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An AC induction motor is supposed to be a constant power motor, which implies it draws more current on low voltage. Consider a motor running a constant torque load at a particular speed. Suppose now the voltage is reduced, which should cause it to settle down at a lower speed supplying the same torque as per the new torque speed characteristic.
Power losses of ferromagnetic core depend from voltage and frequency. In case where is no-load secondary winding, power transformer has a power losses in primary winding (active and reactive power losses) which are very small, due to low current of primary winding (less than 1% of rated current) and power losses of ferromagnetic core (active and reactive power losses) which are the highest in case of rated voltage between ends of primary winding.
The transformer core can saturate due to, High Voltage, Low Frequency or a combination of both. Protection element V/Hz (ANSI 24) can be used to protect the transformer against over excitation as this can cause damage due to overheating / excessive core loss. This protection element is commonly used on generator step-up transformers.
Many years ago I had an experience of 4nos 37kW fin-fan motors wrongly connected at site to a star. After running for almost 1 year, the operators reported these motors were very warm and felt unusual. We removed one of them to the workshop and opened for inspection. All windings were OK but the rotor lamination surface had turned to light blue colour which showed a sign of abnormal heating.
The high frequency edges of switched waveforms can cause capacitively coupled currents to flow from windings to frame, returning through the bearings, and these can accelerate corrosion in the bearings, causing early failure. Small filters on the motor leads allowing these currents to return locally to ground will avoid this.
Variable speed drive switches very fast which brings high dv/dt on motor. How often do we face with problems coming with VSD? How harmful is the common mode currents in windings and other parts of motor due to high dv/dt. Do we see winding isolation failure? How much does the life of motor reduce? Also, is the filtering of voltage at the output of inverter common or applicable practice in the field?
When designing gate drivers for IGBT's, how reliable are the gate driver IC's ? Now there are a lot of gate driver IC's available in the market. For example i am using the Hybrid IC M57962L for driving IGBT's for 3 phase inverter application. The peak output current of this Hybrid IC is 5A and it's written in data sheet that it can be used for driving IGBT's up to 200A, 1200V and many features in it.
I hate to call them harmonic currents. The do submit to Fourier analysis, but you are probably dealing with AC to DC power supplies. If you look at the current pulses, you will see that each pulse is about 1-2 milliseconds in duration in alternating directions. If you sum these all in the neutral there is the appearance of what looks like 180 Hertz in the neutral.
In a balanced 3-phase system with pure sine waves, the neutral current is zero, ideally.
If there is phase imbalance, it shows up in the neutral, so check for imbalance.
The other major cause of high neutral currents is full wave rectification, where the current of each phase is flowing only at its peak voltage. In this case, the neutral current can be as high as three times the phase currents, theoretically.
What are the general guide lines for snubber circuit design in Inverter applications? When i referred the literature for snubber circuits for IGBT protection i found that we can either go for "individual" snubber circuits ie across each device or we can go for Lump snubber circuits connected between the power supply bus and ground for centralised protection.
There are different types of system configuration for grounding like TT,IT,TN-C etc. How do we decide which configuration is suitable for the particular inverter (string or central). What are the factors that help us to decide the configurations?
NGR stands for Neutral Grounding Resistor. When an earth fault current occurs on a plant, assuming that there is no external device presented to limit the earth fault current, the magnitude of the earth fault current is limited only by the earth impedance presented between the point of fault (to earth) and the return path (typically a star point of a transformer).
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