Understanding the intricacies of locating high voltage (HV) electrical systems in passive mode is crucial for Certified Locators. Let’s delve into the essential aspects and best practices for accurately identifying these critical infrastructures.
The Basics of Power Passive Mode
First, it’s important to remember that the passive noise detected in Power Passive mode is created by the nine harmonics resulting from current flowing through the cable. The signal strength is influenced by the amount of current. If a cable is dead (no voltage or current) or alive (voltage but no current), it won’t produce the harmonic noise we detect. If passive signal detected in either of these situations it is due to harmonic noise from another source.
Distinguishing HV from LV
In the image, we see both High Voltage (HV) and Low Voltage (LV) cables.
Which one is which:
- Insulators: HV cables have larger insulators than LV cables.
- Aerial cable to house. This will be LV.
- Conductors: LV cables typically have four conductors—three actives and one neutral, with current flowing out on the active conductors and returning on the neutral conductor. HV cables have three active conductors but no neutral, with the return path being through the ground via a Power System Return Current Earth Grid.
The Power System Return Current Earth Grid is potentially very dangerous and distinct from fault protection earths, a topic for another day.
Balancing the Load
To minimise current on the Return Current Earth Grid, power distribution companies strive to balance the load across the phases. When the current is equal on each phase, the harmonic noise is neutralised, and no Power Passive signal is detected. An unbalanced load results in a Power Passive signal proportional to the imbalanced load (current).
Voltage increases as you approach the generation source and the load balance improves, too. The higher the voltage, the less likely it is to be detected using Power Passive mode.
This is specific to multi-phase transformers, such as two-wire or three-wire systems. Single Wire Earth Return (SWER) systems are different and potentially more hazardous, meriting another article.
Differences in Locating Practices
Locating practices vary between regions. In North America, for example, electrical grids often involve centre-tapping of transformer windings, leading to inevitable out-of-balance currents. Therefore, far more likely to be detected in Power Passive mode.
Key Takeaways
Always remember the following:
- Power Passive signal does NOT identify HV or even LV power cables: It only identifies something metallic or conductive in the ground.
- Verify HV location: If someone else locates the HV for you and says it’s not in the work area, ask them to specify its exact location.
- Exercise extreme caution: High Voltage is one of the most dangerous assets in the ground and is challenging to locate. Always approach any electrical cables with the utmost caution.
Understanding these principles helps ensure the safety of workers and the community, reducing the risk of accidental strikes on critical infrastructure. Stay informed, stay cautious, and continue promoting industry best practices for a safer working environment.