TRANSMISSION & DISTRIBUTION TECHNOLOGY
“Depending on protective relays to
provide DDR data is clunky, expensive and maintenance intensive,” says Gehringer. “Even if a utility could stream all the data from the relays to a central computer in real- time, the bandwidth required is massive and the amount of storage space needed would add to the cost,” he adds. Utilities, therefore, have a need for simplified, economical solutions that can be retrofitted into existing substations to ensure compliance with PRC-002-2. According to Gehringer, one solution between relay-based recording and DFRs is small, three-phase single-line devices that can use existing CTs and PTs that are already routed to protective relays. Tis is an attractive retrofit option that is more cost effective than installing full-size DFRs.
PURPOSE-BUILT TOOLS Tese intelligent electronic devices (IEDs) are purpose built for this task and only require the space of a relay. One solution on the market, the 70 Series made by Bitronics, is compliant with NERC standards in SER, FR and DDR recording. Operating at a rate of 30 samples per second, it captures frequency, total watts and VARs and all three phases of volt and phase amps. One of the specific challenges of the new
NERC standard is preserving 10 days of continuous DDR recording data. R8 in the PRC-002 distinguishes continuous DDR recording from triggered DDR recording. Continuous is preferred. Te Bitronics M871 resolves this issue
by supporting multiple logical recording functions in each unit. Each logical recorder includes two independent fault recorders, two independent disturbance recorders,
The Bitronics solutions are compliant with several NERC standards
a trend recorder, and a SER recorder. Te various logical recorders in the unit can capture data often with a different duration, range and resolution. Tey can also be triggered by entirely different criteria and can be programmed to operate simultaneously or independently. Because each logical recorder requires a few seconds to convert the data and store it in non- volatile memory, the disturbance recorders are run in alternating hours producing a sequence of COMTRADE (common format for transient data exchange) files that are each one hour in duration. By allocating sufficient memory to store 240 one-hour-long COMTRADE
files, no data is lost and a circular buffer is created that resides on the M871 with new data overwriting old data after 10 days. In other words, the DDR data doesn’t need to be streamed in real time across a network to a separate computer. It does not even need to be downloaded, organised or archived, except when NERC requests the data. At that point, only the data in the range of time NERC requests needs to be downloaded.
ACCURATE REAL-TIME DATA In addition to providing all the recorded data required for PRC-002-2, the IEDs are expandable and can also provide additional real-time data to SCADA systems with tremendous accuracy. Te IEDs can be configured to perform power quality functions not available in a protective relay, thereby effectively operating as a substation SCADA recorder device. In this way, the unit can provide more information on current and power than a power quality meter, which is usually focused mostly on voltage anomalies.
The Bitronics solutions are compliant with several NERC standards
As utilities assess their options for compliance with the NERC standard, the emergence of the IED-based distributed event recording model sits somewhere between protective relays and DFRs on the recording spectrum, offering better recording capabilities than relays and lower costs and easier deployment than DFRs.
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