Article Abstract

User Contributions

Over the past many years, a lot of discussions occurred on the topic of Personal Protective Grounding (PPG).  It was once believed that bracket grounding was all that was needed to adequately protect a person on a transmission or distribution pole and that “personal protective grounds” or “work-site grounds” to establish an equipotential zone around a worker was not absolutely necessary.  As time progressed and more studies were performed, it became more and more apparent that personal grounds were indeed needed and equipotential zones for workers were essential in maintaining a safe working environment for employees.

Austin Energy (AE) initiated a detailed Personal Protective Grounding (PPG) study to verify and validate AE’s own personal protective grounding policies and procedures.  The PPG Study consisted of computer modeling techniques to analyze various PPG configurations in order to determine the adequacy of the modeled configurations. The analysis provides the current distribution in all bracket PPG sets, the worksite PPG set and the current through a person’s body working from a steel platform of a Condor.  The safety assessment of the person working from the steel platform of a Condor during an inadvertent energization of the phase conductor is based on the criteria established by the ANSI/IEEE Std. 80-2000, “IEEE Guide for Safety in AC Substation Grounding” [1] and input parameters provided by AE.

 

Modeling a Polyurethane Foam Backfill in CDEGS

 

W. K. Daily, P.E.

Austin Energy

Polyurethane backfill systems have been in use for over 30 years.  They are convenient, impervious to moisture, more resistant to heat, cold, micro-bacterial attacks and physical stress than other types of backfill systems.  Other advantages of polyurethane foam backfill systems include:

à Sets up in rock, sandy soils and wet soils

à Increased strength reduces storm damage

à Helps protect the environment by sealing in pole preservatives

à Polyurethane kits can be carried on line trucks

à Makes setting operations easier requiring less manpower and equipment

à Provides a structurally superior backfill system that has been under development for over 30 years.

Austin Energy (AE) has been using, very successfully, the polyurethane foam backfill systems for over 15 years.

More recently, Utility Structural Systems (USS) has developed a product to compliment their current polyurethane foam backfill system (Poly-set).  The new product is called “Poly-ground” and has been in existence for approximately 3 years.  Poly-ground has essentially the same structural properties as their polyurethane foam, but is substantially more conductive having a resistivity of only 1-2 Ω-m.  For this analysis, the conductive polyurethane foam is assumed to have a resistivity of 2 Ω-m.  The polyurethane foam (poly-set) has an extremely high resistivity.  For this analysis, it is assumed to have a resistivity value of 1,000,000 Ω-m.

 

An Alternative to Impervious Cover Requirements

 

W. K. Daily, P.E.

Austin Energy

 

Last year, during the 16th User’s Group Conference a presentation was given by Austin Energy (AE) that showed how vegetation in and around substations can present a potential safety hazard for utility workers and the public at large.  Removing all vegetation from in and around a substation helps to prevent accidents, but is only part of the process.  Providing the proper yard cover both inside and outside the substation to restrict a person’s body current to the IEEE Std. 80-2000 allowable limits is a significant part of the process.  However, providing and maintaining a sufficient yard cover is sometimes a problem due to encroachment on the allowable limits of impervious cover set by regulators and legislation.  The amount of impervious cover allowed at an AE facility is directly related to the specific site and zoning requirements, AE Watershed Protection Plan, and the impact on adjacent properties.  Typically, AE is restricted to an impervious cover of 10-20%, depending on the location of the specific site.  Things that constitute an impervious cover include compacted road base, structure and equipment foundations, driveways and control building foundations.  Anytime AE uses crushed limestone to restrict touch and step voltages, a good base needs to be established prior to installation of the crushed limestone.  This is important in maintaining the crushed limestone over a period of time.

 

The purpose of this paper is to discuss how AE has overcome the impervious cover restrictions for substations.

 

Analyzing Lightning Performance of Various Network Scenarios

 

David R. Stockin

E&S Grounding Solutions

This paper discusses some possible additions and enhancements to SES software in order to assist the design engineer in conducting productive comparisons on the effectiveness of various lightning system design alternatives. The performance of the bonding and grounding design is analyzed in the time-domain using the HIFREQ and FFTSES computation modules.

Briefly stated, the required tool will compare the effects of a lightning strike on different aboveground bonding and buried grounding system scenarios that have been proposed for installation at a given facility.

A recent lightning study is described and discussed as an example.

And So …. the Saga Continues – a PPG Study Update

 

W. K. Daily, P.E.

Austin Energy