In theoretical examples, 3-phase circuits are shown as either Wye or Delta type. Wye obviously containing a neutral line.

Recently I watched a Youtube video where the uploader re-purposed an old motor and turned it into a generator. The motor (from what I can tell) is wired in a 3-phase Wye type setup (circled in red). See figure 1 below: Figure 1

Note: The figure resembles the actual model. There were no other connectors shown aside from the X,Y,Z as shown above.

EDIT: We are assuming the motor has now been converted and is being used as a generator.

Scenario 1: Now lets pretend lines X,Y,Z are led off and connected to a Delta-type transformer.

  • Q1: How does this complete the circuit if there is no neutral or ground? Will the current return path occur during the negative cycling of the other two phases?

"Wye obviously containing a neutral line"

Of course not. You connect only three phases without neutral, the ground goes to case for safety. $$i_a+i_b+i_c=0$$ The summ of all currents is zero.

The ground is mandatory, there is no such possibility without having the earth/ground.

The casing is isolated from windings, no current flows from earth/ground to the phases. The ground is just for safety purposes.

A three phase motor can't run on single phase.

  • \$\begingroup\$ Apologies, I should have stated in theory problems the Wye configurations have a neutral line when going from Wye-Wye...Thus my confusion when I saw this motor. How does the current return? In other words, how is the circuit completed? We can't just have an infinite source of electrons being generated and flowing from a single point? \$\endgroup\$ – SheerKahn Oct 4 '17 at 14:11
  • \$\begingroup\$ @SheerKahn each of the three phases is 120 degrees out of phase from the others. The current balances between the three phases (some are sourcing some of the time, some are sinking some of the time) \$\endgroup\$ – Tom Carpenter Oct 4 '17 at 14:21
  • \$\begingroup\$ See this animation \$\endgroup\$ – Tom Carpenter Oct 4 '17 at 14:22
  • \$\begingroup\$ @SheerKahn You should start with basics of three phase network, load. As stated the sum of all currents is zero, so whatever comes into one wire it goes out from other twos and vice versa. \$\endgroup\$ – Marko Buršič Oct 4 '17 at 14:42

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