The key requirements of a SCADA system are speed and reliability. The SCADA system needs to have sufficient speed that the system effectively operates in real time. Using multiple redundant ethernet rings with dual redundant couplings between the rings where a hard wired watchdog system is incorporated in each ring maximises the reliability of the communication system.
The SCADA system needs to report the status of the starters even when they are switched off; for this reason within a MCC the SCADA system and multi-function transducers operate at 24Vdc derived from batteries.
As each starter can be controlled by the SCADA system and has inputs and outputs to the SCADA system an interface unit is included in each starter.
The interface unit has input modules that use power derived from the modules to indicate the status of the starter, output modules with relay contact outputs for isolation, serial input modules to input the data from the multifunction transducer and a coupler module which connects the interface unit to the SCADA system using an ethernet connection.
Each starter interface unit connects to the MCC ethernet ring via an ethernet switch the link speed is 100megabit/sec. The MCC SCADA ring is based on a 1000megabit/sec redundant ethernet ring with each MCC having an internal 1000megabit/sec ethernet ring with a dual redundant coupling to the primary SCADA ethernet ring.
A sample of a screen display for a 55kW motor is included in the pdf version of this article. It is a separate file entitled SCADA screen display.pdf with an original paper size of A1 (841mm x 594mm) printing on to an A1 sheet will give a scale of 1:1, A2 a scale of 0.707. To be able to read the drawing a recommended minimum paper size of A3 should be used, at the stated scaling the text on the drawing has a minimum height of 1.125mm.