vlcsas Posted March 8, 2021 Posted March 8, 2021 Good day to everyone I have a problem that maybe someone can assist with I installed 3 x 5kw MKS inverters running in 3 phase mode and 30kwh of storage. Which seems to be working fine The 3 phase was installed primarily to run a lift in the house which is 5 stories high. But the lift failed to operate. The lights come on but no other response. I assumed that the lift was faulty as it has not run for 9 years previous and as all other levels of the house had power I waited for the owner to get it serviced. We decided to add a 3 phase backup generator. Upon comittioning and running through the inverters on bypass mode. Suddenly the lift burst into life and operated perfectly. as soon as the generator turned off. The lift returned to a non operation state. Inverters show no errors at all. We have also tried nutral to earth bonding which made no difference. Any help would be happily received Quote
Coulomb Posted March 8, 2021 Posted March 8, 2021 38 minutes ago, vlcsas said: as soon as the generator turned off. The lift returned to a non operation state. What power is the lift motor? What sort of controller does it have? If it's phase control, the inverters may not like it. Even if it's a 3-phase rectifier followed by a DC-3phase AC inverter, the current waveform won't be quite sinusoidal (≈6% ripple), which the inverters may not like. But it sounds like the lift controller doesn't like the inverter's 400 VAC output. What voltage is the generator? Maybe you just need to switch the three inverters to 240 VAC output (240 V line to neutral, 415 V phase to phase); they default to 230 V L-N (400 V P-P). Are all the inverters' AC-out neutrals connected together? My guess is that the controller doesn't connect to neutral at all, and if the neutral outputs aren't connected to each other, the inverters can't "push" against each other. Except when the generator is connected, the commoned AC-in neutrals will connect the AC-out neutrals. Quote
vlcsas Posted March 9, 2021 Author Posted March 9, 2021 Hi Coulomb Thank you for coming back to me. The lift motor is 2.9KW The Axperts are configured as phase 1,2,3 and in the matched breakers points in the breaker box. All Neutrals are linked across the inverters so all bonded. The inverters are locked to 230v and cant see anyway to change that. The generator is matched to 230v as well. We measured the voltages across the all phases with the inverters only and then the generator on and the phases all measure the same (say within a couple of volts) The lift control is a massive great big unit but I dont have full details about it with me at the moment. We tried neutral to earth bonding which made no difference. I feel it must be a phase issue but im at a loss at the moment Best Regards Quote
Coulomb Posted March 9, 2021 Posted March 9, 2021 15 hours ago, vlcsas said: We measured the voltages across the all phases with the inverters only and then the generator on and the phases all measure the same (say within a couple of volts) Did you measure each phase with respect to neutral, or phase to phase? You should measure close to 400V phase to phase (check all three pairs of phases) if the inverters are spacing their outputs 120° apart as they should. If you had say a P1 and two P2s (no P3), then one of the 3 pairs of phases would read near zero volts. When 3 phase rectified, this might produce less than the expected 560V, and that might cause the lift controller to refuse to work. Or maybe the bus voltage would dip too far and fast under load, and/or the ripple would be excessive. Quote
Beat Posted March 18, 2021 Posted March 18, 2021 this is a tricky one. First determine whether the 3-phase motor is directly fed from the line by a smooth starting provision or if it is variable speed controlled by an electronic variable frequency control. In the first case check if the phase sequence is correct. You may change the sequence by interchanging two of the 3 phases at the inverters connection to the system. Or you may change the phase attributions of the inverters to P3-P2-P1 instead of P1-P2-P3 in program 28. In the second case the phase sequence should not matter. If it is a ripple problem you might solve it by connecting capacitors on each phase to neutral. The capacitors must withstand at least 350V AC. Jacques Ester 1 Quote
vlcsas Posted May 7, 2022 Author Posted May 7, 2022 Sorry for delay in coming back to this issue. I resolved it in 5 mins in the end. Just tried every phase combination and a last the lift worked. Quote
Steve87 Posted May 7, 2022 Posted May 7, 2022 Had a similar issue with a 3 phase Air conditioner. They are phase sensitive these 3 phase machines and if one doesn't have a phases correct when turning them on, you can actually blow a PCB board. Just glad you had a good outcome. My problem in the end was slightly different and I had one bad phase and two good phases. After restoring the bad connection of the poor phase all was good. Quote
Beat Posted May 7, 2022 Posted May 7, 2022 (edited) 23 minutes ago, Steve87 said: Had a similar issue with a 3 phase Air conditioner. They are phase sensitive these 3 phase machines and if one doesn't have a phases correct when turning them on, you can actually blow a PCB board. Just glad you had a good outcome. My problem in the end was slightly different and I had one bad phase and two good phases. After restoring the bad connection of the poor phase all was good. It's the matter of understanding the 3 phase system and how 3 phase motors work. The 3 phase currents create in the motor a rotating magnetic field. The rotor follows this rotating field. The direction of rotation is determined by the phase connection on the motors terminals. If the phase sequence is wrong, the motor would want to rotate in the wrong direction. Most applications wont like that. Edited May 7, 2022 by Beat Jacques Ester 1 Quote
Steve87 Posted May 7, 2022 Posted May 7, 2022 Very well put...It was my first encounter with a 3 phase big appliance and it was a good teacher to look into the subject. Quote
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