Historically, electric utilities send linemen to the field to gain situational awareness by visibly inspecting wires to detect circuit anomalies. In many cases, linemen on these truck rolls find no significant problems before returning to the utility.
This is because many of the problems are caused by the electric equivalent of “things that go bump in the night” – electrical disturbances such as intermittent power interruptions caused by animal or vegetation contact, pre-failure conditions of equipment, or even too much wind and rain.
The utility’s only indication of the problem often is a customer call report, which kicks off a truck roll to patrol the power line. However, many times the linemen cannot find the problem just from visually inspecting the line.
But one technology offers a way to eliminate truck rolls and gain the situational awareness necessary to identify the location of faults to improve system reliability and customer satisfaction.
3 Situations Where Utilities Roll Trucks
Here are three situations where truck rolls may be employed.
1. Fault and outage events
In outage restoration, it is critical to determine where a fault is located as quickly as possible. This can be done in a few ways, including getting RMS fault current data from substation equipment, and then:
- Doing manual calculations using asymmetrical, RMS fault current, which is measured at the head end of a feeder or just outside the substation getaway, as an input.
- Using application programs from companies such as Milsoft Utility Solutions (Milsoft), Eaton (CYME Power Engineering Software), DNV GL (Synergi Electric), or Aspen (DistriView), for example, to calculate the fault distance using the circuit model impedance and each individual program’s fault calculation tools.
- Exporting RMS fault current via DNP to a SCADA, ADMS, OMS, or FLISR programs and automatically using it in a fault distance calculation for automated switching and isolation of the fault.
2. Line maintenance
Utilities use an understanding of line operating conditions, as defined by available line data, metering data, and modeling programs, to justify and determine the scheduling of line maintenance. Many of these projects cost ratepayers millions of dollars, so utilities strive to collect the best information that they can. Truck rolls are often used to send linemen out to collect this information.
However, often there are missing pieces of information that are estimated or assumed based on known circuit construction, load types, load density, and other tools to fill in all necessary values to help make the major and minor maintenance repair determinations.
3. New business work
New business, or new customer budget jobs, differ from maintenance in they are usually large-scale feeder additions, substation transformer bank upgrades, or new substations that can cost 10’s of millions of dollars. Construction of these expensive projects is done either in phases or as new loads are being added to existing infrastructure. In both cases, the loads to be added are estimated by the developer and often checked manually by the utility.
This checking process is accomplished with models and using load monitoring at the substation or on the feeder. These loads are estimated, and upgrades are made based on a timeline of new construction, which is verified by rolling a truck to the field.
One Technology to Eliminate Truck Rolls
Using grid monitoring with smart grid sensors can limit truck rolls required for customer response, line monitoring, manual reads, or hot-stick line condition measurements. For example, deployment of smart grid line sensors can:
1. Reduce fault location times
Installing a grid monitoring solution on the backbone feeder helps to reduce fault location times by identifying which portion of the segmented feeder has recorded fault currents. They operate like faulted circuit indicators, identifying which segment last saw the fault based on the number of sets of line sensors deployed.
Two sets of smart grid line sensors will give you three segments of the circuit where a problem could be located. For example, the fault could be in the substation, on the section of line between location 1 and location 2, or on the section of the line located after location 2 down to the end of the line.
2. Reduce assumptions
Grid monitoring reduces the amount of estimated or assumed data values by filling in those blanks with actual field data at a fraction of the cost of any other solution. Smart grid line sensors give engineers, operators, and analysts accurate and timely data to afford all these individuals the ability to make good, economical maintenance budget decisions.
Here is an example. A budget job was planned by one utility to reconstruct a 20-mile section of line because of poor circuit performance based on logged customer complaints and a known outage history. After 4 sets of smart grid line sensors were strategically installed along the backbone of the feeder it was found that one 4-mile segment of the feeder accounted for 90% of the events, anomalies, and outages.
In this case, the budget job was reduced from the entire 20-mile rebuild to the 4-mile segment, reducing the cost of the maintenance job by 80%. The savings also paid for the entire fleet of smart grid line sensors at that utility.
3. Eliminate field visits
Grid monitoring with smart grid line sensors can eliminate all the field visits for construction progress verification, load reading, or estimates by monitoring loads in near real-time and reporting that information remotely. So, cognizant utility personnel can evaluate project needs from the comfort, safety, and security of their office.
In conclusion, grid monitoring with smart grid line sensors, allows utilities to obtain, without rolling a truck, valuable and timely line data and circuit condition information remotely and safely from key nodes on the network. In fact, smart grid line sensors can be placed in areas that in the past were thought to be too difficult or costly to be reached and considered for data collection.