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The mgnetic inrush current is the current drawn by the transformer when power is applied to the primary winding
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An uncharged capacitor acts like a short circuit when voltage is first applied to it?
Yes it does. Capacitors and capacitor banks have a high inrush current when first energized. As an example this is the reason that VFD's place a resistor in series with the capacitors for a short period of time when they are first energized to prevent damage to the rectification componente. They call it a precharge circuit. Current leads voltage by 90 deg in a purely capacitive circuit.
How capacitor introduces phase difference of 90 between voltage and current?
When you turn on a switch between a battery and capacitor, there is an inrush of current, but we measure zero volts across the cap because it is effectively shorted at this instant. As the cap charges, current drops and voltage rises. When it's fully charged, the voltage is max, and no more current flows. If we put AC across the cap, it does this every half cycle. Max, current, zero volts, building up to max voltage, zero current. Then it does this for the other half cycle. If we plot this on a graph, the voltage goes from zero to max at the same time current goes from max to zero. We say that "The voltage lags the current". Do this over several cycles and you'll have a sine wave for voltage and cosine wave for current. Sine and cosine are 90 degrees out of phase. Here's more information: http://www.allaboutcircuits.com/vol_2/chpt_4/2.html
What is the advantage of a Star Delta Motor Starter?
The inrush current to the starting motor is lower due to the the motor coils being in series across the line creating a higher impeadence. When the starter connects to delta connection the motor is already turning and it does not have to go through the locked rotor phase. This system is being phased out now with the use of electronic soft starts and by-pass contactors.To start a motor direct on line (DOL) in delta requires approximately 6 to 8 times the full load current of the motor and delivers full torque. Delta places 415v across each of the windings on the motor. A Star-Delta starter starts the motor in Star which places 240v across each winding on the motor. This results in a lower starting current and also a lower starting torque.
How does a solid state relay work?
A solid state relay (SSR) is an electronic device to switch the electrical current, rather than an electromechanical device. An electromechanical relay uses a magnetic coil and mechanical contacts. When current flows through the coil, it pulls down a piece of iron called an armature, causing the mechanical contacts to touch and thus close an electrical circuit. A solid state relay (SSR) has no mechanical moving parts, but instead uses a three terminal device such as a triac (triode AC), SCRs (back-to-back thyristors), or FET (field effect transistor) to conduct the electrical current. When the third terminal (gate) is energized by the control input, the device conducts. Essentially the solid state relay controls a larger electrical current by accepting a small control signal. There are no moving parts. Advantages of solid state relays are: they have no internal arcing or contacts to wear out, can last virtually forever, can have extremely low control input requirements, and are immune to vibration or G-force chatter. There are 3 installation parameters that must be planned for. Avoid over-amperage (inrush > than SSR rating), over-voltage (voltage surges) and over temperature. Solid state relay has also opto isolation feature. control signal & power line is completely isolated by an internal LED. It is just like a big version of Opto Coupler.
Why we want to improve the power factor?
The best way to improve power factor is by adding capacitors. Low power factor is due to reactive loads (motors, pumps, etc.) that are connected to your electrical system.ADDITIONThe best way to improve power factor in the case of motors is to use a motor drive, like a Variable Frequency Drive. These drives allow very precise control over a motor, unlike the very sudden, jerky starting and stopping across the line seen when using a motor starter. They eliminate the huge inrush current required to start motors that causes low PF.Answer:1) Power factor can be calculated by connecting an energy meter [P] (voltage coil in parallel & current coil in series with the load), a voltmeter [V] across load and an ammeter [A] in series with the load. Measure P, V & I.Since, Active Power (P) = V.I.Cosϕpower factor = Cosϕ = P/VI2) Power factor is usually (industrially) improved by connecting a shunt (parallel) capacitor bank at feeding end.How it works??Inductive loads contain both inductors and resistors. But due to phasor difference of coils and caps when voltage is applied across both, the two currents results in a smaller net current finally. So now the angle (ϕ) between the voltage phasor and current phasor is lessened. When ϕ is reduced, Cosϕ is risen resulting in a higher power factor.
Magnetic inrush current in power transformer?
When a transformer is initially connected to a source of AC voltage, there may be a substantial surge of current through the primary winding called inrush current. Inrush current can be up to ten times higher than the continuously needed current because there is low initial resistance.
Does a transformer draw a lot of current when first connected to a source?
Yes it does as it is an Inductor and an Inductor needs to build up a magnetic field. It is called INRUSH current.
What are the factors affect the magnitizing inrush current in power transformer?
1- residual flux existing before enegizing the transformer . 2- size of transformer . 3- size of power system. 4- type of magnetic material of the core. 5- the method of energizing the transformer.
What is the difference between the inrush current and the fault current?
Magnetizing inrush current has bigger 2nd harmonics compare to short circuit current. the second harmonics content is about >60% of fundamental harmonic. magnetizing inrush current happened when we energised the transformer, and short circuit current happened if there is a short circuit between different alive phase.
What is meant by transformer charging?
Most likely this is referring to the initial inrush that occurs when a transformer is energized. The core of a transformer is designed for a specific magnetic field strength; When a transformer is switched into a circuit, it usually will not be switched at exactly a voltage peak. When the voltage is at its' peak, the induced magnetic field will be at zero. If the switching occurs at a voltage zero, the magnetic field strength will attempt to climb to double the designed value; since the transformer core is not generally oversized to this degree, it will saturate. This causes large inflows of current to the transformer, and shows up as even harmonics (mainly second harmonics) in the current waveform. This settles out within a few seconds (generally) to a small energizing current, usually less than 1% of the transformer's rated current.
What is inrush current in transformers?
When a transformer is first energized, a transient current up to 10 to 50 times larger than the rated transformer current can flow for several cycles. Toroidal Transformers, using less copper for the same power handling, can have up to 60 times inrush to running current. Worst case inrush happens when the primary winding is connected at an instant around the zero-crossing of the primary voltage, (which for a pure inductance would be the current maximum in the AC cycle) and if the polarity of the voltage half cycle has the same polarity as the remnance in the iron core has. (The magnetic remanance was left high from a preceding half cycle). Unless the windings and core are sized to normally never exceed 50% of saturation, (and in an efficient transformer they never are, such a construction would be overly heavy and inefficient) then during such a start up the core will be saturated. This can also be expressed as the remnant magnetism in normal operation is nearly as high as the saturation magnetism at the "knee" of the hysteresis loop. Once the core saturates however, the winding inductance appears greatly reduced, and only the resistance of the primary side windings and the impedance of the power line are limiting the current. As saturation occurs for part half cycles only, harmonic rich waveforms can be generated, and can cause problems to other equipment.For large transformers with low winding resistance and high inductance, these inrush currents can last for several seconds until the transient has died away (decay time proportional to ~XL/R)and the regular AC equilibrium is established. To avoid magnetic inrush, only for transformers with an air gap in the core, the inductive load needs to be synchronously connected near a supply voltage peak, in contrast with the zero voltage switching which is desirable to minimize sharp edged current transients with resistive loads such as high power heaters. But for toroidal transformers only a premagnetising procedure before switching on allows to start those transformers without any inrush current peak.
In-rush current phenomena in transformer?
Inrush is due to the saturation of the core of the transformer.When the highside device closes to energize the transformer, it does not always do so right at a voltage peak. The transformer core B (magnetic field) will be 90 degrees out of phase with the applied voltage, so a peak voltage close is ideal. Once it is closed, the B will continue up and down 90 degrees out of phase with the voltage. Assuming there is no residual magnetic field (B starts at zero), it will be offset by the initial non - peak close. This offset in magnetic field will cause the core to go into saturation; depending on the core design it may be further or less into saturation on different transformers.When the core saturates, large currents flow, and these currents (normally) have a high 2nd harmonic component which is used in protective relaying to restrain for inrush.
What is the inrush current for halogen?
the answer ur looking for is incandescent
What does the term VA mean when applied to a control transformer?
VA refers to the effective load that is placed upon the Control Transformer (also known as Selection Inrush VA).
How inrush current limited in ups?
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Why does a three phase transformer not short itself out when the phases are connected through the transformer?
I asked this very question to my professor in electronics 101 in college! He explained to me the load side of the transformer if not connected to any load is open. This is a great resistance to completing the circuit. This is transferred to the primary side of the transformer as a great resistance thus no current flow.
More the transformer impedance less the fault current... so is a high value of transformer impedance good for it?
It depends a lot on the application, i would go with low impedance transformers if am using the transformers for distribution as it will really increase the the maximum fault current. If am using the transformers as step up specially for generators or to charge capacitors, using a high impedance transformer is a good idea as it will decrease the inrush current of the system. you have to see your application and decide what fit that best. Mohammad Jaradat Power Generation Project Manager
