Transformer Inrush Currents – Analysis and Practical Solutions for Protection Security Steven Hodder, Hydro One Networks, Inc. (a) With the secondary open circuited and 120 V applied to the primary (120 V) winding, calculate the primary current and the secondary voltage. es 2 Department of Electrical Engineering. The magnetizing inductance is drastically reduced by the lack of a magnetic core, resulting in large magnetizing currents and losses if used at low frequencies. Vo: output voltage. Raman College of Engg. (i) Draw the equivalent circuit after the snap-off of the switch. 5 mm to ﬁt into the window of a standard EI42 ferrite core. Magnetics Designer is a standalone software program for Windows that designs all types of layer (and sector/split bobbin) wound transformers and inductors, and generates a corresponding SPICE model. % These calculations are done using an equivalent % circuit referred to the primary side. 4 H referred to the HV side. The reactance X mp represents the transformer magnetizing inductance as referred to the primary coil, and the reactances X p and X s represent the leakage inductance of the primary and secondary coils. For the core, however, effective diagnostic methods are scarce. Figure 5 – Wound Primary Current Transformer (Low ratio, wound primary current transformer, suitable for primary currents from 2. The flux linkage expression of switching on an unload transformer is deduced and influence factors of inrush current are analyzed firstly. User Instructions: Select the number of phases from the drop-down menu; Enter the transformer rating and select the appropriate unit. Inductance L, which is the series. A simple (linear) model of a real transformer which takes into account winding resistance and magnetizing inductance as well as leakage inductances and core losses looks like this: Where there is an ideal transformer Np:Ns. The winding leakage inductance is due to leakage flux not linking with all turns of each imperfectly. The winding loss depends on the RMS current value, the length and the cross-section of the. Looking for online definition of inductance or what inductance stands for? inductance is listed in the World's largest and most authoritative dictionary database of abbreviations and acronyms Inductance - What does inductance stand for?. 6 ?) is assigned to the equivalent circuit portion representing the forward-rotating mmf waves and the other half to the portion representing the backward-rotating mmf waves. The researches done on calculating leakage inductance of a toroidal transformer were rare. The primary inductance (Lp) is 160 µH for 40 turns, and inductance ratios as N 2 so 10 turns will give 10 µH (see appendix). B pk = f(H) Flux density (B) is a non-linear function of magnetizing field (H), which in turn is a function of winding number of turns (N), current (I), and magnetic path length (l e). The Voltage Ripple On The Output Must Be Less Than 1%. I left the secondary open and have an AC voltage on the primary. Design For Continuous Current In The Transformer Magnetizing Inductance. The importance of instrument transformer tests is often underestimated. 28FL (F= frequency, L=henries) to find the reactance in ohms (unless it's a tiny transformer the dc resistance can be ignored). Talati1 Prof. and the core loss resistance R. Although maximum flux will link with both windings through the core of. 25% to about 5% of full load current (0. We still suppose that the nonlinear load is switched-in when the mag-netizing linkage of the transformer magnetizing branch is just crossing zero and this time is regarded as 0 s. 5-MVA, 60-Hz, 4160V/480V (nominal Values, Line-to-line RMS Voltages) Industrial Service Transformer, Both The Primary And Secondary Series Resistance R = R2 = 0. The saturation model of the transformer is shown in Fig. Then the difference of two kinds of phase compensation methods, from star to delta and from delta to star connection, is compared. Your magnetizing inductance is what the transformer actually "uses", so to say, to build the magnetization. Transformers, DC commutator machines, three-phase asynchronous motor, synchronous machines and small appliance motors are treated. Wu are with the Department of Electrical and Computer Engineering, NYU Polytechnic School of. The values indicated are indicative for a particular transformer and the values will vary depending upon the source, material and construction features. transformers. However, too large size goes against circuit. What is the DC bias characteristic of an inductor for power circuits? Inductors (Coils) > Inductors (Coils) > Inductors (Coils) A. Calculate Iop, the minimum primary operating current (primary sensitivity) that causes the relay to operate, as follows: Iop = n • (IR + m• Im + Iv ) (6) Where IR = the relay operating current m = the number of CTs needing magnetization (generally three) Im = the magnetizing current at the set voltage (to be obtained. ) In a “true” transformer (Fig. 8 Linear Transformer (linear magnetizing inductance - potentially unlimited energy storage) 1. An ideal transformer would have an infinite magnetizing inductance. The inductance caused by the effect of flux coupling between two coils is called Mutual Inductance. A transformer is a device made of two or more inductors, one of which is powered by AC, inducing an AC voltage across the second inductor. The configuration of magnetic components for LLC resonant converter is exactly the same as a real transformer with magnetizing inductance. Because the cable is coaxial, in zone 4 the magnetic field is zero. The magnetizing inductance is drastically reduced by the lack of a magnetic core, resulting in large magnetizing currents and losses if used at low frequencies. The capacitor \(C_p\) represents the capacitance between the turns in the primary winding, as does \(C_s\) for the secondary winding. This causes the coupling leakage inductance and coil resistance to appear as zero. (a) With the secondary open circuited and 120 V applied to the primary (120 V) winding, calculate the primary current and the secondary voltage. 9 we know that the magnetizing current is not transferred to the secondary side. LLC Power Stage Design Example: Transformer • Calculate secondary side currents – = × =16×0. Choose The Transformer. Choose The. The magnetizing inductance can vary significantly from one transformer to another due to material variations, temperature and frequency. High and Low Freq Pulse in adjacent pins - Parasitic Capacitance - CROSSTALK - Impulse -Reduced Resistance- Glitches 17. Note that unlike an ideal transformer a real transformer stores energy the energy stored in the transformer is modeled by the magnetizing inductance, and if you ever need to calculate the value of this energy stored in the transformer, you can use the standard formula for energy in an inductor to calculate it. A transformer equivalent circuit has two reactive elements which can both consume vars: there is magnetizing reactance in parallel which you have accounted for. The tap-changer position is set to tap 1, corresponding. Design For Continuous Current In The Transformer Magnetizing Inductance. Regards, Szzuk. The winding leakage inductance is due to leakage flux not linking with all turns of each imperfectly. In this case the capacitor is sized so that LI^2 = CV^2 where I is the peak magnetizing current (for the magnetizing inductance) or total current (for leakage inductance) and V is the peak voltage it is permissible to allow the capacitor to charge to. 6 ?) is assigned to the equivalent circuit portion representing the forward-rotating mmf waves and the other half to the portion representing the backward-rotating mmf waves. With neat circuit diagram, explain the open delta connection in poly phase transformer. Every body is aware. The magnetizing current is in fact the same as the maximum current which we have calculated for a coil. Mutual inductance is where the magnetic flux of two or more inductors are "linked" so that voltage is induced in one coil proportional to the rate-of-change of current in another. Magnetizing Inrush urrent in Transformers results from any abrupt changes of the magnetizing voltage. The Load Resistance Is 20 22. o bypass the inserted resistor after decay. dimensions, complex permeability, number of primary turns to calculate magnetizing admittance as well as magnetizing impedance and inductance. (lower inductance), the output signal may distort or “droop” (in positively sloped unipolar input signal) which may also cause instability in the control circuit and inaccuracies in measurements. The magnetizing inductance is a function of the average magnetic path length in the core. An ideal transformer would have an infinite magnetizing inductance. 2% of magnetizing inductance at 10 kHz, and 0. The response to DC magnetizing force is affected by the level of peak AC flux density present. Faraday's law tells us that a changing magnetic flux will induce an emf in a coil. A gap (560gm) is adjusted to obtain the magnetizing inductance of Lm=24uH needed to obtain Z VS transitions in all the switches. The following equations calculate the minimum magnetizing inductance of the primary of the transformer (T1) to ensure the converter operates in current-modecontrol. Also, a given inductance value will have a higher impedance at higher frequencies. The researches done on calculating leakage inductance of a toroidal transformer were rare. Ll can be calculated using the magnetic coupling coe cient (k). 1 Low Second-Harmonic Content in Transformer Inrush Currents - Analysis and Practical Solutions for Protection Security Steven Hodder, Hydro One Networks, Inc. magnetizing inductance ≅ Vi E i t di fl b k IP •Energy is stored in flyback transformer: Function of L, D and Ts -Secondary diode in blocking state +V i Io •FET turns OFF -During commutation: Leakage energyabsorbedbyclampcircuit 1:n2 Vo a mp I out-- + energy absorbed by clamp circuit IP -Stored energy transferred to output through diode. Make the best transformer you can with tightly coupled windings, measure your prototype, and expect the manufacturer to match it. 55×105 A-t Wb-1. • Magnetizing inductance, L M , represents energy stored in the magnetic core and in small air gaps which arise when the separate core halves forming a closed magnetic loop core come together. To determine the total leakage inductance in fig. is the operating frequency = 50 kHz B is the peak working flux density of the core, at elevated temperature = 200mT Ae is the magnetic cross-sectional area of the core = 180mm2. ” L = V / (di/dt) It is correct if instead of "voltage" it would written “ back- EMF” [back-electromotive force]. The value of the leakage inductance is more constrained because. 2 shows the equivalent circuit of a normal current transformer, in which L is a magnetizing inductance of the current transformer; i m is a magnetizing current; i 2 ′ is a secondary current in accordance with the current transformation rate; and i 2 is an actual measured secondary current. Sketch an equivalent circuit model for the tapped inductor that includes a magnetizing inductance and an ideal transformer. Therefore, the size of pulse transformer will be large. Circuit Equations:Transformer. To overcome such an issue, a method is proposed to distinguish inrush current from inner fault current based on box dimension. The transformer behaves the same regardless of where the leakage inductance, or. A system for identifying magnetizing inductance and rotor resistance of an induction machine comprises an induction machine comprising a rotor and a stator, a DC voltage bus, and a DC-to-AC voltage inverter coupled to the DC voltage bus and to the induction machine. 2) [35 points] A forward converter operating in the continuous conduction mode is to be. Calculate the Magnetizing Reactance, The magnetizing reactance essentially is equal to the no-load reactance. The number of winding turns are selected to give a reasonable magnetizing current while keeping the peak flux density below the saturation point of. A current I 2 is assumed to exist in coil 2 for the purposes of these inductance calculations. The inductive parameters (e. The Inrush Current affects the magnetic property of the core. The self-inductance for coil 2 and the mutual inductance L 12 can also be computed using equation 1. 3At for 75% reduction. Abstract – This paper presents an analytical. Hi, I can do a quick estimate without doing any measurements. Power transformers are a vital part of the modern power grid, and much attention is devoted to keeping them in optimum shape. 2(b) shows the considered MF transformer equiva-lent circuit and the corresponding short-circuit and open-circuit inductances. I2 = Kn I1: secondary current for a perfect CT. Design For Continuous Current In The Transformer Magnetizing Inductance. Stranding level. For the time being one can assume that the power transformer magnetizing and leakage inductance will behave as current sources. On the left there is a blue button which can be used to modify the inductance. Primary inductance (L1) and secondary inductance (L2) can be measured directly by connecting the instrument as shown in Figure 1 and Figure 2. 4 Phasor diagram Modelling of Magnetic Core rc: core loss resistance (hysteresis & eddy-current loss) xm: magnetizing reactance Ie: exciting current Ie Ic Im c c r g 1 m m jx jb 1 Im lags E1 by 90º Ic in phase with E1 gc: core loss conductance gc-jbm: magnetizing admittance bm: magnetizing susceptance Modelling of Leakage Flux dt d v 1 1 Let us express the voltage drop due to leakage flux in. Keywords: variable inductor, induced currents, transformer, switching, saturation, magnetic effect 1 Introduction. • The filter circuit elements like, inductors and capacitors are assumed loss-less. 9 Energy Stored in a Magnetic Field 23. Results from the magnetization of an 80 kVA power transformer, using a directly coupled nonfiltered three-phase voltage-source inverter (VSI), are presented. Electrical Engg. The transformer is the most common application of the concept of mutual inductance. ¶ w u w N! lcore Figure 1. • The transformer used in the circuit is assumed to be ideal requiring no magnetizing current, having no leakage inductance and no losses. The equivalent resistance of transformer referred to the secondary is represented by R 02. The CT should be demagnetized after the completion of winding resistance test. LECTURE 27 Basic Magnetic’ s Issues in Transformers A. Level 1 models an ideal transformer with piecewise linear magnetizing inductance. To calculate full load current, use this formula:. Your magnetizing inductance is what the transformer actually "uses", so to say, to build the magnetization. In the case of a transformer, this current must be calculated as the net current after subtracting any opposing currents, such as primary and secondary ones, giving proper care to the number of turns. General Comments on Transformer Inductance’ s L m and L l (leakage) as well as Transformer resistance’ s The magnetic’ s issues in transformers involve one core and several sets of current carrying coils wound around the core. loaded condition. Performing In-Circuit Inductor and Transformer Measurements in SMPS. 1 Filter inductor design constraints Pcu = Irms 2 R Objective: Design inductor having a given inductance L, which carries worst-case current Imax without saturating, and which has a given winding resistance R, or, equivalently, exhibits a worst-case copper loss of. the transformer. All quantities are in per unit on the transformer base. The importance of instrument transformer tests is often underestimated. A simple (linear) model of a real transformer which takes into account winding resistance and magnetizing inductance as well as leakage inductances and core losses looks like this: Where there is an ideal transformer Np:Ns. In a real transformer there is a leakage inductance in series with the primary and with the secondary windings, due to the fact that the two windings are not perfectly coupled (Figure 2). In terms of inductance so core has inductance with associated inductive reactance Define above as the magnetizing inductance with associated magnetizing reactance X m No-Load Circuit Model Lesson 8_et332b. Magnetizing Currents in Power Transformers - Measurements, Simulations, and Diagnostic Methods. Question: Q1 [40 Marks (a) A Flyback Converter Produce An Output Of 32 V From An Input Of 24 V As Shown In Figure Q1. So here is how I thought about it :- formulae = H = NI/l N = 1. secondary impedances of 0. The Minimum Current In The Magnetizing Inductance Should Be 20% Of The Average Current. Isolation Transformer 18. 414 between. A Forward converter operating in a Continuous-Conduction Mode with a demagnetizing winding (N3=N1) is chosen. PAPER 1 3E1645 J. The inductance of the entire (N1+N2) turn winding is L. If we change the transformer design to have better magnetic coupling between the primary and secondary coils, the figures for voltage between primary and secondary windings will be much closer to equality again:. The algorithm based on equivalent instantaneous inductance can reflect the essential characteristic of the traction transformer operating conditions and correctly distinguish magnetizing inrush and sympathetic. 1, and monitor on an oscilloscope. The magnetizing inductance is calculated by L m = N2 p 2( R c a +R c b +R c c)+ R ag a +R ag b. Transformers, DC commutator machines, three-phase asynchronous motor, synchronous machines and small appliance motors are treated. For three-legged Y-YG core type transformers, due to the high reluctance of zero-sequence magnetic return path, the zero-sequence magnetizing impedance is low. Calculate this based on the magnetic field, determined above. Step down Voltage Transformer Number of primary turns > Number of secondary turns Primary voltage > Secondary voltage. Calculating a ferrite core transformer is actually quite simple, if you have all the specified parameters in hand. The leakage inductance referred to the primary side can be calculated by the energy stored in the magnetic field, 11 2 22 kp V E B HdV L I ³ (1) where V is the total effective volume and I p is the current in the primary winding. Transformer calculator NOTE: If you need assistance with circuit protection devices such as fuses or breakers, or wire sizing, please consult a licensed electrical contractor or electrician in your area who will be familiar with state and local codes. large capacity transformer has an iron core and a coil in a tank and the medium and low capacity transformer has a molded coil. Microwave Transformers The microwave oven transformer is possibly one of the simplest methods of making some big high voltage arcs, mainly because they are robust, cheap, and easy to hook up. Assume all components to be ideal except for the presence of transformer demagnetization inductance. The response to DC magnetizing force is affected by the level of peak AC flux density present. The magnetizing inductance increases the insertion loss at low frequencies and degrades the return loss. The formula is based on the solution of Maxwell's equations for coils on ferromagnetic cores and as such offers the ultimate in accuracy. In AC circuits,. The phasor equivalent circuit uses the equivalent impedances of the inductances. 1, and monitor on an oscilloscope. 3 Saturation Model of the Transformer In this model, L is the. 1 Answer to Show transcribed image text 4. 5-MVA, 60-Hz, 4160V/480V (nominal Values, Line-to-line RMS Voltages) Industrial Service Transformer, Both The Primary And Secondary Series Resistance R = R2 = 0. The formula in the body of the graph is used to calculate the DC Magnetizing Force in oersteds. With both switches open, there cannot be any primary or secondary currents flowing. As a result, the resonant period is longer than the turn-on period of each of the switches in the primary circuit. A current transformer can be modeled as a constant current source where ratio current is injected into a magnetizing impedance in parallel with the burdens shown in Figure 1. Inductance, L is actually a measure of an inductors "resistance" to the change of the current flowing through the circuit and the larger is its value in Henries, the lower will be the rate of current change. The total self-capacitance of the planar windings seen on the primary side is measured to. Mutual inductance of two coils that are 100% coupled (like a perfect transformer) is: - Given that primary magnetizing inductance is L1, M can equal L1 when L1 = L2. The calculated flux density is then compared to the capability of the steel used in the core of the CT and a determination is made whether the core will saturate or not for that fault current. Required inductance L, core size, and core nominal inductance (A L) are known. to determine transformer core loss in high frequency SMPS is proposed, which is suitable for core loss measurement under PWM excitation, with or without a DC bias. As this figure shows, the magnetizing branch (LMAG) is located at one end of the winding [7]. Inductance Formulae Inductance of a certain number of turns on a ferrite core can be calculated by using the AL value found in the datasheet which is given in nano-Henries-per-turn-squared or nH/N^2. 6 ?) is assigned to the equivalent circuit portion representing the forward-rotating mmf waves and the other half to the portion representing the backward-rotating mmf waves. The saturation model of the transformer is shown in Fig. specs and simulations. Magnetics Designer produces a complete transformer or inductor design based upon electrical specifications, including a winding sheet report and a. We construct the vector diagram of a transformer, calculate the magnetizing inductance, determine the energy losses (copper and iron losses) and draw as a result a T-equivalent circuit for a transformer. 3, the ideal transformer can be moved out to the right or to the left of the equivalent circuit by referring all quantities to the primary or secondary, respectively, as shown in Fig. Transformer number of turns calculator. Jurado2 1 Department of Electrical Engineering University of Jaén Campus of Lagunillas - 23071 Jaén (Spain) e-mail: [email protected] Many technical questions regarding PLECS are answered on the Technical Solutions page of our website. frequency response of the transformer and it has its physical origins in the finite magnetizing inductance in the coils. 2k½ is selected. But we stated earlier that the power into a transformer is equal to the power out of the transformer, therefore the efficiency equals 100%. The transformer winding formula only holds true when the angles of primary and secondary windings are in phase with one another. Talati 2Prof. We construct the vector diagram of a transformer, calculate the magnetizing inductance, determine the energy losses (copper and iron losses) and draw as a result a T-equivalent circuit for a transformer. No-load losses are caused by the magnetizing current needed to energize the core of the transformer. Also, a given inductance value will have a higher impedance at higher frequencies. ) In a “true” transformer (Fig. The magnitude of the inrush current depends on the point on the AC wave the transformer is switched on. Therefore, the value of inductance is known for the next design step. 12 where , , , and are equivalent resistance, leakage inductance of transformer, core losses resistance, magnetizing inductance and source resistance respectively. 28FL (F= frequency, L=henries) to find the reactance in ohms (unless it's a tiny transformer the dc resistance can be ignored). R PLOSS is the core loss component representing energy dissipated by the core as it is magnetized and de-magnetized. Two coils have a mutual inductance of 1 henry when a current change of 1 ampere per second in either coil induces 1 volt in the other one. ½ ½ A standard resistor of 33. Because of the resistance, eddy current and hysteresis there are no losses in the transformer. Energy is expressed in Joule (J). The gap length, magnetizing inductance, and turns count of a transformer or inductor are interrelated. The simplified equation often used to calculate the peak value of the first cycle of inrush current in Amps is as follows: ( ) ⋅ + − ⋅ + = N N R S pk B B B B L R U I 2 2 ω 2 2 [Amps] Equation [1] Where: U = Applied voltage, Volts L = Air core inductance of the transformer, Henry R = Total DC resistance of the transformer windings, Ohms. 4 H referred to the HV side. (b) DIm = Im, max - Im, min is set equal to 0. Another DCM advantage is that the design eliminates D1 reverse-recovery losses in standard rectifiers, since the current is zero at the end of t2. For this reason, the transformer should have the highest possible main inductance. By increasing the ampere- turns you increase the magnetizing force. Magnetizing inrush current in transformer is the current which is drown by a transformer at the time of energizing the transformer. To calculate KVA, use this formula: KVA = Volts x Amps x 1. Calculator. Transformer Magnetizing Inductance and Turns Ratio. 41 17 ×× × × = × µ× × × == Calculate the required transformer turns ratio (k) using the expressions as follows: s OUT D NEW p NEW IN(MIN) s p N (V V ) (1 D ) k N D V. Design For Continuous Current In The Transformer Magnetizing Inductance. If you have a loop of wire, and apply 1 Volt to the loop during 1 second, the magnetic flux in the loop will change by 1 Weber. For this reason an inductance tolerance is imposed; it is transformed into a maximum magnetizing force requirement by use of manufacturer curves simi- lar to those in Figure 1. The very high saturation region of the iron core magnetizing characteristic is modified with the accurate measurement of the air-core inductance. This causes the coupling leakage inductance and coil resistance to appear as zero. A transformer draws inrush current that can exceed saturation current at power up. As a result, the resonant period is longer than the turn-on period of each of the switches in the primary circuit. 2) [35 points] A forward converter operating in the continuous conduction mode is to be. For example if we neglect the resistance in the winding, a short circuit on the secondary side (i. It consists of an ideal transformer and an ideal inductor (which equals the magnetizing inductance Lm). A system for identifying magnetizing inductance and rotor resistance of an induction machine comprises an induction machine comprising a rotor and a stator, a DC voltage bus, and a DC-to-AC voltage inverter coupled to the DC voltage bus and to the induction machine. and the core loss resistance R. The Voltage Ripple On The Output Must Be Less Than 1%. An ideal transformer would have an infinite magnetizing inductance. This quick-start calculator helps streamline the selection and optimization of transformer turns ratios, magnetizing inductance and winding resistance parameters. A Discussion on Power Transformer Magnetizing Inrush, Remedy, Fault Detection in Matlab–Simulink Environment J. In this model, the magnetizing inductance of the transformer is the dominant reactive element. At low temperature, low-frequency insertion loss tends to increase because of decreasing permeability of the magnetic core. ψ = ψ s + ψ σ + ψ m , where ψ s , ψ σ and ψ m are cre-. DC can reduce the inductance in the windings, it is best to avoid a DC magnetizing component DC-saturation (how to measure DC saturation in a ferrite core). The primary winding refers to the powered inductor, a circuit element that induces a magnetic. Magnetizing inrush current can lead to the maloperation of transformer differential protection. The inductance at 15A will decrease the inductance by 54% compared with at 0A. I left the secondary open and have an AC voltage on the primary. , the magnetizing and leakage inductances observed from each side, as discussed in the next section. Problems of transformer, snubber and freewheeling design of push pull DC-DC converter using SG3525 by magnetizing inductance and magnetizing current? does it also need to be discharged? And if so, should I use a freewheeling diode (fast Problems of transformer, snubber and freewheeling design of push pull DC-DC converter using SG3525. Calculate the inductance using a mathematical formula. 5 term within the denominator comes from half the switching frequency of the output inductor (the operational frequency of the transformer) and is better linked to fs rather than the output ripple inductor current - please correct me if wrong. Introduction: There are various Test required on Transformer to conform performance of Transformer. The frequency response analysis (FRA) of the transformer impedance is known as a diagnosis method for the damages in a transformer [1]. Mathematically, the A L has the SI unit henry (H), but the the relationship to inductance is non-linear and the practical unit is nanohenry per square turn or nH/turn 2. It also removes any dc offset and uses averaging to calculate the inductance value. At higher frequencies, the capacitiveeffect between windings (C W) and between the turns of each winding (C P and C S) also become important. (ii) Assuming the snubber resistance is not equal to zero (assume the stray inductance is equal to the transformer magnetizing inductance Lm, input voltage is 24 V, Irr= 9x10-14 A, Lm=6 mH, and Cs=470F); calculate the energy losses in the snubber circuit resistor Rs. This quick-start calculator helps streamline the selection and optimization of transformer turns ratios, magnetizing inductance and winding resistance parameters. The Load Resistance Is 20 12. A transformer equivalent circuit has two reactive elements which can both consume vars: there is magnetizing reactance in parallel which you have accounted for. The safety code is giving one some minimum safety requirements that you may exceed, if you are concerned with the transformer safety and lifecycle. 9 Mutual inductance. The Voltage Ripple On The Output Must Be Less Than 1%. 1 Low Second-Harmonic Content in Transformer Inrush Currents - Analysis and Practical Solutions for Protection Security Steven Hodder, Hydro One Networks, Inc. The CT should be demagnetized after the completion of winding resistance test. Calculate the primary current and power factor when secondary current is 280 A at power factor 0. The next step is to calculate the coaxial transformer magnetizing inductance. The setup of the experiment is shown in Figure 12. A current I 2 is assumed to exist in coil 2 for the purposes of these inductance calculations. Since 1994, Ametherm has provided the most reliable and effective inrush current limiting solutions available. Design For Continuous Current In The Transformer Magnetizing Inductance. 1/80 A) is selected. to determine transformer core loss in high frequency SMPS is proposed, which is suitable for core loss measurement under PWM excitation, with or without a DC bias. Inductance Formulae Inductance of a certain number of turns on a ferrite core can be calculated by using the AL value found in the datasheet which is given in nano-Henries-per-turn-squared or nH/N^2. Design For Continuous Current In The Transformer Magnetizing Inductance. E: induced electromotive force. I would argue that you, in principle, would want the magnetizing inductance to be as big as possible, because it would mean that the transformer is as ideal as possible. CHALLENGES OF FLYBACK CONVERTER TO HIGH POWER Transformer with relatively large energy storage is always a challenge. A simple (linear) model of a real transformer which takes into account winding resistance and magnetizing inductance as well as leakage inductances and core losses looks like this: Where there is an ideal transformer Np:Ns. Choose The. But we stated earlier that the power into a transformer is equal to the power out of the transformer, therefore the efficiency equals 100%. L1/L2=(N1/N2)^2. However, too large size goes against circuit. I attached the equivalent circuit of the transformer. The first parameter to be simulated is the magnetizing inductance. This happens even if the transformer has no load with its secondary open. The most common application of mutual inductance is the transformer. As a part of that process, it is important to establish proper testing procedures in order to maintain efficient production. magnetizing inrush current wav eforms considering transformer connections wye-wye and wye-delta, and how to estimate the residual ﬂ ux needed to calculate the correct ﬂ ux-current curve. I am learning about transformers and in the equivalent circuit the magnetizing inductance of the excitation branch is supposed to represent the current needed to "set up" the flux in the core due to finite permeability of iron. The Voltage Ripple On The Output Must Be Less Than 1%. For three-legged Y-YG core type transformers, due to the high reluctance of zero-sequence magnetic return path, the zero-sequence magnetizing impedance is low. 63 cm^2 Ic= 11. Equivalent circuit of induction motor. M=sqrt(L1 L2) assuming the coupling is 1. It is copper shielded for very low EMI, and it packaged as a surface mount device. Claes Carrander. The primary inductance of an AC transformer determines the magnetizing current. The figure below shows the magnetizing line as the inductor Lm is varied from 10 uH to 40 uH. For the present application, the switching frequency is selected as 150kHz. This current in transformer may be caused by energizing an unloaded transformer, occurrence of an external fault, voltage recovery after clearing an external fault and out-of phase synchronizing of connected Generator. Figure 47 The number of turns and the thickness of airgap vs. The Inrush Current affects the magnetic property of the core. Choose The. Mutual inductance is where the magnetic flux of two or more inductors are "linked" so that voltage is induced in one coil proportional to the rate-of-change of current in another. Equivalent Circuit. Faraday's law tells us that a changing magnetic flux will induce an emf in a coil. Power Factor Definition : Power factor is the ratio between the KW and the KVA drawn by an electrical load where the KW is the actual load power and the KVA is the apparent load power. There is also leakage reactance in series which absorbs a load-dependent quantity of vars that you have not accounted for. This is the ideal case. magnetizing inductance and large leakage inductance comparing with a closely conventional transformer. The number of winding turns are selected to give a reasonable magnetizing current while keeping the peak flux density below the saturation point of. 85µH at nominal switching frequency and R1 = 19mΩ. The magnetizing inductance increases the insertion loss at low frequencies and degrades the return loss. 55×105 A-t Wb-1. The parallel inductance, XM, called the magnetizing inductance, accounts for the finite permeability of the magnetic core. In order to model the nonlinear behaviour of the core, voltage dependence of an equivalent inductance and resistance shall be also included. The switch turns on to decrease the equivalent magnetizing inductance so as to obtain the high voltage gain. Using the same procedure, as before, the magnetizing inductance observed from the secondary side was calculated, leading to the same result. 6 (µH) = 143. Transformers, DC commutator machines, three-phase asynchronous motor, synchronous machines and small appliance motors are treated. The magnetizing inductance is drastically reduced by the lack of a magnetic core, resulting in large magnetizing currents and losses if used at low frequencies. Because the cable is coaxial, in zone 4 the magnetic field is zero. The coupling coefficient is the ratio of the mutual inductance to the square root of product of primary and secondary self inductances:. the return conductor is some considerable distance away. Thus, in-circuit measurements of inductors and transformers, made under operating conditions, can provide important information. All quantities are in per unit on the transformer base. DC to DC Transformer (no magnetizing inductance - no energy storage) The transformer winding subcircuits are DC coupled and, when connected to a "core" (1TΩ in parallel with 1pF) that supports DC without drawing current, they combine to make a transformer that draws no magnetizing current, stores no energy and therefore is immune to errant. The magnetizing inrush and the sympathetic inrush may cause the malfunction or operating delays of differential protection for traction transformers, and affect their normal operation. 95 is reasonable. 3At for 75% reduction. Bogdan Kasztenny, Normann Fischer, and Yu Xia, Schweitzer Engineering Laboratories, Inc. 2% of magnetizing inductance at 10 kHz, and 0. The Load Resistance Is 20 12. Quality control is an integral part of any manufacturing process. • Magnetizing inductance, L M , represents energy stored in the magnetic core and in small air gaps which arise when the separate core halves forming a closed magnetic loop core come together. I presume the 0. L m is equivalent magnetizing inductance. During the. inductance requirements. Hi, I can do a quick estimate without doing any measurements. Solution: Answer for (i) Maximum value of flux in the core,. magnetizing inrush current (IC) with high amplitude. The Minimum Current In The Magnetizing Inductance Should Be 20% Of The Average Current. L1/L2=(N1/N2)^2. For more information on our transformers, baluns, ununs and isolators, click here Baluns Transformer, Audio, Cable, 10 Hz, 50 kHz, 600ohm, 1 dB. Compare with the energies calculated based on the inductance and the maximum currents. BVM Engineering College, Anand-388120. Leakage inductance Magnetizing inductance Detailed Models of Transformer (1-k2)L1 k2L1 K:1 K>0. Well i think you can ignore the primary inductance for now and start with the transformer equation for square waves: B=E*10^8/ (4*F*A*N). The clamp diode is used to clamp the voltage spike across the. The next step is to calculate the coaxial transformer magnetizing inductance. Now without disturbing the source at coil 2, we connect a time varying current source across the coil 1. The following equations calculate the minimum magnetizing inductance of the primary of the transformer (T1) to ensure the converter operates in current-modecontrol. The value of the leakage inductance is more constrained because. The second link [coil calculator] describes so the inductance: “The inductance of a coil is the property which describes the relation between the voltage across the coil, and the change of current through the coil. The characteristic of the nonlinear magnetizing branch of the three saturable-type transformers can be given in the Characteristic tab of the component dialog box. Overview 1. 9 Mutual inductance. According to the fundamental difference in waveform between the two, the algorithm can extract the three-phase current and calculate its box dimensions. 5-MVA, 60-Hz, 4160V/480V (nominal Values, Line-to-line RMS Voltages) Industrial Service Transformer, Both The Primary And Secondary Series Resistance R = R2 = 0. The flux linkage expression of switching on an unload transformer is deduced and influence factors of inrush current are analyzed firstly. In this paper, the total. Electrical Engg. Label the values of the magnetizing inductance and. The frequency response analysis (FRA) of the transformer impedance is known as a diagnosis method for the damages in a transformer [1]. de León, and N. A transformer turns ratio is the division of the number of turns in the primary winding by the number of turns in the secondary winding by the equation T R = N p /N s. These devices have to first create the necessary magnetic field in order to be able to work. As has been stated by Rohat Kılıç xL (Reactive Resistance) = (2 x pi) x frequency(f) x inductance(l) However it is not as simple as that, as a transformer represents a tuned circuit as shown in the representative diagram Rohat Kılıç has shown. This is the ideal case. Raman College of Engg. 1 Magnetic flux quantum = 2,06783460999999E-15 volt second [V·s] De :. Transformer winding consists Copper and copper losses are occurs in winding due to current(I). (a) Calculate N1/N2. By analyzing some forward reasoning application mechanisms of the Pro/3, this work had also created a transformer fault diagnosis knowledge base rule model based on dissolved gas analysis in transformers such that using the rules of sentence in model had implemented an expert system of transformer fault diagnosis. The most straightforward method of measuring the magnetizing inductance is by using an inductance meter, but a function generator, resistor, and oscilloscope can also be used. 2 Add a resistance of 1e6 in parallel to both the switch and the diode in the tertiary winding, as. The capacitor \(C_p\) represents the capacitance between the turns in the primary winding, as does \(C_s\) for the secondary winding. That means, flux wave will reach its maximum value, 1/4. An ideal transformer would have an infinite magnetizing inductance. The tap-changer position is set to tap 1, corresponding. 55×105= 2200 nH per turn2. Method 1 – Determine B pk from DC Magnetization Curve. Self-inductances and mutual inductances can be detected in. The equivalent resistance of transformer referred to the secondary is represented by R 02. Higher ratios indicate a weaker source, or the transformer is further from the substation. Problems of transformer, snubber and freewheeling design of push pull DC-DC converter using SG3525 by magnetizing inductance and magnetizing current? does it also need to be discharged? And if so, should I use a freewheeling diode (fast Problems of transformer, snubber and freewheeling design of push pull DC-DC converter using SG3525. 4 H referred to the HV side. supply is short-circuited. By applying the same metho- dology described to obtain the leakage inductance, the magnetizing inductance can be theoretically determined by 2 4 3 ln, 2. By increasing the ampere- turns you increase the magnetizing force. • For the simplified steady-state analysis of the circuit the switch duty ratio (δ), as defined. I attached the equivalent circuit of the transformer. And The Leakage Inductance L1 = L2 = 0. This inductance is a function of the core permeability, cross sectional area and number of windings around the core. We can find the magnetizing and iron loss current using above equations now we will solve a math. It should be noted that the voltage drop of the magnetizing branch of transformer core in equation (1) has been considered as follow: m m m d(t) d(t)di (t) v(t) dt di (t) dt OO (2). • Calculate transformer voltage regulation and efficiency. L [H] Transformer magnetizing inductance L sc [H] Short circuit inductance of network L' s [H] Saturation inductance L s [H] L sc + L ' s L' m [H] Magnetizing inductance below the knee point L m [H] L sc + L ' m S. 06 H on 60 Hz? Calculate to one decimal place. This paper focus on analysis, optimum design results of the winding contactless transformer using resonant converter. It also determines the turns ratio and type of transformer. 53uF capacitor and the primary is excited with \$10V_{RMS}\$ at 1kHz: - Conclusion, adding a load of any description does not affect the primary magnetizing inductance of a transformer. Another DCM advantage is that the design eliminates D1 reverse-recovery losses in standard rectifiers, since the current is zero at the end of t2. The Ampere-turns in the sec-ondary winding, resulting from load current, are. In the case of the pulse transformer, the shunt inductance causes the top of the pulse to droop, because, during the pulse, the magnetizing current in Lp. Winding resistance, leakage inductance, topologically correct core, capacitance. A current I 2 is assumed to exist in coil 2 for the purposes of these inductance calculations. H is the inductance in henry, while A refers to the amount of ampere magnetizing the core. Question: For A 1. A transformer is a device made of two or more inductors, one of which is powered by AC, inducing an AC voltage across the second inductor. Faraday's law tells us that a changing magnetic flux will induce an emf in a coil. AC converter with the resonance transformer. The formula method uses the fundamental transformer equation to calculate the effective flux density for a particular value of fault current. (7) For the example of application 3 this suggests a value of 2. Energy is expressed in Joule (J). The transformer shown diagrammatically in Fig. We construct the vector diagram of a transformer, calculate the magnetizing inductance, determine the energy losses (copper and iron losses) and draw as a result a T-equivalent circuit for a transformer. Power transformers are a vital part of the modern power grid, and much attention is devoted to keeping them in optimum shape. Your magnetizing inductance is what the transformer actually "uses", so to say, to build the magnetization. Required inductance L, core size, and core nominal inductance (A L) are known. The magnetizing inrush and the sympathetic inrush may cause the malfunction or operating delays of differential protection for traction transformers, and affect their normal operation. The Load Resistance Is 20 12. Duty Cycle D = 0. With neat circuit diagram, explain the open delta connection in poly phase transformer. The major benefits of this topology are reduction in switching filter size as well as filter losses. B pk = f(H) Flux density (B) is a non-linear function of magnetizing field (H), which in turn is a function of winding number of turns (N), current (I), and magnetic path length (l e). This transformer calculator helps you to quickly and easily calculate the primary and secondary full-load currents of the transformer. In [5], a method is proposed to calculate transformer copper loss by measuring winding AC resistance for each harmonic in the PWM current. This is usually referred to as the induced electromotive force (emf). Apply a pulse to the primary winding with all other windings open circuited as shown in Fig. magnetizing inductance This equation determines the minimum required primary winding magnetizing inductance (see LP in [4]) that is needed in order the transformer low roll-off frequency was as required provided the source and the load impedances are strictly defined. To the bottom left I have a picture of an MOT. Two coils have a mutual inductance of 1H when an emf of 1V is induced in one coil by current changing at the rate of 1 A/s in the other coil. Self and Leakage Inductance Method • Coupling measurements are made for each pair of windings • Measure the self inductance of each winding (L11 and L22) • The inductance measured at a winding when another winding is shorted is called the leakage inductance L leakqr = inductance measured at winding q when winding r is shorted 11 12 12 1 L. Electrical Engg. 4, a view of the coaxial cable with the magnetic field profile is shown. The formula for calculating the magnetomotive force is: Where. Question: Q3: Flyback Converter With Two Winding Inductor Consists Of An Ideal Transformer And An Ideal Inductor (which Equals The Magnetizing Inductance Lm). 9 we know that the magnetizing current is not transferred to the secondary side. Step 6: Primary Inductance. This current in transformer may be due to switching unloaded transformer, external fault, and voltage recovery after fault and out of phase synchronizing of connected generator. The value of the leakage inductance is more constrained because. The magnetizing inductance of a line frequency transformer so that the magnetizing current is small. Level 1 models an ideal transformer with piecewise linear magnetizing inductance. 1(b) before is closed, we can calculate the steady-state magnetizing linkages of the inductances on each branch. ATPDraw connects the inductances in Y or D dependent on the selected connection for actual winding for a 3-phase transformer. Design For Continuous Current In The Transformer Magnetizing Inductance. If you have a loop of wire, and apply 1 Volt to the loop during 1 second, the magnetic flux in the loop will change by 1 Weber. current factors based on transformer full-load-to-available-fault-current ratios. Mutual inductance is where the magnetic flux of two or more inductors are "linked" so that voltage is induced in one coil proportional to the rate-of-change of current in another. Using a reactance to represent the magnetizing leg of a ct, as shown in Figure 1, is a useful visual concept. A 3D model (Fig. Wu are with the Department of Electrical and Computer Engineering, NYU Polytechnic School of. Re: Magnetizing current of a Current transformer It's just the voltage on the secondary divided by the impedance of the magnetizing inductance (so it's dependent on frequency, as well as the burden resistance). The task of core loss calculation is to determine B pk from known design parameters. Fly-back transformer Design July,2016 DT_Fly-Back_transformer AN-174E Rev10 7/8 Step-13: Calculate current (at rated output) fsw D Ton Vr Vdc Vr D (min) Obtain the current value at the rated output or at the maximum output Obtain the currents at the primary and secondary sides for a rough guide of coil material to be used for the transformer. INDUCTANCE Inductance is the circuit property that opposes any change in current. The magnitude of the initial peak magnetizing current, which is a function of residual flux and energizing voltage, can have an equivalent rms value many times greater than the full-load rating of the transformers. The magnetizing current is in fact the same as the maximum current which we have calculated for a coil. • Develop transformer equivalent circuits from open-circuit and short-circuit test data. By analyzing some forward reasoning application mechanisms of the Pro/3, this work had also created a transformer fault diagnosis knowledge base rule model based on dissolved gas analysis in transformers such that using the rules of sentence in model had implemented an expert system of transformer fault diagnosis. Choose The. de León, and N. The model is shown in Fig. This causes the coupling leakage inductance and coil resistance to appear as zero. On the secondary there is a 2. Calculate the inductance using a mathematical formula. Many translated example sentences containing "magnetizing inductance" non-linearity of the motor inductance with reducing magnetizing current by increasing speed [] during field-weakening. Inductance and Excitation Current The current transformer’s secondary inductance will determine the fidelity of the output signal. The last entry in the K statement is the coupling coefficient, which can vary between 0 and 1, where 1 represents no leakage inductance. 100 mH) X (8² Amps) = 6. LLC Resonant Converter for Battery Charging Application G. The transformer works on the principle of mutual inductance and Faraday’s law of electromagnetic induction. (e) Find vsw during Toff. Magnetizing Inrush urrent in Transformers results from any abrupt changes of the magnetizing voltage. 4 the calculation of the magnetic field in zones 1 to 4 is necessary. E: induced electromotive force. Transformers, DC commutator machines, three-phase asynchronous motor, synchronous machines and small appliance motors are treated. Although maximum flux will link with both windings through the core of. Transformer data is often not available in this format. The reactance X mp represents the transformer magnetizing inductance as referred to the primary coil, and the reactances X p and X s represent the leakage inductance of the primary and secondary coils. On the example of a flyback type DC/DC converter, this tutorial shows how flyback transformers can be pareto-optimally designed. Inrush currents are unsymmetrical, contains harmonics and de component. Use the formula L = R * sqrt(3) / (2 * pi * f). magnetizing inrush current wav eforms considering transformer connections wye-wye and wye-delta, and how to estimate the residual ﬂ ux needed to calculate the correct ﬂ ux-current curve. How to Calculate Ferrite Core Inverter Transformer. Inductance, L is actually a measure of an inductors "resistance" to the change of the current flowing through the circuit and the larger is its value in Henries, the lower will be the rate of current change. • The transformer used in the circuit is assumed to be ideal requiring no magnetizing current, having no leakage inductance and no losses. Odulio, Member, IEEE, Miguel T. The magnetizing inductance L is not a constant. transformers. Re: Magnetizing current of a Current transformer It's just the voltage on the secondary divided by the impedance of the magnetizing inductance (so it's dependent on frequency, as well as the burden resistance). To overcome such an issue, a method is proposed to distinguish inrush current from inner fault current based on box dimension. 1 1 0 0i Ts 1 dt di i q Ts 1 dt di + ⋅= + ⋅ (4) where Ts = (L0+ L2)/R2≈ L0/R2is the secondary time constant of the CT q = L2/(L0+ L2) ≈ L2/L0is the ratio of inductances. Where: L is the inductance in Henries, V L is the voltage across the coil and di/dt is the rate of change of current in Amperes per second, A/s. Calculate: • Primary magnetizing inductance • The magnetizing (inductive) current at full nominal input voltage • The power consumed at full input voltage but no load • Core loss equivalent resistance referred to the primary from your secondary drive meas- urements 0. Step 6: Primary Inductance. The formula method uses the fundamental transformer equation to calculate the effective flux density for a particular value of fault current. The Voltage Ripple On The Output Must Be Less Than 1%. Wu are with the Department of Electrical and Computer Engineering, NYU Polytechnic School of. Well i think you can ignore the primary inductance for now and start with the transformer equation for square waves: B=E*10^8/ (4*F*A*N). Transformer transmit high electrical energy so reduce the unite of voltages level engineers used kilo(K) unit for transformer. Required inductance L, core size, and core nominal inductance (A L) are known. Calculate the Magnetizing Reactance, The magnetizing reactance essentially is equal to the no-load reactance. 4Transformer with an air gap in the core In some applications, there is a need for an air gap in transformer cores. • "Recycles" transformer magnetizing energy. Escoto, Jr. Primary inductance (L1) and secondary inductance (L2) can be measured directly by connecting the instrument as shown in Figure 1 and Figure 2. Recall from part 1 of this article series that leakage inductance in the transformer model can be referred to the primary, secondary, or both. The peak of the inrush current is found to be as high as 10 times that of the rated current of the transformer lasting for a few cycles. In the transformer equivalent circuit of Fig. I am trying to determine the primary magnetizing inductance + core shunt resistance of a transformer. PAPER 1 3E1645 J. 95 is reasonable. Current transformers play an important role in the monitoring and protection of electrical power systems. This current in transformer may be due to switching unloaded transformer, external fault, and voltage recovery after fault and out of phase synchronizing of connected generator. Also, (t) and im(t) are the flux linkage and magnetizing current, respectively. (ii) Assuming the snubber resistance is not equal to zero (assume the stray inductance is equal to the transformer magnetizing inductance Lm, input voltage is 24 V, Irr= 9x10-14 A, Lm=6 mH, and Cs=470F); calculate the energy losses in the snubber circuit resistor Rs. Overview 1. Like self-inductance, mutual inductance is measured in Henry (H). inductance values. 10 Mutual Inductance For transformers and other coupled coils the effect of the magnetic field generated by the secondary (and other) coils on the primary coil must also be considered. • Copper (winding) losses. The inductance of the entire (N1+N2) turn winding is L. With the permeability of the core decreased, the inductance of the coil decreases. Re: Magnetizing current of a Current transformer It's just the voltage on the secondary divided by the impedance of the magnetizing inductance (so it's dependent on frequency, as well as the burden resistance). An ideal transformer would have an infinite magnetizing inductance. This paper focus on analysis, optimum design results of the winding contactless transformer using resonant converter. 2 shows the equivalent circuit of a normal current transformer, in which L is a magnetizing inductance of the current transformer; i m is a magnetizing current; i 2 ′ is a secondary current in accordance with the current transformation rate; and i 2 is an actual measured secondary current. The energy stored in the. 8 lagging, 1. But for the maximum coil current we calculated the peak value, in for the transformer magnetizing current we calculate the RMS value, so there is a factor 1. In the equivalent circuit of a real transformer, mutual inductance appears in parallel with the primary windings only. (i) Draw the equivalent circuit after the snap-off of the switch. Getting Started - Design of a Flyback Transformer GeckoMAGNETICS is a tool that enables fast, accurate and user-friendly modelling and pareto-optimal design of inductive power components. The magnetizing inductance is drastically reduced by the lack of a magnetic core, resulting in large magnetizing currents and losses if used at low frequencies. Step down Voltage Transformer Number of primary turns > Number of secondary turns Primary voltage > Secondary voltage. The inductance caused by the effect of flux coupling between two coils is called Mutual Inductance. As the drive level needed at the secondary side (on the receiver of the XTR40010) is the same as the drive level of the primary side, i. Σl/A= le/ Ae= 27. When an electrical power transformer is switch on from primary side, with keeping its secondary circuit open, it acts as a simple inductance. Keywords: variable inductor, induced currents, transformer, switching, saturation, magnetic effect 1 Introduction. In this paper, a novel method is proposed to determine the residual flux based on the relationship between residual flux and the measured magnetizing inductance. During the. transformer in order to achieve zero voltage switching (ZVS) over a wide load range and a wide battery voltage variation. A single-phase 60-Hz transformer has a nameplate voltage rating of 7. To determine the total leakage inductance in fig. 6 (Oe) The inductance at 15A will decrease the inductance by 54%. Then the difference of two kinds of phase compensation methods, from star to delta and from delta to star connection, is compared. V 2 = 0) causes a current to flow (assuming aL 12 >> L 2). The clamp capacitor (C10) helps in resetting the flux in the transformer core as well as helps absorb leakage inductance energy, and forms a complex pole-zero pair with the magnetizing inductance (L MAG) of the transformer, at a frequency f R. The primary inductance of an AC transformer determines the magnetizing current. To determine inductance, scope-based power-analysis software integrates the voltage over time and divides by the change in current. Notes Pulse Inductance may be determined by measuring magnetizing current. Stranding level. Furthermore, based on this approximation, a fast analytical calculation of the flyback converter with saturable magnetizing inductance is presented. Jurado2 1 Department of Electrical Engineering University of Jaén Campus of Lagunillas - 23071 Jaén (Spain) e-mail: [email protected] (a) With the secondary open circuited and 120 V applied to the primary (120 V) winding, calculate the primary current and the secondary voltage. Rather than specifying the air gap length, the equivalent quantity AL is used. Current transformers play an important role in the monitoring and protection of electrical power systems. 85µH at nominal switching frequency and R1 = 19mΩ. The inductance at 15A will decrease the inductance by 54% compared with at 0A. In literature [13], a capacitor is connected in series with the magnetizing inductance. The next step is to calculate the coaxial transformer magnetizing inductance. This transformer calculator helps you to quickly and easily calculate the primary and secondary full-load currents of the transformer. de León, and N. The figure below shows the magnetizing line as the inductor Lm is varied from 10 uH to 40 uH. The formula method uses the fundamental transformer equation to calculate the effective flux density for a particular value of fault current. 2 10 1 L C D f MAG MAX R × × − = π. Stranding level. In the case of a transformer or inductor, the air gap only reduces the slope of the B/H loop, reducing permeability and inductance, and hence increasing the magnetizing current in the primary.