Changing Objectives for Relay Protection Testing
Technical training is important to ensure the smooth operation of utilities, industrial plants, power plants and testing companies. A lack of training can bring operations to a halt if problems occur and properly trained staff are not present. Staff involved in protection and substation engineering are in particular need of technical training as they use a variety of tools for testing of relays, circuit breakers and other equipment.
Technical training for relay protection has gained importance due to the following factors:
- The rapid evolution of relay protection technology.
- Increased government regulations for protection testing.
- A wave of retirements by experienced engineers and relay technicians coupled with a shortage of new professionals entering the energy industry workforce.
- Fewer universities and community colleges offer power system and relay testing courses.
Current protection technology landscape
In the United States, there are three different types of relays that are applied: electromechanical, solid state and microprocessor. Approximately 50% of the relays in the U.S. are electromechanical, with 8-10% percent solid state relays included in that 50%. The percentage of electromechanical relays continues to decline each year as a result of ongoing replacement programs.
With a diverse population of relays, it becomes imperative to design a training program that covers both old and new technologies. In spite of significant advances in relay protection technology, the basic philosophy of protective relaying remains unchanged. The concepts developed during the early days of relay protection are still very much alive; it is the implementation of those concepts has changed. The electromechanical relays are not designed to implement the newer concepts or algorithms.
Any training on relay protection testing must incorporate three elements: basic protection philosophy, an understanding of electromechanical relays and knowledge of microprocessor relays. Some organizations may opt to simply train technicians to use protection software for relay testing. This is not a suitable alternative for a variety of reasons.
Advanced algorithms in relay protection
Protection technology is mature enough to incorporate dynamic and adaptive elements, like adaptive slopes for transformer restraints, within microprocessor relays. Testing of these elements requires dynamic testing tools. Similarly, current transformer saturation algorithms are now available in microprocessor relays.
When relays expect current transformer saturation, they adjust operating characteristics to take into account the expected saturation. These algorithms are implemented within the relays in various ways and testing these features requires a solid understanding of the relay algorithm and development of an appropriate test method. Conventional methods of steady state testing are no longer applicable in all cases. Tools such as COMTRADE replays or State Simulations (also referred to as State Sequencers) are required for dynamic testing.
As implementations of dynamic features in relays become commonplace, protection staff must be familiar with COMTRADE files and how they are replayed. State simulations can be used and also require a clear understanding of dynamic operations within a relay in order to prepare a test using state simulations.
This advanced method of testing requires highly trained testing technicians familiar with basic electricity theory who also possess advanced knowledge of electrical engineering. While engineers responsible for recommending relay settings can assist testing staff, the testers must still be knowledgeable about advanced theories implemented in the relays. This will require more training in this specific area of advanced testing.
At some utilities, engineers prepare test plans and are more familiar with relay algorithms. The test plans are handed off to relay technicians who use the controls on the test set to perform the tests. This approach is not recommended. The technicians cannot always rely on engineers to support the test. If the test doesn’t run as expected, the technician should be able to either troubleshoot an issue or at least be able to effectively discuss the issue with the responsible engineers. Test technicians must understand relay theory and the algorithm within the relays.
Other utilities prefer to use highly automated relay testing programs. These programs contain canned testing procedures with constant communication between the software and the relays. This allows for quick retrieval of relay settings and online changes to relay settings. However, if the test does not run, the staff member must contact the vendor for a solution in most instances. Since the tester does not require knowledge of relay protection, the tester does not develop the skills to become a fully-trained protection relay technician. Such technicians will not be able to perform troubleshooting tasks when a need arises in the field. The remedy for this shortcoming is for testers to take courses in basic protective relaying.
A better approach to training
The following approach is needed to conduct a productive training:
- Test staff must be provided with a foundation of basic electric theory.
- Training must involve education on the relay design and its functioning principles. Learners must be taught the working principles of both electromechanical and microprocessor relays. The differences between the two must be made clear.
- Training programs should be tailored to learners with different levels of experience. A simple solution is to offer courses at the basic, intermediate and advanced levels.
- In the U.S., engineers typically are not involved in testing of relays. Engineers select relays, design relaying systems, perform coordination studies and recommend relay settings. However, as relay applications using microprocessor relays have become more complex, engineers are now being asked to support testing of relays and protection systems. In addition, it will be beneficial for engineers to take courses in relay testing in order to interact effectively with testing technicians.
- Training programs should be developed in-house at utilities, power plants and industrial facilities in collaboration with reputable companies specializing in conducting training courses. Larger companies are more likely to utilize this model. However, for smaller companies with fewer resources, outsourced training is likely the preferred option.
- Some smaller utilities, such as cooperatives, do not hire technicians solely dedicated to relay protection. The technicians at cooperatives are often jacks-of-all-trades, conducting transformer testing, circuit breaker testing and relay testing. These technicians may only perform relay testing every six or seven months and may find it challenging to recall the correct steps after a long period of time.
Technicians should have access to clearly written instructions in hard copy or an online format to refresh their memories when they move from one type of testing to another.
ADDITIONAL INFORMATION
