Figure 11: Power Supply AssemblyThe power supply outputs are used to provide isolated power supply rails to the various modules within theunit. Three voltage levels are used by the unit’s modules:● 5.1 V for all of the digital circuits● +/- 16 V for the analogue electronics such as on the input board● 22 V for driving the output relay coils.All power supply voltages, including the 0 V earth line, are distributed around the unit by the 64-way ribboncable.The power supply board incorporates inrush current limiting. This limits the peak inrush current toapproximately 10 A.Power is applied to pins 1 and 2 of the terminal block, where pin 1 is negative and pin 2 is positive. The pinnumbers are clearly marked on the terminal block as shown in the following diagram.MiCOM P747 Chapter 3 - Hardware DesignP747-TM-EN-1 39
