• 7,2 kV and 12 kV Compressor Motors Start-up with Autotransformer
• The aim of sturt-up process with autotransformer is to decrease current, withdrawn from the network during start-up, thus preventing excessive voltage drops in connected with the motor network and avoiding influence of these excessive voltage drops on other motor & devices.
• Start-up is performed in 3 stages with 3 switches as explained below.
• Before start-up switch Q3 is closed, Q1 & Q2 are opened.
• Stage 1: After closing switch Q1 motor is started up by voltage.
• Stage 2: When motor has sped up enough, after attaining secondary rated speed of %85-95, excitation current is cut off by opening Q3 switch of the autotransformer in marked by a star place.
• Stage 3: At the third stage when the motor has sped up enough, switch Q2 is closed. Thus, all network voltage will be implemented through switches Q1 & Q3.
• This 3-staged start-up with automatic flow is carried out with the help of PLC.
• In this system 12 kV Withdrawable Metal Clad Panel of “Egesim” production are used.

Principle Diagram of Start-up with Autotransformer: