SkyCables Say Eid Mubarik to All of You

IGBT GATE Driver Using PC817

IGBT GATE Driver Using PC817

AC (Alternating Current) Fundamentals ( Understanding Singal Phase, 3 Phase)

Phase

Phase in sinusoidal functions or in waves has two different, but closely related, meanings. One is the initial angle of a sinusoidal function at its origin and is sometimes called phase offset or phase difference. Another usage is the fraction of the wave cycle that has elapsed relative to the origin.

Singal Phase

In electrical engineering, single-phase electric power is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors. A single-phase supply connected to an alternating current electric motor does not produce a revolving magnetic field; single-phase motors need additional circuits for starting, and such motors are uncommon above 10 or 20 kW in rating.

In contrast, in a three-phase system, the currents in each conductor reach their peak instantaneous values sequentially, not simultaneously; in each cycle of the power frequency, first one, then the second, then the third current reaches its maximum value. The waveforms of the three supply conductors are offset from one another in time (delayed in phase) by one-third of their period. When the three phases are connected to windings around the interior of a motor stator, they produce a revolving magnetic field; such motors are self-starting.

Standard frequencies of single-phase power systems are either 50 or 60 Hz. Special single-phase traction power networks may operate at 16.67 Hz or other frequencies to power electric railways.

In some countries such as the United States, single phase is commonly divided in half to create split-phase electric power for household appliances and lighting.

 Understanding 3 Phase

Three phase is nothing more than single phase with 2 extra coils slightly out of phase with first.  Basically "Phase" relates to the timing of the magnets passing over the coils at different times. With single phase the magnets and coils all line up with each other and are said to be in "phase". The diagram below shows single phase wiring....

In a single phase unit the coils are wound opposite of the first.   That is to say one is wound clockwise and the next is counter clockwise.  If your unit has 8 magnets then it would also have 8 coils.  With 3 phase you would have 3 coils for each pair of magnets.  A pair meaning one north and one south magnet.   There are many combinations for any one set up.  For instance you could use 8 magnets and only have 6 coils without overlapping them... or 3 set of 4 coils in series.   For now we won't worry about the combinations and stick with the basics.   Below shows a diagram of 4 magnets with the placement of each of the coil sets...

As you can see the first phase covers only the north pole magnets and are wound all in the same direction.  The other of the two are identical to the first with the exception they are offset equally.  The next diagram shows all the sets in place for a 4 pole alternator.  You end up with 3 start wires labeled A,B,C and 3 end wires labeled D,E,F.   The output wires to this arrangement would be A, C and E.   The reason E is an output or ends up being a "start" wire is because when the magnet passes over the 2nd phase its out of phase between the 1 and 3 so the ends are reversed instead of winding them in the opposite order.

Now to connect the ends and change the AC to DC for battery charging... Below shows the star and delta symbols and 2 different types of rectifiers.  Either rectifier can be used for star or delta.  You can use diodes and make your own rectifier set up or you can purchase the standard rectifiers.  Notice on the standard rectifiers one AC lead isn't used.  Similar to the diodes, a rectifier that is already made up for such use and my personal preference is a unit from a GM alternator.   They seem to give the best rectified output out of all of them.  I'm not sure why but they do.  They are expensive to buy new but usually you can get them from the junk yard fairly cheap.  Sometimes get the whole alternator for around 15 bucks.   They also make a nice clean set-up.

There are basically two ways to wire a 3 phase alternator, star ( or Wye) and Delta.  With Delta you get lower voltage but more amps.  In star you get higher voltage but less amps.  You can calculate these by using the square root of 3 ( or 1.732 ).  Each coil set is a "phase" of the alternator so when you measure voltage,ohms or current to test one phase of the alternator you would measure the "phase".  Once you know what the output will be from one phase you can calculate the "line" output of either delta or star. The line voltage would be measured from any 2 of the 3 outputs.  If one phase measured 22 volts in your test and 10 amps then the star configuration would produce 38 volts and 10 amps ( 22 x 1.732 ).   The amps remain the same as the phase measurement because the star is basically series'd to another phase.  In Delta you would get 22 volts at 17.32 amps (10 amps x 1.73 ).  If you calculate this out 22 volts x 17.32 = 381 watts and 38 x 10 = 380 watts... so what is the advantage?  Typically the resistance in Delta is 1/3 the resistance of star.  If the resistance of star was 1.5 ohms we could calculate the output ( see formula section ).  Lets assume the test was at 600 rpm, we achieved 38 volts in star ( about 16 rpm per volt ) so at 1000 rpm we would get 62.5 volts less battery voltage of 12.6 = 49.9 volts / 1.5 ohms = 33.26 amps * 12.6 = 419 watts... not to bad.  Now in delta we had 22 volts at the same rpm ( about 27 rpm per volt ).   So at the same 1000 rpm we get 37 volts - 12.6 battery = 24.4 volts / .5 ohms = 48.8 amps * 12.6 = 614 watts.  Almost a 200 watt gain !!!  The advantage of star is the higher voltage at lower rpm which means our unit would have to make 201 rpm to start charging at 12.6V where the Delta woul

Some Basic factoids about 3 phase....  Most of the electric power in the world is 3 phase.  The concept was originally conceived by Nikola Tesla and was proven that 3 phase was far superior to single phase power.  3 phase power is typically 150% more efficient than single phase in the same power range.  In a single phase unit the power falls to zero three times during each cycle, in 3 phase it never drops to zero.  The power delivered to the load is the same at any instant.   Also, in 3 phase the conductors need only be 75% the size of conductors for single phase for the same power output.