Functional Testing of System Integrity Protection Schemes

by Alexander Apostolov, USA

Introduction

Misoperations under non-critical system conditions may also result in the unnecessary tripping of multiple loads, in both cases leading to economic losses. That is why it is so important to ensure the correct operation of SIPS using proper testing and monitoring methods and technologies.
Functional and application testing is the most widely accepted testing practice for protection and control systems and is required to ensure that a System Integrity Protection Scheme (SIPS) and each of its components are going to operate as designed under different system conditions. The integration of different multifunctional devices in complex SIPS distributed over a wide area requires the use of a standard protocol that will meet the requirements for high speed and reliability necessary to execute protection functions over the wide area network. The assumption at the start of the SIPS testing process is that all devices selected for use are compliant with the selected communications protocol and can interoperate with each other in case of use of devices from different manufacturers.

System Integrity Protection Schemes (SIPS)
System Integrity Protection Schemes are distributed applications based on exchange of information and control signals between substation intelligent electronic devices located in different substation throughout the system. SIPS play a very critical role in maintaining the stability of the electric power system through load-shedding or shutting down generators. That is why it is very important to ensure that they are properly tested before being put in service.

SIPS (System Integrity Protection Scheme) can be considered as systems that have three main types of functional elements:

  • System monitoring elements
  • Protection elements
  • Execution elements

The functions of the system monitoring elements are to detect changes in the electric power system topology, system load and generation
The function of the system integrity protection is to determine if any of the above changes or their combination represents a threat for the stability of the electric power system. If there is a possibility for a local or wide area disturbance, it needs to make a decision and send signals for some action required to prevent the disturbance or at least limit the effect from the event.

The function of the execution elements is to receive the signals from the protection system and execute locally the required action. SIPS can be simple and complex with different number of levels in the hierarchy depending on the complexity of the system. Figure 1 shows a multilevel SIPS that uses multifunctional protection IEDs as the devices at the monitoring and execution levels of the system and requires different types of communications between IEDs at the bottom of the hierarchy and the substation level (Local SIPS), as well as between SIPS at the same or different levels.

All of the above communications interfaces may be based on different protocols and use different types of communications links. IEC 61850 is playing an increasingly important role due to the significant benefits that high-speed peer-to-peer messages play in the implementation of different functional elements of the scheme. The monitoring functions are typically based on:

  • Current, voltage, active, reactive power and synchrophasor measurements
  • Monitoring the status of breakers

The execution elements usually operate a breaker to reduce the load. They may also reduce the output of a generator or completely shut it down (Figures 2 and 3).

Functional Testing of SIPS
Understanding what has or has not been tested in a complex system is still a major challenge for many organizations, and the time commitment required for quality assurance functional testing needs to become increasingly one of the greatest concerns for ensuring the successful operation of the SIPS. With functional testing the engineering, commissioning and maintenance teams translate functional requirements into executable test cases that confirm how well the SIPS satisfies the requirements at any given time or under any specific conditions. A test plan needs to be developed in order to build a suite of executable tests that define and verify the functionality requirements, providing a fast and objective way to assess the performance of the tested functionality. These tests can then be executed regularly to ensure that functional modifications or firmware upgrades do not change previously verified functionality.

An effective functional testing practice involves the definition of guidelines for using functional testing technologies effectively, and then the implementation and integration of those guidelines into the asset management system. To achieve effective system testing, the user or manufacturer must not only have a defined practice for its use, but that practice must be implemented and integrated into the engineering process so that it can be used consistently across the organization. The definition of the functional tests should be part of the design of the SIPS.
System testing is testing conducted on a complete, integrated system to evaluate the system's compliance with its specified requirements.

BeijingSifang June 2016