1) Reliable distance protection based on measured line parameters
Selective distance protection as well as accurate impedance-based fault location highly depends on the accuracy of line parameters, which in this case are the positive-sequence impedance Z1 and the zero-sequence impedance Z0. Very often Z1 and Z0 are calculated based on the conductor geometry and estimated soil properties. This approach is quite accurate for Z1. However, Z0 is highly influenced by unknown soil properties, such as soil resistivity in different soil layers or parallel buried conductors, like gas or water pipes. The measurement of Z1 and Z0 is therefore highly recommended in order to parameterize a distance relay with true line parameters and achieve reliable, selective and accurate performance of the relay. OMICRON’s CPC 100 and CP CU1 allows testing line impedances fast (less than 1 hour), accurately, safely and easily.
2) Comprehensive Ground Testing
All in all, there are four different ground tests which are usually performed in the power industry:
• Soil resistivity, also called Wenner or 4 pin measurement: Performed prior to the design and construction of the ground grid. Needed to determine the multi-layer soil model which is required for ground grid design.
• Ground Potential Rise (GPR), also called fall-of-potential or ground impedance measurement: This measurement is performed to determine the overall impedance between the ground grid and the surrounding soil. The GPR can be compared to the simulated value from the design software (e.g. CDEGS) to verify the quality of the ground grid’s construction. A comparison over time can detect deterioration of the grid.
• Step & touch potential measurement: This measurement is performed according to IEEE 80 in order to ensure human safety in and around substations.
• Point-to-point, also called ground grid continuity or micro-ohm measurement: This measurement verifies if all elements of a ground grid (such as risers) are interconnected with a low resistance. Poor construction or deterioration can be identified with this measurement.
The CPC 100 in conjunction with the CP CU1 and HGT1 as well as the guided workflow software Primary Test Manager (PTM) allow performing all of the mentioned tests. Beside safety, ease of use and accuracy, features like map support, GPS positioning of test points and automated assessment according to relevant standards is supported. Sign up