Pagsulay sa Electromagnetic Relay | Mga Tipo sa Electromagnetic Relays
Electromagnetic Relay
Ang mga electromagnetic relays mao ang mga relays nga gipagana pinaagi sa electromagnetic action. Ang modernong electrical protection relays adunay basehan sa micro processor, apan ang electromagnetic relay padayon nagsilbi. Kini mahimong mogahin og dako nga panahon aron mapalit tanan ang electromagnetic relays pinaagi sa micro processor-based static relays. Busa, bago mobisita sa detalye sa protection relay system, kinahanglan nato mopasabot ang uban pang types of electromagnetic relays.
Electromagnetic Relay Working
Praktikalmente, tanang relaying device basehan sa usa o daghan pa sa sumala nga types of electromagnetic relays.
Magnitude measurement,
Comparison,
Ratio measurement.
Ang principle sa electromagnetic relay working basehan sa pipila ka basic principles. Pinaagi sa working principle, kini makapartition ha sumala nga types of electromagnetic relays.
Attracted Armature type relay,
Induction Disc type relay,
Induction Cup type relay,
Balanced Beam type relay,
Moving coil type relay,
Polarized Moving Iron type relay.
Attraction Armature Type Relay
Ang attraction armature type relay ania ang labi na simple sa construction ug sa iyang working principle. Kini nga tipo sa electromagnetic relays makapamolo isip magnitude relay o ratio relay. Kini nga mga relays gigamit isip auxiliary relay, control relay, over current, under current, over voltage, under voltage, ug impedance measuring relays.
Ang hinged armature ug plunger type constructions ania ang labi na kasagaran gamiton para niining types of electromagnetic relays. Sa duha nga constructional design, ang hinged armature type ania ang labi na kasagaran gamiton.
Kita kabalo nga ang force exerted sa armature directly proportional sa square sa magnetic flux sa air gap. Kon kita igignore ang effect sa saturation, ang equation sa force experienced sa armature makapresentar isip,
Diin, F ania ang net force, K’ ania ang constant, I ania ang rms current sa armature coil, ug K’ ania ang restraining force.
Ang threshold condition para sa relay operation mahimong maabot kon KI2 = K’.
Kon kita moobserve ang above equation carefully, mahimo nato masabot nga ang relay operation dependent sa constants K’ ug K para sa particular value sa coil current.
Gikan sa above explanation ug equation, mahimo nato masummarize nga, ang operation sa relay influenced pinaagi niini
Ampere – turns developed by the relay operating coil,
The size of air gap between the relay core and the armature,
Restraining force on the armature.
Construction of Attracted Type Relay
Kini nga relay essentially ania ang simple electromagnetic coil, ug ang hinged plunger. Kung ang coil magiging energized, ang plunger gi-attract sa core sa coil. Ang NO-NC (Normally Open and Normally Closed) contacts arranged mechanically ha kini nga plunger, nga, ang NO contacts mag-close ug ang NC contacts mag-open sa end sa plunger movement. Normal nga attraction armature type relay ania ang DC operated relay. Ang contacts arranged, nga, pagkahuman sa relay operation, ang contacts dili magbalik sa ilang original positions even after the armature de-energized. Pagkahuman sa relay operation, kini nga types of electromagnetic relays reset manually.
Ang attraction armature relay pinaagi sa ilang construction ug working principle, ania ang instantaneous
sa operation.
Induction Disc Type Relay
Ang induction disc type relay main consists of one rotating disc.
Induction Disc type Relay Working
Tanang induction disc type relay nagtrabaho pinaagi sa sama nga well known Ferrari’s principle. Kini nga principle says, ang torque produced pinaagi sa duha ka phase displaced fluxes, proportional sa product sa ilang magnitude ug phase displacement ha tibuok nila. Mathematically, kini makapresentar isip-
Ang induction disc type relay based ha same principle ha that of an ammeter or a volt meter, or a wattmeter or a watt hour mater. Ha induction relay, ang deflecting torque produced pinaagi sa eddy currents ha aluminum or copper disc pinaagi sa flux ha AC electromagnet. Hito, ang aluminum (or copper) disc placed between the poles ha AC magnet which produces an alternating flux φ lagging from I by a small angle. As this flux links with the disc, there must be an induced emf E2 in the disc, lagging behind the flux φ by 90o. As the disc is purely resistive, the induced current in the disc I2 will be in phase with E2. As the angle between φ and I2 is 90o, the net torque produced in that case is zero. As,
In order to obtain torque in induction disc type relay, it is necessary to produce a rotating field.
Pole Shading Method of Producing Torque in Induction Disc Relay
Ha this method, half of the pole surrounded with copper ring as shown. Let φ1 is the flux of unshaded portion of the pole. Actually total flux divided into two equal portions when the pole is divided into two parts by a slot.
As one portion of the pole is shaded by copper ring there will be induced current in the shade ring which will produce another flux φ2‘ in the shaded pole. So, resultant flux of shaded pole will be vector sum of φ1 and φ2. Say it is φ2, and angle between φ1 and φ2 is θ. These two fluxes will produce a resultant torque,
There are mainly three types of shape of rotating disc are available for induction disc type relay. They are spiral shaped, round and vase shaped, as shown. The spiral shape is done to compensate against varying restraining torque of the control spring which winds up as the disc rotates to close its contacts. For most designs, the disc may rotate by as much as 280o. Further, the moving contact on the disc shift is so positioned that it meets the stationary contacts on the relay frame when the largest radius section of the disc is under the electromagnet. This is done to ensure satisfactory contact pressure in induction disc type relay.
Where high speed operation is required, such as in differential protection, the angular travel of the disc is considerably limited and hence circular or even vane
types may be used in induction disc type electromagnetic relay.
Some time it is required that operation of an induction disc type relay should be done after successful operation of another relay. Such as inter locked over current relays are generally used for generator and bus bar protection. In that case, the shading band is replaced by a shading coil. Two ends of that shading coil are brought out across a normally open contact of other control device or relay. Whenever the latter is operated the normally open contact is closed and makes the shading coil short circuited. Only after that the over current relay disc starts rotating.
One can also change the time/current characteristics of an induction disc type relay, by deploying variable resistance arrangement to the shading coil.
Induction disc relay fed off a negative sequence filter can also be used as Negative-sequence protection device for alternators.
Induction Cup Type Relay
