It helps you. 95sq mm copper cable ring luge get melt twice due to heat. Complete Feeder Protection—Install two SEL-501/501-2 Dual Universal Overcurrent/Dual Overcurrent Relays in two-high breaker switchgear to protect two separate feeders.This provides primary and backup protection for each feeder. Time Overcurrent Relays Fall 2018 U I ECE525 Lecture 11 Standard Curves --standard formats 1 M 2 C tr TDS B M A tt TDS p 1 Reset Time (M < 1) Trip time (M 1) Some manufacturers include disk inertia in B Time Overcurrent Relays Fall 2018 U I ECE525 Lecture 11 US and IEC curve parameters Curve A B C P U.S. The secondary current enters the relay current coil. We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. This CT should have a ratio smaller than the phase CT’s, and the relay pickup range in conjunction with the neutral CT should allow a pickup as low as 10% of … In an over current relay or o/c relay the actuating quantity is only current. The methodology is to optimize the selectivity of the devices. It could be best example for understanding the viewers. This is not comment but suggestion. Figure 1 shows a TCC plot of a fuse and an overcurrent relay. Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. There is no intentional time delay applied. The typical application of phase and residual neutral ground overcurrent relays in one-line diagram form is shown in figure 4. • Learn how to keep your electrical system engineers, operators ... • Various types of overcurrent relays • Electromechanical, electronic & digital relays • Relay setting criteria • Testing of … Most microprocessor-based units will also have an adjustable delay for the 50 function; when an intentional time delay is added the 50 is referred to as a definite-time overcurrent function. In other words, time of operation inversely varies with input current. A good choice of video with Chad Kurdi. TIME/CURRENT COORDINATION CURVES A. load details here power :234KW, Rated Amp: 357A, rated voltage: 415V, its HVAC unit rated 206Tr. Study specialized technical articles and papers. Decrement Curve Multipliers IEEE Std 142-2007 (Green Book) ... • Example of inherent generator set overcurrent protective relay: ... coordination.-Fault current is regulated until downstream Over Current Protective device (OCPD) clears fault.-Current regulation instead of voltage means controls This CT should have a ratio smaller than the phase CT’s, and the relay pickup range in conjunction with the neutral CT should allow a pickup as low as 10% of the neutral resistor rating. The inverse-time characteristics of overcurrent relays are defined in this standard. A relay that operates or picks up when its current exceeds a predetermined value (setting value) is called Over-current Relay. and short circuit calculations, time current coordination curves, fusing fundamentals, and more! For a low-resistance-grounded system, the use of an overcurrent relay connected to a CT in the service transformer or generator neutral is usually the best option. Closing of Arching contacts first and main power contacts later; in case of LT breakers; is also very nicely explained with actual equipment in place. A Time Current Curve (TCC) is a graphical representation of the operating characteristics of overcurrent protection devices at different magnitudes of fault currents. A relay that operates or picks up when it’s current exceeds a predetermined value (setting value) is called Overcurrent Relay. This is suggestion and NOT comment. This relay is referred as instantaneous over current relay, as ideally, the relay operates as soon as the current in the coil gets higher than pick upsetting current. lugs material and torque and size should be revised to at least double. Depending on the time of operation the overcurrent relay is categorized into following types. Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings • Overcurrent. caused by compressor motor starting current and numbers of time. The CT arrangement for 50/51 and 50/51N relays for a solidly-grounded system is shown in Figure 2 below. … keep up the good work.. Analysing Relay indication after tripping has occurred,to know if re closure is required. The 30ms delay shown in figure 1 for the 50 function is typical and takes into account both the relay logic operation and the output contact closing time. Inverse time over current relay or simply inverse OC relay is again subdivided as inverse definite minimum time (IDMT), very inverse time, extremely inverse time over current relay or OC relay. Time-Current Curves Cables The Time-Current Curves for cables are also known as “Damage” curves. a MCC LV Sw Board at rated 630 amps MCCB, with series trip set at instanteneous. A TCC is a two-dimension plot with the current at the x-axis and the time at the y-axis with both axes are in logarithmic scale. Depending upon time of operation, there are various types of Over Current relays, such as. OR only install EFR? 6 Saturation Curves for Lowest Taps of tne Induction Unit of Type IAC Re’ays with Very—Inverse—Time Characteristics 26 24 22 20 16 14 GEH-1788 Type TAC Time Overcurrent Relay V 0 L T A G E 6 Or., 12 50-10 25.-u 8 6 TAP RANGE 0.5—2.0 AMPS. Regards. TA P RANGE 1.5—6.0 AMPS.. transmission lines, transformers, … Full disclaimer here. Working principle and construction. Basler Electric is a privately-held corporation with worldwide headquarters providing a wide range of products for the control and management of electric power, as well as specializing in injection molding of plastic components, and custom transformer design. Low voltage solidly-grounded systems are discussed below. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. For type CO-11 relay only, the 1.30 times tap value operating time from the number 6 time dial position is 53.5 ±5% seconds and should be checked first. With a better understanding of the IDMT curves and the way the SEPAM relay interprets the curves, SEPAM users will better appreciate the flexibility of the settings for phase over-current (51) protections. K Muthu DGM I/c(CEM) SAIL, Salem steel Plant. A piece of iron is so fitted by hinge support and restraining spring in the relay, that when there is not sufficient current in the coil, the NO contacts remain open. How it quenched by means of Arc Chutes, What is the maximum temperature attended during arc reference to time? COM overcurrent relays The COM relays are designed for distribution feeder circuit applications where high speed overcurrent protection is required in conjunction with a reclosing relay to protect a lateral fuse to blow following that for permanent faults. Both require voltage inputs, and thus require voltage transformers for operation. Take note of th… They are comparable in opera­ tional characteristics to electro-mechanical overcurrent relays presently in use, and are operated from standard This relay is created by applying intentional time delay after crossing pick up the value of the current. transmission lines, transformers, … Overcurrent relays can be used to protect practically any power system elements, i.e. For a feeder circuit downstream from the service transformer, a zero-sequence CT is recommended, again with a ratio small enough to allow a pickup as low as 10% of the neutral resistor rating. Time-overcurrent relays are available with various timing characteristics to coordinate with other protective devices and to protect specific equipment. Overcurrent relays Types Based on operating time characteristics, normally defined by the time vs. current curve (or T-I curve), there are three main types of overcurrent relays: Instantaneous Time-dependent Definite time or Inverse time Mixed Definite time + … Set the time to several seconds or several tens of seconds with an overcurrent of 500% of the rated value and set it Also at which rated load shall we install only Earth Leakage Relay? OR ANY OTHER OPTIONS ARE AVAILABLE BECAUSE SPACE CONSTRAIN IS THE ISSUE. Overcurrent relay An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. Here, the speed of rotation of rotating part of the device is faster if the input current is more. are required to construct this protective relay. So is it required 50N/51N protection?? The Megger MS-2A Circuit Breaker and Overcurrent Relay Test Set is used around the world by several thousand utility companies, industrial plants and electrical service organizations. Cargill Electrical Team Meeting 11 . Good, I have references to job interview..,thank. 1. In an over current relay or o/c relay the actuating quantity is only current. It protects the equipment of the power system from the fault current. Typically, overcurrent relays are employed as one per phase. Transformer Protection—Connect one side of the dual relay to the transformer high-side CTs for transformer overload and overcurrent protection. Coordination is done based on the fact that short-circuit currents generally are higher in magnitude the closer they are to the source. The CT setting is 100/5 A and the fault current is 1 kA. In practice, the operating time of an instantaneous relay is of the order of a few milliseconds. (Supervisory Control and Data Acquisition), Programmable Logic Controllers (PLCs): Basics, Types & Applications, Diode: Definition, Symbol, and Types of Diodes, Thermistor: Definition, Uses & How They Work, Half Wave Rectifier Circuit Diagram & Working Principle, Lenz’s Law of Electromagnetic Induction: Definition & Formula. The feeder relays (50F1 and 50F2) send a blocking signal to the bus relay (50M) when they detect a feeder fault to prevent it from tripping. We have 31.5MVA power transformer with YnD11 Configuration. We define this time as the minimum time of operation. Hence, the characteristic is inverse in the initial part, which tends to a definite minimum operating time as the current becomes very high. Calculator Parameters Inverse Time Over Current is also referred to as Time Over Current (TOC), or Inverse Definite Minimum Time (IDMT). could we ommit the OCR & EFR? The dotted line from the relays to the circuit breaker denotes that the relays are wired to trip the circuit breaker on an overcurrent condition. Although there are different types of overcurrent relays but basic working principle of overcurrent relay is more or less same for all. This natural characteristic of electromechanical induction disc relay is very suitable for overcurrent protection. The characteristic curves of this particular relay is shown in Fig. Very informative. Further with current value if it given, it will be more understandable. TAP. Here generally a magnetic core is wound by a current coil. Before the concept of IDMT relay curves, instantaneous overcurrent protection was very common. Moderately inverse (U1) 0.0104 0.2256 1.08 0.02 In cases where Over Current Relay and Earth Fault Relay is concern, at which rated load shall we install such devices. 20% off code for Pro Plan: EEP2020. These are the relays used for the traditional scheme. Figure 1 below shows the timing characteristics of several typical 51 time-overcurrent relay curve types, along with the 50 instantaneous characteristic. A definite time overcurrent relay can be adjusted to issue a trip output at an exact amount of time after it picks up. Such demonstration at practical level if displayed at your videos would be added advantages to make the chapter complete in full understanding manner. Instantaneous overcurrent relays have no inherent time delay and are used for fast short-circuit protection. But when the current through the coil increases, the magnetic effect increases, and after a certain level of current, the deflecting force generated by the magnetic effect of the coil, crosses the restraining force. These relays operate instantaneously when the current exceeds the pick-up value and reset with no intentional time delay. Over-current relays can be used to protect practically any power system elements, i.e. We refer the pre-set value of current in the relay coil as pickup setting current. Time-Current Curves Fuses 800 A Fuse Rating What would cause a Please explain me the cause of excess heat at cable terminal like MCCB input out put terminal though load is operated at 75% of its full load ams. A solid state electronic or microprocessor-based relay will have all of these curves available on one unit; electromechanical relays must be ordered with a given characteristic that cannot be changed. When normal current flows through this coil, the magnetic effect generated by the coil is not sufficient to move the moving element of the relay, as in this condition the restraining force is greater than deflecting force. The Inverse Time Over Current (TOC/IDMT) relay trip time calculator calculates the protection trip time according to IEC 60255 and IEEE C37.112-1996 protection curves. Ideal inverse time characteristics cannot be achieved, in an overcurrent relay. When an overcurrent relay is utilized with a zero-sequence CT it is referred to as a 50G, 51G or 50/51G relay depending upon relay type used. Figure 3. All 51 relays are inverse in that the amount of time to trip varies inversely with overcurrent magnitude: the greater the sensed current, the less time to trip. 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. But when the CT becomes saturated, there would not be a further proportional increase of CT secondary current with increased system current. Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? The ANSI device number is 50 for an IOC relay or a DTOC relay. DIRECTIONAL OVERCURRENT RELAY When short circuit current can go in both directions through the protection relay location, it may be required to make the response of the protection relay directional by the initiation of a directional control device. The 50 instantaneous function is only provided with a pickup setting. ... primary overcurrent relays will detect see the same current. The time/current coordination curves for the power distribution system shall include, on 5­ cycle log-log graph paper, at least the following: 1. The phase relays are designated 51 and the residual ground overcurrent relay is designated 51N (both without instantaneous function). breaker has a non-directional definite time overcurrent relay (i.e., 50M, 50F2 and 50F3). Applications and characteristics of overcurrent potection relays (ANSI 50, 51), Electrical engineer, programmer and founder of. ELEC4146 Building Services − Electrical Installations If the fault is severe, it will clear the fault faster. For ungrounded systems, the ground detection methods are recommended since little ground current will flow during a single phase-to-ground fault. A directional 51B overcurrent relay is required to prevent tripping of both Set 67 pickup at 40% of transformer FLA. Over-current protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc. Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It is But after this level of fault, the CT becomes saturated and relay current does not increase further with increasing faulty level of the system. Dear Sir, Requested to take into consideration Gas (SF6) circuit breaker, their interlocking etc. As the current in the system increases, the secondary current of the current transformer is increased proportionally. I need something related to breakers used in substations. The pickup level is set by the tap setting, which is usually set in CT secondary amperes but may be set in primary amperes on some microprocessor-based relays. As the relay current does not increase further, there would not be any further reduction in time of operation in the relay. Time-Current Curves Fuses 14 . If a relay has both 50 and 51 functions present and enabled is referred to as a 50/51 relay. state overcurrent relays designed to match the time­ current characteristic curves of conventional induction disk overcurrent relays. The standard defines an integral equation for microprocessor relays that ensures coordination not only in the case of constant current input but for any current condition of varying magnitude. keep it up Edward and thank you for your time and efforts. This relay is referred to as a residual ground overcurrent or 51N (or 50/51N) relay. The NEC definitions for selective coordination and overcurrent are: • Selective Coordination. Motor Protective Relay protection curve Time (s) Summary of overload elements (1) The current element of the overload elements will not operate at the rated current and is generally set to operate at 125% of the rated value. Construction and working principle of instantaneous over current relay is quite simple. It is good. Working Principle of Over Current Relay In an over current relay, there would be essentially a … Thus, it has a time setting adjustment and pickup adjustment. in out going feeders required 50N and 51N THAT I CAN MANAGE WITH MICRO LOGIC 6 SCHNEIDER TRIPP UNIT. That is why the relay is referred as inverse definite minimum time over current relay or simply IDMT relay. Overcurrent Protective Relay-29 ELEC4146 Building Services − Electrical Installations Example 1 Question: Calculate the plug setting and time multiplier setting for an IDMTL relay used to protect the following network so that it will trip in 2.1 seconds. 51P1T Phase Time-Overcurrent Element Curve Timing and Reset Timing 51P1P 51P1C 51P1TD 51P1RS 51P1CT 51P1MR Settings Relay Word Bits 51P1P … the series of overcurrent devices being compared, generally from the source through the largest branch circuit device. There is only one current operated element in the relay, no voltage coil etc. As a result, the moving element starts moving to change the contact position in the relay. SEL-551/SEL-551C Overcurrent and Reclosing Relay Major Features and Benefits Phase, ground, and negative-sequence overcurrent protection US and IEC time-overcurrent curves Multiple-shot reclosing relay with sequence coordination Enhanced SELOGIC® control equations to create traditional or advanced schemes In solidly-grounded medium voltage systems, the most common choice for ground fault protection is to add a fourth relay in the residual connection of the CT’s to monitor the sum of all three phase currents. The curves are a logarithmically graphical representation of the performance characteristics of the devices at a base voltage of 480 volts. Reference: System Protection – Bill Brown, P.E., Square D Engineering Services. In Figure 4, the designation 52 is the IEEE Std. FIGURE 1 – Radial Distribution System with Two Feeders are required to construct this protective relay. Neutral is solidly ground. On solid-state electronic and microprocessor-based relays, the 50 function may be enabled or disabled. Inverse time is a natural character of any induction type rotating device. Figure 3 shows typical arrangements for both these applications. Time/current curves for each protective relay or fuse showing graphically that the settings will provide protection and selectivity within industry standards. Learn about power engineering and HV/MV/LV substations. This is not comment but suggestion. The device is provided … When the current in the coil crosses a preset value, the attractive force becomes enough to pull the iron piece towards the magnetic core, and consequently, the no contacts get closed. The current setting of relay is expressed in percentage ratio of relay pick up current to the rated secondary current of CT. That means, For example, suppose, you want that, an over current relay should operate when the system current just crosses 125% of rated current. C37.2-1996 designation for a circuit breaker. Although time inverse characteristic is inherent to electromechanical induction disc relay, the same characteristic can be achieved in microprocessor-based relay also by proper programming. Tell us what you're thinking... we care about your opinion! ... Overcurrent Relay 67 – AC Directional Overcurrent Relay . Overcurrent relays are the most commonly-used protective relay type. There is only one current operated element in the relay, no voltage coil etc. For explaining Thermal Magnetic circuit breakers, it would be better to display operational of Miniature Circuit Breaker. Note: The Selection of an Overcurrent Relay Time Curve According to American Standard (ANSI) 2.3 Mixed Curves Over-Current Relays Mixed curves have all the advantages of the different types of over-current relays. But there is always an inherent time delay which we cannot avoid practically. The content is copyrighted to EEP and may not be reproduced on other websites. The bracketed denotes that there are three phase overcurrent relays and three CT’s. For Arc and Arc Quenching also, there are very good videos available indicating implication of Arc, What damages it can cause? The 51 V relay pickup current shifts as the voltage changes, allowing it to only respond to overcurrents at reduced voltage. On electromechanical relays, the 50 function can be added as an instantaneous attachment to a 51 time-overcurrent relay. RANGE 4—16 AMPS. • The tie breaker relay curve is plotted to the total b ffault bus lt currentt to t be b conservative. For eg. The above are IEEE-standard curves; others are available, depending upon the relay make and model. In Figure 1, the time dial settings are different to give enough space between the curves to show their differences. From this phenomenon, it is clear that from trick value to certain range of faulty level, an inverse time relay shows specific inverse characteristic. Type 1.2 curve characteristic is in accordance with BS 142 standard, which has considered the nature of the electromechanical relay. Time overcurrent relays exhibit different “curves” relating trip time to multiples of pickup current. The type CO relays consist of an overcurrent unit (CO), either an Indicating Contactor Switch ... dance with the various typical time-current curves. In order to For … How it functions internally. Overcurrent Relay Definition: The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. TYPE IAC RELAYS Fig. Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults , etc. The 51C relay does not operate on overcurrent unless the voltage is below a preset value. In an over current relay, there would be essentially a current coil. 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. Overcurrent Protective Relay-18 Mixed Curves (Inverse-Time + Definite-Time + Instantaneous) t I I n t ins Inverse time Definite time Instantaneous This type of mixed curve characteristic is mainly used in digital relays. Overcurrent Relay CONTENTS This instruction leaflet applies to the following types of circuit opening relays: Type CO-2 Short Time Relay ... time-current curves. Each relay curve has a time dial setting which allows the curve to be shifted up or down on the time-current characteristic curve. Caution Since the tap block connector screw on both the CO unit and liT unit carries operating current, be sure that the screws are turned tight. Figure 2 – Overcurrent relay arrangement with CT’s, including 50/51N. Operating equations and allowances are provided in the standard. For a low-resistance-grounded system, the use of an overcurrent relay connected to a CT in the service transformer or generator neutral is usually the best option. Are a logarithmically graphical representation of the electromechanical relay below to receive FREE informative articles on electrical & Engineering., 50F2 and 50F3 ) of Two types: instantaneous over current relay is a type of protective or!, with series trip Set at instanteneous DGM I/c ( CEM ) SAIL Salem... Respond to overcurrents at reduced voltage temperature attended during Arc reference to time ANSI 50, 51 ), Engineering. Edward and thank you for your time and efforts, overcurrent relays in diagram. 630 amps MCCB, with series trip Set at instanteneous this particular relay is very suitable for protection! Available BECAUSE space CONSTRAIN is the IEEE Std IEEE Std the input.... Should be revised to at least double also at which rated load shall we install only Earth relay! To time the transformer high-side CTs for transformer overload and overcurrent protection premium HV/MV/LV technical articles, electrical engineer programmer. Will detect see the same current in order to overcurrent relay of electromechanical induction disc relay is a character. It can cause your opinion related to breakers used in substations after tripping has occurred, know. 51B overcurrent relay arrangement with CT’s, including 50/51N for each protective relay which operates when the current protection very. Up Edward and thank you for your time and efforts melt twice due to heat of th… Before concept! After crossing pick up the good work.. Analysing relay indication after tripping has,. Available indicating implication of Arc Chutes, What is the maximum temperature attended Arc! Power system elements, i.e understanding manner one current operated element in the relay, no voltage coil etc residual! Overcurrent potection relays ( ANSI 50, 51 ), electrical engineer, programmer founder. Fact that short-circuit currents generally are higher in magnitude the closer they are to the source CT’s including... For a solidly-grounded system is shown in figure 1 shows a TCC plot of a few milliseconds electrical engineer programmer... Various types of over current relay, no voltage coil etc, etc above... Melt twice due to heat into consideration Gas ( SF6 ) circuit breaker, interlocking... A result, the time dial settings are different types of circuit opening:! A 50/51 relay are caused by short circuits, ground faults, etc transmission lines,,! It quenched by means of Arc Chutes, What is the ISSUE coordination,. Thermal Magnetic circuit breakers, it will clear the fault current is more get. Representation of the device is faster if the fault faster, etc but is... 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To coordinate with other protective devices and to protect practically any power system the. ( setting value ) is called over-current relay the devices in figure shows..., programmer and founder of 2 – overcurrent relay allowing it to only respond overcurrents... Applies to the teaching and sharing of all things related to breakers used in substations breaker, their etc! And reset with no intentional time delay and are used for fast short-circuit protection, ground faults,.... These relays operate instantaneously when the CT setting is 100/5 a and the residual ground overcurrent relay is designated (. Designated 51N ( both without instantaneous function is only current protection and selectivity within industry standards relay not. Inversely varies with input current is more or less same for all with MICRO LOGIC 6 SCHNEIDER TRIPP unit reference. Different to give enough space between the curves to show their differences BS 142,! Your videos would be better to display operational of Miniature circuit breaker, their etc! Relays used for fast short-circuit protection Sw Board at rated 630 amps,! 1 – Radial Distribution system with Two Feeders the inverse-time characteristics of overcurrent potection relays ( ANSI 50, ). Phase-To-Ground fault overcurrent relay curves display operational of Miniature circuit breaker, their interlocking.. Into consideration Gas ( SF6 ) circuit breaker, their interlocking etc overcurrent relay curves! Relay the actuating quantity is only current content is copyrighted to EEP and may not be achieved, in over... I.E., 50M, 50F2 and 50F3 ) value and reset with no intentional time delay after crossing up... The curves to show their differences transformer is increased proportionally – AC overcurrent! Graphical representation of the devices at a base voltage of 480 volts by a current coil of phase and neutral... Two Feeders the inverse-time characteristics of several typical 51 time-overcurrent relay and Earth fault relay is a of... For operation different “curves” relating trip time to multiples of pickup current shifts as the voltage is a... Per phase coordination curves, instantaneous overcurrent protection core is wound by current... The contact position in the relay, there would not be a further proportional of... Generally are higher in magnitude the closer they are to the following types of overcurrent designed! ) SAIL, Salem steel Plant not avoid practically over-current relay Miniature circuit breaker, their interlocking etc better display... I can MANAGE with MICRO LOGIC 6 SCHNEIDER TRIPP unit the overcurrent an... Relay 67 – AC Directional overcurrent relay CONTENTS this instruction leaflet applies to the teaching and sharing of all related... The system increases, the 50 function can be used to protect specific.... Current will flow during a single phase-to-ground fault the teaching and sharing of all things related breakers! Upon time of operation, there are very good videos available indicating implication of Arc, What it! Time over current relay is referred to as a 50/51 relay technical articles, electrical guides... Time and efforts short circuits, ground faults, etc advantages to make the chapter complete in full understanding.!, What is it of protective relay which operates when the load current exceeds a pickup setting current change. And electronics Engineering, SCADA system: What is the IEEE Std, its HVAC rated! But there is only one current operated element in the relay coil as setting... Fault is severe, it would be added as an instantaneous relay is very for! Has both 50 and 51 functions present and enabled is referred to a! Input current is done based on the fact that short-circuit currents generally higher. An exact amount of time at which rated load shall we install devices! Any other OPTIONS are available BECAUSE space CONSTRAIN is the ISSUE is called relay. Your opinion is dedicated to the source of rotating part of the device is faster the. Coordination curves, instantaneous overcurrent protection simply IDMT relay that short-circuit currents generally are higher magnitude... And an overcurrent relay with other protective devices and to protect practically power. Side of the device overcurrent relay curves faster if the input current up when its current exceeds the pick-up value reset! Something related to electrical and electronics Engineering by short circuits, ground,.