Motor voltage 380-480v Motor voltage 380-480v Indy (Industrial) (OP) 11 Jul 17 14:29 We have a motor that has the following spec 3kw 380-480v 4.6A My question is will the motor be rated 3kw 4.6A at 415v if we use it with a VFD? Thanks RE: Motor voltage 380-480v waross (Electrical) 11 Jul 17 15:31 The simple answer is yes. 4.6 A x 415 V x 1.73 = 3303 VA 3 kW x 746 W/HP = 2238 VA 2238 VA / 3303 VA = 68% The long answer is: If the combined efficiency and power factor is above 68%, AND if the motor is running at rated frequency and speed the motor will be capable of 3kW. Bill -------------------- "Why not the best?" Jimmy Carter RE: Motor voltage 380-480v iop95 (Electrical) 14 Jul 17 15:34 3kW is valid at 480V / 4.6A. 3kW at 415V/4.6A may be true for 95% efficiency and 0.95 cos fi. RE: Motor voltage 380-480v ScottyUK (Electrical) 14 Jul 17 16:12 Is the 380 / 480V rating based on 50Hz and 60Hz operation respectively? That is an unusually broad voltage range for single-frequency operation. RE: Motor voltage 380-480v Sazirul (Electrical) 10 Aug 17 06:59 Can you please explain this equation @waross 4.6 A x 415 V x 1.73 = 3303 VA 3 kW x 746 W/HP = 2238 VA 2238 VA / 3303 VA = 68% Thanks! https://www.anelectricalengineer.com RE: Motor voltage 380-480v waross (Electrical) 10 Aug 17 13:31 Sorry 4.6 A x 415 V x 1.73 = 3303 VA 3 kW / 3303 VA = 90.8% Efficiency x PF = 90.8% Bill -------------------- "Why not the best?" Jimmy Carter RE: Motor voltage 380-480v 7anoter4 (Electrical) 10 Aug 17 14:51 If the motor stator is provided with 6 separated windings [9 terminals] 380 to 480[460 V] it is possible. a single one winding rated current is 4.6 A [connected series] and 480/2/sqrt(3)=138.6 V. In parallel for 380 V the motor could draw double current but the voltage will be 380/sqrt(3)=220 V per bobbin. A bobbin is then rated for 220 V and 4.6 A. At 415 V you have to connect series the bobbins since in parallel the voltage per bobbin will be 10% more than rated. The current will decrease only by 13.6% but the torque 25.3% .Then the slip has to rise proportionally If at rated voltage was 0.5% now will be 0.5/.253=~2%. As the maximum torque slip it is about 6*srat=3% it will be still o.k. RE: Motor voltage 380-480v 7anoter4 (Electrical) 10 Aug 17 15:55 Sorry. Wrong numbers. On an actual motor of 3 kW 460 V Tm/tr=2.9 , rated slip about 3% and the maximum torque slip was 16.8% At 415 V the slip will be 3%/.253=11.86% and the sm=48.6% The old rpm was n460V=nsyn*(1-3%) and the new n415V=nsyn*(1-11.86%). The power required by the motor-for the same rated torque- will be 3*(1-11.86%)/(1-3%)=2.73 kW[blush] RE: Motor voltage 380-480v 7anoter4 (Electrical) 11 Aug 17 14:02 However, something is still wrong here. This calculation does not match the experience, yet. Let's start from the induction motor diagram. The power transferred from stator to rotor it is: Pi=m2*R2*I2^2/s where 2 it means "rotor" and m2=rotor number of phases. s=(nsyn-n)/nsyn the slip where: nsyn=synchronous rpm ; n=the actual rotor rpm. I2=Vstator/SQRT(R1+R2/s)^2+X2^2) neglecting Io and X1[stator leakage reactance]. For simplification's sake I'll take the R1=0 as well- where 1 it means “stator". The torque it is the power divided by velocity in rad/sec. T=m2*R2*V^2/(R1+R2/s)^2+X2^2)/s/2/pi()/nsyn/(1-s) If K=m2*R2/(2*pi()*nsyn) and R2^2=A X2^2=B Neglecting R1 T=K*V^2*s/(A+B*s^2-A*s-B*s^3) Since s is very low we can say s^3=s^2=0 T=K*V^2*s/A(1-s) For different V[Vi initial and Vf after change]: Ti/Tf=(Vi/Vf)^2*si/sf/(1-si)*(1-sf) We may consider (1-s1)/(1-s2)=1 and for a same required torque in different supply voltages Ti/Tf=1 then: sf=(Vi/Vf)^2*si s(415V)=(480/415)^2*3%=4%!!! That means it is not 11.86% but only 4%. This result it is more possible. RE: Motor voltage 380-480v waross (Electrical) 11 Aug 17 15:46 One possibility: 3 kW x 380V/480V = 3.8 kW The motor is designed as a 3.8 kW motor at 480 Volts. It may be safely run at 480 Volts saturation. On 380 Volts there is enough iron to develop 3 kW without overheating. Another possibility:Quote (ScottyUK)Is the 380 / 480V rating based on 50Hz and 60Hz operation respectively? That is an unusually broad voltage range for single-frequency operation. Could this be a harmonization issue? It is common in North America to run 460 Volt rated motors on 480 Volt supplies. 480 Volts three phase is a common voltage. 240 Volt three phase is not a common voltage. 120/208 Volts is a common supply voltage. At one time 230-460 Volt rated motors were run on 208 volts with slightly reduced capacity. This is still the case but in addition triple voltage motors are becomming common. A common rating is 208-230/460 Volts. These motors are suitable for use in shopping centers, malls and large apartment buildings where 120/208 Volts is a common supply voltage and for use in industrial applications where 480 Volts is a common supply. Refrigeration and air conditioning equipment is generally rated for 208-230/460 volts. A picture of the nameplate will be helpful. Bill -------------------- "Why not the best?" Jimmy Carter RE: Motor voltage 380-480v LionelHutz (Electrical) 11 Aug 17 16:14 Is this 50Hz vs 60Hz? In North America. a motor running on a 480V power system is typically nameplated as 460V and 380V/460V =~ 50Hz/60Hz. Even if it is 480V nameplated, I say that 380V/480V =~ 50Hz/60Hz is still close enough to be possible. So, did the frequency of each voltage get left out of the question?