Calculating inverter for motor

[Quang_Lo]

Dear All,
I have a problem. It's calculating inverter for 3 pharse non-synchronous. I mean that i don't know the formula. My colleagues show
Here we go :
P[SUB]1[/SUB]/P[SUB]2[/SUB] = (n[SUB]1[/SUB]/n[SUB]2[/SUB])[SUP]3

[/SUP]Please help me out
Thanks

 

[Marvo]

If the motor is driving a pump or a fan impellor them read up on the Affinity Laws to calc correct inverter specs.

 

[Besoeker]

Dear All,
I have a problem. It's calculating inverter for 3 pharse non-synchronous. I mean that i don't know the formula. My colleagues show
Here we go :
P[SUB]1[/SUB]/P[SUB]2[/SUB] = (n[SUB]1[/SUB]/n[SUB]2[/SUB])[SUP]3


[/SUP]Please help me out
Thanks

Rate the inverter for the motor being used.
It really is that simple.

 

[SheffSimon]

Rate the inverter for the motor being used.
It really is that simple.

It really isn't always that simple, length of cable run and other factors can also affect the choice of inverter size.

 

[LeeH]

It really isn't always that simple, length of cable run and other factors can also affect the choice of inverter size.

Can you please expand.

I always spec a drive on its load and its available functions for task in hand.

The cable spec is done as normal.

Cheers.

 

[Besoeker]

It really isn't always that simple, length of cable run and other factors can also affect the choice of inverter size.

If the motor is rated at 100A, would you really rate the inverter differently?
I wouldn't. But then I have only been in the VSD field for forty some years.
Maybe I'm just a slow learner.

 

[Bobster]

The only real effect on a drive with cable length is if it needs line filters for EMC compliance. Otherwise as Besoeker has stated, match the dive for the motor size.

Most drives will have 2 ratings heavy duty and normal duty, pick which is suitable.

Cable size is then specified using the normal methods.

 

[SheffSimon]

The only real effect on a drive with cable length is if it needs line filters for EMC compliance. Otherwise as Besoeker has stated, match the dive for the motor size.

Most drives will have 2 ratings heavy duty and normal duty, pick which is suitable.

Cable size is then specified using the normal methods.

Currently commissioning an MCC fitted with ABB ACS 800 drives, some of which ABB oversized wrt motor rating plate because of long cable runs.

 

[LeeH]

Currently commissioning an MCC fitted with ABB ACS 800 drives, some of which ABB oversized wrt motor rating plate because of long cable runs.

Can you please explain why?

 

[Besoeker]

Can you please explain why?

To make more money maybe.

 

[SheffSimon]

It was because they were very small (0.18kW) motors on long (300m) cable runs. Something to do with cable charging currents from memory.

 

[Besoeker]

It was because they were very small (0.18kW) motors on long (300m) cable runs. Something to do with cable charging currents from memory.

Chokes would sort that out.

 

[Darkwood]

Motors with excessive torque demand on ramping start/stop set-ups may require larger inverters to avoid shock load tripping issues, I know 2 brands that recommend this, also excessive start/stop duty may warrant a larger inverter too.

2 reasons off the top of my head for getting larger inverters than motor rating.

 

[Marvo]

Occasionally our choice of inverter will be driven by a requirement for a wider range of carrier frequencies than normal.

Frequency of stop/start cycling would be an issue that we'd address with uprated forced ventilation rather than oversizing.

 

[LeeH]

Don't understand how you would get excessive start up current with a correctly designed and set up system.

Not saying you cannot, but just cannot see it in my experience of moving heavy loads with VSD's.