Application of SLANVERT Inverter on Fan of Chemical Plant

1. Introduction
Technology of frequency-conversion speed regulation is widely applied because of its obvious power saving result, convenient speed regulation mode, wide speed regulation range, reliable operation and perfect protection function as well as other advantages. 

2. Frequency Conversion Transformation of the Blowing Fan

2.1 Conditions Prior to Transformation
This air supply system employs 350kW 380V fan which controls the air supply volume by adjusting the air damper, so as to fit the change of production load. Because the fan with big power is selected when the project is put into construction, which results in the conditions of “large horse pulling a small cart”, most of electric energy is consumed by the air damper, causing the efficiency of fan reduced.
This system employs self-coupling step-down starting mode during operation, however, the startup current is still great, which causes great mechanical and electrical shocks on the motor. Motor squirrel-cage bar is always broken. The control system of blowing fan shall be altered to solve the above problems. Frequency-conversion speed regulation method of motor is utilized to realize control of air supply volume and soft start of motor, so as to achieve the aim of energy saving and reliable control. 

2.2 Brief Introduction on Transformation Scheme
A frequency-conversion device shall be added between the previous motor and the switch, and the previous power frequency circuit is reserved as the by pass, and its circuit diagram is as shown in Fig. 1. 

Fig. 1 Circuit Diagram

3. Effect after Transformation of Inverter
The fan motor of this system is 350kW and two-pole, with the rated current of 629A. When operated under the previous power frequency, the average running current is 530~590A. The power consumption per hour is about 317kWh (active power) if taking 550A for calculation; when operated after the frequency-conversion system is put into operation, the average power consumption per hour is 207kWh (active power). The voltage is still 380V and the running current is 280~ 320A when tested at the input side (power end) of the inverter if taking 300A for calculation.

(1) Power saving per hour 
If calculated as per active power, the result of the above formula shall be multiplied with the power factor of 0.93.
Power saving per hour: 317-207=110(kWh)