Transmission line design project proposal

Upgrading the 69 kV transmission line between Demerara and Berbice

A Proposal Submitted by Selwin Collier

Electrical Engineering Faculty of Technology University Of Guyana January 30th, 2015

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Summary/Abstract

This proposal is merely based on the upgrading of the 69kV transmission line between Demerara and Berbice. The design and construction of the previous transmission line between Demerara and Berbice has experienced an appreciable increase of loads in Berbice resulting in inconsistencies in transferred power. These inconsistencies are causes for concern since there are plans to incorporate the future Amaila falls project on this very network for the transfer of power to Berbice. Through the use of calculations, modeling and operational data, identifying the transfer capability of the present 69 kV line between Demerara and Berbice would be objectified. The present and future Berbice loads would be accessed or developed and the possibility of a new transmission line would be designed with specific voltage and current carrying capacity to meet the requirements of the system over the next 20 years. Further analysis also would include possible route for this new transmission line where all designs would be modeled to demonstrate their operational capability.

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Table of Contents Summary/Abstract ........................................................................................................................ 2 List of Figures ................................................................................................................................ 4 Background ............................................................................................................................... 5 Statement of Problem ............................................................................................................... 6 Scope of Work ............................................................................................................................... 7 Overview .................................................................................................................................... 7 Literature Review ..................................................................................................................... 8 Transmission Constraints .................................................................................................... 9 Thermal Constraints ........................................................................................................... 10 Voltage Constraints ............................................................................................................ 10 System Operated Constraints ............................................................................................ 11 Alternative Solutions .............................................................................................................. 13 Evaluation ................................................................................................................................ 15 Decision .................................................................................................................................... 16 Implementation of Work ............................................................................................................ 17 Facility .......................................................................................................................................... 18 Schedule ....................................................................................................................................... 19 Budget .......................................................................................................................................... 20 Bibliography ................................................................................................................................ 21

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List of Figures Figure 1 Short Line Transmission................................................................................................... 8 Figure 2 HVDC and HVAC Transmission systems cost ................................................................ 9 Figure 3 Transmission-line loadability curve for 60-Hz overhead lines - no series or shunt compensation ................................................................................................................................ 13

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Introduction There has been an increased percentage of load in the Berbice area resulting in a percentage voltage drop along the Demerara – Berbice transmission link. Other contributions to voltage drops arrived from mechanical and electrical factors. With the advent of the hydropower project scheduled to come online in the near future, expectations are that this same transmission link would be used to continue distributing electrical power to Berbice. Coupled with the existing voltage drop on the current transmission system and the expected increase in load demand, expectations are that further voltage drops will occur requiring an improved design as well as a proposed new transmission link.

Background

The first form of transmission link was in 1886 in Great Barrington, Massachusetts where a 1 kV alternating current (AC) allocation system was established. AC power at 2 kV, transmitted 30 km, was also installed at Cerchi, Italy, the same year. Nikola Tesla, a mechanical engineer, on May 16, 1888, conveyed a lecture on the topic “A New System of Alternating Current Motors and Transformers”, explaining the equipment which let resourceful generation and use of poly-phase (a means of distributing alternating current electrical power) alternating currents. The initial transmission of three-phase alternating current using high voltage happened in 1891 at the time of the international electricity exhibition in Frankfurt. The quick industrialization in the 20th century made electrical transmission lines and grids a significant part of the infrastructure in many countries [1]. Guyana took a while but in the late 1980s they had an installed electricity-generating capacity of about 168,000 kilowatts, and annual production was some 385 million kilowatt-hours, nearly all generated in thermal facilities [2]. The mining areas of Linden and Everton (Upper Berbice) received power from Alcan and Reynolds, both expatriate companies that respectively owned the Mackenzie (Linden) and Berbice-based bauxite operations [3] hence establishing the first transmission link to Berbice from Linden. 22nd June, 2014 history was made when Guyana Power and Light (GPL) completed the

6 transmission interconnection of the Demerara and Berbice Interconnected Systems. Overall available generation capacity in Demerara and Berbice was then 100.6MW and the peak demand was 95MW [4]. Since then there has been an increase in load resulting in low transferred power from Sophia to Berbice as well as other contributing factors.

Statement of Problem

In the event of the loss of all its power generation in Berbice, and more particularly because of the government's proposal to establish the Amaila Falls hydropower facility with cheaper electricity supplies, GPL would like to have the transmission capability such that it can supply the entire Berbice area from Demerara.

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Scope of Work

Overview

Research has been done on understanding transmission upgrades and what are the requirements for upgrading and possibly redesigning a new transmission link system, for, developing and implementing a stable and highly efficient transmission system. Some results indicated that voltage drop increases as transmission line length increases. Similarly, the terminating voltage at the receiving end may vary above or below the recommended or nominal operating voltage, depending on the types of loads connected to the receiving end. The criteria required the receiving-end voltages to be maintained within specified bounds (usually ± 5% of the nominal voltage). Customer and utility equipment operates most efficiently when operated near the nominal voltage level [5]. The design of this project would be based on installing a capacitor bank to improve the transferred power in the transmission network. The Demerara – Berbice transmission link will be modelled by creating equivalent circuits. Different sub – stations would be represented by bus bars, each having varying characteristics such as load, generating and slack bus. Power world and Matlab would be used to simulate practical operating conditions and analyze systems parameters.

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Literature Review

Electric power transmission or "high voltage electric transmission" is the bulk transfer of electrical energy, from generating power plants to substations located near population centers. This is distinct from the local wiring between high voltage substations and customers, which is typically referred to as electricity distribution. Transmission lines, when interconnected with each other, become high voltage transmission networks [6]. Alternating current (AC) is the main driving force in the industries and residential areas, but for the long transmission line (more than 400 miles) AC transmission is more expensive than that of direct current (DC) [7]. Other approximations of transmission lines are: 1. Short transmission line (less than 80 km) 2. Medium transmission line (between 80 and 250 km) 3. Long transmission line (more than 250 km) The longest single line transmission within the Demerara – Berbice transmission link is 55.904 km highlighting that short line approximations are used for carrying out line analysis. Only the series resistance and reactance are included for short line approximations. The shunt admittance is neglected [8].

Figure 1 Short Line Transmission

Current and voltage limits are the two important factors of the high voltage transmission line. The AC resistance of a conductor is higher than its DC resistance because of skin effect, and eventually loss is higher for AC transmission. The switching surges are the serious transient over voltages for

9 the high voltage transmission line, in the case of AC transmission the peak values are two or three times normal crest voltage but for DC transmission it is 1.7 times normal voltage. High voltage direct current (HVDC) transmission has less corona and radio interference than that of high voltage alternating current (HVAC) transmission line [7]. In other words, it is safe to use HVAC transmission for this identified area of study especially due to cost attached.

Figure 2 HVDC and HVAC Transmission systems cost

Transmission lines, however, have been susceptible to many influential factors that determines its effectiveness in terms of its ability to transfer power effectively. Some of these factors include environmental, electrical, mechanical and economic factors. As a result reliability and congestion issues are birthed such as (1) transmission constraints, (2) thermal constraints, (3) voltage constraints and (4) system operated constraints [5]. Transmission Constraints As the transmission system has expanded over the years, surplus capacity available on transmission lines always seems to be consumed as the system grows or as transmission users find more economical ways of meeting system demands. Expansion leads to more usage that leads to more expansion. Transmission congestion results when a particular electricity transmission path

10 cannot accommodate increased power flow. Although the reasons for congestion vary, the common consequence is that increased power flow on a particular transmission path is not possible without risking system reliability. Thermal Constraints Line sag caused by exceeding a transmission line’s thermal limit can result in a line fault, which is an arc between the transmission line and nearby vegetation, structures, or ground. When line faults occur, protective transmission line components remove the line from service to protect terminal equipment from serious damage. Once the faulted line is removed from service, other transmission lines in the system experience increased loads as they compensate for loss of the faulted line. Overloading can then occur on these transmission lines, which might exceed thermal operating constraints. If not controlled promptly, additional transmission line faults may occur. To ensure reliable system operation, a thermal operating constraint (specified in real power, or megawatts) is often placed on troublesome transmission lines to control the permissible power transfer across the lines. This limit establishes an upper bound on a particular line’s transfer capability. It is important to note that in some cases, the transfer limit set on a particular line may actually minimize the overheating of a different transmission line. Transmission line additions tend to alleviate the potential for exceeding transmission line capacity limits, at least until future uses of the additional transfer capacity are discovered and new limiting factors are reached. System operators understand that, as a short-term workaround, the thermal limit may be exceeded in emergency situations. For this reason, transmission lines may also carry an emergency rating subject to a length of time that permits a higher transfer limit as long as the length of time the transfer is in effect does not exceed the specified period, for example, a 10-min emergency rating. In general, thermal constraints are more common in areas where the transmission system is tightly interconnected (shorter lines) [9]. Voltage Constraints Primarily as a result of transmission line reactance, the voltage at the receiving end of a conductor will be less than the voltage applied on the sending end. Large voltage deviations either above or below the nominal value may damage utility or customer equipment. Therefore, operating voltage constraints are employed to preserve operating conditions that meet necessary voltage requirements. In general, voltage constraints are more typical in areas where transmission lines are

11 sparse and long [9]. It may be more economical to address voltage constraints by modifying existing lines, such as adding capacitance, rather than by adding new transmission capacity. System Operated Constraints Parallel Flows System operators can estimate the impacts of contract flows (those flows defined as point-to-point transactions) on parallel paths in the transmission system. These estimates allow operators to adjust contract schedules to minimize the likelihood of encountering a transfer limit on system transmission lines caused by loop flows. Therefore, specific operating constraints may be in place to mitigate the effects of parallel path power flows. Operating security To ensure system operating reliability, an industry-derived set of standards and procedures has been recommended by the North American Electric Reliability Council (NERC). These recommendations suggest, for example, that the system should be operated so that it remains reliable in spite of disruption of a single system component (e.g., loss of one generator or loss of one transmission line). As a result, NERC operating guides tend to limit the maximum allowable operating capacity of a transmission line to a value less than its actual thermal limit to ensure available capacity in the event of a nearby transmission line outage. Similarly, NERC guidelines call for a generation margin to assure that sufficient generation remains on-line in the event of a generator outage. Likewise, operating guides exist to limit system effects caused by other types of conditions that affect system stability. All of these operating conditions are recommended as a means to improve overall system reliability while underutilizing specific system components. In addition, all system operators follow preventive operating guidelines to assure overall system integrity and reliability. System and Voltage Stability Because loads constantly change, small variations in frequency occur as the mechanical power at generator turbines adjusts to variations in electrical power demand. As long as frequency variations are small (i.e., small-signal stability), the interconnected system remains synchronized. The system will continue to operate in a stable manner unless the variations continue to gain in magnitude and

12 oscillate at low frequencies. These oscillations can lead to more threatening voltage and frequency problems that may lead to instability and potentially to cascading outages. Larger oscillations occur when system components are removed from service because a fault or disruption occurs. For example, frequency variations caused by a generator that goes off-line tend to be larger in magnitude than small-signal oscillations caused by load variations. Larger frequency swings provide more potential for uncontrolled swings that could lead to steady-state instability. Preventative measures are needed to minimize the likelihood of system instability, which could lead to widespread system outages. A system that lacks transient stability can produce these operating characteristics if corrective measures are not exercised to eliminate the condition. Voltage instability occurs when the transmission system is exposed to large reactive power flows. As previously described, large reactive power flows on long transmission lines result in voltage drops at the receiving end of the line. Lower voltage causes increased current, which causes additional reactive losses. The end result is voltage collapse, which can damage equipment and cause additional outages, if left unresolved. In general, long transmission lines are stability limited, not thermally limited [9]. Generally, depending on the system conditions, equipment enhancements to add more reactive power or additional transmission lines can relieve steady-state and voltage stability problems. Moreover, in practice, power lines are not operated to deliver their theoretical maximum power, which is based on rated terminal voltages and an angular displacement δ = 90˚ across the line. Figure 3 shows a practical line loadability curve plotted below the theoretical steady-state stability limit. This curve is based on the voltage-drop limit VR/VS ≥ 0:95 and on a maximum angular displacement of 30 to 35˚ across the line (or about 45˚ across the line and equivalent system reactance’s), in order to maintain stability during transient disturbances. The curve is valid for typical overhead 60-Hz lines with no compensation. Note that for short lines less than 80 km long, loadability is limited by the thermal rating of the conductors or by terminal equipment ratings, not by voltage drop or stability considerations [8].

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Figure 3 Transmission-line loadability curve for 60-Hz overhead lines - no series or shunt compensation

Alternative Solutions

There are a variety of approaches that may provide incremental improvements to transfer capability [5]: 1. Permit Higher Line Operating Temperatures: - This approach is not generally recommended for extended periods of time, higher line operating temperatures may be permissible as line ratings are increased. However, increased sag and insulator integrity may be compromised. This alternative should be used with caution and should not be viewed as a permanent solution to a thermal line limit. 2. Improve Transmission Line Real-Time Monitoring: - The actual temperatures occurring on transmission lines depend on the current, as well as on ambient weather conditions, such as temperature, wind speed, and wind direction. Because the weather affects the dissipation of heat into the air, an effort to monitor environmental conditions can result in higher line loading, if ambient conditions permit. When actual monitored values are used to establish

14 line ratings, generic ratings based on nonspecific environmental conditions that are often very conservative can be avoided. 3. Uprate Substation Equipment: - Just as thermal limits define maximum current flow values on transmission lines, equipment located at the terminating ends of a transmission line also have maximum current limits. In some situations, the limiting capacity may be linked to the equipment capabilities at the substation and not to the transmission line. If this is the case, the equipment at the substation can be replaced with larger components to increase the effective transfer limit of the line and its associated equipment. 4. Re-conductor Existing Transmission Lines: - To mitigate underrated transmission lines, the actual line conductors can be replaced with larger conductors to increase the transfer limit of the transmission line. Sometimes, multiple conductors are bundled together to obtain this improvement. As long as existing tower structures are adequate to support the additional weight of the new conductors, this alternative is useful to increase transfer capability. In some situations, this alternative may be cost-effective even when tower structures and insulators require modifications. 5. Install Phase-Shifting Transformers: - Loop flows can have a significant effect on designated transfer limits. One method to reduce loop flows is to uses phase-shifting transformers to help direct flows to transmission lines with sufficient transfer capability. As a result, transfers that take place on transmission lines that are not part of the primary flow path are lessened so that transfer limit violations are not attained. Although phaseshifting transformers are costly and consume additional energy. 6. Install Capacitors for Reactive Power Support: - In situations where voltage support is problematic, capacitor banks can be used to increase the reactive power at a system bus to return voltage levels to nominal operating values. This method of increasing reactivepower support is often used to minimize voltage support problems and improve system stability. 7. Design a new transmission line: - Transmission lines may reach the point of no return whereby upgrades to existing transmission lines may not be too effective. Hence, the implementation of a new transmission line is advised. In other scenarios where new designs may be very effect but not necessary due to the status of the current transmission line are not advised. This is mainly due to the financial impact new design inflicts.

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Evaluation Solutions

Permit Higher Line

Time

Efficiency

Risk Level

Cost Short

Long

Term

Term

1

Low

High

Cheap

Costly

3

Low

Medium

Cheap

Cheap

4

Medium

Low

Costly

----

5

High

Low

Costly

Costly

4

Low

Low

Costly

----

4

High

Low

Costly

----

5

High

Low

Costly

----

Operating Temperatures Improve Transmission Line Real-Time Monitoring Uprate Substation Equipment Re-conductor Existing Transmission Lines Install Phase-Shifting Transformers Install Capacitors for Reactive Power Support Design a new transmission line

Table 1 Decision Matrix Time: - 0 means very little time 5 means requires allot of time Time was rated from 0 to 5 for every possible alternative solution.

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Decision

The primary objective of this project does not lead to a definitive decision. The research invested in this project is to explore all possibilities associated with not just upgrading the current transmission line between Demerara and Berbice but through parameters manipulation be able to establish a close to ideal transmission line to facilitate primarily the eventual implementation of the Amaila Falls hydro project. This in itself may most likely lead to the design of a new transmission line.

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Implementation of Work

The upgrade to the 69 kV transmission link will be designed and modelled using the MatLab/Simulink software as well as the Power World software. The processes that needs to be undertaken in order to complete this design are as follows:  Obtain all the system’s parameter information as it relates to the present transmission link between Demerara and Berbice  Develop an equivalent circuit of the network  Developing an equivalent model makes model the entire system very simple cause you generally sum all the main parameters such as Load, Generation etc.  Model equivalent circuit using Matlab and Power World simulation softwares  Apply various load ratings on transmission line to analyze system behavior  Doing the following allows us to understand the actual capability of the system. We would then have an idea exactly where maximum voltage drop occurs in the system as well as how to implement solutions.  Improve system conditions by applying various alternatives solutions for the improvement the system’s stability and efficiency  The objective at this point of the project is to improve the maximum power transfer capabilities of the present transmission line.  Maximum load will be applied to the line in order to observe reactions after system improvements  Carryout various calculations to develop further solutions based on forecast load demand for next twenty (20) years for loads in Berbice.  The concept of developing a new transmission line beckons at this point of the project.  Analysis will be done to identify if the present transmission line can withstand future load capacities applying considerations for electrical, mechanical, environmental and economic factors.  Design new transmission line

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Facility

This project design will be done in an Integrated Development Environment (IDE) which is a software application that provides comprehensive facilities to computer programmers for software development Schedule. The computer softwares that would be used are the MatLab/Simulink and the Power World software.

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Schedule

Gantt chart

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Budget

Items

Cost

Printing

$5000

Transportation

$10000

Total

$15000

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Bibliography

[1]

InnovateUS, "What are the limits on Electricity Transmission?," 2013. [Online]. Available: http://www.innovateus.net/science/what-are-limits-electricity-transmission. [Accessed 17 January 2015].

[2]

A. Khan, "History," 1 January 2015. [Online]. Available: http://www.guyana.org/Handbook/history.html. [Accessed 17 January 2015].

[3]

GPL, "Our History," 17 January 2015. [Online]. Available: http://www.gplinc.net/about/history. [Accessed 17 January 2015].

[4]

S. Editior, "Demerara, Berbice power systems connected for first time," 24 June 2014. [Online]. Available: http://www.stabroeknews.com/2014/news/stories/06/24/demeraraberbice-power-systems-connected-first-time/. [Accessed 1 January 2014].

[5]

J. C. Molburg, J. A. Kavicky and K. C. Picel, "The Design, Construction, and Operation Of Long-Distance High-Voltage Electricity Transmission Technologies," Arronne National Laboratory, Illinois, 2007.

[6]

CC-BY-SA, "Electrical Power Transmission," Princeton University, 23 January 2015. [Online]. Available: http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Electric_power_transmission.ht ml. [Accessed 24 January 2015].

[7]

K. Meah and S. Ula, "Comparative Evaluation of HVDC and HVAC Transmission Systems," IEEE Xplore, Wyoming, 2008.

[8]

J. D. Glover, M. S. Sarma and T. J. Overbye, Power System: Analysis and Design, Connecticut: Global Engineering, 2012.

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[9]

A. R. Burgen and V. Vittal, Power Systems Analysis, New Jersey: Prentice-Hall Inc., 1986.

[10] Artsofte, "Reactive Power Compensation Devices," SverdlovElektro Group, 2015. [Online]. Available: http://svel.ru/en/catalog/ukrmsvel?id=53. [Accessed 26 January 2015].