Meeting Continuous Power Needs

PG&E Uses Portable Generation to Keep Power Flowing During Infrastructure Changes


The level of dedication to customer service varies among utilities. Adherence to meeting customer expectations compels utilities to focus on quality-determining metrics, such as the Customer Average Interruption Duration Index (CAIDI). Against this backdrop of customer expectations, Pacific Gas & Electric Co. (PG&E), one of the nation’s largest utilities, operates in a region where outages are not tolerated. To minimize customer outages, particularly during periods of transmission and distribution (T&D) infrastructure changes and upgrades, PG&E relies on mobile power generation resources to inject power into those constrained sections of grid undergoing upgrades.

Aging Infrastructure

The massive T&D infrastructure in North America is aging and breaking down in many areas, keeping utilities’ maintenance crews busy proactively upgrading infrastructure as well as reacting to expedient repairs. Capital infusion to upgrade T&D infrastructure is forthcoming, but due to the scale of T&D investment needed, the necessary improvements will span a couple of decades, rather than a couple of years. In addition to major T&D improvements, utilities must also carefully balance capital investment on “clean” power sources as they divest from baseload power sources, such as coal.

It was noted at a recent industry seminar that by 2020, North American electric utilities will add 48 GW of solar-based energy and 65 GW of wind-based energy, further increasing the urgency to upgrade and expand T&D grids. This is an area where the temporary power solutions serve an important role by delivering uninterrupted power during T&D infrastructure improvements.

Depending on areas served, much of the nation’s T&D grid dates back to the 1950s, or earlier, constraining some utilities’ ability to provide stable capacity to new types of electric users that didn’t exist a generation ago, like new data storage facilities, expanded hydrocarbon processing units, etc. As planned grid improvements go forward to meet new consumer requirements, the lack of redundant power sources at outermost radial networks exposes utilities to CAIDI-related events.

When there is a lack of redundancy, utilities can benefit from partnering with a power generation provider set up with a network of service centers, making it capable of maintaining mobile diesel generators and providing engineering expertise to support grid challenges. Such capability enables utilities to obtain temporary power generation from outside experts during scheduled maintenance events, while also avoiding outages.

PG&E Reduces Outages

PG&E leverages robust portable generation systems by Aggreko for continuous power support while performing improvements to power lines and substation equipment. One such project recently took place when a 7 MW/12 kVA power generation solution energized more than 1,500 PG&E customers in San Luis Obispo County for 13 hours while upgrades were completed at the Cholame substation.

Without the use of portable generators, customers in the San Luis Obispo County area would have experienced a “planned” outage for several hours while this work was being performed.

“This is something that we are going to be doing a lot more in the future so customers don’t see interruptions. We can deal with unplanned interruptions, and we can respond to those, but it’s really the planned work where we can make a lot more headway in how we take clearances and if we take clearances,” said Robert Cupp, superintendent of transmission line maintenance for the south region of PG&E’s service area.

In a typical scenario, medium voltage lines put up 60 years ago must be upgraded because they are undersized to meet current demand. The preferred option is to perform the upgrade without taking customers offline.

It has been typical during such upgrades to take customers offline for incremental periods until the project is completed, increasing the utility’s CAIDI. However, whether the end-user is industrial, commercial, residential, a combination of these, or a new type of electrical consumer, such as an urban medical center, any planned or unplanned offline incident is unacceptable, even for short increments, no matter how much notification the utility provides. For these constraints, PG&E can now provide temporary power and avoid interrupting customers’ services. In addition, PG&E can use portable generation systems for both large and small scale projects.

Because PG&E serves a large area where unplanned events, such as earthquakes and large wildfires can’t be prevented, it also sees portable power as a way to restore service faster during unplanned outages.

“As we become better at deploying these units, we’ll be able to respond quicker to emergencies like earthquakes and fires and restore power to customers in a more rapid time frame than years past where we had to wait for lines to be restored,” said Branden Ezell, construction supervisor for PG&E.

Portable generation projects demonstrate the importance of optimizing strategies for staging crews and equipment in heavily impacted areas. Whether the requirement is for 1 MW or 100 MW, these temporary power projects validate the mobile distributed power plant concept’s ability to deliver repeatable and scalable solutions. PG&E’s efforts to modernize an aging grid sooner rather than later is why the utility sought outside expertise to resolve this challenge.


Unplanned outages cannot be controlled, but in the many instances where infrastructure needs to be upgraded or repaired, a portable system can be built reflecting a distribution-level power plant. The portable infrastructure consists of generators, distribution equipment (stepped up to the utility’s line voltage) and protective devices. Switchgear and the protective measures necessary to ensure synchronization with required voltage and frequency (12 kV, 60 Hz) are included.

If there is a fault in the line, for example, protective systems (relays, breakers, etc.) ensure the temporary service remains capable of disconnecting from the grid, if necessary. In many cases, the lead time is needed until the utility’s new assets (transformers, etc.) are delivered and energized. Other examples include sections of distribution lines that are at overcapacity and that overcapacity can be alleviated with temporary power until adequate resources are available to upgrade the line.


Mobile power generation can be interconnected to the grid at almost any location to keep customers energized. The time required to commission a temporary power project is largely dependent on factors such as project size, terrain, proximity from a service center, weather and available space. A typical 10 MW medium voltage power project, for example, would take five to six days to fully commission and test before being ready for operation, and about half of that time to fully decommission.

Whether in PG&E’s or some other utility’s service territory, most customers no longer tolerate power outages. Best practices for minimizing outages and improving customer service through mobile power solutions, therefore, should be combined with utilities’ other quality measuring metrics to ensure planned outages are a thing of the past and unplanned outages are short.

Frank Pizzileo is business development manager for Aggreko.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at

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