The Business Case for IEC 61850

Author: Alexander Apostolov, USA

Accelerated Protection Schemes

One of the problems with hardwired protection and control schemes is the fact that they are not supervised and as a result may represent a hidden failure component. Problems with hardwired interfaces are discovered only due to the failure of a protection scheme to operate as required or during time based maintenance testing. Maintenance testing is time consuming and requires outages, which is not acceptable in many cases. One of the significant benefits of IEC 61850 is the continuous repetition of GOOSE messages which represents a heartbeat that can be used for interface supervision.  (Figure 6.)  As soon as a message is not received, it will indicate a problem with the communications interface or the publishing IED that can be fixed as quickly as possible.

A higher level of monitoring of the communications interfaces is achieved when the IEC 61850 PAC system is using a redundancy protocol such as PRP or HSR (Figure7). The fact that there are redundant copies of each message allows the detection of communications component failure (if one copy of the message is lost) or failure of the publishing IED (if both copies are not received).
Such monitoring significantly reduces (practically eliminates) the need for time based maintenance testing, resulting in cost and time savings.

IED / HMI Data Maintenance
The changes in firmware of IEDs using protocols different than IEC 61850 require remapping of the IED data to the HMI due to changes in the data allocation in the memory of the IED. This work is performed by the utility specialists or the system integrator and requires not only update of the mapping, but also testing to verify that the update is successful.
In the case of IEC 61850 based systems changes in the firmware do not require remapping. This is because the internal IED data is still available with the same IEC 61850 name as before the update. The mapping of the data from new different registers in the memory to the same IEC 51850 data attributes is the responsibility of theIED manufacturer. 

Improved Safety
IEC 61850 process bus based solutions also improve the safety of the substation by eliminating one of the main safety related problems - an open current circuit condition. Since the only current circuit is between the secondary of a current transformer and the input of the merging unit is located right next to it, the probability for an open current circuit condition is very small. It becomes non-existent if optical current sensors are used.

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