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Do you know Power Formulas in Electrical Circuits ?
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Wednesday, 30 September 2020
Saturday, 26 September 2020
AC Waveforms
When an alternator produces AC voltage, the voltage switches polarity over time, but does so in a very particular manner. When graphed over time, the “wave” traced by this voltage of alternating polarity from an alternator takes on a distinct shape, known as a sine wave: Figure below
Graph of AC voltage over time (the sine wave)
In the
voltage plot from an electromechanical alternator, the change from
one polarity to the other is a smooth one, the voltage level changing
most rapidly at the zero (“crossover”) point and most slowly at
its peak. If we were to graph the trigonometric function of “sine”
over a
Monday, 21 September 2020
Three-Phase Induction Motor parts and cross section
- The frame - is the supporting structure of the assembly; manufactured of iron, steel, die-cast aluminum, resistant to corrosion and with cooling fins
- The lamination core - constructed with magnetic steel plates
What is Alternating Current (AC) ?
Most students of electricity begin their study with what is known as direct current (DC), which is electricity flowing in a constant direction, and/or possessing a voltage with constant polarity. DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other.
Alternating Current vs Direct Current
As useful and as easy to understand as DC is, it is not the only “kind” of electricity in use. Certain sources of electricity (most notably, rotary electromechanical generators) naturally produce voltages alternating in polarity, reversing positive and negative over time. Either as a voltage switching polarity or as a current switching direction back and forth, this “kind” of electricity is known as Alternating Current (AC): Figure below
Direct vs alternating current
Whereas the familiar battery symbol is used as a generic symbol for any DC voltage source, the circle with the wavy line inside is the generic symbol for any AC voltage source.
One might wonder why anyone would bother with such a thing as AC. It is true that in some cases AC holds no practical advantage over DC. In applications where electricity is
Friday, 18 September 2020
Tuesday, 15 September 2020
The Zener Diode
A Semiconductor Diode blocks
current in the reverse direction, but will suffer from premature
breakdown or damage if the reverse voltage applied across becomes too
high
However, the Zener Diode or “Breakdown Diode”, as they are sometimes referred too, are basically the same as the standard PN junction diode but they are specially designed to have a low and specified Reverse Breakdown Voltage which takes advantage of any reverse voltage applied to it.
The Zener diode behaves just like a normal general-purpose diode consisting of a silicon PN junction and when biased in the forward direction, that is Anode positive with respect to its Cathode, it behaves just like a normal signal diode passing the rated current.
However, unlike a conventional diode that blocks any flow of current through itself when reverse biased, that is the Cathode becomes more positive than the Anode, as soon as the reverse voltage reaches a pre-determined value, the zener diode begins to conduct in the reverse direction.
This is because when the reverse voltage applied across the zener diode exceeds the rated voltage of the device a process called Avalanche Breakdown occurs in the semiconductor depletion layer and a current starts to flow through the diode to limit this increase in voltage.
The current now flowing through the zener diode increases dramatically to the maximum circuit value (which is usually limited by a series resistor) and once achieved, this reverse saturation current remains fairly constant over a wide range of reverse voltages. The voltage point at which the voltage across the zener diode becomes stable is called the “zener voltage”, ( Vz ) and for zener diodes this voltage can range from less than one volt to a few hundred volts.
The point at which the zener voltage triggers the current to flow through the diode can be very accurately controlled (to less than 1% tolerance) in the doping stage of the diodes semiconductor construction giving the diode a specific zener breakdown voltage, ( Vz ) for example, 4.3V or 7.5V. This zener breakdown voltage on the I-V curve is almost a vertical straight line.
Zener Diode I-V Characteristics
The Zener Diode is used in its “reverse bias” or
Friday, 11 September 2020
Sunday, 6 September 2020
uniPLC-TI-10DI8DO1AI-NT - Test 05
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uniPLC-TI-10DI8DO1AI-NT - Test 05
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