IEC 61869-13-2021 Instrument transformers – Part 13: Stand-alone merging unit (SAMU).
4 Normal and special service conditions
4.3 Special service conditions
4.3.3 Ambient temperature
Subclause 4.3.3 of IEC 61 869-1 :2007 is applicable with the following addition:
For a SAMU mounted inside an outdoor cabinet, the maximum temperature for very hot climates shall be increased to +55 °C. In the most demanding applications, temperatures up to +70 °C may be specified.
5.3 Rated insulation levels
5.3.2 Rated primary terminal insulation level Subclause 5.3.2 of IEC 61 869-1 :2007 is not applicable because a SAMU does not have high-voltage primary terminals. Insulation requirements for analogue inputs connected to instrument transformer secondary circuits are given in 5.3.1 301 .
5.3.3 Other requirements for primary terminals insulation Subclause 5.3.3 of IEC 61 869-1 :2007 is not applicable because a SAMU does not have high-voltage primary terminals.
5.3.4 Between-section insulation requirements Subclause 5.3.4 of IEC 61 869-1 :2007 is not applicable because a SAMU does not have high-voltage primary terminals.
5.3.5 Insulation requirements for secondary terminals Subclause
5.3.5 of IEC 61 869-6:201 6 and of IEC 61 869-1 :2007 is not applicable because a SAMU does not have high-voltage instrument transformer secondary terminals. The SAMU output is Ethernet based and in case of optical implementation does not have insulation requirements. In case galvanic interface is used (e.g. RJ45 based communication port), insulation requirements shall be in accordance with IEC 60255-27. It is recommended not to use galvanic interface. When present, the galvanic interface shall not be used for distances above 1 0 m. 5.3.1 301 Insulation requirements for inputs from instrument transformers Analogue inputs connected to instrument transformer secondary circuits shall be rated for a minimum working voltage of 300 V, pollution degree 2, overvoltage category III, in accordance with IEC 60664-1 .
When overvoltage above category III is expected (e.g., gas insulated substation installations and direct connection to low-voltage mains systems), overvoltage category IV should be considered in accordance with IEC 60664-1 :2020, Annex B. See Annex 1 3B for GIS switching and lightning surge voltages examples. Minimum insulation requirements for analogue input terminals are summarized in Table 1 301 . Requirements apply from the input terminals to any grounded part, and between independent circuit terminals. Insulation voltage rating also depends on the circuit configuration (e.g. insulation voltage for analogue inputs connected to open delta VT circuits is multiplied by a square root of three).IEC 61869-13 pdf download.