Friday, August 6, 2010

IEC 61850 Data Acquisition Options - An Overview

IEC 61850 provides several options to access the values of modeled information in sever devices. The following slide lists all options of IEC 61850-7-2 (ACSI - Abstract Communication Service Interface):


Depending on your needs you may use one or the the other option. Reporting is the most elaborated service. The behavior of reporting depends on the configuration of so-called Report Control Blocks. Reporting with Integrity Period set, e.g., to 1 second is more efficient than polling a list of data objects every second! Because polling needs two messages: request with then object references of all data to be polled and response with all values. Reporting with Integrity Period requires a single report with all values every second only. You save 50 per cent of the messages and a lot of processing resources. You can combine integrity period (e.g., 1 minute) with immediate transmissions of changes (events). This would save even more (in case there are events very seldom).

Before you can configure an optimized traffic (messages going back and forth in a Network in real-time or relaxed in seconds) you need to understand your needs - the arrival rate of values and the needs of the applications that access these values. And of course you need to understand the standard and what vendors have implemented. Some applications require information from other devices in the range of a few microseconds - this requires usually GOOSE. The various options serve different requirements with regard to the timeliness. It is easy to fill up the bandwidth of 10 GBit/s with wrong configurations. Monitoring for deadband changes (delta changes) of 0.001 per cent could cause a lot of messages ... ;-)

Smart Grids require smart systems and smart devices - all need smart people!

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