This current is related (with a reasonably good approximation) to the transformer equivalent primary inductance value and the applied primary voltage and given source frequency. Magnetising current flows into the primary irrespective of transformer load condition .
How is magnetising current calculated?
This is the magnetizing current ( no secondary current ) and is governed by the differential equation V(t) = L x d(I)/dt + Rp x I(t) , with units of volts, henries, amps, and seconds.
What are magnetizing currents?
[′mag·nə‚tiz·iŋ ‚kə·rənt] (electricity) The current that flows through the primary winding of a power transformer when no loads are connected to the secondary winding ; this current establishes the magnetic field in the core and furnishes energy for the no-load power losses in the core.
What is magnetising current in induction motor?
In order to set up magnetic flux inside the air gap of induction motor, large magnetizing current is required. During no load, the current drawn by induction motor is 30%-60% of rated current whereas current drawn by transformer during no load is 2%-6%.
What is magnetising current in CT?
Simply stated, the magnetizing current at the knee-point voltage is another way of defining the secondary current magnitude error at the knee-point voltage. Think of the CT as a black box. Primary current comes in and secondary current comes out as a function of the turns ratio.
What is CT excitation current?
A ct excitation curve provides a measure of the steady-state performance . Excitation curves have a knee-point voltage defined by the 45° line drawn tangent to the curve. However, it is important to note that the knee-point is the point of maximum permeability and not the point of saturation.
What is excitation current?
Excitation current is the current flowing into the high voltage winding with the low voltage side open . This current should be proportional to the No-load acceptance test but with the difference resultant from the use of test voltages different from nominal values.
What is the function of no load current?
The no-load current I 0 is the vectorial sum of the magnetizing current Im and core loss or working component current Ic . [Function of Im is to produce flux φm in the magnetic circuit and the function of Ic is to satisfy the no load losses of the transformer].
What is magnetising current test?
Magnetizing Current test on transformer is performed to locate defects in the magnetic core structure , shifting of windings, failure in between turn insulation or problem in tap changers.
What are the components of no load current?
No load current of large power transformers consists of active and reactive component . Active component covers hysteresis and eddy current losses in the core. Reactive component (usually called magnetizing current) creates magnetic field / magnetic flux and lags the voltage by 90°.
Why magnetizing current is important?
A certain amount of current is drawn by a transformer from the source connected to it primary even when no load is connected to its secondary. A part of this current is used to create flux in the transformer core . This current is known as magnetization current.
What is the magnetizing current in a transformer is rich in?
The magnetic inrush currents contain a strong DC component to produce the unidirectional flux during the transient period and the wave contains only positive peaks and is not symmetrical about the x-axis. Therefore Fourier series of this waveform contains both odd and even harmonics.
How leakage flux depends on load current?
This flux is called leakage flux which will pass through the winding insulation and transformer insulating oil instead of passing through the core. ... This phenomenon in the transformer is known as magnetic leakage. This depends on load current, independent of voltage, frequency, and power factor .
What is the relation between magnetising current and power factor?
What is the relation between the magnetizing current and power factor? Explanation: Magnetizing current is indirectly proportional to the power factor . As the magnetizing current is large, the power factor is poor.
Why is the power factor low under no load conditions?
At low load or no load condition because of presence of only magnetizing current in the stator windings , causes low power factor operation of the power system, since magnetizing current is highly inductive in nature.
What is the value of air gap of induction motor?
The number of slots/pole/phase should not be less than 2 otherwise the leakage reactance becomes high. The number of slots should be selected to give an integral number of slots per pole per phase. The stator slot pitch at the air gap surface should be between 1.5 to 2.5 cm .
