Hoffman
Member
Also, from the Freescale site search for DRM039/D. This is an application note by Motorola.
Kataeb said:Concerning, the connection of all three leads (U1+Z1, U2, Z2) of the motor...to the three outputs of the VFD, can you send a sketch of the wiring diagram?
On the other hand, the pump is a self priming electropump. And we need steady flow proportional to the production speed to avoid too much liquid waste. But I will discuss the valve issue with the mechanical engineer…
On the 3rd hand, I contacted our Siemens agent, and he indicated that we could use the Micromaster mm440 for our application (but it is not system tested, so no guarantee). I made a sketch for the wiring taking into consideration the protection of the motor using an lc filter and a transformer. What do you think of this? Will it work? (see attached)
When I have a bottleneck in my project, I like to have many plans for the solution…because the devil is in the details…
Wise decision, Kataeb! (Sigh!)Kataeb said:Due to the pressure issue, we will finally opt for the valve solution (our mechanics will have more work to do!).
Not really sure if I understand your question correctly... Do you mean what happens if the starter winding is disconnected while running? Disconnecting a motor from a VFD should be done when the output of the VFD is not active. When disconnecting while running, the spark (read: high voltage) over any regular contact might and eventually will destroy the VFD.Sparkz, concerning your circuit, will any damage happen if while running, the vfd tripped a fault (because the current will be automatically disconnected)?
I noticed that you only used 2 of the 3 VFD outputs. The VFD's output capacity would still have to be 1.73 (square root of 3) times higher than the motor's rated power, since all power has to be delivered over just 2 instead of all 3 outputs. So, a 0.75kW-1Ph motor needs a 1.3kW-3Ph VFD. But there's something else why a single phase transformer won't help...On the other hand, in my circuit I added a transformer to use a vfd with lower power (reaching on its output 400v) to reduce the overall cost.
I don't see why this could be a problem... The VFD also does this when a 3 phase motor is used, so why would it be any different with a single phase?Kataeb said:The vfd that we are using, turn off their power transistors automatically when a fault occurs on the drive. So the current will be interrupt suddenly, wouldn't it?
NO, this is not correct! I used the inverted 'RUN' output signal of the VFD and just delayed that for about 0.3s. In my application (with the speed set to approx 75Hz and an acceleration time of 1s) the starter winding stayed connected until 0.3s after start, so the winding got disconnected above approx 25Hz.In your circuit, the starter winding is supplied as long as the motor is running and for 0.3s after its stoppage, correct?
In order to get sufficient torque at lower rpm's the capacitor has to be removed and the starter winding must be fed directly with a third phase. The problem with any starter winding is that current through it has to be limited (normally by the capacitor), or at least limited in time (in my case by the solid state relay). You can leave the starter winding directly connected to the third phase up until approx 30...35Hz, resulting in maximum torque. At higher speeds the starter winding current would exceed its maximum value, so the winding has to be disconnected: At those higher speeds, torque would be acceptable/almost standard.Kataeb said:Hi Sparkz,
I have one question: our motor is with permanent split capacitor (20 microfarads, 450 volts), so normally when this motor is directly supplied by 220vac, its starter winding will be supplied as well. I think that in this case we could use your circuit without the ssr (see picture)
This is something I can't confirm. You could use a 3-phase 400/230V stepdown transformer to adjust the 400V output of a 1.5kW-400V VFD for a 230V 1-phase motor. But I'm starting to think you're trying to use a 0.75kW-400V VFD! I have serious doubts about just how symmetrical the load to the VFD will become with this transformer.Kataeb said:On the other hand, siemens technical people suggested the following:
to use on the vfd output a 3 Phase Delta to Star 200V/220V Transformer instead of the single Phase one (the Phase to Phase voltage after filter is only 200V not 380V), this will symmetry the inverter load and compensate the lost of the filter as well as transient peak voltage for motor winding and permanent split capacitor. This configuration works with several customers’ applications The MICROMASTER 420 and 440 ore SINAMICS G110 can be used with single-phase motors.
What do you think about this?