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

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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

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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

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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 lines 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 lines 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

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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

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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 = 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

reactances), 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

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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 phase-

shifting 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 reactive-

power 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 Time Efficiency Risk Level Cost

Short

Term

Long

Term

Permit Higher Line

Operating Temperatures

1 Low High Cheap Costly

Improve Transmission

Line Real-Time

Monitoring

3 Low Medium Cheap Cheap

Uprate Substation

Equipment

4 Medium Low Costly ----

Re-conductor Existing

Transmission Lines

5 High Low Costly Costly

Install Phase-Shifting

Transformers

4 Low Low Costly ----

Install Capacitors for

Reactive Power Support

4 High Low Costly ----

Design a new

transmission line

5 High Low Costly ----

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 systems 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 systems 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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Connecticut: Global Engineering, 2012.

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