IEC 61869-13:2021 pdf download – Instrument transformers – Part 13: Stand-alone merging unit (SAMU).
5.5 Rated output Subclause 5.5 of IEC 61 869-6:201 6 and of IEC 61 869-1 :2007 is not applicable. 5.6 Rated accuracy class Subclause 5.6 of IEC 61 869-6:201 6 is applicable with the following additions: Accuracy classes for SAMU instrument transformer channels are given in 5.6.1 301 and 5.6.1 302. Accuracy class specifications apply between the device analogue input terminals and the digital output quantity contained in the corresponding digital stream. SAMU accuracy class specifications include all errors introduced by the device and apply throughout the ambient temperature range stated on the device rating plate. When protection rated channels are present, the manufacturer shall declare separate temperature ranges for measurement channels and protection channels. Channels with common function shall have a common accuracy class designation (for example set of three phase voltages or currents). For this purpose, channels are arranged in channel groups and listed jointly on the device rating plate (see 6.1 3.1 302). SAMU output is expressed in SI units (V, A) and represents the power system primary quantities as specified in IEC 61 869-9. To accomplish this task, the SAMU shall support settings for the external instrument transformer ratio (see 5.6.1 305). SAMU accuracy specifications directly incorporate all errors associated with time synchronization. Time synchronization requirements are described in IEC 61 869-9:201 6, 6.904. With regards to accuracy classes, SAMU current channels shall be classified as: • measuring channels, • protection channels.
In accordance with IEC 61 869-9, all protection-capable current channels shall be specified with dual accuracy class ratings. Dual rating is intended to document the measuring and protection accuracy class applicable to a given current channel. Dual rating means that protection rated current channels shall also meet all measuring specifications including the frequency response defined in IEC 61 869-6:201 6, Table 6A.2 and the anti-aliasing requirements specified in IEC 61 869-6:201 6, Clause 6A.1 . Measuring accuracy classes 3 and 5 are not allowed in the SAMU. Output current channels rated for quality metering shall meet the frequency response specified in IEC 61 869-6:201 6, Clause 6A.3. The SAMU protection channel accuracy designation shall be given as a slash “/” symbol separated pair in accordance with IEC 61 869-9:201 6, 5.6. EXAMPLE 0,2/1 0TPM means 0,2 % measuring accuracy and protection class 1 0TPM. SAMU voltage channels can be used for both protection and metering, making it unnecessary to have dual designation. Voltage channel suitability for protection is accomplished by selecting the appropriate input voltage factor defined in 5.6.1 302. Voltage channel frequency response shall be consistent with current channels and is defined in IEC 61 869-6:201 6, Table 6A.2 with the anti-aliasing requirements specified in IEC 61 869-6:201 6, Clause 6A.1 . EXAMPLE 0,5 means 0,5 % accuracy class. 5.6.1 301 Accuracy requirements for SAMU channels 5.6.1 301 .1 Standard accuracy classes for SAMU current channels measuring accuracy class designation The standard accuracy classes for SAMU current channels measuring accuracy designation are: 0,05 – 0,1 – 0,2 – 0,5 – 1 Accuracy class 0,05 is introduced in support of the most precise current transformer accuracy classes 0,1 and 0,2. See Annex 1 3A for details regarding combination of accuracy classes. Accuracy class 0,05 anti-aliasing filter attenuation shall be greater than or equal to 40 dB (new value addition to IEC 61 869-6:201 6, Table 6A.1 ). Errors defined in IEC 61 869-6:201 6, Table 6A.2 are extended as shown in Table 1 302. Ratio and phase errors at harmonic frequencies shall be one half of the values specified for the class 0,1 in IEC 61 869-6:201 6, Table 6A.3 and Table 6A.4.
SAMU current channels with measuring accuracy designation shall withstand 20 times the maximum current to which the stated measuring accuracy applies (20 × I max ). If I max exceeds the rated continuous thermal current I cth this current shall be used instead (20 × I cth ). A SAMU shall withstand this current for 0,5 s without damage or long-term performance degradation (in alignment with IEC 62053-22). Protection rated current channel inputs shall be able to withstand 1 00 times the rated current for 1 s without damage or long term performance degradation (in alignment with IEC 60255-27). Continuous withstand current shall be at least 4 times the rated current. Current input crosstalk (any current channel operating at the rated input current to any other channel including voltage channels) shall be below the accuracy limit for that channel defined at rated input level. See Annex 1 3C for low-power instrument transformer input requirements.