in a 3 phase delta motor connection u  no longer need the neutral, how does current flow back?
927155
The addition of a neutral wire with a three phase electrical supply allows a lower voltage, single phase sub-assembly or appliance to be powered by the same line in (one phase to neutral).\nThree phase alone merely conducts between phases.
846799
It takes energy to push that current through your lights and appliances, and that's what your paying for. One way to see it is to consider that what comes out the downstream prong is at 0 volts and therefore of no use to anyone. Or, you could just wire all your lamps in series and see how that works!
458600
You say 3 phase, so the simple amps times volts doesn't work.\n\nThe complete formula is KW= 1.73 * amps * volts * power factor /1000\n\nThe 1.73 is the square root of 3.  The amps is your line current (same as phase current if it is wye, not the phase current of a delta) and the volts is the phase to phase voltage (not phase to neutral of a wye).  Power factor is 1 for simple resistive loads, and is less than 1 for inductive loads such as motors and fluorescent light ballasts.\n\nIf you take the power factor out of the formula, you get apparent power measured in KVA.
107875
Limit the load current.\nEDIT: This is often done by adjusting the stator field current if it's a generator with an electromagnet (not permanent magnet) field.
225095
How about this one?\n\n"This calculation module allows you to quickly calculate fault currents for a complete radial system. It can simultaneously handle a main distribution transformer, service lateral, second transformer, up to 40 main-feeders, with 8 main-feeders having 40 sub-feeders for a total of 360 nodal points. \n\nAccommodating both single-phase and three-phase circuits, the module will calculate from either infinite or known fault current values at either the transformer or the main-bus. \n\nThe module accommodates multiple conduit types, bus types, multiple conductors and motor contribution. The program is based on the popular LICE (point-to-point) calculation method. \n\nOur unique Help file (of which we are quite proud) includes complete practical guidance on Fault Calculations, and even includes a theoretical derivation of the LICE method. "\n\nhttp://www.edreference.com/fault.asp
229900
Electicity in a commercial application is 3 phase, residential electricity is single phase
982631
The equations you post are the not correct.  If you close the switch on the circuit you describe, the CURRENT level is given by\ni = (V/R)e^-t*R/L.  The current starts out at zero, and ends up (after a long time) at V/R.  This equation is derived from the fundamental relation V=L*dI/dt.  If you open the switch, you must go back to this fundamental relation.  If you stop the current instantly, dI/dt = ∞, so the voltage must also go to ∞.  Of course this cannot happen.  What does happen is that the air in the switch breaks down at some voltage, and that limits the level to which the voltage can rise.  There will also be a big spark at the switch.
1121007
yes. electricity flows one direction,comes to a stop, then flows in the  other direction. the alternator pushes the electrons in one direction for 1/120 of a sec.then the other direction for the same amt. of time.( for 60 cycle current ) one direction is the pos.1/2 cycle the other is the neg. 1/2 cycle.  the zero crossing point is the instant between one direction and the next, when current flow is stopped.
741176
DC is battery and they do not generate a current. They store energy for use upon demand. They also do not store enough energy to maintain transmission for long periods.
93725
Three phase or two phase?
656571
b) and c)\n\nthe transformer works in such a way that electric current flows through the secondary circuit only when the electric current in the primary circuit is changing.\n\nwhen you close the switch the electric current in the primary circuit suddenly rises from 0amp to some value\nwhich causes electric curent to flow through the secondary circuit\n\n.. b) is true\n\nwhen you open the switch the electric curent in the primary circuit changes from the maximum value to 0amps thus electric curent flows through the secondary.\n\n.. c) is true\n\nbut \n..a) is false\n\nsicne a battery is a dc source wich means that as long as the switch is closed it supplies a steady amount of electric current through the primary. thus ther will be no current through the secondary.
508767
It sounds to me like you have an Interruptible Power Supply (UPS) where you have a primary AC power supply and a battery backup. It seems from your question that you are looking to automatically switch to the battery backup if the AC fails. Of course you must rectify the DC from the battery to AC of the proper current and voltage. Assuming this is the case, you can wire the load through an AC relay. Connect the AC power source to the relay coil in parallel to the load. Hot on one side, Neutral on the other.  Wire the primary AC hot wire to load  through the Normally Open contacts. Wire the DC rectified AC Hot wire through the Normally Closed contacts. When you have good AC power the relay coil will energize, closing the Normally Open contacts (and opening the Normally Closed contacts). This will energize the load with primary AC power. If you loose primary AC power, the relay will de energize. This will close the Normally Closed  contacts(and open the Normally Open contacts)  and port DC converted AC to the load. \n\nYou will probally have to come to a common point after the relay contacts such that power takes the path of either the AC or DC but goes through to the load via the same path after the relay.\nEnsure that you have compadible neutrals between the AC and the DC they will probally be common. Only the hot wires go throughthe relay. \nChoose a relay that will be able to handle the current and voltage you desire. Ie you need enough power to energize the relay coil and you do not want to melt the contacts by giving them too much current. You can obtain them as mentioned above frpm granger.com there real cheep. Order the relay and base. \nEnsure the load works well with both power sources.
961185
You cannot do this directly. Assuming you are talking about a motor, It may be possible to get the motor to turn using a capacitor but you will not get the rated torque (turning force). I'm sure there is plenty 3 phase theory on the internet if you want to see why they are so different\n\nOne way it can be done is by using an inverter that takes single phase input (providing the voltage you require is not higher than the voltage you have or you will then need a transformer as well). The inverter gives you the added value of being able to vary the speed but it may be cheaper to simply buy a single phase motor. As you didn't actually specify the device to be motor, be aware that VSD inverters may not work on other equipment.\n\nYou need to be wary of the size of the device you are trying to operate. Often 3 phase is used for higher powered devices that becomes in-practical to try and run on single phase anyway.
739563
I am unaware of any 2-phase electrical systems.  \n \nTo get 3-phase power from a single phase (as in your home electrical) system you need to have a single phase motor run a 3-phase generator.
733256
Single phase circuits have two terminals one "hot" and the other ground.  v(t)=120*cos(2*pi*60*t)\n\nThree phase have three hot terminals (each 120 degrees out of phase with one another) and one ground:\nv1(t)=120*cos(2*pi*60*t+0 deg)\nv2(t)=120*cos(2*pi*60*t+120 deg)\nv3(t)=120*cos(2*pi*60*t+240 deg)
648766
The other 2 answers are basically right, but Kes has no clue.\n\n3 phase voltages are normally specified by the phase to phase voltage (say 480V).  If a neutral is present from a wye transformer, the phase to neutral may be specified second, such as 480Y/277.  But just saying 480Y means 480 phase to phase in the wye configuration.  The phase to neutral voltage is the phase to phase voltage divided by the square root of 3 (about 1.73).\n\n480V 3 phase is not something to play with.  If you don't know what you are doing, you shouldn't even be in a position to be able to measure the voltage.\n\nTo Kes, normal home wiring is single phase 240/120.  2 phase is a system that existed before 3 phase became standard.  For what you call "440 V" for motors, it would be 440 V between phases.
539640
Okay it seems that you have a dc motor, a transformer and a switch. I would imagine the transformer is a multi-tapped step down. You can verify this by disconnecting all the secondary wires from the transformer and putting power to the primary. Get a meter and go from the common on the secondary side and to every output on the transformer. If the wires on the transformer are color coded the common may be black and the hi output may be red. Other colors will be different voltages. If this is the case the switch is wired with the exception of the secondary common through multiple poles to provide different voltages to the motor. The switch will have a common output and all other wires will be inputs from the transformer. The output of the switch then must go to a rectifier of circuit board that converts the voltage from ac to dc. This connects to the motor. You might be missing the ac to dc converter circuit if you dont see a circuit board or Bridge rectifier. If you go throught the switch wiring and get it set up to where you have different voltages at the output of the switch you can always go to your local parts store and buy a 2 amp bridge rectifier. The common output of the transformer will have one wire going to one of the ac sides of the rectifier and the other will go to the other ac side of the rectifier. The two remaining outputs will go to the motor and polarity will not matter. Hope this helped!