Why transformer has harmonic in the current?
Transformers:Harmonics in transformers cause an increase in the iron and copper losses. Voltage distortion increase losses due to hysteresis and eddy currents and causes overstressing of the insulation material used. The primary effect of power line harmonics in transformer is, thus the additional heat generated.
Why is the exciting current of a transformer non sinusoidal when the applied voltage is sinusoidal?
If the transformer is operated at a very low flux density, the magnetising current will be sinusoidal but the transformer would be bulky and expensive. From economic considerations, transformers are operated at the knee of the saturation curve and hence the magnetising current is non sinusoidal.
Why excitation current of transformer is non sinusoidal?
If the transformer iron core did not saturate, the magnetizing current (Im), generated by the flux, would be sinusoidal in shape and in phase with the flux. The result is that the magnetizing current is symmetrical, but cannot be sinusoidal due to the magnetization curve nonlinearity.
How harmonics are generated in a transformer?
The transformer cores have a non-linear behavior in the saturated part of the magnetizing curve. This non-linear behavior generates harmonic currents. Depending on the switching-on instant with the voltage waveform the transformer core may be highly saturated and generates a large amount of harmonic currents.
Why transformer has harmonic in the current which harmonic has significant effect and why?
The harmonic is the distortion in the waveform of the voltage and current. It is the integral multiple of some reference waves. The harmonic wave increases the core and copper loss of the transformer and hence reduces their efficiency. It also increases the dielectric stress on the insulation of the transformer.
What is a harmonic current?
Harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency. If the fundamental power frequency is 60 Hz, then the 2nd harmonic is 120 Hz, the 3rd is 180 Hz, etc.
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.
Why no-load current of transformer is not sinusoidal?
When a sinusoidal voltage is applied to the primary winding of the transformer, then the mutual flux set-up in the core is assumed to be sinusoidal and the no-load or exciting current (I0) will be non-sinusoidal due to hysteresis loop. …
What is the use of potential transformer?
A Potential transformer is actually a instrument transformer that used in power systems to step down primary current voltages and secondary voltages from a higher level to lower secondary potential output voltage level.
What is magnetization current in transformer?
Magnetization current can be defined as “the portion of the no-load current that is used to establish flux in the core of a transformer“. Generally, when a transformer is energized under no-load conditions, it draws a small amount of current. This current is known as excitation current (I0).
What is harmonic current in transformer?
What is the source of harmonic current?
Harmonics are the result of nonlinear loads that convert AC line voltage to DC. Harmonics flow into the electrical system because of nonlinear electronic switching devices, such as variable frequency drives (VFDs), computer power supplies and energy-efficient lighting.
What is the typical harmonic level of a transformer?
Typical harmonic levels of transformer exciting current shown in percentage of full load current. Third harmonic current is approximately around 50\% of the fundamental, fifth around 15\% and seventh around 1-2\%.
What happens when voltage is impressed across the terminals of Transformers?
If normal voltage is impressed across the primary terminals of a transformer with its secondary open-circuited, a small exciting current flows. This exciting current consists of two components, the loss component and the magnetizing component.
What is the total exciting current of a transformer?
As discussed above, the total exciting current of a transformer includes a magnetizing and a loss component. The economic design of a transformer dictates working the iron at the curved part of the saturation curve at normal voltage; hence any increase in terminal voltage above normal will greatly increase the exciting current.
What is the normal magnetizing current in a transformer?
Typically magnetizing current (I m) can vary from about 0.25\% to about 5\% of full load current (0.05 pu) and can be as high as 10\% in some special transformers. Below is a summary of actual exciting current and no-load losses test results for modern dry type transformers that can be used as a reference.