IntelliRupter® PulseCloser® Fault Interrupter revolutionises reclosing
For over 70 years, traditional reclosing was the only way to test the line after a fault. This operation repeatedly threw the full force of the fault back onto the system, repeatedly stressing all the network components, and causing expensive damage to the 132/11 kV primary substation power transformer.
Author: Isobel Parsonage
The IntelliRupter ® PulseCloser ® Fault Interrupter offers a gentler alternative to traditional reclosing, reducing the stress on network components and the risk of damage to the 132/11 kV primary substation power transformer, while using just 5% of the energy. Examples of deployment in Chattanooga, USA, and in Birmingham, UK, show how the IntelliRupter ® PulseCloser ® Fault Interrupter can play a vital role in the wide-scale deployment of smart grids and extending asset life.
For over 70 years, traditional reclosing was the only way to test the line after a fault. This operation repeatedly threw the full force of the fault back onto the system, repeatedly stressing all the network components, and causing expensive damage to the 132/11 kV primary substation power transformer. This can often lead to problems with the power supply, meaning customers suffer from low power quality, the resulting cost, and inconvenience. Traditional auto-reclosers can actually cause an upstream fault via this violent testing procedure since the repeated testing causes cables to ‘swing’ from the current surges. If two phases touch, then another fault will be created. This is a common industry problem, which has the potential to turn a small incident into a much larger and more expensive time-consuming fault to fix. This has led to S&C Electric Company coining the term that a traditional recloser acts as a ‘fault multiplier’. IntelliRupter ® PulseCloser ® Fault Interrupter utilises revolutionary PulseClosing Technology™ – a unique means for verifying that the line is clear of faults before initiating a close operation (Fig 1).
Fig. 1 IntelliRupter ® PulseCloser ® Fault Interrupter pole mounted unit
IntelliRupter® PulseCloser® Fault Interrupter
PulseClosing uses just 5% of the energy used by conventional reclosers, to test if the fault is transient or persistent, greatly reducing stress on system components, as well as voltage sags experienced by customers upstream of the fault. This is a much more gentle approach to fault finding and greatly reduces stress on the system, causing no damage, and reducing power quality and supply problems. Therefore, by reducing the stress exhorted onto the system, PulseClosing Technology™ extends asset life. This saves electric utilities, time, and money in repairs, and causes less interruptions to customers. IntelliRupter Fault Interrupters also allow for increased series fault interrupting sectionalising, producing a more reliable power network.
IntelliRupter Fault Interrupters also uses PulseFinding Technology™, which enables intentional protection miscoordination but recovers from miscoordination automatically within seconds, without the need for communication or batteries. This allows for a virtually unlimited number of series protection devices for improving reliability.
Case study: Deployment of the IntelliRupter® PulseCloser® Fault Interrupter in Chattanooga, USA
IntelliRupter ® PulseCloser ® Fault Interrupter has been well received on the American grid with an estimated 8000 units being deployed. About 1100 of those units were deployed in Chattanooga, Tennessee, which equates to one unit for every 0.6 circuit miles, or one device for every 150 customers. Electric Power Board of Chattanooga (EPB), the local Municipal Utility, wanted to improve electrical service reliability across its service area but it also wanted to improve quality of life for the community to attract new employers and residents. That meant ensuring the power stayed on in all weather conditions. Chattanooga knew that the way to accomplish these goals was to become a Smart City, so it invested in a fibre-optic network and a self-healing smart grid in hopes to improve power reliability by 40%. Estimates based on industry studies suggest that across EPB's 600 square mile service area, Chattanooga's economy was losing $100 million each year due to power outages.
EPB chose to install a self-healing network combining IntelliRupter ® PulseCloser ® Fault Interrupter PulseClosing Technology™ with IntelliTeam ® SG Automation Restoration System software to reconfigure the distribution system after a fault to quickly restore service to unaffected feeder segments. This system alone was able to eliminate 40% of the interruption minutes.
When outages could not be automatically restored for customers in the damaged section, the system would enable crews to go right to the affected area and fix problem segments faster. IntelliRupter Fault Interrupters detect faults on the system and use PulseClosing™ Technology to test and determine whether the fault is transient or persistent. If transient, the devices restore power in seconds without damaging equipment with fault currents. If the fault is persistent, the devices use the intelligence in the IntelliTeam SG software to isolate the faulted segment and reroute power from other available sources in a matter of seconds.
With these smart grid self-healing solutions now in place, Chattanooga now experiences dramatic decreases in the duration of power outages. EPB has exceeded its projected 40% improvement in reliability, with 42 and 51% respective improvement in the duration (system average interruption duration index (SAIDI)) and frequency (system average interruption frequency index (SAIFI)) of power outages.
In July 2012, the city was hit by an unusually strong storm that caused power outages in about 80,000 homes and businesses. In terms of severity, it was one of the top five storms in the city's history. Via the smart grid self-healing upgrades, EPB was able to prevent an interruption or automatically restore power to 53% of customers, or 42,000 homes, during the storm. This improvement reduced the total restoration time for the event by nearly 17 h. EPB projects using this system will save customers some $40 million or more per year in power-outage costs.
Dave Wade, Executive Vice President and Chief Operating Officer, EPB said, ‘We are frequently in excess of 60–65% improvement in every metric that exists. Even if a person's outage cannot be automatically restored because they are in the damaged section, automating the system improves reliability for everyone because it allows our crews to go right to the problem and get to work sooner’.
Case study: the FlexD Grid project, Birmingham, UK
In the UK, the IntelliRupter ® PulseCloser ® Fault Interrupter has been deployed by Western Power Distribution in a new and innovative way. The project will be rolled out on the Birmingham network and is funded through Ofgem's Low Carbon Networks Second Tier funding mechanism.
At certain times in the day, several commercial and industrial customers operate machinery or initiate activities that increase the fault level on the network. The FlexD Grid project uses the ‘pulse’ from the PulseClosing™ Technology to create an artificial disturbance on the network. This data will then be used to monitor the fault level. The FlexD Grid project aims to develop and trial an advanced fault level management solution to improve the utilisation of distribution network operators’ 11 kV electricity networks while facilitating the cost-effective and early integration of customers’ generation and demand connections.
Using the PulseClosing Technology™, two negligible ¼-cycle 11 kV network disturbances are created using a 20 Ω, 30 Ω, or when combined, a 50 Ω resistance. The periodic PulseClosing of these phase-to-phase connected resistances is initiated by a remote terminal unit using DNP 3.0 level II protocol over a fibre-optic cable connection.
The phase-to-phase resistive PulseClosing operations occur at predetermined time intervals and may vary as 11 kV network conditions change. These PulseClosing operations only use one of the three resistance values per interval, and the resistances used per interval change, always following the same sequence, e.g. 20–30–50–20–30–50 Ω and so on.
The remote terminal unit also monitors the position status of the 11 kV circuit breaker connected to the IntelliRupter ® PulseCloser ®Fault Interrupter and automatically halts PulseClosing operations whenever this circuit breaker is not in the closed position. When this circuit breaker is returned to its closed position, the remote terminal unit initiates the next PulseClosing operating sequence. The interval the PulseClosing sequence runs at is configurable. The remote terminal unit then resumes the periodic PulseClosing operations starting from the next hour.
Hence, in times of high fault level, the electrical components in the system are protected from any potential impact from a fault on the network.
The IntelliRupter ® PulseCloser ® Fault Interrupter can play a vital role in the wide-scale deployment of smart grids, and extending asset life. Two examples of deployment illustrate how this technology can minimise problems with power quality and supply, and reduce stress on system components. Chattanooga has seen smart grid self-healing solutions limit the impact of grid interruptions by reconfiguring the distribution system after a fault to quickly restore service, while the FlexD Project in Birmingham uses PulseClosing Technology™ to monitor network fault levels and protect electrical components from faults in the system.
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