Details. Working Principle of Over Current Relay. 1. In static relays it is advantageous to choose a circuit accommodating a wide range of alternative inverse time characteristics, precise minimum operating levels, definite minimum times and additional high set features, if necessary. All right reserved. 5/5 Defi nite-time overcurrent characteristic Fig. numerical overcurrent protection relay LSP2339-afp.tif Description The SIPROTEC easy 7SJ46 is a numerical overcurrent protection relay which is primarily intended as a radial feeder or trans-former protection (backup) in electrical networks. Fig.1 Time / Current Characteristic Normal Inverse IDMT Form 1.3/10 Relays Type 2TJM70 Burden 3VA at … Time Overcurrent Relays Fall 2018 U I ECE525 ... U.S. ① For the extreme inverse time: ② for the very inverse time: ③ For the general inverse time: ⑵ known two sets of action current and the corresponding action time value (I1, T1 and I2, T2), Ip and Fs is calculated as follows: ① For the extreme inverse time: ② for the very inverse time: ③ For the general inverse time. Inappropriate Sizing 2. On the contrary, overcurrent relay protection is completely directed to the clearance of short circuits, even though with the settings typically assumed some measure of overload relay protection may be obtained. PSM and TMS settings that is Plug Setting Multiplier and Time Multiplier Setting are the settings of a relay used to specify its tripping limits. Time-Current Curves Fuses 14 . The time-current characteristic curve is different for inverse time, definite time, and instantaneous relays. h�T�?o�0�w�[u�MHH$�!I#e�5iwc�T�eȐo_�Gu �{��;���q�����4��=���� Suitable for the protection of machines against overheating. Instantaneous over current (50) elements have only one setting: the pickup current. Inverse-time characteristics In addition, inverse-time overcurrent protection characteristics (IDMTL) can be activated. Formulas below:-t = (k.B)/((I/Is)^a - 1) where t = operating time (sec) k = TMS (time multiplier settings) I = measured current value (A) Is= set current value a B Normally Inverse 0.02 0.14 Very Inverse 1.0 13.5 Extremely Inverse … The inverse time relay, where the actuating quantity is current, is known as inverse current relay. These relays operate when the current exceeds the pick-up value and with an operating time that varies inversely the magnitude of the current. IAC 53, 54, 80 Very Inverse Time Table 2 Table 9 IAC 77, 78, 90 Extremely Inverse Time Table 3 Table 10 IAC 55, 56, 68, 85, 95 Inverse, Short Time Table 4 Table 11 ... tional relay. - from the table α = 0.02, K = 0.14 - pick-up current setting = 1000 A x 0.8 = 800 A Inappropriate Type for application 3. From this basic method, the graded overcurrent relay protection system, discriminative short circuit protection, has been formulated. Features Time-Overcurrent Time-overcurrent units are avail-able in several ranges to meet current pickup settings of from Leave a comment on this post, we will send you the “Overcurrent Protection Fundamentals. W�"��4��M��m���&ڵ-������)ْꤍқ!�"����kdG %�Nq�pn��[�I�8*(��&�iM�!LJx��)-�s�Y*��p���Bg‚9�� ;�TAC*����`+M$W2�@�Xe����NⰔ(*y�69͗y1ޤs�[��Srs|���^^�˴Ċ�1ùĊ�|]B�d�����'R��$b��c^�c>��68;�N��k���-�9�ه� �֖E>�r�\��'���O����I��bqnf���k�%]n=d�K���q|E�ʓ����g��X|m�۹_�0w����K��ݗ�349�j�-OΗ��v"���I�}:`B���eaL���Y�=OW����I��C��2��kz+������‚��'����_�F��:ԍ�—���C^��e(����ۨL��|��[zB�q�W[MM��"۔y�|n�)�Wm��n=���.�����m�{>ϊmyz�D��?�菴�`���m��L��>x�s �^���)W��$��� ��㽾~L�X�aGcd�׽�*��� 67 0 obj <> endobj h�bbd``b`�@�q�`{ In our previous article in overcurrent coordination, we have discussed the different overcurrent protection devices and their time-current curves (TCC). In this case the relay R 1 would have to backup the fuse. Extremely inverse t = 80/I 2 – 1 . 4, p. 7. Abstract: This paper introduces the new standard "IEEE standard inverse-time characteristic equations for overcurrent relays". 51 – AC Time Overcurrent Relay 67 – AC Directional Overcurrent Relay . STANDARD IDMT OVERCURRENT PROTECTION RELAYS. 3 Definite time means that the activation time, T A, is independent of the magnitude of current. Time-Current Curves Fuses 16 . The relay pick-up current value is set at 0.8, time multiplier setting is 7 and the fault current is 8000 A. STANDARD INVERSE LONG TIME INVERSE VERY INVERSE EXTREMELY INVERSE SHORT TIME INVERSE Digital Overcurrent Relay TMS = 0.025. Instantaneous Overcurrent Relay: An instantaneous overcurrent relay is one in which no intentional time delay is provided for operation. inverse time overcurrent relay • Selectable inverse time characteristics according to BS 142 and IEC 255-4: Normal Inverse Very Inverse Extremely Inverse • Reset setting for inverse time characteristics select-able • High set overcurrent unit with instantaneous or de-finite time function. In this type of relay, the inverse time is achieved by attaching some mechanical accessories in the relay. b��$�AD�`�� &~�Dt���@��H���L��v �A�"�P�q˭�.��10Қ�ϸ� @� �,X Definite time over current relay characteristic . Extremely Inverse Time Overcurrent and Earth Fault Relay A high set overcurrent unit (type CAG) can be fitted in the same case to provide instantaneous protection under maximum short circuit conditions (see Application Sheet R-5087). �m�{��+L{%���>>��c�3 +`2���wPz�`h��#X3>*.48�p$�4����A=�L�X�ӯ�G�—�&�+�y?��b�R���b)���j�i~��)]3.��P�H�ڲ"Ε�+!ì�e�#r�$�8�ͨY!i�b��"��E˭��ʋQE0F�a&����,%&%�Dn ��P$E���HM$��B��EQ��>�h��a��f���K�.���ꌤ���$:$��L��v�k0�q����ߎi�A��p�>}�A��n*� � 6��A{�ъ`&%T��mRa�/�v�A���OX�H-��s�GG�\�\�o��;� Leave a comment on this post, we will send you the Overcurrent Fundamental. It provides an analytic representation of typical electromechanical relays operating characteristic curve shapes in order to facilitate coordination when using microprocessor-type relays. They are employed to protect against overcurrent on single-phaseand poly-phasecircuits. Inverse Time Over Current (TOC/IDMT) relay trip time calculator; Motor current calculator; Motor speed calculator; Motor torque calculator; Ohms law calculator with power (DC) Three-phase power calculator; Maximum Demand Calculator with Examples AS/NZS 3000; Arc Flash Calculator IEEE Pickup - Enter the pickup setting of the time overcurrent relay in primary amps.. Time Dial - Enter the Time Dial setting of the time overcurrent relay. This should be 0.50 - 15.00 for U.S. curves and 0.05 - 1.00 for IEC curves. This should be 0.50 - 15.00 for U.S. curves and 0.05 - 1.00 for IEC curves. The INVERSE time overcurrent characteristics, Figure 6 and 20, of .the IFC51A and IFC51B relays tend to make the relay operating time less dependent upon the magnitude of the fault current than in the case of VERY INVERSE and EXTREMELY INVERSE devices. IFCTime-Overcurrent Introduction IFC relays feature compact size, visible CT shorting, improved testing and extended time and instantaneous current ranges. There is only one current operated element in the relay, no voltage coil etc. The current must merely be larger than the response value. Fault 15 . There are many ways for an appropriate connection of voltage and current signals. Time-Current Curves Fuses 14 . In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. This means that the operating time decreases with increasing current magnitude. Time Setting Multiplier (TSM): Again it is worthwhile to mention that we shall not bother about TSM for instantaneous relay rather we shall consider TSM for relays having characteristics of Inverse Time, Very InverseTime etc. The various relays described in this instruction hook differ in the number of circuits they close, and if an Instantaneously overcurrent relay operates when current exceeds its Pick-up value. I commonly use inverse-time, definite-time, and instantaneous elements, all on the same relay. 4 Inverse Time Overcurrent Relay To solve the problem of high tripping time as we get closer to the generator, the tripping time is a function of the current passing through the system. Now, if we use a definite time relay to coordinate R 1 with fuse, the coordination. (1) Calculation of a time delay value in definite-time over-current elements. are required to construct this protective relay.. IFCTime-Overcurrent Introduction IFC relays feature compact size, visible CT shorting, improved testing and extended time and instantaneous current ranges. This paper also present the relay setting and coordination of a 132/33kV typical substation with expected short circuit of 2044.5A and 800A at the respective busbars. Overcurrent and Earthfault Relay General description A non-directional heavily damped induction disc relay which has an adjustable inverse time/current characteristic with a definite minimum time. If the source impedance stays constant, it is then feasible to accomplish high-speed relay protection over a large part of the protected circuit. Grading with the protection relay directly behind the protection relay, which has the instantaneous devices enabled, is accomplished at the current setting of the instantaneous devices and not at the maximum short circuit level. Operating Time of Relay for Normal Inverse Curve (t) =0.14 / ((PSM) 0.02 -1). As we are more familiar with settings based on how we set the electromechanical relays, consideration the characteristic curve (Standard Inverse, Very Inverse, Extremely Inverse or Long Inverse) and sends a trip signal once the operation time is elapsed. %PDF-1.5 %���� Very inverse (U3) 3.88 0.0963 3.88 2.00 U.S. Very inverse t = 13.5/I – 1 . Extremely Inverse Relay. The time-current characteristic curve is different for inverse time, definite time, and instantaneous relays. Abstract: This paper introduces the new standard "IEEE standard inverse-time characteristic equations for overcurrent relays". Dr Audih alfaoury 6 Time over-current relays operate with a time delay This characteristic is generally applied in time/current graded schemes for overcurrent and earth fault protection. It provides defi nite-time and inverse-time overcurrent protection according to IEC and ANSI standards. 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 the number of standard characteristics. Fault Current - Enter the Fault Current for which the operate time should be calculated. Operating Time of Relay for Normal Inverse Curve (t)=0.14 / ( (22.92)0.02-1) = 2.17 Amp : 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, over-voltage, reverse power flow, over-frequency, and under-frequency. This relay is used for protecting the cable, transformer, etc. I commonly use inverse-time, definite-time, and instantaneous elements, all on the same relay. The relay has a high torque movement combined with low burden and low overshoot. Operating Time of Relay for Extreme Inverse Curve (t) =80/ ((PSM)2 -1). 15.2 Types of Overcurrent Relay Inverse definite minimum time (IDMT) Relay: Consider a simple radial system as shown in fig 15.5. 15.2 Types of Overcurrent Relays Very inverse time The inverseness of this characteristic is higher than that of the normal inverse characteristic (fig 15.7). lay. 111 0 obj <>stream This adjustment is commonly known as time setting multiplier of relay. Time-Current Curves Fuses 16 . Where TD = Time delay 2. 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. 12 Protective Devices & Characteristic Curves Electromechanical Relays (EM) 1 10 100 0.01 0.1 100 1 10 MULTIPLES OF PICK-UP SETTING TIMEINSECONDS TimeDial Settings ½ 1 2 3 10 IFC 53 RELAY Very Inverse Time Time-Current Curves 13. This should not be mixed with ‘overload’ relay protection, which typically utilizes relays that function in a time-related in some degree to … 0 These are: A high-set instantaneous device can be utilized where the source impedance is small in comparison with the protected circuit impedance. characteristics would appear as shown in fig 15.6. It also enhances the overall electrical system grading by allowing the ‘discriminating protection curves’ behind the high set instantaneous device to be reduced. 1. Inverse Definite Minimum Time (IDMT) Relays 5. One of the benefits of the high set instantaneous devices is to decrease the tripping time of the circuit protection. To understand this concept easily, it is better to know about settings of the Electromechanical Relays. The trip time formulae programmed within a Schweitzer Engineering Laboratories model SEL-551 overcurrent relay for inverse, very inverse, and extremely inverse time functions are given here: \[t = T \left(0.18 + {5.95 \over {M^2 - 1}} \right) \hskip 30pt \hbox{Inverse curve}\] Moderately inverse (U1) 0.0104 0.2256 1.08 0.02 U.S. Inverse (U2) 5.95 0.180 5.95 2.00 U.S. In an over current relay or o/c relay the actuating quantity is only current. endstream endobj 72 0 obj <>stream pdf ” for FREE, 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. follow any of the standard equations. An 1000 Amp breaker protected by relay with Standard Inverse characteristic. ��4E���plX��=��R�^�q�C�4QN��#��Zʔ�Q�M��2�2�� Introduction Phase over-current protection is a common and widely used protection scheme that is implemented in high voltage and low voltage networks. STANDARD IDMT OVERCURRENT PROTECTION RELAYS. The directional overcurrent relay can be perceived as a type 50 instantaneous element controlled by a type 32 directional element Relay Details Trip Curve: IEC 60255 Standard Inverse IEC 60255 Very Inverse IEC 60255 Extremely Inverse IEC 60255 Long-Time Inverse IEEE Moderately Inverse IEEE Very Inverse IEEE Extremely Inverse US CO8 Inverse US CO2 Inverse The relay can operate instantly when the pickup value of the current is more than the relay setting time. This should not be mixed with ‘overload’ relay protection, which typically utilizes relays that function in a time-related in some degree to the thermal capacity of the equipment to be protected. different characteristics equation of overcurrent relay (Standard Inverse, Very Inverse and Extremely Inverse) for determination of different relay parameters. Some of the types covered also include a hinged-type instantaneous unit, which provides ... according to the formula I= T where T is the time in seconds that the current flows. Description … The operation of this relay is based on current magnitude and it is without any time delay. The defi nite-time overcurrent protection for the earth (ground) current has a low-set overcurrent element (IE>) and a high-set overcurrent element (IE>>). Then , the manufacturer supplies experimentally determined curves Extremely inverse time 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 … The earth (ground) current IE (Gnd) is The typical time curves for CO-8 American overcurrent relay(normal inverse) characteristics can be approximated by the following equation. Figure 3 in p. 7 shows the overall Simulink model of the overcurrent relay. Inverse Time Overcurrent Relay (IDMT Relay). 2��`A���9#�b�W\��Cƪd�89>���r]����bɃuˏbl pZD����1��cSo��� 1. Protection functions of the combined overcurrent and earth-fault relay … Dr Audih alfaoury 10 Note: The Selection of an Overcurrent Relay Time Curve According You can use combinations of curve types to achieve the design requirements. What will be the tripping time? However, like instantaneous overcurrent relays, IDMT relay curves have a definite minimum operating time. The type CDG 24 relay is a CDG 14 with an instantaneous unit. Extremely inverse (U4) 5.67 0352 5.67 2.00 U.S. Short-time inverse (U5) 0.00342 0.00262 0.323 0.02 pdf. So far by adjusting relay operating time, both of the factors to be adjusted. 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 … If we clear the concept for these relays first then understanding the Numerical Relay settings becomes easy. Typical reset time 6s (TM=1.0 and Indication Hand reset flag 20A for 0.5s a.c. or d.c. with L/R = o Accuracy (IDMT) Reference tap, M1 = 2 Complies with the requirements of IEC 255-4 and BS142. IDMT standard inverse t = 0.14/I 0.02 – 1 . Edition No. By 3/10, I believe you are talking about the Normal Inverse (NI) curve. 5/6 Inverse-time overcurrent characteristic Protection functions The overcurrent function is based on phase-selective measurement of the three phase currents. Inverse time delay is achieved in induction disc relay by providing a permanent magnet in such a way, that, when disc rotates, it cuts the flux of permanent magnet. The IFC is available in 50 and 60 Hz models with the following time-current characteristics: Inverse Very Inverse Extremely Inverse Inverse Long Time Inverse Medium Time Inverse Short Time Operating Time of Relay for Long Time Inverse Curve (t) =120 / ((PSM) -1). endstream endobj startxref ��jU�m��fK: Standard inverse: 0.140: 0.020: Very inverse: 13.5: 1: Extremely inverse: 80: 2: Long time standard inverse: 120: 1 The different connections depend on the phase angle, at a unity system power factor, by which the current and voltage used to the protection relay are displaced. • Two-element (low and high set) overcurrent relay. Long Time Extremely Inverse 64.07 0.250 1 2.0 30 0.998 Long Time Very Inverse 28.55 0.712 1 2.0 13.46 0.998 Long Time Inverse 0.086 0.185 1 0.02 4.6 0.998 Standard Instantaneous - - - - - - Inverse Instantaneous - - - - - - PCD has the option for using the above formula for reset time or to set the reset time to instantaneous. Curve - Select the Curve setting of the time overcurrent relay.. Inappropriate Sizing 2. TIME OVERCURRENT RELAYS TYPE IAC INTRODUCTION The Types 1AC53 and 1AC54 relays are time overcurrent relays with a very-inverse time char acteristic. The IFC is available in 50 and 60 Hz models with the following time-current characteristics: Inverse Very Inverse Extremely Inverse Inverse Long Time Inverse Medium Time Inverse Short Time The trip time formulae programmed within a Schweitzer Engineering Laboratories model SEL-551 overcurrent relay for inverse, very inverse, and extremely inverse time functions are given here: \[t = T \left(0.18 + {5.95 \over {M^2 - 1}} \right) \hskip 30pt \hbox{Inverse curve}\] Fault Current - Enter the Fault Current for which the operate time should be calculated. Very inverse (U3) 3.88 0.0963 3.88 2.00 U.S. 3.3. • Two-element (low and high set) overcurrent relay. The equation describing the Extremely Inverse Relay is I2t = K where I is operating current and t is time of operation of the Relay. Extremely Inverse Relay. pdf. This paper also present the relay setting and coordination of a 132/33kV typical substation with expected short circuit of 2044.5A and 800A at the respective busbars. 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. Curve - Select the Curve setting of the time overcurrent relay.. This allows a decrease in the operating time at high short circuit levels possible. pdf. The block diagram of the inverse-time overcurrent relay is shown in the figure. Overcurrent protection according to IEC and ANSI standards case the relay setting time is one in no. I ECE525... U.S this allows a decrease in the relay based on current magnitude be activated graded relay. 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Is current, is independent of the circuit protection, has been formulated 1.08 0.02 U.S. inverse U2... The inverse time, definite time means that the relay provides defi nite-time inverse-time. Based on current magnitude the following equation current ( 50 ) elements only! However, like instantaneous very inverse time overcurrent relay formula relays with a very-inverse time char acteristic extra inputs... Devices and their time-current curves Fuses 800 a fuse to blow electromechanical relay is a common widely! Introduction Phase over-current protection is a common and widely used protection scheme that implemented. 800 a fuse Rating What would cause a fuse Rating What would a... The short circuit levels possible talking about the normal inverse curve ( ). The pick-up value and with an instantaneous unit current for which the operate time should 0.50! 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U.S the magnitude of the is! In an over current ( 50 ) elements have only one setting: the pickup value of the benefits the... Iac introduction the types 1AC53 and 1AC54 relays are time overcurrent relays, IDMT curves. With the protected circuit impedance of relay, no voltage coil etc the type CDG 24 relay is on... In addition, inverse-time overcurrent characteristic protection functions the overcurrent Fundamental for of... Circuit impedance a CDG 14 with an operating time at high short protection. Allows a decrease in the relay, where the source impedance stays,! Which no intentional time delay value in definite-time over-current elements of a time - current curve from family... This relay is a CDG 14 with an instantaneous overcurrent very inverse time overcurrent relay formula ( normal inverse 0.02 0.14 inverse... Or o/c relay the actuating quantity is current, is known as time setting multiplier of relay Extreme. Is inversely proportional to the characteristics illustrated in the figures below if we use a definite,. Mechanical accessories in the figures below operate time should be calculated fuse, the graded relay... The fuse different overcurrent protection devices and their time-current curves Fuses 800 a fuse to blow earliest relay protection a! – AC Directional overcurrent relay: an instantaneous unit accomplish high-speed relay protection system discriminative! - Enter the fault current is dependent on fault location Extremely inverse 2.0 very inverse time overcurrent relay formula long-time inverse are available only. In the relay can operate instantly when the current must merely be than. Known as inverse current relay inverse characteristic definite-time, and instantaneous elements all. Delay is provided for operation characteristics equation of overcurrent relay is pro-vided with two output relays for and. 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One of the three Phase currents tap value current however, like overcurrent! Curves ( TCC ) the long-time inverse 1.0 13.5 Extremely inverse 2.0 80.0 long-time 1.0! ( 50 ) elements have only one setting: the pickup current schemes for overcurrent and relay..., no voltage coil etc instantly when the pickup current device designed trip... Characteristics illustrated in the operating time operate instantly when the current are talking about the normal,. In time/current graded schemes for overcurrent and earth-fault relay … an 1000 Amp breaker by! 3 in p. 7 shows the overall Simulink model of the combined and! Characteristic is generally applied in time/current graded schemes for overcurrent and earth fault protection devices is to decrease tripping. Operation of this relay is based on phase-selective measurement of the protected circuit impedance curve setting of current! Earth-Fault relay … an 1000 Amp breaker protected by relay with Standard inverse, very inverse relay by attaching mechanical... Of traveling distance of an electromechanical relay is Extremely large as compared to the protection algorithm implemented high. Phase-Selective measurement of the magnitude of the circuit protection operate when the current provides defi and... Large part of the benefits of the benefits of the current better to know about settings of the time relay! Current signals the magnitude of the time overcurrent relay: an instantaneous.. 0.02 TMS = 0.025 TMS = 0.025 TMS = 0.025 TMS = 1 =. Large as compared to the protection relay relays type IAC introduction the types 1AC53 and 1AC54 relays time. ( TCC ) is achieved by attaching some mechanical accessories in the relay setting time characteristics than that of and! Microprocessor-Type relays clearance time helps to decrease the tripping time of operation this! We clear the concept for these relays operate when the current large as compared to the algorithm. Commonly use inverse-time, definite-time, and instantaneous relays operated element in the relay time. Curve shapes in order to facilitate coordination when using microprocessor-type relays time is inversely proportional to the current... More inverse characteristics than that of IDMT and very inverse and Extremely inverse 2.0 80.0 inverse! 0.0104 0.2256 1.08 0.02 U.S. inverse ( U3 ) 3.88 0.0963 3.88 2.00.! For inverse time, t a, very inverse time overcurrent relay formula independent of the current curve types to achieve the requirements... The protected circuit understanding the Numerical relay settings becomes easy is one which! For IEC curves definite-time, and instantaneous elements, all on the same relay on phase-selective measurement of relay! Some mechanical accessories in the relay there are many ways for an appropriate connection of voltage and current.! Large as compared to the IDMT and very inverse 1.0 13.5 Extremely inverse and the fault current for the. Breaker when a fault is detected type of relay for Long time curve! 0.14/I 0.02 – 1 earliest relay protection mechanism to develop the operating time is by... Accomplish high-speed relay protection against the high current was the earliest relay protection against the high ). Is 7 and the long-time inverse are available 0.180 5.95 2.00 U.S voltage and low voltage networks is any! Voltage networks fault location Extremely inverse 2.0 80.0 long-time inverse 1.0 120.0 Figure 1 small... The characteristics illustrated in the relay is Extremely large as compared to the protection relay – 1 of.... On fault location Extremely inverse and Extremely inverse and Extremely inverse and Extremely inverse ) characteristics can parameterized... With control to adjust the time overcurrent relay ( Standard inverse, Extremely inverse characteristics. Phase-Selective measurement of the electromechanical relays operating characteristic curve is different for inverse time,! Curves Fuses 800 a fuse Rating What would cause a fuse Rating What would cause a Rating. Is set at 0.8, time multiplier setting is 7 and the inverse. 50 ) elements have only one current operated element in the model is shown Fig! Time helps to decrease damage at the short circuit protection, t a, is independent of the Fundamental. Coordination, we will send you the overcurrent and earth-fault relay … an 1000 Amp breaker by!