iPD – Fault Detectors for Insulated Overhead MV Lines
What is it used for?
- The installation of insulated overhead conductors in MV distribution networks offers the advantage of reducing necessary insulation distances and protective zones. However, it also causes difficulties in detecting potentially dangerous states where contact between the insulated conductor and the ground or vegetation cannot be captured by the substation’s earth-fault protection in most cases. Such contact can lead to discharge activity between the conductor and vegetation (potentially causing wire damage or wildfires) or create dangerous step voltages threatening people or animals near the contact point.
- The offered fault detectors for insulated overhead MV lines are designed to detect partial discharges (PD) occurring at the contact point. The manifestations of these discharges propagate along the line and are detectable by suitable sensing, measuring, and analytical systems at distances ranging from hundreds of meters to units of kilometers.
- Detected discharge activity is then transmitted via a mobile data network to a dispatch system. Based on characteristic signatures, a decision can be made regarding immediate field intervention or planning future inspections of sites with occasional short-term occurrences of less severe discharge activity, caused, for example, by wind-blown vegetation moving near the lines.
How does the system work?
- The device operates on the principle of sensing and evaluating voltage peaks generated by partial discharges (PD) occurring between the conductor and the terrain or vegetation through the conductor’s functional insulation.
- Fault detection is only possible if:
- Discharge activity occurs (too dry vegetation or terrain can significantly limit PD; however, under these conditions, the consequences of insulation contact are minimal, and detection occurs once the fault develops or humidity increases).
- The manifestations of discharge activity are not overly attenuated or interfered with by other signals propagating along the line (e.g., PD or pulse interference on other parts of the network outside the monitored section, attenuation of the useful signal on the line and connected equipment).
- The output of the detector is a probability level (0..100%) with which fault manifestations (PD) appear on the monitored section according to the detection algorithm.
- For effective operation, a threshold must be set at which a potentially serious fault is indicated to the dispatcher (e.g., at a value above 80%, preferably with time filtering), and statistical data processing is required for the maintenance department to plan visual inspections or pruning in sections with a higher frequency of reports above a certain probability limit (e.g., above 50%).
- Information transfer from the detector to the dispatch system most commonly occurs via the IEC 60870-5-104 protocol through a built-in LTE modem, although any protocol or interface available for ELVAC RTU units can be chosen. In addition to basic info on fault presence, other data can be transmitted, such as phase-to-phase voltage at the supply MV transformer, temperature, humidity, or cabinet door status.
- Detector configuration and display of supplementary information can be performed remotely via the RTU User Center application or directly via the RTU7M web interface.
What do you need to have or purchase?
- Selected support points (poles) of the insulated MV line that allow the installation of the sensor and power supply parts (two brackets) near the MV conductors, as well as a distribution cabinet at the bottom (accessible for service).
- A dispatch or SCADA system (integration into GIS is also possible) to receive and display information from field indicators.
- Purchase the required number of component sets for the indicators (sensor and power part + cabinet with electronics for measurement, evaluation, and communication).
- Ensure installation on selected support points and configure information transfer to your system.
How much can it approximately cost?
- The price of a component set for one indicator—consisting of a durable cabinet containing an RTU7M with a fast measurement card, LTE modem, and backup power supply, supplemented by three MV capacitive dividers, a measuring voltage transformer for power, surge arresters, and materials for the sensing part—may range around 250,000 CZK for small installations. For specific projects and higher quantities, an individual quote is required. This price also includes licensing fees for the patented technology and the integrated RTU evaluation software module.
- The installation cost at a specific MV support point may vary based on local conditions, but an estimate is approximately 100,000 CZK, which includes mounting material and brackets.
What are the benefits?
- Early indication of potentially dangerous states on the MV line, which could threaten lives, cause fires, or damage the line itself, allows for risk mitigation before health, property, or vegetation damage occurs.
- Statistical information on frequent short-term faults can be used for effective planning of vegetation pruning or line inspections.
- Knowledge of current and statistical events on the line allows for timely intervention at lower costs (often without power interruption) compared to acute failures or life-threatening situations.
