| Electronics > Beginners |
| Induction Motors and Inrush Currents Questions |
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| Benta:
Ain't no such thing as 230 V 3-phase mains, and it would never give 115 V phase-neutral. 400 V 3-phase means 400 V phase-phase and 230 V phase-neutral. |
| Zero999:
--- Quote from: Benta on May 27, 2018, 04:49:41 pm ---Ain't no such thing as 230 V 3-phase mains, and it would never give 115 V phase-neutral. --- End quote --- Yes there is. It's what you get from VFD, run off a 230V single phase mains supply. It will have 230V phase-to-phase and no neutral. --- Quote ---400 V 3-phase means 400 V phase-phase and 230 V phase-neutral. --- End quote --- Yes I know that. What I was stating was: a motor designed to work from 230V across each winding, would run from a 400V supply connected as star, or a VFD run off 230V, connected as delta. EDIT: See links below: http://www.vfds.org/single-phase-vfd-with-220v-input-output-924125.html https://www.amazon.co.uk/1-5KW-Single-Phase-Variable-Inverter/dp/B0151B2S2K |
| Gregg:
For single phase motors requiring high starting torque the old school solution was repulsion start induction run motors. The major drawbacks are the cost of manufacture and the mechanical parts needed to transfer form repulsion to induction that can wear out and seize in poor environments. However it is a very interesting concept. Today it is cheaper and reliable solution to use 3 phase motors with VFD even with single phase input. |
| oldway:
With motors up to 7.5HP, the single phase solution is virtualy impossible, that's why I did not asked this question...It are three phases motors for sure. A single phase 5.5KW 230V motor has a nominal current of 33A and a starting current of 5.5 x 33A = 49.5A Let's imagine two of those motors start at the same time, the start current would be 99A....far to much for a single phase 230V mains supply. Edit: Other reason: single phase motor is not a favorite technical solution in industry because single phase motors are less reliable than 3 phase ones. |
| Zero999:
--- Quote from: oldway on May 27, 2018, 05:52:45 pm ---With motors up to 7.5HP, the single phase solution is virtualy impossible, that's why I did not asked this question...It are three phases motors for sure. A single phase 5.5KW 230V motor has a nominal current of 33A and a starting current of 5.5 x 33A = 49.5A Let's imagine two of those motors start at the same time, the start current would be 99A....far to much for a single phase 230V mains supply. Edit: Other reason: single phase motor is not a favorite technical solution in industry because single phase motors are less reliable than 3 phase ones. --- End quote --- Normally yes, but it's possible to get a VFD with a built-in boost converter, to generate 380VAC three phase, from a single phase 220VAC input. I've never used one before. I just stumbled on it today. Link to Aliexpress --- Quote from: Mukrakiish on May 25, 2018, 01:39:42 pm ---With inverters, the peak currents are usually double their capacity and from what I understand the DC-DC bridge inside is what is most sensitive to voltage/current spikes. So it's not a matter of linear heat generation and more of the DC-DC bridge shutting down the system before the inrush passes. --- End quote --- It sounds like the inverter is incorrectly configured or faulty. The variable frequency drive should automatically limit the motor current to the correct level. A modern VFD will also include power factor correction and inrush current limiting. |
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