Session 2 Synchronous Interconnections or Grids 1 Woody

Session 2. Synchronous Interconnections (or “Grids”) 1

Woody Allen “I took a speed-reading course and was able to read War and Peace in 20 minutes. It’s about Russia. ” 2

What is a “Grid”? Battle of the Currents (late 1800 s) DC (Edison) vs. AC (Westinghouse) • • • The concept of economy exchanges The concept of load diversity The concept of emergency assistance The concept of reserve sharing The concept of INTERCONNECTION 3

Grid = “Synchronous Interconnection” • System or group of systems all of which are connected together with AC lines. Anything that happens anywhere is felt everywhere else. Sometimes called being “in synchronism” – whence the expression, “in synch. ” (Are you listening, Justin Timberlake? ) • An “interconnection” is a single large machine. • Sort of like “The Borg” (but no “Seven of Nine”). 4

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Loehr’s Second Law • Power flows in an interconnection … – Via all paths – Inversely proportional to impedance • All lines will be affected by every power transaction or contingency The effect of a transaction over one portion of the interconnection on other portions is often called “Parallel Path Flow. ” 7

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Four “Interconnections” (“Grids”) in North America • Synchronous interconnection: a single large machine. Everything’s connected with AC. • What happens here affects there. • • Eastern Interconnection Western Interconnection ERCOT (Texas) Hydro-Quebec 580, 000 MW 140, 000 MW 60, 000 MW 30, 000 MW 9

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North American Interconnections 11

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Eastern Interconnection • • • 101 Control Areas Tightly coupled Disturbances propagate Today’s system highly stressed Failures beyond criteria likely to result in widespread outages 13

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Control Area Major Responsibilities • Tie Line Control Make certain that actual net interchange matches schedule – minimize “Area Control Error” (ACE) – typically every 6 sec. • Frequency Contribute toward maintaining exact 60 Hz freq. (Participation factors developed by NERC OC) • Time Error Correction Contribute toward corrections in clock time error caused by accumulated deviations from 60 Hz (In Eastern Interconnection, when gets to 2 sec. ) 15

Control Area Major Responsibilities All of above done by specified generating units placed on “Automatic Generator Control” (AGC) ALSO • Usually responsible for monitoring key interface flows compared to the established Transmission Transfer Capabilities, and monitoring conformance with reliability criteria in general • Often responsible for dispatching the outputs of individual generators within the Control Area (“economic dispatch” in old world order) 16

Control Areas Asynchronous ties – HVDC, isolated generation or load HQ/TE Ontario MARITIMES NEW ENGLAND NEW YORK ECAR Areas PJM 17

US/Canada Control Areas 18

Control Area Size • PJM, NYISO and ISO-NE represent 20% of the load in the U. S. portion of the Eastern Interconnection but have only 3 control areas; the other 80% have 91 control areas • Average control area sizes, by region, Eastern Interconnection/U. S. (based on forecast peak load 2001): • • • ECAR 5, 993 MW FRCC 3, 359 MW MAAC 51, 762 MW MAIN 3, 663 MW MAPP/US 2, 161 MW NPCC/US 27, 055 MW SERC 9, 037 MW SPP 2, 308 MW. . . . . . Eastern Interconnection/U. S. 5, 474 MW 19

How Many? • Some ISO/RTOs are single Control Areas – NY, NE, PJM • Others aren’t – key issue: giving up control • Eastern Interconnection has 100+ Control Areas • Western Interconnection has about 30 • ERCOT and Hydro-Quebec Interconnections each have 1 Control Area • WHAT’S THE RIGHT NUMBER? • My opinion: reduce number in Eastern & Western Interconnections • Maximum 15 -20, each interconnection 20

Why Not Just One? (Quebec, ERCOT) • “Centralization” can get to be too much of a good thing in a large interconnection can’t keep track of everything knowledge of local conditions conformance monitoring • best to proceed in smaller, evolutionary steps 21

The Importance of Being Earnest System Operator of the Control Area • know all schedules & all changes, monitor all interfaces, assure TTCs not violated • authority to order changes in schedules & generation • authority to take any action necessary in an emergency, including tripping generation or disconnecting firm load • exchange data with other Control Areas • Both judge and jury • Military authority in emergencies 22

NYCA Major Emergency April 17, 2005 • L/O Millstone #3 in NE at 1165 MW • NY Central-East voltage collapse limit exceeded • NYISO declared major emergency @ 8: 32 • Terminated @ 8: 35 • Duration = 3 min. • Compare/contrast with transcripts of conversations from Midwest during the Aug. 14, 2003 incident 23

10 Regional Reliability Councils 24

Reliability Regions NPCC ECAR MAAC 25

Power Pools, ISOs & RTOs Traditional Power Pools • Single control area, centralized dispatch, transmission monitoring • PJM, New York Power Pool, New England Power Pool ISOs & RTOs – FERC 2000 • Open transmission system to all comers on a fair and non-discriminatory basis • Form independent associations to manage the transmission system 26

SOME MODELS OF THE ELECTRIC GRID AND WHY THEY’RE WRONG TELEPHONE SYSTEM • The telephone system is not “on” all the time. In fact, when you make a call, only you and the other party are connected. • The electric system, however, is all on all the time. You are connected to every generator and every other customer on the interconnection – every minute of every day. 27

Models … Wrong (cont. ) GAS OR WATER PIPELINE • The electric system is several orders of magnitude more complicated than even the most complex gas or water systems. A gas or water pipeline (transmission) system is essentially point-to-point; an electric transmission system is essentially a network. • You can’t make the power flow down certain lines and not others by opening and closing valves. 28

Models … Wrong (cont. ) RAILROAD OR HIGHWAY • You can’t direct the power down this line rather than that one like a train or truck on a railroad or highway – or make the power stop like a train or truck. • It takes several days or more for a train or truck to cross the country; it takes electricity less than a tenth of a second. 29

Models … Wrong (cont. ) THE POWER LAKE “The lake is an enormous reservoir from which you can draw a lot of water before you have to add some or run out. ” • Electricity cannot be stored; you have to generate it exactly as you use it. • There are no constraints to water going from one end of the lake to the other. But there are major constraints on the electric network. 30

RELIABILITY CRITERIA (a. k. a. “STANDARDS”) CRITERIA: The standards by which an electric system is planned and operated. • Generation Adequacy -- having enough generation to meet the load • Transmission Security -- getting power from one point on the grid to another without overloading the lines or causing system separations and blackouts • National? Regional? Local? Yes!! Bill Richardson after 2003 Blackout: “The power industry has never had reliability standards. ” Horsefeathers!!! 31

PROBABILISTIC VS. DETERMINISTIC CRITERIA Generation Adequacy • Probabilistic • “One day in ten years” Transmission Security • Deterministic • Experiments with probabilistic for over 30 yrs. • Problem: a x b where: – # of things that can happen (a) approaches infinity – prob. of one thing happening (b) approaches zero 32

Contingencies • A “contingency” is a sudden disturbance to the power system • Before the contingency: Steady state condition, often referred to as “base load flow, ” “pre-contingency” or “zero minus” condition 33

TYPICAL TRANSMISSION CRITERIA (PLANNING & OPERATIONS) • three-phase fault on any transmission circuit, transformer or bus section, with unsuccessful reclosure • loss of any generating unit, with or without a fault • double-line-to-ground fault on any two adjacent circuits of a multiple circuit transmission line • line-to-ground-fault on any transmission circuit, transformer or bus section, with a stuck breaker • Loss of both poles of an HVDC line No overloads, low voltages, instability, loss of customer load 34

EXTREME CONTINGENCIES • loss of all lines on a right-of-way • loss of all units at a generating station • loss of all lines emanating from a switching station or substation • three-phase fault on any element with a stuck breaker Test of system strength Reasonable measures should be taken to minimize consequences Moderate loss of load permitted 35

After a Contingency Occurs Loss of a line or other transmission element (without a fault): • Sudden change in configuration of the network • Generator power angles oscillate • Line flows (MWs & MVARs) oscillate • Voltages oscillate • After some seconds, things settle down into a new “postcontingency” or “post disturbance” steady state condition (if it’s stable, of course!) • But, usually with the differences in generator power angles a little larger, line flows a little (or a lot) higher, and voltages a little lower 36

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After a Contingency Occurs (cont. ) Loss of a generating unit (without a fault): • System load now greater than generation; frequency declines; all generators connected to the interconnection increase their MW outputs roughly proportional to their capacities – they are converting the potential energy of their rapidly spinning rotors to kinetic energy • This increased MW generation flows into the area where the generating unit was lost • After some seconds, things settle down into a new “postcontingency” or “post disturbance” steady state condition (if it’s stable, of course!) • But, usually with the differences in generator power angles a little larger, line flows a little (or a lot) higher, and voltages a little lower 38

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After a Contingency Occurs (cont. ) • At the same time, automatic equipment on generating units begin to open valves etc. to allow more fuel flow • “Spinning reserves” will be brought up, too, to restore net interchange to its scheduled amount These last two actions will tend to restore system frequency to 60 Hz If an electrical fault occurs with L/O either line or gen. : • Load in the vicinity of the fault will be much reduced, tending to accelerate the generators and cause greater oscillations • A contingency with a fault is not always more severe and less stable than one without a fault 40

After a Contingency Occurs … We’re Not in Kansas Anymore! • After a contingency, system is in a new “state” • New line/impedance or generation matrix • Have to reconfigure the system to prepare for possibility on next contingency • Double-contingency design? No!!! • Once that first element is out, you’re at a new “zero minus, ” or base condition 41

Albert Einstein “Since the mathematicians got hold of the Theory of Relativity, even I don’t understand it. ” 42