AS 61869.9:2021 pdf download.Instrument transformers Part 9: Digital interface for instrument transformers (IEC 61869-9:2016 (ED 1.0) MOD).
5 Ratings
5.6 Rated accuracy class
Accuracy classes for electronic LPIT with digital output are defined in the applicable IEC 61869 series product standards Part 7, Part 8, Part 12, Part 13, Part 14, and Part 15. Accuracy class specifications apply end-to-end, representing all errors introduced between the instrument transformer primary and the properly time-stamped message created at the digital output.
Accuracy specifications direct’y incorporate all errors associated with time synchronization. Time synchronization requirements are as described in 6.904.
With regard to accuracy classes, instrument transformers with digital output shall be classified in two groups:
• measuring instrument transformers.
• protection instrument transformers.
To make best use of the dynamic range enabled by the 32-bit message format specified in this standard, all protection instrument transformers and protection capable SAMU channels shall be specified with dual accuracy class ratings. Dual rating is intended to precisely document the measuring and protection accuracy class applicable to a given channel.
The dual rating requirement acknowledges the fact that protection rated instrument transformers are commonly also used for measurement and indication purposes. It establishes a proven, well understood method for documenting this performance.
The protection instrument transformer accuracy class shall be given as a slash /“ symbol separated pair, with measuring accuracy class taking the first position and the protection accuracy class followed by the accuracy limit factor KALF at the end. Dual specification shall be reported on the digital instrument transformer nameplate.
Rating examples:
O,2S 0,2S class measuring instrument transformer (not rated for protection)
O,2S15P20 5P20 protection Instrument transformer meeting class O,2S measuring accuracy class requirements
5.901 Performance requirements
Electronic LPIT with digital output shall meet all the requirements defined in IEC 61869 specific product standards Part 7, Part 8, Part 12, Part 13, Part 14. and Part 15, if applicable. This requirement therefore extends to the merging unit component which is an integral part of the instrument transformer apparatus, and is therefore subject to the same environmental and EMC conditions.
Depending on the device conformance class defined in 6.903.13, the merging unit component may be exposed to various levels of Ethernet network traffic. Although it is impossible to foresee all operating environments, the following recommendations are provided based on real life field experience:
• merging unit behaviour should be well defined under all operating conditions:
• if present, the test signal generating capability should be disabled by default:
• all data included in the same ASDU (including quality bits) should be mutually consistent and represent the same time instant as required by the applicable accuracy class specification:
• data shall be synchronized to a common time reference as described in 6.904.
Merging units should have well defined behaviour under all operating conditions. This especially applies during power-up, power-down and self-diagnostic system failure indications (as required by IEC 61869-6:2016, 6.604). While the merging unit output (data stream) may become unavailable at any time (through component failure), when present, quality bits within the stream should faithfully represent the electronic LPIT operating state in accordance with the built-in self-check, diagnostic capabilities or external alarm inputs (when present). Quality bits are used by protective relays, and are relied upon to prevent protective scheme maloperation.
For example, when powering up, an optical current transformer may need to activate thermoelectric coolers, perform carefully controlled laser start-up, and wait until the system has stabilized to allow operation within stated accuracy. During this process, merging unit (digital) output should be disabled. If data output is enabled, all affected data values should be tagged as ‘invalid’, and detailed quality set to either ‘failure’ or ‘inaccurate’ In accordance with 6,903.9. The same requirement applies during power-down (loss of power) and selfdiagnostic system activation (i.e. DSP subsystem failure). The merging unit should guarantee no un-flagged bad sampled value data is output.
Built in test signal generating capability is generally encouraged, but should be considered at the substation system level. It should be disabled by default. This applies to shipping and to all active power system installations. When present, test values shall be accompanied by the associated test bit activation as described in 6.903.9.AS 61869.9 pdf download.