3 Phase Motor Questions

[ryanm]

Hi All,

Just a few questions I'm not too sure about.

1. The majority of the time, if running 3-phase, 400v, you would connect the terminals in the junction box in Star, and single phase, with Capacitor would be in Delta. (I'm trying to describe the formation of the brass connectors across the terminals, which connect to the windings).

When you introduce a Frequency inverter, if it had an input with 3-phase and output of 3-phase, you would connect this up in Star, as it is 3 phase?!

What about a Frequency Inverter, with single phase input, but 3-phase output? I think it would be in Delta, due to only originally using a single (L + N) input. Correct, or am I missing something?

2.

At work a motor has failed recently, and we got a replacement sent, but the current doesn't seem to "add up".

The original failed motor was 3-Phase, 400v, 1.5kW, 3.7A, but the new motor is 3-Phase, 400v, 1.5kW, 5.7A. How can this be?! We tried fitting it, but it is pulled too much current which the frequency inverter doesn't like as it is only rated to 4A. Both motors are 2 pole too.

Thanks a lot

Ryan

 

[ryanm]

Thanks a lot for the answers.

In reply to Q1, 99% of the motors are under 2.2kW, so I've only really seen the 400 V Star / 230V delta. Thanks for the explaination RE the links on the single phase motor, I've never really looked at one before, but I understand what you mean

Q2: Yes the new motor was deinitely wired correctly, even the name plate says 400 V STAR at 5.7 Amps, and 230 V Delta at 9.x Amps. I phoned Stroter where we got the motor (and gearbox) from, and he couldn't undertand it, but could see what he had supplied us as was going to get back to us (but hasn't).

The original motor was from Germany, but the new one doesn't actually have a name on the nameplate weirdly, but the terminal box lid has Siemens on it.