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Aghvel NiaziPower-User

Join Date: Mar 2010Location: Islamic Republic of PakistanPosts: 100Good Answers: 14VFD and Motor Power Calculation06/30/2010 7:51 AM

We have an Induction motor (7 KW, 400 V, 50 Hz, Delta, 15.5 A, P.F 0.75, 1465 RPM ) driving a conveyor belt. Motor is connected to the VFD ( ACS-800-01-0016-3, 8.1 KW, 3 X 400 VAC, 12 A, 50 Hz). Some values taken from the LCD of VFD at different times at different loadPower (in Percentage) Current (A), Frequency(Hz),Speed ( RPM)1. 25.57 %, 13.24 A, 28.49 Hz, 857 RPM2. 29.21 %, 12.72 A, 32.79 Hz, 966.6 RPM3. 31.22 %, 13.08 A, 34.95 Hz, 1031.1 RPM4. 34.88 %, 13.20 A, 39.25 Hz, 1160.0 RPMHow the Power (%) is being calculated by the drive in the above four reading?Drive name plate shows 12 A, but on Display panel we have current 13 A. Is it due to Delta connection?What will be my V/f ratio in this 7 KW motor case?Is it will be fix or have some range?Often we observe that low power rating motors when operated under no load condition they consume 30-40 % of the rated Power but here why power is below 30-40 % even at loaded conditions?if I assume V/f ratio to be 8 (400/50). then at 13.24 A, Voltage will be equal to 228 V ( V= 28.49*8 = 228 V) and P = 1.732*228*13.24*0.75*0.9173 = 3.6 KW which is 51 % of 7 KW.Kindly help me in understanding this LCD display information of ACS 800Maple Leaf Cement Factory

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I am not a VFD expert but your calculation looks ok (except the use of 0.9173 ? in the formula). Yes, it is true that the actual % value of power is showing less. The VFD display shows the actual power in percentage of the Motor Nominal Power (parameter 99.09). I am in doubt that the value of the parameter 99.09 (parameter group # 99, parameter # 09) is not set correctly. Please verify the value of this parameter. Its value should be 7 kW (motor nameplate kW). You can use the document from the below link and follow the instruction in page 28 to view the parameter value.http://www05.abb.com/global/scot/scot201.nsf/veritydisplay/4b7e4f55e27c97fcc12577150030cfde/$File/EN_800_IPC_FW_C.pdf- MS__________________"All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)

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Aghvel NiaziPower-User

Join Date: Mar 2010Location: Islamic Republic of PakistanPosts: 100Good Answers: 14#2In reply to #1Re: VFD and Motor Power Calculation 06/30/2010 1:12 PM

91.73 is the efficiency of the motor. Now I came to realize that the power shown by the drive Display is the Electrical input Power i-e P = 1.732 *V *I*P.FActually the original nameplate is like thatVEM :11/ 7 Kw, 400 V, 50 Hz, 21/15.5 A, P.F 0.85/ 0.75, 1450/1465, 40/52 C(Normally temperature in our region remains hot (45 C) during these days therefore I assume that it will be 7 KW like many other motors where we put de-rated values in Simocodes but I will check it tomorrow the parameter U have mentioned).but how these values are wright. Let say 11 KW case for first measurement i-e(25.57 %, 13.24 A, 28.49 Hz, 857 RPM). The Power will be P = 1.732 *228*13.24*.85 = 4.444 KW which is 40 % of 11 KW instead of 25.57 %(34.88 %, 13.20 A, 39.25 Hz, 1160.0 RPM). P= 1.732*314*13.20*0.85 = 6.10 KW which is 55.47 % of 11 KW instead of 34.88 %.Actually where the problem lies i-e Value of the P.F or the value of the Voltage applied at the terminals.( I tried to measure the voltage at the terminals of the motor but Digital meter shows wrong values, for one moment it shows KHZ, other moment resistance, then a Buzzer sound and so on etc)

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Anonymous Poster#8In reply to #2Re: VFD and Motor Power Calculation 08/10/2010 2:09 AM

Check parameters for voltage and torque and review your calculation,check your motor parameter settings,moreover,your motor shows different kw11 and 7 at the same voltage is this correct or there are different terminal connections.

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JRaefGuru

Join Date: Sep 2006Location: California, USA, where the Godless live next door to God.Posts: 3913Good Answers: 593#3Re: VFD and Motor Power Calculation 06/30/2010 2:20 PM

You are calculating power based on what it COULD be in the drive, but the drive is measuring what the power ACTUALLY IS. Assuming you have a centrifugal (quadratic) load such as a pump or fan, the power required by the load varies at the cube of the speed reduction. So at 857RPM, that is (857/1465=) 58% speed. So the LOAD will require only .583 or roughly 20% power, plus whatever losses exist in the VFD, motor and power train components. The VFD is measuring this and displaying it; their formula is simply Power In - Power Out.__________________** All I every really wanted to be, was... A LUMBERJACK!.**

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Aghvel NiaziPower-User

Join Date: Mar 2010Location: Islamic Republic of PakistanPosts: 100Good Answers: 14#4In reply to #3Re: VFD and Motor Power Calculation 06/30/2010 9:52 PM

The Load is not Variable torque Load Like Fan or Pump. The load is a conveyor belt.It is a constant Torque Load. This conveyor belt take material of 180 Ton/ hr to the Cement mill. Fluctuation will be from 170 to 190 t.If it is a constant Load. As there should not be so huge difference in the calculated values vs the actual values. There is something wrong here may be V/f ratio or something elseNow take another example of a VFD. There is a 2000 KW, 690V, 46.4 Hz, 1985 A, P.F 0.87, 923 RPM motor attached to a fan.A reading Taken from the VFD812.2 RPM, Frequency 40.6 Hz, Current 1520 A, Torque 74 %, Power 1374 KW Now V/F = 690/46.4 = 14.87 So at 40.6 Hz V= 604 VP = 1.732 *604*1520*0.87 =1383.4 KWNow in our calculated values and values given by the VFD we have only a minor difference i-e 0.07 %

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Anonymous Poster#5Re: VFD and Motor Power Calculation 07/01/2010 8:41 AM

Hellohave you checked if the drive is woking in V/F mode or DTC mode?I work on ABB ACS800 multidrive inverters with ambient temp above 50C but with Aircon.have some problems in calculated torque.

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SalarAssociate

Join Date: May 2010Posts: 31Good Answers: 3#6In reply to #5Re: VFD and Motor Power Calculation 07/02/2010 7:53 AM

Yes the Drive is in DTC mode. Motor Power is 11 KW and and drive rating is 12.5 KW

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Anonymous Poster#7Re: VFD and Motor Power Calculation 08/10/2010 1:58 AM

Percentage power,current frequency and Rpm are insufficient parameters,we require voltage and Torque parameters as well to calculate the exact power to the motorI feel there may be a parameter setting problem in the motor map,kindly check motor parameters..

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ahmed89Participant

Join Date: Aug 2014Posts: 1#9Re: VFD and Motor Power Calculation 08/20/2014 12:56 AM

I am a newbie; sorry for a kiddy question.I came across ACS800 multi drive system.In Drive Window;______________________________________P01.06: Motor Current is 1150AP01.11: Motor Voltage is 695.0VP01.09: Power Percentage is 35.98Nominal Power entered is 2990kWcos(phi) = 0.85____________________________________I calculated Power as Root(3) V I Cos(phi) = 1176.8 kW which is 39.35% of 2990kWOn other hand parameter P01.09 says 35.98%..Am I doing something wrong in the calculation ? Or how drive is calculating the percentage of power?"Lost in ACS800"

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