Understanding the nameplate

[MIER]

Hi there,

I have tried to figure this one out buy searching, but without any results.

My case: On the nameplate for my motor it says:

Star: 3x400V / 2.2kW / 6.0A
Delta: 3x230V / 2.2kW / 10.4A

I am not sure about the efficiency but why is the motor power 2.2kW?!?

400 x 6 x 1.73 = 4.15kVA
230 x 10.4 x 1.73 = 4.14kVA

How do I know what the power factor is? Let us assume 0.85:
4.15kVA x 0.85 = 3.53kW

If this is the truth, then the efficiency is:
2.2 / 3.53 = 0.62

What am I missing?

 

[ScusaMe]

Power = E x I x 1.73 x P.F. x Eff.

where: P.F. = Power Factor

 

[ScusaMe]

Add:

What you don't say is what is the RPM on the nameplate.

Looking in an ABB motor catalog ..... here's some data on a

400v 2.2kW 1000 RPM motor.

Full Load Eff. 80.1 %

Power Factor .74

I 5.4 amps


Another motor I looked at of similar design and rating had these numbers

Eff. 83 %

P.F. .73

I 5.24 amps

When we look at an 750 RPM (8-pole) motor, we find this data ...


Eff. 80.5 %

P.F. .67

I 5.9 amps


From this I would conclude that your motor has a low efficiency and a low power factor.

 

[electricpete]

Yup.
smaller motors tend to have lower pf*eff than larger.
slower motors tend to have lower pf*eff than faster.
older motors tend to have lower pf*eff than newer.
there are plenty of exceptions.
Manufacturer's info is the best available data for your motor (except perhaps actual measurements taken yourself).


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(2B)+(2B)' ?

 

[ozsalty]

why 2.2Kw....equals the old 3H.P.

 

[MIER]

Sorry guys,

It is 6 poles and 930 rpm - so I guess the effency is "low" due to a slow engine.

We am trying to size a UPS towards worst case - and even though full load is the best efficiency it will be still be "worst case" right?

Meaning: 400 x 6 x 1.73 = 4.15kVA.
4.15k x 0.83 = 3.44 kW

Just an info; it will be started up by a soft starter limited to 6.0 A.

 

[waross]

Worst case will be the motor not starting.
Limiting the starting current to 6 amps on a motor rated at 6 amps may inhibit the motors ability to start somewhat.
Check the specs on the inverter. It may be current or KVA rated rather than kW rated. You may have better luck with a VFD instead of a soft start in that size. Then you may be able to go with a single phase UPS.
Do you want the motor to be able to drive the occasional overload?
Many designers consider it good practice to oversize motor supply components by 25%. In many instances the codes mandate 125% capacity for some motor supply components.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

I guess you are starting with an assumption that the motor operates at it's nameplate loading. (that probably deserves to be checked... the actual load is determined by load, not motor nameplate).

You know the product of efficiency times power factor is 2.2 / 4.15 = 0.53

It could be that the product pf*eff = 0.53 consists of eff = 0.83 and pf = 0.64.

But is it conservative? What if pf is a little higher and eff a little lower.

If you wanted to be really conservative (with respect to these particular factors), you might choose pf = 1, eff = 0.53, which leads to UPS requirement of 4.15kw. (I am assuming it is the real power drawn from stored energy of battery that is of interest)

=====================================
(2B)+(2B)' ?

 

[electricpete]

If you are looking at kva power rating, then the split of pf and efficiency doesn't matter.

If you are looking at total power requirement (such as for battery amp-hour sizing), then you need to make an assumption about the split as I discussed above.

=====================================
(2B)+(2B)' ?

 

[electricpete]

total power requirement

(should've said total energy requirement)

=====================================
(2B)+(2B)' ?

 

[7anoter4]

From ABB Catalogue ABB / LV Motors / 9AKK103506 EN 04-2007
General purpose aluminum motors
Technical data for totally enclosed squirrel cage three phase motors
IP 55, IC 411; Insulation class F, temperature rise class B
2.2 kw 400 V 50 Hz 940 rpm
pf=0.71 eff.=0.77
Irat=5.9 A

 

[jraef]

Sorry guys,

It is 6 poles and 930 rpm - so I guess the effency is "low" due to a slow engine.

We am trying to size a UPS towards worst case - and even though full load is the best efficiency it will be still be "worst case" right?

Meaning: 400 x 6 x 1.73 = 4.15kVA.
4.15k x 0.83 = 3.44 kW

Just an info; it will be started up by a soft starter limited to 6.0 A.

Several flaws in the concept here.
As Bill pointed out, limiting the starting current to 100% of FLC will result in a stall and an unsuccessful application. A soft starter can only limit current by limiting voltage, which limits torque. To attain a Current Limit at 100% of FLC when it wants to be 200% of FLC (the minimum required for even the lightest of loads) the soft starter will have to phase back the voltage to approximately 50% of RMS, so the torque will be approx. 25% of BDT, which would have been maybe 220% of FLT, so you will have roughly only 55% of FLT at the motor shaft at 100% Current Limit. I have never seen that work. Typical Current Limit for something easy like a pump or fan is 250-300% FLC, anything heavy may be 350-450%. In addition, Soft Starters need relatively clean power on the input so they can sense when to fire the SCRs. If the output of your UPS is PWM, chances are the Soft Starter will not work properly anyway.

Aside from that, your math is flawed as well. 2.2kW is 2.2kW, it doesn't matter how you get there. But in a motor, that 2.2kW rating is the MECHANICAL output of the motor, not the electrical input. The electrical input is the output (2.2kW) divided by the efficiency, which you do not know. But ASSuming (from the other posts) a 71% eff, the the electrical input would be 2.2kW/.71 = 3.1kW. But that would ONLY be for running load capability. Assuming the Soft Starter will not work (as I said above), your choices are DOL or VFD.

A VFD would be OK with PWM on the input because all it is doing is converting back into DC anyway, and because it controls frequency AND voltage, you will likely be able to start that motor with 3.1kW from the UPS, as long as starting time is irrelevant to you.

If you go with a DOL start, you will likely need a UPS that is capable of 18kW because unlike other power sources, a UPS is typically not built with any "reserve capacity" in the design. They are generally NOT intended to be used on induction motors.

The only other viable reduced voltage starting method for you would be an Autotransformer starter, but nobody makes one that small, you would have to roll your own from scratch.

Do NOT, I repeat, NOT attempt to use Star-Delta on this, the result will be a dead UPS and/or motor.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[7anoter4]

UPS system could support 1.25*Irated for 1 min or 1.5*Irated for 30 sec[check with the Manufacturer].
If Istart=6*5=30 A [D.O.L] a UPS of 20 A 400 V will be fair.

 

[MIER]

Okay I follow you jraef, especially about the soft starter.

Worst case could be kVA equal kW if we are looking at the UPS. We have a lot of equipment connected to this UPS (cameras, computers, IFF, radio, radar etc.). Which typically uses a controlled and know amount of power. But for the radar antenna running out in the open by a 3 phase engine - it gets a bit more complicated.

We have been looking at ABB motor controller (ACS550), and I got two choices. Either I will go for a three phase or one phase.

It looks like the 4.0 kW threes phase could do the job, but if I have a 4 kW ABB single phase, will this be enough? I am thinking current limitation from this one.

I have attached the name plate for the motor (not sure how it is shown since it is my first time to attached a link for a picture).

 

[waross]

With a single phase motor you can't easily use a VFD or a soft start.
You can often feed small a VFD with single phase or three phase and drive a three phase motor.
Worst case, KW=KVA, NO, when a motor is starting the KVA may be several times the KW.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MIER]

Yes during startup, but under normal running condition.

What to expect from a ABB during start up? I know there is many ways to set up the ABB for starting up the motor, but the time is not an issue, an example could be 15 sec. But can I expect 2 x kVA during start up? I know the UPS needs to be oversized but how much extra is needed for a motor like this?

 

[waross]

I think that it may be the safest for you to list your loads and then ask the UPS vender to suggest an appropriately sized UPS. You don't have the background or experience to properly size the UPS. I am sure that you have learned a lot here, but each new question reveals new areas where your knowledge is lacking.
Pass the buck and try to get the UPS vender to take responsibility for sizing the UPS. That will be a lot safer, career wise.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MIER]

Thank you all for the help.

 

[burnt2x]

Pass the buck and try to get the UPS vender to take responsibility for sizing the UPS. That will be a lot safer, career wise.

A very good solution and perhaps the best thing to do, IMO.