Test Strategy for PAC functions in a fully digital substation based on IEC 61850 applications

by Working Group B5.53

In 2014, CIGRE Study Committee B5 (Power System Protection and Automation) instigated the formation of the Working Group B5.53 to investigate and report on the state of the art related to Test Strategy for Protection, Automation and Control (PAC) functions in a fully
digital substation based on IEC 61850 applications. The reason for creating this working group is the fact that the testing of a complete digital functional chain, including the use of process-bus for the transmission of the analogue values and station bus for the transmission of trip and other signals have not been covered before.
The testing of protection, automation and control functions implemented as fully digital functional chains becomes an important issue with the deployment of IEC 61850-based digital substations using Stand Alone Merging Units (SAMU), Switchgear Interface Units (SIU) or their combination in Process Interface Units (PIU), as well as Non-Conventional Instrument Transformers (NCIT) interfacing with the multifunctional protection  IEDs or other substation PAC devices over station bus (IEC 61850-8-1) and process bus (IEC 61850-9-2).

The use of digital buses completely changes the approach required for testing due to the elimination of the hard-wiring and the traditionally used test switches. It also adds new test cases to the existing functional tests for both protection, automation and control functions. The design of the digital substation systems and the corresponding testing solutions has to take into account the constraints related to maintenance related functional tests after the commissioning of the substation protection and automation systems.
This 760 Brochure covers the testing of the complete digital substation functionality, including the use of process bus for the transmission of the analogue values and station and process bus for the transmission of trip orders and other signals for substation protection, automation and control systems (SPACS).

The focus is on testing of fully digital IEC 61850 substations and equipment. The tests in all phases of the lifecycle of this equipment are covered:

  • Certification (NCIT- Non-Conventional Instrument Transformers, SAMU, SIU, PIU and PAC IEDs)
  • Interoperability tests
  • Factory Acceptance Tests
  • Commissioning and Site Acceptance Tests
  • Maintenance tests after commissioning

Recommendations for the following types of tests for protection and SAS functions are formulated:

  • Testing of complete functional chains of different possible configurations
  • Test of functions acquiring values from different sources
  • Test scenarios related to communications: loss of SV, jitter, loss of synchronization
  • Latency
  • Isolation of test objects for FAT (Factory Acceptance Tests), SAT (Site Acceptance Tests), maintenance tests
  • Possible approaches for partial testing of a function with verification of recovery of the different partial tests
  • Time synchronization, time quality
  • Time synchronization between the test set and the testing object, being local or remote
  • Loss of Sampled Values
  • Test of accuracy

The scope of the working group was limited to functional testing only. The following topics were excluded:

  • Test of hybrid systems, i.e. systems featuring both conventional analogue inputs and process bus
  • Test and certification of metering chains
  • Conformance testing of devices
  • Test of complete RAS (Remedial Action Scheme) / SIPS (System Integrity Protection Scheme)
  • Environmental testing of IEDs for climate, Electromagnetic compatibility (EMC), etc.
  • Primary equipment
  • Loss of auxiliary power, supply supervision, trip circuit supervision
  • Security relevant functions, intrusion testing

One of the goals of the report developed by the CIGRE B5.52 working group was to help the industry better understand and apply IEC 61850 in digital substations. At the same time, it had to identify if there is anything missing or incomplete in the standard and provide feedback to the IEC TC 57 working group 10 for the future development of the standard.

The specialists involved in the testing of protection, automation and control systems are used to a physical isolation of the object under test based on the use of test switches.
The replacement of part or all of the hardwired interfaces with communication links requires the development and implementation of methods and tools that maintain the same level of security during the testing process, while at the same time taking advantage of all the benefits that IEC 61850 provides. Identifying the challenges and proposing solutions is an important contribution of the brochure.

The first part of the brochure provides a detailed description of the testing related aspects of IEC 61850 Edition 2, followed by the testing methods and tools for the different types of test and the description of different use cases.
The requirements for isolation – one of the key issues related to the testing of digital substations - depend mainly on what is being tested and the purpose of the test.
The brochure highlights in which cases the test should be performed using normal operating configuration and when we should use the different operating modes that support virtual isolation.

The approach of the working group to the development of the methods for testing of digital substations also is reflecting the opinion of the industry expressed in the answers to the questions of the industry survey conducted at the beginning of the work by the working group.
The detailed results from the utilities and manufacturers surveys are published in an appendix at the end of the brochure.

The requirements for functional testing of devices and distributed functions also determine the methods for testing of both types of systems and are proposed based on the following order of system components tests:

  • Functional testing of individual IEDs used in the scheme
  • Functional testing of distributed functions within a substation

The testing of the protection, automation and control functions in digital substations is a critical requirement for their acceptance as a key component of the Smart Grid.
This CIGRE B5 brochure is an important document that can help the specialist from our industry to better understand the principles and methods for testing of digital substations.

The brochure can be downloaded from the e-CIGRE web site at:

Working Group B5.53

A. Apostolov (USA) – Convener
Volker Leitloff (FR) – Secretary 

H. Jacques (FR), B. Shi (CN),
R. Loken (NO), N. Kearns (IR),
M. Hacker (DE), G. Maioli (SE),
I. Ferrero (ES), J. Verzosa (US),
I. Visic (HR), H. Li (UK),
S. Meliopoulos (US),
A. Woynarovich (HU), F. Matsuki (JP), T. Shono (JP), W. Ji Feng (CN)

Corresponding Members:
O. Rintamaki (FI), L. Crompton (UK),
V. Naumov (RU), P. Junior (BR),
R. Hunt (US), F. Rahmatian (CA),
D. Jenkins (NZ), A. Redekopp (CA),
R. Schimmel (NL)

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