single phase to 3-phase converter

longthrow wrote:
t1=220v 0-30 sec timer relay
olr=overload relay set @ 2-3 sec; starting time depends on the motor size

longthrow wrote:ways of producing 3 phase ac from single phase:

1)a motor-generator set (m-g set) where a single phase motor drives a 3
phase generator which is bulky, expensive & complex

2)electronic inverters using power igbts or mosfets controlled by
processors which produces the "ideal" 3-phase but is very expensive and
more comlpex.

3)Static converters that use a transformer to produce 2 phases from one,
and at the required voltage, plus a capacitor to produce a third phase when
a load motor is connected. Such a converter is cheap to manufacture but has
four serious disadvantages:

a) the load must be a motor and it must be known in advance if it is star
or delta connected
b) if the load has more than one motor then the highest power motor must
always be switched on first
c) the load motor will only run at 70% of normal torque
d) there is a minimum power limit as well as a maximum so the capacitor
value must be manually switched to match the load.

4)Rotary converters add an unloaded motor-generator to the static
converter, eliminating problems a) to d). The motor-generator can be
considered as analogous to the flywheel of an internal combustion engine;
it smooths the flow of power and maintains the equal time relationship
between the three phases. Efficiency is much higher than for an inverter
solution, reaching 95% for most of the power range.


basic rotary converter: Tesla polyphase induction motors


modified with magnetic contactors & relays:

pb=push-button switch (start=green, stop=red)
k1=k4=20-50A 220vac magnetic contactor (150% of motor FLA rating; limit under 10hp)
k2=k3=5A 220vac relay
t1=220v 0-30 sec timer relay
olr=overload relay set @ 2-3 sec; starting time depends on the motor size
c1=c2=12-16uf per motor's hp
c3=50-100uf per motor's hp
l=220v pilot lamps
m=1-10hp 220v 3-ph induction motor

okis to...