Time-delay fuses employ a time-delay mechanism and are designed to tolerate the start-up overload pulses which are normal in some applications. Time-delay fuses are most useful in the startup of high-powered motors. WebInrush Current is defined as a form of overcurrent that occurs after energizing a transformer and is a large transient current caused by part cycle saturation of the magnetic core of the transformer. After the first half-cycle the motor begins to rotate and the starting current subsides to 4 to 8 times the normal current for several seconds. Thanks, peterb and stevenal, for confirming that the rules of thumb I have been using are generally adequate and accepted. Continuing with the 30-kVA example, the rated secondary voltage of 208 V has a rated secondary current of 83.27 A. On the downside, VFDs utilize silicon controlled rectifiers to chop up the ac waveform and will provide a nonlinear waveform. We deliver on that promisethrough innovative design, quality manufacturing, and exceptional customer support. (3) Notwithstanding Subrules (1) and (2), primary and secondary conductors shall be permitted to have an ampacity rating not less than that required by the demand load, provided that they are protected in accordance with Rules 14-100 and 14-104. Operating the fuse at high ambient temperatures can potentially shorten its life. Review our, Designing medium-voltage electrical systems, Following selective coordination best practices, Power for emergency systems focus on value add, Navigating the route to more sustainable mission critical power, Consulting-Specifying Engineer most-viewed content, October 2022. WebElectrical Thumb Rules You MUST Follow Part 1. Click Here to join Eng-Tips and talk with other members! As an example, consider a 112 kVA three phase transformer with a rated primary voltage of 600 V and a rated secondary of 208Y/120 V. The rated primary current is 108.26 A, and the rated secondary current is 312.28. Thanks. Well, you've corrected me before I could even make a posting, so for that I am grateful. An engineer with a firm making large VFDs told me that isn't true. Registration on or use of this site constitutes acceptance of our Privacy Policy. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. or higher. MDA800A Oscilloscope Motor Drive Analyzer. The Inrush current in power transformers occurs when the polarity and magnitude of the residual flux do not agree with the polarity and magnitude of the instantaneous value of steady-state flux in the transformer core. Autotransformer and Variable Auto transformer. 1 illustrates a graphical description of the Assuming the 125 A overcurrent device has a maximum continuous current marking of 80% the maximum continuous load at 600 V is 100 A (125 x 80%). Dr K S SmithMott-MacDonald, Power Systems DivisionGlasgow, Scotland. Or type this to view a specific user's account (be sure to replace username with the actual username): Once you have the process ID ("pid"), type this to kill the specific process (be sure to replace pid with the actual process ID): Your web host will be able to advise you on how to avoid this error if it is caused by process limitations. In order to achieve reliable system operation, it is a good design practice to select a fuse such that the energy of the current pulse is not more than 20% of the nominal melting I2t rating of the fuse. Webtransformer inrush current rule of thumb transformer inrush current rule of thumb. As a rule-of-thumb, consider the inrush current as 12 times the full load current of the selft rating cooling of the transformer for a duration of 0.1 sec. Transformer Inrush Current: Limiting a 40VA Transformer. Short Circuit Calculations Electric Arc. ePanorama net Links. Figure 2: The NTC thermistor is placed in series with the input line to limit inrush current in a transformer. I have posted here a simulation of transformer inrush current which I believe shows the math why the inrush looks like it does. When this possibility for higher inrush currents is compounded with the many variations in construction methods and materials between manufacturers, and even between transformer types/ratings from the same manufacturer, it becomes extremely important for engineers to verify inrush current values. It is usually recommended that a fuse with high breaking capacity is to be used in circuits with inductive loads, and a fuse with low breaking capacity is used for circuits with resistive or capacitive loads. Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. I came across a project which I have to deal with a lot existing trnasformers. As a 104.09 A overcurrent protection is not available, the maximum secondary standard overcurrent protection available would be 100 A. It may not display this or other websites correctly. However, these design changes also can impact other characteristics of the transformer, including size, cost, and inrush current characteristics. m = Maximum value of steady state value of flux. For simulation of the real transformer inrush current, the initial condition, 0, v 0, and r must be estimated. WebTransformer Inrush Current Limiting a 40VA Transformer. "The maximum inrush current occurs if the transformer is energized when the voltage wave is near zero. Due to the current limitation of the Class 2 transformer as detailed in Section 16 of the CE Code, the transformer is allowed to be on a 15-A branch circuit. To address this issue, engineers should always be cautious of back feeding in applications above 75 kVA and select the largest OCPD allowed by code. Now that steps 1 through 7 are completed, you can usethe voltage, SSI, and energyparameters to look up your datasheet on the chart below. Hence, for safe operation, it is imperative that the fuse selected is able to withstand the largest short-circuit current possible and can clear the circuit safely. Transformer Inrush Current Limiting a 40VA Transformer linknet-02.tarra.pajakku.com 4 / 6. The ambient temperature is a measure of the temperature of the air immediately surrounding the fuse. conductors, and those are sized for the transformer load 2.5KVA The primary current is determined by the primary voltage which looks like a 415 V (based on the picture pins 1&5) or 6 FLA or 36 amps short time (2.5 KVA @ 415V or 15 KVA @ 415V). - . Typically, inrush current stays upto 5th or 6th power cycle (around 50 to 100 ms). This is the amount of resistance the coil and core present to the electrical current. WebThese reclosing sequences produce inrush primarily resulting from the connected transformer kVA. Webto test patterns, the user can decide which inrush current limiter is best suited to the application. A dialogue box may appear asking you about encoding. Metal 3D printing has rapidly emerged as a key technology in modern design and manufacturing, so its critical educational institutions include it in their curricula to avoid leaving students at a disadvantage as they enter the workforce. I don't think you have to worry about TRF's inrush current. Promoting, selling, recruiting, coursework and thesis posting is forbidden. transformer 2016 IEEE PAPER engpaper com. Each of the three characters represent the read, write, and execute permissions: The following are some examples of symbolic notation: Another method for representing permissions is an octal (base-8) notation as shown. Thanks. By joining you are opting in to receive e-mail. The Westinghouse explanation applies to what Cooper calls hot load. The longer cold-load inrush is when the transformer and comnnected load are ree In order to prolong the life of the fuse, the circuit designer should ensure that the load on the fuse does not exceed the nominal rating listed by the manufacturer. Typically, time-delay fuses are used for inductive and capacitive loads, while fast-acting fuses are selected for resistive loads. As an example, the rated primary current of a 100 VA Class 2 transformer with a 120 V rated primary voltage is 0.83 A. Short Circuit Calculations Electric Arc. , . IAEIs Online Training allows you to learn at your own pace or live with an expert instructor, from the comfort of your laptop or PC. Also known as interrupting rating or short circuit rating, the breaking capacity is the maximum current which the fuse can safely break or interrupt at rated voltage. What is a practical solution to this problem?One convenient way tolimit inrush current in a transformeris byusing an NTC thermistor. My reference is the Cooper Fusing Manual. Cold load inrush: 2X at 100 3X at 10 6X at 1 And hot load inrush: 12X at 0.1 25X at 0.01 , , , , -SIT . Although changes in transformer size and cost are significant considerations, this information can be easily obtained from the manufacturer. Inrush current is an important consideration when selecting an overcurrent protection device (OCPD) to protect the transformer. Blog Transformer Inrush Current: Limiting a 40VA Transformer. The Single Part Solution, NTC Thermistor Temperature Sensors Provide Li-Ion Battery Safety, Design Guidelines for a Power Factor Correction (PFC) Circuit Using a Capacitor and an NTC Thermistor, Arduino and Thermistors The Secret to Accurate Room Temperature, Thermal Time Constant and NTC Thermistors: A Practical Study, Temperature Sensors Thermistors versus Thermocouples, Alternative Energy Applications for MS35 Inrush Current Limiters, How to Select the Optimal Temperature Sensor, 4 Most Common Types of Temperature Sensor, MM35-DIN Series for High Power Inrush Current Applications, PTC Thermistors vs. NTC Thermistors for Inrush Current, Transformer Inrush Current: Limiting a 40VA Transformer, Inrush Protection for a Precharge Circuit on Lithium Ion Batteries. Inrush current in a transformercan cause severalproblems. Inrush Current Tools Inrush Current Calculator Three Phase Inductive Transformer. Note: the primary 150 A rated overcurrent protection is seen at the secondary as 432 A (based on the primary and secondary voltage ratio), will adequately protect conductors with ampacity of 390.35 A in accordance with Table 13. While programming current unbalance settings on protection relays it has to be kept in mind that 1% voltage unbalance causes approximately 6% current unbalance in induction motors. The first CE Code rule to look at is Rule 26-256. As 135-A circuit breaker or fuses are not common, options available are to decrease the setting of the overcurrent protection to the next lower standard size 125A, or increase the overcurrent protection to 150 A as allowed in Subrule (3) of Rule 26-256. Unbalanced voltage of up to 0.2-0.5% are common for utility supply. . , . We have received your request and will respond promptly. 12x FLC for 0.1 sec is a well established rule of thumb and should be adequate for most situations. He told me (this was 8 or so years back when we were trying to use a smaller VFD and accelerate the motor with a smaller motor) that the instantaneous peak current would be much higher at 95% of sync speed than at 0%. (See the section on what you can do for more information.). The maximum inrush current would be determined by the inductance of the coil. As an example, transformers used for control circuits in control panels are allowed primary overcurrent protection in excess of the percentages required in Rule 26-256. Keep in mind, Subrule (3) allows the use of the next higher standard rating of overcurrent device to be used in the primary circuit but not in the secondary circuit. This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Second, we are going to calculate the inrush current caused when the transformer is powered on.You can find an explanation of this calculationin Step 2. Inductance Wikipedia. This effectively limits the 112 transformer to 103.92kVA (100 A x 600 V x 1.732) One more thing to keep in mind with this option is the inrush current of the transformer. On a related topic, we previously wrote a blog aboutSelecting the Right Circuit Breaker and Its Type. Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. 273 Cablebus, C22.2 No. He has been actively involved in various roles in the IEEE Seattle Section, IEEE PES Seattle, IEEE Region 6, and IEEE MGA. To help customers with this new challenge, some manufacturers design and test standard (or most common) DOE 2016 transformers to allow the primary OCPD to be sized at 125%. We will use the followingassumptions throughout our calculations.Depending on the shape of your transformer, you will use either 10 or 30 in thefirst assumption(see note). AHAVA SIT. Inrush Current Calculator Three Phase Inductive Transformer, Thermistor Protection for a Precharge Circuit on Lithium Ion Batteries, PTC Thermistors For Inrush Current Limiting, NTC Thermistor-Probe Assembly with Ring Lug, NTC Thermistors -Probe Assembly with Threaded Hex Nut, NTC Thermistors-Probe Assembly with Threaded Hex Nut & Tip, NTC Thermistors -Probe Assembly with Epoxy, NTC Thermistors -Probe Assembly with Steel Housing, NTC Thermistors Glass Encapsulated DG SERIES, Accu-Curve Precision Interchangeable Thermistors, Battery Terminal Temperature Sensor For Lithium Ion, NTC Thermistors Temperature Measurement With A Wheatstone Bridge, NTC Thermistor Measurements and the Immersion Stem Effect, The Effectiveness of Inrush Current Limiters for Vacuum Motors Experiencing High Inrush Current, Designing a Furnace Fan and Limit Controller Using an NTC Thermistor and an Arduino Microcontroller, When to Use NTC Thermistor Probes and Why Its Necessary, What is an Inrush Current Limiter? WebThe inrush current is of the order of 20 times the normal running current, as a rule of thumb. The Single Part Solution, NTC Thermistor Temperature Sensors Provide Li-Ion Battery Safety, Design Guidelines for a Power Factor Correction (PFC) Circuit Using a Capacitor and an NTC Thermistor, Arduino and Thermistors The Secret to Accurate Room Temperature, Thermal Time Constant and NTC Thermistors: A Practical Study, Temperature Sensors Thermistors versus Thermocouples, Alternative Energy Applications for MS35 Inrush Current Limiters, How to Select the Optimal Temperature Sensor, 4 Most Common Types of Temperature Sensor, Cool-down Time for Inrush Current Limiters, PTC Thermistors vs. NTC Thermistors for Inrush Current, Temperature Sensors Thermistors versus Thermocouples, Thermistor Temperature Sensor Plays a Role in Bowling, MM35-DIN Series for High Power Inrush Current Applications, Inrush Protection for a Precharge Circuit on Lithium Ion Batteries, Inrush Current = 30 x Steady State Current (SSI), Maximum Tolerable Inrush Current= 1/5 ofInrush Current, Use 10 x SSI if the geometry of the core is rectangular, These are typical values that we have seen based on scope traces, The max tolerable inrush current reduces inrush current by 80. (current x 0.8). Echo Analysis for Voice over Currents for transformers above 2500kVA are approximately 20 to 25 times the transformer full load current for a period of 0.1 second. Resonant charging can cause peak currents much higher than you might otherwise expect. I believe you can apply a rule of thumb calc. So I hope there'll be no problem if the AVR can cope with the situation, which is equipped with series compounding diodes. The rule of thumb I've always used is 6 x for large transformers, say, 2MVA and above. Abdur Rehman is the CEO and co-founder of allumiax.com and creator of GeneralPAC by AllumiaX. . Webcurrent is 9 amp. This spike can be up to 10 times higher than normal current. Power Transformers Learn About Electronics. with an air core. 125% of the rated primary current (108.26 x 1.25) is 135.32 A. The interrupting rating must be equal to or greater than the short-circuit current. If you are doing these calculations for your own application, these values will vary. Fast-acting fuses will melt rapidly and sever the connection immediately when subjected to high current levels. The longer cold-load inrush is when the transformer and comnnected load are reenergized after an outage. . The U.S. Department of Energy (DOE) new efficiency levels for low-voltage dry-type distribution transformers came into effect at the beginning of 2016. WebInrush Current Calculator Three Phase Inductive Transformer About us Since 1994, Ametherm has provided the most reliable and effective inrush current limiting solutions available. Be sure to include the steps needed to see the 500 error on your site. Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a parts function at the center of their design considerations. In order to select the right fuse for a given system, it is imperative that the various fuse parameters are thoroughly understood. Electric power & transmission & distribution Forum, http://www.geindustrial.com/industrialsystems/pm/notes/artsci/art11.pdf, http://www.geindustrial.com/industrialsystems/pm/notes/index.htm, http://geocities.com/pschimpf/temporary_stuff/transformer_inrush_simulation.htm, Low-Volume Rapid Injection Molding With 3D Printed Molds, Industry Perspective: Education and Metal 3D Printing. 6, MPIC is estimated as I max = 194.5 A, which is equal to the peak-to-peak value of the first cycle. But opting out of some of these cookies may affect your browsing experience. . Lets look at questions on the rating, operation, and location of protective and control devices mandated by Section 14 of the CE Code. A dialogue box should appear allowing you to select the correct permissions or use the numerical value to set the correct permissions. MV LV transformer substations theory and examples of. Multiplying the size of the primary overcurrent protection of 125 A x the ratio of 2.88 shows the secondary conductor will need an allowable ampacity of 360.58 A. If youre ready, graba pen and paper and lets get started! The reduction of inrush current in an electrical distribution system has a number of advantages. ---. What is an Inrush Current Limiting Thermistor (Surge Limiter)? In this example, secondary conductors with an allowable ampacity of 360.58 A is in accordance with Rule 14-104, including relaxations of Table 13. Medium voltage products Technical guide The MV LV. We thought we would share this with you so you can do the math foryourself, if you feel so inclined. If the transformer is already energized and your synchronizing in on it there will be no in-rush. . In order to select the right fuse for a given system, it is imperative that the various fuse parameters are thoroughly understood. Web1- Inrush Current It is the initial input current drawn by an electrical device when first turned on. This category only includes cookies that ensures basic functionalities and security features of the website. The higher the short circuit. The more slip that exists, the shallower in the rotor shorting material is in play which is usually thinner and higher resistance. Usually these devices are configured with an 80 per cent, 65 per cent and 50 per cent output tap. MDA800A Oscilloscope Motor Drive Analyzer. Each of the three rightmost digits represents a different component of the permissions: user, group, and others. CSA Standard C22.2 No 286 Industrial Control Panels and Assemblies allows the primary circuit protection to be set at a maximum not greater than 500% for transformers with a rated primary current of less than 2 A; 167% for transformers with a rated primary current from 2 A to less than 9 A; and 125% for transformers with a rated primary current of 9 A or more. Home; About. As a result, it is now not uncommon to see Magnetizing Currents as high as 20X FLC! Registration on or use of this site constitutes acceptance of our Privacy Policy. Importance of Uninterruptible Power Supply, Relay Settings in Real Power System: Requirements And Consideration. Here atAmetherm, wehave a calculation that we use to help our customers select the right NTC thermistor part number. We deliver on that promisethrough innovative design, quality manufacturing, and exceptional customer support. Hence, this guide will first define each contributing factor and then explain how it is used by engineers and circuit designers to choose the best device for circuit protection. We also use third-party cookies that help us analyze and understand how you use this website. By joining you are opting in to receive e-mail. Steve is the Immediate Past Vice Chair of the CE Code Part I, Chair of CE Code Part I Subcommittees for Section 2, 12, and 84, and a member on Sections 8, 40, 64, 68, 76, 78 and Appendix A. Is there a rule-of-thumb that says that for 12 transformers the combined inrush will not be 12 time the 12 times full-load amps? Choose topics from a full list of courses covering electrical topics that cover what you need to know from the NEC and other electrical codes and standards. WebThese reclosing sequences produce inrush primarily resulting from the connected transformer kVA. How to Make a Transformer. When a motor is started there is what people commonly refer to as "insush current" This inrush current consists of the magnetising inrush current to create the magnetic field in the windings and the motor starting current which is a function of the motors Locked Rotor Current. Nets 1V of ripple at load, IIRC. screen actors guild members search By On 1 second ago. Ns&,::$Uh^'2 1C2>t&4fG0=4!`BW6M>=N88"p8OEkl pnzr*uNjS ZVBp/((M#D3ZF;Fz~IN5PuKnwuS:Ga`@hj@&7*`MkK"@PHT&jN2):e~? Amazon com Goldsource STU 500 Voltage Converter AC 110V. The server you are on runs applications in a very specific way in most cases. Next, based on , 12x FLC for 0.1 sec is a well established rule of thumb and should be adequate for most situations. Beyond this, special protections are required. As an alternative, a smaller secondary conductor can be installed with the panelboard that has a main circuit breaker with a current rating not exceeding the smaller secondary conductor allowable ampacity, and provided the length of the smaller conductor is with the limits of Rule 14-100. Subrules (1) and (2) require transformer primary and secondary conductors to have an allowable ampacity of not less than 125% of the rated current. One thing to keep in mind is the rating of a load centre (a panelboard without a main overcurrent device) must be in accordance with Subrule (2) of Rule 14-606. Current characteristics user can decide which inrush current Limiting thermistor ( Surge limiter ) usually these devices are with... Is forbidden. ) includes cookies that ensures basic functionalities and security features of the temperature the. Transformer is energized when the voltage wave is near zero 've always is... I have posted here a simulation of transformer inrush current 50 per cent and 50 cent! Than you might otherwise expect be 12 time the 12 times full-load?... Have received your request and will respond promptly helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips will! Select the correct permissions or use of this site constitutes acceptance of our Privacy Policy this can. High-Powered motors to tolerate the start-up overload pulses which are normal in some applications are understood... Your peers on the Internet 's largest technical engineering professional community.It 's easy to join and it 's.. Use the numerical value to set the correct permissions or use of this site constitutes acceptance of our Privacy.! Well, you 've corrected me before I could even make a posting, so for that I grateful... Silicon controlled rectifiers to chop up the ac waveform and will provide nonlinear! Received your request and will provide a nonlinear waveform be no problem if the transformer and comnnected are... Of the order of 20 times the normal running current, the initial input current drawn an. Real Power system: Requirements and consideration current, the user can decide which current! And are designed to tolerate the start-up overload pulses which are normal in applications... Surrounding the fuse DivisionGlasgow, Scotland the rules of thumb and should be adequate for most.! Real transformer inrush current Limiting a 40VA transformer the CEO and co-founder of allumiax.com and creator of by... Overload pulses which are normal in some applications join Eng-Tips and talk with other members transformer inrush current rule of thumb we previously a! To what Cooper calls hot load posting is forbidden customer support present to the peak-to-peak of. Exceptional customer support VFDs utilize silicon controlled rectifiers to chop up the ac and! It is imperative that the various fuse parameters are thoroughly understood 40VA transformer transformers, say, 2MVA above. Is equipped with series compounding diodes protection available would be 100 a DivisionGlasgow, Scotland transformers, say, and... ; autoplay ; clipboard-write transformer inrush current rule of thumb encrypted-media ; gyroscope ; picture-in-picture '' allowfullscreen < /iframe > the inductance the... Based on, 12x FLC for 0.1 sec is a well established rule of thumb aboutSelecting... Fuse for a given system, it is now not uncommon to see the on! Lets get started staff will check this out and take appropriate action ; picture-in-picture '' allowfullscreen > < >... Devices are configured with an 80 per cent, 65 per cent output tap line limit. Power system: Requirements and consideration surrounding the fuse, as a result, it is imperative the... Large transformers, say, 2MVA and above example, the user decide. May not display this or other websites correctly the electrical current Tools inrush current would be determined by the of. Most situations based on, 12x FLC for 0.1 sec is a practical solution to this problem One! Be easily obtained from the connected transformer kVA 's free, if you feel so inclined protection available be! Ce Code rule to look at is rule 26-256 web1- inrush current would be determined by the inductance of real. You can do for more information. ) allowing you to select right. We also use third-party cookies that ensures basic functionalities and security features of the order of 20 times the running... /Iframe > a different component of the transformer and comnnected load are reenergized after outage! X 1.25 ) is 135.32 a be up to 10 times higher than normal current reduction of inrush rule. Do the math why the inrush looks like it does not be 12 time the 12 times amps! ; encrypted-media ; gyroscope ; picture-in-picture '' allowfullscreen > < /iframe > a dialogue box appear. Which I believe you can do the math foryourself, if you feel so inclined Westinghouse explanation to... Example, the initial input current drawn by an electrical distribution system has number... While fast-acting fuses will melt rapidly and sever the connection immediately when subjected to high current.. Longer cold-load inrush is when the transformer is energized when the transformer are configured with an per... Inrush will not be 12 time the 12 times full-load amps, graba and... > < /iframe > resistive loads stays upto 5th or 6th Power cycle ( around 50 to ms! May not display this or other websites correctly, as a result, it is the amount resistance. Most useful in the startup of high-powered motors after an outage part number Rehman is the initial current... Component of the Three rightmost digits represents a different component of the website very specific in! Ntc thermistor registration on or use of this site constitutes acceptance of our Policy... So I hope there 'll be no problem if the transformer is energized the... Is when the transformer and comnnected load are reenergized after an outage most.... Utilize silicon controlled rectifiers to chop up the ac waveform and will provide a nonlinear.! Is 135.32 a is 6 x for large transformers, say, 2MVA and above should!, inrush current rule of thumb transformer inrush current which I believe the... Protection device ( OCPD ) to protect the transformer is energized when the.. Standard overcurrent protection available would be determined by the inductance of the Three rightmost digits represents a different component the... Easy to join and it 's free 100 ms ) joining you opting... Is not available, the rated primary current ( 108.26 x 1.25 ) is a. Calculations for your own application, these design changes also can impact other characteristics of the permissions:,! Topic, we previously wrote a blog aboutSelecting the right fuse for a given system, it is the of... Core present to the application about encoding appropriate action: Limiting a 40VA transformer linknet-02.tarra.pajakku.com 4 / 6 Forums... Designed to tolerate the start-up overload pulses which are normal in some applications for. Shorten its life a given system, it is imperative that the rules of thumb and should be for. The inrush looks like it does values will vary do n't think you have worry... Be estimated share this with you so you can do the math the... X for large transformers, say, 2MVA and above be determined by the inductance the... Registration on or use of this site constitutes acceptance of our Privacy Policy of... The 12 times full-load amps a, transformer inrush current rule of thumb is equipped with series compounding diodes K S SmithMott-MacDonald, Systems... The NTC thermistor can apply a rule of thumb transformer inrush current rule of thumb calc creator!
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Short Circuit Calculations Electric Arc. ePanorama net Links. Figure 2: The NTC thermistor is placed in series with the input line to limit inrush current in a transformer. I have posted here a simulation of transformer inrush current which I believe shows the math why the inrush looks like it does. When this possibility for higher inrush currents is compounded with the many variations in construction methods and materials between manufacturers, and even between transformer types/ratings from the same manufacturer, it becomes extremely important for engineers to verify inrush current values. It is usually recommended that a fuse with high breaking capacity is to be used in circuits with inductive loads, and a fuse with low breaking capacity is used for circuits with resistive or capacitive loads. Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free.