Testing Protective Relays: Best Practices

Many power utility companies use protective relay systems to prevent long outages. Utilities test these systems to make sure they react appropriately to real or simulated fault scenarios. To do this, you need a versatile test-set that can perform many tests for different types of relays. Here are some features to look for.

NETA Compliance

Protective relays are complex devices with numerous settings groups and communication-based protection schemes. Testing these devices individually is very time consuming. It also creates an opportunity for human error, such as missing a decimal point or forgetting to apply the proper time delay. These errors can lead to misoperation of the protective element once it is in service.

Testing these devices involves checking the following items:

Verify metering function on local and remote relays. Test and verify the registration of all microprocessor relay analog inputs, and test SCADA metering values at remote terminals. Verify operation of all light-emitting diodes and liquid-crystal displays. Verify the ability to actuate all relay output contacts and SCRs, including trip and current transfer.

All of these tests are critical to the safety and integrity of the power system. A well-designed protective relay test set is capable of performing these tests automatically and will be able to identify errors. It will also have the capability of importing files with specific settings from the protection relays being tested.

Detailed Test Reports

A Protective relay tester should produce detailed test data reports that allow you to verify a relay operates as expected. For example, the results of a settable impedance directional element test plot in the positive sequence plane should be easy to read, revealing any errant points that may cause the relay to overtrip.

The test set should also provide an event report, SER information, and internal logic statuses. This helps you ensure the tripping bits are assigned correctly for inverse-time overcurrent elements, that the metering is calibrated, and that control circuits and current transfer systems are functioning properly.

Automated impedance plotting tests are a good choice for testing most relay types, but for the most comprehensive system-wide verification, state simulation tests based on fault program data should be used. These tests go a step further in sophistication than manual or impedance plotting and will help you be more confident that the entire line-protective system is working together as expected.

Easy To Operate

The Relay Tester has the ability to perform inspections of electrical and mechanical equipment. They are comfortable working with energized equipment and can examine diagrams and blueprints. The Relay Tester can also make decisions based on data and analysis to help improve the performance of a system.

Relay testers can be configured to work with different fault types based on equipment specifications and industry standards. They can also be configured to import equipment nameplate data and relay settings so they can create dynamic testing routines that take those factors into account.

Relay tests can be difficult to complete without a test-set that is easy to use and understand. Be sure to look at a set’s user manual and any introduction videos that the manufacturer has. If you have questions about a particular test-set, contact the manufacturer and ask for a live demonstration to get a feel for how it works. Then, you can see how well it meets your specific needs.


Relay testers have a critical role to play in maintaining regular types of protective relays and associated equipment connected with a single trip function in an active state. They play an active part in planning major substation and power plant construction projects and review the control and protection circuit diagrams. They have to be willing to work on energized electrical and mechanical equipment.

Relays are electromechanical devices attached to medium voltage circuit breakers that detect faults. These devices are subject to thermal and electric stresses that can cause mechanical failures. These failures can lead to unsafe situations. Routine tests that are performed at specific intervals can help to prevent these failures.

Manta’s MTS-5100 and earlier MTS-5000 Protective Relay Test System make it very easy to test protection relay elements that respond to specific fault types. The video explains how this is done using the F8 key to select the fault type. The MTS-5100 then calculates the individual current and voltage phasors for you, making it extremely easy to perform complex testing scenarios that would be difficult or impossible on manual test sets.


The proper operation of protective relay systems is the only real defense against long, costly outages and equipment damage. Our NETA-certified experts are abreast of regulatory requirements and use advanced testing solutions to test protective relay devices or systems.