Most relays work by energizing a small electromagnet. A big difference between conventional electromechanical and static relays is how the relays are wired. I hope you will find this article informative and helpful. Over current relay working principle types electrical. Protection relay or protective relay is a device designed to trip a circuit breaker when a fault is detected as matter of fact it is designe to protect power system. This book contains a description of electrical relays, their principles of operation, and. The third part is the tripping circuit which may be either ac or dc. Based on operation mechanism protection relay can be categorized as electromagnetic relay, static relay and mechanical relay.
Numerical relays protection and control products for. This type is widely used where control is from simple switches or singleended outputs of a control system, and such relays are found in avionics and numerous industrial applications. When the relay is deactivated, the circuit connects. Although there are various relay designs, the ones most commonly found in low voltage auto and marine applications are electromechanical relays that work by activating an electromagnet to pull a set of contacts to make or break a circuit. A relay is an electrical switch that uses an electromagnet to move the switch from the off to on position instead of a person moving the switch. How relays work relay diagrams, relay definitions and. This is the normal type of relay that we use for failsafe switches. It consists of a source of supply, the trip coil of the circuit breaker and the relay stationary contacts. A solid state relay may be defined as an electrical switch that changes its state when an external voltage is applied to it. Polarized relays use the magnetic flux of the permanent. Two types of relay technology are available, mechanical and solid state. Relay is a electromechanical switch used to control high power application through low power signal electronic circuits, for an example a simple timer circuit working under 5v dc bias can not control high voltage light bulb, by introducing relay component we can easily control light bulb.
Types of relays the relay may be defined as an electrical device interposed between the main circuit and the circuit breaker in such a manner that any abnormality in the circuit acts on the relay, which in turn if the fault is dangerous then it causes the circuit breaker to isolate and so to remove the faulty element. Nonpolarized relays nonpolarized relays do not use a permanent magnet in their. Type load current points typical relays ssrs integrated with heat sinks 150 a or lower the integrated heat sink enables a slim design. Depending upon time of operation, there are various types of oc relays, such as, instantaneous over electric current relay. Changeover co double throw dt contacts this type of contacts are used to control two types of circuits. It is a metal which doesnt have magnetic property but it can be converted into a magnet with the help of an electrical signal.
Iso micro relay types below are two popular micro iso relay configurations. Also, the design, construction, working, applications, and also relay selection is explained in detail. The heat produced by the overload current is utilized to trip the motor circuit. Different types of solid state relays ssr and their working classification of solid state relays ssr ssr definition. The electromagnetic attraction type relay has a solenoid which is attracted towards the poles of the electromagnet. Types of relays there are different ways to classify relays. The protection relays are normally provided for different objectives and aims. These classifications include electromagnetic, solid state, high voltage, thermal relays, and so on. Although there are different types of over electric current relays but basic working principle of over electric current relay is more or less same for all. The working of the relay is either depends on the electromagnetic attraction or electromagnetic induction. Relay types in addition to the electromechanical and electromagnetic relay, there is a wide variety of relays with different working principles. As relay diagrams show, when a relay contact is normally open no, there is an open contact when the relay. The second part consists of the secondary winding of the current transformer and circuit breaker and the relay operating coil.
The latter is a special application although normal in plants, but in this case the relays cannot be considered as network and plant. A thermal overload relay works on the heat produced by the excessive overload current. This terminal is normally connected with com terminal of the relay when there is no control input. Electromechanical relays are switches that typically are used to control high power electrical devices. Contactors and relays contactor relays eaton wiring manual 0611 53 55 the system and the standard european standard en 50011 terminal markings, distinctive numbers and reference letters for certain contactor relays has a direct bearing on the use and application of the modular system. Other than the electromagnetic relay there are many other types of relays which work on different principles. Here we will learn about relay logic control circuit, its symbols, working and how they can be used as digital logic gates. We will use the relay shown below enclosure is cut away. By doug wifb hat could be more ordinary than a switch. This is comparable to a momentary button switchit stays on only while you press the button. How does a relay work and types of relays a relay is an electromagnetic switch that is used to turn on and turn off a circuit by a low power signal, or where several circuits must. In this article, the basics of a relay like energized relay and deenergized relay are explained in detail.
The relay contactor switch is springloaded and returns to the preset position unless power is applied to the coil. Electrothermal relay when two different material gets in contact, bimetallic strip is formed, and when it is energized, it bends. But when fault or undesirable condition arrives relay must be operated and. Overvoltage and undervoltage relay product guide spau 121 c 1mrs750358mbg 4 design the combined overvoltage and undervoltage relay spau 121 c is a secondary relay that is connected to the voltage transformers of the object to be protected. Therefore, this document is intended to describe about a few basic types of relays that are popularly used in typical loadcontrol. Electromagnetic attraction relays working,construction. The relay is designed to operate when the actuating quantity equals, or exceeds, its pickup value. Other types of relays also used know as solid state relay in which dc voltage used as input. The size of a iso micro relay is a 1 x 1 x 12 square 12 as thick as a mini relay. A relay is a switch that is turned on or off using electricity. R efrigeration and airconditioning technicians know that the hermetic compressor is the heart of the cooling system.
Lets examine mechanical switching devices and become acquainted with how they look and perform. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solidstate relays. Latching relay is really a generic term that is used to describe the type of relay that maintains its position after the power is removed. Today, many of those applications have been supplanted by. Types and revolution of electrical relays introduction. But when fault or undesirable condition arrives relay must be operated and function correctly. Induction type relay these are used as protective relays in ac systems alone and are usable with dc systems. Microcontroller do not have considerable amount of current to operate relay. It takes a relatively small amount of power to turn on a relay but the relay can control something that draws much more power. Only some of the relays are explained in this document for making. The first static relays developed were the high speed differential relays and the distance relays. Technical explanation for generalpurpose relays omron. This p roduces a retarding effect on motion of the rotor in either di rection.
Nc or normally closed terminal is the other load terminal of a relay. Relays are classified into several types based on their functionality and application they are implemented for. Inside the world of control relays, including how theyre constructed, how they work, and where theyre used. A relay is essentially a switch that is operated electrically rather than mechanically. Ac coil for reliable operation of the relay, the coil voltage supply should be with i the. All the relays react to voltage or current with the end goal that they open or close the contacts or circuits. These relays are employed as auxiliary relay, control relay, over current, under current, over voltage, under voltage and impedance measuring. Working of relayshow relay works,basics,design,construction. Electromechanical and static relays have fixed wiring and the setting is manual. Types of electrical protection relays or protective relays. The overcurrent relays, even though simplest of all types of electromechanical relays, are the most difficult static relays. The following groupings will be used in this technical guide. Relays control one electrical circuit by opening and closing contacts in another circuit. Mos fet relays have control circuits that ar e different from those of traditional ssrs.
This is because the induction disc characteristics of the overcurrent relays inverse characteristics are not amenable to simple mathematical analysis. Both relay types are frequently provided in one relay case and are actuated by the same current. White paper on different types of relays the relay is an automatic protective and switching device which is capable of sensing abnormal conditions in electrical circuits. Under normal power system operation, a protective relay remains idle and serves no active function. Hi friends, in this article, i am talking about thermal overload relay working principle and its function in a dol starter. Medium voltage products technical guide protection.
Introduction to relay logic control symbols, working and. Thus, this is all about thermistor, thermistor working principle, its types and its applications, these are used for various temperature sensing applications. A mechanical relay is essentially a combination of. Changeover co doublethrow dt contacts this type of contacts are used to control two types of circuits. Thermistor basics, working principle, types and applications. These are operated to open or close the load contacts in response to one. A control circuit shown in green and a load circuit shown in red. The control circuit has a small control coil while the load circuit has a switch.
Protective relays work in concert with sensing and control devices to accomplish their function. This document explains each and every relay and its working principle with appropriate figures. Power system protection relays can be categorized into different types of relays. What is relay and different types of relays pdf elprocus. Types of relay based on the principle of operation. When the operating current becomes large, the magnetic field produced by an electromagnet is so high that it attracts the armature or plunger, making contact with the trip circuit contacts. Different types of solid state relays ssr and their working. Electromechanical relays are used in many of todays 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. The relay generally measures the phasetophase voltage of the system. Relays are switches that open and close circuits electromechanically or electronically.
The operation of a normally closed relay is the same to that of a normally open. An electromagnet plays a major role in the working of a relay. In electromagnetic attraction relays, there is a coil which energises an electromagnet. Numeric relays, on the other hand, are programmable relays where the characteristics and behavior can be programmed. Latching relays are bistable, meaning they have two relaxed states. Diagnosingsolving relay problems learn about the successful application of a starting relay, including proper installation, wiring, troubleshooting and replacement of the relay. Attraction armature type relay is the most simple both in construction as well as in its working principle. Over the years, control relays of various types have been used by the hundreds even thousands to control nearly every function in commercial and industrial processes. Types of electromagnets relays are classified into the following types, depending on whether or not they have a permanent magnet. Different types of relays and their working principles relays are the primary protection as well as switching devices in most of the control processes or equipments. Relays a relay is defined as an electrically controlled device that opens and closes electrical contacts, or activates and deactivates operation of other devices in the same or another electrical circuit. Besides these magnitude changes of the ac quantities, other changes may occur in one or more.
When two different materials are joined together it forms into a bimetallic strip. Electromagnetic relay working types of electromagnetic. Contact voltage rating typical control relays rated 300 vac or 600 vac, automotive types to 50 vdc, special highvoltage relays to about 15,000 v operating lifetime, useful life the number of times the relay can be expected to operate reliably. Thermal overload relay working principle your electrical. Different types of relays, their construction, operation.
983 1650 1283 1648 965 1556 238 1536 985 1578 54 1239 1627 369 688 1166 984 1033 891 1392 407 446 462 434 473 878 255 71 1514 394 1206 762 678 1218 165 1121 327 1158 721 1454 1348 147 373 1379 713 1188