1 Scope
This standard specifies general principles, contents, methods, criteria and cycles for the test of parameters of grounding connections for power plant, substation and transmission line tower and the test of soil resistivity.
This standard is applicable to the evaluation of in-operation grounding connection condition and the acceptance test of grounding connections for the newly-built power plant, substation and line tower.
Testing on parameters of other grounding connections for communication facilities and buildings etc. may refer to relevant contents.
2 Normative References
The following normative documents contain provisions which, through reference in this standard, constitute provisions of this standard. For dated references, subsequent amendments (excluding any corrections) to, or revisions of, any of these publications do not apply. However, all parties coming to an agreement according to this standard are encouraged to study whether the latest editions of these documents are applicable. For undated references, the latest editions of the normative documents referred to apply.
DL/T 62l-1997 "Grounding for AC electrical installations"
DL/T 887-2004 "Power Frequency Ground Resistance Measurement for Poles & Towers"
3 Terms and Definitions
For the purpose of this standard, the following terms and definitions apply.
3.1
Grounding electrode
It refers to the metallic conductor embedded in the ground and contacting with the ground directly.
3.2
Grounding conductor
It refers to the metallic conductor, also named as grounding downlead, between the electric equipment part that shall be grounded and the underground grounding electrode.
3.3
Grounding connection
It refers to the assembly of grounding conductors and grounding electrodes.
3.4
Large grounding connection
It refers to the grounding connection for substation with the voltage grade being 110kV or above, that for thermal power plant and hydraulic power plant with the installed capacity being greater than 200MW or that with the equivalent area being greater than 5000m2.
3.5
Grounding grid
It refers to the horizontal netlike grounding connection composed of vertical and horizontal grounding electrodes and used for power plant and substation, which also has such function of current discharging and voltage balancing.
3.6
Parameters of grounding connection
Referring to parameters or indexes like electric integrity, ground impedance, surface potential distribution, touch potential difference, step potential difference and diverting potential of the grounding connection. Except for the electric integrity, others are power frequency parameters.
3.7
Electric integrity of grounding connection
It refers to the electric connectivity, namely the d.c. resistance value and also known as the electric conductivity, among various in-grounding connection electric equipments that shall be grounded, between each several part of the grounding connection and each equipment.
3.8
Ground impedance
It refers to the impedance from the grounding connection to the distant zero potential point. Its value is the ratio of the potential difference between the grounding connection and the distant zero potential point to the current flowing into the ground through the grounding connection. The ground impedance obtained through calculating from the impulse current is named as impulse ground impedance, and that obtained through calculating from the power frequency current is named as power frequency ground impedance. All those not indicated to be impulse ground impedances in this standard are power frequency ground impedances.
3.9
Surface potential distribution
It refers to the potential gradient formed on the field ground surface where the tested grounding connection is located when the grounding short-circuit current or the test current flows through the grounding connection.
3.10
Step potential difference
It refers to the potential difference between two points with the horizontal distance of 1.0m over the ground when the grounding short-circuit current flows through the grounding connection.
3.11
Touch potential difference
It refers to the potential difference between the point 1.0m horizontally from the equipment over the ground and the point 1.8m vertically from the ground along the equipment enclosure, framework or wall while the grounding short-circuit current flows through the grounding connection.
3.12
Diverting potential
It refers to the potential of grounding connection transferred by the metallic conductor with one end connecting with the grounding connection while the grounding short-circuit current flows through the grounding connection.
3.13
Current electrode
It refers to the grounding electrode arranged in the distance in order to form the current circuit for testing parameters like ground impedance and surface potential distribution etc. of the grounding connection.
3.14
Potential electrode
It refers to the grounding electrode arranged to test the selected reference potential while parameters of grounding connection are tested.
Foreword I
1 Scope
2 Normative References
3 Terms and Definitions
4 Basic Requirements for Testing of Parameters of Grounding Connection
5 Electric Integrity Test of Grounding Connection
6 Test of Power Frequency Parameter of the Grounding Connection
7 Ground Impedance Test of Grounding Connection for Transmission Line Tower
8 Test of Soil Resistivity
Appendix A (Informative) Typical Example to Test Power Frequency Parameter of Large Grounding Connection
Bibliography
