This part specifies the procedure for the selection of the rated withstand voltages for the phase-to-earth, phase-to-phase and longitudinal insulation of the equipment and the installations of three-phase a.c. systems. It also gives the lists of the standard withstand voltages from which the rated withstand voltages should be selected.
This part applies to three-phase a.c. systems having a highest voltage for equipment above 1 kV.
The selected rated withstand voltages shall be associated with the highest voltage for equipment. This association is for insulation co-ordination purposes only. The requirements for human safety are not covered by this part.
Although the principles of this part also apply to transmission line insulation, the values of their withstand voltages may be different from the standard rated withstand voltages.
The rated withstand voltages and the test procedures suitable for the relevant equipment shall be specified according to the requirements of this part during making the standard for equipment.
Note: In GB/T 311.2, Application Guide, all rules for insulation co-ordination given in this part are explained in detail, in particular the association of the standard rated withstand voltages with the highest voltage for equipment. When more than one set of standard rated withstand voltages is associated with the same highest voltage for equipment, guidance is provided for the selection of the most suitable set.
1.1 Application scope
This part is applicable to the following indoor and outdoor electric transmission and transformation equipment in three-phase a.c. power systems having a highest voltage for equipment above 1 kV:
a) Transformers: power transformer, shunt reactor, current-limiting reactor, arc suppression coil, electromagnetic voltage transformer and current transformer;
b) High-voltage electric equipment: circuit breaker, disconnecting switch, load switch, earthing switch, fuse, prefabricated substation, enclosed switchgear, closed combined electrical equipment and combined electrical equipment;
c) Power capacitor, coupling capacitor (including capacitor voltage transformer), shunt capacitor and a.c. filter capacitor;
d) High-voltage power cable;
e) Post insulator, wall bushing, etc.
1.2 Inapplicable scope
a) Equipment installed at places with severe contamination or gas , vapor and chemical sediment harmful to isolation;
b) Indoor equipment in places with high relative humidity where condensation is prone to occur.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 311.2 Insulation Co-ordination - Part 2: Application Guide for Insulation Co-ordination for High Voltage Transmission and Distribution Equipment (IEC 60071-2: 1996, EQV)
GB/T 2900.19-1994 Electrotechnical Terminology High-voltage Test Technique and Insulation Co-ordination (IEC 60071-1: 1993, NEQ)
GB/T 11022 Common Specifications for High-voltage Switchgear and Controlgear Standards (GB/T 11022-2011，IEC 62271-1: 2007,MOD)
GB 11032 Metal Oxide Surge Arresters without Gaps for a.c. Systems (GB 11032-2010，IEC 60099-4: 2006, MOD)
GB/T 16927.1 High Voltage Test Techniques - Part 1: General Test Requirements (GB/T 16927.1-2011; IEC 60060-1: 2010, MOD)
GB/T 26218.1 Selection and Dimensioning of High-voltage Insulators Intended for Use in Polluted Conditions - Part 1: Definitions, Information and General Principles (GB/T 26218.1-2010; IEC/TS 60815-1: 2008, MOD)
IEC 60060-1：2010 High-voltage Test Techniques - Part 1: General Definitions and Test Requirements
IEC 60071-2 Am 1 Ed.3.0 Insulation Co-ordination - Part 2: Application Guide
IEC 60721-2-3 Classification of Environmental Conditions - Part 2-3: Environmental Conditions Appearing in Nature - Air Pressure
3 Normal and Special Service Conditions
3.1 Normal environmental conditions
Normal environmental conditions for withstand voltages selected from Tables 2 and 3 are as follows:
a) The ambient air temperature does not exceed 40 °C and its average value, measured over a period of 24 h, does not exceed 35 °C; the minimum surrounding air temperature is classified into three grades: -10℃, -25 ℃ and -40℃;
b) The altitude doesn't exceed 1,000m;
c) The ambient air is not significantly polluted by dust, smoke, corrosive gases, vapours or salt; pollution grade does not exceed Grade C (see GB/T 26218.1);
d) The presence of condensation or precipitation is usual. Precipitation in form of dew, condensation, fog, rain, snow or hoar frost is considered.
