Protection Relays

The protection relay’s main function is to detect primary-sided faults or overloads as rapidly as possible. It uses circuit breakers to selectively isolate the affected assets or parts of the grid from the rest of the grid or substation. This protects affected or adjacent equipment and people, keeps outages to a minimum, and plays a key role in providing a highly reliable supply and ensuring high availability. It also enables cost-effective operation, as equipment loss and lengthy outages go hand in hand with enormous costs. Protection relays must be tested regularly to ensure they can function properly during an emergency.

The timing and intervals of tests depend on country-specific regulations and individual strategies defined by a system operator.

Generally speaking, there are four phases in a protection relay’s life cycle, in which different types of tests are appropriate:

• Type tests and factory acceptance tests are performed during the production and development phases by protection relay manufacturers
• Laboratory tests are conducted when new substations are being planned
• Site acceptance tests and commissioning tests are done in substations
• Recurring functional and maintenance tests are performed on site during operation

The framework conditions for testing during commissioning and regular maintenance that utilities must comply with are specified by country-specific guidelines, such as the Forum Netztechnik/Netzbetrieb (FNN) in Germany, or the North American Electric Reliability Corporation (NERC) in the USA. Protection relay manufacturers then test them for conformity, for example, with the IEC 60255 standard, which defines rules and requirements for measuring relays and protective equipment.

This question can only be answered on a case-by-case basis by individual system operators. It can be stipulated to some extent by country-specific guidelines or regulations. In principle, testing is advisable if after initial commissioning tests, a change is noticed in the protection system, such as a firmware update. However, protection relays remain in operation for long periods of time, and undetected changes may occur. Maintenance intervals and respective testing scopes are defined to detect these types of changes.

Numerous factors must be considered when defining testing intervals, such as:

• Criticality of the protected grid section for the overall supply security
• The protection relay’s age and type
• Country-specific laws, regulations, or guidelines
• The number of available protection engineers and their level of training
• Their experience level with certain device types

As these factors are variable, the testing intervals may also change dynamically. Therefore, a uniform testing strategy must be established with documentation integrated into a general quality management system.

When you are testing protection relays, the number one priority is your own safety. When you are preparing to test protection relays, all relevant safety and protection measures must be adhered to before testing commences.

Aspects of protection relay testing

1. Visual assessment of the relay's condition
2. Wiring verification following commissioning or rewiring
3. Testing and matching the protection relay's settings with predefined requirements
4. Verifying the relay's functionality by testing individual protection functions
5. Checking if the pick-up and trip time values are within defined limits
6. Verification of relay behavior from a system perspective

Yes, test plans can be easily adjusted in both directions. All that is required are the licenses for the respective Test Universe modules.

To efficiently adapt test plans to an IEC 61850 test setup, use the System Configuration Language (SCL) data as a starting point. This speeds up the configuration and avoids errors.

In Test Universe, switching between GOOSE and conventional binary I/O can be done by simply adding/removing the GOOSE Configuration module. Afterward, you can simply re-use existing test plans created for conventional protection relays in your digital substations by replacing hardwiring with GOOSE messaging.

Adapting an existing test plan to Sampled Values is also simple, as all analog outputs are configured in a single location. In Test Universe some adaptations to the Test Object may be required, as most test plans in Test Universe are based on secondary values while Sampled Values are defined as primary values. In typical applications, we recommend changing the instrument transformer ratio to 1 and verifying the set residual factors and maximum values.

In end-to-end testing, all ends of a section of a protected line or a protected electrical installation area are tested simultaneously. The testing routines at all ends must be time-synchronized with one another. An end-to-end system-based test can focus on both verifying individual protective functions as well as the correct behavior of the protection system as a whole.

The biggest challenge in end-to-end testing is coordinating the tests. Protection testing solutions that facilitate test execution and document the results from a single side considerably reduce testing complexity and personnel costs. Using system-based end-to-end testing with RelaySimTest lets you run the test from a single end and make adjustments as needed.

Until recently, testing traveling wave protection functions wasn’t carried out during relay commissioning as it proved very difficult. That's why OMICRON developed the TWX1 accessory, the world's first solution for testing traveling wave protection functions in an uncomplicated manner, even with conventional protection test sets.

The test setup is the same as an end-to-end test with the addition of two TWX1 accessories. With RelaySimTest, the test can be carried out from one side, and the results are automatically documented. For this purpose, the system and line data are entered in RelaySimTest. Desired test cases are defined by placing different fault types at desired positions in the power system model. The simulation then automatically calculates the transient signal and the traveling wave pulses. During execution, the CMC test set supplies the transient signal, and the TWX1 accessory superimposes the three-phase voltage and current traveling wave pulses with nanosecond accuracy. The generated signal can be used to effectively test both the traveling wave protection and the location function of traveling wave protection relays.

Testing traveling wave protection relays easily

The IEC 60255-1xx standards specify functional requirements for protection functions. In this standard series the xx stands for the IEEE/ANSI C37.2 protection function number, e.g., IEC 60255-151 specifies requirements for overcurrent protection (51), but also covers related functions like undercurrent (37) and negative sequence overcurrent (46).

The IEC 60255-1xx standards also specify requirements for steady state accuracy and the protection function’s transient performance. Typically, Test Universe is well-suited to verify steady state accuracy, while RelaySimTest covers transient performance.

Many relay manufacturers rely on our solution to perform extensive type testing on their relays and IEDs to verify conformance with these standards. Utilities may perform a subset of such tests to compare and select suitable relay types (acceptance testing).

OMICRON Engineering Services provides support for such testing tasks.

A distinction can be made between the settings-based approach for protection relay testing (currently the most widely used), and the system-based approach. Furthermore, a differentiation can be made between manual and automated execution.

With minimal effort, system-based protection testing can verify that the individual components in a protection system will behave correctly as a group during a fault. This approach enables the detection of hidden errors in the settings, logic and design of protection systems, regardless of the relay type or manufacturer. RelaySimTest provides the tools you need to prepare and run system tests optimally.

Settings-based protection testing focuses on the protection functions and the associated set values of the individual protection relay. Modern protection relays offer thousands of settings, which is why automated testing is far superior to a manual approach. Test Universe provides an extensive range of options for standardization and automation, including fully automatic test report generation. Test plans allow you to test with maximum efficiency. Combining them with the immense functionality of our testing software provides the flexibility necessary to test protection relays and other secondary assets in detail.

Testing approaches

• System-based protection testing: RelaySimTest
• Settings-based protection testing: Test Universe

Watch Video

For an in-depth discussion listen to our podcast: Protection Testing – Settings-based and system-based Aproaches

The term automation is often used prematurely, especially when it comes to protection testing. In reality, protection engineers are confronted with assets from many different manufacturers, making it much more difficult to fully automate test procedures. In some cases, suppliers talk about automation when their solution only automates individual parts of protection testing. Hence, caution is advised.

Achieving a high degree of automated protection testing requires adaptable test templates for protection relays from different manufacturers and the ability to flexibly combine individual test modules in test plans. Efficiency can be improved by defining uniform standards for testing protection relays. Fully automated test result documentation is also a basic requirement, as it involves considerable effort when performed manually. Our Protection Testing Library (PTL) allows you to use automated test procedures for a wide range of applications with both Test Universe and RelaySimTest. In addition, these test templates can be easily customized to suit your specific needs, thereby increasing automation even further. Compared to manual protection testing efforts, a reduction of up to 80 percent can be achieved.

Available test templates

We provide a suite of powerful testing software and various additional modules, including

• Test Universe
• RelaySimTest
• CMC CT-Check
• CMC Swift
• EnerLyzer
• CMEngine

You can tailor these options to your needs or choose one of the four available software packages to operate the CMC 500 and the CMC 430:

• Essential
  offers basic functions and modules, that can be individually extended.
• Standard
  provides all the modules that are typically used for settings-based protection tests.
• Enhanced
  extends the Standard package with functions for system-based testing and transient simulation, as well as a flexible programming interface.
• Complete
  covers all functions and software modules provided for the CMC test set.

Our configuration tool can help select the best combination for your applications.