5000 Electrical Switchyard Design Report Group 8 Final
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Transcript of 5000 Electrical Switchyard Design Report Group 8 Final
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Nuclear Plant Design
Design Description for Switchyard
Terry Price 100350844Brian Liang 100442577Thayer Bai 100425385
Alex Robitaille 100423915Nadeem Murji 100394550Karndeep Gill 100367967
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Contents
Acronyms ........................................................................................................................................ 3
Executive Summary ......................................................................................................................... 3
Design Overview ............................................................................................................................. 4System Overview ............................................................................................................................ 6
Site Layout ....................................................................................................................................... 8
System Components ..................................................................................................................... 10
Distribution Bus......................................................................................................................... 10
Wave Trap ................................................................................................................................. 11
Insulator .................................................................................................................................... 11
Lightning Arrestor ..................................................................................................................... 12
Resistor Bank ............................................................................................................................. 12
Step-Up Transformer ................................................................................................................ 13
Step-Down Transformer ........................................................................................................... 15
Emergency Circuit Breakers ...................................................................................................... 16
Emergency Circuit Connectors .................................................................................................. 16
Connectivity Switching Mechanism .......................................................................................... 17
Galvanometers .......................................................................................................................... 18
Voltage Stabilizing Autotransformer ........................................................................................ 19
Grounding ................................................................................................................................. 20
Soil Preparation ..................................................................................................................... 21
Ground Rod Design ............................................................................................................... 21
Filter Capacitor Banks ............................................................................................................... 21
Phase Angle Adjusters............................................................................................................... 22
Emergency Backup Power Redirection Bus .............................................................................. 24
Output Monitoring .................................................................................................................... 24
Digital Control Computer .......................................................................................................... 24
Site Features ............................................................................................................................. 25
Fencing .................................................................................................................................. 26
Fire Protection .......................................................................................................................... 26
Site Grading ............................................................................................................................... 26
Environmental Impact............................................................................................................... 27
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Review of Design Requirements ................................................................................................... 27
Functional Requirements .......................................................................................................... 28
Performance Requirements ...................................................................................................... 28
Safety Requirements ................................................................................................................. 29
Client Requirements: ................................................................................................................ 32
Reliability and Maintainability Requirements .......................................................................... 32
Cost Requirements .................................................................................................................... 33
Environmental Requirements ................................................................................................... 33
Human Factor Requirements .................................................................................................... 34
Layout Requirements ................................................................................................................ 34
Assumptions .................................................................................................................................. 35
Turbine Generator Assumptions............................................................................................... 35
Bibliography .................................................................................................................................. 35
Acronyms
CSM Connectivity Switching Mechanism
ECBD Emergency Circuit Breaker Device
ECCD Emergency Circuit Connector Device
Executive Summary
The report that follows details the conceptual design of the electrical switchyard for the
ART25 nuclear power-plant. This switchyard transfers power from the electrical power
generators, conditions it, and supplies it to both the electrical power grid and the nuclear
power-plant itself. Furthermore, the switchyard provides backup power routing capabilities
and some electrical power dissipation capability. Components designed include: the
distribution bus, the wave trap, the insulators, the lighting arrestors, the resistor banks, the
step-up and step-down transformers, the emergency circuit connectors, the emergency circuit
breakers, the galvanometers, the voltage stabilizing autotransformers, grounding, site layout,
filter capacitor banks, phase angle adjusters, the emergency backup power distribution bus, the
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supplied from the generator to the plant. This connectivity and re-routing is controlled by a
CSM.
Additionally, the entire switchyard can be isolated from the grid and the plant via a CSM.
Connectivity to the plant and grid is maintained with independent parallel connections so that
any maintenance operations can occur without discontinuing power distribution.
Grounding shall be provided via a pair of conductive rods driven into the ground. Using
two conductive rods provides redundancy in case of any sort of system failure. All systems will
be provided with a ground. Furthermore, to mitigate against the risk of spatial transients, the
grounding rods shall be embedded at spatially distinct locations.
Power monitoring is a key capability of the switchyard. All power paths into the switchyard, out
of the switchyard, and between elements within the switchyard must have their parameters
continuously monitored so that any transients can be monitored and interrupted to prevent
system damage. The particular parameters to be monitored shall be noted in the system
components section of the report.
The parameters of the supplied power shall be controlled to match grid and plant-system
requirements through a system of autotransformers, to adjust voltage output, and capacitor
banks, to adjust phase angle.
The entire switchyard shall be controlled via a control room. This control room is to
provide a suitable working environment for switchyard personnel and includes amenities that
include a break-room, wash-rooms, heating, air conditioning. From within this control room,system performance can be monitored and the parameters of various elements of the
switchyard can be altered. Furthermore, a data connection is installed between the switchyard
control room and the reactor control room so that information about the grid demand and
switchyard status can be communicated to the reactor control room.
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System Overview
A functional diagram of the system is as follows:
Electric Generator
Step-Up
TransformerAutotransformer
Filter Capacitors
Banks
To Power Grid
Distribution Bus
Step-Down
TransformerAutotransformer
Filter Capacitors
Banks
Phase Angle
Adjustment
Phase Angle
Adjustment
Single Phase Tap-Off
Three-Phase PowerPhase Angle
Adjustment
To Plant Single
Phase Power
To Plant Three
Phase Power
Resistor Banks
Wavetrap
From BackupEmergency Power
Distribution System
Figure 1 System Layout
The switchyard is divided into three sub-systems: distribution bus and power dissipation
area; the grid-side power distribution system; and, the plant-side power distribution system.
The electric generator provides power to the distribution bus. The distribution bus distributes
power in three directions: upwards to the plant, right to the resistor banks, and down to the
power grid. The resistor banks dissipate any excess-power transients, in particular the Back-
EMF from the transformers or electric generator.
Considering the power-grid side of the switchyard, the step-up transformer is steps up
the voltage from that which is provided by the generator to that which is accepted by the grid.
The autotransformer (variac) is a transformer is capable of differentially changing its winding
ratio so that the voltage output of the step-up transformer matches the voltage demanded by
the power-grid. The filter capacitor banks filter out any short time-scale power transients that
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might occur in system. The phase angle adjustment is achieved by a bank of variable capacitors
that align the output phase angle to the phase angle of the grid.
The plant-side power side of the switch yard works in a manner similar to that of the
power-grid side of the switch yard, except for several differences. First, there are two outputs:
three-phase power and single-phase power. The three-phase power system directly feeds the
three-phase power coming off the electric generator through the step-down transformer and
into phase angle adjustment whereupon it is directly fed into the plants three-phase power
system. The single-phase power system takes a single phase out of the three-phase power,
feeding it to phase-angle adjustment and then to the plants single phase power output.
Between each element in the system, a current sensing galvanometer is installed. This
galvanometer trips an over-current protection system if it detects a high-current transient. This
overcurrent protection system signals the emergency circuit breakers that connect the
switchyard to the electric generator to trip, thereby disconnecting the switchyard from the
power source. The element that is experiencing the over-current transient is also disconnected
from the rest of the system using emergency circuit breakers that are installed between each
element of the system. The element that is experiencing the over-current transient is thensunk to the resistor banks through an emergency circuit connector so that any stored charge in
the element can be dissipated safely.
Continuous inspection of the switchyard shall be performed. This inspection looks for changes
in operating parameter, physical attributes and human performance of the switchyard and
adjusts them if the drift too far off their nominal values.
Conductors transmitting power to each component in the switchyard shall be insulated with a
thickness of insulation that prevents electrical arcing to an unprotected ground in any transient
scenario with a factor of safety. Furthermore, a membrane with a low magnetic susceptibility
shall shield each conductor to prevent electromagnetic interference with proximate equipment.
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Finally, each conductor shall be spatially separated from each other to prevent cross-talk. If this
spatial separation is not possible, then additional shielding shall be used to mitigate the risk of
arcing and cross-talk. Regular inspections of this insulation shall occur. This insulation shall be
weather resistant and able to last the lifetime of the switchyard under elevated-severity
weather conditions.
The switchyard itself receives demand data from the power distributor through the
power-lines themselves using a power-line communication protocol. This protocol operates in
superposition with the power signal, but at a much higher frequency. A wave trap separates
the power-line communications protocol signal from the power signal and sends the power-line
communications signal to the control room for processing.
All components within the switchyard shall be seismically qualified for the region in
which they are installed Furthermore, all components shall have a nominal operation lifetime
that is either greater that the in-service life of the ART25 reactor or designed to be replaced or
refurbished during the operational life of the switchyard. Furthermore, each component in the
switchyard shall be designed so that it is able to withstand any sort of extreme weather
condition that has a reasonable probability of occurring during the lifetime of the switchyard.Furthermore, corrosion resistant materials should be used wherever possible. All bare metal
surfaces shall be painted to further mitigate against corrosion.
Workers entering the switchyard shall be inspected upon entry to ensure that they are
wearing insulated rubber boots and other appropriate personal protective equipment.
Furthermore, personnel at the switch yard shall all be given high voltage safety training.
Furthermore, safety officers shall routinely patrol the switchyard to ensure that no safetyviolations are occurring.
Site Layout
The layout of the switchyard is depicted in the figure below.
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Figure 1 Site layout
The layout of the switchyard is designed so that it can send 25MW of electrical power to the
grid and the station. The generator sends the power to the bus where it can be divided. The
electric bus is connected to the capacitor bank so that the lag is corrected early, minimizing
losses within the switchyard itself. The control devices also connect at the bus, which is
monitored by the control room. The resistor bank is connected to the bus to open and absorb
energy if a transient is experienced, and is connected to a cooling system to extend the life of
the resistors.
The station service transformer is labeled as a step down transformer and is controlled
to take as much power as the station needs. The transformer is cooled to extend its life. It is
sent to an autotransformer where it is regulated within tolerances, and from there it is filtered
and divided to a single phase tap and 3 phase power lines. From there it is sent to the plant
services transmission which also connects to the control room.
From the electrical bus the step up transformer distributes most of the power to the
grid. This is accomplished by regulating it with an autotransformer, being filtered and phase
corrected similarly to the station services power. However the size and amount of components
is increased due to the increase in power flowing through them. The power grid also has a
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wave trap to prevent high frequency feedback into the switchyard from the grid. The
emergency power distribution is used to send power to the plant from the grid in case the
station loses its ability to produce electricity. The power is stepped down from the grid and
sent to plant.
System Components
A more detailed description of individual system components follows.
Distribution Bus
The distribution bus, also called the electric bus, is responsible for distributing power
from the electrical generator to the plant-side, grid-side and resistor banks. It does this by
connecting the conductor leading from the electrical generator to conductors connecting to the
plant-side, grid-side, and resistor banks through CSMs. Furthermore, there are emergency
circuit connectors that connect the distribution bus to the resistor banks and emergency circuit
breakers are installed on each branch of the distribution bus.
The distribution bus has the current and voltage flowing through each branch of it
measured via galvanometers. These galvanometers are fed a stepped-down voltage that is
congruent with their operational parameters via a step-down transformer. The galvanometers
digitize their signal by actuating a rotary encoder. This signal is then sent to the control room
for continuous monitoring. Furthermore, distribution bus temperature is recorded on the
surface of the insulator of the conductors by an infrared pyrometer. The signal from the
pyrometer is also sent to the control room for continuous monitoring.
The conductors in the distribution bus are shielded from cross-talk via magnetic field
shields (such as mu-metal) that are present whenever the conductors are in close proximity to
each other. The entire distribution bus is built inside a weather-proof metal box that has access
hatches built in for easy maintenance. This metal box features elastomer expansion joints to
prevent structural fatigue from the pulsating magnetic fields that are induced by the alternating
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current flowing through the conductors. The distribution bus shall be seismically qualified and
able to withstand any sort of seismic event with a reasonable probability of occurring.
Wave Trap
A wave trap is a device used to trap the high frequency communication signals sent
through the HV transmission power lines. Its purpose is to filter out only the pertinent
communication signals and divert them to the teleprotection panel in the control room (this is
done with a combination of a capacitor and inductor). This is required because substations
communicate through Power Line Carrier Communication (PLCC) systems. These systems do
not depend on telecommunication company networks.
The communication carrier waves are at a much higher frequency than the power
signal. Each of the wave traps is designed to prevent such carrier waves from entering the lines
and affecting station equipment. They are also protected with a lightning arrester in case of
surges.
The design will need to include several of these in order to ensure that unwanted
frequencies are left out of the station machinery. The wave trap shall be seismically qualified
and able to withstand any seismic event with a reasonable probability of occurring.
Insulator
Insulators are important when designing structures to support electrical equipment and
transmission lines. They are designed to insulate and resist the flow of electrical current while
being able to physically support the wires which carry such currents.
The main type of insulator used to support the transmission lines will be suspension
type insulators. These insulators have a number of ceramic discs connected in series with metal
links to form a chain. Each disc is designed for a certain voltage, the greater the line voltage,
the greater the number of discs required. In addition, the chain like linking of the discs allows
for a minimization of stresses via free swinging. This allows for movement of these insulators
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from wind or seismic events, thus being seismically qualified. Such an insulator is also easy to
repair and modulate by simply replacing broken discs or adding on more discs. The insulation
also provides protection to the lines from currents that would come from the tower, meaning
that there is partial protection from lightning.
Lightning Arrestor
Lightning arrestors are electrical protection tools designed to protect electrical
equipment and insulation from switching and lightning surges. These transients of overvoltage
are captured by the lightning arrestors and sent to the earth. It is the first piece of equipment
in electrical substations.
These will be installed on all towers and poles, transformers, circuit breakers, bus
structures and steel towers in a substation. The lightning arrestors shall be seismically
qualified and able to withstand any seismic event with a reasonable probability of occurring
Resistor Bank
The resistor bank is the device that is responsible for dissipating any excess energy or
residual energy in the switchyard. It consists of a set of parallel branches of resistors in series
(see the figure below).
Figure 2 Sample resistor bank layout
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This arrangement of resistors is to ensure that no single resistor has its maximum voltage rating
or maximum current rating exceeded. The resistor bank must have a total resistance that
ensures the power time-constant of the entire switchyard system, upon a loss-of-power
incident, dissipates power at a rate at which the heat flux from the resistors in manageable.
Each resistor shall be cooled using a recirculating cooling oil system. Each resistor is
installed in a coolant oil reservoir. The size of this oil reservoir is such that the oil in the
reservoir can store the entirety of the heat generated by a complete system discharge from
nominal conditions without failure. Under normal conditions, this cooling oil is circulated by a
pump through a radiator. The temperature of the coolant oil and surface temperature of the
resistors are monitored by thermocouples. These temperature readings are fed back into the
control room to provide process monitoring. The temperature is additional fed back to as a
microcontroller that controls the duty cycle of the recirculating cooling oil pump in a manner
such that the resistor in the oil reservoir is kept at its nominal operating temperature.
There are several input conductors to the resistor bank so that if one input conductor
fails, the resistor bank will still be accessible via another pathway. Furthermore, the current
and voltage parameters of each input conductor is monitored by galvanometers and this data isfed back to the control room. The resistor bank shall be seismically qualified and able to
withstand any seismic event with a reasonable probability of occurring
Step-Up Transformer
The step-up transformers steps-up the voltage on the primary side to a higher voltage
on the secondary side. For the power-grid step-up transformers, the voltage is stepped up to a
level that is congruent with the distribution voltage. Fine adjustment of the voltage is achieved
by using the succeeding autotransformer.
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Step-Down Transformer
The step-down transformer is the conceptual complement to the step-up transformer.
The step-down transformer converts a higher voltage on its primary side to a lower voltage on
its secondary side. fine adjustment of output voltage is achieved by using a succeeding
autotransformer.
The step-down transformer is encased in a magnetic field insulator that provides
shielding which prevents the magnetic field of the step-down transformer from interacting with
proximate equipment. The whole apparatus is encased in a weather-proof box. Both the shield
and the box are constructed with elastomeric expansion joints that prevent material damage by
repetitive bending caused by the alternating magnetic field of the transformer.
The step-down transformers shall be installed in parallel with the resistor bank. In this
way, the back-emf caused by an isolation or loss-of-power event will be dissipated as heat in
the resistor banks.
A nominal operating temperature in the step-down transformer shall be maintained by
a placing the transformer itself in a cooling-oil reservoir. The cooling-oil reservoir shall be sized
so that it can absorb the heat generated by a loss-of-power induced back-EMF event and keep
the step-down transformer below its maximum temperature rating.
Current flowing through the step-down transformer shall be monitored by a
galvanometer. The voltage drop across the step-down transformer shall be calculated by
multiplying the current passing through the transformer by the impedance of the transformer
itself as a function of primary and secondary coil temperature. The step-down transformer
itself will be connected to other elements in the system through CSMs and ECBDs. The step
down transformers shall be seismically qualified and able to withstand any seismic event with a
reasonable probability of occurring.
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Emergency Circuit Breakers
The emergency circuit breakers are devices that break the connectivity of a component
to the switchyard or the switchyard from the grid. Circuit breakers are designed to fail open to
protect any component that may be connected to them from transients that may occur while
the breaker is unavailable. The ECBDs shall be seismically qualified and able to withstand any
seismic event with a reasonable probability of occurring
The emergency circuit breakers use a high-pressure pneumatically operated switch to
connect the two sides of the breaker. When the trip signal is given, a solenoid valve retracts
the pneumatic actuator operates and disconnects the two sides of the switch. There is only
enough air in the reservoir tank for a single operation. An onboard compressor keeps the
reservoir tank pressurized. This use of a reservoir tank allows the ECBDs to operate without any
power other than the trip signal. The trip signal itself originates from the control room and is
sent to the ECCBs by a standard insulated control cable.
Emergency Circuit Connectors
The emergency circuit connectors are fast acting switches that connect an element in
the switchyard to the resistor bank so that residual charge in the element can be safely
dissipated. This emergency circuit connector consists of a normally closed switch that is held
open via an electromagnetic clutch. When de-energized, the switch will close and connect the
switchyard element to the resistor banks. The ECCDs shall be seismically qualified and able to
withstand any seismic event with a reasonable probability of occurring
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Connectivity Switching Mechanism
The connectivity switching mechanism (CSM) is a device that controls the connectivity of
an element in the switchyard to another. It works by using a pneumatically actuated high-
voltage, high-current switch to connect and disconnect a conductor between two elements of
the switchyard. Altogether, there are four switches in each CSM: two parallel sets of two series
switches (see the diagram below)
Figure 3 CSM switch layout
In this way, control is only lost if two out of the four switches are unresponsive. Air is
supplied to the pneumatic actuators of these switches via an onboard reservoir that is
connected to an onboard compressor. The onboard reservoir contains enough air so that
several typical power-maneuvers can be performed; this ensures switchyard operability in case
of a loss of backup power incident. Furthermore, the onboard compressors have an externalshaft that can be connected to a gas-powered portable motor that can power the compressor.
The CSM is controlled through a standard electrical control signal. This control signal is
transmitted from the control room to an onboard controller board via an insulated signal cable.
Furthermore, manual control is enabled by using normally-closed solenoid valves on the
pneumatics lines that have a manual-override lever installed. In this way, if there is a loss-of-
power incident, the CSMs can still be operated via these levers.
The entire CSM, except the switches themselves is to be covered in a weather-proof
metal box. This metal box features elastomer expansion joints to prevent structural fatigue due
to movement induced by the alternating magnetic field created by the power moving through
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the conductors. Due to the tendency for the contacts of the switches to arc, these are left open
to the environment. This metal box is grounded so that any arcing to it will be safely arrested.
Arcing at the CSM switches is unavoidable. The switches contacts themselves are
constructed from a thick conductor that is resistant to damage due to electrical arcing and
weathering. The lifespan of the switch contact should be designed so that sum of the
replacement cost over the lifetime of the plant is minimized. Furthermore, the CSM is housed
within an exclusion cage that prevents people and equipment at a safe distance away from any
arcs induced by the CSM. Furthermore, this cage is grounded so that any arcs that do make it
to the cage perimeter can be safely sunk to ground. A mean looking scarecrow should be placed
on the cage to prevent birds from sitting on the cage or nesting in the equipment. The CSMs
shall be seismically qualified and able to withstand any seismic event with a reasonable
probability of occurring
Galvanometers
The galvanometers serve two purposes: monitoring of the voltage on a conductor, and
monitoring of the current on a conductor. The galvanometer is connected to a low-friction
rotary encoder that allows it to respond to events on the same time-scale as a typical power
transient. The signal from this rotary encoder is sent via a standard signal cable to the control
room so that the galvanometer can be continuously monitored.
Voltage measurements require the use a high resistance resistor in parallel with the
galvanometer. Since a high resistance resistor would need to dissipate many MW of power if a
sizable fraction of the plants output were to be passed through it, galvanometers that measure
voltage first have the voltage passed to them stepped-down by many orders of magnitude such
that the power dissipated by the resistor is a quantity that is manageable by a forced-air heat-
sinking system.
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A regular benchmarking program shall be implemented with the galvanometers so that
the accuracy degradation due to spring-force loss in the restoring spring of the galvanometers
can be compensated for.
The galvanometers are connected to the other elements in the system via CSMs in the
input and output sides as well as emergency breakers. Since there are no capacitive or inductive
elements in the galvanometers, a connection does not need to be made to the resistor bank.
The galvanometers shall be seismically qualified and able to withstand any seismic event with a
reasonable probability of occurring
Voltage Stabilizing Autotransformer
The voltage stabilizing (or regulating) autotransformer is a transformer that allows for
differential adjustment of its winding ratios. In this way, the magnitude of the output voltage
can be changed.
A transformer that is rated to the power requirements of its installation (grid, 3-phase,
or single phase power) is installed with a secondary winding with multiple taps. These taps are
connected to the output conductor of the transformer via a mechanical interlock that only
allows for a single tap to be connected to the conductor at a time.
The autotransformer receives a control over a standard signal line from the control
room. This signal is computed by calculating the difference between the demanded voltage
and the output voltage of the autotransformer. The tap that is the closest match to the
demanded voltage is then selected.
The autotransformers are installed such that there is a parallel connection to the
resistor bank. In this way, any back-emf generated by a power transient will have a time-
constant large enough that it does not generate a damaging spike in transformer voltage.
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3. Place ground rods and wells around the substation to better dissipate faultcurrent.
Soil Preparation
The preparation of the soil before the ground rods are inserted aides in lowering the
resistivity resulting in adequate ground resistance. The design will have an initial layer of clay
for a half-metre, followed by five metres of loam and above the loam will be half a metre of
gravel. Lastly a well for any maintenance is to be installed. The well will be slightly covered with
gravel but can be accessed easily by electrical technicians. Using this layering will provide the
most resistivity to ground potential rise and other hazards.
Ground Rod Design
The ground rod design will consist of two conductive copper rods. The average ground
rod used in substations is three metres long. The rods used for this design will be six metres in
length and will be distanced six metres away from each other as well. Doubling the length of
the two ground rods wherever grounding is needed will reduce the resistance by a value of 45%
under uniform soil conditions. A groundwire will be used to connect the the ground rod and
the service ground connection which will be found in the control room.
Capacitor Banks
Filter Capacitor Banks
The filter capacitor banks serve the purpose of removing any fast time-scale power
transients from the system. The capacitors in this circuit should be installed in parallel so that
the current passing through any one capacitor does not exceed the nominal operational
parameters of the capacitor. Furthermore, on the power grid side the capacitors shall be high-
voltage ceramic type capacitors. The parallel branches of the filter capacitor banks shall feature
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a multitude of individual capacitors so that the voltage drop across each capacitor is within the
maximum voltage parameters of the individual capacitors.
The filter capacitor bank shall be connected to other elements in the system through
CSMs in series with ECBDs. The shall be an ECCD that connects the filter capacitor bank to the
resistor bank. In the event of an isolation event or excess power transient (that has a timescale
that is within the resolving time of the ECCD), the ECCD will drain the filter capacitor bank to
the resistor bank.
Figure 4 Capacitor bank layout
Voltage and current shall be monitored entering and leaving the filter capacitor bank
and fed back to the control room. Furthermore, a regular maintenance program shall be
implemented in which the operational parameters (time constant, frequency response, etc) of
the individual capacitors in monitored for drift. The filter capacitor banks shall be seismically
qualified and able to withstand any seismic event with a reasonable probability of occurring
Phase Angle Adjusters
The phase angle adjusters adjust the phase angle of the incoming power to match the
demanded power phase angle. A phase angle adjuster shall be provided for each phase of
power being supplied to it. The phase angle adjusters accomplish this by a series of variable
capacitors that are in series with a series of variable inductors. The number of variable
capacitors and variable inductors is determined by the maximum voltage rating of each
component; enough elements should be put in the series so that the maximum voltage rating
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of each component is not exceeded. furthermore, this series of series of variable capacitors and
series of variable inductors shall be in parallel with further series of series of variable capacitors
and series of variable inductors such that the maximum current rating of each component is not
exceeded. See the diagram below for clarification.
Figure 5 Prototypical phase angle adjuster
These variable capacitors and variable inductors shall be controlled by actuators based
on a control signal from the control room. The control signal shall determine the positioning of
the variable capacitors or inductors such that it alters phase angle of the output power so that
it is congruent with the demanded power output angle. The input and output voltages and
currents of the phase angle adjusters shall be monitored by galvanometers and the signals from
these galvanometers shall be fed back into the control room to compute the error value of the
phase angle adjuster system.
Each of the variable inductors shall be wired up in parallel with the resistor bank so that
the back-EMF time constant is large enough that the maximum voltage rating is not exceeded
during a loss-of-power transient. Furthermore, the variable capacitors are connected to the
resistor bank via an ECCD. In the case of an isolation event or an excess power transient that
can be intercepted within the operational-time scope of the ECCD, the ECCD will trip and safely
drain the charge of the capacitors to the resistor bank where it will be dissipated as heat. The
phase angle adjusters shall be connected to the rest of the system through CSMs and ECBDs.The phase angle adjusters shall be seismically qualified and able to withstand any seismic event
with a reasonable probability of occurring
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Emergency Backup Power Redirection Bus
The emergency backup power redirection bus redirects power from the grid to the plant
power supply systems in the event of a loss-of-power incident. It does this by stepping down
grid voltage to the plant distribution voltage with three phase power. A single phase of this
three phase power is the taken off to distribute power to the single phase power systems. The
emergency backup power redirection bus can also accept power from the emergency backup
power systems.
Upon a loss-of-power incident, ECBDs fire and disconnect the plant power supply from
the electrical generator. The emergency backup power redirection bus then switches on to
supply power from the electrical grid to the plant itself. If there is no power available in the
electrical grid the redirection bus will switch again to take power from the backup power supply
systems.
Output Monitoring
Output current and voltage are continuously monitored on both the plant-power side
and grid-power side. This data is recorded in the control room and fed to the digital control
computer so that it can adjust the autotransformers and phase angle adjusters so that the plantoutput is congruent with the grid and plant demands. Furthermore, CSMs are placed between
the switchyard and each output so that the outputs can be disconnected if the need arises.
Digital Control Computer
All component parameters such as temperature, current and voltage will be input into a
centralized digital control computer. This digital control computer will be housed in a
seismically qualified air conditioned room; installed with an uninterruptable power supply to
prevent disruptions due to loss-of-power incidents; and, mounted on a spring table to prevent
damage due to seismic events
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This digital control computer can either be set in manual or automatic mode. In manual
mode, the switchyard is controllable by a human operator at a control panel. In automatic
mode, the switchyard responds programmatically to system demands.
The digital control computer shall take inputs from the grid operator via the power-line
communications protocol. The digital control computer shall output all of the switchyards
parameters to the reactor control room via a data link so that the reactor control room
operators can see what is happening in the switch yard.
Site Features
The foundation of the switchyard shall be made of steel-reinforced concrete. The
concrete pad will be 110x 70 m and shall be built on a slight grade so that water is able to drain
off it.. Concrete foundations below ground level provide an excellent means of obtaining a low-
resistance ground electrode system. Since concrete has a low resistivity a rod embedded within
a concrete encasement gives a very low electrode resistance compared to most rods buried in
the ground directly . It is possible to use the reinforcement rod as the conductor of the
electrode by ensuring that an electrical connection can be established with the main rebar of
each foundation. The size of the rebar and the bonding between bars of each concrete member
must be done so that ground fault current will not cause excessive heating, otherwise such
heating may weaken the concrete member and cause it to fail.
The use of Ufer grounds to turn the concrete foundation into a grounding electrode
means there are some factors to keep in mind. One of these factors is steam. Moisture in the
concrete may turn into steam if a high fault current such a lightning surge or heavy ground fault
occurs. This expansion of the water content in the concrete can produce cracks and damage the
concrete. Another factor to be concerned about is possible corrosion of the rebar when an AC
current flows through it. Corrosion would cause the rebar to expand and produce cracks in the
concrete. Damage to the concrete can be minimized by limiting the duration of the fault current
flow or providing a path from the rebar through the concrete to an external electrode.
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Fencing
There will be a metallic security fence around the perimeter of the switchyard. Like
every other structure the fencing will be grounded in the event of arcing, lightning strike or a
power line snapping and falling on the fencing. The fencing will enclose any part of the
switchyard which is open to the air, contains live equipment which is not encased and the
control building, with a fence that is at least 1.8m in height. The fence will be topped with
barbed wire to keep intruders out. There will be gates to allow entry to the switchyard located
along the fencing. The gates shall not come into contact with the frame or enclosure of any
electrical equipment when fully opened. The gates and fencing shall have high-voltage warning
signs to inform people of the danger of the site. The gates like the fencing will be grounded.
Fire Protection
There are a variety of potential causes of fires in a substation so the fire protection
measures must be robust. An automatic fire suppression system will serve as active fire
protection by detecting fires and spraying an extinguishing agent such as carbon dioxide into
the hazard area. A secondary water sprinkler system will douse the fire in the event that theprimary suppression system fails. Fire protection walls and barriers will serve as passive fire
protection by separating the components of the switchyard to prevent fire from spreading.
There will be self-closing fire doors in the fire walls to eliminate the possibility of fire spreading
due to human negligence. A separation distance of 10-15m from trees or any vegetation will be
maintained to reduce the risk of damage from external fires. Gravel will be used to cover this
separation area to prevent weeds from growing. The main source of flammable material in a
switchyard will be the oil used for cooling the transformer and the resistors, to minimize therisk from these catching fire all the fuel sources shall be separated from each other.
Site Grading
For site grading we will perform a soil report of the proposed sites to test for stability,
shearing strength and sloping of the site. The site will be on higher ground and at a very slight
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grade to minimize the risk of water pooling around the site and allow for easy drainage of water
away from the site. In location one the proximity of the lake allows for drainage to be diverted
into the lake and avoid disturbing the environment.
There are two sites being considered for the ART25. Location one is close to the lake
and the terrain consists of lots of sand and loose rock. There does not appear to be good
foundation rock at location two. For location one, bedrock is near the surface providing for a
stable site. In addition, there is reasonable room for large scale helicopters and small air
transports to land. Of these two locations, location two is a better site to build the switchyard
on.
A surface water drainage system shall be provided to deal with run-off from the concrete pad
and buildings. The run-off will be diverted into the lake to prevent it affecting natural drainage
in the area . Oil interceptors shall be installed to protect the surface water from pollution by oil
leakage from switchyard equipment.
Environmental Impact
The Switchyard is composed of electrical equipment and wiring, and therefore does not
produce any air pollution. Grounding, lightning arrestors, and insulation will protect the
surrounding area from any power surges. Construction and maintenance will cause a minimal
impact on the environment since it is a relatively small system and the parts are easily
replaceable. Noise pollution from the transformers poses the biggest concern regarding the
environmental impact.
Review of Design Requirements
Below is a review of the design requirements as they are listed in the design requirements
document. The congruence of our design with each design requirement is analyzed.
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Functional Requirements
The Switchyard shall admit all electric power coming from the Main-OutputTransformer.
o The conceptual design admits power coming from the electrical generator. If themain-output transformer (IE some sort of isolation transformer installed on the
electrical generator to interface between the electrical generator itself and the
switchyard) is a device on the electrical generator then the conceptual design
produced meets this requirement.
The Switchyard shall transmit electric power to the power grid.o The conceptual design transmits electrical power to the power grid through the
power-grid side of the switchyard
The Switchyard shall be controllable from a control room.o All the instrumentation readings arrive at a central control room. All the control
signals are sent from the control room. In this way, the switchyard is
controllable from a control room.
The Switchyard shall contain the automatic switching mechanisms (such as fuses orcircuit breakers) that inter-connect the station and power grid.
o The CSMs placed at the external interfaces of the switchyard interconnect thestation to the power grid. This requirement has been met.
The Switchyard shall be able to supply electric power to the station in the event of anoutage.
o The emergency power redirection bus enables both grid power and backuppower be redirected to power both the three phase and single phase plant
power systems. If an outage does occur, this redirection bus provides electrical
power to the plant. This design requirement has been met.
Performance Requirements
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The Switchyard shall transmit 3 phase AC power to the grid, offset at 120 degrees tomaintain a consistent flow of power to the grid.
o The switchyard transmits the three phases generated by the electrical generatorto the power grid. This requirement has been met.
The Switchyard shall be backed by redundancy by utilizing extra lines and double busbar setups.
o The critical components in the switchyard have multiple conductors leading toand from them. In this way, this requirement has been met.
The Switchyard shall have a lifetime of at least that of the ART25.o Each of the individual components in the switchyard have a lifetime that is
greater than that of the ART25 reactor or are able to be easily replaced (such asthe CSM contacts) within the operational life of the switchyard. This
requirement has been met.
The switchyard shall be able to accept continuous 30MWe electric power (normaloperations output 25MWe).
o The switchyard is designed to continuously transmit 30MWe of electrical powerfrom the electrical generator to the grid. This is accomplished by using
components in parallel and series so that the power across each component is
within its operational parameters. This requirement has been met.
The Switchyard shall be able to continuously operate automatically. This impliespersonnel free operation under normal operating conditions.
o The digital control computers allow for hands-free operation of the switchyard.This requirement has been met.
Safety Requirements
The Switchyard shall be seismically qualified.
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further protected from extreme temperature conditions. This requirement has
been met.
The Switchyard shall be protected against direct lightning strikes.o The lighting arrestors, grounding of components, and ECBDs protect the system
against direct lightning strikes. Furthermore, the filter capacitor banks protect
the system from power transients with a time scale congruent with a lighting
strike. In this way, this requirement has been met.
The Switchyard shall have a grounding mechanism emplaced to deal with over-currenttransients and over-voltage transients.
o Over-current and Over-voltage transients are dealt with by isolating systemcomponents and sinking them to the resistor banks. Furthermore, theautotransformers can handle minor power transients. This requirement has
been met.
The Switchyard Shall be able to admit electric power to station service transformerfrom auxiliary backup generators if necessary.
o The emergency backup power redirect bus is able to redirect power from thebackup power service to the station power supplies. In this way, the essential
functionality of this requirement has been met.
The fence of the switchyard shall prevent intrusion from animals or humans.o The fence installed at the perimeter of the switchyard prevents unauthorized
intrusion by humans or animals. Without subversive measures, the only way
into the site is through the entrance gate. This requirement has been met.
The Switchyard shall be resistant to corrosion.o Corrosion resistance is provided by three measures. First, corrosion resistant
materials such as stainless steels are used wherever possible. Second, all bare
metal surfaces are painted to prevent any initial corrosive attack. Finally much
of the equipment is housed in weatherproof boxes that prevent the ingress of
water. This requirement has been met.
The Switchyard shall be well insulated to prevent arcing.
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o All the conductors in the switchyard are insulated, spatially separated, andshielded where possible. Where this insulation is not possible, and exclusion
cage is installed. This requirement has been met.
Client Requirements:
The Switchyard shall be constructed above ground.o The switchyard is constructed above ground, on a grade. This requirement has
been met.
The Switchyard shall transmit 25MWe to the power grid.o The switchyard is able to transmit 30 MWe to the power grid. Since 30 MWe is
greater than 25 MWe, this requirement has been met.
Reliability and Maintainability Requirements
The Switchyard shall undergo maintenance at least once per year.o The continuous inspection routine performs maintenance on any system
components if they drift too far off from their nominal operating values. The
once per year aspect of this requirement is unfounded. Nevertheless, the intent
of this requirement is met.
The Switchyard shall have voltage and current monitors to facilitate inspection.o The voltage and current measurement devices implemented in each system
component. The readings from these instruments are recorded in the control
room. Inspection personnel can be given access to these records to facilitate
their inspection routines. This requirement has been met.
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Cost Requirements
The Switchyard shall be financially reasonable.o No new technology needs to be developed for this switchyard. Standard, off-the-
shelf components can be used for many of the components. A priori, this
enables the switchyard to be financially reasonable. This requirement has been
met.
Environmental Requirements
The construction, maintenance and operations of the Switchyard shall not leave asignificant environmental footprint.
o There are no reaction chambers or effluent streams leaving the switchyard. Theonly environmental impact is that which is created by its construction and
production of replacement operating equipment. A priori, there is no significant
environmental impact. This requirement has been met.
The Switchyard shall not be loud during normal operations.o The switchyard has no large-scale motors or other devices that produces
elevated noise levels. There will be some hum due to the alternating magnetic
fields in the transformers, but this is hardly what one would consider loud. This
requirement has been met.
The insulation used in the Switchyard shall not create significant pollution problems.o Due to its lifespan, there is minimal atmospheric pollution created by the
degradation of the insulation. The insulation used in the switchyard can be
disposed of in a method that traps any leaching material. In this way, the
pollution created by the insulation is manageable. This requirement has been
met.
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Human Factor Requirements
The Switchyard must be easy to operate and easy to access for inspection.o The centralized control room and site layout provides easy control of the
switchyard and easy access for inspection. This requirement has been met.
The Switchyard is remotely operated from the control room and easy access is grantedfor routine inspections and maintenance.
o All control signals originate from the control room. The layout of the switchyardenables easy access. This requirement has been met.
Workers given access to the Switchyard shall be outfitted in safety gear duringoperations.
o Compliance with personal protective equipment policy is ensured at the gate tothe switchyard. This requirement has been met.
Workers shall wear insulated safety gear when working within the switchyard toprevent any shocks from the electrical systems.
o The regular safety patrols will ensure the personal protective equipment policy isfollowed by employees working in the switchyard. This requirement has been
met.
Layout Requirements
The switchyard must be placed between the Main Output Transformer and PowerGrid.
o The main output transformer (step-up transformer) is located within theswitchyard and has transmission lines to the grid. The intent of this requirement
has been met.
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Assumptions
Since all information on the other systems was not presented or given in design
documents it is necessary to make and state assumptions in order to do a proper analysis of the
switchyard system.
Turbine Generator Assumptions
While the ART25 Turbine Generator describes in detail what the turbines operating
conditions are the only given as 25MWe output at either 50 or 60Hz. For an electrical system
this knowledge is inadequate to design a switchyard around. The assumptions made are:
1) The turbine generates AC power.
2) The stator is divided into three equally sized regions at 120 to each other.
This will generate three phase power, as opposed to a single phase, which will
increase efficiency as one phase is always peaking.
3) The stators are connected in a wye configuration, as opposed to a delta configuration.
This will allow one phase to be disconnected without disconnecting the other
two phases. Delta configuration is also not regularly used in practise (Rizzoni, 2007).
4) The output potential of the turbine generator is a typical 18kV (Rizzoni, 2007).
Bibliography
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Dr. Glenn Harvel, Chief Engineer. (2013). Phase IIIa conceptual designs.Advanced Reactor
Technologies.
Electrical4u. (n.d.). Types and Operation of SF6 Circuit Breaker. Retrieved from
http://www.electrical4u.com/types-and-operation-of-sf6-circuit-breaker/
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Julia. (2010). Site Characteristics of Blue Valley Mineral Deposit.Advanced Reactor
Technologies.
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Pansini, A. J. (2005). Guide to Electrical Power Distribution Systems.CRC Press.
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