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GB 39220-2020: Limits and monitoring methods of total electric field of DC transmission project
GB 39220-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
Limits and monitoring methods of total electric field of
DC transmission project
ISSUED ON: MAY 20, 2020
IMPLEMENTED ON: DECEMBER 01, 2020
Issued by: Ministry of Ecology and Environment;
State Administration for Market Regulation.
Table of Contents
Foreword ... 3 
1 Scope of application ... 4 
2 Normative references ... 4 
3 Terms and definitions ... 4 
4 Limits ... 5 
5 Monitoring technical requirements ... 5 
6 Quality assurance ... 7 
Appendix A (Normative) Calibration method of field mill ... 9 
Limits and monitoring methods of total electric field of
DC transmission project
1 Scope of application
This Standard specifies the limits and monitoring methods of total electric field
of DC transmission project.
This Standard is applicable to the monitoring, evaluation and management of
total electric field of DC transmission project.
2 Normative references
The content of this Standard refers to the provisions in the following documents.
For undated reference documents, the effective edition is applicable to this
Standard.
HJ 24 Technical guidelines for environmental impact assessment of electric
power transmission and distribution project
3 Terms and definitions
The following terms and definitions apply to this Standard.
3.1 DC transmission project
The project which transfers direct current from a power supply location to a
power demand location. DC transmission project includes DC transmission
lines, converter stations and grounding electrode systems.
3.2 Total electric field
The combined electric field OF the electric field generated by the charge on the
DC charged conductor AND the electric field generated by the space charge
caused by the conductor corona. The physical quantity, which measures the
intensity of the total electric field, is the electric field intensity. Its unit is volts per
meter (V/m); kilovolts per meter (kV/m) is commonly used in engineering.
3.3 Percentile level of total electric field (En)
SORT the continuous measurement data (equal time interval sampling values)
of the total electric field at the monitoring point according to the absolute value
from small to large. The n% data is called the percentile level of total electric
field, En. Its meaning is that, the absolute value of n% of the measured data
during the measurement period is less than or equal to En. For example, E95
and E80 respectively indicate that, the absolute value of the measured data
within 95% and 80% of the measurement period is less than or equal to E95 and
E80.
4 Limits
In order to control the public exposure caused by total electric field, the limit of
total electric field intensity E95 in the environment is 25kV/m; the limit of E80 is
15kV/m.
For places such as farmland, garden plots, pastures, livestock and poultry
breeding grounds, breeding water surfaces, and roads under the DC overhead
transmission line, the limit of the total electric field intensity E95 is 30kV/m.
Warning and protection signs shall also be given.
5 Monitoring technical requirements
5.1 Monitoring instrument
The monitoring instrument of the total electric field shall be able to measure the
size and polarity of the total electric field at the same time; and, have the
function of automatic continuous measurement and recording.
The field mill is generally used to monitor the total electric field. The field mill
shall use a square metal plate with an area of 1 m×1 m and good conductivity
as the ground reference plane. It must be grounded reliably.
The field mill shall be within the validity period of calibration. See Appendix A
for its calibration method.
5.2 Environmental conditions
The monitoring of the total electric field shall be carried out under the weather
with wind speed (2m above the ground) less than 2m/s, no rain, no fog, and no
snow.
5.3 Monitoring method and frequency
The monitoring point shall be selected at a place where the terrain is flat and
there is no obstruction. The field mill shall be placed directly on the ground. The
distance between the upper surface and the ground shall be less than 200mm.
PLACE a square metal plate with an area of 1 m×1 m and good conductivity on
the wall of the converter station; is arranged in a direction perpendicular to the
wall. The distance between two adjacent monitoring points may be 5m.
Generally, monitor to a distance of 50m from the wall.
5.4.3 Building
When monitoring outside the building, the total electric field monitoring point
shall be arranged on the side of the building close to the DC transmission
project; and not less than 1m away from the building.
When monitoring on the balcony of the building or the platform used for living,
working or studying, the points shall be arranged in an area not less than 1m
away from walls or other fixed objects (such as guardrails). However, the points
should not be arranged in a location, which needs to be reached with the help
of tools (such as ladders) or by special methods (such as climbing).
5.5 Data recording and processing
5.5.1 Data recording
During monitoring, it shall record meteorological conditions such as wind speed,
wind direction, temperature, relative humidity, air pressure, and weather
conditions during the monitoring period. In addition to recording the monitoring
data of each monitoring point, it shall record the specific location of the
monitoring point and the start and end time of each monitoring.
When monitoring DC overhead transmission lines, it shall also record the line
parameters of the pole wire at the monitoring point or monitoring path, such as
wire height, distance between poles, wire type, operating voltage, operating
current, tower number, line direction, number of circuits on the same pole and
line arrangement. When monitoring the converter station, it shall also record
the operation mode of the converter station, converter valve power, DC voltage,
etc.
For each monitoring point, it shall monitor for at least 30min; sample at equal
intervals during the monitoring period; record at least 100 data.
5.5.2 Data processing
In the continuous monitoring of the total electric field, the monitoring data is
highly dispersed. The cumulative probability method shall be used for data
processing.
6 Quality assurance
The monitoring organization shall have the capabilities and conditions suitable
Appendix A
(Normative)
Calibration method of field mill
A.1 Overview
Since the DC total electric field cannot be coupled with the plates like the AC
electric field, the monitoring of the DC total electric field requires a special
sensor; to make the electric flux received on the sensing element periodically
change; and the corresponding induced charge also changes periodically. By
using the current formed by the periodically changing induced charge, the
corresponding field intensity can be measured. The electric field tester must not
only be able to accurately monitor the DC total electric field, but also be able to
introduce excess adsorbed ions into the ground without affecting the reading.
At present, the sensor of the commonly-used monitoring instrument is the field
mill sensor.
The total electric field of the bipolar DC transmission line not only changes in
size, but also changes in its polarity due to the existence and drift of space ions.
Therefore, the monitoring instrument can not only measure the size of the total
electric field, but also determine the polarity of the total electric field.
A.2 Working principle of field mill sensor
The structure of the field mill sensor is shown in Figure A.1. The probe is
composed of two coaxially-installed circular sectors. The upper sector is driven
by a motor to rotate with the shaft. The lower sector is fixed.