
COMPLETE SPECIFICATION
(See Section 10)
LOW CONSUMPTION PERMANENT MAGNET BASED DC ELECTROMAGNET SYSTEM
Numbered as dated
INVENTOR:
a) RAJESH K. PANDA
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai 400 001, Maharashtra
INDIA.


THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
NATURE OF THE INVENTION

LOW CONSUMPTION PERMANENT MAGNET BASED DC ELECTROMAGNET SYSTEM
Technical field of the invention:
[0001] The present invention generally relates to a low consumption permanent magnet based DC electromagnet system. More particularly it relates to a unique DC electromagnet system for an air break contactor using DC coil and rare - earth permanent magnet.
Background of the invention:
[0002] A contactor is used for switching loads with a controlled power flow, which is activated by an electric power. The contactor is composed of three different systems, a contact system (an ac control system or a DC control system), an electromagnet system, and an insulated housing system. The contact system consists of a current carrying part of the contactor, which results the current to flow further in a circuit in the closed position. The contact system includes a power contact, an auxiliary contact and a contact spring arrangement for flowing current in the circuit. The electromagnet system is a driving unit of the contact system, which provides the intended force to close the contact system. The insulated system is an external frame housing of the contact system and the electromagnet system.
[0003] Devices like PLC and other electronic drives are used for switching contactor with the DC control system. Switching through low power


active electronic components under the holding state restricts their usage for low power. Therefore there have been regular demands of the contactor, which consume low electric power.
[0004] Earlier methodology for the DC control system type contactor is to opt for a pure DC coil with increase in number of turns of the coil, to maintain the continuous electric power with desired pick-up. Increase in the number of turns of the coil, increases the hold on voltage and height of the coil. This increase in the height of the coil, increases overall volume of the enclosure system. Also the power consumed by such devices is very high.
[0005] Over the years, various types of contactors are introduced to overcome the aforesaid problems. Some of the contactor solving said problems is: a DC coil with economy resistor and late break "NC"; a DC coil with dual winding and late break "NC"; a DC coil with electronically controlled coil drive for "low wattage" consumption.
[0006] All mentioned contactors are able to eliminate aforesaid problem of higher volume of the insulator system by reducing the copper area of the coil. Most of the contactors with above mentioned methodologies have some limitation such as frequent chattering, coil burning, poor electrical and mechanical life due to malfunctioning of the add-on device which switches the state of the winding. Especially devices like coil drive introduces an additional add-on to the contactor. Hence there is a need for a new and improved contactor with a reduction in the overall volume of the contactor, sturdy and provides robust design of coil, higher starting and sealing force, avoid sluggish


operation of the contactor and is committed towards lower wattage dissipation of the coil with higher breaking velocity.
Objects of the invention:
[0007] The primary objective of the invention is to develop a unique DC electromagnet system for an air break contactor using DC coil and rare - earth permanent magnet.
[0008] An additional objective of the invention is to provide an improved contactor with a reduction in the overall volume of the contactor, sturdy and provides robust design of coil, higher starting and sealing force, avoid sluggish operation of the contactor and is committed towards lower wattage dissipation of the coil with higher breaking velocity.
SUMMARY OF THE INVENTION:
[0009] The present invention relates towards a unique DC electromagnet system for an air break contactor with the blend of two technologies "The dedicated pure DC coil" and "The rare earth type permanent magnet". It also ensures a reduction in the overall volume of the contactor, sturdy and robust design of coil, higher starting and sealing force, avoids sluggish operation of the contactor and provides lower wattage dissipation of the coil with higher breaking velocity. The poor electrical life and premature failure of the contactor which was a major limitation for a conventional DC electromagnet system is


solved with current system. The basic contactor consists of a DC electromagnet having a "C" shaped core and "I" shaped flat faced cylindrical plunger with higher window area to accommodate higher number of turns with thinner standard wire gauge enameled copper wire and two permanent magnets at the adjacent side of the core so as to hold the moving mass in its rest position and provide the desired higher starting force during pick-up condition. Beneath the pole face a permanent magnet is suitably placed with similar polarity to that of the permanent magnet placed in the bottom core so as to utilize the desired restraining magnetic stored energy for higher breaking velocity of the contactor. Such a design avoids the usage of the return spring normally used for maintaining the resting position of the contactor and to provide the desired breaking velocity of the contactor.
[0010] The device is an air break contactor consisting of front housing assembly, the arc shield, side cover, top cover with a provision of lens for position indication of the contactor. The front housing assembly essentially comprises of an insulated front housing, a metallic arc interrupting device, fixed current carrying assembly and terminal assembly. The front housing insulated parts is provided with three rectangular openings at the middle to accommodate the bridge assembly, which is an integral part of the rear housing assembly. A positive insulated wall is provided between the openings so as to provide the desired phase barrier between the respective poles of the contactor. At the front plane of the contactor, the wall is suitably extended towards the top and bottom end of the front housing so as to accommodate the fixed current carrying assembly in each pole of the contactor. Under the current carrying parts, suitable scooping of the insulated material is done to absorb the


shock transmitted via the fixed contact, which is imposed by the moving assembly during closing operation. For entry of the fixed current carrying parts in each pole, suitable path is provided along the adjacent surface of the front housing.
[0011] This ensures proper resting of the part and restricts its motion upwards even in the event of contact micro welding during opening operation. In the front plane of the contactor, at the top and bottom end, for each pole holes provided for easy insertion of the screw stud. Just beneath the fixed contact, at the adjacent surface of the housing, suitable grooves are laid, which accommodates the "U" shaped arc interrupting device such as de-ion plate encircling the entire periphery of the moving contact assembly. Suitable guided path is provided in each pole of the contactor so as to fit the arc shield upon the front housing through a screw fitment. At the front plane of the front housing, along the adjacent side, is provided with grooves with a hole for fitment of the top cover assembly. Similarly at the rear plane of the front housing means for resting the bridge assembly along with the electromagnet system is provided. At the bottom plane, "U" shaped rib is provided along the entire periphery. At the adjacent side of the rib, just above the rear plane of the front housing, are two rectangular through holes extending downwards. Along the front plane of the housing, there are two rectangular ribs attached at the bottom and top end. The side cover assembly is click fit between the rectangular ribs and the adjacent holes. Along the top plane of the housing, at the top and bottom end two projected parts serves the purpose of click fit fitment with respect to the rear housing of the contactor. The Front housing is


given a curvilinear shape along each plane through surfaces with variable radii so as to have an ergonomic industrial design.
[0012] The insulated arc shield along the front plane has suitable slots for fitment of the top add-on housing. At its rear plane, there are insulated ribs along with scooping of the insulated material for arresting the motion of the arc interrupting device. Adjacent to each such rib, at the top and bottom plane are projected ribs per pole, which is then suitably guided in the front housing. The side cover is designed ergonomically with variable radii surface along the entire possible plane so as to suitably match with the front housing shape. The side cover has a concave and convex surface along the contour formed by the front housing. Along the concave surface, there are two "L" shaped projected parts at die extreme two ends of the bottom plane and a "C" shaped rib at the top plane for positive click fit with the front housing. Similar to that of side cover the top cover consists of a concave and convex surface with at the rear plane, are insulated ribs through out the outer periphery so as to match with the front housing profile. The Top cover along the concave surface, at the left end side is provided widi cylindrical shaped projected solid parts suitably placed at the top and bottom end and at the right hand side, is provided with "L" shaped projected parts for click fit with respect to the front housing. This arrangement ensures the right polarity of the cover assembly with the front housing. Along the convex surface of the top cover, at the centre, suitable opening is provided for fitment of a click fit lens.
[0013] The rear housing assembly comprises of insulated rear housing, DC electromagnet assembly, rubber pad, coil terminal assembly, Bridge

assembly and means of contactor mounting assembly. The rear housing externally is ergonomically designed to provide multidimensional surface along all possible degree of freedom so as to match with the front housing profile. Along die front plane of the contactor, the rear housing has a rectangular opening with a uniform thickness of the insulation all along its periphery. At its top and bottom end, there are rectangular insulated ribs projecting upwards. Each of the ribs is provided with rectangular slot opening for resting the click fit parts of the front housing. Inside the rear housing, at the central coordinate axis, it has a circular slot up to a certain depth for resting die magnet assembly. Also there are two smaller circular slots for resting a rubber pad in between die rear housing and that of the magnet assembly. Along die width of the contactor, the central axis has two protruded parts at die extreme end inside the rear housing for holding the magnet assembly. Inside the rear housing, at the four corners is provided with protruded parts with holes up to a certain depth for resting the coil former.
[0014] The DC electromagnet assembly consists of a "C" shaped core, rectangular core, "I" core assembly, two vanes, plunger, coil assembly, permanent magnet, insulation strap and bridge strap. The "C" shaped and rectangular core essentially is of a steel material or other means which is suitably coated with an abrasive material through electrolysis etching process. The core has higher width as compared to its thickness thus provides higher window area for winding accommodation. At the centre of the core along its front plane, there is a circular through whole opening for entry of the plunger. Opposite to this limb of the core, at the other end is another opening but up to a certain depth so as to accommodate a circular permanent magnet. Along the


width of the core, at the central axis, suitable opening is provided so as to provide an intentional insulated air gap. The core at its bottom end along the central axis is provided with two projections for entry into the slotted protruded part provided in the rear housing.
[0015] The vanes are made out of sintered material through powder metallurgy process and are in rectangular shape. At the extreme top and bottom end, is provided with a chamfer for easy entry of the vane into the former. It has four projections at the corners to hold the permanent magnet along its surface. The Plunger is a flat faced cylindrical type with suitable threading at die top and bottom pole face. At one of its end where bridge strap is to be connected, it has central through hole for entry of a screw. However at the extreme other end, it has a hole up to a pre-determined depth for holding a permanent magnet by crimping or other means. It is made up of steel or other means without any abrasive coating over it. The permanent magnets attached to the vane are of rectangular type where as that attached to the plunger and opposite to that is of cylindrical type. They are made out of rare-earth permanent magnet or by other means. "I" core assembly essentially consists of a rectangular core which is suitably joined to the plunger through a threaded joint or by similar means. To this plunger surfaces, the bridge strap is connected by screw fitment or other means. Bridge assembly consists of Moving contact assembly, contact spring and insulated bridge, whose assembly arrangement is similar to that of a conventional contactor. The mounting assembly essentially consists of a spring loaded din rail clip.
[0016] Coil assembly comprises of insulated former for accommodating the winding around its inner periphery. The former has two flanges at the top


and bottom and a hollow cylindrical tubular form attached between the two the flanges. Upper flange has a central rectangular rib to provide desired insulated air gap in the "C" shaped core. At the front plane of the former, there are two ribs at the adjacent side to hold the "C" shaped core. Outer surface of the bottom flange is provided with a cylindrical projected part, which rests upon the circular slot provided in the rear housing. Below the top flange are two slotted path for routing the start and end winding coil towards the coil terminal placed in the adjacent side of the former. The coil terminal essentially is made out of a current carrying metallic part (Brass or other means), which has two right angular bending at the top and bottom plane of the contactor. The loose end coil assembly is suitably placed inside the "C" shaped core and then the "I" shaped core assembly is inserted inside the coil former. The other end of "I" shaped core assembly is then joined with a rectangular core, which under assembled condition with the rear housing, will rest on the coil former bottom surface. Under this assembled condition, the coil terminal is placed inside the former and the start and end of the winding is soldered at the crimping end provided. The complete DC electromagnet assembly is then connected with the bridge assembly through the bridge strap and the whole assembly is suitably placed inside the rear housing with the two cylindrical rubber pads in between the electromagnet and rear housing for absorbing the shock imparted during closing operation.
BRIEF DESCRIPTION OF THE DRAWINGS:
[0017] Figure 1 shows a sectional view of the magnet system.


[0018] Figure 2 shows a front view of the low consumption DC electromagnet contactor.
[0019] Figure 3 shows a top view of the low consumption DC electromagnet contactor.
[0020] Figure 4 shows a sectional view of the low consumption DC electromagnet contactor.
[0021] Figure 5 shows a "C core "of the electromagnet representing the fixed magnet.
[0022] Figure 6 shows the lower vane of the electromagnet.
[0023] Figure 7 shows the upper vane of the electromagnet.
[0024] Figure 8 shows the side vane holding the permanent magnet.
[0025] Figure 9 shows the insulating strap for providing desired air gap.
[0026] Figure 10 shows the plunger representing the moving magnet.
[0027] Figure 11 shows the bridge strap responsible for holding the bridge with the moving magnet.
[0028] Figure 12 shows the coil former.


[0029] Figure 13 shows the cylindrical permanent magnet to provide the desired repulsive F-S characteristics to the magnet system.
[0030] Figure 14 shows the rectangular permanent magnet.
[0031] Figure 15 shows the top cover.
[0032] Figure 16 shows the front housing.
[0033] Figure 17a, b shows die Arc shield.
[0034] Figure 18 shows the rear housing.
[0035] Figure 19 shows the Bridge.
[0036] Figure 20 shows the side cover.
DETAILED DESCRIPTION OF THE EMBODIMENTS:
[0037] Figure 1 shows a sectional view of the magnet system. The device is an air break contactor (110) consisting of (Figure 2 & 3) Front housing assembly, (Figurel7a and b) the arc shield (360), side cover (310, Figure 20), top cover (320, figure 15a and b) with a provision of lens (340) for position indication of the contactor. The front housing assembly (300) essentially


comprises of an insulated front housing (300), a metallic arc interrupting device (410), fixed current carrying assembly (380) and terminal assembly (420).
[0038] As shown in Figure 16, the front housing insulated parts is provided with three rectangular openings (301) at the middle to accommodate the bridge assembly (370), which is an integral part of the rear housing assembly (330). A positive insulated wall (302) is provided between the openings so as to provide the desired phase barrier between the respective poles of the contactor. At the Front plane of the contactor, the wall (303) is suitably extended towards the top and bottom end of the front housing so as to accommodate the fixed current carrying assembly (380) in each pole of the contactor. Under the current carrying parts, suitable scooping of the insulated material (304) is done to absorb the shock transmitted via the fixed contact (381), which is imposed by the moving assembly (390) during closing operation. For entry of the fixed current carrying parts in each pole, suitable path is provided along the adjacent surface (306) of the front housing. This ensures proper resting of the part and restricts its motion upwards even in the event of contact micro welding during opening operation. In the front plane of the contactor, at the top and bottom end, for each pole holes (305) provided for easy insertion of the screw stud. Just beneath the fixed contact button(382), at the adjacent surface of the housing, suitable grooves(309) are laid, which accommodates the "U" shaped arc interrupting device(410) such as de-ion plate encircling the entire periphery of the moving contact assembly(390). Suitable guided path (307) is provided in each pole of the contactor so as to fit the arc shield upon the front housing through a screw fitment. At the front plane of the front housing, along the adjacent side, is provided with grooves


with a hole (308) for fitment of the top cover assembly. Similarly at the rear plane of the front housing means for resting the bridge assembly along with the electromagnet system is provided. At the bottom plane, "U" shaped rib (309b) is provided along the entire periphery. At the adjacent side of the rib, just above the rear plane of the front housing, are two rectangular openings (309c) extending downwards. Along the front plane of the housing, there are two rectangular ribs attached at the bottom and top end. The side cover assembly is click fit between the rectangular ribs and the adjacent holes. Along the top plane of die housing, at the top and bottom end two projected parts (309a) serves the purpose of click fit fitment with respect to the rear housing of the contactor. The Front housing is given a curvilinear shape along each plane through surfaces with variable radii so as to have an ergonomic industrial design.
[0039] The insulated arc shield (360), as shown in Figure 17a, b, along the front plane has suitable slots (361) for fitment of die top add-on housing. At its rear plane, there are insulated ribs (362) along with scooping of the insulated material for arresting the motion of the arc interrupting device. Adjacent to each such rib, at the top and bottom plane are projected ribs per pole (363), which is then suitably guided in die front housing. At the adjacent side of the arc shield, in the front plane, insulated cylindrical protruded parts (364) is provided for positive polarity of assembly. The side cover (310, Figure 20) is designed ergonomically with variable radii surface along the entire possible plane so as to suitably match with the front housing shape. The side cover has a concave and convex surface along the contour formed by the front housing. Along the concave surface, there are two "L" shaped projected parts


(171) at the extreme two ends of the bottom plane and a "C" shaped rib (172) at die top plane for positive click fit with the front housing. Similar to that of side cover the top cover (Figure 15a and b) consists of a concave and convex surface at the rear plane, are insulated ribs (111) through out the outer periphery so as to match with the front housing profile. The Top cover along the concave surface, at the left end side is provided with cylindrical shaped projected solid parts(112) suitably placed at the top and bottom end and at the right hand side, is provided with "L" shaped projected parts(113) for click fit with respect to the front housing. This arrangement ensures the right polarity of the cover assembly with the front housing. Along the convex surface of the top cover, at the centre, suitable opening (114) is provided for fitment of a click fit lens.
[0040] The rear housing assembly (150) comprises of insulated rear housing (330, Figure 18), DC electromagnet assembly (100), rubber pad (430), coil terminal assembly (450), Bridge assembly (370) and means of contactor mounting assembly. The rear housing externally is ergonomically designed to provide multidimensional surface along all possible degree of freedom so as to match with the front housing profile. Along the top plane of the contactor, the rear housing has a rectangular opening with a uniform thickness of the insulation all along its periphery. At its top and bottom end, there are rectangular insulated ribs (151) projecting upwards. Each of the ribs is provided with rectangular slot opening (152) for resting the click fit parts of the front housing. Inside the rear housing, at the. central coordinate axis, it has a circular slot (153) up to a certain depth for resting the magnet assembly. Also there are two smaller circular slots (154) for resting a rubber pad in between the rear


housing and that of the magnet assembly. Along the width of the contactor, the central axis has two protruded parts (155) at the extreme end inside the rear housing for holding the magnet assembly. Inside the rear housing, at the four corners is provided with projected parts (156) with holes (157) up to a certain depth for resting the Coil former.
[0041] The DC electromagnet assembly consists of a "C" shaped rectangular core (210), "I" shaped core assembly (214, 218,211,212,216,219) two vanes (211,212,213), plunger (214), coil assembly (220), permanent magnet (215, 216), insulation strap (130, Figure 9) and bridge strap (219). As shown in Figure 5, 6 & 7, the "C" shaped and rectangular core essentially is of a steel material or other means which is suitably coated with an abrasive material through electrolysis etching process. The core has higher width as compared to its thickness thus provides higher window area for winding accommodation. At the centre of the core along its top plane, there is a circular opening (131) for entry of the plunger. Opposite to this limb of the core, at the other end is another opening (132) but up to a certain depth so as to accommodate a circular permanent magnet (216, Figure 13). Along the width of the core, at the central axis, suitable opening (133) is provided so as to provide an intentional insulated air gap. The core at its bottom end along the central axis is provided with two projections (134) for entry into the slotted protruded part provided in the rear housing. As shown in Figure 6 and 7, the vanes (211 & 212) are made out of sintered material (preferably through powder metallurgy process) and are in rectangular shape. At the extreme top and bottom end, the side vane (213, Figure 8) is provided with a chamfer (136) for easy entry of the vane into the former. It has four projections (135) at the corners to hold the permanent


magnet (215, Figure 14) along its surface. The Plunger (214, Figure 10) is a flat faced cylindrical type with suitable threading (218) at the top and bottom pole face. At one of its end where bridge strap (Figure 11) is to be connected, it has central through hole for entry of a screw. However at the extreme other end, it has a hole (139) up to a predetermined depth for holding a permanent magnet (216) by crimping or other means. It is made up of steel or other means without any abrasive coating over it. The permanent magnets attached to the vane are of rectangular type (Figure 14) where as that attached to the plunger and opposite to that is of cylindrical type (Figure 13). They are made out of rare-earth permanent magnet or by other means. "I" shaped core assembly essentially consists of a rectangular core which is suitably joined to the plunger through a threaded joint or by similar means. To this plunger surfaces, the bridge strap (219, Figure 11) is connected by screw fitment or other means.
[0042] Bridge assembly (370) consists of moving contact assembly (390), contact spring (400) and insulated bridge (370, Figure 19), whose assembly arrangement is similar to mat of a conventional contactor. The mounting assembly essentially consists of a spring loaded din rail clip.
[0043] Coil assembly comprises of insulated former (217) for accommodating the winding around its inner periphery. As shown in Figure 12, the former has two flanges at the top and bottom (141) and a hollow cylindrical tubular form attached between the two flanges. Upper flange has a central rectangular rib to provide desired insulated air gap (142) in the "C" shaped core. At the front plane of the former, there are two ribs at the adjacent side to hold the "C" shaped core. Outer surface of the bottom flange is provided with


a cylindrical projected part (143), which rests upon the circular slot (157) provided in the rear housing. Below the top flange are two slotted path (144) for routing die start and end winding coil towards the coil terminal placed in the adjacent side of the former. The coil terminal (220 & 450) essentially is made out of a current carrying metallic part (Brass or other means), which has two right angular bending at the top and bottom plane of die contactor.
[0044] The coil assembly is suitably placed inside the "C" shaped core. A suitable insulated strap (130) is placed over the "C" shaped core to provide the desired compensated air gap in the magnet circuit. The "I" shaped core assembly is then inserted inside the coil former. The other end of I core assembly is then joined with a rectangular core, which under assembled condition with die rear housing, will rest on die coil former bottom surface. Under this assembled condition, the coil terminal is placed inside the former and the start and end of the winding is soldered at the crimping end provided. The complete DC electromagnet system is then connected with the bridge assembly through die bridge strap and is suitably placed inside die rear housing with the two cylindrical rubber pads (460) in between the electromagnet and rear housing for absorbing the shock imparted during closing operation.
[0045] In the assembled condition of the contactor when the coil is not excited, the complete moving assembly will be in its state of rest condition maintaining the desired contact and magnet gap of die contactor. The permanent magnet attached to the vane has a North and South Pole, which is shorted via the "C" type core. At the lower portion of "I" shaped core assembly, die rectangular core having the least path will get shorted with the


adjacent two side vanes. The lower rectangular core being a part of the moving assembly will restrict its motion. This condition serves the purpose of providing the initial stored energy of the return spring, normally observed with a conventional contactor. When the coil is energized, depending upon the excitation voltage "NI" developed is sufficient to cause a movement of the plunger. The resultant force developed should be able to overcome the force due to the Permanent magnets located at the side plates of "C" shaped core. Hence due to this, there is always a sharp pick - up of the electromagnet as compared to conventional contactor with a sluggish motion. The Permanent magnets located at the bottom parts of DC Magnet assembly are nothing but a set of permanent magnets with similar polarity (N — S — S - N) Hence they will repel with respect to each other. Due to this there will be repelling force acting between the respective permanent magnets. However initially since the gap between the opposite polarities cylindrical permanent magnet is equivalent to the M.G. of the contactor, there shall not be any repulsion between the two magnets or the force developed would be of low order. While closing as the moving assembly moves further, the resultant force now has to overcome both the force i.e. force of attraction due to the adjacent permanent magnet attached to the side vane and force of repulsion due to adjacent opposing cylindrical permanent magnets attached to the respective pole face. Under this state of operation, lower vane is about to open.
[0046] Magnet Force = Fl (F2 ««F1)
[0047] Restraining Force Fr = F2 + JLIM


[0048] In the intermediate state of operation, as the moving assembly further moves along with the stroke of the magnet, lower vane further moves apart from the side vane and hence force F2 reduces further. Until at the dead center, where lower vane reaches at the mid MG, F2 force upon lower vane is neglected. But now the flux due to adjacent side vane permanent magnet will aid to the main flux and hence increases the resultant force for a particular magnet gap, which will take care of overcoming the restraining opposing force due to lower cylindrical shaped PM and additional force required to hold the moving mass assembly.
[0049] Magnet Force = Fl + F2 (F2 is fixed & Fl is variable)
[0050] Restraining Force Fr = F3 + F2 + M + Fc (F2