The project experience listed here was obtained during Reigh A. Walling’s 31 year career at GE Energy Consulting, from which Mr. Walling retired in November, 2012. In each of these projects, Mr. Walling was either the project leader or a primary technical contributor. Client names are not provided here out of respect for the former employer’s client relationships. For specific projects, client references can be provided on request.
The project experience has been in a wide range of areas. For the convenience of the reader, this listing of project experience has been organized into the following subject areas:
- Large-Scale Renewables Integration
- Renewable Generation Plant Design and Interconnection
- AC Transmission
- HVDC Transmission
- Root-Cause Analysis
- Geomagnetic Disturbance Impacts on Power Systems
- Advanced Distribution Planning
- Grid Modernization
- Distribution Equipment and Operating Practices
- Distributed Generation and Distributed Renewables
- Advanced Research and Development
Analysis of Wind Generation Impact on Ancillary Services Requirements
A large ISO was planning major transmission additions to support large increases in wind penetration into their synchronously-isolated system. One of their major concerns was the impact of the large wind additions to the ancillary services needs of their system. Mr. Walling directed a very large and intense study of the requirements for increased operating reserves, including frequency regulation, spinning, and non-spinning reserves. Specific focus was given to the meteorological causes for large-scale wind ramping events, characterizing these ram events, and dealing with the potential for ramps in the operation of the system. Protocols for determining the amount of ancillary services were reviewed, and modifications to these protocols were recommended to support the greater variability and uncertainty introduced by the wind generation.
Assessment of Wind and Solar Penetration in a Semi-Isolated Region
A utility with relatively transmission ties to neighboring utilities has large wind and solar generation developments that plan to connect to its system in the near future. Due to the small size of this semi-isolated utility, flexibility of the thermal generation fleet to balance the variability and unpredictability of the wind and solar production is a major issue. The study includes significant focus on sub-hourly modeling of system operations.
Non-Synchronous Generation Technical Interconnection Requirements
A large ISO wished to develop standard technical interconnection requirements for transmission-connected non-synchronous generation resources, including wind and large-scale solar. Working with the counsel for the ISO, a comprehensive set of technical performance requirements were drafted, covering disturbance ride-through, reactive power support, voltage regulation, frequency response, and curtailment.
Wind Plant Grounding Transformer Specification Studies
Mr. Walling directed performance of grounding transformer specification studies for a number of wind plants. These studies used detailed models of the wind turbines implemented in the Electromagnetic Transients Program (EMTP).
Renewable Plant Transformer Rating Optimization
Using known application parameters such as the hourly wind speeds and ambient temperatures, the transformer thermal modeling principles described in IEEE C57.91 were applied to optimize the rating of transformers for specific wind plant applications. Because of the negative correlation between high wind (and thus high loading) and high ambient temperature, the study determined that a transformer kVA rating significantly less than the rated kW output of a wind turbine could be successfully and economically applied as a unit wind turbine step-up transformer.
Wind Plant Loss Evaluation Analysis Tool
A highly detailed economic analysis tool was developed which allowed the life-cycle cost impact of transformer load and n0-load losses to be evaluated on an equal basis with purchase price. This tool was a major factor leading several major wind plant developers to specify high-efficiency transformers for their plant designs.
Underground Transmission Technical Feasibility
Major 345 kV transmission expansion was needed to reinforce the power infrastructure of a portion of a utility’s system which has limited generation resources. In this particular state, a requirement existed at that time to install all transmission underground, unless technically infeasible. A massive transient simulation study was performed to assess the technical feasibility of using underground cables for all of this transmission expansion. Low-order resonances were found to result from the large amount of cable in a relatively weak portion of the system, with the potential for faults and other disturbances to cause serious temporary overvoltages. As a result of this study, only portions of this system were constructed with underground cable, and the remainder was overhead construction.
FACTS Device Specifications
Developed functional performance-based specifications for FACTS devices to mitigate voltage stability issues in a highly-stressed semi-isolated power system. These specifications allowed vendors to compete with different FACTS solutions (e.g. SVC or STATCOM) to meet the utility’s needs. Consulting support was provided to the utility during the bid evaluation stage, and review of vendor designs and design reports during the post-award implementation phases of these projects. This work culminated in the installation of three FACTS devices in the utility’s system, in two separate phases.
Large-Scale Transmission Shunt Capacitor Deployment
A utility planned to deploy a large number of shunt capacitor banks to their transmission system, as a replacement of the reactive power support previously provided by must-run generating units that were to be retired. Mr. Walling directed a large transients analysis study to evaluate the impacts caused by switching these new capacitors, with a particular emphasis on identifying any voltage magnification phenomena.
330 MW VSC-HVDC Interconnection
Drafted the performance specifications, reviewed designs and design studies, and monitored commissioning of a 330 MW voltage-source converter HVDC interconnection.
660 MW LCC-HVDC Interconnection
Drafted the performance specifications, reviewed designs and design studies, and monitored commissioning of a 660 MW line-commutated converter (conventional or “classic”) HVDC system.
Review of Proposed Multi-Terminal HVDC Network as an Alternative to Underground AC Transmission
A utility client was under legal and political pressure to construct several hundred circuit-miles of EHV ac transmission underground, but technical infeasibility of the ac option had been determined. A vendor of HVDC systems offered that a multi-terminal HVDC network would be a feasible alternative. The proposed HVDC network alternative was critically evaluated in terms of performance and economics, on behalf of the client.
Remote Industrial Loads
A utility is planning to serve large industrial loads which are to be constructed in a remote area with little present power transmission infrastructure. At the request of this client, Mr. Walling provided a report assessing the functional practicality of HVDC transmission as a means to serve this remote area.
Mr. Walling co-authored chapters of EPRI’s High Voltage Direct Current Handbook. These chapters covered “Converter Operations and Calculations”, and “AC Overvoltage and Temporary Distortion”.
Core-Saturation Instability Resolution
An international utility determined that an undersea HVDC link was particularly prone to the “core saturation instability” phenomenon during pre-construction dynamic studies. Mr. Walling was a key technical contributor on a team that developed an analytical understanding of this complex phenomenon, using sophisticated state-space analysis tools, and proposed a system re-design solution that avoided this instability.
HVDC Dynamic Performance Studies
As the director of GE’s HVDC real-time simulation facility, Mr. Walling directed the dynamic performance studies of several HVDC projects, investigating transient behavior and complex system interactions.
HVDC Line Dedicated Metallic Return Insulation Requirements Study
A multi-terminal HVDC system was planned to have a long dedicated metallic return circuit located on the line structure. Faults of this DMR, that occur at the same time as HVDC pole faults, are difficult to clear and negate the benefits provided by the DMR. A study led by Mr. Walling investigated the potential for DMR faults resulting from electromagnetic coupling to transients resulting from pole faults, as well as lightning events capable of simultaneously faulting a pole and the DMR. DMR insulation requirements were identified by this study which minimize the probability of the simultaneous pole and DMR fault situation.
Asymmetric Voltage Instability
A large utility had repeated incidents of voltage collapse on one phase of a distribution system, with the voltages rising above nominal on the other phases. The involved distribution systems were served by primary substation transformers with relatively high impedance, and neutral reactors at the substation provided an X0/X1 ratio at the limits of an effectively-grounded system. Mr. Walling developed dynamic simulation software capable of phase-by-phase representation. Using this tool, it was revealed that single-phase motor loads, interacting with the unique characteristics of these distribution systems, resulted in an asymmetric voltage phenomenon. Modifications to system design and operations were recommended to minimize risk of future recurrence of this instability.
An industrialized Latin American country suffered a near-total blackout of their national power grid. Mr. Walling and a colleague were retained by the utility to investigate the cause. The blackout was determined to be due to interaction of a series-compensated transmission lines with current transformers, leading to a protection misoperation severing the country’s transmission grid.
Industrial Rectifier Transformer Failures
Investigated the cause of repetitive power transformer failures in a 300 kA (load current) industrial rectifier system serving an electrochemical process. The root cause was determined to be control system issues causing uneven winding current distribution in the parallel secondary windings of the transformers. Replacement of an inexpensive control component, as recommended by Mr. Walling, eliminated further failures.
Phase-Angle Regulator Tap Changer Failures
A phase angle regulator on a major transmission link between operating systems experienced recurring failures of the tap changer. Detailed analysis and transient simulation identified the root cause and a modification of the design, recommended by the study, eliminated further failures.
Substation Autotransformer Failures
The causes for failure of two critical autotransformers, in the same substation within a few weeks of each other, were investigated at the request of the utility. From oscillographic fault data, the cause of the failures were identified.
Industrial Rectifier Harmonic Instability
During certain operating conditions, an industrial rectifier serving an electrochemical process would go out of control and simultaneously inject large amounts of even-order harmonics into the power system. The cause was identified to be a complex core saturation instability, where the rectifier interacted simultaneously with an even-order impedance resonance in the power system and the saturation characteristics of the rectifier transformer. A modification of the rectifier’s power factor compensation banks was recommended, and this resolved the issue.
Geomagnetic Disturbance Impacts on Power Systems
Indirect GIC Measurement
Measuring GIC normally requires specialized sensing equipment because ordinary current transformers are incapable of registering the very low frequency currents composing GIC. The client wished to monitor GIC levels in a critical transformer indirectly, by use of the second-harmonic component of differential current. Mr. Walling created magnetic models of the transformers and developed the calibration relationships between this differential current component and the amount of GIC in the transformer.
GIC Flow Analysis
Analysis of GIC flow patterns, and the resulting saturation of system transformers, was performed by the New York power transmission system. With the support of a geophysical subcontractor, the complex deep-earth geologies of the Northeast were modeled and finite element electromagnetic analysis was used to define earth electric field gradients throughout the system. These gradients were applied to a power system model to analyze the resulting complex GIC flow patterns.
GMD Vulnerability of an HVDC System
The vulnerability of an existing multi-terminal HVDC system to the effects of geomagnetic disturbances was assessed at the request of a system owner. The assessment included impacts on harmonic filters, transformers, and the potential for control issues.
Neutral Blocking Device Development
Developed a robust and self-protected design for a series capacitor neutral blocking device intended to block dc and quasi-dc earth currents from flowing through transformer neutrals. This device used metal-oxide varistors to limit voltages across the capacitor. However, protective bypassing of the device was not needed for ordinary faults.
Advanced Distribution Planning
Distributed Resources Study
The client wished to explore the potential for use of distributed resources (DR) as a planning option to serve distribution load. Technical requirements for DR to provide capacity were quantified, and extensive economic analysis was performed to indicate the niches where DR could be considered as a viable alternative to conventional means of supporting utility load.
Third Generation Urban Distribution Design
The client serves a large and extremely dense urban area. The present secondary network topology, by which the client serves most of its customers, has very high reliability but also high costs. Although the networks are highly reliable, the infrequent outages affect many customers. The client commissioned this study to conceptualize new distribution topologies and technologies that can provide similar levels of reliability at less cost and with less potential for newsworthy outage events.
Conservation Voltage Reduction Evaluation
A study of the effectiveness of conservation voltage reduction (CVR) in reducing peak demand and energy usage was performed for a multi-utility distribution research consortium. Tradeoffs between investment in the feeder infrastructure, such as added capacitor banks and voltage regulators, and the energy reduction obtained were quantified.
Volt-VAR Control Algorithm
An optimization algorithm for controlling substation transformer on-load tapchangers, series regulators was developed.
Distribution Equipment and Operating Practices
Inter-Circuit Fault Mitigation
A utility had recurring instances where transmission circuits and underbuilt distribution circuits would become faulted together, exposing distribution equipment and customers to very high voltage levels. This issue was investigated and a solution based on sacrificial metal-oxide arresters on the distribution circuits was developed.
Ferroresonant Overvoltages Related to Low-Loss Distribution Transformers
On behalf of a utility research consortium, Mr. Walling directed an extensive research and testing project to understand the relationships between ferroresonant overvoltages, in distribution systems with low-loss transformers, and system parameters. The findings of this research dramatically changed the industry’s understanding of this complex phenomenon and how it relates to the system characteristics, disproving much of the previous “conventional wisdom”. Detailed guidelines for operating practices that avoid these overvoltages were prepared in this project.
Distribution Surge Arrester Withstand of Ferroresonant Overvoltages
The ability of metal-oxide distribution surge arresters to withstand ferroresonant overvoltages was researched on behalf of a multi-utility distribution research consortium. The research was based on an extensive full-scale testing program, and this work showed that ferroresonant overvoltages are a current-limited source and often distribution arresters can withstand this duty for significant periods of time. The results of this research were the subject of a paper which was awarded the 1995 IEEE PES Prize Paper Award.
Padmounted Distribution Transformer Fault Withstand
An extensive laboratory testing program was performed, under the sponsorship of a utility research consortium, to quantify the fault energy withstand capabilities of padmounted distribution transformers. Mr. Walling led the analysis of the results of this testing project, which resulted in new guidelines regarding protection requirements for this common distribution transformer type.
Floating Wye-Delta Distribution Bank Overvoltages
On behalf of a multi-utility distribution research consortium, the occurrence of severe overvoltages during the switching of floating-wye delta distribution transformer banks was researched. Testing during this project discovered a previously undocumented phenomena producing extreme temporary overvoltages (approaching nine p.u., and lasting for seconds). Guidelines developed in this project allowed the client utilities to avoid similar overvoltage problems in the field.
Unbalanced Secondary Analysis Software
Mr. Walling developed software for a utility consortium that allowed the convenient analysis of unbalanced transformer banks, and unbalanced loads on either balanced or unbalanced distribution transformer banks.
Underground Distribution Switching Transients
The utility members of a distribution research consortium expressed concern that routine switching events in underground distribution systems could cause voltage transients damaging to equipment and cables. An extensive field measurement project was undertaken, using sophisticated instruments and measurement techniques to record the very fast voltage risetimes caused by switching. An assessment was provided of the transient stresses introduced by switching.
Distributed Generation and Distributed Renewables
Large PV Facility Interconnection Studies
Studies were performed for several utilities confronted with applications to interconnect large multi-MW PV generation facilities with distribution feeders. These studies examined the impacts of these facilities on steady-state feeder voltage profiles, and short-term voltage variations and the resulting excess duty on feeder voltage regulators. Mitigative measures were investigated, including various schemes involving voltage regulation provided by the PV facilities.
Distributed Generation Reference Report
A comprehensive reference report on distributed generation, covering the types and technologies of DG, system impacts, economic and commercial issues was developed for a utility research consortium.
PV Impact on Distribution Systems
At the request of a utility distribution research consortium, a reference report on the impacts of photovoltaic generation on distribution systems was prepared. This report included extensive cloud shadowing modeling analysis to assess the role of geographic diversity in mitigating the variability impacts of PV.
Dynamic Impacts of Non-Ride-Through of DG
A utility has a large amount of IEEE-1547 compliant distributed generation (DG) facilities concentrated into an area where the transmission interconnections are weak and the voltage stability of the area approaches a marginal state. The utility had concern that simultaneous loss of many of the DG, due to the voltage dip caused by a transmission fault, could threaten the stability of the area. A dynamic study, including modeling of the DG tripping behavior, was performed to assess this increased vulnerability.
Advanced Research and Development
Fault Current Limitation Technology
A novel approach to fault current limitation, using purely passive components, was researched in detail on behalf of a large international utility client.
Transmission Line Magnetic Field Limitation
A novel scheme was developed for substantially mitigating transmission line electromagnetic fields. At the time, there was considerable health concern raised about transmission line EMF. The scheme developed in this project used a series capacitor compensated passive shield along the transmission line. Extensive studies of fault performance and self-protection of the series capacitor device were essential parts of this research carried out for a domestic utility. A US patent was awarded for this invention.