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DFA (‘Distribution Fault Anticipation’) is a technology to monitor MV distribution lines and determine in real time, and with minimal false positives, if there are any developing issues with the line components and what the nature of that issue is.  Warnings are passed to the asset owner accordingly. A characteristic of this technology is that it can determine the occurrence of developing issues prior to these being known to the asset owner by conventional means.

HiZ (‘High Impedance Line Fault’) is a technology similar to DFA in many respects but is primarily focused on determining line drop scenarios in real time with maximum levels of confidence.

Being of a common platform and with similar base technology, both technologies will be integrated on the one operating platform from January 2015.

DFA has been about for about 15 years and HiZ for about 25 years. The two technologies employ similar concepts.

It is extremely relevant to comment that the DFA / HiZ technologies were commissioned by the USA power industry to address real issues of fire risk reduction and a desired improvement in MV line management.  The technology was never a research project in search of a use. Both the DFA and HiZ technologies were developed by the electrical engineering department of Texas A&M University (‘TAMU’) in Texas USA. Research and field demonstrations have been done over the years by TAMU and EPRI (Electrical Power and Research Institute, USA), in close cooperation with multiple utility companies. Some 12 patents apply.

Thousands of protection relays employ the HiZ technology.  DFA has been field demonstrated for hundreds of feeder-years. From December 2015 the two technologies will be combined into a single device and more than 100 units are being immediately deployed into the USA market for the Texas Wildfire Mitigation Project and other demonstration projects.

Approximately 20 distribution utilities in the USA have demonstrated DFA in trials. More than a thousand distribution feeders use the HiZ technology in feeder protection relays.

No other maker is offering DFA technology and it remains a unique concept in the market.  HiZ is has been historically licensed to a third-party relay maker.  The combination of DFA and HiZ is also totally unique.

No technology is a panacea for all line issues, but DFA/HiZ technology provides a quantum advance for MV line management. It can detect a variety of line failures, pre-failures, and other events. It has documented electrical signatures related to all the events outlined in TABLE 1. It features automated, mature algorithms for characterising some types of failures. Other algorithms continue to be developed and deployed.  A positive improvement in cumulative line reliability statistics (‘SAIDI’ and ‘SAIFI’) and reduction in bushfire risk is likely from the technology.

TABLE 1 Issues documented by DFA/HiZ

  • Switch and clamp failures
  • Tree/vegetation contacts
    • Contacts with primary
    • Contacts with secondary services
  • Fault-induced conductor slap detection
  • Voltage regulator failure
  • LTC controller maloperation
  • Recloser failures
  • Cable failures
    • Main substation cable
    • URD primary cables
    • URD secondary cables
    • Overhead secondary cables
  • Lightning arrestor failures
  • Repetitive over-current faults
  • Pole-top xfmr bushing failure
  • Pole-top xfmr winding failure
  • URD pad mount xfmr failure
  • Bus capacitor bushing failure
  • Capacitor problems
    •  Controller maloperation
    •  Blown fuses
    •  Switch restrike
    •  Switch sticking
    •  Switch burn-ups
    •  Switch bounce
    •  Pack failure
Yes, things like recording operation of reclosers that are not SCADA connected, motor starts, normal operation of switches and capacitor banks, power quality data (V, I, real / reactive power, power factor).

The DFA/HiZ technology is unique and unlike any other technology in current use.  Users are urged to not fall into the convenient trap of attempting to view DFA/HiZ as similar to any other technology. DFA/HiZ connects to CTs and VTs, as do traditional monitoring devices, but it senses these inputs much more sensitively to detect subtle events that may indicate developing problems that are not even recorded by conventional technologies. Also for this reason, data recorded by other technologies is not adequate for specialized DFA/HiZ analysis. Because DFA/HiZ records even subtle anomalies, it necessarily records much more data than conventional technologies. The large data volume can be managed because DFA/HiZ relies on automated algorithms, rather than human effort, to report system events and health.

It also should be noted that the DFA/HiZ system also provides numerous conventional functions, such as logging of conventional power system quantities and other functions. Whilst certain functions may be covered by myriad discrete technologies, the DFA/HiZ system advantageously provides these multiple functions in a single, unified platform and database. The integration of so many unique processing and data assembly capabilities in the DFA system make its contribution unrivaled.

No.  It is not conceived as SCADA per se and operates as an independent web-accessed intelligent MV line monitoring system with alarms being activated by assessed line condition abnormalities and passed to the network and operation team via email, SMS, or web. DFA reports operations of station breakers, as does SCADA, but DFA also reports operations of remote reclosers and capacitors, including those without communications, by using sophisticated digital techniques to detect these operations from waveforms it measures from conventional CTs and VTs.

The DFA/HiZ is not conceived as a power quality analyser per se.  Power quality analysers primarily focus their interest upon voltage irregularities, often have set points for triggering recording or alarms, and do not make interpretations of the issues, simply recording data for later analysis by those trained in the art.  The DFA/HiZ technology, by converse, focuses primarily on current signatures. DFA technology diagnoses line events via proprietary digital signal processing and reports actual interpreted findings only.  The technology allows ‘high fidelity’ recordings showing minor signatures, that not being possible with a power quality device.  DFA/HiZ devices will record virtually all disturbances recorded by PQ devices but also will record issues that initially cause too little variation to be detected by PQ devices. The principle of analysing and characterising waveforms is quite different.

No.  Whilst sophisticated in their operation, modern protection relays still function primarily to clear present faults.  Conversely, DFA/HiZ reports assessed and qualified data, sometimes with probability functions attached.  The exception is the HiZ part of the technology which was historically licensed to a traditional relay vendor, but neither these nor any other relays integrate the DFA concept.

Presently the technology has not been tested on SWER lines as they are not used in the USA. The designers believe the basic concepts are universal but that peculiarities of SWER lines likely will require adaptation to detection algorithms. They therefore propose an initial cooperative period to assess and adapt, including remote web access from the USA to observe the outputs from such line configurations. It is critical to note that the system design of the DFA/HiZ system provides for the ability to update algorithms seamlessly, via Internet, as needed.

DFA/HiZ devices, applied on a per-feeder basis at substation, continuously digitize waveforms from conventional CT’s and VT’s.  Waveforms are recorded when anomalies are detected, even small anomalies that are ignored by conventional technologies. Advanced digital processing and patented analytical techniques, based on a library of over 1 million referenced issues recorded to date, are applied to each recorded waveform, with the intent of determining the power system event that caused the waveform anomaly.  The techniques employed are biased so as to minimize false alarms.  The substation DFA/HiZ device then reports diagnosed events to a central master station, which then makes the information available to personnel, thus increasing their situational intelligence regarding the condition of the power system. The system architecture is inherently adaptable and upgradable as refinements are implemented.

Sampling rate is often asked about, sometimes in conjunction with the order of harmonics that can be resolved. The DFA sample rate is 256 points per cycle, which equates to 12,800 samples per second per channel on 50Hz systems, and is sufficient to capture the waveform data and characteristics of interest, although sample rate is not considered the most important aspect of the DFA’s data.

Also often asked is the number of bits of the DFA’s A/D converters. To answer this question properly, one must distinguish the A/D converter’s raw number of bits from its number of effective bits. An A/D converter can have a high raw bit count but, if its associated analogue circuitry is electrically noisy, a substantially smaller effective bit count, after the noise bits are considered and discarded. Unfortunately most waveform recorders’ spec sheets provide only raw A/D bit counts and do not consider or reveal effective bits. Effective bits, also referred to as small-signal resolution, is necessary for detecting certain incipient failures, and DFA provides 18+ effective bits of resolution to make this possible. It should be noted that systems claiming to remove noise digitally, after conversion from analogue form to digital, may improve effective resolution for steady-state signals but cannot improve effective bits for transient signals, such as those important to detection of certain incipient faults and other transient conditions.

Results have been successfully recorded on line lengths of at least 200 km from the connection point to the line.

This is sufficient to hold abnormal events for nominally 4 weeks, depending on the activity level of the feeder.  After that it uses a FIFO concept.

The DFA/HiZ technology will report findings quickly in a simply-read code of characterised issues, along with associated timings.  Reports are simply-read and decoded to allow a clear understanding of the issue(s) immediately.  Through the decoding process and the use of the network’s own line modelling software one can determine the likely site of many reported events.  If one so wishes to view it, associated waveform data is also saved with abnormal events and can be retrieved, although it is important to comment that this data generally is NOT required for a normal assessment or response to a reported event.

No. The data is simply interpreted by operational teams with minimal training.

Reports of abnormal events are able to be conveyed to nominated staff by SMS, email, or web.

No.  Indeed, not having to do such a thing was one of the key design parameters from the outset.  The line to which it is connected can be configured or reconfigured at will with no impact per se on the outcomes.

No.  The DFA/HiZ operates as a single-ended device with very good results and very acceptable accuracy of site identification being possible.

The DFA/HiZ does not give location information per se but, instead, presents all the required information to allow the asset owner to determine the likely location of the site at issue to an acceptable level of accuracy.

One unit is required per feeder, connecting to the CT’s and VT’s in place for the line.  The unit is rack mounted and purposefully powered from battery-backed 12 volts DC, typically obtained from station batteries.  A high bandwidth continuously-available web connection is required.

No. Indeed, not having to install special such equipment was one of the key design parameters from the outset.  Ratio details are entered but the unit performs with a wide range of normally-used such transformers.

A ‘Master Station’ server-class PC is employed in the architecture of an installation and typically would be installed at the utility’s headquarters. The Master Station is responsible for managing the utility company’s entire fleet of DFA/HiZ devices, including collection of data, aggregation of information from multiple feeders and dissemination of reports to utility personnel. It contains both software for communicating to feeder devices in substations, as well as all website-related software, and SMS messaging functionality. For large utility companies, with large feeder counts, the “Master Station” may be split across multiple physical computers (e.g. one web server, combined with a DB server, combined with a communication server, etc.).

Each substation-based feeder device continuously connects to the central Master Station via broadband Internet.  Should the data line be lost temporarily, the DFA/HiZ unit has a generous buffering capability to ensure data collected during the communication downtime is not lost.

12VDC, battery-backed, typically derived from station batteries.

This question arises from the observation that DFA and other devices both take their inputs from CTs and VTs. That is where the commonality ends, however, as non-DFA devices do not monitor or record waveform data with the sensitivity or fidelity that the DFA employs. Consequently data from other devices and systems is not suitable for analysis by DFA software. For further detail, the reader is urged to review the companion discussion question, “How does the DFA/HiZ technology differ from other industry technologies?”

There is no need to poll the unit manually, the Master Station handling that function.  Events are communicated to a pre-set list of names via SMS or email. Data may be accessed at any time via the web.

he DFA is not intended to communicate via protocols such as DNP3, as these are unsuited to passing the types and volume of data necessary, with encrypted communications over TCP/IP being more suitable. The DFA/HiZ Master Station maintains a relational database that can be integrated into enterprise-level systems such as outage management systems.

The makers prefer to have remote web access to data from the system but it is not essential. They offer associated support to users and it has been a popular service in the USA. Such support will be included in the unit price of the DFA/HiZ device.

Yes.  The makers would normally do this as part of the standard support, if granted web access to do so.

Intial implementation will be accompanied by a training and orientation service from LORD Consulting.  It will include scenario modelling and training on how to turn the information provided into efficient responses on the network.  It is expected that those trained will include the field operations team through to the senior engineering team.

As the unit will uniquely inform of issues and in many cases well ahead of any other corroborating data from conventional technology or customer complaints or the like, it will facilitate a greatly enhanced level of operational response.  In addition, experience to date has shown responses often can be made in a more timely and cost-effective manner (ahead of an actual failure to follow), in daylight hours, and in a much safer manner.  The improvement in line failure and outage statistics as a result of the technology can be dramatic, as will be customer and stakeholder relations.

There are several main factors determining the initial uptake of DFA units.  Firstly, there is a level of operationalising effort that is required and that is independent of DFA numbers.  Second, there is a clear need to have sufficient installed base of DFA units to ensure an adequate flow of data from them in a sensible time period to allow their performance to be tested and assessed.  Thirdly, when customers also wish to enhance the initial implementation with a special project site installation (e.g.:  to gain experience on SWER lines) enough units also need to be allocated to the project sites as well as the ‘mainstream’ ones to ensure a good assessment of the data flow.  Field experience in the USA over many years of installations suggest that the initial installed base would be in the area of at least 10 pieces, with more optimal assessments being when 5-10% of the feeders owned by a network are so monitored.

LORD Consulting will be engaged by the local suppliers (AVO New Zealand and LORD Power Equipment) to liaise with the asset management team to select the installation sites, prepare the installation details at each site, arrange any necessary training of staff and change management required.  Installation would be intended to be done by the distribution company or its preferred contractor.

LORD Consulting and the USA makers, PSI, intend offering as part of the purchase price a uniquely-conceived package of support to ensure the technology continues to remain a viable and relevant asset management tool.  This support will include on-going monitoring of the unit remotely with comment passed back promptly on the issues being encountered, liaison across the operational team to the engineering team to the asset management team as to outcomes and contribution of the technology, regular generic updates as to intersting results observed from various clients, and a review of the continued contribution being made by the technology.

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