Types of Studies With XGSLab Software

Grounding Study

Summary

The study of a metallic system (grounding electrodes) in the earth. Typical applications of this study are at substations, switchyards, generation sites, communication sites, and industrial facilities.

Why is this needed:

  • For personnel and public safety.
  • To facilitate proper equipment operation under normal and faulted conditions.
  • To prevent or reduce equipment damage or fault escalation.
  • To prevent or reduce equipment damage from lightning effects.

How To Do a Grounding Study:

  • Evaluate soil resistivity measurements to approximate the electrical characteristics of the soil.
  • Determine permissible touch or step voltage limits per the applicable standard (such as IEEE Std 80).
  • Develop a system model and calculate the grounding system impedance.
  • Assess the portion of the available fault current that will return to its source going through the grounding system to earth compared to the portion that takes alternative paths.
  • Determine the worst-case ground potential rise, touch voltage, and step voltage.
    • If any criteria are exceeded, redesign the grounding system and repeat the process.
  • Documentation for future engineering work and review.

Related Terms:

  • Ground Potential Rise (GPR) - This is the electrical potential that a ground grid and the surrounding soil may attain. Ground potential rise may also be described as the Earth Potential Rise.
    • V(GPR)=I(Ground_Current) R(Grid_Resistance)
  • Touch and Step Voltages - Voltages that an individual may be subjected to during a ground fault

 

Transferred Voltage Study

Summary

Similar to a grounding system analysis; however, the focus of the study is to evaluate the conductive effects of the ground potential rise at adjacent structures, equipment, or utilities. The grounding system effects must be known to evaluate the effects on nearby recipients. Typical applications of this study are at substations, switchyards, generation sites, and industrial facilities.

Why is this needed:

  • For personnel and public safety.
  • To facilitate proper equipment operation under faulted conditions.
  • To prevent or reduce equipment damage.

How To Do a Transferred Voltage Study:

  • Evaluate soil resistivity measurements to approximate the electrical characteristics of the soil.
  • Determine agreeable touch/step voltage limits with affected parties (often applying the IEEE Std 80).
  • Calculate grounding system impedance.
  • Assess the portion of the available fault current that will return to its source going through the grounding system to earth compared to the portion that takes alternative paths. Note that the recipient may be considered an alternative path for the current and must be accurately assessed.
  • Determine the worst case ground potential rise, touch voltage, and step voltage at and near the recipient object.
    • If any criteria are exceeded, mitigation may be applied to the grounding system or recipient.
  • Documentation for future engineering work and review.

 

Cathodic Protection Study

Summary

Buried and submerged metals corrode as a part of an electrochemical reaction. One method to reduce this corrosion is to provide active cathodic protection, in which a DC current is impressed upon the system to be protected and an anode.

Why is this needed:

  • To increase the lifespan of buried or submerged metals.
  • It provides adjustable levels of protection.
  • It provides monitoring of the protected system corrosion.

How To Do a Cathodic Protection Study:

  • Data acquisition for the system to be protected, such as material, layout/routing, and coating material.
  • Data acquisition of field measurements in existing sites and soil resistivity measurements.
  • Develop a model of the protected system with ICCP system design including sources and anodes.
  • Adjust the location, voltage, or design of the ICCP system to meet the target voltage on the protected system.
  • Documentation for future engineering work and review.

 

AC Interference Study

Summary

This is the evaluation of the AC transmission lines collocated or adjacent to other metallic objects. Typical recipients are other utilities such as pipelines or railroads. Transmission lines crossing or parallel to other linear utilities can have voltages induced, capacitively coupled, or even conducted from the transmission line to the recipients.

ac interference image showing power lines next to a pipeline and rail lines

Why is this needed:

  • To protect personnel and the public during normal and faulted conditions.
    • Touch voltages and step voltages may occur near the recipient.
  • The transmission line steady state condition may affect the equipment operation.
    • AC corrosion can accelerate the normal pipeline corrosion and reduce the cathodic protection system effect.
    • Railroad track equipment may operate incorrectly as signaling interference occurs.
  • The transmission line faulted condition may damage pipelines or railroad equipment.
    • Lightning protection systems, supporting equipment, and coating materials may all be damaged from power system faults.

How To Do an AC Interference Study:

  • Determine agreeable criteria with affected parties based on available guides.
  • Data acquisition for the transmission line, such as plan and profile, phasing, electrical loading, and fault current availability.
  • Data acquisition for the recipient such as alignment drawings, appurtenance locations, equipment types, and other applicable concerns.
  • Data acquisition of field measurements in existing sites and soil resistivity measurements.
  • Develop a model of the collocated transmission line and recipient to calculate inductive, capacitive, and conductive effects. Most AC interference studies are too complex to perform hand calculations.
  • Mitigation for any criteria that are exceeded that may be applied to the transmission line or recipient (pipeline/railroad).
  • Documentation for future engineering work and review.

 

5 mA Rule and Calculation

Summary

A transmission line’s electric field may capacitively couple with nearby objects. When standard transmission line heights are not feasible or create additional risks that make coupling hazardous, an analysis may be performed to calculate the voltage on objects and buildings.

Why is this needed:

  • An electric field (capacitive coupling) may occur on semitrucks, combines, storage buildings/tanks, metal roofed buildings, etc., to cause 5 mA (the “letgo” threshold) to flow when an individual touches the metal object.

How To Do a 5 mA Calculation:

  • Data acquisition for the transmission line—primarily conductor elevation and voltage level.
  • Develop a model of the collocated transmission line and recipient object.
  • Determine if personnel or public contact with the object and soil could cause 5 mA to flow. Mitigate if needed.
  • Documentation for future engineering work and review.