Overcurrent Relay Setting Calculation Example


Other overcurrent protection devices include fuses and additional 51 relays at different locations along the same line. Current constantly updates the thermal model calculation motor protection relay setting calculation guide greenbookee. Overcurrent Relay Setting Model for Effective Substation Relay Coordination International organization of Scientific Research 29 | P a g e Step 5. For GE relays, divide the current obtained in step 3 by 3 and assign this value to its 51Q pickup element. System faults outside the protective zones of the relays for a single contingency primary equipment outage (line, transformer, etc. Alternative Methodology to Calculate the Directional Characteristic Settings of Directional Overcurrent Relays in Transmission and Distribution Networks October 2019 Energies 12(19):3779. The purpose for having different curves in time-overcurrent relays is related to a concept called coordination, where the 51 relay is just one of multiple overcurrent protection devices in a power system. to calculate relay settings and produce the optimum directional overcurrent relays in transmission and subtransmission systems • Distance relay setting calculation (coordination) Example: for a fault at F1, breakers 29 and 35 automatically open in 5 cycles. There are two settings for this type of relay: Pickup current is determined by adjusted current coil taps or current tap settings (C. All the 4. When the set operate time at definitetime characteristic or the calculated operate time at inverse definite minimum time (IDMT)characteristic elap. The ANSI device number for over current relay is 51. 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. You can determine the. The result shows using the algorithm the new set value of 0. 22 TB MRI1 09. Required Over Load Relay Plug Setting = 480 / 600 = 0. The style number together with the model number describe the features and options in a particular device and appear on the front panel, drawout cradle, and inside the case assembly. The SEL-751 relay provides the tools necessary for sensitive fault protection while accommodating heavily loaded circuits. Determine relay type ( t ) and calculate the time of operation using the following equations(9),(10) and (11). Made text changes throughout Section 7: Serial Port Communications and. 1 Where Tm = the effective time-multiplier setting. 82 4700W/(square3*440V*0. 6 connected to supply circuit through a 400/5 current transformer when the circuit carries a fault current of 4000A. A variable is a way of naming and storing a value for later use by the program, such as data from a sensor or an intermediate value used in a calculation. overcurrent protection relay which is primarily intended as a radial feeder or transformer protection (backup) in electri-cal networks. (4) When solid-state relay s are used, overtravel. Defination: Overcurrent Relays respond to the threshold value of the current i. xls, Electromechanical Idmt Relay Setting Calculation, IDMT Relay Setting, Example For IDMT Relay Setting, Idmt Setting Calculation, idmt relay setting calculations, relay setting calculation example, relay setting calculation, overcurrent relay setting calculation. Overcurrent device settings are chosen to provide an acceptable compromise between sensitivity and selectivity in overcurrent protection. These spreadsheets below will make your endless calculations much more easier! Calculation of IDMT Over Current Relay Settings (50/51/50N/51N) Calculation model for thermal relay Siemens 7SJ64; Motor Protection Relay Selection Curves. Protection Riddle No. (2) Selection in inverse-time over-current elements of a time - current curve from a family of curves. ABB RET670 Calculations. REJ603 User's manual Switch setting matrix example 43 , be avoided. The 7SJ46 relay has an AC and DC. Inverse Time Over Current is also referred to as Time Over Current (TOC), or Inverse Definite Minimum Time (IDMT). 67 = directional overcurrent relay. When used in conjunction with thermal or time-overcurrent relays, it can be used to protect a motor against very high currents since it will operate before the main relays respond. The protection relay domain has made significant progress, mainly in order not to limit the transmitted power. The objective function of the problem is to minimize the sum of the operating times of all primary relays. Over current relays generally have 50% to 200% setting while earth leakages over current relays have either 10% to 40% or 20% to 80% current settings. Setting Calculation Protocol for IDMT Overcurrent Relay SettingsStation: Contract: Consultant: Contractor: Feeder ID: Outgoing Feeder (Typical) Relay: Relay Type:CT Ratio. The operating time of the overcurrent relay can vary due to relay type, time-dial setting (TDS) and magnitude of fault currents. Most tests are performed using single relays. ADDC Testing and Protection Section Setting Calculation Protocol for IDMT Overcurrent. Required Over Load Relay Plug Setting = 480 / 600 = 0. Single-Phase Fault The A phase CT will have an excitation voltage of V exA I Asec(Z CT 2Z. The time of operation is 3. If latch on last trip is selected the output will stay active until the M20E has been reset. Author : Faizullah Bajwa - From: Pakistan. My question is if I have a tap setting of 5, does it matter which Tap range I choose?. 410 2 SN VA 10 VA is enough, but any decaying DC component might saturate the CT causing some inaccuracy for the high-set overcurrent stage. These relays are required provide thermal protection against excessive. We need to setting the value of overload relay properly depend on our application and motor full load ampere. testin g relays to eliminate setting errors. My question is if I have a tap setting of 5, does it matter which Tap range I choose?. instantaneous setting the relay provide immediate trip command bypassing IDMT delay. 3 Setting value calculation 5. The Relay Testing Handbook #6D: Testing Overcurrent Protection (50/51/67) - Ebook written by Chris Werstiuk. The current signal is converted to a proportional voltage signal by the input transformer and then rectified, filtered and compared with a reference voltage of the level detector (1) set by the potentiometer P 1. This is to set and coordinate overcurrent IDMT relay distribution network. 3 * 2264 = 2943 A Plug setting = 2943 / 200 = 14. Nameplate = 1200 A / delay setting = 200 seconds Overcurrent Trip time 2400 A 200 seconds 3600 A 60 seconds 4800 A 12 seconds 6000 A 6 seconds 7200 A Instantaneous Example 2 Table 2. 3 Setting value calculation 5. Made text changes throughout Section 7: Serial Port Communications and. Calculate Low current Setting(I>). Current rating is set within the range of 105% to 125% of the current setting prescribed in JEM 1357 for all motors unless otherwise specified. 44 times rated). Line Differential. TDS and PSM, how long it takes that the backup relay sends the tripping signal. Thus, the distance relay has a fixed reach, in contrast to overcurrent units where the reach varies depending on system conditions. 30, 2011 Title 46 Shipping Parts 90 to 139 Revised as of October 1, 2011 Containing a codification of documents of general applicability and future effect As of October 1, 2011. Setting Calculation Protocol for IDMT Over Current Relay; prev. Values up to 600% are allowed by the NEC, depending on system parameters and. All the 4. Another type of overcurrent relay is the voltage-restrained overcurrent relay 51 V and the voltage-controlled relay 51C. In-tentional trip delays can be parameterized from 0 to 60 seconds. Earth leakage relay setting calculation Earth leakage relay setting calculation. 2: Relay Time Setting Calculation Industrial Power System Protection Calculation Of Relay Settings (b) Ring Circuits ¾ Applied to a situation where the continuity of supply is the priority: a. The ability to work comfortably with primary/secondary conversions and per-unit calculations is important when working with protective relays. They combine all the functions of monitoring, control, and protection in one device. Rsr = 850 Omhs. 40 could help the overcurrent relay to discriminate fault from no-fault. It illustrates how time coordination is achieved between the inverse time – overcurrent relays at each. Module-4 Overcurrent Protection. [The earth-fault may continue for a long time and cause considerable damage before if ultimately develops into a short circuit and removed from the system under these circumstances, it is profitable to employ earth fault relay is essentially an over current relay of low setting and operates as soon as an earth-fault or leak develops. The advantage of cellular communication like GSM technology is a potential solution for such remote controlling activities. Specific relays by catalog number are shown in Table 1-1. Protection settings are displayed on the relay front panel (see section A. 02 − = pi i I I K (7) and pi I and i I are known from the system requirements [4]. to, herein, as an “element” in the relay. Chapter 5-Overcurrent Protection Calculations & Settings – Tutorial. Before they are used, all variables have to be declared. operate only under fault conditions. For this example, assume a 5,000 A ground fault current. Multiply its amps by \sqrt3. 4 kV main and feeder breakers, and motor contactor interrupting ratings. The current flowing through the primary relay is used to calculate TB in order to determine that with the backup protection setting, i. – Typically set for 25% • Slope 2 “breakpoint” – Typically set at 2X rated current – This setting assumes that any current over 2X rated is a through fault or internal fault, and is used to desensitize the element against unfaithful replication Phase Differential Digital Relay Application. You can determine the. 3 shows the application of Time-delay overcurrent relays for protection of radial transmission line with multiple sections. For Schweitzer relays assign this resulting value to its 51Q pickup element. The relay provides circuit-breaker control, further switching devices and automation functions. Elements that are only enabled during a loss of communications. In the example the overcurrent function is required on the HV side of the transformer. These relays can also be used for other applications, which require single, two, or three-phase over-current protection. PHASE LOSS Active when one or more phases are below 40V. The most important task when installing numerical overcurrent relay on the system is selecting their suitable settings such that their basic protection function is met under sensitivity, selectivity, reliability and speed. The relay time-overcurrent unit is to be set for 5 A, and the instantaneous unit for 40 A. Dr Audih alfaoury 10 Note: The Selection of an Overcurrent Relay Time Curve According. of the FLC to calculate maximum overcurrent protection. 6 kV side = 415 / 6600 * 36000 = 2264 A Pick up setting = 1. Relay pickup current (A). these become opposite. To replace an existing Westinghouse/ABB type CO Overcurrent Relay (hereinafter referred to as ABB relay), perform the following steps. Pickup settings on a phase overcurrent device are normally set below the expected fault current levels on that line by some margin. Overcurrent Relay Setting Model for Effective Substation Relay Coordination International organization of Scientific Research 27 | P a g e associated with temperature rise of the equipment whose permissible limit is based on insulation class and material problems. Acceleration time setting requirements: limits the speed up current below the VFD's over-current capacity, make the over current speed loss don't cause the VFD drives tripped; The deceleration time set point is to prevent smoothing circuit voltage excessive, make regeneration overvoltage don't cause the variable frequency drive tripped. Values up to 600% are allowed by the NEC, depending on system parameters and. The protection relay domain has made significant progress, mainly in order not to limit the transmitted power. 6 connected to supply circuit through a 400/5 current transformer when the circuit carries a fault current of 4000A. My question is if I have a tap setting of 5, does it matter which Tap range I choose?. 88 Tp Relay M1 6 0. However proper coordination between the downstream relays shall be done before selection a value for such a setting. Made text changes throughout Section 7: Serial Port Communications and. B19 – Dry type transformer Fig. 3 times the nominal current of the. Relay setting calculation formula Relay setting calculation formula. The Type PJC relay is also used for other current-control functions. 64 = earth fault protection relay. At 25 percent voltage the relay picks up at 25 percent of the relay setting (1. 3(A) allowed the next higher STANDARD overcurrent protective device (OCPD) rating to be used when the transformer calculation resulted in a non-standard size OCPD. 2400 A in terms of primary and relay setting equal to 1 A in terms of secondary i. These spreadsheets below will make your endless calculations much more easier! Calculation of IDMT Over Current Relay Settings (50/51/50N/51N) Calculation model for thermal relay Siemens 7SJ64; Motor Protection Relay Selection Curves. These are the only settings relevant to the upstream relays. OVER CURRENT Alarm is active immediately when the level exceeds the over current setting. Pickup settings on a phase overcurrent device are normally set below the expected fault current levels on that line by some margin. (1) Calculation of a time delay value in definite-time over-current elements. Overcurrent protection devices. ABB RED670 Fault Locator Calculations. 8 , the lead resistance is 0. protection relays are designated numerically as follows: 49 = thermal relay. 100 Sec, Relay Curve is selected as Normal Inverse Type; Calculation of Over Current Relay Setting: (1) Low over Current Setting: (I>) Over Load Current (In) = Feeder Load Current X Relay setting = 384 X 125% =480 Amp. 0 W/1000 ft ´ 2 = 3. These relays can also be used for other applications, which require single, two, or three-phase over-current protection. Overcurrent relay setting calculation example Overcurrent relay setting calculation example. Both are used in generator applications to allow the relay to be set below the generator full-load current due to the fact that the fault contribution from a generator will decay to a value less than the full-load current of the generator. Protection systems intended for the detection of ground fault conditions. Over Load Current (In) = Feeder Load Current X Relay setting = 384 X 125% =480 Amp. Problem 1: – Determine the time of operation of a 5-ampere, 3-second over current relay having a current setting of 125% and a time setting, multiplier of 0. Time Overcurrent The principle of time overcurrent protection is that relays are applied appropriately at the terminals of zones, and each relay is then given both a current pickup and a time delay setting. pdf), Text File (. The Type PJC relay is normally used for over-current protection of feeder circuits. Weak Infeed Condition. The operating time of the over current relays ac-. 5 A, the multiple of pickup is 1. The overload protection device must be sized no more than 125 percent of motor nameplate current in this example [430. 25 times the fault current, for an earth fault on the 25 kV bus at the traction substation. 13 Jul 2018 Calculation of IDMT Over Current Relay Settings (50/51/50N/51N) an excel sheet for the transformer differential protection relay RET615. Their load limit is normally quoted in MVA, at nominal operating voltage at some specified power factor. Naresh Kumar says:. The current setting of the relay may correspond to 10% of the rated current of traction power transformer. Electrical engineers use PowerTools to perform harmonic analysis, transient stability analysis, short circuit analysis, and to determine demand load, voltage drop, arcflash hazard analysis and protective device coordination. autorecloser. Overcurrent Relay Technical Reference Manual 3. Internal/external CT connection compensation (ICOM) If ICOM = N, the traditional CT connections external to the relay must be used (e. The details of the system (parameter such as line impedance, relay setting, power rating and etc. Delta-Wye Transformers Delta-Wye transformers are of great interest when doing a protection coordination study. If we setting low from FLA,it can cause motor trip c0ntinues and process […]. 3 Setting value calculation 5. MiCOM P546 Calculations. 12 Calculation of phase fault. The pickup current is the current that causes the relay to operate and close the contacts. operate only under fault conditions. 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. Working Principle of Over Current Relay. 216: 43 Setting Example for the KAB Bus. 11 591 GENERAL ELECTRIC HGA Generic without Setting Auxiliary Relay 592 GENERAL ELECTRIC HGA-18 Generic without Setting Auxiliary Relay 593 General Electric HGM-11A Generic Time Relay Time Relay 594 GENERAL ELECTRIC IAC CAPE_TOC_IOC Overcurrent Protection 595 GENERAL ELECTRIC IAC-51 CAPE_TOC_IOC Overcurrent Protection 596 GENERAL ELECTRIC IAC51. • Remove the existing IAC relay. It means that the trip time is inversely proportional to the fault current. The setting applied is usually higher than the maximum short circuit cur-rent beyond the closest downstream device (breaker or fuse) and above the feeder inrush current. The SEL-751 Feeder Protection Relay is ideal for directional overcurrent, fault location, arc-flash detection, and high-impedance fault detection applications. Motor protection relay settings. ABB RET670 Calculations. The purpose for having different curves in time-overcurrent relays is related to a concept called coordination, where the 51 relay is just one of multiple overcurrent protection devices in a power system. The response of the over-current protection devices is visualized in the Time-Current Characteristic (TCC) curve. The ability to work comfortably with primary/secondary conversions and per-unit calculations is important when working with protective relays. Calculate Actual Operating time according to Various IES Curve. BE1-50/51B-214 and BE1-50/51B-225 Overcurrent Relays are driect repal cements for General Electric, IAC relays. 30, 2011 Title 46 Shipping Parts 90 to 139 Revised as of October 1, 2011 Containing a codification of documents of general applicability and future effect As of October 1, 2011. 1st the current should be higher than the preset value and secondly, the fault should persist for the minimum time which has been set in the relay. Determine relay type ( t ) and calculate the time of operation using the following equations(9),(10) and (11). These spreadsheets below will make your endless calculations much more easier! Calculation of IDMT Over Current Relay Settings (50/51/50N/51N) Calculation model for thermal relay Siemens 7SJ64; Motor Protection Relay Selection Curves. INSTRUCTION MANUAL. Calculate Actual Operating time according to Various IES Curve. Overcurrent Elements The motor will catch fire if it is overloaded and overcurrent is. 1 Standard Inverse characteristic (SI 3 or SI 1). 5 A, the multiple of pickup is 1. Examples Example 1. ) or a single contingency failure of another relay scheme. The Relay Testing Handbook: Testing Overcurrent Protection (50/51/67) provides step-by-step procedures for testing the most common overcurrent protection applications. Protection systems intended for the detection of ground fault conditions. Current constantly updates the thermal model calculation motor protection relay setting calculation guide greenbookee. Figure 11 shows the phase overcurrent coordination of the protective devices for 1862. 6M + products from 1,300+ manufacturers. should never be set more sensitive than the normal system unbalance. pdf - Free download as PDF File (. Lecture -14 Fuse Protection; Lecture -15 Fundamentals of Overcurrent Protection; Lecture -16 PSM Setting and Phase Relay Coordination (Tutorial) Lecture -17 Earth Fault Protection using Overcurrent Relays; Module-5 Directional Overcurrent Protection. The relay characteristic is shown in Figure2. Declaring a variable means defining its type, and optionally, setting an initial value (initializing the variable). 9 x 25% = 1. setting is 100/5 A and the fault current is. A relay settinglike PSM, TSM, ROT and RCOT was shown in this table. Pickup is typically chosen at approximately 140% of nominal transformer current or higher if coordination considerations dictate that. Text: General characteristics of C-type relay modules Features Low-set neutral overcurrent stage with , definite minimum time ( IDMT ) operation characteristic High-set neutral overcurrent stage I0>> with , non-directional earth-fault relay module SPCJ 1C8 is a single-pole neutral overcurrent relay module. Relay setting values are normally plotted on the time-current plane to verify the closing or intersection between relay pairs. Overcurrent Relay Setting • 51 elements SEL-751A Voltage Calculation. Large in-stock quantities able to ship same day. 50 = instantaneous overcurrent relay. Here I am assuming fault current in terms of CT secondary to be 6 A i. The educational resource for the global engineering community. Easiest way to solve numerical problem on the topic relay. Since Plug Setting Multiplier is ratio of Fault Current to relay setting, therefore the PSM will be equal to (6/1) i. Relay 1 also is graded with R 2 at 14QQAa d instead of at 23QQA. Kids will match and drag puzzle pieces onto building blueprints, as they learn about shapes. 8 is not a standard size. The SEL-751 relay provides the tools necessary for sensitive fault protection while accommodating heavily loaded circuits. For example, the relay can be set for 175 percent of generator rated current with rated voltage applied. The pickup current is the current that causes the relay to operate and close the contacts. Protection Coordination Wizard The Protection Coordination Wizard for automatic overcurrent protection relay settings calculation is used to: Verify that the settings (thresholds, time delays and curve shapes) of the overcurrent devices satisfy the requirements to achieve the protection of the circuit respecting the selectivity constraints and guaranteeing “normal operation” of the system. The use of IDMT overcurrent relay has some disadvantages. precise setting of operating time will be necessary. Working Principle of Over Current Relay. Required Over Load Relay Plug Setting = 480 / 600 = 0. B19 – Dry type transformer Fig. 2 Testing the output relays and LEDs 6. The model number, BE1-46N, designates the relay as a Basler Electric Class 100 Negative Sequence Overcurrent Relay. Distress excess its calibration setting it. 13 Jul 2018 Calculation of IDMT Over Current Relay Settings (50/51/50N/51N) an excel sheet for the transformer differential protection relay RET615. The overcurrent relays are usually placed secondary side of the currentat the transformer. The educational resource for the global engineering community. Magnetic relays are unaffected by changes in ambient temperature. Single-Phase Fault The A phase CT will have an excitation voltage of V exA I Asec(Z CT 2Z. 23 multiple. Working Principle of Over Current Relay. The SELCO T2500 is a high quality Over-Current and Short-Circuit relay intended for protection against thermal damage and faults caused by excessive currents. The current pickup establishes the sensitivity. Grading of over-current is the adjustment of the settings of the over-current relays to ensure discrimination and selectivity. Overcurrent Relay Setting SEL-751A Voltage Calculation. The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. Voltage Magnitude Calculation (Minimum Phase Voltage Magnitude) • Example setting: OUT301 = SV05T • Operation: OUT301 closes after 50P1P has been asserted for 0. 355 margin is widely used i n field-tested systems employing very inverse and extremely inverse time overcurrent relays. System faults outside the protective zones of the relays for a single contingency primary equipment outage (line, transformer, etc. 216: 43 Setting Example for the KAB Bus. For an overcurrent protective relay, the ‘pickup’ value is the minimum value of current that causes the relay to start timing and ultimately close its contacts. Publication: 9289900990. Determine relay type ( t ) and calculate the time of operation using the following equations(9),(10) and (11). IDMT Relay High Current setting lug setting of Relay is 2. When the set operate time at definitetime characteristic or the calculated operate time at inverse definite minimum time (IDMT)characteristic elap. 5 Amp and Time Delay (TMS) is 0. Dr Audih alfaoury 10 Note: The Selection of an Overcurrent Relay Time Curve According. You can use this feature to control the motor load within set limits. Naresh Kumar says:. 15,we can setting 125% from FLA and if service factor is 1. The protection objective is the set the relay pickup as sensitive as possible so to operate as fast as possible with out violating coordination principles. • Remove the existing IAC relay. Relay pickup current (A). Nameplate = 1200 A / delay setting = 200 seconds Overcurrent Trip time 2400 A 200 seconds 3600 A 60 seconds 4800 A 12 seconds 6000 A 6 seconds 7200 A Instantaneous Example 2 Table 2. The definite-time overcurrent protection for the earth (ground) current has a low-set overcurrent element (I E>) and a high-set overcurrent element (I E>>). Introduction 3. Relay R2 characteristics % VI (HT side of transformer) Fault level on 415 V side = 36000 A Reflected fault current on 6. M value of 8. 334 Use of Equipment Cargill Electrical Team Meeting 9. 3 Setting value calculation 5. coordinating a system of directional relays (either overcurrent or distance) involves setting relays one by one so that at each stage the relay being set coordi-nates with all its primary relays. 2 amps x 150 %( T430-152) = 22. The tap settings or the pickup settings for time-overcurrent function. Yet, some relays are simply set in terms positive-sequence impedance Z1 (magnitude and angle) and zero-sequence impedance Z0 (magnitude and angle). 8 Independent (definite) time overcurrent relays 9. Pick up Setting of Over Current Relay (PMS) (I>)= CT Secondary Current X Relay Plug Setting. 100 Sec, Relay Curve is selected as Normal Inverse Type. The REJ 523 is based on a microprocessor environment. It protects the equipment of the power system from the fault current. In an over current relay or o/c relay the actuating quantity is only current. Time Overcurrent The principle of time overcurrent protection is that relays are applied appropriately at the terminals of zones, and each relay is then given both a current pickup and a time delay setting. The relay time-overcurrent unit is to be set for 5 A, and the instantaneous unit for 40 A. thread238-307149 I hope the attached excel file will help you to get the operating current values for transformer differential protection up to 4 winding and al excel sheet to calculate all. This in-volv es calibrating the relays to the coordination cu rves and adjusting time dials to achieve specifi c op erating times. This programming position is used only if the TC posi-tion is set to LIn. The relay at circuit breaker 2 is set at the shortest possible time necessary for the breaker to operate (typically 0. Is more sensitive than phase overcurrent protection for phase-to-phase faults Is easy to calculate negative sequence in relay Improves protection for second most common fault type • Disadvantage – not sensitive to three-phase faults Phase-to-Phase Fault Detector Negative-Sequence Overcurrent Element. An example relay settings shown in the figure below. We have to always look at I/I N and set the relay from 0. (See Programming Example #2). Grading of overcurrent-time relay and HV HRC fuse As an example of the power system shown in Fig. 11 Recommended grading margins 9. relays the ratio RE/RL is used to compensate the resistance part and the ratio XE/XL is uses to compensate the reactance part separately. 5 Thesis Outline This thesis is separated into five chapters. Up to 20 additional protection functions can be created by the user. Tap Range: The range of tap settings which is applicable to the relay. Overcurrent Protection Negative Phase Sequence Overcurrent (NOC) protection can be used in applications where certain fault conditions may not be detected by the normal phase and earth overcurrent protections, for example, in the case of a relay applied on the delta side of a delta-star transformer, to detect an earth fault on the star side. Protection by means of over current relay with adequate characteristic and settings is preferred (Schneider Electric VIP relay range for example). txt) or view presentation slides online. The objective function of the problem is to minimize the sum of the operating times of all primary relays. Just calculate from motorplate: Watts/(Square3*V*cosP)=> example motorplate says: 4. [The earth-fault may continue for a long time and cause considerable damage before if ultimately develops into a short circuit and removed from the system under these circumstances, it is profitable to employ earth fault relay is essentially an over current relay of low setting and operates as soon as an earth-fault or leak develops. 2 amps x 150 %( T430-152) = 22. To understand this concept easily, it is better to know about settings of the Electromechanical Relays. View 39984912-Setting-Calculation-Protocol-for-IDMT-Over-Current-Relay from SING 007 at Englishville School. 4 s (see Figure 1). Overcurrent elements that are only enabled during loss of potential conditions. Therefore, protection of change for frequency or reverse power protection can be realized, for example. The purpose for having different curves in time-overcurrent relays is related to a concept called coordination, where the 51 relay is just one of multiple overcurrent protection devices in a power system. In order to avoid such a state. 6 kV side = 415 / 6600 * 36000 = 2264 A Pick up setting = 1. 2 amps x 150 %( T430-152) = 22. once the current through the relay goes, beyond the set Value, it operates ANSI Code : Its ANSI Code is 50. Set the time to several seconds or several tens of seconds with an overcurrent of 500% of the rated value and set it longer than the motor's startup time. 1 The setting of the instantaneous overcurrent relay on the primary side of the transformer should be a little above asymetrical value of the fault current for 3-phase fault on the secondary terminals of the trans- former. These settings are summarized and. The educational resource for the global engineering community. To find more books about relay setting calculation example, you can use related keywords : relay setting calculation, relay setting calculation example, Idmt Relay Setting And Calculation. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. xls, Electromechanical Idmt Relay Setting Calculation, IDMT Relay Setting, Example For IDMT Relay Setting, Idmt Setting Calculation, idmt relay setting calculations, relay setting calculation example, relay setting calculation, overcurrent relay setting calculation. These are the only settings relevant to the upstream relays. overcurrent relay to ascertain the pick-up current, plug setting and the time multiplier setting protection coordination of over-current relays (OCRs) that will facilitate the calculation of the TMS. 4 Very Invepe Overcurrent Relays Very inverse over current relays are particularly. The Relay Testing Handbook #6D: Testing Overcurrent Protection (50/51/67) - Ebook written by Chris Werstiuk. (2) Selection in inverse-time over-current elements of a time - current curve from a family of curves. Calculation of Over Current Relay Setting: (1) Low over Current Setting: (I>) Over Load Current (In) = Feeder Load Current X Relay setting = 384 X 125% =480 Amp. For this example, assume a 5,000 A ground fault current. Example: 5-hp, 230V single-phase motor with a service factor of 1. 11 Recommended grading margins 9. PLUG SETTING MULTIPLIER (PSM)-On Induction Disc relays current setting is made by inserting a plug into a plug bridge-Hence “Plug Setting”-If relay setting and CT ratio are known, can find fault current as a multiple of current setting – PSM-Relay characteristics give operating times at multiples of current setting (PSM)-Therefore the characteristics can be applied to any relay. setting in the relay will automatically calculate the TAPn setting if MVA is set to a value other than OFF. Relay elements that are only enabled when other relays or associated systems fail. 4 Indication of measuring and fault values 5. Intentional trip delays can be parameterized from 0. However proper coordination between the downstream relays shall be done before selection a value for such a setting. The block diagram of the inverse-time overcurrent relay is shown in the figure. overcurrent relay to ascertain the pick-up current, plug setting and the time multiplier setting protection coordination of over-current relays (OCRs) that will facilitate the calculation of the TMS. Example of Setting Radial System The results of these relay setting calculations are shown in Table 2. It provides defi nite-time and inverse-time overcurrent protection according to IEC and ANSI standards. Settings 5-8 will allow the LP setting to display in HP. The response of the over-current protection devices is visualized in the Time-Current Characteristic (TCC) curve. (4) When solid-state relay s are used, overtravel. Grading of over-current is the adjustment of the settings of the over-current relays to ensure discrimination and selectivity. M value of 8. Elements that are only enabled during a loss of communications. Internal/external CT connection compensation (ICOM) If ICOM = N, the traditional CT connections external to the relay must be used (e. Should the relay react to such starting over current, the motor will be in operation fault status. The SIPROTEC 7SJ80 features “flexible protection functions”. 02 − = pi i I I K (7) and pi I and i I are known from the system requirements [4]. The NEC requirements for overcurrent protection for specific applications are found in sections other than 240. Example: Calculate the plug setting and time multiplier setting for an IDMTL relay on the following network so that it will trip in 2. 5 Amp and Time Delay (TMS) is 0. We have to always look at I/I N and set the relay from 0. (1) Calculation of a time delay value in definite-time over-current elements. Module-4 Overcurrent Protection. (3) Overcurrent protection modification. The Config page is where the relay settings will be entered. 12 Calculation of phase fault. Relay - Relay coordination requires (1) that there be a minimum of 0. Motor protection relay settings. The inherent mul-ti-loop structure of a typical transmission system entails a large number of relay setting calculations to be done iteratively around. PS=100% PS=100% PS=125% PS=150% Table 2. 11 591 GENERAL ELECTRIC HGA Generic without Setting Auxiliary Relay 592 GENERAL ELECTRIC HGA-18 Generic without Setting Auxiliary Relay 593 General Electric HGM-11A Generic Time Relay Time Relay 594 GENERAL ELECTRIC IAC CAPE_TOC_IOC Overcurrent Protection 595 GENERAL ELECTRIC IAC-51 CAPE_TOC_IOC Overcurrent Protection 596 GENERAL ELECTRIC IAC51. To find more books about idmt relay setting and calculation xls, you can use related keywords : Idmt Relay Setting And Calculation. 1 Power-On 6. Using the calculated fault currents, this condition is satisfied, so modifications to the CT ratios are not required. Depending on the time of operation the overcurrent relay is categorized into following types. IDMT Relay High Current setting :Plug setting of Relay is 2. Author : Faizullah Bajwa - From: Pakistan. IDMT Relay High Current setting lug setting of Relay is 2. MJT 315 Three Pole Over Current and Earth Fault Relay with two High set elements 1. In the example the overcurrent function is required on the HV side of the transformer. The purpose for having different curves in time-overcurrent relays is related to a concept called coordination, where the 51 relay is just one of multiple overcurrent protection devices in a power system. The information needed for a relay protection setting analysis is:. The current pickup establishes the sensitivity. 3 Equipment Considerations In comparing protection design to the objectives and criteria set forth, consideration must be. Selective coordination is generally achieved by using the following minimum recommended margins between device characteristics: 1. overcurrent relay to ascertain the pick-up current, plug setting and the time multiplier setting protection coordination of over-current relays (OCRs) that will facilitate the calculation of the TMS. The setting applied is usually higher than the maximum short circuit cur-rent beyond the closest downstream device (breaker or fuse) and above the feeder inrush current. Trip is active when the level exceeds the over current setting and after the definite time delay expired. 4 , and the CT resis-tance is 0. Substations. Overcurrent Relay Setting Model for Effective Substation Relay Coordination International organization of Scientific Research 29 | P a g e Step 5. The relay time-overcurrent unit is to be set for 5 A, and the instantaneous unit for 40 A. 51P2TD = _____ For this exercise, set the time dial to 3 to provide time coordination with downstream devices. Another type of overcurrent relay is the voltage-restrained overcurrent relay 51 V and the voltage-controlled relay 51C. 5 A, the multiple of pickup is 1. The Relay Testing Handbook: Testing Overcurrent Protection (50/51/67) provides step-by-step procedures for testing the most common overcurrent protection applications. xls, relay setting calculation guide, Siemens Relay Setting Calculation, protective relay setting calculation, areva relay setting calculation, micom relay setting calculation, overcurrent relay setting. Where heavy loading prevents sufficiently sensitive setting of the phase overcurrent elements to detect lower magnitude phase-to-ground faults, residual-ground overcurrent elements are available to provide. Relay setting calculations, programming of relay logics, configuration, verification of setting calculations, setting files etc. 16 and a nameplate current rating of 28A. 4(G) Overcurrent Protection for Specific Conductor Applications. (2) Selection in inverse-time over-current elements of a time - current curve from a family of curves. Acceleration time setting requirements: limits the speed up current below the VFD's over-current capacity, make the over current speed loss don't cause the VFD drives tripped; The deceleration time set point is to prevent smoothing circuit voltage excessive, make regeneration overvoltage don't cause the variable frequency drive tripped. Problem 1: – Determine the time of operation of a 5-ampere, 3-second over current relay having a current setting of 125% and a time setting, multiplier of 0. Relay setting calculation ppt Relay setting calculation ppt. Category: Setting Calculation Protocol for IDMT. Depending on the time of operation the overcurrent relay is categorized into following types. (1) Overload elements Overcurrent elements Time elements (2) Open-phase elements (3) Reverse-phase elements These functions are described in more detail below. 4(G) Overcurrent Protection for Specific Conductor Applications. Generator Protection – Setting Calculations • Over Current pickup = 4. Setting parameter1; 1-4 I S : Rated CT current1; 5-8 Choice of characteristics2; 1-4 I>: Pick-up value of the definite time over current element or startvalue of the inverse time. Relay setting calculations, programming of relay logics, configuration, verification of setting calculations, setting files etc. Dear Guest, Different feeders can have different Phase current setting based on the size of cable and maximum permissible load current in that feeder. This paper presents the solution of directional overcurrent relay (DOCR) problems using Simulated Annealing based Symbiotic Organism Search (SASOS). Relay Functions Settings Rated Current (In) Frequency Auxiliary Power Supply Time Multiplier Low Set Delay. operate only under fault conditions. The relay provides circuit-breaker control, further switching devices and automation functions. The current signal is converted to a proportional voltage signal by the input transformer and then rectified, filtered and compared with a reference voltage of the level detector (1) set by the potentiometer P 1. Motor Calculations Part 1: Motors and Branch-Circuit Conductors. 5 kV line protected by the instantaneous element of the overcurrent relay associated with breaker 6. With inverse time-delay characteristics, the time characteristics are normally set for quick activation with high currents and slow activation with low currents. Relay R2 characteristics % VI (HT side of transformer) Fault level on 415 V side = 36000 A Reflected fault current on 6. 4 Relay overcurrent settings – Relays 1/2 These relays perform overcurrent protection of the cable feeders, Busbar C and backup-protection to relays F1, F2 and their associated fuses FS1 and FS2. 1 (OCR1) acts as the main relay, while the other two relays are back up relays, in case the main relay fails to operate. 2 , the residual relay burden is 1. Transformer Differential Relay Setting Calculation Example. 5 A, the multiple of pickup is 1. Line Differential. Chapter 4 describes the format for input file RCDIN for distance relay co. Overcurrent Relay Setting Model for Effective Substation Relay Coordination International organization of Scientific Research 29 | P a g e Step 5. The time of operation is 3. We have to always look at I/I N and set the relay from 0. (1) Calculation of a time delay value in definite-time over-current elements. The Vip 300 is a self-powered three phase overcurrent and earth fault protection relay. In this video we have explained calculation for IDMT over current relay setting calculation. To replace an existing IAC relay, perform the following steps. Module-4 Overcurrent Protection. 13 Jul 2018 Calculation of IDMT Over Current Relay Settings (50/51/50N/51N) an excel sheet for the transformer differential protection relay RET615. 821seconds 9. Relay setting values are normally plotted on the time-current plane to verify the closing or intersection between relay pairs. Overcurrent Relay Setting Model for Effective Substation Relay Coordination International organization of Scientific Research 27 | P a g e associated with temperature rise of the equipment whose permissible limit is based on insulation class and material problems. 4 s (see Figure 1). overcurrent relay to ascertain the pick-up current, plug setting and the time multiplier setting protection coordination of over-current relays (OCRs) that will facilitate the calculation of the TMS. • Numerical display of setting values, actual measured values and their active, reactive. The model number, BE1-46N, designates the relay as a Basler Electric Class 100 Negative Sequence Overcurrent Relay. ADDC Testing and Protection Section Setting Calculation Protocol for IDMT Overcurrent. txt) or view presentation slides online. Engage in comprehensive discussions and analysis about enhanced features of next generation protective relay systems that adapt to changing conditions. IDMT Relay High Current setting :Plug setting of Relay is 2. The CYMTCC software addresses Time Over-Current protection for Industrial, Commercial and Distribution Power systems. Lecture -14 Fuse Protection; Lecture -15 Fundamentals of Overcurrent Protection; Lecture -16 PSM Setting and Phase Relay Coordination (Tutorial) Lecture -17 Earth Fault Protection using Overcurrent Relays; Module-5 Directional Overcurrent Protection. Relay - Relay coordination requires (1) that there be a minimum of 0. Appendix A gives an example of a loadability calculation for a transmission line overcurrent relay. An overcurrent relay having a time-multiplier setting which is calculated as a proportion of the system voltage according to the expression: - EMI4. 5 Amp and Time Delay (TMS) is 0. 1) that group all required protection functions are commonly used for generator protection. My question is if I have a tap setting of 5, does it matter which Tap range I choose?. The relay characteristic is shown in Figure2. the directional over current relay acting when the current flow in perticular direction above relay setting. 51 and 51N are both inverse time relay and used to detect phase fault and earth fault respectively. This in-volv es calibrating the relays to the coordination cu rves and adjusting time dials to achieve specifi c op erating times. For example, a relay including function 51 would be a timed overcurrent protective relay. The series is titled “Motor Calculations” and covers the Code and calculations for single general motor applications. You can use this feature to control the motor load within set limits. The program comes with an extensive database of over 15000 protective devices from more than 100 different manufacturers that are easily accessed to produce Time-Current curve plots and device settings reports. Also these relays have the ability to communicate with each other to share statuses and orders using GOOSE (generic object‐oriented substation events) messages based on. Separate ground relays are generally favored because they can be adjusted to provide faster and more sensitive protection for single phase to ground faults than. Protective Relay Calculations and Settings. • Remove the existing IAC relay. Selective coordination is generally achieved by using the following minimum recommended margins between device characteristics: 1. Relay 1 also is graded with R 2 at 14QQAa d instead of at 23QQA. Pickup is typically chosen at approximately 140% of nominal transformer current or higher if coordination considerations dictate that. OVER CURRENT Alarm is active immediately when the level exceeds the over current setting. For example, a relay including function 51 would be a timed overcurrent protective relay. When addressing the problem of calculating the settings for directional overcurrent elements, the focus is usually the determination of the pickup, time dial and operating characteristic, in order to ensure proper selectivity with adjacent protection elements, thus limiting the problem related to the settings calculation of the direction determination characteristic to the application of. Protection Riddle No. With inverse time-delay characteristics, the time characteristics are normally set for quick activation with high currents and slow activation with low currents. PS=100% PS=100% PS=125% PS=150% Table 2. current relays, from electro-mechanic with or without an induction disc to modern numerical relays. 3) Compute the time required by relay R 2 to clear SLG fault at bus B. the directional element sence direction of current then o. Settings) to include the new settings PTCONN and VSCONN. The T2500 Overcurrent & Short Circuit Relay. Selective coordination is generally achieved by using the following minimum recommended margins between device characteristics: 1. If the main overcurrent relay fails in operating in the presence of a fault, the backup relay should be operating at a specified delayed time [1, 2]. 3 shows the application of Time-delay overcurrent relays for protection of radial transmission line with multiple sections. 79 = reclosing relay. Find the phase overcurrent pickup amps of this relay. The protection objective is the set the relay pickup as sensitive as possible so to operate as fast as possible with out violating coordination principles. From current setting we calculate the trick current of the relay. Examples Example 1. precise setting of operating time will be necessary. 2 Distance Relays These relays respond to an impedance of varying magnitude which depends on the power factor of the load impedance. Magnetic relays are unaffected by changes in ambient temperature. The style number together with the model number describe the features and options in a particular device and appear on the front panel, drawout cradle, and inside the case assembly. Example of Setting Radial System The results of these relay setting calculations are shown in Table 2. The details of the system (parameter such as line impedance, relay setting, power rating and etc. Home; Python graphene example. 64 = earth fault protection relay. In other words, the time setting of relays is so graded that in the event of fault, the smallest possible part of the system is isolated. When addressing the problem of calculating the settings for directional overcurrent elements, the focus is usually the determination of the pickup, time dial and operating characteristic, in order to ensure proper selectivity with adjacent protection elements, thus limiting the problem related to the settings calculation of the direction determination characteristic to the application of. 2) along with manual reset and trip flags. are required to construct this protective relay. Cold load pickup logic senses when a feeder is being connected after a period of being de-energized. For example, if we calculate that the contribution through. 1 Where Tm = the effective time-multiplier setting. The overcurrent relay is defined as the relay, which operates only when the value of the current is greater than the relay setting time. When the set operate time at definitetime characteristic or the calculated operate time at inverse definite minimum time (IDMT)characteristic elap. 3(B), if the primary current of the transformer is less than 9 amps, an overcurrent device rated or set at not more than 167% of the primary current shall be permitted. 02 − = pi i I I K (7) and pi I and i I are known from the system requirements [4]. The REJ 523 is based on a microprocessor environment. 30, 2011 Title 46 Shipping Parts 90 to 139 Revised as of October 1, 2011 Containing a codification of documents of general applicability and future effect As of October 1, 2011. This setting limitation means that load or system induced zero-sequence current can severely impact the sensitivity of a zero-sequence overcurrent element [11]. Tap Range: The range of tap settings which is applicable to the relay. Another type of overcurrent relay is the voltage-restrained overcurrent relay 51 V and the voltage-controlled relay 51C. The DOCR problem is nonlinear and highly constrained with two types of decision variables, namely, the time dial settings (TDS) and plug. (2) Selection in inverse-time over-current elements of a time - current curve from a family of curves. considered for all overcurrent relays. These TCC curves can be viewed on the selectivity diagram using which the user can adjust the settings of these devices to protect the cable, transformer, etc. − Updated BRE W command to allow trip counters and accumulated interrupted current values to be pre-loaded for each individual phase. It is a general practice to use a set of two or three overcurrent relays for protection against inter-phase faults and a separate overcurrent relay for single phase to ground faults. MULTIPLE CHARACTERISTICS MJT315 relay is suitable for various inverse characteristics and also for definite time lag characteristic, any one of them selectable at site independently for phase and earth fault. Flexible I/O options, easy mounting, and fast settings make the SEL-751 the right solution for industrial and utility feeder protection. These values are defined as follows: Pick up voltage (also defined as pull in voltage, or must operate voltage): As the voltage of a de-energized Relay is increased, this is the value at or below which all contacts must function. setting is 100/5 A and the fault current is. 2 with the aid of a load flow and fault study programs. the directional element sence direction of current then o. Current rating is set within the range of 105% to 125% of the current setting prescribed in JEM 1357 for all motors unless otherwise specified. The Relay Testing Handbook: Testing Overcurrent Protection (50/51/67) provides step-by-step procedures for testing the most common overcurrent protection applications. (See Programming Example #2). Lecture -14 Fuse Protection; Lecture -15 Fundamentals of Overcurrent Protection; Lecture -16 PSM Setting and Phase Relay Coordination (Tutorial) Lecture -17 Earth Fault Protection using Overcurrent Relays; Module-5 Directional Overcurrent Protection. When normal current flows. Here I am assuming fault current in terms of CT secondary to be 6 A i. The NEC requirements for overcurrent protection for specific applications are found in sections other than 240. The T2500 can be used to protect generators, power transmission lines and various types of consumer supplies. 2 , the residual relay burden is 1. Overcurrent device settings are chosen to provide an acceptable compromise between sensitivity and selectivity in overcurrent protection. The purpose for having different curves in time-overcurrent relays is related to a concept called coordination, where the 51 relay is just one of multiple overcurrent protection devices in a power system. —Overcurrent relay is an important relay used to protect transmission and distribution feeders, transformer, bus coupler etc. considered for all overcurrent relays. This setting limitation means that load or system induced zero-sequence current can severely impact the sensitivity of a zero-sequence overcurrent element [11]. With inverse time-delay characteristics, the time characteristics are normally set for quick activation with high currents and slow activation with low currents. OVERCURRENT PROTECTION SYSTEM. Over-current relays can be used to protect practically any power system. In an over current relay, there would be essentially a current coil. Before they are used, all variables have to be declared. 3) Compute the time required by relay R 2 to clear SLG fault at bus B. Before determining the size or rating of the overcurrent devices, observe that Notes 1 and 2 of NEC Table 450-3(A) permit the rating or setting of primary and/or secondary OPD to be increased to the next higher standard or setting when the calculated value does not correspond to a standard rating or setting. Grading of over-current is the adjustment of the settings of the over-current relays to ensure discrimination and selectivity. 7Kw 440V cosP: 0. make offer - westinghouse overcurrent relay, c0-8h1101n,1-12 amps tested free shipping Westinghouse Overcurrent Relay Cat #C0-9H1111N Style 264C901A09 Type C0-9 $175. Changed the title of Section 6 to Section 6: Setting the Relay; moved information on differential elements and overcurrent elements and application guidelines for overcurrent elements to Section 3. Single-Phase Fault The A phase CT will have an excitation voltage of V exA I Asec(Z CT 2Z. Consider a radial feeder with multiple feeders in series. The percentage of the 34. 2000 A in terms of primary. These spreadsheets below will make your endless calculations much more easier! Calculation of IDMT Over Current Relay Settings (50/51/50N/51N) Calculation model for thermal relay Siemens 7SJ64; Motor Protection Relay Selection Curves. Zack, Quack, and Kira are on their way to beat the heat when they pick up some rowdy gorillas on their way!Sing along as Dora and Pablo prepare and practice. The Config page is where the relay settings will be entered. 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. The style number together with the model number describe the features and options in a particular device and appear on the front panel, drawout cradle, and inside the case assembly. A relay settinglike PSM, TSM, ROT and RCOT was shown in this table. Depending on the time of operation the overcurrent relay is categorized into following types. 0 GUIDELINES FOR RELAY SETTINGS A. The response of the over-current protection devices is visualized in the Time-Current Characteristic (TCC) curve. The means of limit control is normally an overcurrent protective device, which at the electrical-power distribution level is a fuse or circuit breaker (as seen in Figure 4). Both are used in generator applications to allow the relay to be set below the generator full-load current due to the fact that the fault contribution from a generator will decay to a value less than the full-load current of the generator. • Two-element (low and high set) overcurrent relay both for phase and earth faults. characteristics curves of overcurrent relays, for example: T i = K *TDS i (6) Where: ( ) 1 0. Confidence. Selective coordination is generally achieved by using the following minimum recommended margins between device characteristics: 1. • Inverse definite minimum time (IDMT) overcurrent relay with the following selectable characteristics in accordance with BS 142 and IEC 60255-3: - Normal Inverse - Very Inverse - Extremely Inverse - RI-Inverse - Long Time Inverse • High set overcurrent unit with instantaneous or definite time function • Two stage overcurrent relay both. So we have considered numerical relay in our case-study. Nameplate = 1200 A / delay setting = 200 seconds Overcurrent Trip time 2400 A 200 seconds 3600 A 60 seconds 4800 A 12 seconds 6000 A 6 seconds 7200 A Instantaneous Example 2 Table 2. From the motor characteristics given, the overcurrent relay settings (Relay A) can be found using the following guidelines: Thermal element. ) or a single contingency failure of another relay scheme. These relays operate magnetically in response to an over current. 1 Result for overcurrent relay setting in Zon 1, UTMTable 4. The curve type and the time dial can match the values of the downstream relay. The REJ 523 is based on a microprocessor environment. Defination: Overcurrent Relays respond to the threshold value of the current i. However, there are enough connections on the Protection and Relay Test Set to test two relay modules at the same time. 304(e), the installation safety requirements for overcurrent protection. These TCC curves can be viewed on the selectivity diagram using which the user can adjust the settings of these devices to protect the cable, transformer, etc. or 5A), will be determined in the general settings of the relay. relays the ratio RE/RL is used to compensate the resistance part and the ratio XE/XL is uses to compensate the reactance part separately. element acting. definite time overcurrent relay and inverse time overcurrent relay • Selectable inverse time characteristics according to BS 142 and IEC 255-4: Normal Inverse (type A) Very Inverse (type B) • Reset setting for inverse time characteristics select-able • High set overcurrent unit with instantaneous or de-finite time function. I understand that these relays have both a tap range and a tap setting within that range. 67 = directional overcurrent relay. Read this book using Google Play Books app on your PC, android, iOS devices. 2 while maintaining a grading margin between relays of 0. The overall protection graph for Phase Overcurrent Protection (ANSI 50-51) is presented by multiple segments as follows: Calculation of tripping time in terms of settings for each curve/segment can be summarized as detailed in attached file. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. 1 The setting of the instantaneous overcurrent relay on the primary side of the transformer should be a little above asymetrical value of the fault current for 3-phase fault on the secondary terminals of the trans- former.