6 replies to this topic

[chris1373]

I have a few ABB UA95-30 contactors and they have printed a power table in kvar, not in kw. Are they specialy made for condensers aplications? Can i use them to build a delta wye motor starter?
Finaly, is there a phisical diference betwen the contacts in a kvar contactor and a kw or hp contactor?
Fon any help, thenks in advance.

Chris.

[Tua]

Don't worry, there is no any difference between contactor with kVA and contactor with kW. But you should remember that kVA is full power and kW is only active power(may be I am not right, but in Russia we call it like that). The difference betwen these two powers is cosF. For example: Pf=100kVA, cosF=0.9 then Pa=Pf*cosF=100*90kW. It means if in your contactor you have 100kVA power you can use this contactor near 90kW. But it is in general sometimes you can meet the load with cosF less then 50%, cosF<0.5 it is serious problem and you shoul spend more attention for this calculation!

I am sorry, I've done smal mistake
Pa=Pf*cosF=100*0.9=90kW

[CJC_PE]

From http://library.abb.com -- Dated November 2004
UA..RA contactors for inrush currents exceeding 100 times the rated currents are now available up to 80 kvar. The UA..RA contactors are equipped with a special front mounted contact block which ensures the insertion of damping resistors in each phase, limiting the peak current at energization of capacitor banks. The contactors UA16..RA up to UA75..RA were released in June this year, and now the UA..RA range is completed by the addition of UA95..RA for 70 kvar and UA110..RA for 80 kvar.

As indicated above, contactors designed for connecting power factor correction capacitors must withstand high inrush current compared to the continuous current. Motor starting contactors must withstand moderate inrush current, but more importantly, they must break locked rotor current in the event that the motor stalls and the overload relay de-energizes the contactor. They may not be physically different, but they may have different ratings according to the duty. They may also may have different certifications indicating which code requirements they meet.

[jraef]

Yes, the contactors are physically the same, but the ratings are different. ABB used to just publish a chart that p[rovided the kVAR ratings of their contactors. Unfortunately, a lot of people had no idea what they were reading and misapplied the contactors. Now they released a separate line of contactors that only have the kVAR ratings so that this (supposedly) won't happen. The problem is, yopu don't necessarilly know that the inductive rating (AC3) is on them, the part numbers don't directly interchange I am told.

[AB2005]

Unfortunately, a lot of people had no idea what they were reading and misapplied the contactors.

Dear Mr. Jraef,

I am also in those people but want to know more about contactor rating (AC1, AC2, AC3.....). We have designed a PF correction panel for our new project and used "National" brand FC-85 contactors for switching 50kvar capacitors as I didn't know about kvar rating of contactor.
I would be very thankful to you or any member who provide me any link which help me in understanding the contactor's rating.

[chris1373]

Thanks for all your answers.

The specific contactors have printed this particulary numbers.

Ue kVAr
220-240 35
380-400 60
415 65
500 70
660-690 75

We have here 380V. How can i calculate the kW rating that this contactor can handle starting from the 60 kVAr?

Chris.

[jraef]

Sorry, I just learned something new today. I now work for Siemens, and in looking up our capacitor switching ratings, it appears that there is a slight difference in the construction of the contacor. For capacitor switching they have a set of "early make" (leading NO) aux contacts that place a resistor in parallel with each pole just immediately prior to the main contacts closing. This is to absorb the spike that occurrs as the capacitor is charged. Also, there is an IEC utilization catagory assigned to the contactors themselves, so you can look up any contactor and determine all AC ratings. In Siemens case, the S3 contactor is rated for 65kVAR at 400V according to AC-6b (capacitor switching duty), and also 45kW motors according to AC-3. So when used in a Start-Delta control scheme, the motor could be up to 80kW at 400V. I would imagine ABB and others are similarly rated although you may need to extrapolate the numbers since your contactor is ratred only for 60kVAR. If your contactors have the early-make aux contacts and resistors on them, be sure to remove them when using a on a motor.

AB2005,
I don't know about other brands, but if you can get hold of a Siemens catalog, look up the 3RT16 contactors for a description of how they work and a link to wiring diagrams, ratings etc.