DL/T 436-2021 Technical guide for HVDC overhead transmission lines
1 Scope
This document specifies the meteorological conditions for HVDC overhead transmission lines (hereinafter referred to as DC lines), as well as the technical conditions for conductors and earthwires, fittings, insulators, lightning protection and earthing, radio interference, ground clearance and crossing, etc.
This document is applicable to DC lines with voltage levels of ±400kV~±800kV, and may also serve as a reference for DC lines of other voltage levels.
2 Normative references
The following documents contain requirements which, through reference in this text, constitute provisions 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 1179 Round wire concentric lay overhead electrical stranded conductors
GB/T 6113.101 Specification for radio disturbance and immunity measuring apparatus and methods - Part 1-1: Radio disturbance and immunity measuring apparatus - Measuring apparatus
GB/T 7349 Methods of measurement of radio interference from high voltage overhead power transmission line and substation
GB/T 19443 Insulators for overhead lines with a nominal voltage above 1,500V - Ceramic or glass insulator units for d.c. systems - Definitions, test methods and acceptance criteria
GB/T 22707 Artificial pollution tests on high-voltage insulators to be used on d.c. systems
GB/T 26218.4 Selection and dimensioning of high-voltage insulators intended for use in polluted conditions - Part 4: Insulators for d.c. systems
GB 50790 Code for designing of ±800kV DC overhead transmission line
GB/T 50698 Standard for AC interference mitigation of buried steel pipelines
DL/T 501 Methods for measurement of audible noise from high voltage overhead transmission line
DL/T 859 Artificial pollution tests on composite insulators used on high-voltage AC systems
DL/T 1000.4 Application guide of insulators for overhead lines with a nominal voltage over 1,000V - Part 4: Composite insulators for d.c. systems
DL 5497 Technical code for design of HVDC overhead transmission line
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
total electric field strength
electric field strength resulting from the combination of the field strength formed by the space charge generated by DC corona and the nominal field strength, expressed in kV/m
3.2
ion current density
ion current intercepted per unit area of the ground, expressed in nA/m2
3.3
large crossing
section of a line that crosses a large navigable river, lake, strait, etc., where special considerations are required for conductor type selection or tower design due to large span or high tower, and the failure of which will seriously affect navigation or is particularly difficult to eliminate
3.4
heavy icing area
area with a design ice thickness of 20mm or more
Note: Areas with a design ice thickness of 10mm or less are classified as light icing areas, and areas with a design ice thickness greater than 10mm but less than 20mm are classified as medium icing areas.
3.5
equivalent salt deposit density; ESDD
mass per unit area of natural pollutants dissolved in a quantitative deionized aqueous solution, when their conductivity is equivalent to that of sodium chloride, expressed in mg/cm2
3.6
salt deposit density; SDD
mass per unit area of sodium chloride manually applied to the surface of the insulator (fittings and connecting parts are not to be included in this surface), expressed in mg/cm2
3.7
non soluble deposit density; NSDD
mass per unit area of non-soluble residues obtained from the surface of the insulator, expressed in mg/cm2
3.8
site pollution severity; SPS
equivalent salt deposit density and non soluble deposit density obtained from the surface of the insulator on site during a pre-maintenance contamination period
3.9
contamination ratio between DC and AC voltage insulators
Kp
ratio of the SPS measured from the reference DC insulator under DC voltage to that measured from the reference AC insulator under AC voltage in the same contamination period under the same environment, generally expressed by the ratio of site equivalent salt deposit density measured from both insulators
3.10
reference DC insulator
insulator used to measure the DC SPS
Note: For disc suspension insulators, a suspension string composed of no less than 5 insulator string elements is generally used, with string elements of UD210B170/560H20R (UD160B 170/560 H2 0R) or UDG 210B 170/550 H 20R (UDG 160B 170/550H 20R), a disc diameter of 320mm±10mm, a structural height of 170mm, and a creepage distance of 550mm±20mm.
4 Meteorological conditions
4.1 The design meteorological conditions shall be determined based on the mathematical statistical results of meteorological data along the line and the operating experience of existing nearby lines. The typical meteorological zones shall be selected according to the requirements of Annex A.
4.2 The recurrence interval for reference wind speed and design ice thickness of ±400kV, ±500kV, and ±660kV transmission lines shall be considered as 50 years, while that for ±800kV transmission lines shall be considered as 100 years.
4.3 The meteorological conditions for ±400kV transmission lines shall refer to the requirements for ±500kV line in DL 5497, while the meteorological conditions for ±500kV and ±660kV transmission lines shall meet the requirements of DL 5497.
4.4 The meteorological conditions for ±800kV DC lines shall meet the requirements of GB 50790.
5 Conductors, earthwires and fittings
5.1 Conductors and earthwires
5.1.1 The conductors and earthwires used in DC lines shall generally comply with the valid national technical standards for wire products. When non-standard products or foreign products need to be used, they shall meet the technical standards for similar products in the international or producing countries, and the conductor types with existing operating experience shall be preferred. When new types of conductors or earthwires are to be used, they shall be confirmed through tests in accordance with GB/T 1179. The corona loss of the conductor shall be determined through calculation in accordance with Annex B.
5.1.2 The conductors and earthwires for large crossing sections must be used in full length without joints, and their individual wires should also have no joints.
Foreword II
1 Scope
2 Normative references
3 Terms and definitions
4 Meteorological conditions
5 Conductors, earthwires and fittings
6 DC insulators, insulation coordination, lightning protection and earthing
7 Conductor arrangement
8 Radio interference
9 Audible noise
10 Impacts of DC lines on telecommunication lines and relevant protection
11 Impacts of DC transmission lines on buried oil and gas pipelines and relevant protection
12 Ground clearance and crossing
Annex A (Normative) Typical meteorological zone
Annex B (Normative) Calculation of corona loss of conductor
Annex C (Normative) Calculation of the maximum potential gradient on the surface of conductors
Annex D (Normative) Simplified theoretical method for calculation of total electric field strength above ground
Annex E (Informative) Main dimensions and characteristics of typical disc suspension insulators
Annex F (Normative) Calculation methods for configurations of DC insulators under different polluted conditions
Annex G (Informative) Examples of DC line insulation configurations
Annex H (Informative) Altitude correction method for gap discharge voltage
Annex I (Normative) Calculation of the impact of DC transmission lines on telecommunication lines
Annex J (Informative) Minimum distances between conductors and the ground in residential and non-residential areas
Bibliography
