In an over current relay or o/c relay the actuating quantity is only current.There is only one current operated element in the relay, no voltage coil etc. Instead, a FET or a TRIAC is used to simulate the contacts. Turn ON/OFF operation The relay is used for the protection of the distribution lines. The number of contacts:…Just the number of contacts. The package: Last but not least is the package. The device that forces the terminal to move, is actually an electromagnet! Relay manufactures design them for special applications to full fill industries needed and coupe with advanced technologies. Thus, the setting is called the “time dial setting - TDS”. They have significantly more lifetime than the conventional relays, as their contacts will not corrode due to humidity, dust or other causes. Above 2 contact pairs, the x gets the number of poles, eg for 3 poles it would be 3P etc etc. The current axis may be expressed in amperes and can be scaled in multiples of 10 while the time axis is usually in the range of 0.01s to 1000s. Or become one of the thousands of small businesses joining our community today. Academia.edu no longer supports Internet Explorer. So we have: The coil can operate with either AC or DC voltage. The power for the contacts: This characteristic indicates the maximum power that the contacts can handle. The devices are categorized and stored by manufacturer name and device type for easy retrieval. As in any craft, an intimate ... consider the fundamental relay types. You may know these relays with another name… thermostats, used extensively in heating applications. Every time the wheel rotates and the magnet passes in front of the reed relay, it sends a pulse to a microcontroller. This magnetism can overcome the force of the spring and can pull the contact towards it, thus it changes it’s position! This is very handy in modern house lighting. If this electromagnet is powered, then the relay will be forced to break connection, as if it was overheated. For security reasons, the relay can only be restored mechanically by moving the lever by hand. We'll assume you're ok with this, but you can opt-out if you wish. The first sub-type is the current-leaking protective relay, and the other type is the overload protection relay. Another common application for reed relays is on the speed meters of the bicycles. The relay symbols are unlimited. Overload Relays 8 Ambient Temperature other than 40˚C For a thermal overload relay in an ambi-ent temperature higher or lower than the motor 40°C (104°F), the overload trip current can be calculated by applying a correction factor from the curve in Figure 1. A permanent magnet is attached to a door, while the reed relay is right above the magnet. Sorry, preview is currently unavailable. I don’t have a word for u sir, superb or I should say khatarnak nice…. This armature is magnetized from both electromagnets. Between them, there is the armature. DPDT? The major difference is that the bi-metallic strip is not heated by the current that flows within the strip, but from an external factor. There are many other types of relays like the timers and the function relays, but they use some kind of circuitry to perform different actions. In this relay, the operating time is approximately inversely proportional to For safety reasons, if this happens, the relay can only be restored mechanically, if someone pulls the lever of the relay up again: Very common relays in motor applications, as well as in all electrical installations. The max voltage: This characteristic is determined by the gap that exists between the contacts, as well as the alloy that the the contact is made of. If you see the above 3 animations, you will notice that one time an F force is applied to the COMMON terminal, and the other time there is no force applied. There are two types of contacts: the NO and the NC. On the other hand, a Normal Closed contact allows the current to flow when the contact is still. Also have two settings: 1- pick-up current and 2- curve level. relays. The single-line curve, characteristic of overcurrent relays, indicates the approximate time that the device will close its contacts to initiate the opening of a circuit breaker. The characteristic curves of electromechanical relays are developed by testing. This type of relay is widely used in applications where the state of the relay needs to be kept as is, even after a power failure or a restart. Therefore, the armature is actuated only if the polarity of the coils’ magnetic field is opposite to the polarity of the permanent magnet’s magnetic field. (Distributed Control System), Siemens S7 1200 PLC configuration in TIA Portal, Programmable Logic Controllers Multiple Choice Questions, Three-valve Manifold on Remote Seal DP Transmitter, Pressure Temperature Compensation Flow Measurement, Communicating Delta PLC Software to Simulator. The relay time characteristics differ by the rate at which the time of operation of the relay decreases as the current increases. And how can this happen? Draw Various IDMT Relay characteristic Curve. Ambient temperature is the temperature surrounding the overload relay enclo-sure. Look the following animation: A relay may have a combination of the above contacts. When the contacts are ‘in contact’ then the current flows from Terminal 1 to Terminal 2. You press the pushbutton once and the lights are turned on. The armature is actuated when current goes through the coil, regardless the polarity. You should consider the contacts as a pair of metals like the following diagram: The two terminals operates as a switch. IDMT Relay Setting & Curves Calculation of Actual Plug (Relay Pick up) setting of Various IDMT Relay. The higher the gap the higher the voltage that a relay can cut-off. 5. Easy, if somehow an amount of current flows to the ground of the installation. The NO and NC contacts are referred to the COMMON terminal. 2. The ANSI and IEC curves approximate the characteristics of electromechanical relays. When the contact is still, then no current flows through it (because it is an OPEN circuit). Therefore, i will categorize the types of the relays in terms of: 1. When current is flown through this coil, a magnetism is created. You could imagine a reed relay like a relay without an electromagnet. Also, relays are the best way for galvanic insulation between high and low voltage portions of a circuit. The lighter the construction, the faster the switching. 3. If the diode is correctly biased, the coil will have power and the armature will be actuated. In other words, the NORMAL state is defined as the state that there is NO other force applied to the COMMON terminal except the one from the spring. Very important characteristic to take into account when designing the driver of the relay. Thus, the load will only operate when the relay is actuated. The following animation shows how a NO contact operates by lighting a light bulb: As for the NC contacts, it works exactly opposite as the NO contacts. The directional overcurrent relay can be perceived as a type 50 instantaneous element controlled by a type 32 directional element If the type 67 relay element is to provide backup protection, they use definite time delay for downstream coordination The 67 element requires more attention to detail for coordination than do type 51 relays 1.3.3 Mixed Curves (Inverse-Time +Definite -Time) IDMT – Characteristics The most commonly used type of relay is the inverse definite with minimum time lag relay (IDMT) in which inverse characteristic plus definite time characteristic are used. Between the NC and the NO contact, there is no contact at any time! pdf. For each set of curves determined by the relay selection, the actual response is adjustable by means of the time dial. The characteristic curve for the relay is shown in the figure below. Each relay curve has a time dial setting which allows the curve to be shifted up or down on the time-current characteristic curve. There is indeed another force that pulls the contact towards UP and this force is applied ALL the time. It will only change state again on the next pulse that will actuate the coil. Enter the email address you signed up with and we'll email you a reset link. The first electromagnet is placed in series with the Phase, while the other is connected in series with the Neutral. This value should indicate also if the current is AC or DC. The inverse time relay is of three types. Inverse Definite Minimum Time Relay. Two basic forms of characteristic curves are drawn: single-line and banded. The only difference is that these relays does not have the permanent magnet, instead they have a diode in series to the coil. When the bimetallic strip is bended, the relay will cut-off the power supply. The first type is the normal on/off relay. A coil is placed right under the contact. Leave a comment on this post, we will send you the Overcurrent Fundamental. The current/time-tripping characteristics of IDMT protection relays may need to be changed according to the functioning time needed and the characteristics of other relay protection elements used in the electrical network0.10 For these needs, IEC 60255 determined … In this category i separate the relays according to the way that their coil is powered to actuate the armature. Excellent information with perfect explanation. The polarization of the magnetic field of the coil depends on the polarity of the supply. The relay will not operate when the value of current is less than the pick value. 4. The process is done automatically according to the temperature of the bimetallic strip. This website uses cookies to improve your experience. The equation describing the Extremely Inverse Relay is I2t = K where I is operating current and t is time of operation of the Relay. Curves of operating time versus the magnitude of the actuating quantity. The thicker the contacts the higher the current that a relay can handle. Time vs. PSM Curve of Relay. The CYMTCC software includes an Integrated Device Library Manager program that allows the user to add new device characteristics to the database and to modify existing curves. But if the current that flows through the second electromagnet is less than the current that flows through the first electromagnet, then the armature is pulled to the first electromagnet that has greater magnetic force! I will illustrate the most basic types of relays: The things that characterizes a relay are the followings: The coil voltage: This is the voltage that the coil can actuate the armature. These relays operates similarly to the overload protection relays above. Instead, they remain armed all the time. But which state is considered as NORMAL? So, here is the relay opened: You can clearly see the common contact, the NO and NC contacts as well as the electromagnetic coil and the return-to-normal spring. This is the basic idea of the overload protection relay figure below, If one line is overloaded, the bimetallic strip is overheated and thus it bends, breaking this way the contact. There are so many different types of relays, that it would be literally impossible for me to add them in this article. It will only change state (to RESET position) only if the other coil is actuated. Note that our team can also add curves for you if you provide the data. Time-Current Curves Extremely Inverse Relay is one in which CT saturation occur still at a later stage as compared with Very Inverse Relay and hence the characteristic remain inverse up to a larger range of fault current. Double Throw (DT) means that the relay has pairs of NO/NC contact. Electrical Characteristics of Relays. The third and last category is the contacts of the relays. These relays wave no electromagnetic coil to move the armature. Download Relay Tripping Curves PRO - This specialized software will allow you to plot and visualize the graphs for the setting curves of ANSI 50/51 functions of protection relays These relays are easy to open (either with screws or clips), and are big enough to have a clear view. The number/type of contacts: Is it an SPST? A permanent magnet is attached to the wheel of the bicycle, while the reed relay is fixed on the “fork” of the bike. For a fault current F1, the device operates at time T1. The switching frequency: This characteristic is determined by the mechanical construction of the relay. The time classification and curve slopes are characteristic of the relay selected, although for some solid-state relays these may be adjustable to some degree. Working Principle of Over Current Relay. The reed relay’s armature is actuated from any other external magnetic field. When the first coil is actuated, the relay goes to the SET position and it remains there no matter if this coil is kept actuated. Look the following image: Now you can see who is pulling the COMMON terminal UP all the time. Extremely Inverse (EI) Type. Calculate Total Grading Time of Various IDMT Relay. The ‘x’ is the number of “POLES” that a relay has. Going one step closer to the relay operation, we find the spring. The following animation shows how this pair operates: OK, we have the NORMAL open and NORMAL closed contact. This type of relay operates exactly like the R-S flip flop. Calculate PSM of Various IDMT Relay. If the voltage goes bellow this value, the spring will overcome the magnetic force and the relay will change state. The major disadvantage is the price…. Another type of relay categorization is the coil. These relays does not have a coil, nor any other moving part, that’s why they are called Solid State. Actually, they do not have contacts! When the coil is once actuated, the relay will change state, and will remain in this state even if the coil in no more actuated. Let’s find out first how a relay operates. The current that goes through the driver must be enough to actuate the armature. This type of IDMT curve is most suited for coordination with fuses. are required to construct this protective relay.. In this case, there is a 3rd terminal called “COMMON”. They does not actually have an electromagnetic coil. •Determine the characteristics, ratings, and settings of overcurrent protective devices •Ensure that the minimium, un-faulted load is ... Time-Current Curves Protective Relays 50 – Instantaneous Overcurrent Relay 51 – AC Time Overcurrent Relay 67 – AC Directional Overcurrent Relay . Save my name, email, and website in this browser for the next time I comment. NO stands for Normal Open contact, while NC stands for Normal Closed contact. Keep it up. A load-Relay should be used for this application. Coordination of protective relays in mv transformer stations using easypower protector software, Electrical Fundamentals 15 th December 2014, Protection against earth faults with Residual Current Devices. This can be represented graphically by the relays TCC curve (Time Current Characteristic). If the current that flows through both electromagnets is equal, then the armature is kept in balance. In early electromechanical relays the curve is set by means of a dial. This type of relay operates just like a toggle flip flop. Because the highest FR values (ie, prices) ... delivery de vice and an electrom echanical relay th at provided. I used an octal-type relay. The higher the gap the higher the voltage that a relay can cut-off. The operating temperature: The temperature that the relay can operate without problems, Switching frequency: The maximum make-break frequency. curves for food determined under open and closed economic. The VI type IDMT relay curve has faster operating times for higher currents and slower operating time for lower currents. Bellow i illustrate both of these contacts: You may notice that the NC contact is turned upside-down compared to the NO contact. An DPST? For two contact pairs, it would be DP as for Double Pole. Thus, if a relay has 1 contact pair (POLE), the code would be SP as for Single Pole. 14 FUNDAMENTAL RELAY-OPERATING PRINCIPLES AND CHARACTERISTICS 2 FUNDAMENTAL RELAY-OPERATING PRINCIPLES AND CHARACTERISTICS Protective relays are the "tools" of the protection engineer. Tripping Curves IEC 60255 Characteristics. This is done in purpose. The IEC 60255 standard defines four standard current time characteristics – standard inverse (SI), very inverse (VI), extremely inverse (EI) and long-time inverse. The material and the thickness of this strip is carefully selected, so that it will be heated (and thus bended) above a specified current value. This is the last part of the relay operation. You can fit the IAC curves to an equation that has the same general form as the ANSI and IEC curves; this is how computer aided coordination programs work. The magnetic power of the electromagnets is not equal, thus the relay will cut the power supply and our friend will be saved. I will distinguish this type of relays in two sub-types. The ‘EI’ type IDMT relay curve operates at very fast at high short-circuit currents and very slow at low short-circuit currents. 3. This is the modern type of relays. The third and last category is the contacts of the relays. 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