A REPORT TO
THE BOARD OF COMMISSIONERS OF PUBLIC UTILITIES
Electrical
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Mechanical
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9 RMAN J.: UNGAY
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Transmission & Distribution
Telecontrol
System Planning
REPLACE COMPRESSED AIR SYSTEMBay d'Espoir Terminal Station 1
April 2010
newfoundland labrador
h d roa nalcor energy company
Replace Compressed Air System Bay d'Espoir Terminal Station I
Table of Contents
1 INTRODUCTION 1
2 PROJECT DESCRIPTION 2
3 EXISTING SYSTEM 33.1 Age of Equipment or System 63.2 Major Work and/or Upgrades 63.3 Anticipated Useful life 63.4 Maintenance History 63.5 Outage Statistics 73.6 Industry Experience 73.7 Maintenance or Support Arrangements 73.8 Vendor Recommendations 73.9 Availability of Replacement Parts 83.10 Safety Performance 83.11 Environmental Performance 83.12 Operating Regime 8
4 JUSTIFICATION 94.1 Net Present Value 94.2 Levelized Cost of Energy 94.3 Cost Benefit Analysis 94.4 Legislative or Regulatory Requirements 104.5 Historical Information 104.6 Forecast Customer Growth 104.7 Energy Efficiency Benefits 104.8 Losses during Construction 104.9 Status Quo 104.10 Alternatives 11
5
CONCLUSION 125.1
Budget Estimate 125.2
Project Schedule 13
Newfoundland and Labrador Hydro
Replace Compressed Air System Bay d'Espoir Terminal Station 1
1
INTRODUCTION
Bay d'Espoir Generating Station is Newfoundland and Labrador Hydro's (Hydro's) largest
hydroelectric generating station serving the Island Interconnected System, with seven
generating units producing a total capacity of 604 MW. Bay d'Espoir represents
approximately forty percent of Hydro's total Island Interconnected System generating
capacity. The power generated at Bay d ' Espoir is transmitted to the Island Interconnected
System via Bay d'Espoir Terminal Station 1 (Bay d'Espoir).
Circuit breakers play an integral role in the operation of the Island Interconnected System.
The circuit breakers provide fault protection to transmission lines and transformers. They
also provide isolation for the safe execution of work on the same equipment. On the Island
Interconnected System there are 66 air blast circuit breakers, 13 of which are installed at
Bay d'Espoir. There are no plans to replace the 13 230 kV air blast circuit breakers located
at Bay d'Espoir Terminal Station. These breakers are in good working condition and with
overhauls, are expected to last an additional 20 years. These circuit breakers require
compressed air to open and close as well as to extinguish the arc generated by the circuit
breaker operation. To ensure the reliable and optimal operation of these circuit breakers,
high quality compressed air is required.
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Replace Compressed Air System Bay d'Espoir Terminal Station 1
2
PROJECT DESCRIPTION
The Bay d'Espoir compressed air project is required to replace the existing terminal station
compressed air distribution system in order to improve the quality of the air supplied to the
air blast circuit breakers.
This project will replace the existing copper, brazed joint air distribution system with
stainless steel piping and welded joints. The supply lines from the plant will be replaced
along with all compressed air lines within the terminal station yard. The compressed air
header enclosure, shown in Figure 1, is the termination point of the supply line from the
plant. Inside the enclosure is a piping arrangement called the header from which
compressed air is distributed to the circuit breakers. The structure also contains
instrumentation such as pressure reducing valves. The enclosure is in disrepair and does
not provide sufficient space to construct a new piping system while keeping the existing
piping system in service. Therefore, a new enclosure will be constructed in the terminal
station yard to house the new header piping and instrumentation for the new compressed
air system.
Figure 1: Bay d'Espoir compressed air header enclosure and three compressed air tanks
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3
EXISTING SYSTEM
To ensure the reliable and optimal operation of these circuit breakers, high quality
compressed air is required. The compressed air must be free of moisture and residue for
proper circuit breaker operation. At Bay d'Espoir, this is provided by a high pressure
compressed air system located in the Bay d'Espoir Generating Station which is maintained
and operated by Hydro personnel. Ambient air is compressed to a pressure of 2.48
megapascals (MPa). Upon leaving a compressor, air is filtered and moisture is removed by
an air dryer. The existing compressed air system includes two air dryers (one primary and
one backup), which dry air to a target dew point temperature of -40 Celsius. This dew point
temperature has historically been Hydro's standard. From the air dryer, the compressed air
flows through distribution piping to supply four receiver tanks. One receiver tank is located
in the power house to operate governors, devices that control the speed of the generators,
and the 13.8 kilovolt (kV) switchgear. Three more receiver tanks are located in the Bay
d'Espoir terminal station. When needed, compressed air flows from the air dryer through
two copper tubes to the receiver tanks in the terminal station yard, approximately 100
metres away. When air is consumed by any of the breakers, replacement air is provided by
these receiver tanks through two pressure reducing valves which reduce air pressure to 1.6
MPa, the operating pressure required for the circuit breakers. One of the two copper tubes
is unable to serve the terminal station and is presently isolated due to high air losses
because of leaks. Leaks in compressed air piping cause air compressors and air dryers to
operate more frequently and for longer periods which result in increased wear on the
equipment, and increased operating and maintenance costs.
High quality compressed air is free of residue and moisture. The water content of
compressed air is expressed as the dew point temperature, i.e. the temperature at which
water vapour starts to condense into liquid water, or form ice when the temperature is
below zero degrees Celsius, for a given volume of air at a constant pressure. The
compressed air supplied to air blast breakers is required to have a very low dew point
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temperature. Hydro has historically accepted -40 Celsius due to standards in equipment
design, however, lower dewpoints are being used by other utilities for the same application.
-50 degrees Celsius is now the adopted standard for all of Hydro's air blast circuit breakers
and is consistent with other utilities' standards and manufacturers' recommendations. If
the dew point temperature of the compressed air exceeds ambient temperatures,
condensation or frost will form in the system. Frost may restrict air flow or block air lines
completely. When frost melts, liquid water can cause corrosion on internal surfaces and
short circuiting. Figure 2 shows internal corrosion on a high voltage breaker's receiver
tank. In a dry air system, this tank should appear as new with no corrosion. This can also
result in catastrophic, explosive failure of a circuit breaker potentially resulting in injury to
any personnel in the area and damage to other equipment. Hydro has experienced two
circuit breaker failures which have been attributed to moisture contamination. One
occurred at the Stony Brook Terminal Station in 1992 and the other at the Hardwoods
Terminal Station in 2002. Figures 3 and 4 show the damage done at the Hardwoods
Terminal Station. Fortunately, those incidents did not result in any personal injury. Repairs
have been made at those sites to fix leaks in the compressed air systems.
Figure 2: Corroded Air Blast Circuit Breaker from Hardwoods Terminal Station
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Figure 3: Breaker B1L36 Failure Due to Moisture Ingress at the Hardwoods Terminal Station.
Figure 4: Failure of Phase B (middle phase) Breaker B1L36 at Hardwoods Terminal Station
It is possible for moisture to enter the existing system downstream of the dryer through
leaks in the tubing. The consequence of these leaks is that the dew point temperature at
the point of use (the circuit breakers) can be higher than at the compressed air source. The
piping joints of the terminal station compressed air system have deteriorated allowing leaks
to develop. In addition, frost heave has displaced trenches and tubing runs, putting stress
on the tubing and joints, which increases the incidence of joint failure and additional leaks.
With these mechanisms for ingress of moisture into the compressed air system, the ability
to maintain the target dew point has been compromised. A leak free compressed air
system should show consistent dew point temperatures throughout the year. Dew point
records for 2009 show a trend for higher dew points during the summer months when
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Replace Compressed Air System Bay d'Espoir Terminal Station 1
humidity is higher. This is an indicator of moisture ingress through leaks in the piping
system. Between April 2009 and August 2009, dew points have regularly exceeded -40
Celsius, and have exceeded -35 Celsius on three occasions with a maximum of -31 Celsius
recorded. The sources of moisture ingress will be eliminated by replacing the copper tube
with stainless steel pipe and welded connections. Stainless steel pipe is stronger, more
durable and more corrosion resistant than the existing copper tube and welded joints are
stronger than brazed joints.
3.1 Age of Equipment or System
The Bay d'Espoir Terminal Station air distribution system was constructed in 1968, however,
the power house compressors and air dryers have been replaced since that time. One
compressor was replaced in 1997 and the other compressor was replaced in 2001. The
main air dryer was replaced in 1993 and the back up air dryer was replaced in 2008.
3.2 Major Work and/or Upgrades
There have been no major upgrades to the terminal station air distribution system since
construction. The power house compressors and air dryers have been replaced in recent
years as detailed in Section 3.1.
3.3 Anticipated Useful life
Compressed air systems are depreciated over 40 years.
3.4 Maintenance History
There is no detailed maintenance history available for this asset as Hydro does not maintain
records for these components.
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3.5 Outage Statistics
There have been no forced outages attributed to problems or failures with the compressed
air distribution system.
3.6 Industry Experience
Hydro participates in a discussion forum managed by Doble Engineering, a company that
aids clients in the electric power industry to improve operations and optimize system
performance. Utilizing this forum, Hydro posted a questionnaire to other utilities regarding
moisture problems for air blast circuit breakers. One respondent to the questionnaire,
Manitoba Hydro, addressed air quality issues at their terminal stations by replacing hose
and copper piping with stainless steel pipe and welded connections. This immediately
corrected moisture problems and improved the dew point temperature from -20 degrees
Celsius to -80 degrees Celsius.
The current standard for Hydro Quebec is -80 degrees Celsius at atmospheric pressure
which corresponds to approximately -62 degrees Celsius at the 1.6 MPa operating pressure
in Bay d'Espoir.
3.7 Maintenance or Support Arrangements
Bay d'Espoir is maintained by Hydro personnel.
3.8 Vendor Recommendations
Recommendations vary by source. Air blast circuit breakers are no longer manufactured
and so there is no longer active development or refinement of the requirements of these
breakers. ABB, the manufacturer, has made sometimes conflicting recommendations that
vary from moisture removal by high pressure compression, to one recommendation of -45
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Celsius. Atelier AHR, a manufacturer of replacement parts for the air blast circuit breakers,
recommends an atmospheric dew point temperature of -80 degrees Celsius as used by
Hydro-Quebec. Veronics Instruments, a supplier of dew point monitoring equipment
recommends stainless steel piping for best air quality.
3.9 Availability of Replacement Parts
Replacement parts are readily available for all components of the compressed air system.
3.10 Safety Performance
There is risk of catastrophic failure of a circuit breaker if the dew point temperature rises
above minimum seasonal temperatures, allowing condensation to form inside breakers. A
breaker failure could result in metal and sharp ceramic debris being thrown from the circuit
breaker during an explosive failure which poses a serious risk to personnel in the area at the
time of failure. Hydro has experienced two such failures at other terminal stations.
Fortunately, there were no injuries as a result of these failures. Adequate control and
monitoring of the dew point temperature will reduce this risk.
3.11 Environmental Performance
There are no environmental concerns with the compressed air system.
3.12 Operating Regime
This compressed air system operates continuously.
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4
JUSTIFICATION
This project is justified on the requirement to replace deteriorated infrastructure in order
for Hydro to provide safe and reliable electrical service.
The compressed air distribution system is approximately 42 years old. Leaks have become
common in the brazed joints and compromise compressed air quality. Replacement is
required to restore the integrity of the system.
The compressed air header enclosure is in disrepair and there is insufficient space within
the enclosure to construct a new piping system while maintaining compressed air service to
the terminal station with the old piping system. There is also insufficient clearance between
electrical equipment and piping inside the enclosure to perform modification,
replacements, or repairs to either electrical wiring or piping in close proximity to the
electrical equipment. As a result, it is recommended to construct a new enclosure with
sufficient separation between mechanical and electrical equipment to allow future
replacement or repairs as needed and transfer service to the new system upon completion.
4.1 Net Present Value
A Net Present Value calculation was not performed as there are no viable alternatives.
4.2 Levelized Cost of Energy
Levelized cost of energy is not applicable as there is no new generation source considered.
4.3 Cost Benefit Analysis
A cost benefit analysis is not applicable for this project as there are no quantifiable benefits.
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4.4 Legislative or Regulatory Requirements
There are no legislative or regulatory requirements for this project.
4.5 Historical Information
Hydro received approval, under Board Order No. P.U. 1 (2010), to replace the Holyrood
Terminal Station compressed air system in 2010/2011. The budget cost estimate of the
project is $496,000.
4.6 Forecast Customer Growth
This project is not impacted by forecast customer growth.
4.7 Energy Efficiency Benefits
It is expected that energy efficiency benefits will be realized through reduced operating
hours on the power station compressors. Leaks in the compressed air system result in a
pressure drop in the system. This causes the compressors to operate more often in order to
re-pressurize the system. Implementation of this project will reduce compressed air leaks
and result in lower compressor operating hours. However, the leakage rate has not been
measured; therefore, the benefits can not be quantified.
4.8 Losses during Construction
There will be no losses during construction.
4.9 Status Quo
If the status quo is maintained, the integrity and reliability of the compressed air system
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and thus the circuit breakers and ultimately the Island Interconnected System will continue
to be compromised and the safety risk will remain high.
4.10 Alternatives
There is no viable alternative to replacement of the compressed air distribution system.
As an alternative to replacing the supply line from the powerhouse to the enclosure in the
Bay d'Espoir Terminal Station, Hydro considered construction of a new terminal station
compressed air supply independent of the existing one in the powerhouse. This alternative
would be brought up to the same functional design standard as the replacement option.
However, the cost estimate for new construction exceeds the cost estimate of the
replacement of the existing system by $106,500 which is 16.4 percent higher. The
operating and maintenance cost of this alternative is estimated to be the same or
marginally higher than the proposed new installations.
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5
CONCLUSION
Replacement of the copper piping with stainless steel piping will eliminate air leaks and
reduce the probability of piping failure. This will eliminate moisture ingress in the
compressed air distribution piping and reduce compressor run time. It will also ensure that
consistently dry air is provided to the air blast circuit breakers for optimal, safe operation.
This will improve the reliability and safety of the Bay d'Espoir Terminal Station by reducing
the probability of moisture related breaker failure.
5.1 Budget Estimate
The budget estimate for this project is shown in Table 1.
Table 1: Budget Estimate
Project Cost:($ x1,000) 2011 2012 Beyond Total
Material Supply 11.5 0.0 0.0 11.5
Labour 28.0 105.4 0.0 133.4
Consultant 0.0 0.0 0.0 0.0
Contract Work 33.0 318.3 0.0 351.3
Other Direct Costs 4.5 33.2 0.0 37.7
O/H, AFUDC & Escln. 6.9 53.3 0.0 60.2
Contingency 0.0 53.4 0.0 53.4
TOTAL 83.9 563.6 0.0 647.5
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5.2 Project Schedule
The project schedule is shown in Table 2.
Table 2: Project Schedule
Activity Milestone
Project Initiation March 2011
New enclosure construction July 2011
Engineering and Design of Piping System December 2011
Tender for Piping System May 2012
Piping Installation Complete July 2012
Project Closeout August 2012
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