Chicago Secondary Network

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ChicagoSecondaryNetwork

• EE 455 Presentation
• Monday, October 14, 2002
• G. Hillesland

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An extensive complex electrical power network
that serves the heart of the city The Loop
providing the highest possible reliability
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Distribution Engineering EE455Topics covered so
far?One topic Transformer Connections on three
phase systems
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End of the line, before reaching customers
equipment.Forerunners are Transmission and
Generation.
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Function to deliver a quality product in
whatever amount customers require

• On 120 volt base - 120 volts at the meter
• Frequency of 60 Hertz
• Very high reliability

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Involves equipment to take energy from the
substation to the customer Cable
Conductors Primaries Secondaries,
Services Meters Transformers
Regulators Relays Fuses Capacitors
Insulators
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Involves a protection system, to minimize
interruption of service to customersFuses,
Circuit Breakers,Lightening Arresters
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System requirements Balanced 3 phase load
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Typical components in electrical service to a
residence
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Distribution transformer, connected to one phase
of a primary feeder 7.2/12.47 KV to 120/240
V Leg X1 120 V to midpoint Leg X2 120 V to
midpoint Neutral Midpoint connected to neutral
and (earth) ground.Typical sizes 10 KVA, 15, 25,
37½, 50, 75
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SecondaryConductors one or two spans either
direction from transformer
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Service Conductors from secondary
Customers service entrance Meter
Customers service panel
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Protection components, to minimize impact of
faults on customers Transformer Fuse Secondary
Breaker Customers Fuses
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Susceptibility to interruptions Primary feeder
wind, ice, autos Transformer lightening,
squirrels Secondary Service
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Service to the Chicago Loop
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Physical Characteristics Large buildings No
open spaces between Many customers in each
block All facilities must be underground Streets
and alleys all concrete
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Electrical Requirements 3 phase, 208 V for air
conditioning and ventilating, escalators and
elevators 120 volts for lights and
outlets Varying demands from 100 KW to 500
KW Uninterruptible service
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Electrical System Chosen 120/208 volt,
grounded WYE system Transformers in vaults
under sidewalks Primary 12 KV dedicated
feeders with paper insulated lead covered cable
in concrete conduit and manholes Secondary
Mains Large size insulated cable in duct runs
between vaults Services Large size insulated
cable in raceways or duct to customers switchgear
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Schematic Diagram of Secondary Network System
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Schematic Diagram of Secondary Network System
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Components of the network systemNetwork
transformers
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Transformer Primary Switch Secondary Protector
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Transformer Basic transformation 12 KV
120/208 compact, submersible 3 phase units,
250, 500, 750, 1000, 1500, 2000, 2500
KVA Liquid cooled cooling tubes/fins Askarel
/silicone Temperature indicator Liquid level
indicator Oil sample valve
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High Voltage Switch Compartment bolted to
transformer Contains a 3 position switch ?
Closed connects transformer leads to 12 KV
cable ? Open opens connection to 12 KV
leads ? Ground connects 12 KV phase leads to
ground ? Switch is non-load break but can
drop transformer charging current
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Secondary Protector Bolted to
transformer Connects to transformer
secondary leads and to secondary
mains Contains circuit breaker controlled
by relays
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Reverse Power Relay (Master Relay)Prevents
power from grid backfeeding into the transformer
and primary cablePhasing RelayPrevents closing
circuit breaker unless its unit has a leading
phase angle and higher voltage than bus, so when
closed, it will prick up load.Desensitizing
RelayTo prevent opening breaker under light load
conditions and elevator regeneration activity
circuit breaker interrupting rating
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Secondary Mains 500 MCM cable in conduit
under streets Between network street vaults
connections made in manholes in streets Cable
is insulated but no metallic sheath Spiraled
to reduce reactance (Quadraplex) Ring bus in
manholes Limiters installed where fault current
inadequate to burn off cable
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Services to Customers Tapped off secondary
mains Sized for customers load and to minimize
voltage drop Installed in service
conduit Connected to main conduit Limiters
installed if service is too large to burn
clear if faulted
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MetersCustomers Entrance Equipment
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Extent of 120/208 Voltage Network System Total
of approximately 600,000 KVA separated into
about 8 areas. Each area about 80,000
KVA Average vault capacity about 4000
KVA About 20 vaults in each area Served with
4 to 8 12 KV dedicated lines
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Designed for Double ContingencyMust carry load
for loss of two most critical components during
max load periods
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From 1936 to 1986 there had not been a network
area outage
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Spot Networks Advent of large, modern
buildings Much greater loads10,000 to 60,000
per building Too much for 120/208
network Advent of 12 KV distribution within the
building and 12 KV to 277/480 V vaults on site
with max 4-2500 KVA, 12 KV 277/480 volt Netwo
rks confined to each vault
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Source for Low Voltage Networks Original
street network 69 KV transmission system
serving several 69/12 KV substations Undergrou
nd cable in conduit Substations in large
buildings
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69 KV system fed from 138 KV systemJefferson TSS
138 KV to 69 KV 800,000 KVA
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The electrical supply system to Downtown Chicago