Designing the GroundHound
Ground Potential is the voltage of the ground at a location on the work-site relative to remote earth. The current that is injected into the soil at the work-site generates a rise in ground potential.
Factors that influence Ground Potential Rise include:
- The resistivity of the soil
- Worksite ground resistance
- Worksite configuration – A work-site will change during the day, which impacts grounding
- System configuration & changes
- Working in parallel line conditions
- Switching and parallel line loading
- Multiple crews (i.e. work sites)
- Circulating currents between work sites
- Ground switches used with work-site grounds
GPR Is NOT limited to accidental energization
Real Time Monitoring was needed to address ground potential rise
Electric Power Training Center determined that, even with proper training, we couldn’t control the factors needed to ensure a safe work site.
There are tools that can be used to reduce the work-site ground resistance, but resistance varies from Work-site to work-site and will depend upon soil characteristics
There is a limit to the amount of resistance the work-site ground can be reduced. Some simply can’t be brought to a safe level.
Work procedures impact ground resistance (i.e. structure removal)
Multiple work-sites and system switching (i.e. ground switches) will impact current flow
GPR is only present when current flows to ground at the work-site
Current flow is not always present
Current flow is not constant,
…And it may fluctuate during the day
So, if training and/or work procedure doesn’t always detect GPR what is the best solution?
Real-Time Monitoring & Alarming
Commercial development of a GPR Monitoring Instrument was begun in 2009. With more and more crowded corridors and greater transmission speeds, it has become imperative that a solution to this problem be developed.
The Department of Energy (DOE) and Western Area Power Administration (WAPA) representatives took the problem to Advantage Electronic Product Development. Advantage reviewed the situation with the trainers at Training Center and performed its due diligence regarding what kind of an instrument would address the GPR issues.
Advantage designed an instrument that fit DOE core capabilities well. In April of 2010 we secured exclusive licensing rights to the Department of Energy’s now patented technology to commercialize an instrument consisting of a sensor that detects GPR in real-time with a warning system that informs the crew of what is happening on the worksite.
Determining the Instrument Feature Set
Over the next year and a half, Advantage worked closely with both Western Area Power Administration and Bonneville Power.
We went into the field with the crews to hone the instrument’s feature set and test the results in real-world application on the job site with actual line work being done.
We gathered a lot of information – had some interesting adventures.
- Field testing confirmed that the prototype instrument was capturing actual and correct GPR Rise.
- The impact of transients from switching events became clear. What were previously thought to be artifacts that we had planned to filter out, were actually important events that we decided to monitor, capture & alarm.
- Linemen requested additional features
- The concept was fleshed out with these new features and the instrument was streamlined.
- We named our instrument – Safety Warning System “GroundHound”
- We made changes and tested again.
The Resulting Commercial Instrument Features
The commercialized instrument consists of a Sensor Unit and a Handheld Remote Unit
The Sensor Unit provides real-time monitoring of Ground Potential Rise and Transients.
The Sensor is connected to the worksite ground with cables that a crew typically already has with them.
There are 3 distinct Alarms, which occur for 3 distinct conditions:
1. Warning that voltage level exceeded – protective gear is necessary
2. Voltage has exceeded safe level change to energized line techniques
3. Transient – peak voltage – data and time stamped
The Sensor communicates – via ZigBee wireless protocol – to the Handheld Unit, which the Forman clips to his belt.
The foreman receives audible and vibratory warning with messages of what the sensor is detecting. He can choose a course of action and turn the alarm off. Unlike previous instruments, he does not have to step on dangerous ground or touch accidentally charged equipment.
System Component Details
Positioned on the work-site – connected to worksite ground with cables and clamps that crews already has with them. The instrument is placed 20 feet away
- Rugged, waterproof, safety-yellow all enclosed case.
- Can be controlled remotely – no need to walk up to it to read a display or get information.
- Events are logged so it can be reviewed later.
Handheld Remote Unit Configuration
- iPhone or iTouch in an Otterbox case makes it rugged and waterproof
- Software application written specifically to control the Sensor Unit and log transient information.
- Training is already loaded on the phone.
Position on the work-site – connected to worksite ground with cables and clamps that crews already has with them. Placed 20 feet away
- Rugged, waterproof, safety yellow, all enclosed case.
- Instrument is controlled remotely – no need to walk up to it to read a display or get information.
- Scheduled release date is August 15th
- Together with line crews and safety officers we have done extensive field tests
- Final agency approval testing will be completed in September 2012 – this year!
- Approximate cost $3800
- Discounts offered for Pre-Orders
- Discounts are offered for higher quantities