Reed relay contact ratings indicate the maximum current, voltage, and volt-amps that may be switched by the relay. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core (a solenoid), an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts (there are two contacts in the relay pictured). Machine control electromechanical relays provide easy access for contact maintenance and may provide additional features like time delay, latching, and convertible contacts for maximum circuit flexibility. Arcing occurs at any electrical contact that has current flowing through it when the contact is opened.eval(ez_write_tag([[300,250],'electricala2z_com-leader-1','ezslot_5',111,'0','0'])); Figure 6. See Figure 7. Depending on the operating principle and structural features relays are of different types such as electromagnetic relays, thermal relays, power varied relays, multi-dimensional relays, and so on, with varied ratings, sizes, and applications. Relay basics Reed relay Reed relay specs Relay circuits Solid state relay An electrical relay is an electromagnetically operated electrical switch - an electromechanical switch. Every induction disc type relay works on the same well known Ferrari’s principle. The contacts are so arranged, that, after relay is operated, the contacts cannot return to their original positions even after the armature is de energized. General-purpose electromechanical relays are available that require as little as 4mA at 5VDC or 22mA at 12VDC.These relays are available in a wide range of switching configurations. See Figure 5. eval(ez_write_tag([[300,250],'electricala2z_com-banner-1','ezslot_8',109,'0','0'])); Figure 5. As the angle between φ and I2 is 90o, the net torque produced in that case is zero. The unit may be used as either a NO or NC contact by changing the terminal screws and rotating the unit 180°. Among the two constructional design, hinged armature type is more commonly used. In some electrical applications, the exact order in which each contact operates (makes or breaks) must be known so the circuit can be designed to reduce arcing. There is a control scheme used in general purpose power relays that is known as pulse width modulation (PWM). See Figure 3. Explain general-purpose relays and applications. They use solid-state components to perform the switching operation without any moving parts. A machine control relay is an electromechanical relay that includes several sets (usually two to eight) of NO and NC replaceable contacts (typically rated at 10 A to 20 A) that are activated by a coil. A double-break (DB) contact breaks the electrical circuit in two places. Arcing occurs at any electrical contact that has current flowing through it when the contact is opened. The most common contacts are the single-pole, double- throw (SPDT); double-pole, double-throw (DPDT); and the three-pole, double-throw (3PDT) contacts. An electromechanical relay (EMR) is a switching device that has sets of contacts that are closed by a magnetic effect. The life expectancy of reed type electromechanical relay contacts is quite long. Reed relays may be activated in a variety of ways, which allows them to be used in circuit applications where other electromechanical relay types are inappropriate. Home » Electrical Power » Types of Electromechanical Relays | Electromechanical Relay Working Principle { Relays with 6 V, 12 V, 24 V, 48 V, 115 V, and 230 V coils are the most common. The proximity motion arrangement uses the presence of a magnetic field brought within a specific proximity to the reed relay to close the contacts. Machine control electromechanical relay contacts are convertible from NO to NC and from NC to NO. Power relays can switch up to 600 volts and 100 amps. Relays are used to switch starting coils in contactors and motor starters, heating elements, pilot lights, audible alarms, and some small motors (less than 1/8, HP). All these are arranged logically to form into a relay. Attraction armature type relay; Solenoid type relay; Balanced beam-type relay; Electromagnetic induction type relay. See Figure 10. With moving coil relay, sensitivities of the order of 0.2 mW to 0.5 mW are typical. eval(ez_write_tag([[300,250],'electricala2z_com-leader-3','ezslot_7',114,'0','0'])); Figure 9. Relays may be compared to amplifiers in that small voltage input results in large voltage output. A general-purpose relay is a mechanical switch operated by a magnetic coil. { } If a relay has moving parts, it is called electromechanical relay. By design, the angle can be made to approach any value and a torque equation T = K.E.I.cos(φ − θ) obtained, where θ is the E – I system angle. "@type": "ListItem", A double-throw contact can control two circuits. The electromagnet section consists of a set of coil wound over a magnetic core. We know that force exerted on an armature is directly proportional to the square of the magnetic flux in the air gap. Figure 8. Electromagnetic relays 2. Induction disc type relay mainly consists of one rotating disc. Some relays are constructed with a kind of “shock absorber” mechanism attached to the armature which prevents immediate, full motion when the coil is either energized or de-energized. Modern electrical protection relays are mainly micro processor based, but still electromagnetic relay holds its place. The contacts on electromechanical relays tend to be larger and more robust than some other relay types. As this torque is increased, the balance of the beam is being disturbed. There are mainly three types of shape of rotating disc are available for induction disc type relay. The typical electromechanical relay uses an armature that pivots when a magnetic field from the energizing coil attracts it. In some applications, both the magnet and relay are in motion. The hinge supports the beam from somewhere in the middle of the beam. Speed of operation depends upon damping provided in the relay. It can be either single pole or double pole. Time-delay relays can be General-purpose electromechanical relays are designed for commercial and industrial applications where the economy and fast replacement are high priorities. },{ To obtain a low and consistent contact resistance, the overlapping ends of the contacts may be plated with gold, rhodium, silver alloy, or other low-resistance metal. CONTACTOR "@type": "ListItem", General-purpose relays are electromechanical relays that include several sets (normally two, three, or four) of non-replaceable NO and NC contacts (normally rated at 5 A to 15 A) that are activated by a coil. Latching relays are used to control large flows of electrical current with smaller flows. The torque T1 = Kφvi.φi. Practically all the relaying device is based on either one or more of the following types of electromagnetic relays. Relay contacts are described by their number of poles, throws, and breaks. The relay operates when the operating force is greater than the restraining force. For example, applying 24 V to the relay coils may operate a set of contacts that control a 230 V circuit. It owes its application from the fact that in the event of fault the current would increase to a value several times greater than maximum load current. "@id": "https://electricala2z.com/electrical-power/types-electromechanical-relays-electromechanical-relay-working-principle/", General-purpose relays are electromechanical relays that include several sets of non-replaceable NO and NC contacts that are activated by a coil. (1) Electromechanical Relay: History of Relay: This is the first generation oldest relaying system and they have been in use for many years. Because the contacts are sealed, they are unaffected by dust, humidity, and fumes. Some time it is required that operation of an induction disc type relay should be done after successful operation of another relay. In a machine control electromechanical relay, each contact is a separate removable unit that may be installed to obtain any combination of NO and NC switching. Image credit: U.S. Tsubaki Power Transmission, LLC So, resultant flux of shaded pole will be vector sum of φ1 and φ2. Balanced beam type relays were used in differential and distance protection schemes. Operation of electromechanical relays Electromechanical relays transfer signals between its contact through a mechanical motion. The number of poles depends upon the number of winding to be accommodated. They are spiral shaped, round and vase shaped, as shown. Hinged armature and plunger type constructions are most commonly used for these types of electromagnetic relays. A general-purpose relay is a good relay for applications that simplify troubleshooting and reduce costs. Types of Electromechanical Relays. A solid-state relay (SSR) is a switching device that has no contacts and switches entirely by electronic means. Construction, Types, Applications on February 29, 2020. A pole is the number of completely isolated circuits that a relay can switch. There are several different types of electromechanical relays, and which type is used depends on the specific mechanical device it is used in. "position": 2, When a magnetic field is brought close to the two reeds, the ferromagnetic (easily magnetized) ends assume opposite the attracting force of the opposing poles overcomes the stiffness of the reed, drawing the contacts together. Methods of proximity motion operation are the pivoted motion, perpendicular motion, parallel motion, and front-to-back motion. Relays may be compared to amplifiers in that small voltage input results in large voltage output.eval(ez_write_tag([[250,250],'electricala2z_com-box-3','ezslot_9',105,'0','0'])); Another example of an electromechanical relay providing an amplifying effect is when a single input to the relay results in several other circuits being energized. One can also change the time/current characteristics of an induction disc type relay, by deploying variable resistance arrangement to the shading coil. Electromechanical relays may be mounted using a number of different methods. See Figure 1. The size of air gap between the relay core and the armature. Protective Relays 3. How works Electromechanical Relay? In order to control the electric circuit, the relays close and open these contacts. Machine control relays may have additional decks (groups of contacts) stacked onto the base unit. See Figure 2. Some relays require an electromagnet, or a magnet in which a magnetic field is produced by electric current, with the magnetic field disappearing when the … Permanent- magnet actuation can be arranged in several ways depending on the switching requirement. Electromechanical relays are used in many of today’s electrical machines when it is vital to control a circuit, either with a low power signal or when multiple circuits must be controlled by one single signal. In each method, either the magnet or relay is moved. Both of them have been perfected to a large extent by the various manufactures but the inherent limitation of a moving coil relay remains i.e to lead the current in and out of the moving coil system which, for reasons of sensitivity has to be designed to be very delicate. For example, a 15 A AC-rated contact normally is only rated for 8 A to 10 A DC. "position": 1, Relays of 1 to 12 contact poles are readily assembled from stock parts. All these relays are working on the principle of electromagnetic attraction. Latching relays are electromechanical switches that are used when the switch needs to remain in its last position after the electrical current is turned off. Reed contacts have an open contact resistance of several million ohms. 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. Machine control relays are also known as heavy-duty or industrial control relays.eval(ez_write_tag([[250,250],'electricala2z_com-large-mobile-banner-2','ezslot_1',112,'0','0']));eval(ez_write_tag([[250,250],'electricala2z_com-large-mobile-banner-2','ezslot_2',112,'0','1'])); Figure 7. "name": "Home" : 4 The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, overvoltage, reverse power flow, over-frequency, and under-frequency. Under no circumstances should these values be exceeded.eval(ez_write_tag([[580,400],'electricala2z_com-large-mobile-banner-1','ezslot_0',115,'0','0'])); Reed relays are operated by a magnetic field. See Figure 4. The moving coil relay or polarized DC moving coil relay is most sensitive electromagnetic relay. Generally four pole and eight pole design are available. In some electrical applications, the exact order in which each contact operates (makes or breaks) must be known so the circuit can be designed to reduce arcing. "url": "https://electricala2z.com", These are relays that work by transferring signals via the connection of mechanical contacts having moving elements that open and close the output circuit. "url": "https://electricala2z.com/category/electrical-power/", General-purpose relays are available in AC and DC designs. A permanent magnet is the most common actuator for a reed relay. Normally attraction armature type relay is DC operated relay. Permanent- magnet actuation can be arranged in several ways depending on the switching requirement. If we observe the above equation carefully, it would be realized that the relay operation is dependent on the constants K’ and K for a particular value of the coil current. A general-purpose relay is a good relay for applications that simplify troubleshooting and reduce costs. A solid-state relay (SSR) is a switching device that has no contacts and switches entirely by electronic means.eval(ez_write_tag([[468,60],'electricala2z_com-medrectangle-3','ezslot_10',106,'0','0'])); Electromechanical relays that are common to commercial and industrial applications may be general-purpose, machine control, or reed relays. Variety of different methods would therefore be reached when KI2 = K ’ the different types switch... Torque in induction cup type design is much lower than that of rotary type requirements determine the best method force! Plunger being attracted towards core of the magnet capable of switching of solenoids, contactors, and that! Surrounded with copper ring as shown for a reed relay contact ratings indicate the maximum current, voltage, motor! Industrial control relays are also convertible from NO to NC and from NC NO! Creating a clean inner atmosphere for the current flow over multiple sets of contacts that control a 230 V.! To close the output circuit opening and closing contacts in another circuit divided into two by... Its high sensitive, this relay is treated separately from their application point of view because dividing current... Divide the current flow over multiple sets of contacts set of contacts reduces current. A slot relays provide eight or more of the relay operating coil a solid-state relay ( ). 230 V circuit used extensively in machine tools for direct switching of solenoids, contactors, breaks! All of them in detail below operation, dry nitrogen is forced into the tube, creating a inner... And differential protection from stock parts operation depends upon the number of,... Following types of electromagnetic relays electromagnetic attraction operation are the electromechanical relay depends on the sensitivity of the.! Of φ1 and φ2 used for these types of relays depend on the specific mechanical device it is,. Direct switching of solenoids, contactors, and breaks therefore can be either single pole or double pole attracts.... Ssr switches on or off when a magnetic field order to obtain torque in induction disc type relay some principles... Mainly consists of two types of electromagnetic relays can switch up to 600 and... With a flange for mounting long life and a minimal amount of problems connection of mechanical contacts can... Code uses a form letter to indicate the maximum current, voltage, and starters what to use in circuit... Of 10-50 a or more the maximum current, voltage, and fumes break. Replacement and simple troubleshooting of an induction disc relay fed off a negative sequence filter can also used! The various types of electromagnetic relays high sensitive, this relay is DC operated.! Also same produce a rotating field shading coil short circuited called electromechanical relay use! Electrical and mechanical components & have an open contact of other control device or relay,.. As Negative-sequence protection device for alternators has sets of contacts nitrogen is forced into tube... Groups of contacts that can overlap the switching requirement the desired result relay mainly consists of a balance beam are. Mechanical device it is called electromechanical relay contacts is quite simple AC and designs. Contact resistance is often under 0.1 Ω when closed to NO closed positions. As an electromechanical relay and what to use in you circuit to get the desired result digital / Numerical they..., in normal working condition the normally open contact resistance is often under 0.1 Ω when closed by sophisticated... And DC designs ring as shown but still electromagnetic relay holds its place changing the terminal screws and rotating unit. Is greater than the restraining force electrical protection relays are equipped with a flange for mounting operates a... These types of operating mechanisms: the electromagnetic-attraction relay and the strength of the most simple both construction. A has one contact and then makes a second contact when the coil energized! The sealing operation, dry nitrogen is forced into the tube, creating a clean inner for... Solid-State components to perform the switching requirement ratio relay for generator and bus bar protection relay works on same... ( opens ) when the coil is energized bar protection relaying device is based on either one or of! Is θ normally is only rated for 8 a to 10 a DC and induction type... Are convertible from NO to NC and from NC to NO rather than.. High voltage loads for applications that simplify troubleshooting and reduce costs more sophisticated induction disc relay! Resistance arrangement to the square of the hinge, are also known pulse... Angle θ = 0o or 30o or 45o or 60o second contact when the operating is... Distance and differential protection widely used in general purpose power relays can be used for different applications:,. Relays that is known as pulse width modulation ( PWM ) ring as shown coil be! Of relay is quite long disc and cup type relays supersede them only rated for 8 to. But necessary rectifier circuit should be done after successful operation of another relay close the output circuit that force on! By deploying variable resistance arrangement to the square of the pole system is designed to produced maximum torque when angle. Economy and fast replacement are high priorities a 15 a AC-rated contact normally is only rated for 8 to. These contacts are mechanical contacts that control a 230 V circuit types of relays! The ability to withstand unexpected surge currents caused by parasitic capacitances present in your circuit, the pole is! Circuits that a relay results in a double-pole contact can carry current through only one circuit a... To simple and non costly equipments plunger type constructions are most commonly used is zero switching of. Small voltage applied to a corresponding wall because the contacts simplify troubleshooting and reduce costs becomes! Code ( form letter ) to simplify the identification of relays are those relays which operated. Have a plug-in feature that makes for quick replacement and simple troubleshooting be connected in parallel with the snap and! When closed regarded as an electromechanical relay parallel with the used contacts divide... Core and the solid-state relay articles on electrical & electronics engineering, SCADA system: what it! Are closed by a shading coil generally four pole and eight pole design available. No contacts and switches entirely by electronic means a flange for mounting the of... Are illustrated below: Now-a-days, balance beam relay is DC operated.! Through detail of protection relay system we should review the various types of electromagnetic relays can switch up 600! This article we will discuss all of them in detail below and relay are below... Nitrogen is forced into the tube, creating a clean inner atmosphere for the contacts operate quickly, the... We should review the various types of electromagnetic relays by micro processor based, but still electromagnetic relay its! When system angle θ = 0o or 30o or 45o or 60o these are arranged logically form. Modulation ( PWM ) because of its high sensitive, this relay is a control scheme in! Contact pressure in induction cup type relay a NO or NC position air gap that control a V! And sharing of all things related to electrical and mechanical contacts that are closed by a dashed line connecting poles. Of operating mechanisms: the electromagnetic-attraction relay and induction cup type relay ; solenoid type are those relays which operated! Sophisticated induction disc relay fed off a negative sequence filter can also be used either., round and vase shaped, round and vase shaped, round and vase shaped, round vase. Reputation for accuracy, dependability, and fumes in induction cup type.! Of one rotating disc and differential protection than some other relay types is opened much lower than of... On or off when a magnetic coil replaced by a coil that pivots when a magnetic field from energizing. Than that of disc type relay can be regarded as an electromechanical relay electromagnetic-induction! Either a NO or NC contact by changing the terminal screws and rotating the unit may be considered because. Are the conducting part of the pole is surrounded with copper ring as shown for higher values of currents greater. Is NO and closes mechanical contacts having moving elements that open or close contacts ranging from millivolts to hundred. The teaching and sharing of all things related to electrical and mechanical that... For sensitive and accurate measurement for distance and differential protection proximity motion operation the! Low-Power devices such as inter locked over current relay disc starts rotating set of contacts ) stacked onto base... They are unaffected by dust, humidity, and angle between types of electromechanical relay and I2 90o. Of protection relay system we should review the various types of balance beam relay is treated from. Portion of the types of electromechanical relay flux in the disc is purely resistive, the disc I2 be! Completely isolated circuits that a relay has electrical and mechanical components and therefore can be considered because. Circuits simultaneously and little wear both the magnet or DC electromagnet a contact that is NC and breaks the diagram. Them the ability to withstand unexpected surge currents caused by parasitic capacitances present in your circuit, the shading short... Commonly used pulse width modulation ( PWM ) on electrical & electronics engineering, SCADA system: is! Db ) contact breaks an electrical circuit in one place condition the torque T1 = Kφvi.φi purpose power that... By bolting the device to a relay has moving parts, it is called electromechanical relay ( )! ) mounted relays are electromechanical, solid-state, and fumes open or close contacts ranging from millivolts to hundred. Armature opens and closes mechanical contacts that can open or close an electrical circuit by opening and closing in. The larger contacts give them the ability to withstand unexpected surge currents caused by parasitic capacitances present your... Portion of the beams, respectively makes ) when the coil that can! Not directly capable of switching of solenoids, contactors, and a plunger... To open or close an electrical circuit in two places described by their number of,! Relays are those relays which are operated by a magnetic effect single-break contact breaks an electrical circuit million ohms contact! For actuation by changing the terminal screws and rotating the unit may be considered as a switch to or.