DEVELOPMENT OF AN ENVIROMENTAL FRIENDLY POWER SOURCE FOR SUBSTATION SERVICES FOR CREZ PROJECT IN TEXAS, USA

Presented by:

Nick S. Powers -ABB Global High Voltage Instrument Transformer Marketing Manager nicholas.s.powers@us.abb.com; +859-219-6060

Executive Summary In response to the clean and renewable energy movement in the USA in the last 10 years, the CREZ project (Competitive Renewable Energy Zone) was initiated in 2008 as a response of the PUC (Public Utilities Commission) in Texas. The project goals were to provide clean wind energy and to transmit this energy from remote wind farm locations to some of the most populated areas within the state of Texas. One aspect of the project was to minimize the impact on the environment and landscape of the state while providing 18.5 Mega Watts of clean energy. Several utilities within the state were granted defined subprojects for CREZ. An important question addressed was whether it was possible to install the desired infrastructure with minimal impact on the rural landscape. Would the project have an irreversible impact on lands and ecosystems? The real question was how to minimize this impact. This is why two important utilities with CREZ subprojects reached out to ABB Kuhlman - Arteche to develop a clean energy solution for some of the many CREZ substations requiring constantly available and reliable control power. The solution was feasible, but new technology had to be created. Since this was an innovative solution, a thorough study and engineering work was performed by a group of USA and Mexican engineers to understand the customer’s needs, and to develop a robust, reliable, clean solution for the challenge presented. Using the framework of existing product knowledge for station service voltage transformers, this challenge was accepted and the team developed a solution for the customers at a much higher voltage than had previously been achieved. The design and development consisted of 7 phases that included: understanding the needs, brainstorming and grounding of ideas for the new design, design of the product using tools such as FEA, and ABB Kuhlman’s innovative design for small high-voltage station service transformers, full documentation, prototype manufacturing, QA plan, modification process, manufacturing, testing and delivery of the final units to the customer. So far this solution is now in service with over 30 units delivered and installed. Over 900 miles of distribution lines were made unnecessary, and the usage of polluting technologies was reduced.

KEYWORDS

CREZ, Innovative Technologies, Station Service Voltage Transformer, SSVT, PVT Power Voltage Transformer

STATION SERVICE VOLTAGE TRANSFORMERS FOR THE CREZ PROJECT

INTRODUCTION TO CREZ PROJECT

The CREZ Project was founded in 2008 as a response to the 1975 legislation of the Public Utility Commission of Texas (PUC). [2] It was assigned 4.9 billion USD with 7 main projects, plus distribution utilities. The objective was to produce and transmit 18.5 MW of renewable energy power throughout the state of Texas. CREZ divided the project in five main zones (McCamey, Central, Central West, Panhandle A, Panhandle B), each of them with specific needs and companies attacking the project. [3] The objective of the CREZ project is to produce and transmit renewable, clean wind energy from some of the most remote places in Texas to the most populated areas, displacing the traditional energy sources which generate pollution and carbon emissions. Another aspect of the project was meeting the long term needs of energy transmission in the state, building lines that would fulfill those needs and provide the infrastructure for future state development.[4]

Image 1

Image 1 illustrates the map location of the CREZ project. A total of over 180 projects in 70 transmission lines and about 3600 miles have to be developed in order for the CREZ project to be completed. All this has both an economic and environmental impact on each zone and even the whole state. Due to the size of the project, a thorough study of the best environmental and economical routes for the transmission lines was assigned by ERCOT (Electric Reliability Council of Texas) and completed by ABB in December 2010. [2] The objective was to identify the size, type, and locations for the equipment needed to control, condition and route the power through the added CREZ transmission projects to the electric grid. Even with the studies, the

routes of the lines were only approximate, since the actual routes may not follow a straight line and may vary from +10% to +50% more than the estimated route [2]. The total cost was estimated by a standard per mile rate, and even though it has high economical costs, the higher impact might be ecological. At present, an estimated total of 6.9 Billion USD is

expected for the completion of the project. .Table1[2] and Image 2[2] show the overall costs of

sub-projects within the CREZ project.

Table 1

Image 2

THE NEED

One of the important directives of the CREZ project was to provide clean energy with the least impact on the environment. Since the CREZ project is distributed within the whole state of Texas, wind farms, and associated distribution and transmission lines are invading pristine

lands having a direct impact on the natural ecosystems and landscape. Therefore all this has to be considered for the overall completion of the project. [3] The remote locations of wind farms in the large state of TX, plus wind generated electricity not being constant, are in conflict with the substation requirements for full energy backup at all times. Non-constant generation means that redundancy in the low voltage energy system is critical to keep the substation systems working. This means that the needed distribution lines have to be installed to keep the system and the grid working. These redundancies are expensive, especially when the required distribution lines come from distant locations. These investments could be about 2% to 3% of the overall project; an important figure when that amount is in the hundreds of millions of dollars. That is why two of the utilities with CREZ subprojects approached ABB to find a feasible solution to transform power from 362kV to 120/240VAC, in an reliable way. Both needed a better solution to the energy supply for their substations. The objective was to reduce costs and impact on the construction of the projects. About 150 million USD was estimated for distribution line costs alone, plus the ecological costs of the lines needed for the project. In the next section is the compilation of a variety of solutions that can be provided for such projects. ABB-Kuhlman/Arteche already had a similar solution to these needs called the SSVT. The Station Service Voltage Transformer is a reliable single unit solution that provides reliable power from high voltage (up to 230 kV at that time) from the transmission line, to any required low voltage. This solution integrated inside the substation gives the utility the full control of the energy supply in a limited space and directly from the transmission grid. This reduces the overall distribution line miles needed to provide energy and backup to the substations. For the selected CREZ projects, about 30 million USD were saved in distribution lines.

THE POSSIBLE SOLUTIONS…

The options for the problem stated are varied and they have different implications and costs.

Even though some may have less expensive first cost numbers, they have higher impact on the environment and have high on-going operation and maintenance costs. SSVT’s are a preferred alternative to the usual power solutions for substation control power needs, over the various means employed for this function as each option has important elements to consider. The options are:

Redundant Grid Distribution Network. It means bringing distribution lines to the substation. This entails both investment and maintenance on every distribution line, and in some cases two distribution lines per substation A downside of the solution is the dependency on other substations, reliability of the distribution lines, etc. [5]

Diesel Generator. This solution can have an immediate effect with a medium cost and limited space inside the substation. It also gives the utility full control of the generation and costs. Nevertheless the operation and maintenance costs are higher than other solutions, along with concern for lower reliability and availability, and the higher environmental and carbon emission. The amount of fuel in stock is limited, which limits the hours it can run unattended. Also this solution goes against the green core message of the CREZ project.

Using the power transformer tertiary to supply energy. Considering that the power transformer is the most expensive part of the substation, using the tertiary may not be the best solution given that any misconnection or overload on the tertiary can reduce the remaining life of the substation transformer. This important concern is that the take-off of the tertiary winding increases the potential that the main power transformer could be subject to a through fault, with high costs of repair. Also loading

on a tertiary limits the capability of the tertiary to support power quality by reducing higher level harmonics. Besides these factors, bringing out the tertiary on a large power transformer has greater costs. In switching stations such as many of those installed for the CREZ project, power transformers are not available.

Medium circuit within the substation. Where the substation has a power transformer with medium voltage output, a relatively low cost distribution transformer can be used to supply 120/240VAC for substation control power. One disadvantage is that if the power transformer is de-energized for servicing, the control power source is lost. This option is only available in substations having HV to MV step-down transformers, and for CREZ this was not an option.

Traditional power transformer dedicated to the application. In this application, a dedicated single or three phase power transformer can be assigned the task to supply the needed control power. But due to the large format of this design, the transformer is generally greatly oversized for the power needs, and valuable energy is wasted to support the high losses within the unit. The cost of this solution is generally prohibitive.

Other companies’ solutions or traditional voltage transformers. Other manufacturers can provide some stand-alone solutions derived from potential transformer sized packages, but without proper designs to insure voltage regulation under substantial station load, or insufficient kVA power levels to power the application, and they have had little success in completing similar projects.

The SSVT gives the best option to provide efficient, low loss, clean energy directly from the transmission line without increasing the overall cost (2% of the project) while making control power available at any time without significant added space, cost or infrastructure. In Table 2 below, the costs of traditional distribution lines on two of the selected projects and the costs of the SSVT projects can be compared. [2] It is evident that the cost of the SSVT solution is less than 0.5% of the overall cost.

Company Total Project Cost Estimate[2] Miles[2] Line cost[10]

SSVT Solution Project Cost

% Line Cost

% SSVT Project Cost

% Overall Saving

Lonestar $ 1,533,951,548.00 643 $ 18,614,850.00 $ 2,264,400.00 1.21% 0.15% 1.04%

ETT $ 768,900,000.00 331 $ 9,582,450.00 $ 1,300,120.00 1.25% 0.17% 1.08%

Table 2

NEEDED SOMETHING THAT DOES NOT YET EXIST ….

Two electrical manufacturers, ABB Kuhlman and Arteche, came together to combine our technical resources so that a higher voltage station service product could be developed to meet the CREZ need for reliable control power. Kuhlman and Arteche have enjoyed a 15 year working relationship, bringing many products to the North American market, and have the most experience in the industry in the design and manufacture of station service voltage transformers. This relationship has continued even after the acquisition of Kuhlman Electric by ABB in 2008. At our two companies, it is our core mission to provide the best fit solution to our customers at a value price. Both teams set about researching the best way to develop the new 362kV station service device. The engineering teams worked side-by-side using each of our specific strengths to come up with the most reliable, cost effective solution. Our customer needed a single unit that could provide a minimum of 100kVA at 120/240VAC from the 362 kV lines, was rugged enough to withstand common carrier freight transport to site, withstand the most corrosive environments with special coatings, required high creepage insulators, and built-in reliability from an experienced supplier.

The real challenge was being able to deliver this solution in a 362 kV, 1300kV BIL insulation level in record time. Competitive suppliers were not able to deliver it properly the first time, and presented lower power levels with a low first pass test yield. ABB-Kuhlman and Arteche` created a specialized design and development team comprising engineers and applications experts from both companies. In Table 3 the technical characteristics of a standard unit and the new design are presented. As shown, the voltage levels and special characteristics vary the standard design in critical aspects. Nevertheless these slight changes triggered innovative deeper changes. The real complication was to fully develop the unit. From the internal windings, to the shipping method everything was redesigned. The new SSVT was more rugged, leaner, and with an optimal design. Done right the first time!

THE FIRST PASS

The first draft of the design for the project was thought out in September 2010. Through 6 months of study, the unit was conceived and the R & D Departments gathered the required information to start a formal project. From the very beginning, every aspect of the design was carefully calculated to involve and consider several aspects:

Customer needs

Quality assurance

Failure detection

Cost reduction

Efficiency and manufacturing time

Actual resources and needed investment

Environmental impact

A whole quality assurance plan and chart was designed in order to review every aspect of the design and concept of the project. This was documented according to ISO recommended standard procedures. The project completion and prototype generation included the following phases:

Phase 1: Project Requirements (Gathering and reviewing customer needs)

Phase 2: Idealization of the project (Brainstorming and grounding of ideas)

Phase 3: Design of the product and manufacturing processes.

Phase 4: Manufacturing and testing of the prototype

Phase 5: Final Design, Manufacturing processes and QA Plan.

Phase 6: Manufacturing and delivery of units

Phase 7: Project closure.

Technical Specification Standard Unit New Design

Operating Temp. - 40 deg C + 40 deg C - 40 deg C + 40 deg C

Rated Voltage Level 230 kV 345 kV

Impulse withstand voltage 1.2 / 50 us 900 kV 1300 kV

One minute low frecuency withstand voltage on

Primary Winding (1 minute dry) 395 kV 575 kV

Primary Windings (10 sec wet) - 575 kV

Seconary Windings 3 kV 3 kV

Frecuency 60 Hz 60 Hz

Standards IEEE C57.13-2008 IEEE C57.13-2008

Ratio 1104x552:1 (138,000:125/250 kV)

1660 x 830:1 (199,200:120/240 V)

Outputs 4 LV Bushings 4 LV Bushings

1st Secondary (x1-x2-x3-x4) 125 / 250 VAC - 100 kVA for LV power needs

120 / 240 VAC - 100 kVA and 167 kVA LV power

Rated Voltage Factor - MCOV = 1.1 Cont MMOV = 1.15 fo 60 sec

Rated Thermal power (with 55 deg. C rise) 100 kVA 100 kVA

Maximum System Voltage 245 kV 380 kV

Insulator ANSI 70 Gray ANSI 70 Gray

Primary Terminals

H1 Terminal NEMA 4 Hole NEMA 4 Hole

Secondary Terminals

Power terminals Four NEMA 4 Hole Spades Four NEMA 4 Hole Spades

Ground Connection NEMA 2 Hole Pad NEMA 2 Hole Pad

Oil Type Nynas LEO II oil Nynas LEO II oil

Creepage Distance 268.7" (6825 mm) 391.9" (9955 mm) Min

Strike Distance 75.79" (1925 mm) 98.8" (2510 mm) Min

Special Needs NA

High creepage required 390" Stainless steel or Galvanized steel tank, cover and dome

Table 3

During the first 4 phases the team determined which important changes and considerations had to be met to design the new unit. Also, they adhered to the strictest standards to achieve a robust design, seeking at all times to comply with the following standards:

IEEE C57.12.00-2010: Standard General Requirements for Liquid – Immersed Distribution , Power and Regulating Transformers [5]

IEEE C57.12.90-2010: Standard test code for Liquid – Immersed Distribution , Power and Regulating Transformers [11]

ANSI C57.13 2008: IEEE Standard Requirements for Instrument Transformers [6] After the first brainstorming and analysis of the needs, the highlights of the design challenges for the units appeared as follow:

Avoid Critical Stress Zones (needed security margins over 25%): o Bushing shields, o Tank cover, o Oil chamber between bushing and tank, o Coil shields, o Primary terminal.

Design of a new insulation method for coil and bushings to improve usage of kV / mm. This was performed per Kulkarni’s innovative isolation method for power transformers.[7][1]

Coil design constraints for an optimized usage of space, copper and optimization of cooling.

Achieving Specific Thermal Power at 65°C rise (100 kVA and 167 kVA)

Polymer insulator usage for extra creep distance and durability in handling.

Redesign of the manufacturing process to improve: o Winding o Assembly o Drying o Oil filling o Soaking

Redesign shipping method for an over-height transformer Considering all of these, ABB Kuhlman – Arteche, together with Weidman and a recognized university in Mexico, plus specialized engineers, performed FEA analysis of the design, evaluating the critical stress zones. That helped to corroborate the optimal design of the insulation system before construction, installation and operation. (Images 3 and 5) FEA is the preferred method for analyzing complex geometries with known stress values especially in 3 dimensions were the calculations become complex and the analysis can highlight important details that might not be observed in a 2D analysis. (Image 4) [8] [9]

On the FEA analysis the objective was to represent the worst condition to analyze the behavior of the transformer’s insulation system under unusual stress. Taking advantage of the symmetry of the unit, the 3D model over the FEA was divided in fourths to have an optimization of the computer resources. [9] That was performed without implying any loss of information or precision over it. This allowed obtaining a higher detail level, and a better mesh. The complete analysis consisted of over 1.6 million nodes over the space. [8] In some cases special considerations for electric distances in construction and for design had to be modified after the conclusions of the analysis. Even several parts of the first hand design had to be eliminated or modified to comply with the needs. Some of the elements that changed after the FEA included the shields, the distance of the springs, some dielectric materials and even the position of some fasteners. [8] [9]

Image 5

Image 3

Image 4

Source

The unit had to be designed for horizontal shipment to be able to transport along the Mexican and American roads. This might at first appear minor, but due to the important mechanical stress on the core/coil frame, a special method had to be developed and the tank reinforced to withstand the transition from the vertical to the horizontal position, and then back into the vertical position on site. Lastly, the crate was designed to be stong enough for a 1000 mile trip. Images 6 and 7 show the unit being prepared for placement into the horizontal position for crating.

THE FINAL DESIGN…

After all the previous investigations, the necessary documentation to build the transformer was finished. These included drawings, material specifications, production technical notes, and personnel training course. The prototype was built on time to perform the type tests needed per standard. On table 4 all the tests performed are listed, all with satisfactory outcome on the first try.

Test Test Value Result Routine Type

Full Load Losses 760 W OK YES NO

No Load Losses 717 W OK YES NO

Impedance (%Z) 6.35% OK YES NO

Excitation Current - OK YES NO

Partial Discharges - OK YES NO

High Voltage Applied 19 kV OK YES NO

Low Voltage Applied 2.5 kV OK YES NO

Induced 575 kV OK YES NO

Temperature rise 65 °C OK NO YES

Short Circuit

OK NO YES

Basic Impulse Level 1300 kV OK NO YES

RIV

OK NO YES

Capacitance 541 pF OK YES NO

Disipation Factor < 0.35% OK YES NO

Table 4

After prototype testing, the engineers made final preparations for the product to be delivered to the customer. Over the final stages of the project the team concluded the final drawings and the full production tests run. On Image 7, the final approval drawing for the utilities that prefered our solution over the other control power options. [11]

Image 3

The most important part for the project success was the dedicated people participating in it. Images 8 and 9 show just some of the engineering and work teams participating on the project with one of the SSVT-1300 units completely tested and ready to be crated and shipped. So far, over 25 units have been succesfully delivered to customers.

WE HAVE IT, WOULD IT WORK?

Installation has been accomplished on the 25 units delivered to various sites in Texas. Many have also been energized for some time without problems and all are functioning as designed. It is estimated that the utilities have saved over 30 million USD and over 900 miles of distribution lines. Image 10 shows two of the units at one of the CREZ substations. The units have almost 1 year in service without any operational problems.

Image 8

Image 9

Image 10

Conclusions and Relevant Implications Should clean energy solutions be only interested in the source and emissions of generation? What can happen if federal lands are used for energy generation without thinking about the impact to the environment? How does the construction of passive elements like power lines affect the environment? These questions are both ethical and practical. No energy project can claim to be pollution free, green or clean, if it does not answer these questions and measure the impact of the overall system. It is important to consider carbon emissions to the atmosphere as well as the impact on the existing ecosystems. ABB-Kuhlman and Arteche` believe we have helped with this goal by bringing SSVTs to the market through 362kV. Responsible companies will search for innovative solutions to these challenges, and with an effective prepared team, cost effective solutions will be made available. The SSVT-1300 was the answer ABB Kuhlman - Arteche gave to the CREZ project. Investment of many working hours and many engineering hours went into creating the most efficient solution required by an industry seeking to provide clean power. This investment was worth the effort in providing a lean, robust, lower loss design that from the beginning proved to be a fully functional, built by capable companies. This demonstrates that a new product can be produced, and done right the first time, by thoroughly running many studies and cross studies before the first screw is tightened. A complete quality assurance plan, and the complete documentation and training were also critical to achieving and sustaining the goal of reliable supply of this product. The 25 units on the project will supply control power for reliable low voltage power for CREZ substations without the distribution lines or diesel generators. Yes, redundancy will be needed, but in those remote places were constructing a new distribution line means passing over farmlands or pristine lands, or were making a long distribution line is just too expensive and unreliable, the SSVT offers a solution. Satisfaction comes from knowing that for the units delivered and in operation, none have had a problem. By working closely with our customers, ABB Kuhlman and Arteche provides the reliability and the power they need without a deep environmental impact.

References [1] Transformer Engineering, Design and Practice. Kulkarni S.V, Khaparde S.A., Marcel

Deeker Inc.

[2] CREZ Progress Report No. 10 (January 2013 Update)

[3] CREZ Progress Report No. 1 (October 2010)

[4] CREZ Progress Report No. 3 (April 2011Update)

[5] IEEE C57.13 – 1993, “IEEE Standard Requirements for Instrument Transformers”.

[6] IEEE C57.12.00 “IEEE Standard General Requirements for Liquid Immersed

Distribution, Power, and Regulating Transformers”.

[7] On Electric Stresses at Wedge-shaped Oil Gaps in Power Transformers with Application

to Surface Discharge and Breakdown, Ding H. Z., Wang Z. D., Jarman P. 2008 IEEE.

[8] 345 kV Bushing Analysis by Weidmann. Proj Num. 423985.

[9] Tridimensional Electrostatic Simulation of a 345 kV Voltage Transformer. Espino

Cortez, Fermín; Gomez Zamorano, Pablo. Instituto Politécnico Nacional.

[10] Estimates of 29.5 k USD per mile.

[11] IEEE C57.12.90 “IEEE Standard General Requirements for Liquid Immersed

Distribution, Power, and Regulating Transformers”.