How is the source of a power outage located?

Question

The other day my entire neighborhood lost power, about 20 square blocks. It took almost 10 hours for power to be restored. Several hours into this someone called the power company and were told they were "still locating the problem." It got me wondering, how do they sniff out the source of the outage?

I would have thought the power company would have a big screen with a map of the city or something, so they could easily say "the problem is on this block" but apparently not. Do they have to drive around town and manually try to connect a circuit between various electrical boxes?

Just thought maybe someone here works for a power company and could answer this.

Answer 1

Most electric utilities do not have the “big screen” map of the entire distribution system.  Transmission systems have computerized displays, but those are mostly point-to-point with intelligent substations at each end.

Some utilities have an automated meter reading system (AMR) that reports loss of power.  However most utilities still rely on customers calling in to report the outage.  If only one person calls, the problem is suspected to be limited to that one customer.  Two or more or more outage calls on the same transformer are analyzed as a transformer outage.  Calls from multiple transformers on the same phase of the same circuit are analyzed as a device (i.e. fuse) outage.  To some extent, the more customers affected, the higher the restoration priority.

Troubleshooting an electric power outage depends on the type of installation.  Overhead systems tend to have fused taps off the main line of the circuit.  Any problem on a tap will blow an individual fuse, minimizing the extent of the outage.  If the problem is on the mainline, the line workers need to visually patrol the line looking for the case of trouble.  In many applications they use switches to isolate sections and temporarily route power from a nearby circuit.  This can quickly restore power to a large group of customers while they continue to trouble shoot.

Underground circuits are much more difficult to find, since nothing is visible.  Equipment is often daisy-chained together in a giant loop.  The utility uses fault circuit indicators (FCI) to tell whether the surge of fault current went past that location.  They basically have to check piece of equipment looking at the FCI’s.  If they see a target, they know the fault current went past that point.  Once they find an unfaulted FCI, they know they went too far.  The problem is not isolated between the faulted and unfaulted FCI’s.  They can now isolate the cable segment and restore power to the front portion.  They also go to an open switch to an adjacent circuit and feed backwards to the equipment with the unfaulted FCI.

Some of the delays in the troubleshooting and restoration process include:

1)  Inaccessible equipment.  Customer fences, trees, bushes, etc can prevent the workers from opening the doors to check the FCI status.

2)  Circuits that in an abnormal switching condition or out-dated maps that do not represent the actual connectivity of the circuit.

3)  Fault circuit indicators that did not sense the fault current and do not provide the proper indication.  This causes incorrect conclusions regarding the location of the outage and the workers can close into a fault while trying to restore service.

4)  Successive faults.  The surge of fault current that caused the initial outage also caused collateral damage to other upstream equipment.  The workers will troubleshoot the first problem and close into the second fault while trying to restore service.

5)  Some overhead equipment such as insulators and arresters can fail in ways that make it difficult to see the problem.  This makes troubleshooting very time consuming.

6)  Miss-coordination of fuses or other protective devices.  Most electrical circuits have multiple over-current devices in series.  The devices are intended to operate so the one closest to the fault condition operates.  If an upstream device operates first, the workers will be troubleshooting the wrong segment of the circuit.

7)  Staffing levels.  If you have more outages than lineworkers, the dispatchers must decide which outages to investigate and restore first.  In general, outages with the most customers get priority.  Other factors include critical customers such as hospitals, police stations, water and sewage treatment plants, airports, etc.

The “Smart Grid” of the future will bring intelligence to the distribution system.  

- Some technologies will help pinpoint the location of the problem and display the information on a mobile terminal in the line worker’s vehicle.  

- Other technologies will sense the outage and automatically reroute power around the problem area -- restoring service to most customers without any human intervention.  

- Advanced equipment can even sense "pre-fault" conditions and notify workers to take proactive steps and prevent outages before they happen.  

- All of this equipment is expensive.  It will take substantial time and money to incorporate the technologies in distribution systems that has been evolving for over 100 years.

Answer 2

I do not work for the electric company, but I have seen them work.  When I had a power outage, the guy looked up the electrical grid drawings for my neighborhood, walked right up to a pole, and replaced the fuse on it.  We were back up pretty quickly.  

More than likely, they just work their way up the power grid using hand-held equipment and replacing fuses and looking for damaged equipment to find the problem.  Bear in mind, you are talking about voltage greater than 10,000 volts carried by wires either located 25 feet overhead or 10 feet underground.  Even if they know what the problem is, it can take time to get to it, put it in a safe condition, and to fix it.  It takes even longer when equipment is damaged.

The big high voltage power grids are probably closely monitored because they affect many thousands and millions of people, but, the neighborhoods are probably not monitored like that.  First, it would be cost prohibitive to do so, and also, they have a built in monitoring system:  people and the emergency hot line.