Chicago Secondary Network

1. ChicagoSecondaryNetwork EE 455 Presentation Monday, October 14, 2002 G. Hillesland

2. An extensive complex electrical power network that serves the heart of the city ~ The Loop ~ providing the highest possible reliability

3. Distribution Engineering EE455Topics covered so far?One topic �Transformer Connections� on three phase systems

4. End of the line, before reaching customers equipment.Forerunners are Transmission and Generation.

5. 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

6. Involves equipment to take energy from the substation to the customer� Cable & Conductors;� Primaries & Secondaries, � Services & Meters; � Transformers & Regulators; � Relays & Fuses; � Capacitors & Insulators

7. Involves a protection system, to minimize interruption of service to customersFuses, Circuit Breakers,Lightening Arresters

8. System requirements � Balanced 3 phase load

9. Typical components in electrical service to a residence

10. 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, 37�, 50, 75

11. SecondaryConductors one or two spans either direction from transformer

12. Service� Conductors from secondary� Customers service entrance � Meter� Customers service panel

13. Protection components, to minimize impact of faults on customers Transformer Fuse Secondary Breaker Customers Fuses

14. Susceptibility to interruptions Primary feeder � wind, ice, autos Transformer � lightening, squirrels Secondary Service

15. Service to the Chicago Loop

16. Physical Characteristics Large buildings No open spaces between Many customers in each block All facilities must be underground Streets and alleys all concrete

17. 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

18. 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

19. Schematic Diagram of Secondary Network System

20. Schematic Diagram of Secondary Network System

21. Components of the network systemNetwork transformers

22. Transformer Primary Switch Secondary Protector

23. 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

24. 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

25. Secondary Protector� Bolted to transformer� Connects to transformer secondary leads and to secondary mains� Contains circuit breaker controlled by relays

26. 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

27. 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

28. 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

29. MetersCustomers Entrance Equipment

30. 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

31. Designed for Double ContingencyMust carry load for loss of two most critical components during max load periods

32. From 1936 to 1986 there had not been a network area outage

33. Spot Networks� Advent of large, modern buildings� Much greater loads�10,000 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� Networks confined to each vault

34. Source for Low Voltage Networks� Original street network� 69 KV transmission system serving several  69/12 KV substations� Underground cable in conduit� Substations in large buildings

35. 69 KV system fed from 138 KV systemJefferson TSS � 138 KV to 69 KV 800,000 KVA

36. The electrical supply system to Downtown Chicago