In recent years, the global energy landscape has witnessed unprecedented change and extraordinary transformation driven by growing global consumption, aging grid infrastructure, urgency towards decarbonization objectives, and the rapid expansion and integration of renewable energy resources. This transformation presents many challenges, but with those challenges also come significant opportunities, and grid protection systems hold major influence.

Renewable resources are expected to account for 40%+ of energy generation worldwide by 2030, according to the International Energy Agency. This, along with the availability of distributed energy resources (DERs) and the increasing integration of renewables, has introduced new variables into the grid that affect reliability and stability.

At GE Vernova’s Electrification business, the mission is to get power to customers where and when they need it without interruption, while protecting people, assets, equipment, and infrastructure. But as they integrate more renewables into the power mix, this pathway from the power generation source to distribution presents new challenges for grid protection.

Unlike conventional power generation, renewable energy sources are intermittent and contingent on local environmental conditions. The grid protection relays we have deployed in the past were designed to deliver stable frequency in systems run with fossil fuels that power spinning synchronous generators running at predictable cycles. These older, unmodernized systems are unable to understand or react to the behavior of solar PV or wind power, which interface with inverters, or inverter-based resources (IBRs). IBRs significantly impact the grid’s response during fault conditions observed by protection relays. IBRs, such as wind and solar PV, do not inject high flows of current when a fault occurs so they do not trip the circuit breakers that disconnect the damaged area from the grid. Grid fault levels decline as IBR penetration increases in the power system, challenging conventional grid protection strategies.

As electrical networks transition to renewable power, there will be a need for new technologies to protect the grid and ensure the safety and stability of the system. IBRs that interface with renewable sources have outputs that are controlled and thermally limited. As a result, existing grid protection infrastructure that measures fault current magnitudes may also be affected by the fault type, the generation mix prior to the fault, and more. Ultimately, many of the operational relays of grid networks today have been configured and tested for grid characteristics that were prevalent with conventional generation, and everyone is now facing the grid of the future.

At GE Vernova’s Electrification business, they have spent the past two decades learning about the behavior of renewables and developing innovative solutions and digital grid protection systems that can manage numerous variables in real-time to protect the grid.

Digital intelligence evaluates hundreds of data points in milliseconds. If unusual changes in current or voltage are detected, it can send a signal to disconnect or isolate the area anywhere on the grid – whether a transmission wire or substation – where the fault occurred. This “quick thinking” is essential for managing the intermittent nature of renewables and for detecting and responding to faults when renewables are in play. In other words, this communication-aided adaptive grid protection system can take advanced measurements and make split-second decisions to preempt damage without the need of a short circuit energy surge.

These technologies provide many of the solutions that is needed, but fully answering this global challenge will require collaboration with network infrastructure owners. Such collaborations will enable GE Vernova to better understand the challenges posed on their networks and create the next generation of grid protection.

With collaboration and robust investment in both renewables and grid modernization, the industry can meet the energy demands of the coming decades in a way that is affordable, reliable, sustainable, and accessible. The future of energy is here.

This article was written specifically for and originally published on T&D World’s website, www.tdworld.com. 

Utilities around the world will embark over the next decade on grid modernization at a monumental scale. With grid resilience and reliability top of mind combined with ambitious decarbonization goals, smart microgrids will undoubtedly be part of the plan.

A microgrid is a local, self-sufficient energy system that serves its own network. In a microgrid, a group of interconnected distributed energy resources (DERs) can operate both independently of the grid or as part of it—a self-sufficient island of energy amid a larger grid ocean. Hospitals, military bases, airports, and other essential services have used microgrids for decades to combine and control a variety of energy sources as a way to lower energy costs and as insurance against power disruption.

Read the full article on Power Magazine’s website.         

Gas-insulated substations (GIS) represent a key element of high-voltage electrical transmission networks thanks to its reliability, low maintenance requirements and compact dimensions. Here is a brief history of its development and pioneers.

[1966 - The first 245 GIS installed at Plessis-Gassot, near Paris in France]

The roots of HV encapsulated substations go back to the metal enclosed concept of the 1920s when oil was used as the insulating medium. Compressed air and different gases were the focus of much research work, and the first Freon-based solution at 33 kV appeared in 1936. The following decades brought new versions until developments in industrial processes, chemistry and physics led the switchgear industry, towards the end of the 20th Century, to the use of SF₆ (Sulfur Hexafluoride) for arc extinguishing and insulation as the main GIS technology.

SF₆ gas was already known during the 1940s. Westinghouse holds the original patent for the use of SF₆ as an interrupting medium, and their engineers developed the first applications for switches and circuit breakers in the early 1950s. In the 1960s major manufacturers such as BBC-Calor Emag, Siemens, Magrini, Merlin-Gerin, NEI-Reyrolle, the Japanese and Delle-Alsthom had started intensive developments on the basis of SF₆. The dual-pressure SF₆ circuit breakers of the early GIS systems were soon replaced by single pressure, while circuit breakers were adopting puffer and combined thermal-puffer arc extinguishing chambers. The GIS focus was on the benefits of a compact indoor solution, protected from the environment and closer to users, whereas some markets preferred outdoor rugged solutions using hybrid GIS solutions.

GE Vernova's Contribution

GE Vernova's Grid Solutions business has a rich GIS development history through its ancestor companies, Delle-Alsthom, Sprecher & Schuh, GEC, and AEG.
 
Delle-Alsthom France started GIS development in 1958 and in 1966-1967 delivered a world's first with its “Fluobloc” at 245 kV in several Paris substations, demonstrating the benefits of underground GIS to supply bulk power close to city users. Achievements in the higher voltage ranges were subsequently marked by the deliveries of the first substations for 420 kV in 1976 and for 550 kV in 1977. Another “world-first” was the completion of AEP’s 800 kV GIS in Joshua Falls in 1979.
 
Sprecher & Schuh studied compact metalclad installations as early as 1954 with oil insulation systems, but soon concluded that SF₆ gas insulation offered greater advantages. Their first GIS for 220 kV was delivered in 1970 and the 145 kV, 40 kA in 1971. The original circuit breakers with double-pressure SF₆ systems (220 kV, 50 kA), developed together with ITE USA, were operated by the well-known Sprecher motor-wound spring operating mechanisms, which contributed to the success of subsequent GIS families. The exclusive third-generation FK mechanism today serves all Grid Solutions' GIS products in applications around the world.
 
AEG in Germany has also long been involved in GIS and SF₆, with its first GIS substation delivered in 1971.
 
Meanwhile, GEC in England was collaborating with Siemens, and their first GIS was a 145 kV substation in London in 1982. As GIS systems developed and their extensive use in HV networks grew, Grid Solutions became the manufacturer of complete GIS ranges of 72.5-800 kV in which single-phase and three-phase encapsulation was and continues to be used.

Looking ahead

Clearly, the most significant development factor was the adoption of SF₆ as an insulation medium. This boosted the development of smaller switchgear requiring less operating energy and reduced materials and resources, leading to higher performance. So far 420 kV, 63 kA with a single break is possible with the spring mechanism.



After 50 years in the making, GIS development is accelerating thanks to the availability of simulation tools and the capability to integrate environmental needs into the design. Future trends could be influenced by the substitution of SF₆ technology, which, however, is likely to be a very complex task. Other steps have already been taken. Moving HV substations closer to consumers results in reduced transmission losses. Indoor GIS reduce the environmental influences on the switchgear, reducing maintenance needs and increasing lifetime. More and more “intelligence” is integrated into the GIS using electronic devices, forming part of digital substations. Ecological and economic considerations, together with ongoing technological developments have made even further optimisation of GIS conceivable.

[2018 - GE Vernova's first 145 g³-GIS installed at Axpo's Etzel substation, in Switzerland]

Besides playing a major role in power plant protection, Generator Circuit Breakers (GCBs) offer more flexibility for plant operation and enable the implementation of efficient solutions to reduce investment cost. Maintenance, energy efficiency and carbon footprint are now also enhanced thanks to GCB architecture improvements.

What are Generator Circuit Breakers (GCBs)?

Generator circuit breakers are power plant devices located between the generator (which produces electricity at a voltage of around 15-25 kV) and the step-up transformer (which increases this voltage up to the grid transmission voltage – 200 kV to 800 kV). They play a key role in the protection of the transformer and the generator in case of fault (short circuit on the power transmission system), and their major function in normal operation is to connect and disconnect the generator to and from the grid with high availability and reliability. For decades, generator circuit breakers have existed for generator ratings ranging from 50 MVA to 1,400 MVA. More than 7,000 units are in service today throughout the world, and they have improved the overall life cycle cost of power plants through efficient protection of generators and transformers and simplifying synchronization to the grid.

GCBs: an insurance policy

What concerns a power producer is to generate and deliver energy. With a GCB, a producer can gain flexibility by making the plant’s strategic connections safer; it can also reduce the effects of a generator or transformer failure by reducing its duration. “Equipment today has reached a very low failure rate, but a rare phenomenon can still have disastrous effects,” says Jean-Marc Willième, Senior Expert at GE Vernova's Grid Solutions’ High-Voltage Switchgear Research Center in France.

“Generator circuit breakers are something of an insurance policy: as long as everything goes well, it could be seen as an unnecessary cost, but when things go wrong, what a relief to have it there!”
 
A financial study, based on life cycle cost, has compared the situation of power plants with and without a generator circuit breaker. Analyzing the risk of fault, which includes, on the one hand, the cost of not producing, and on the other hand, the cost of a GCB solution, it validated the installation of GCBs. “A typical example, based on a 400 MW power plant, demonstrates that the generator circuit breaker solution is cost-effective if, during 20 years, the presence of the breaker has avoided less than 14 hours of outage,” explains Willième. Moreover, if some cost reductions in generator circuit breaker schemes are taken into account, such as eliminating HV circuit breakers and HV/MV transformers and replacing them by a GCB and an MV/MV transformer to feed auxiliaries (see sidebar 2), “savings could be identified from the very beginning of the project”.

In the world of circuit breakers, breaking capability is a very important feature to have adequately specified in case of a major fault in a power plant. This kind of failure is extremely rare, but has very heavy consequences, so the design of the interrupting chamber – the heart of the generator circuit breaker – is a crucial factor.

GCBs are something of an insurance policy.

GE Vernova's Grid Solutions business has continually developed and improved this mechanism. Thanks to the thermally assisted puffer-type technology, it is possible to interrupt short-circuit currents of at least 160 kA with a spring-operating mechanism. Some years ago, a CIGRE study on high-voltage circuit breaker failures and defects in service revealed that the availability of the circuit breakers depends mainly on the reliability of the operating mechanism, and that the most reliable mechanism, by far, is the full spring mechanism. 

For its latest generation of GCBs, Grid Solutions has enhanced its spring-operating mechanism to make it simpler, save energy and reduce stresses and impacts during operation. As a result, the improvement in reliability and availability of the generator circuit breakers using spring mechanisms is now accessible for power plants up to 1,400 MVA. Generator circuit breakers originally used air blast technology for electric arc extinction. Air blast was progressively replaced in the mid-80s by sulphur hexafluoride (SF₆) technology, where the SF₆ is used instead of compressed air.

Keeping losses as low as possible

To reduce life cycle cost, the conception of a GCB focuses on the status of the arcing contacts, which suffer heavy wear when operating and can be considered as strategic for the breaker. However, “another important feature of the generator circuit breaker is its capability in terms of rated current,” says Willième.
 
The most reliable mechanism, by far, is the full spring mechanism.
 
Although this is around one-tenth of the breaking capability, manufacturers have to carefully design their breaker around this issue. “As the main current specification is related to a function that is active almost 100 % of the operational lifetime of the generator circuit breaker, what is needed is a current-carrying capability with losses as low as possible.” This concern is reinforced by the fact that circuit breakers are traditionally associated in series with line disconnectors, whose role is to provide personnel with visible safety during maintenance. Unfortunately, disconnectors also have permanent disadvantages: they are a source of loss during energy production phases; they also increase the occurrence rate of minor risks such as mechanical failure, and major risks such as thermal runaway of contacts; consequently, they need more maintenance.
 
The sizing of both circuit breaker and disconnector for loss reduction requires the full attention of the designer. This is reinforced by the fact that the environmental footprint of electrical equipment is mainly related to the energy dissipated during the total generator circuit breaker's life operation, rather than to the energy or material consumed during manufacturing process. “The most efficient way to avoid energy waste in this equipment is to reduce energy sources by design,” Willième points out.

A breakthrough in efficiency and environmental friendliness

The classical SF₆ circuit-breaker layout is not 100 % effective regarding loss reduction. As SF₆ pressurized volume is linked to contact sizing, designers have to make compromises between Joule loss reduction and minimizing SF₆ volume. Another drawback is that the main contacts are in the same environment as the arcing contacts and consequently are subjected to the hot, current-breaking gas flow as well as corrosive SF₆ by-products. “An innovative architecture – the FKGA2 – avoids these compromises by allowing the main contacts to be completely isolated from the heated current-breaking SF₆ gases, contaminated particles and the associated by-products within the interrupter chamber,” explains Willième. Their lifetime is therefore independent of the breaking events experienced by the interrupter chamber. The integration of the circuit-breaker main contacts and disconnector function into a single piece of equipment is particularly effective in decreasing losses: the electrical resistance is far less compared to the classical solution (circuit breaker and disconnector in line), so heat dissipation is reduced throughout the equipment lifetime. Additional benefits include a reduction of the equipment’s total phase length; hence less material is used, and manufacturing processes are reduced, resulting in less impact on the environment. The combination of these different factors, including reduction of SF₆ volume, leads to a significant decrease in the equipment’s environmental footprint.

Use of multi-physics optimization for designing circuit breakers
The development of digital simulation tools and the exponential increase in computer power allow engineers to greatly accelerate the design of industrial applications such as high voltage breakers. They can pre-evaluate a design on computer models to examine its behavior for different operating conditions and therefore optimize the product before the first prototype is built and tested. As a result, test duration and cost can be substantially reduced. “Generator circuit breakers are extreme products due to the very high currents imposed by their position on the network,” says Gwenael Marquezin, HV Switchgear Expertise Development Manager. “Improving their design for higher performance and efficiency, making them more robust and compact (such as in the FKG series), leads to increasingly complex problems to solve as design constraints are closer to the limits.” Therefore, “multi-physics simulations are necessary to better understand and evaluate the combination of physical constraints and their effects on the breaker’s behavior, performance and lifecycle. ” Besides the complex simulations of breaking tests, generator circuit breaker designers rely on the simulation teams to recognize such effects as the electromagnetic forces generated by the high short-circuit currents, Joule power and related temperature rise due to the high nominal current, seismic response of the equipment, etc. However, beyond theoretical knowledge, these teams “must possess the practical competencies to be able to cast a very critical eye at simulation results, their significance and correlation with test results.” Dielectric, thermal and mechanical phenomena involved in the circuit-breaker design are nowadays relatively well understood; others, like coupled electromagnetic and fluid approaches, are highly complex and require extra care.

This station is among the best performing power plants in the world with low NOx, SO2 and CO2 emissions. It features a high operational flexibility, since it can run at base load and part loads as well as in two-shift operation mode. It is designed around two GT26 combined cycle modules rated at 435 MW each for a gross output of 870 MW at 59 % efficiency.

Easier inspection for the main contacts

Beyond environmental considerations, power plant owners are concerned by the reliability and availability ratio of their plant and by the immediate negative consequences of a failure. For this reason, it is crucial to detect the predictive signs of future failure at the earliest possible stage. As the main contacts are a major contributor for the transmission of the energy produced by the power plant, it is a big advantage to be able to easily observe the main contacts throughout the equipment’s lifetime in order to detect any trace of abnormal wear on the contact surface. The value of having accessibility to the main contacts is enhanced by the fact that contact resistance measurement cannot alone be considered as reliable evidence of an increase in temperature. Furthermore, the new joint IEEE-IEC GCB standard draft recommends visual inspection of main contacts as an efficient “verification of the capability of the generator circuit breaker to carry the rated normal current”.
 
Heat dissipation is reduced throughout the equipment lifetime. 

Contact inspection consumes a large portion of maintenance time with a classical breaker architecture, where main contacts are hidden in a sealed envelope containing SF6 gas under pressure and subjected to hot gas flow; currently it is only possible to inspect the contacts during complete overhaul sessions of several weeks. By segregating the main contacts from the interrupting SF₆ gas, the new FKGA2 provides simple access from outside the breaker during a short, normally scheduled power plant shutdown. The main contact inspection is considerably easier than with the conventional GCB architecture and, when necessary, parts replacement is also significantly less burdensome.

Generator circuit breaker solutions – lower cost, flexible and more protective  
There are two major options when designing the electrical single-line diagram for a power plant:

• the block diagram scheme: the generator output is directly connected to the Generator Step-Up Transformer (GSUT), and the connection of the unit to the grid is through an HV circuit breaker; this scheme requires a Station Service Transformer (SST) to feed the unit auxiliaries when the generator is not connected to the grid;
• the generator circuit breaker scheme: the HV circuit breaker always remains closed and the unit auxiliaries are permanently fed through the GSUT and the Unit Auxiliary Transformer (UAT).

For the user, the GCB scheme has three main advantages:

• it is a more economical solution, as the generator circuit breaker’s cost is made up for by the savings from avoiding an SST and its associated connection to the HV grid;
• it avoids auxiliary power supply changeovers at unit starting and stopping; for large power plants these changeovers may be complex and induce important transients if the 2 supplies are not in phase;
• generator circuit breakers enable fast elimination of faults (80 ms) on the energy transmission system (GSUT, UAT, busbars), and therefore limits the consequences of the fault, whereas with the block diagram scheme, the generator will continue to feed the fault for several seconds until the generator is fully de-excited.

As customers increasingly push to adopt condition-based maintenance for Gas-Insulated Substations (GIS), new opportunities are arising for periodic or permanent measurement of partial discharge.

Traditionally, high-voltage substations are air insulated. But the clearances required between phases and between phases and earth are huge. This results in rather large installations, making them difficult to house in urban environments where space is at a premium. To overcome this constraint, a parallel technology was developed, the Gas-Insulated Substation (GIS), using a gas, for example sulphur hexafluoride (SF₆), at high pressure. SF₆  has excellent dielectric properties and is used as the insulating medium between the phases and between the phases and earth. As a consequence, a GIS is much more compact. In fact, gas-insulated substations can be down to one-tenth the size of their air-insulated cousins, depending on the voltage level.

The use of gas insulation in the power system network has developed rapidly due to its compact nature, low maintenance requirements, and reliable operation. But the reliability of the GIS equipment can be undermined by the presence of free particles that originate mainly from the mechanical vibrations, from moving parts in the system such as breakers or disconnectors, or even from the manufacturing process.

According to David Gautschi, electrical engineer with GE Vernova's Grid Solutions business, “they are rare, but can locally generate high electric fields exceeding the structure’s design limits and initiate partial discharges (PD) forming free electrons and ions in the insulation. Repeated partial discharges are capable of triggering a progressive carbonisation of spacers that can slowly build up over years until they produce a flashover, or failure of the switchgear insulation structure resulting in the entire installation, or parts of it, being shut down.” Repairs – often involving the manufacture of specific parts – can take several weeks to complete.

Measuring partial discharges

When partial discharges occur (resulting in voltage drops of less than a nanosecond), they generate electromagnetic waves that propagate through the switchgear. These waves can be measured by means of different technologies operating in a variety of frequency ranges. Detecting partial discharges in lower frequency ranges can be carried out by taking measurements with acoustic sensors. Says Gautschi, "In the medium frequency range, between a few kHz and a few MHz, measurements are usually made by means of a coupling capacitor. The disadvantage of using this device is that it is large and not suitable for online monitoring. However, partial discharges in pressurised gas can be measured in the Ultra High Frequency (UHF) range between 100 MHz and 2 GHz. The added advantage here is that this allows the whole substation to be permanently monitored and the location of PD activity can also be pinpointed.” Demand for this level of monitoring is particularly high in the Middle East, though less pronounced in Europe, where utilities are more hesitant to make the additional outlay required.

UHF range measurements

Different types of equipment are available to carry out measurements in the UHF range. GE Vernova's Grid Solutions business has developed its own solution, called PDwatch. The center of competence for the PDwatch product is located in the BHT unit in Aix-les-Bains, France. The PDwatch system can be used either for periodic measurement (PDwatch portable) or for permanent (online) condition monitoring. The second method has the obvious advantage of tracking all partial discharge activity over time and therefore offering a better basis on which to decide when maintenance is required rather than relying only on spot checks using a portable system. “The benefit of measurements in the UHF range is the effective avoidance of external noise,” explains Jean-François Penning, PDwatch project manager.

The PDwatch Portable offers frequency spectrum and time analysis.

The frequency range can be chosen to measure in a band with low external noise. The suppression of external noises, for example in the GSM mobile phone range, can be achieved in the following way: the measurements made by the sensors fitted in the GIS are compared with the results of those installed in other compartments or those of an additional external antenna. This method avoids using additional band stop filters on the input ports, as generally required by standard wide band monitoring systems. It also maintains a good signal level. Once the partial discharge activity has been measured, the next task – and the more complicated one – is to interpret the partial discharge patterns and classify them into degrees of severity.

“Part of the complexity is that partial discharge patterns will vary according to the switchgear design,” notes Gautschi. “So it is essential to have access to the manufacturer's database to make sure that partial discharge information will be accurately interpreted. Grid Solutions is going to make its databases available to customers.”

PDwatch online partial discharge monitoring

The PDwatch Online UHF monitoring system records and displays the UHF signals generated by partial discharges in a gas insulated substation. It is permanently fitted into the substation and can be interrogated remotely at any time. This makes it possible to detect and eliminate emerging dielectric faults before a flashover can occur. Used with suitable sensors, this system can detect critical defects such as particles, coronas, free potentials and insulator voids. It can also be programmed to generate alarms at specified absolute value and time thresholds. “The latest system is very advanced,” points out Gautschi, “and uses fast algorithms to provide very high accuracy.”

PDwatch portable UHF detector

PDwatch Portable is designed to measure campaigns in substations at the commissioning stage or periodically in the course of the substation's life. It is a two-in-one device, offering frequency spectrum analysis and time analysis. By using this equipment at regular intervals, developing dielectric faults can also be detected and eliminated before complete breakdown occurs. The portable UHF detector and its laptop PC are fitted into a travelling case and supplied with all necessary cables and accessories.

PDwatch Manager

This software tool enables event records to be managed while at the same time facilitating defect recognition. It can be used locally on the central unit's human machine interface (HMI) PC or run from a remote PC via the Internet. It includes a constantly updated library of partial discharges that helps to identify PD patterns. It has the added advantage of saving users a considerable amount of time by generating test reports automatically.

Sensors for measuring partial discharge activity 
Different types of sensor can be used to measure partial discharges in a gas-insulated substation. Grid Solutions' latest design uses a conical antenna with a small footprint. Its sensitivity has been tested under laboratory conditions in different calibration cells as well as after having been installed in the switchgear. It offers an extremely high degree of accuracy and high linearity. Furthermore, the cost of the device has been dramatically reduced and its small footprint now allows it to be retrofitted to older substations. Its output has an integrated low frequency cut-off so that no power frequency voltage is visible on the sensor connector. The output can also be adapted to meet customer needs, and it can, for example, be used as a conventional voltage detector to detect whether a particular phase is energized or not.

The new sensor has been fitted in all types of Grid Solutions gas-insulated substations and tested for use in retrofit projects. These latest developments have resulted in an adapted version of the sensor being used in large power transformers to monitor partial discharges in oil. This version has been installed in 800 MVA transformer poles of the Swiss utility Alpiq. The transformers have been in service since 2011.

During the development of the sensor, the existing calibration methods for GIS sensors were tested, and a new high performance calibration cell has been developed to carry out tests when no bays are available to carry out this procedure in situ.

The complexity and huge quantities of data that smart grids generate require transformational control room solutions. The integrated distribution management system (IDMS) gives operators a holistic view with advanced optimisation analytics, helping them make better operational and business decisions.

Radical, transformative technologies often start out by imitating the old school solutions they replace. The “horseless carriages” of the late 19th and early 20th centuries kept many features of horse-drawn vehicles. A similar phenomenon can be seen in the electricity industry. On a simple consumer level, you can buy a light bulb that looks (a bit) like a flickering candle. At the extremely complex level of network control, digital technologies were inspired by analogue systems.

An analogue control room is almost a work of art. The centerpiece is a large map-board of the distribution network that covers the walls. Operators are placed around the room in such a way as to maximise their view of the paper maps, push-pins and various objects stuck onto the board to show the state of the system. Just as the first printed books were designed to look like the parchments they replaced, so a “traditional” digital distribution management system is basically a map-board on a digital screen. The operators don’t have to walk around a room any more to get an overall view of the network, but they do have to consult several screens and rely on a relatively limited amount of data to make critical real-time decisions.

Positive impacts at every level

All that has changed with the new generation of smart distribution control rooms and the introduction of integrated distribution management systems. GE Vernova's Grid Solutions' Network Management Solutions Activity Director IDMS, Dr. Avnaesh Jayantilal, is enthusiastic about the possibilities the new technologies will bring to utilities. “Our IDMS is based on our core e-terradistribution technology and has positive impacts at every level, from enhanced situational awareness, improved reactivity and enhanced safety in the field to improved reliability and operational improvement.” And all that is on “a single pane of glass” providing a comprehensive supervisory control and data acquisition (SCADA) system, distribution management system (DMS) and outage management system (OMS). 
The IDMS is made up of a number of modules. The network analysis module is based on a robust distribution network power flow that supports a fully unbalanced model for both radial and meshed medium-/low-voltage networks. It analyses distribution power flow, distribution state estimation, power quality, losses, short circuits, and load modeling. This allows dispatchers and planning engineers to study the current and future state of the network.

Our IDMS is based on our core e-terra distribution technology and has positive impacts at every level.

The network module provides an enhanced level of analysis allowing the dispatcher to improve the network configuration and achieve one or more predefined objectives: for example, keeping nodal voltages and branch currents inside operational limits, maintaining power factor requirements at specific locations in the network, or reducing total demand or losses in the distribution network. It includes load and Volt/VAr optimisation (VVO), fault location, isolation and service restoration (FLISR), planned outage study (POS) and automated feeder reconfiguration (AFR). 

The switching operations module interfaces directly to the network models. Switching orders can be created manually or generated automatically by the network enhancement functions. In practice, this clearly allows utilities to optimise system resources, but there are significant benefits in terms of human resources too. 

A learning tool

Dr. Jayantilal also highlights the possibilities of using these capabilities of the IDMS as a learning tool. “Major storm events seem to be getting more frequent. The IDMS was developed to process high volumes of data to enhance network resiliency and restoration, but it can also simulate a major event. Utilities can prepare their employees and processes for future events, but also analyse data collected during a storm to see how to improve performance.”

The IDMS includes a state of-the-art training simulator that is able to simulate large-scale outages from major storms. The simulation includes field equipment operations, customer calls, power-on/off messages from smart meters, and crew responses. 

Business process transformation

Dr. Jayantilal illustrates what this means for Stedin, which is one of the largest distribution utilities in the Netherlands, providing electricity and gas to over 2 million private, corporate and government customers, and to one of the largest ports in the world, Rotterdam. “Stedin was performing 6,000 switching orders a year, all manual and paper-based, taking about 90 minutes each. IDMS reduced the processing time to 30 minutes. Stedin was able to reassign two full-time employees to other critical duties thanks to the 6,000 hours they saved. And, by the way, the IDMS only took up one of those 30 minutes; the other 29 went to all the processing and approvals.”

Stedin also shows how digital technologies can quickly be adapted to interesting new uses. One of the key benefits of deploying the IDMS is the ability to automatically transfer relevant network and outage information in real-time through social media to communicate with customers. Stedin’s experience shows that during an outage, customer satisfaction tends to improve when customers are informed about the cause of the outage and, critically, the expected restoration time. Stedin is planning on sharing a real-time, read-only version of their IDMS with the local safety authorities to help improve coordination during major storms. 

Make the most of what you’ve got

For Dr. Jayantilal, one of the most interesting benefits is that the IDMS can help utilities avoid having to invest in new capacity just to manage peak load scenarios and network congestion. “With the IDMS, utilities can better manage their medium- and low-voltage assets in the field and push them harder and closer to their real limits.” The IDMS can also perform automated network self-healing by using the FLISR application to reduce customer outage times. 

On a global scale, Dr. Jayantilal also sees distributed energy resources (DERs) as a major challenge for utilities in the future, and one that GE Vernova will help utilities meet. DER growth driven by regulatory incentives and sustainability objectives has introduced both technical and commercial challenges for the utilities. On the technical side, the network analysis applications have been enhanced to incorporate complex models for DER including solar-photovoltaic, energy storage, demand response and electric vehicle charging, with new real-time dashboards for operators. 

The IDMS is helping utilities all over the world make the most of smart grids. But as Dr. Jayantilal says, it’s also helping them reach a goal that hasn’t changed since the first electricity networks were built: “Provide reliable, safe and affordable electricity to their customers.”

Zoom on the outage management system

IDMS outage management system

The IDMS outage management system (OMS) module collects, coordinates and analyses outage information from customer calls, automated meter observations (AMI), and SCADA data. It assists the dispatcher by determining the most likely point at which customer supply has been lost and coordinating crews and other activities through the repair and restoration process. It is designed to handle storm situations, provide basic workcrew monitoring functionality, and calculate distribution performance indices to meet regulatory reporting requirements. 

Its ability to merge historical and state-of-the-art outage observations is a huge performance benefit in large-scale events. The OMS utilises AMI observations to complement phone calls and to verify the extent of outages and, more importantly, verify complete restorations.

The system treats each customer end-point as an individual entity connected to a dynamic, as-operated wired model. As the OMS system model always reflects actual connectivity, customers are always tied to the correct energisation sources (or not, when de-energized). 

The OMS does not make gross assumptions (for example, assuming a static model); hence the restoration performance and accuracy of outage reporting metrics are improved significantly. Uniquely, it recognizes and models dynamic partial restorations and abnormal energization paths. Accurately handling nested outages and partial restorations also improves the accuracy of outage performance indices. Integration with DMS modules enables automatic creation of switching orders that are validated with the network analysis applications to ensure network resilience is maintained.

Outage analysis

Switch order

Outage calls

The sheer size of converter transformers for ultra-high voltage DC (UHVDC) systems poses special challenges, not only for integration with other equipment, but even for design, testing, manufacturing, and transport to the site.

The names and even external shapes of many electrical components are often the same whether for small household appliances or gigantic industrial structures. For manufacturers, however, it is not simply a matter of scaling up the structure. Today, GE Vernova offers 800 kV converter transformers, but as David Wright, Senior Expert Engineer in the Power Transformer Division, explains, “Developing UHVDC systems meant practically starting from scratch in many cases. Initially there was little information available about the performance of insulation materials for converter transformers at the very high AC and DC voltages involved, so detailed testing on prototypes was needed to generate comprehensive design information."

Even before testing prototypes, bushings had to be developed. When you think of the complexity of grid equipment, power electronics probably come to mind, but even a seemingly simple mechanism like a bushing presents challenges. In a converter transformer, both AC and DC can be present, which adds to the complication. The voltage distribution of a bushing is determined by the capacitance between the foils for an AC voltage but by the resistance between the foils for DC. Special measures are needed to control voltage distribution when the bushing is in the transformer turret.

GE Vernova's Grid Solutions business - 800 kVDC bushing being tested in Graz, Austria

Getting it out of the door

There are physical constraints, too. Ratings have been increasing to achieve higher power transmission levels, but size cannot simply be increased proportionately. “The size and weight of the transformer is limited by shipping constraints,” says Wright.

The size and weight of the 800 kV converter transformer is limited by shipping constraints

“So if you want to get it out of the door and delivered to the site, insulation design has to improve the clearances and component structures to produce the most compact transformer possible but still maintain its thermal performance and respect IEC norms.” Trial and error would be too costly, so Wright and his colleagues took Grid Solutions’ SLIM finite element modeling package and added the capability to analyze the particular challenges of UHVDC bushings and transformers for studies of the core design, harmonics, hot spots, and dielectric components.

Finite Element Modelling

With the results suggesting that the proposed solutions were feasible, the next stage was building a prototype. The Technical University of Graz had a hall big enough for initial tests of the bushing, but to meet the requirements for test voltage supplies and very low levels of background partial discharge for a transformer weighing over 100 tonnes, Grid Solutions upgraded the facilities at its transformer factory in Wuhan, China, where the prototype was manufactured and tested successfully in 2011.

800 kV converter transformers being tested in Wuhan, China

One of the challenges Wright’s team had to overcome in moving from prototype to on-site installation was the fact that the internal, valve-side connections require large electrical clearances and can have a significant impact on the size of the transformer tank. To reduce the clearances, a system of preformed barriers with controlled oil duct spacing was developed and implemented for both 600 and 800 kV DC converter transformers. This allows the connections to remain inside the transformer tank while respecting the size limits for shipping the converter transformer.

Success justifies the investment

Converter transformers for Rio Madeira 600 kV DC bi-pole 2 were manufactured and tested in upgraded facilities in the GE Vernova's factories in Canoas (Brazil), Stafford (UK), and Wuhan (China). The 800 kV DC Champa-Kurukshetra transmission network in India involves the supply of 28 transformers from GE Vernova in the UK and Vadodara, India. Looking back, David Wright insists that “success required a major commitment of resources, expenditure and coordination of the many skills of the Power Transformer Product Line. Our approach enables us to offer transformers comprising the best available technology throughout, no matter which of our factories worldwide is producing them.”

Highly sensitive sensors for GIS health checks

Extending the life of ageing gas-insulated substations (GIS) requires precise data on their dielectric health from partial discharge monitoring. But the physical and electromagnetic environment is challenging for sensor design.  

GIS have been around since the 1960s, and as the equipment ages, reliability can deteriorate. Moreover, the dielectric failure rate of GIS is higher for voltages above 170 kV. GIS could attain even greater availability rates by improving health monitoring through more effective in-service diagnostics. The IEC 62271-203 standard addresses this through stricter on-site testing, and recommends using partial discharge (PD) monitoring diagnostics.

For the user hoping to extend the lifetime of a GIS by retrofitting dielectric monitoring equipment, sensitivity is an issue. Thibaut Mauffrey, GE Vernova's GIS Digital Solutions Support Engineer, highlights a dilemma facing sensor designers: “Signal detection is crucial to diagnosis and the measuring equipment has to find the right compromise between the high sensitivity required to detect mobile particles, the most common defects, and a PD sensitivity value that can be obtained in the field. If the sensor is not shielded in an efficient manner, one can experience electromagnetic interference, even from mobile phones in the 300 MHz to 2 GHz range.” Radio transmitters and electrical corona can also cause problems. 

A reputation to maintain

A number of devices are available on the market, but as Charlie Girard, GE Vernova's GIS Service Product Line Manager explains, “Due to the inadequate quality of existing sensors in terms of sensitivity, we decided not to offer a retrofit solution for PD monitoring with third-party devices as it wouldn’t be compatible with our quality and accuracy criteria. Alstom has built a worldwide reputation in GIS, and our customers have the right to expect more from us than from non-specialists in this field.”

Lab tests carried out by Mauffrey and his colleagues show that the sensors being developed have far better sensitivity and accuracy than the devices with which they were compared – up to three times better in some bandwidths. Another limiting factor with sensors available on the market was the minimum size of coupler to fit with any type of GIS. Girard is pleased with the results: “We achieved satisfactory sensitivity for a 30 mm diameter device, compared to around double that size for those on the market. That was probably the greatest technical challenge we had to overcome.”

Viewport sensor - 32 mm

Specialist knowledge for general purpose

Two types of antenna were designed with the support of a specialist in aerospace and military applications. One is a viewport antenna that can be fitted to inspection viewports, the other is a barrier sensor to put on insulator flanges, where the flange design permits this. The antennas are the most sensitive available today, and each has been improved using finite element electromagnetic modeling. 

Barrier sensor on insulator flanges

This specialist expertise is combined with general applicability. Thanks to their standard Type N socket connector, these new sensors can be connected to any PD monitoring equipment of any gas-insulated substation, whoever the manufacturer. And because it is an external sensor, the mounting components and procedures have been designed so that legacy equipment can be upgraded without having to shut down the installation or to dismantle any of the components under SF₆ gas pressure. 

Girard insists that developing an in-house product is also part of a philosophy: “We can now propose a fully integrated and cost-effective solution for the retrofit of the whole range of GIS and the whole chain of technology, from detection to diagnosis.” Mauffrey adds that the human factor is vital all along the chain. “The technology and software can only do so much. In the end, the GIS and monitoring device expert is the one who is providing the right diagnosis to the customer to undertake the preventive maintenance action.”

Taking advantage of latest design techniques as well as innovative concepts, the newly developed 800 kV GIS substation succeeds in combining compactness, high reliability and performance in compliance with the latest IEC standards.

In large countries such as India, China or Brazil, conventional and new sustainable power sources are often located in regions remote from load centres and need large-scale AC transmission systems. One solution to reduce the power losses and improve the transmission capacity of AC links is to increase the system voltage up to 800–1,200 kV AC. For these high-voltage transmission systems, the use of gas-insulated substations (GIS) is extremely advantageous, as this substation type is highly reliable and requires less maintenance than air-insulated substations (AIS) because all active parts are protected from environmental hazards. In addition, a GIS’s inherent compactness (owing to the superior insulating properties of SF₆ compared with air) reduces bay dimensions and overall substation footprint and height, which is very important in minimising seismic impact.

However, “at 800 kV, existing GIS are based on technologies from the 1990s, so dimensions are still relatively large and 800 kV GIS are mostly installed outdoors,” explains Mathieu Bernard, GE Vernova R&D project manager for bay apparatus and substations. “Responding to a growing demand for greater compactness (notably from the Indian utilities), our main objective was therefore to develop an 800 kV GIS compact enough to be installed in a small building. One key point was the circuit breaker architecture, as it represents a large part of the substation.”

Innovative circuit breaker architecture with smaller footprint and reduced height

“We tried various circuit breaker configurations combining two 420 kV breaking chambers in series,” says Nicolas Garbi, GE Vernova's R&D project manager for the circuit breaker. “The solution was found by positioning the two chambers vertically, side by side, in a single tank, with an oblique conductor in between. This enables us to have the two breakers as close as possible to each other – the shortest distance between them is less than 5 cm. The chambers can also be equipped, where necessary, with closing resistors without greatly increasing the dimensions of the enclosure.”

Circuit breaker section view

With this innovative circuit breaker design, improved substation architecture and other innovations (see below), GE Vernova's new 800 kV GIS not only achieves the reduced footprint required but also, with a maximum height of 5 meters as for the standard architecture, can be easily installed inside a building. Moreover, even though it is the most compact 800 kV GIS, the unit still offers “exceptional access to all components and viewports: the highest drive position is at 3 meters, readily viewable from the floor without requiring specific – and heavy – catwalks.”

Typical diameter arrangement inside a building

Another important objective was to ensure reliability under any and all service conditions, particularly with respect to earthquakes. “As India – a major developing network using 800 kV GIS – can be subject to serious seismic events, one of our R&D missions was to take this risk into consideration in the very early stages of the design of our new substation,” says Bernard. Having a reduced height is already a good point where a high level of seismic withstand is required. In addition, all the most massive equipment is close to the floor (hence a low centre of gravity), and seismic calculations have been conducted jointly with design studies to ensure optimum behaviour of the substation. “As a result, Alstom’s 800 kV GIS offers top-class safety with regard to seismic constraints of 0.3 G and more.” 

Performance and reliability

Development of equipment for such high-voltage ratings cannot be made by simply applying a size-factor ratio from lower voltage products. The characteristics of UHV overhead lines and substation schemes demanded the continuation of fundamental studies and the application of innovative solutions to achieve maximum reliability for the equipment. 

For instance, when the service voltage rises, the bus charging current switching (BCCS) capability of a disconnector has to be increased. As a consequence, managing BCCS implies a better understanding of the complete phenomenon. “When the circuit breaker opens, the load current is interrupted and only a small capacitive current can flow through the closed disconnector,” Bernard explains. “During the opening operation, multiple restrikes can be observed between contacts. The main issue in disconnector development is to ensure that no flashover between the two electrodes will propagate and reach the enclosure. An innovative solution has been found, applied and validated: a specific characteristic of the electrode, which includes mobile parts, allows the gap to be reduced during the closing operation. The reliability of the disconnector in terms of very fast transient overvoltage (VFTO) phenomenon is therefore increased.” At the same time, bus transfer performance has also been studied in depth, for all voltage levels, in order to be able to comply with IEC standard requirements (and even beyond, as some customers may demand). “To do so, we developed an innovative concept of mobile arcing contact, combining fast translation and rotating displacement.” This new solution, which is patented, has been tested and validated on a prototype 800 kV GIS rolled out for the production systems.

Disconnector section view

The kinematics of the equipment was also a topic of concern. A multi-domain simulation programme was used to model many possible kinematics combinations and to enhance connecting rods, crank handles and hydraulic drive to have minimum energy consumption for the required opening and closing speeds. “The kinematics of the circuit breaker is driven by a single hydraulic command, even in the case of a circuit breaker connected with pre-insertion resistor (PIR). The actuation system is installed at the bottom of the circuit breaker tank and moves two different shafts, one for the chambers and one for the PIR,” adds Garbi.

Fully IEC compliant, even for the most constraining performance

Particular efforts have been made to ensure that the 800 kV GIS meets foreseeable reliability requirements. It has been successfully subjected to all IEC-type tests: dielectric testing and temperature rise, bus charging current switching and bus transfer for the disconnector, making test for high speed earthing switch, terminal faults, short line faults and capacitive switching for the circuit breaker. The result of this complex development project, which required enhanced international collaborative R&D work in France, China, and India, is a cutting-edge 800 kV GIS that is super compact, highly reliable and easily maintainable. Manufacturing and after-sales service will mainly be ensured by the GIS manufacturing site in Chennai, India.

Nanodielectrics have shown immense potential for applications in high-voltage transmission systems. The NanocompEIM project explores ways to develop a set of materials design and process rules to achieve reliable production and process scaling in component manufacturing.

Nanodielectrics are expected to make a step change in future AC and DC power plants designs

Nanotechnologies focus on tailored structures from hundreds of nanometers down to a few nanometers in size. They are already known for their ability to produce materials with enhanced thermomechanical performance, such as improved strength and fatigue properties, resistance to corrosion, superhydrophobicity, and fire retardation. Other potential applications include improved conducting and insulating materials and coatings, as well as high performance dielectrics.
 
“To cope with the stresses in high-voltage transmission systems, there is a need to develop materials with controlled and balanced electrical properties, higher thermal conductivity, higher dielectric strength, and enhanced voltage endurance,” explains Fabrice Perrot, Technology Programmes Director at GE Vernova's Grid Solutions business in Stafford, UK. “If the balance of properties, performance and process requirements are achieved thanks to nanotechnologies, this may lead, for example, to HVDC insulation systems and equipment with reduced footprint, higher power densities, and greater multi-stress resilience with longer service lifetimes. All this will open the door to radically new designs.” 

Producing at nanoscale remains very complex

Despite the potential, producing structures and materials at nanoscale remains extremely complex. There are several challenges, not least of which is to develop new materials that significantly outperform the old ones at only a marginal increase in cost. “It is very difficult to incorporate nanostructures into an electrical polymer matrix reliably, consistently and economically with proven long-term stability,” notes Perrot. Nanocomposites lack process specifications, which integrate purity, quality, and reproducibility, and for now, it is only possible to produce them on a relatively small scale. “You can get small samples with differing, step-change improvements in properties, but it is not yet economically possible to produce them at large-enough scales for applications in HVAC or HVDC.”

The NanocompEIM project

To advance on that issue, Grid Solutions launched – with the help of the UK Technology Strategy Board, now Innovate UK – the NanocompEIM project, which aims to “both integrate and advance understanding and practical experience of the processing of nanocomposite electrical insulation materials in order to develop a set of materials design and process rules to achieve reliable production and process scaling in component manufacture”. Scalable processing methods have therefore been developed to produce components using materials with controlled dispersion and interfacial characteristics in order to achieve appropriate balanced property and performance enhancements. “Achieving this is of immense benefit to power equipment users, particularly in the context of integrating renewable power generation and the move to develop smarter, low-carbon networks,” adds Perrot. 

Material selection and process rules

The importance of being (well) dispersed

Nanodielectrics based on epoxy resin systems can be prepared by dispersing nano-sized inorganic fillers in the polymer matrix. A key feature of nanodielectrics is the large specific surface area of nanoscale fillers and the many properties and performance factors linked to interfacial effects. These include increased resistance to surface corona and partial discharge, enhanced dielectric strength and voltage endurance, and the potential mitigation of space charge formation. They also bring the potential to tailor other properties such as permittivity, conductivity, thermal conductivity, mechanical properties, and thermal stability.

On the left: SEM image of an alumina taken as received (x 1000 magnification); On the right: SEM image of the same alumina after ultrasonic mixing (x20,000 magnification)

Grid Solutions recognizes that there is a major need to master dispersion of nanoparticles if property enhancements are to be enhanced and then fully translated into advanced components and systems. “Another challenge is understanding several quantitative structure-property-process relationships for these materials and learning to controllably manipulate them to yield complex nanostructures,” says Perrot. Several methods of dispersion, both mechanical and chemical, have been trialled throughout this project, and using a novel, rapid mechanical-stirring method appears to be the most effective. But high dispersion alone is not sufficient to obtain enhancements in properties. A wide variety of materials containing various nanofiller types, loadings and surface treatments were also investigated and subjected to a range of measurements including thermal, electrical, mechanical, spectral and optical to check the dispersion of the materials. “It is very important to obtain a balanced outcome of properties as modification of composition to optimise one property might lead to a reduction in another important property.”

Electrical breakdown strength increased by more than 40%

Out of all the materials tested it was found that nanosilica treated with epoxide-functionalized agents gave the best performance of electrical properties with no significant decrease in thermal conductivity or mechanical properties. Up to 40% performance increase in electrical breakdown strength is obtained with 2% nanosilica compared to a commercial micro-composite. Also, samples containing boron nitride (BN) could be made with notably higher thermal conductivity without a significant drop in electrical breakdown strength, making BN a strong contender for use in electrical power applications. 

Examples of NanocompEIM demonstrators

In the NanocompEIM project, a number of options for deploying nanomaterials in future HVDC plants and key HVAC equipment have been identified.

Master batches in excess of 20 kg

To ensure that any processes used are scalable from the laboratory to potential future use in industry, the project has generated master batches of up to 20 kilograms in size, which were then mixed and formed into demonstrator medium-voltage components using traditional industrial casting processes. The thorough testing of these demonstrator components has now been completed successfully.

Open innovation with public funding leverage

In building the NanocompEIM project, Grid Solutions developed a vertically integrated “Open Innovation” partnership that combined technology providers, developers, integrators, a component supplier, an OEM (Grid Solutions) and the three UK transmission system operators (TSOs).

Phase I of the project integrated:

• Southampton and Warwick universities, with researchers at the cutting-edge in nanotechnology and nanodielectric materials research and characterisation;
• GnoSys Global Ltd, a nanotechnology-focused SME research organization with a proven international track record for developing processing and design rules for complex material combinations;
• Grid Solutions' Research & Technology Center in Stafford, with its component testing and composite materials process expertise and scaling capabilities together with our applications expertise;
• Mekufa UK Ltd, a composite component manufacturer/supplier;
• The three UK TSOs (National Grid, Scottish & Southern Energy, Scottish Power), a key partnership to include TSO needs and promote them in order to fast-track their use.

In Phase II, technology development will be transferred to Grid Solutions' Supergrid Institute in Villeurbanne (France), with the continued support of developers and TSO customers.

Phase I of the €1 million NanocompEIM project was 50% funded by the UK government’s Innovate UK Materials for Energy competition programme; 25% came from the OFGEM’s RIIO Network Innovation Allowance (NIA) funding mechanism for TSO-supported projects and additional UK government support for the two university partners. The plan is to achieve a similar level of gearing for the funding of Phases II and III for the ultimate deployment of high-voltage equipment containing nanodielectrics.