Choke for Siemens VFD Drives

[John Gaunt]

I have a project coming up using an S7-400 PLC to control
about 40 PID Loops. Of those about 20 loops drive cooling
fans using Siemens Micromaster 420 Drives. The motors are all
three phase and about 5kW.
I would like to know how to size a choke to connect
to the supply in the drive panel for these 20 drives?
I know that I can buy expensive individual chokes for each drive
from Siemens. Is there an advantage in individual chokes?
There will be several other drive panels in the same control room
off the same supply. These other panels each have a large choke
installed. Do I benefit from there already being several chokes
connected to the supply? On the strength of these other chokes
being fitted can I simply not bother to provide a choke for my
drives?
Regards...........John Gaunt

 

[rdrast]

The simple answer is if you have a single INFEED choke, it must be sized current wise based on your upstream protection.

If you have a 20A breaker feeding your 20 drives, you need a 20A choke (minimum). Impedance is generally 3 or 5%; If I know the supply isn't very stiff, I'll go 3%. If I know the supply is stiff, or I dont' know what it is, I'll go 5%.

No matter what, I do like to have seperate output reactors for each drive, especially if the motor leads will be more than 20 or 30 feet long.

Now... About pricing, Siemens, AB, SSD, You name the brand, all charge a very high premium. A reactor is nothing complicated, you should be able to find very high quality reactor manufacturers (even for specific drive applications) who charge literally a fraction of what Siemens (even with an OEM discount) would quote.

 

[John Gaunt]

Thanks Rdrast,
I understand the current and voltage sizing.
What I would like is to understand how to calculate or
guesstimate the number of Henrys the choke should be.
Regards......John Gaunt

 

[rdrast]

The inductance varies according to the reactor sizing, but in general, that isn't what is specified when purchasing a reactor for drives. Rather, the 'nominal impedance', Voltage, and Full Load Current are the specifications, and let the reactor manufacturer figure out the math.

Again, the typical values are 3% and 5%