operating_reactive_and_black_start_reserves.pdf

7/31/2019 operating_reactive_and_black_start_reserves.pdf

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OPERATING, REACTIVE

AND BLACK STARTRESERVES

Asko Vuorinen


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Operating reserves


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Purpose of operatingreserves

Ensure power supply duringdisturbances and unnormal conditions


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Classification of operatingreserves

Spinning reserves Synchronised reserves

Non-spinning reserve

Unsynchronised reserves Supplemental reserves

30 60 minute reserves

Slow reserves 1 12 hours reserves


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Spinning reserves

Operating power plants which canchange their output by P in t

Called as ten minute spinning

reserves in USA (t =10 min)


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Spinning reserveGeneration

By internal combustion engine or gasturbine plants

Can change their output from 40 % to100 % in ten minutes


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Spinning reservesContinued

Spinning reserves = rotating reservesact immetiately by the rotating massof the generator

If the frequency starts dropping, thegenertor intertia tends to resist the

slowing down motion


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Non-spinning reserves

Power plants, which can start up in tminutes to full output P

Called as ten minute non-spinning

reserves in USA (t= 10 min) Called as fast reserves in UK (t = 5

min) and Nordel (t = 10 min)


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Non-spinning reserves,full power in

1 - 5 minutes Diesel engines and

hydro turbines

5 - 10 minutes Gas engines and

aero-derivative GT

10 - 15 minutes Industrial gasturbines

60 - 120 minutes Gast turbinecombined cycles

2 - 12 hours Steam turbineplants


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Dimensioning of spining andnon-spinning reserves

Spin reserve + nonspin reserve > Lc

Spinning and non-spinning reserves shallcompensate the largest contingency (Lc) ina system

Or 5 -7 % of load responsibility (California)


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Supplemental reserves

Shall compensate loss of secondlargest contingency

Dimensioning criteria P > x second contingency


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Supplemental reserves

Thirty minute reserves New England, New York

x second contingency loss

Sixty minute reserves

California

x second contigency loss


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Slow reservesPurpose

Shall generate power during unnomalpeak load conditions


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Slow reserves, continued

Used in Nordel countries, which haveno capacity oblications (t = 1 - 12 h)and very high winter peak load

2000 MW (7 % of peak load) in Sweden

600 MW (4 % of peak load) in Finland


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Reactive reserves


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Purpose of reactive reserves

Compensate reactive losses in thetransmission network

Generate reactive power to electrical

motors and other consumers


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Single line diagram of apower line

Ua, Ub = voltages in the power line

X = reactive load of power line

C = capacitance


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Near maximum load

Ua

Ub

P = --------- sin

X

Ua Ub Ub2Q = P tan = -------- cos - ------

X X


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Maximum capacity of powerline (=stability limit)

If = 90o

, sin = 1

Then P = Pmax

Stability limit is reached


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Reactive power generation

G

GeneratorExcitationgenerator

G

AVR


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Reactive power generation,continued

Generator voltage control system(AVR) increases excitation current inrotor

Generator voltage will rise andreactive power will be generated


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Reactive power generation


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Reactive reserve generation

A Generator stability lineB Maximum mechanical output of

engine

C Maximum current of generatorE Mimimum continuous mechanical

output of engine


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Apparent power (S)

S = (P2 + Q2)where

P = resistive power (MW)

Q = reactive power (MVar)

Determines the capacity of a generator in MVA


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Recommendations

Build power plants near consumpioncenters to avoid consumption ofreactive reserves

Local power plants can generate thereactive power consumed by theappliances


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Black start reserves


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Black start reservesPurpose

To energize power system afterblackout

To generate power for local needs

when the power system is out ofoperation


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Black start reservesEnergize power lines

X

C/2C/2

Ua Ub

G

Black start generator (G) will energize power line

after the switch has been closed

Capacitors (C/2) will consume the most of the current


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Restoration approach

Bottom up Start local generators first and

energize local power lines

Top down

Use power lines to energize local

generators


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Starting of emergencymotors

Induction motors consume reactive power(Xm) at the starting phase.

Starting current is typically 5 6 x In


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Black start generators

Small diesel engines

Started by batteries

Large diesel or gas engines Started using pressurised air

Gas turbines Started by diesel engines


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For details see reference text book

Planning of Optimal Power Systems

www.optimalpowersystems.com

Author:

Asko Vuorinen

Publisher:

Ekoenergo Oy

Printed:

2007 in Finland

Further details and

internet orders see:

operating_reactive_and_black_start_reserves.pdf

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