Why Should You Use Standalone DFRs?

The traditional role of a Digital Fault Recorder (DFR) as a post mortem analysis tool to assess relay and breaker performance during a system fault is being challenged by additional functionality in the protection relays themselves.  So, what exactly are the benefits of a standalone Fault Recorder for substation monitoring as opposed to reliance on the output of multiple relays?

There are 11 major reasons why:

• Independent monitoring of the entire protection scheme including the circuit breaker. Will work when relays fail.
• Monitors complete protection scheme (main & backup relays, signaling channels, trip relay & breaker) on one record.
• Records stored for all disturbances not just line trips meaning data can be used to identify incipient plant defects.
• Superior data to allow more complete analysis of pending problems as well as trip events.
• Cross triggering gives time synchronized substation wide data to see how one piece of the substation interacts with another.
• Slow scan (dynamic disturbance recording or DDR) to give an overview of system events and provide easy analysis for slow clearing faults.
• Large memory capacity to archive different data sets for longer periods without overwriting of information.
• Superior time and magnitude accuracy of parameters to allow fault characterization and analysis of system disturbances.
• One software package to collect and analyze data rather than having to use one or more packages for each relay vendor reduces the need for staff training and ensures greater competence in the use of the single package.
• Other functions can be added to the DFR to convert it into a substation monitor.  Relays are for control while the substation monitor is for DFR, DDR, Power Quality (PQ), Phasor Measurements (PMU) and, in some cases, Traveling Wave fault location.
• The inclusion of new protocols, particularly IEC61850, allows the multi-function DFR to be a component of integrated substations

The flexible triggering, large memory capacity and superior data sets of a standalone DFR make it more suitable to gather valuable information to study network performance in addition to the more traditional task of fault analysis.  Sorting the larger volume of records generated when more sensitive triggering is configured, especially after storm conditions, requires a resource level which is sometimes difficult to justify in modern Utilities.  The use of expert software to automatically analyze records to identify ‘non-compliant’ events where an ‘abnormal’ condition has occurred is therefore crucial to maximizing the benefits of a multi-function monitoring system.