A digital fault recorder (DFR) is an intelligent electronic device (IED)^1 that samples binary data during power system transients, using communications to retrieve fault, disturbance and sequence of event records, captured by protection relays. It stores data in a digital format when triggered by conditions detected on the power system. Harmonics, frequency and voltage levels are some examples of data captured by DFRs. They enable local substation troubleshooting and data archiving for permanent storage and analysis.
Technology Types
DFRs have generally three types of recording mechanism:
- High-speed disturbance recording of the instantaneous waveform signals of both current and voltages.
- Low-speed disturbance recording that is used to capture both long-term and short-term disturbances. In this recording type, the DFR records calculated parameters at a relative high sampling rate (1 – 10 waveform cycles).
- Steady-state recording that is used to capture min, max and average values of calculated parameters such harmonics at relatively low time resolution.
Two recording triggering methods are commonly used:
- Events that the DFR calculates from its input signals.
- Digital signals triggered by the protection equipment.
A DFR with a continuous waveform recording simplifies the installation process and ensures data availability for any event in the grid.
Modern digital relays often include the DFR function. The main differences between a relay with the DFR function and a separate DFR device are as follows:
- Sampling rate, which is usually higher for the DFR device.
- The amount of local storage and thus the recording duration is usually higher for the DFR devices.
- DFR devices can provide additional functions (such as power quality monitoring and others).
- Protection relays do not need additional binary signals like pickup and trip, because they are already generated internally and can be directly adjusted to the fault recorder.
Components & enablers
This is usually part of a dynamic monitoring system that includes:
- Dynamic System Monitor (DSM)
- Power Quality Monitor (PQM)
- Phasor Measurement Unit (PMU)
- Fault Locator
- Circuit Breaker Monitor (CBM)
- Sequence of Events (SER) Display
Advantages & field of application
Proper interpretation of fault and disturbance data is critical for the reliability and continuous operation of the power system.
In short, DFRs:
- Provide a permanent detailed record of all substation activity
- Record Transfer Trip & Block Signals and other messages
- Provide secure data collection while also isolating the IED network
- Permanent recording of internal protection relay operands and calculations in Sequence of Events (SOE) and Fault records
- Have a fairly long lifetime and simplified maintenance
DFRs have been extensively used:
- For substation distributed digital fault recording
- For monitoring of system protection performance
- As components in larger enterprise wide fault and disturbance recording systems
- Monitoring of transient events, e.g. in the case of field experiments, connecting new assets to the grid
The growing need for reliable power system operation, along with the growing demand for digital substation, are expected to drive the digital fault recorder market in the future. Asia Pacific accounted for the largest share of the global DFR Market in 2017.
Technology Readiness Level
TRL 9 - System ready for full scale deployment
Research & Development
Current fields of research: Since their introduction in the 1980s, DFRs have had an important role in monitoring the bulk electric power system. As digital monitoring technology continues to evolve, DFR capabilities are being incorporated into devices that have historically performed other functions.
Innovation priority: There is a trend towards more compact designs.
Best practice performance
DFR performance varies with the type of recorder. The characteristics of a multi-functional, state of the art, DFR can be found below:
- 24-Bit Continuous acquisition at 1,024 sample per cycle [50 / 60 Hz] (ability to record and store all electrical waveform for more than a year with no gaps in data)
- Modular Design
- Centralised and decentralised architecture
- Supreme synchronisation
- Compliance with IEC 61850 MMS, GOOSE messaging and sample value
- Comprehensive web interface
- 7” touch LCD
- Scalable architecture.
Best practice application
Description
The Utility has made a strategic decision to invest in monitoring equipment and use the resultant data to evaluate plant and network performance and identify defects and weaknesses in the system to allow early remedial actions to be taken.
Design
Recorders are present in nearly all 400 kV, 275 kV and 132 kV substations monitoring lines, transformers and circuit breakers. Protection and plant maintenance engineers mainly use fault records, the system operators use the triggered and continuous slow scan data to study low frequency oscillations, effects of frequency disturbances and power swings and the system planners use the power quality data for harmonic surveys and load flow analysis to review system performance and assess the impact of new embedded generation.
Results
The versatility of the multi-function devices and the ability to collect and analyze different types of data with one software package fully justifies the use of stand-alone systems as opposed to reliance on protection relays. Future developments will include the introduction of enhanced data processing software to automatically analyze fault records and minimize the need for manual intervention.
Description
RTE has made a strategic decision to invest in centralizing the reception of all Fault Recordings Files issued on protection arming signals by its various already installed DFRs and in a centralized software to compute automatically fault locations distance based on signal processing, in order to diminish the restoration service delay.
Design
Centralized software that computes fault location distance automatically using signal processing.
Results
The project is currently under deployment.
References
References
[1] GE. Distributed Digital Fault Recorder. [link]
[2] Joe Perez, A guide to Digital Fault Recording Event Analysis. [link]
[3] David Cole, Peter Glover. Fault Recording in a UK Utility. [link]
[4] PRNewswire. Digital Fault Recorder Market Worth 458.2 Million USD by 2023. [link]
^1: IEDs are devices built using microprocessors i.e. single chip computers that allow the devices into which they are integrated to process data, accept commands and communicate information.
