Without smart switches, smart grid benefits, such as improved reliability of electric service and efficiency through grid optimization, will not be realized explains Serge Kabunda, Engineering Applications Manager at S&C Electric Company who will be addressing network reliability at CIRED 2015. Mr Kabunda will be discussing two applications of the S&C IntelliRupter PulseClosing technology.
Understanding the basics of smart switches
The smart switch is an automated device which is capable of opening and closing in response to signals sent from embedded intelligence in the switch’s local control, a centralized computer or utility personnel back at the control centre. Such devices - including automated load-break switches, capacitor switches, conventional reclosers and PulseCloser™ fault interrupters - support a range of electrical applications, including sectionalizing, protective functions and capacitor-bank switching.
A smart switch is required to carry and - in the case of protective devices such as reclosers and PulseCloser fault interrupters - interrupt short circuits of up to several thousand amperes, and then successfully close the circuit again. An automated switch is expected to respond quickly, possibly in milliseconds, when called upon at any given time.
Being an integral part of the electric delivery system, smart switches are expected to perform reliably every day despite extreme weather conditions. In fact, smart switches are needed most when the weather is at its worst, helping to avoid extremely long outages.
Distribution grids are becoming more complex and dynamic as utilities work to meet renewable energy portfolio standards, improve operational efficiencies and facilitate the connection of electric vehicles. Smart switches have to support new functionalities, such as load balancing and peak shaving, and are expected to meet a range of new requirements, including more frequent operations.
Smart switches are truly smart
Today, switches are not merely automated, but really smart. These switches leverage embedded intelligence and sensors to provide superior response to system conditions by tackling problems locally as they occur. Embedded intelligence enables these smart switches to respond more efficiently to changes in system conditions, thereby improving service reliability because power is restored in seconds.
Rapid response is also a requirement as distributed energy sources are increasingly connected to the grid. Utilities need devices capable of rapid response to be able to balance centralized and distributed energy sources with varying customer demand, and to operate service islands for limited periods of time, all while meeting strict reliability standards.
Smart switches can also improve asset utilization, reducing the need for utility capital expenditures. These devices are capable of capturing data that support asset monitoring applications which enable utilities to track the condition of distribution grid equipment and prioritize maintenance work.
PulseClosing™ technology and reclosers
A new type of smart switch - the IntelliRupter® PulseCloser™ Fault Interrupter - can actually prevent system damage by reducing the exposure of grid equipment to the short circuits that significantly shorten their life. The IntelliRupter PulseCloser represents a major advancement in power handling and fault isolation.
Conventional protective switching devices, such as reclosers and circuit breakers, typically reclose several times after initially opening to clear a short circuit. If the fault is permanent, each reclosing attempt re-establishes the short circuit, exposing conductors, switches, splices and even substation transformers to additional thermal and mechanical stress.
In contrast, IntelliRupter PulseCloser tests the line to determine the existence of a fault, without creating high current surges that can shorten equipment life. These close very rapidly and re-open the interrupter contacts at a specific point on the waveform to send a very short, low current pulse down the line, and then analyze the pulse to determine the next action. A software algorithm examines the point-on-wave closing angle, pulse magnitude and length and shape of the pulse, and projects what the current flow would be if the contacts were fully closed. During an operation using PulseClosing™ technology, the let-through energy is only 2% of what typically occurs during conventional reclosing operations.
Smart switch benefits
The intelligence embedded in smart switches provides additional benefits. Smart switches can capture waveforms, event logs with one-millisecond time-stamping and oscillographic data - all of which help utility engineers better perform power system analyses. The data eliminate the need to map the sequence of events following a short circuit or loss of source and reduces unnecessary work.
Smart switches are also easy to update as the distribution system expands and evolves. Engineers and technicians can update software and settings, and even reconfigure the system remotely, eliminating the need for trips to the field to physically update devices. Furthermore, smart switches make it simpler to test smart grid applications, such as self-healing solutions, in the field and ascertain whether the system is working as expected.
The data capture capabilities of smart switches, in combination with the high accuracy sensors furnished on these devices, can often support multiple smart grid applications, helping utilities obtain a better return on their investment in the devices. For instance, a smart switching device may support an automated restoration approach that improves reliability as well as provide support for a volt/VAR management programme that allows the utility to realize an immediate return by reducing power losses.
Choosing the right smart switch
Given the important role that smart switches can have in delivering the benefits promised by the smart grid, extra care must be taken to choose the appropriate smart switch.
Firstly, the smart switch must meet the electrical and environmental demands of the application and should be able to carry and interrupt currents up to its rated level and hold voltage - and perform these duties repeatedly over a long service life. The switch should also operate reliably under a range of environmental conditions.
As no-one knows exactly what functions smart switches will need to support in the future, especially in the face of how renewable and distributed energy sources will fit into the mix, utilities need to future-proof investments by choosing technologies that best position their complex distribution system.