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3.4.6 – Estimating Energy Savings
Basis for estimations:
• 3-phase squirrel cage induction motor, standard type.
• Supply: 380 to 440V, 50Hz.
• Supply voltage > minimum working voltage on motor rating plate.
• Operation 30% rated nameplate full load.
Table 3.4.6.1: Estimations
Table 3.4.6.2: Modifying Factors
Examples of estimated savings:
1) 37.5 kW 4-pole motor
From Table 1, use the estimated savings figure for the next higher rating, ie 55 kW.
The savings would be approximately 3.5% x 37.5 kW = 1.3125 kW.
2) 37.5 kW 2-pole motor
From Table 1, use the estimated savings figure for the next higher rating, ie 55 kW.
From Table 2, apply the pole-number factor of -0.5 %.
The savings would be approximately (3.5 % - 0.5 %) x 37.5 kW = 1.125 kW
3) 37.5 kW 2-pole ‘low slip’ motor
From Table 1, use the estimated savings figure for the next higher rating, ie 55 kW.
From Table 2, apply the pole-number factor of -0.5 % and the %-slip factor of -0.5%.
The savings would be approximately (3.5 % - 0.5 % - 0.5 %) x 37.5 kW = 0.938 kW.
Energy Savings Modifying Factors – Table 3.4.6.2
Motor Poles Motor Slip
Number
of Poles
Add
(% kW)
% Slip
Add
(% kW)
2 -0.5 0.5 -0.5
4 0 2 0
6 0.5 3.3 0.5
8 1 5 1
Energy Savings Estimations – Table 3.4.6.1
Motor Size kW HP
Estimated Savings
(% rated kW)
Less than
5 7.5 10
22.5 30 6.5
55 75 3.5
110 150 2.5
More than 110 150 1.5
Chapter 3: Applications
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019