Digital technology in protective relaying has come a long way in it’s acceptance with utilities and industrial power producers world-wide over the past decade. Reliability, cost efficiencies, and advanced application capabilities continue to improve in these high-tech packages. Manufactures who design and produce these systems continually boast about reliability, and how self-diagnostics can warm the user in the event of relay failure. How true are these claims? Does this mean we no longer need to be concerned with the testing process?
While it is true that self-diagnostics will detect and alert the user to catastrophic failures in the microprocessor, it is the unseen that posses the biggest threat. Self-diagnostics can not detect the health of a dry contact, or the performance of a CT or PT, but most importantly, you will never be alerted to an incorrect function setting or logical configuration. As you may have guessed, through relay testing is more important than ever, but we must take a slightly different approach.
When testing single function relays, we are typically concerned with two basic fundamental testing criteria: pick-up and time delay. These are relatively simple procedures for the relay technician by creating a single timed shot test, and a simple ramp test to validate the pick-up, moving from one relay to the next. The main focus with testing electromechanical relays are issues surrounding calibration.
As most technicians will confess, this process becomes difficult when applied to multifunction digital relays, where as calibration is no longer the focus, rather, a validation that relay function and logic are set correctly. First, you will find many relay functions have multiple settings and time delays, as well as functional logic, such as sensitivity to breaker position. Second and more importantly, is that testing one element can often cause another to respond, interfering with the assessment. Most relay manufacturers suggest disabling the functions not presently being tested. This is where the danger comes in to play.
As an example, lets look at a multifunction relay for generator protection. As you apply voltages and current to the relay, you notice the inadvertent energizing element interferes with your assessment, so you temporarily disable it. If you forget to re-enable the function, or enable it with the incorrect setting or functional logic, you run the risk of leaving the most expensive piece of equipment on the power system unprotected. As expected, no self-diagnostics I know of will alert you to this problem. You must test a relay system as a system, as it will be installed! The big question is how.
The first step in testing any new relay, single or multifunction, is a complete understanding of the relays functionality by the person developing the test. Most modern protective relay systems utilize setting software that allows a better picture of how the relay should function, and allows easy display of function settings and logic. Using a computer to interrogate the device has distinct and obvious advantages over attempting the same via a front panel display. Unfortunately, inadequate testing is often a result of lack of understanding the device being tested. The old adage, “Read the Instructions” comes to mind as an important first step. Most relay manuals provide enough information regarding the operation and applications to understand the functionality, but again, be cautious of test procedures that call for relay setting changes after the testing process.
One way of avoiding interfering functions when testing a multifunction relay is to utilize output functions not designated for use after installation. If, for instance, checking an overcurrent element causes a differential element to trip, interfering with the assessment, the overcurrent element can be mapped out to a contact utilized for only testing purposes. You will also want to map the test function to the main output contact, and set and “and” gate in your test plan to properly asses both the test output, and the main one as well. Simultaneous ramping of multiple CT inputs to verify overcurrent elements will also avoid interference from a differential element as well. This approach is most efficient if two 3-phase sources are available.
It is equally important to verify correct logic settings in a multifunction relay. Communication schemes, breaker failure logic, reclosing functions are all examples of relay functionality that is often missed. One important process during testing is to provide breaker simulation to the relay, if any protective functions are subject to breaker position. Many times, especially for motors and generators, protective elements are enabled only when the main breaker is closed. Verifying that the element only responds during this condition will avoid nuisance trips, and even costly outages due to incorrect relay logic. Modern test equipment allows for easy configuration of breaker simulation.
Dynamic testing of a relay often refers to applying a simulated fault to the device, that would mimic an actual fault the relay may see when in service. This can be accomplished by executing a Comtrade file with a test set, and verifying the test results, comparatively with the fault records in the relay. This is becoming a popular method of testing modern relays, but can be difficult due to the number of test files that must be created and executed to validate all relay element settings.
Modern three phase relay test sets, that are also computer controlled offer the best solution for technicians faced with advanced multifunction relay systems. The ability to create dynamic test situations, that validate actual settings, and system logic can save time, and give technicians and relay engineer’s peace of mind that the relay system will respond correctly when in service. Often times, it would appear as if the use of a personal computer is not so desirable for those not familiar with their use. Relay testing personnel who have used manual testing for years often equate computerized testing to be difficult and inflexible. While this may have been the case with early computerized testing methods, huge advances have been made that provide anyone with relay knowledge to create and execute a relevant test procedure.
Changing relay settings for the purposes of testing is not a procedure brought on by modern digital relays, it was common practice with some electromechanical devices as well. The main reason being that it was too difficult to manually calculate correct simulated fault values for multiple setting combinations. The obvious problem with this practice is not replacing the setting back to the operating position when placed into service, causing potential misoperation. Once again, modern test equipment software should calculate appropriate test values based upon relay settings, allowing for easy testing of complex relay elements.
Relay test set manufactures can provide significant information with regards to modern relay testing techniques. If, as a relay engineer or technician, you are relying on single phase, manual test systems to test modern 3-phase, multifunction relays, chances are you are not doing what is necessary to avoid problems in your protective relay system.
ABOUT THE AUTHOR
Drew Welton is a Sales and Application Engineer for the southeastern region of the US, with OMICRON electronics Corp., USA, a company that designs, manufactures, and sells electronic test equipment for the power industry. He is a graduate of Fort Lewis College, Durango, CO, and a long time member of IEEE. Prior to OMICRON, Drew was an Application Engineer for protective relays, and relay systems, at Beckwith Electric, and Regional Sales Manager for the Western US. He has also served as an instructor at hands-on relay schools at Washington State University, and University of Texas, Arlington, as well as relay training sessions at various utilities and relay testing companies in the southeastern region of the US.
To contact Drew Welton: drew.welton@omicron.at
While it is true that self-diagnostics will detect and alert the user to catastrophic failures in the microprocessor, it is the unseen that posses the biggest threat. Self-diagnostics can not detect the health of a dry contact, or the performance of a CT or PT, but most importantly, you will never be alerted to an incorrect function setting or logical configuration. As you may have guessed, through relay testing is more important than ever, but we must take a slightly different approach.
When testing single function relays, we are typically concerned with two basic fundamental testing criteria: pick-up and time delay. These are relatively simple procedures for the relay technician by creating a single timed shot test, and a simple ramp test to validate the pick-up, moving from one relay to the next. The main focus with testing electromechanical relays are issues surrounding calibration.
As most technicians will confess, this process becomes difficult when applied to multifunction digital relays, where as calibration is no longer the focus, rather, a validation that relay function and logic are set correctly. First, you will find many relay functions have multiple settings and time delays, as well as functional logic, such as sensitivity to breaker position. Second and more importantly, is that testing one element can often cause another to respond, interfering with the assessment. Most relay manufacturers suggest disabling the functions not presently being tested. This is where the danger comes in to play.
As an example, lets look at a multifunction relay for generator protection. As you apply voltages and current to the relay, you notice the inadvertent energizing element interferes with your assessment, so you temporarily disable it. If you forget to re-enable the function, or enable it with the incorrect setting or functional logic, you run the risk of leaving the most expensive piece of equipment on the power system unprotected. As expected, no self-diagnostics I know of will alert you to this problem. You must test a relay system as a system, as it will be installed! The big question is how.
The first step in testing any new relay, single or multifunction, is a complete understanding of the relays functionality by the person developing the test. Most modern protective relay systems utilize setting software that allows a better picture of how the relay should function, and allows easy display of function settings and logic. Using a computer to interrogate the device has distinct and obvious advantages over attempting the same via a front panel display. Unfortunately, inadequate testing is often a result of lack of understanding the device being tested. The old adage, “Read the Instructions” comes to mind as an important first step. Most relay manuals provide enough information regarding the operation and applications to understand the functionality, but again, be cautious of test procedures that call for relay setting changes after the testing process.
One way of avoiding interfering functions when testing a multifunction relay is to utilize output functions not designated for use after installation. If, for instance, checking an overcurrent element causes a differential element to trip, interfering with the assessment, the overcurrent element can be mapped out to a contact utilized for only testing purposes. You will also want to map the test function to the main output contact, and set and “and” gate in your test plan to properly asses both the test output, and the main one as well. Simultaneous ramping of multiple CT inputs to verify overcurrent elements will also avoid interference from a differential element as well. This approach is most efficient if two 3-phase sources are available.
It is equally important to verify correct logic settings in a multifunction relay. Communication schemes, breaker failure logic, reclosing functions are all examples of relay functionality that is often missed. One important process during testing is to provide breaker simulation to the relay, if any protective functions are subject to breaker position. Many times, especially for motors and generators, protective elements are enabled only when the main breaker is closed. Verifying that the element only responds during this condition will avoid nuisance trips, and even costly outages due to incorrect relay logic. Modern test equipment allows for easy configuration of breaker simulation.
Dynamic testing of a relay often refers to applying a simulated fault to the device, that would mimic an actual fault the relay may see when in service. This can be accomplished by executing a Comtrade file with a test set, and verifying the test results, comparatively with the fault records in the relay. This is becoming a popular method of testing modern relays, but can be difficult due to the number of test files that must be created and executed to validate all relay element settings.
Modern three phase relay test sets, that are also computer controlled offer the best solution for technicians faced with advanced multifunction relay systems. The ability to create dynamic test situations, that validate actual settings, and system logic can save time, and give technicians and relay engineer’s peace of mind that the relay system will respond correctly when in service. Often times, it would appear as if the use of a personal computer is not so desirable for those not familiar with their use. Relay testing personnel who have used manual testing for years often equate computerized testing to be difficult and inflexible. While this may have been the case with early computerized testing methods, huge advances have been made that provide anyone with relay knowledge to create and execute a relevant test procedure.
Changing relay settings for the purposes of testing is not a procedure brought on by modern digital relays, it was common practice with some electromechanical devices as well. The main reason being that it was too difficult to manually calculate correct simulated fault values for multiple setting combinations. The obvious problem with this practice is not replacing the setting back to the operating position when placed into service, causing potential misoperation. Once again, modern test equipment software should calculate appropriate test values based upon relay settings, allowing for easy testing of complex relay elements.
Relay test set manufactures can provide significant information with regards to modern relay testing techniques. If, as a relay engineer or technician, you are relying on single phase, manual test systems to test modern 3-phase, multifunction relays, chances are you are not doing what is necessary to avoid problems in your protective relay system.
ABOUT THE AUTHOR
Drew Welton is a Sales and Application Engineer for the southeastern region of the US, with OMICRON electronics Corp., USA, a company that designs, manufactures, and sells electronic test equipment for the power industry. He is a graduate of Fort Lewis College, Durango, CO, and a long time member of IEEE. Prior to OMICRON, Drew was an Application Engineer for protective relays, and relay systems, at Beckwith Electric, and Regional Sales Manager for the Western US. He has also served as an instructor at hands-on relay schools at Washington State University, and University of Texas, Arlington, as well as relay training sessions at various utilities and relay testing companies in the southeastern region of the US.
To contact Drew Welton: drew.welton@omicron.at
