Table of Contents
What causes 2nd harmonics?
The main cause of the harmonics generation are the “non-linear” loads. Non-Linear load In opposition to linear-loads, a non-linear load changes its impedance with instantaneous applied voltage, that will lead to a non-sinusoidal current draw when the applied voltage it’s so.
What is phenomenon of inrush in transformer?
Definition: The transformer inrush current is the maximum instantaneous current drawn by the primary of the transformer when their secondary is open circuit. The inrush current does not create any permanent fault, but it causes an unwanted switching in the circuit breaker of the transformer.
What are VFD harmonics?
Harmonics are defined from the Fourier series that defines any periodic wave shape. Typically a three-phase, six-pulse VFD will draw nonlinear current that introduces the fifth and seventh harmonics on top of the fundamental frequency. The symptoms of the VFD related harmonics are evident as a distorted line voltage.
What is cross fluxing in transformer?
The over fluxing protection operates when the ratio of the terminal voltage to frequency exceeds a predetermined setting and resets when the ratio falls below 95 to 98\% of the operating ratio. By adjustment of a potentiometer, the setting is calibrated from 1 to 1.25 times the ratio of rated volts to rated frequency.
A number of transformer fault conditions can arise practically in any time following some special situations. These include the following five most common internal faults and few external: earth faults, core faults, interturn faults, tank faults, and external factors.
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.
What is 3rd 5th and 7th harmonics?
The fundamental waveform is called the first harmonic waveform. In an AC circuit, the fundamental waveform has the supply frequency. If the fundamental frequency is 50 Hz then the 3rd harmonics will be 150Hz (3 x 50 Hz). Similarly, 5th harmonics will be 250 Hz (5 x 50 Hz) and 7th harmonics is 350 Hz (7 x 50 Hz).
What is inrush detection in a transformer?
Inrush detection was limited to evaluating the harmonic content of the currents available within the specific relay element. One of the complications of energization currents is that transformer inrush is not a consistent condition. The currents will vary from one energization to the next.
What are the characteristics of inrush current?
The inrush current has a significant DC component and is also rich in harmonics. Second harmonic is predominant harmonic in the inrush current. In concern of magnetizing inrush currents, transformer charging is a crucial event. During any external fault system voltages reduces significantly.
What happens when a transformer gets too much excitation?
Normally, a transformer gets over-excitation due to over voltage or under frequency. In this scenario, excitation current increases sharply and the transformer will tend to become overheated due to increased excitation current, hysteresis losses, and eddy currents.