Advanced Digital Relay Systems - Is testing still needed?
Digital technology in protective relaying has come a long way in its 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 warn 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 relay 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, thorough relay testing is more important than ever, but we must take a slightly different approach.
When testing single function relays, typical concerns are 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.
As most technicians will confess, this process becomes difficult when applied to multifunction digital relays. First, many relay functions have multiple settings and time delays, as well as functional logic, such as sensitivity to breaker position. Second and more importantly, 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 we know of will alert you to this problem.
You must test a relay system as a 3-phase system, as it will be installed! The big question is how.
OMICRON electronics has developed some very powerful software modules as part of our Test Universe to greatly help you with this process, but first let us offer you some basic advice.
First - carefully study the operations manual provided with the relay. A complete understanding of how each function responds under various system and logical conditions is essential.
Second - verify that the relay settings and logical configurations have been entered correctly. Most relays come with computer software, or the capability to use a personal computer to interrogate the relay settings and set points. We recommend you take advantage of this rather than attempting interrogation through the relay MMI. With OMICRON’s new Windows based software, you can run tests while communicating with the relay system simultaneously.
Third - keep a one or three line diagram of the protection system handy, showing the enabled functions, PT and/or CT connections, and logical functions associated with the protection scheme, such as breaker positions.
Using the capabilities of OMICRON’s State Sequencer and Ramping modules, you can create the necessary simulated power conditions, functional logic, and automated assessment based on the manufacturer specifications without any interference or confusion from other elements.
With our Advanced Protection modules, a thorough-automated test can be provided for each complex characteristic protection element, giving you the assurance your new protection system will perform the way you expect.
Tie these various test modules together with our OMICRON Control Center, and you combine multiple tests and reporting all in one document! For more information on this feature, please request a copy of our Protection Brochure through any of our sales offices (see Contacts).
EnerLyzer Software for CMC 256
With the introduction of the new CMC256 in Fall 1999, OMICRON has also raised the bar of what a universal test set should do. The EnerLyzer software option empowers your CMC256 with the abilities of a 3-Phase Multimeter and a 10-channel Transient Recorder.
The Multimeter mode allows direct RMS measurement of voltages and currents (with a current clamp), including their phase angle. A second tab uses these quantities to calculate and display active, reactive, and apparent power.
The Transient Recording mode allows waveform capture of the measured signals in the Comtrade transient data format. Flexible settings are provided to configure the usage of the system and provide adjustment of the Sampling Frequency (3, 9, or 28kHz) for both signal resolution and time recording constraints, and pre-trigger and fault length recording times are adjustable as well. Recording times vary depending on configuration; if all 10 channels are used at the max 28kHz rate, recording time is 3.5 seconds. If only one channel is used at the minimum 3kHz rate, recording time is more than 5 minutes. Forced or automatic triggering is provided and any channel can be used to automatically trigger a recording based on level and direction of transition. Records can be automatically or manually saved to a specified path with date and time tag.
Additional features include the TransView analysis module, which permit visual investigations of the waveforms with a Time Signal view, Vector Diagram view, Harmonics (THD) view, and a Z view of the impedance locus. All views are sample by sample interactive showing the dynamic state of the waveform contents. You can also launch the saved Comtrade file directly to the Advanced TransPlay test module for immediate playback to a relay.
Advanced TransPlay Software
Advanced TransPlay goes beyond just importing a Comtrade file and playing it back to a relay. It provides the ability to customize the transient file, automatically assess the response of the relay, and generate a test report with graphics automatically too. And if it’s a test you want to repeat, simply enter the number of repetitions and it will be replayed to the relay that many times with each replay result documented in the report. You can also choose to include statistical calculations for the average Min/Max deviation and standard deviation in the results.
In the flexible Measurements View, you can choose to perform both absolute and relative time measurements. Absolute time measurements for directly assessing the relay’s response, and relative time measurements to evaluate the relay’s response to the stored binary recordings of the native transient file. Tremendous flexibility is provided if you need to edit the transient file.
You can insert repetitions of a portion of the waveform, (i.e. to extend prefault time) or insert State Markers for timing measurement considerations, and insert needed Binary Signals not originally present to provide proper inputs to the relay. All Signal Properties can be edited for Name, Line Style, Line Width, Marker Type and Color. Analog Signals can also be scaled for primary or secondary values or directly scaled by a percentage setting.
Additional key features include: integrated GPS time synchronization with our CMGPS receiver or by any external time pulse applied to a binary input of the CMC; and exporting of the modified waveforms as either 1991 or 1997 standard Comtrade formats. Since it’s a part of the Test Universe, you can use it in the OMICRON Control Center to fully automate your dynamic testing of your relays.