How can you test the accuracy of a protective relay?

1 What is relay accuracy?

Relay accuracy is a measure of how well a protective relay responds to a given input signal and produces a desired output action. It depends on several factors, such as the type of relay, the setting values, the operating conditions, the calibration procedures, and the testing equipment. Relay accuracy can be expressed in terms of percentage error, tolerance, or deviation from the nominal or expected value. For example, a current relay with a 5% accuracy means that it will operate within 5% of the specified current value.

2 Why is relay testing important?

Relay testing is important for several reasons. First, it ensures that the protective relay is functioning properly and can detect and clear faults in the power system. Second, it verifies that the relay settings are appropriate for the system configuration and protection scheme. Third, it identifies any potential problems or defects in the relay or its associated components, such as wiring, sensors, or communication channels. Fourth, it provides documentation and records for maintenance, troubleshooting, and compliance purposes.

3 How to test a protective relay?

Testing a protective relay requires different methods and tools, depending on the type, design, and application of the relay. Manual testing is simple and inexpensive, but it may not cover all scenarios and conditions that the relay may encounter in the field. Secondary injection testing is more accurate and comprehensive than manual testing, but it may not reflect the actual behavior of the relay in the power system. Primary injection testing is the most realistic and reliable method of testing a protective relay, but it is also the most complex and expensive. This involves injecting a high-power input signal to the primary sensors or transducers, such as current transformers or voltage transformers, and observing the relay output action. It can be done using a primary injection test set, which is a device that can generate and measure high-power input signals and output actions.

4 How to choose a relay test method?

When selecting a relay test method, there are several factors to consider, such as the purpose, scope, frequency, cost of testing equipment, type and complexity of the relay, system configuration and protection scheme, and safety and environmental considerations. Generally speaking, manual testing is suitable for simple and routine checks like verifying continuity, polarity, and insulation of the relay and its wiring. Secondary injection testing is useful for verifying accuracy, functionality, and settings of the relay under various input signals and operating modes. On the other hand, primary injection testing is beneficial for validating performance and coordination of the relay with primary sensors, circuit breakers, and other protection devices in the power system.

5 How to perform a relay test?

Performing a relay test may involve various steps depending on the test method, equipment, and relay. Generally, you should prepare a test plan and procedure that outlines the test objectives, criteria, parameters, and scenarios. Then, you must isolate the relay from the power system and disconnect any unwanted connections or loads. After connecting the testing equipment to the relay terminals and/or the primary sensors, set the relay settings and testing equipment parameters according to the test plan. Subsequently, apply the input signals and observe the output actions of the relay and testing equipment. Make sure to record the test results and compare them with the expected values and accuracy specifications. Analyze any errors, deviations, or anomalies that may arise from this comparison. Finally, report your findings and recommendations while documenting the entire process and outcomes.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?