Induction motors as generators, specially the 3 phase can be run as a 3
phase generator in Star or Delta connections.

But few people realize that a 3 phase motor  that can be wire Star or Delta
can be as well wired single phase double voltage with a center tap

The USA Grid system uses the basic 115  VAC and the  230 Vac so called two
phase system where the voltage is  115-0-115 = 230 Vac .

If the motor can be wire DELTA ( it  could be a 6 or a 12 Wire motor) - 6
wires for a single Voltage operation or with 12  wires for a dual Voltage
operation.

To run the motor as a Generator two phase system, wire the motor DELTA
connection -- Select one phase as the primary phase, let's say A phase then
connect  phase B and C in series,

Delta connection normally done  is :

A1 - to - C2
A2 - to - B1
B2 - to -C1

Where is A1 - OUTPUT primary Phase ; B1 OUTPUT second phase ( 120 degrees) ,; and
C1, OUTPUT third phase ( 270 )

Open connection  A1 To C2  to have a two phase generator !!

Generated output will be A1 = Phase 1 ; A2-B1 = center tap ; C2 = phase 2

In USA terms = A1 to A2-B1 = 115 volts , C2 to A2-B1 = 115 Volts  at 180
degrees from A1 and A1 to C2 = 230 Volts with  A2-B1 = center tap = Neutral
.

In this case one needs to GROUND A2-B1 as the neutral in the USA system.

In other systems like 230 Volts with one going to neutral, one needs to
select A1 or C2 and do a neutral connection, and in this case leaving A2-B1
not connected.

One needs to remember that the connection that has two phases in series ( B
& C) has two winding in series which add mathematically to a voltage that is
equal to A1 phase but with 180 degrees offset with DOUBLE winding
resistance -- which reflects into a higher losses .

Comments or questions ?

Nando