what may be d reason??

Because Slip % are different- due to cosΦ differences --with slightly different active Torque( because speeds are definitely not same-although you did not report this) .

Still it is not clear to me. both d motors have same rpm 985 n are driven by vfd at 45hz. how their slip is different.

Think losses.

Think losses? ?

if the motors has same p.f. & same efficiency then under same load dey draw different currents? is it true ??? if it is den y ??? if u say the losses will be different ..then tell me y losses will be different???

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Study text book and learn why motor losses are different at differant rating.

Motors have efficiencies at full , three fourth , half and 1/4 load as well power factor.Full load eff and Pf are higher and motor operates with a better eff and pf.Obviously the 18.5Kw motor is operating near full or at higher load compared to the 30Kw.So operating at lesser load,with a poor eff and pf 30KW is drawing a higher current.Further the driven equipment should be identical for this comparison.One cannot be a pump and other a fan.pl give full details to give more accurate answer.The no load current also will be higher for 30 kw Check the test certificates.

Efficiency changes at different % of load is due to losses. Magnetic loading also changes w.r.t load requirement, causing change of p.f. You can refer to some motor design book, like Golding etc to explore more on this topic.

hi friend.......thx... u have provided good information...as u wana know abt. exact loading...Both d motors have same lading.. both are driving a fan which supplies air to the plant...welll u have cleared my point....