Unexpected service disruptions due to toppled transmission towers from storms, flooding or fires normally might mean a long-term outage situation. Rebuilding affected line sections with towers of the same types as those damaged often will take weeks or even months, depending on time of year. Fortunately, thanks to development of emergency restoration systems (ERS) that can be put up in a matter of hours, normal service can be restored quickly even as work proceeds to complete whatever repairs are necessary to the affected line sections.
In spite of buoyant and growing worldwide demand, the ERS market is presently served by less than a handful of suppliers, based mostly in North America. One of these is located north of Montreal. INMR visits SBB to discuss their solution and how they have organized deliveries to meet customer requirements.
According to SBB General Manager, Patrick Gharzani, the motivation for power supply companies to restore service as quickly as possible following line structure collapses goes well beyond monetary considerations alone. There are also potential political and social repercussions such as risk of unrest when local populations find themselves deprived of power for extended periods. Says Gharzani, “all these issues impact the power system operator and require them to restore service as quickly as possible.”
SBB’s decision to focus on the highly specialized ERS business came about mostly through chance. Once a manufacturer of customized steel structures, they were approached with a request to supply a transmission tower. A market opportunity was seen and in 2015 the firm decided to drop other activities and concentrate solely on this sector. They now claim to have the largest share of an estimated global market valued at about US$ 30 million.
The key to being able to respond quickly when there are service interruptions due to damaged structures is to have the components of the ERS already nearby and available. Orders are therefore typically made in advance, either as single large contracts or in some step-by-step buying process to build up inventory. Stocking also ensures that power utilities have the time needed to issue public tenders to comply with normal purchasing rules.
Gharzani emphasizes that success with any ERS requires being able to install replacement towers quickly and without need for civil engineering work, such as for foundations. All that has to be done is to flatten the ground at the specified replacement tower location. An equally important consideration is that there is no requirement for heavy equipment such as cranes to hoist the different tower elements and hardware. For example, Gharzani reports that restoration towers for a damaged 230 kV line in the Philippines were erected during a hurricane. As for limits to the voltages that can be covered, he states that these towers have been used up to 800 kV and can accommodate 6 or even 8 sub-conductors.
Application of ERS is not limited only to calamitous events that damage line sections. Sometimes there is a need to re-route an existing line for a brief period to accommodate a construction project or to allow continued power flow while a line is being upgraded in some way. Gharzani cites such examples from Ireland and Norway.
In the former case, Northern Ireland Electricity planned to add a new substation to an existing 275 kV double-circuit line. The project included erection of two new terminal towers to serve the substation. Since these towers would be erected along the existing line, the challenge was to find a cost effective way to bypass the 300 m construction site with a temporary line to avoid affecting power flow. The ERS allowed exactly such a low cost bypass. In the latter case, an ERS allowed construction to proceed on a new retail site well ahead of schedule and without waiting for all the work that might normally be needed to engineer a bypass.
Similarly, a situation in Paraguay in late 2011 offered another case study of how ERS can be used in situations that do not involve damage to existing towers. There, the local TSO faced the challenge of increasing capacity on two important 220 kV lines by changing conductor. Since local regulations did not permit a power shutdown, use of ERS offered a convenient methodology to carry out this work, with power flow maintained by being temporarily diverted.
The basic component of SBB’s ERS is a 3 m long section made of an aluminum alloy known as 6061-T6. This section, weighing 135 kg, is typically assembled horizontally before being lifted by winch. Additional sections are then hoisted into place using a gin pole attached to a rail integrated into each module. This lifting system is then removed after assembly, the same way it was installed. There is even a platform for workers to stand on while they attach insulators and conductors.
Support of each structure is achieved using a system of anchors and guy wires that are supplied along with the modular tower sections. Other key elements of each ERS package are the insulators, which are typically installed in a horizontal Vee or delta configuration. The basic components in the case of SBB are polymeric insulators, which are extended, section-by-section to meet whatever the system voltage requirements.
To allow most effective local deployment, each ERS is supplied inside 20 ft. shipping containers, which also serve as convenient storage for everything that is required, including the tools needed for erection. These containers can then easily be transported by truck to wherever the project site is located.
“We asked customers to tell us their ‘worst-case’ scenarios,” notes Gharzani. “When there is an emergency, power operators go into execution mode. The thinking must therefore happen before any emergency so that every need has been anticipated.” “Based on this, we developed a system that is flexible and can cover almost all voltage levels. When there is an emergency, power operators go into execution mode. The thinking must therefore happen before any emergency so that every need has been anticipated.” He also points out that training crews on what to do is an important aspect of ERS deployment and is therefore offered as part of the package.
The largest single market for ERS is now India where a law from 2016 mandates that all transmission system operators must have such capability in stock locally. Other important markets in recent years have included Sweden and Mexico.
Gharzani feels that while there is good annual growth in this business, the market for ERS is still mostly untapped. “Not all power supply companies are yet aware of emergency towers and all their potential applications,” he says. “The key is that they offer modularity, flexibility and portability.”