Power Transfers on the Bulk Power System

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Session 3.

• Power Transfers on the Bulk Power System

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Dave Barry, Bad Habits

• The electric company sends electricity through a
  wire to a customer, then immediately gets the
  electricity back through another wire, then (this
  is the brilliant part) sends it right back to the
  customer again.

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Criteria

• The standards by which an electric system is
  planned and operated
• Transmission Security getting power from one
  point on the grid to another without overloading
  the lines or causing system separations and
  blackouts
• How much power can you transfer from A to B

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Criteria (cont.)

• Transmission Transfer Capability (TTC)
• The maximum flow possible at which the
  limiting facility reaches its appropriate
  rating, either
• without a contingency, or
• following the worst single contingency

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• Blackouts in Mirror
• are Closer
• than they Appear

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Gallia est omnis divisa in partes tres. . . .

• Distribution about 90 of outage MW-hr.
• your house, your neighborhood
• Generation what everybody thinks of when they
  hear the word reliability.
• brownouts, price spikes
• Transmission several orders of magnitude more
  complicated.
• blackouts, often covering large areas

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All Gaul is divided into three parts. . . .

• Distribution
• n1 or in some cases n2 (e.g., Con Ed area
  subs.)
• Performance indices
• Generation
• One day in ten years
• LOLE Installed Reserve Margin (IRM)
• Transmission
• n1 criteria tho sometimes means gt1 element
• Since 1965, Regional Reliability Councils
• Voluntary compliance? mandatory in NPCC incl.
  NY
• Trend toward weaker criteria
• Trend toward uniform national criteria (LCD??)

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Who Should HaveResponsibility/Authority?

• Local level (individual systems, Control Areas)
• State/ISO/RTO etc. (NY NYSRC, NYISO)
• Regional level (RRCs/RROs)
• National level (U.S. Canada) NERC/NAERO
• All of the above!

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Costs of Outages

• Injury/loss of life due to accidents (e.g., no
  traffic lights)
• Injury/loss of life, ill and elderly
• Loss of productivity by industry
• Loss of sales by business
• Loss of wages of labor
• Damage to equipment in industry
• Fires and explosions
• Riots and thefts
• Increased insurance rates
• Higher fees for consulting engineers.

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Consumer Reaction R

• R is a function of F, T, P, t
• where F frequency
• T duration
• P amount of load interrupted
• t time when it occurs

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Top Excuses for a Blackout

• A tree did it July 2, 1996 Western U.S., 2003
  Midwest/Northeast, 2003 Italy, etc.
• Birnam Wood to Dunsinane
• 2. It was an act of God Con Ed CEO
  following July 13-14, 1977 New York City blackout
• 1. A UFO drained power from an Upstate New York
  power line November 9, 1965 Northeast Blackout
• SPECIAL AWARD
• Everything you heard on TV Aug. 14-15, 2003

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Transmission Transfer Capability

• Concept system will be intact
• 1) without a contingency
• 2) following the worst single contingency
• Philosophy
• All in condition pre-disturbance
• Worst single contingency or n -1"
• Single element
• Multiple elements from a common contingency
• Extreme contingencies

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(No Transcript)
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Should Standards (Criteria) be Uniform?

• Same in Albuquerque as Manhattan?
• Same in New Mexico as New York?
• Consequences of a blackout
• 20 story buildings
• But what about the transmission user?

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Uniform Standards/Criteria Example
Interface with 2 345 kV, 1 230 kV, 2 115
kV The 345 kV circuits are on the same towers
i.e., its a double circuit line A-1
--------------------------------------------------
345 X X X X
X A-2 -----------------------------------------
--------- 345 B ----------------------------
---------------------- 230 C
--------------------------------------------------
--------------------- 115 D
--------------------------------------------------
--------------------- 115
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Uniform Standards/Criteria
Interface limit (TTC) based on L/O A-1 2500
MW L/O A-2 2500 MW L/O A-1 and A-2 1800
MW Lower TTC if use L/O both lines on a double
circuit tower as a contingency But, all the user
needs to know is the TTC
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Parallel Path Flow Constraints

• An interconnection is a single large machine
• Every power transaction affects every line
• Every contingency (L/O of line, L/O generator,
  etc.) affects every line
• What you do will affect your neighbors
• What your neighbors do will affect you
• Golden Rule Do onto others as you would have
  done onto yourself or, Dont do onto others
  anything worse than they can do to themselves

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Transmission Constraints

• Thermal Capability -- conductors overheat
• Voltage -- VARs
• Stability -- system dynamics / machine angles
• WHO DEVELOPS, MONITORS COMPLIANCE, etc.?
• NERC
• Regional Reliability Councils
• ISOs/RTOs Other reliability entities
• Control Areas

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Increasing Transmission Capability

• Add new line(s) ---------- duh. . . .
• note these may be in some other system
• Cases where something other than conductor rating
  is limiting fix it !
• Reconductor existing line(s)
• Add series capacitors to lines not loading up
• Add series reactors to lines loading up too much
• note not good if voltage or stability is
  limiting

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Increasing Transmission Capability (cont.)

• If voltage is limiting, put in VAR source(s)
• If stability is limiting, look into power system
  stabilizers, generator control systems, etc.
• Add phase angle regulator(s) or FACTS
  device(s)
• Use sophisticated relay scheme e.g. Special
  Protection Systems (SPSs)
• Add HVDC link (in parallel with existing AC
  system)

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Special Protection Systems

• Special Protection Systems (SPSs)
• Require no intervention on the part of system
  operators for their operation.
• Designed to do more than the simple removal from
  the system of a faulted element e.g., tripping
  lines, generators or other elements many miles
  removed from the point of disturbance. But
• Potential problem unintended consequences,
  mutual effects especially if large number.

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FACTS

• FACTS (Flexible A C Transmission System)
• Largely experimental devices which promise near
  instantaneous control of steady state power flow,
  or system response in a dynamic situation.
• Many believe FACTS technology will permit
  increased power transfer capabilities, without
  having to construct new lines, by allowing
  optimization of flow distribution. But
• Potential problems similar to those of SPSs.
• How are you, Joe Friday?

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Doctor, it hurts when I do this
Henny Youngman

• ALL OF THE ABOVE REQUIRE EXTENSIVE STUDY !!!
• Whatever you do, dont do this
• Lower the criteria

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Things to Remember

• Limiting contingency not always on interface
• Limiting facility not always on interface
• Limiting interface not always on seam
• TTL in one direction not same in other
• Assumed base conditions very important
• Location of sources sinks very important
• Failure to observe TTLs will be dangerous to your
  health i.e., blackouts in mirror may be closer
  than they appear

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OASIS(Open Access Same-time Information System)

• Internet based system for the display of
  available transfer capabilities on transmission
  interfaces
• Total Transfer Capability (TTC)
• Maximum allowable transfer across an interface
• Note TTC is consistent with older FCTTC
• Available Transfer Capability (ATC)
• Transfer capability remaining after commercial
  activity already committed is subtracted
• Two other amounts may also be subtracted
• Transmission Reliability Margin (TRM)
• Capacity Benefit Margin (CBM)

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Congestion orThe Trouble with Tribbles

• Congestion no such thing
• Another term were stuck with like loop flow
• MORE POWER WANTS TO GET ACROSS AN INTERFACE (OR
  FLOWGATE) THAN ITS TTC
• or
• NORMAL SCHEDULING RESULTS, OR WILL RESULT, IN A
  CONDITION UNDER WHICH THE TTC WILL BE EXCEEDED

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Congestion

• The Physics
• Calculated transfer limits based on criteria
• Congestion occurs when sum of desired
  transactions over an interface exceeds the
  transfer limit
• Competition among potential transmission users
  for the (always) finite capability of the system
• Expressed as total power flow on identified
  groups of transmission lines known as interfaces
  or flowgates

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Congestion (cont.)

• All potential solutions boil down to one of the
  following
• curtail transactions
• reschedule generation
• allow auctions or reselling at profit
• But, these are physically the exact same thing!
• The difference is not where there is, but how
  you get there
• e.g., NERCs TLR (Transmission Loading Relief)

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Curtailment Redispatch are the Same (in terms
of the Physics)

• You get to the same place, but by different
  institutional procedural routes
• In both cases, as well as in any others likely to
  be proposed, youre reducing generation in one
  area, increasing it in another
• Note the only way you can control the
  transmission system is by controlling the
  generation or load

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• I canna change the Laws of Physics, Captain
  Kirk!
• Lt. Commander Montgomery Scott (Scotty), aka
  James Doohan, Star Trek