Solar radiation effect on electrical motors
Solar radiation effect on electrical motors
(OP)
Hi all!
We have several outdoor motors and the sun radiation makes the surface temp rise up to 50°C and more.
I was wondering how it affects on the ambient temperature derating of the motor power. And if there's any table, paper, coefficient, formulae, etc. to consider when it comes to the selection of the motor
Thanks all,
Martín.
We have several outdoor motors and the sun radiation makes the surface temp rise up to 50°C and more.
I was wondering how it affects on the ambient temperature derating of the motor power. And if there's any table, paper, coefficient, formulae, etc. to consider when it comes to the selection of the motor
Thanks all,
Martín.





RE: Solar radiation effect on electrical motors
RE: Solar radiation effect on electrical motors
But I was looking for some info about that... I believe that is adding to the ambient temp. but I couldn´t find any info
regards
RE: Solar radiation effect on electrical motors
It likely would end up being some sort of intermediate value. For example, if the sun heats the motor 20C over ambient then that is equivalent to installing the motor in a location with an ambient 10C higher than it really is.
The biggest determining factor is the actual temperature rise of the motor in operation. As long as the motor isn't overheating it is OK.
RE: Solar radiation effect on electrical motors
RE: Solar radiation effect on electrical motors
The effect of the sunlight should be judged when the motor is running, not when it is stopped.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Solar radiation effect on electrical motors
Not an electrical answer but would help to reduce the case temperature during times of intense sun.
RE: Solar radiation effect on electrical motors
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RE: Solar radiation effect on electrical motors
If we could consider a motor as a short cable with a very expanded diameter we could use
IEC 60287 formulae in order to appreciate the supplementary rise of copper temperature due
to sun radiation.
Let's take for copper max. temperature of 130 oC[Class B].
ambient max. temperature of 40 oC
Sun radiation=700 w/m^2.
Motor overall dia. =0.4-1.2 m [length =1m]
Then calculated the maximum rise of temp. due sun exposure= 23 oC
I suppose 15 degrees C temperature drop from copper to outside surface
then:
Max. permitted copper rise temp.=130-40-23-15= 52 [instead of 130-40=90 o C]
RE: Solar radiation effect on electrical motors
If a motor is rated for outdoor use, it is supposed to work in direct sunlight. Make sure that ambient temp is selected for the geographical area.
I have had motors running near full load out in the sun in abmbient temps up to 43 deg.C. The motors of course were rated for 40 deg C ambient and 50 deg rise, (or vice versa, cant recall it correctly now) for Tropical applications.
RE: Solar radiation effect on electrical motors
Max. permitted copper rise temp.=130-40-23-15= 52 [instead of 130-40-15=75 oC as rated]
That means in order to maintain maximum 130 oC on copper one has to reduce the current
I/Irated=sqrt(52/75)= 0.83
RE: Solar radiation effect on electrical motors
They're all class B rise with class F insulation, but the table I have states the power output drop with higher ambient temperatures or higher altitudes, so i started wondering this.
If I can relate this formulae to ambient temp, then I'm done!!
For example, can I add your 23ºC calculated?? (40ºC + 23ºC = 63ºC it's 80% of rated power according to the motor manual) and that matches sqrt(52/75)... but I don't know where does it come from... don't have the standard.
RE: Solar radiation effect on electrical motors
First of all as I already mentioned it is only an attempt to appreciate the copper temperature rise
Based on calculation for cable heating due Sun radiation.
The method is very conservative as doesn't take into consideration the cooling through ventilation.
Most of motor losses are evacuated by forced convection. Also, a great part of the Sun radiation does not
reach the windings as the ventilation eliminates it.
The cable losses-all the losses-are evacuated through the overall surface mostly by radiation and a very
small part through natural convection.
The change of surrounding air temperature and pressure are more important factors for motor current derating.
I translated the cable parameters into motor parameters so:
TC = copper conductor maximum temp.[degrees C] = 130
TA = air ambient temperature = 40
SUN = sun radiation [w/m^2] = 700
SIG = SIG=1 for surface no coated = 1
DE = overall diameter [m] = 0.4
QS = QS=1
H = 0.21 / (DE) ^ 0.6 + 3.94
KA = PI()*DE*H*therm.resist.
DTT = SUN * SIG * KA / H / PI()
DDSO = is initial value for DDSF and [=2.77]
have to change it up DDSO=DDSF
DDSF = ((TC - TA + DTT) / (1 + KA * DDSO)) ^ 0.25= 2.84
Tfive = 1 / PI() / DE / H / DDSF=0.065
TSUN = The temp.rise due to SUN[no ventilation considered] = DE * SIG * SUN * Tfive=18
dTdrop = Temperature drop from copper to surface = Supposed 15 degrees C
Toutsurf = overall surface temperature = TC-dTdrop=115
dtCU = temperature drop of copper due heating[variable] = TC-TA-TSUN-dTdrop=57
dTrated = temperature drop of copper due heating[rated] = TC-TA-dTdrop=75
Inew/Irated = Inew is the reduced value in order to maintain TC = SQRT(dtCU/dTrated)=0.87
NewTC = increased copper temperature if I=Irated = TC+TSUN=148
Newoutsurf = new outer surface temperature = NewTC-dTdrop=133
therm.resist.=dTdrop/P
P is part of losses evacuated through
exterior envelope[most of the losses are evacuated through
forced ventilation]
P=radiation from outside surface to the ambient
P=qrad*PI()*DE=564 w
qrad=krad*(((273+Toutsurf)/100)^4-((273+TA)/100)^4)
krad=3.44 w/m^2 for a varnished surface
Regards
RE: Solar radiation effect on electrical motors
Pradattached=Prad] up to the time where these value will be the same.
RE: Solar radiation effect on electrical motors
hey thanks a lot... but I got lost in H = 0.21 / (DE) ^ 0.6 + 3.94... where that comes from?
sorry my ignorance! but great stuff... this is certainly close to the derating of ABB motors on higher ambient temp
RE: Solar radiation effect on electrical motors
RE: Solar radiation effect on electrical motors