P ∝ Q × H (1)
When the flow rate is changed from Q1 to Q2, the motor's rotational speeds are N1 and N2, and the relationship between Q, H, and P with respect to the rotational speed is as follows:
Q2 = Q1 × (N2/N1)
H2 = H1 × (N2/N1)? (2)
P2 = P1 × (N2/N1)?
And the relationship between the shaft power P and the torque T of the motor is:
T ∝ P/N, therefore: T2 = T1 × (N2/N1)? (3)
From equations (2) and (3), it can be seen that the pump motor's shaft power (output power) is proportional to the third power of the rotational speed, while the torque is proportional to the second power of the rotational speed.
And PL = [0.45 + 0.55 (Q / QN)?] Pe (KW) = √3UICOSφ
ki = 1 - (Q/QN)? /0.45 + 0.55(Q/QN)? ×100%
Where U: rated voltage
I: average operating current
COSφ: power factor
Pe: motor power at rated flow rate
PL: motor power at return valve regulation
QN: rated flow rate