Diagnostics of complex and neverending networks of MV cables can be frustrating, time-consuming, and near-impossible. Seemingly small scale failures can end up depriving hundreds of households the necessity of the modern world – electricity. Correcting these types of failures is expensive, not to mention all of the unsatisfied customers. SORAL, a project we are working on in consortium with Energa Operator, may be a solution to this problem.
SORAL will become a complex system for monitoring and maintaining the condition of cable networks, as well as a risk assessment tool for the DSO and other MV cable operators.
It aims to establish a health index for universal risk assessment of potential failures. It will create innovative criteria for cable health as there are currently no standards in the field. This solution will allow network operators to change the current model of Corrective Maintenance to the beneficial model of Condition-Based Maintenance which will minimize power outages and reduce the cost of maintenance. This improvement will benefit both customers and operators.
How will it work?
- The primary source of information will be based on 2 diagnostic techniques: the measurement of partial discharge (PD) and tan delta (TD) tests.
- The information obtained from the PD and TD measurements can provide knowledge supporting the efficient management of the network cables.
- While TD measurements will bring us the information about the average condition of the entire tested network, PD measurements will give accurate information regarding each fragment of the said network cables.
The interpretation of those measurements together with the health index will be the basis for predicting the probability of failure. This will allow the operators to plan maintenance and modernization in advance.
For diagnostic measurements, the following voltage waveforms are typically used: DAC and VLF. On the basis of examinations carried out for the SORAL project, it has been found that:
- The most common parameter indicating the risk of the failure is reduced PD ignition voltage and the occurrence of increased PD intensity in a power cable.
- Studies have shown the lower the PD ignition voltage, the greater the percentage of cable sections have increased PD intensity resulting in an increased risk of breakdown. The partial discharge measurements provide data on each part of the cable line.
The health of an electrical insulator can be determined by the ratio of the resistive component to the capacitive component, creating a loss factor.
The VLF test voltage is applied across the tested equipment. First, the normal voltage is applied. If the value of tan delta is low enough, the applied voltage is raised doubled. Analyzing the results of the loss factor for normal voltage and higher voltages provides accurate information about the insulation state.
If the insulation is perfect, the loss factor will be approximately the same for all range of test voltages. But if the insulation is insufficient, the value of tan delta increases in the higher range of test voltage.
Tan Delta test gives average condition of the network, while Partial Discharge Measurement gives accurate data of tested fragments.
Reducing or eliminating power outages caused by cable failure
Improving SAIDI and SAIFI rankings – improved distribution quality
Reducing exploitation costs due to reduced numbers of failures and forced maintenance costs
Granting cost and time efficiency because of the condition-based maintenance and planned maintenance based on the health index
SORAL at CIRED 2019
We are proud to announce that paper: SORAL – System for condition monitoring and failure risk assessment of MV cable lines based on offline diagnostic methods has been selected for CIRED 2019 in Madrid, Spain. It’s the leading international conference, where the electricity distribution community gathers. We will be presenting (our paper) in session 5, June 3-6. If you are attending this event, don’t hesitate to come by and meet us there! We’ll be happy to answer all your questions about SORAL and its future.
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