Contactor for a transformer

[conmgt]

Hello,

I need to size a contactor for the switching of a transformer. The transformer is 208V 3ph 30kVA. The inrush, according to the manufacturer is ~410A. I'm looking at an ABB catalog and I'm seeing ratings for HP, lighting, and resistive loads but not for a transformer and I'm wondering how to handle that.

The catalog says: "Switching of transformers: This application is characterized by high current peaks on contactor closing due to magnetization phenomena. The corresponding utilization category according to IEC 947-4-1 is AC-6a. Ratings are derived from test-values for AC-3 or AC-4 according to formula given in IEC 947-4-1."

I think the catalog is just quoting IEC and not making a statement of their own.
So does that mean to take an AC-3 or AC-4 rating and apply an IEC formula to determine which contactor to use for a transformer?

 

[conmgt]

The catalog has a line in the specs that says: "Rated making capacity AC-3 = 10 x Ie AC-3"

 

[conmgt]

I found this handy tool:

http://www.abbcontrol.fr/Appl-AC6a/

 

[Jraef]

Or you could just use a real contactor that is designed to NEMA specs and be done with it. A NEMA spec contactor has that inrush capacity built-in to the design, so you would just size it for the transformer FLA.

 

[jumper]

Or you could just use a real contactor that is designed to NEMA specs and be done with it. A NEMA spec contactor has that inrush capacity built-in to the design, so you would just size it for the transformer FLA.

Sounds good to me.:thumbsup:

 

[templdl]

From what my understanding is that this issue my be much ado about nothing.
The inrush for motors as well as transformers is very similar. Also, has there been any consideration of applying a definite purpose contactor?
One of the other guys brought up using an AC3 rated contactor another good suggestion.
But I don't see this to be a big issue. I supplied tens of thousands of dollars worth of MV motor starters for use to control transformers supply portal cranes at the various US ports.

 

[conmgt]

Or you could just use a real contactor that is designed to NEMA specs and be done with it. A NEMA spec contactor has that inrush capacity built-in to the design, so you would just size it for the transformer FLA.

The transformer draws 82A at 208V and a NEMA3 has a current rating of 90A.
But Square D's Table 16.44 "Application Data for Selection" which specifically addresses contactors for transformers along with motors, jogging motors, capacitors, resistance loads, lighting...specifies a NEMA 5 for a 30kVA transformer which has a 270A current rating.
A NEMA4 on that Table is listed for a 20kVA transformer max and a NEMA3 is listed for 12kVA.

I don't want to price this more than necessary and certainly don't want to undersize the contactor and have issues.