DL/T 401-2017 in English

Analysis of the core content of the standard

Key technical requirements

1. Insulation level selection

Determined based on the system's maximum operating voltage (Um) and grounding method:

• Class A system (fault time ≤ 1min): Select based on lightning impulse withstand voltage
• Class B/C system: Additional consideration of operating impulse withstand voltage
• Outer sheath lightning impulse withstand voltage classification (see Table 2)

2. Conductor cross-section selection

Requires comprehensive calculation:

3. Accessory Selection Specifications

Critical Control Points:

1. Terminal Altitude Correction Factor (for altitudes >1000m, increase by 1% for every 100m increase)
2. Cross-connector joints must be equipped with a Sheath Voltage Limiter
3. Prefabricated accessories are preferred (mandatory requirement for 110kV and above)

Implementation Recommendations

Design Phase

What needs to be collected:

• Soil thermal resistivity measurement report
• Soil temperature curve over the years (at least 5 years of data)
• Short-circuit current calculation sheet (including asymmetric components)

Construction phase

Special attention:

• Consistency of metal sheath grounding method (single point/cross-connection)
• Humidity control for accessory installation (RH≤70%)
• Outer sheath withstand voltage test (10kV/1min)