Relay,Principle of relay,NO and NC relay, use of relay, difference between Contactor and Relay,Classification of Relay

Principle
     
                     Relays are switches that open and close circuits electromechanically or electronically.
Relay control one electrical circuit by opening and closing contacts in another circuit.
                       
Normally open and Normally closed 

                      When a relay is normally open (NO) there is an open contact when a relay is not energized .When a relay is normally closed (NC) there is a closed contact when the relay is not energized. The state of relay will change when we apply the electrical current to the contact. 

Uses of Relay 

                      Relays are generally used to switch smaller current in a control circuit and do not usually control power consuming devices.

Difference between Contactor & Relay


  • Contactor is an electromagnetic switch that can carry huge amount of current max. 12000A, Relay is  an electromagnetic switch that can carry less amount of current max. 20A.
  • Contactors is bigger in size , Relay is smaller in size.    
  • Contactors are mainly used for switching power circuits such as transformer,Induction motors ,Stators, Capacitor bank etc, Where as Relay is mainly used in control and automation circuits, Protection circuits and for switching small electronic circuits.    
  •   In case of Contactor Arc chute must be present for suppressing electric Arc Where as in Relay chute will not be present.      
  • Contactor occupy less space where as Relay occupy more space.     
  • In case of Contactor we have less number of NO and NC contact can be taken , In Relay more number of contacts can be taken.
  • Contactor have high cost than Relay.
Classification of Relays

                      Classification of Relays depend on the function for which they are used .Some of the categories include protective ,reclosing , regulating ,auxiliary and monitoring relays.
 Protective Relay

                           Protective relay continuous monitor some parameters like voltage , current and power and if these parameters violate from the set limits they generate  alarm or isolate the particular circuit.These type of relays are used to protect equipments like motors, generators and transformers and many others.
Reclosing Relays
    
                             Reclosing relays are used to connect various components and devices with in the system network , such as synchronizing process , and to restore the various devices soon after any electric fault vanishes and then to monitors the system condition such as direction of power ans accordingly generates the alarm.These are also called directional relays.

Regulating Relay

                                 Large power and distribution transformers have the possibility of varying the secondary voltage utilizing what is called a tap changer.This is typically done with the use of a voltage regulating relay that controls the secondary voltage by operating the onload tap change.

Auxiliary Relay

                                Auxiliary relays are designed to switch more power (load) than the capacitance of the switching component.They are also used for so called multiplication of contacts where more than one contact is needed.The auxiliary relays have quit operation , LED signalling and switching contacts.

Monitoring Relay

                               A monitoring relay is a protective control device .The basic function are to receive input signal , monitor and determine them and output an alarm signal if a set value (threshold) is reached.

                      
                        

Comments

Post a Comment

Popular posts from this blog

What is full-wave Bridge Rectifier?,Comparision b/w FW-Bridge Rectifier with FW-Center tapped transformer,Working principle of FW-bridge Rectifier ,Comparison of all types of rectifiers,FW-bridge rectifier applications.

Image
Full-Wave Bridge Rectifier                      A Full-Wave Bridge Rectifier is a circuit arrangement which makes use of both half cycles of input alternating current (AC) and converts them to direct current (DC) .In full-wave bridge rectifier we used four diode in the form of a bridge as shown in the diagram below.  Comparison of FW-Bridge rectifier With Center Tapped Transformer                      The FW-bridge rectifier uses four diodes instead of two but the it eliminated the need of a center-tapped transformer.The PIV-rating of the diode used in FW- Bridge rectifier should be better than Vmax rather than 2Vmax if we compared it with FW-rectifier with a center-tapped transformer.This means that the diodes used in FW-bridge rectifiers are cheap as diodes of high PIV-rating are always more expensive used in FW-Rectifier with center tapped transformer ,this is b...
Read more

What is Current Transformer(CT)? ,Function Of CT,Construction of CT,Ratio of CT,Working Principle of CT,Uses /Advantages and Disadvantages of CT

Introduction                A Current Transformer(CT) is a type of transformer that is used to reduce or multiply an alternating current (AC) (used along with measuring or protective device).It produces a current in its secondary which is proportional to the current in its primary. Function of Current Transformer                The current transformers are basically a step up transformers.In case of high magnitude supplies we can not connected the measuring devices directly.we used current transformer to the supply of those devices with currents of magnitude proportional to these of power.Current transformer also isolates the measuring instruments from the high voltage circuits.current transformers supply the protective relays with current of magnitude proportional to those of power circuit but sufficiently reduce in magnitude. Construction of Current Transformer          ...
Read more

What is Star Connections,Voltage ,Current and Power in Star connections,Summary of Star connections,Uses of Star connections,

Image
Star Connection           Star Connections is a method of connecting pohyphase circuit is such a way that one end of each phase line is connected to a common neutral point that may be connected to the earth as protection against lighting or to a wire to which all the other neutral points of the system are connected.            It is also known as three phase four wire system.It is denoted by Y.It is the most preferred system for AC power distribution.            If we connect the balance load across three phase voltage system in parallel,then the three currents will be flow in neutral and their quantities will be same .The angle between them is 120º.So we can say That the sum of all currents is zero.                                                       ...
Read more