load shedding philosophy ppt

8/11/2019 Load Shedding Philosophy Ppt

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LOAD SHEDDING

PHILOSOPHYPRESENTED BY BRIJESH SINGH

BHADAURIA


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WHY LOAD SHEDDING

In general, load shedding can be defined as theamount of load that must almost instantly beremoved from a power system to keep theremaining portion of the system operational. This

load reduction is in response to a systemdisturbance (and consequent possible additionaldisturbances) that results in a generationdeficiency condition. Common disturbances thatcan cause this condition to occur include faults,

loss of generation, switching errors, lightningstrikes, etc. Let us discuss how these transientseffects-


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TYPES OF TRANSIENTS

1. Surge Phenomena- ( extremely fast transients)

This type of transient is caused by lightning (

atmospheric discharge on overhead transmission

line ) and switching. Physically , such a transientinitiates an electromagnetic wave traveling with

almost the speed of light on transmission lines .


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TYPES OF TRANSIENT CONTD.

2. Short circuit phenomena- more then 50 % of the

short circuit takes place on exposed overhead lines

owing to the insulation failure resulting from the

over voltage surge , birds , unsymmetrical faultsetc The occurrence of the symmetrical faults

brings the power transfer across the line to zero

immediately whereas the impact is partial in case

of unsymmetrical faults


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TYPES OF TRANSIENT CONTD.

3. Transient stability

Whenever a short circuittakes place at any part of the integrated system ,there is an instantaneous total of partial collapse ofthe bus voltage of the system . This also results in

the reduction of generator power output .Since ininitially the for some time delay before thecontroller can initiate the corrective action , eachgenerator is subjected to positive acceleratingtorque. This condition if sustained for a long time ,

can result in in the most severe type of transientnamely mechanical oscillation of the synchronousmacnine.


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GTG GOVERNING LOOPS

When a power system is exposed to a disturbance,its dynamics and transient responses are mainlycontrolled through two major dynamic loops. Oneis the excitation (including AVR) loop that willcontrol the generator reactive power and systemvoltage. Another is the prime-mover loop, whichwill control the generator active power and systemfrequency. A brief discussion of these two

dynamic loops is given below


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LOOP DISCUSSION CONTD.

1.Excitation / GeneratorReactive Power

Voltage- During a fault condition, one of the direct

effects of a fault current is the drainage of reactive

power from the system. This reactive power isessential for the transfer of mechanical energy to

electrical energy (and vice versa) in the rotating

machines (generators and motors).


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LOOP DISCUSSION CONTD.

2. Prime Mover / Generator

Real Power

Frequency- Turbine governors and the type of

prime movers also have a dramatic impact on theperformance of the power system during major

disturbances. The frequency conditions of theoverall system directly depend on the amount ofreal power that the generator prime movers candeliver to the system. Also, the mechanical energyavailable to help the generators prime mover ride

through a fault or other disturbances plays animportant role on the system behavior.


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DEFINITION OF LOAD SHEDDING

Introductionthe ability of the power system tocontinue, albeit on reduced levels , after loss ofgeneration is an important consideration in thedesign of any load shedding scheme . for this

purpose under frequency load shedding schemehas been adopted . the basic criteria adopted forthe under frequency load shedding studies asconsidered in this report are based on the

following fact that the


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OBJECTIVE BEHING LOAD

SHEDDING

Amount of load selected to be shed at each stage

should in principle restore frequency to itsnominal value within ten seconds of the

maximum deviation .


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WAYS TO ACHIEVE LOAD SHEDDING

1.Breaker Interlock Scheme - A source breakerwould be interlocked via hardwired or remotesignals to a set of load breakers that have been

pre-selected to trip. When a generator breaker or a

grid connection is lost for any reason, signals areautomatically sent to load breakers to open. Thissystem is very fast since there is no processingrequired and all decisions about the amount ofload to be shed were made long before the fault

occurred.


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DISADVANTAGE WITH BREAKER

INTERLOCK SCHEME

1.Difficult to change load priority since the actions for loadshedding are hardwired and amount of load shedding iscalculated for the worst-case scenario.

2.Only one stage of load shedding is available.

3.More loads are shed than necessary.4.The operation of this type of load shedding system willmost likely shut the entire industrial facility down in a non-orderly way. This unplanned outage may result in

processing equipment damage, reduced equipmentlifetime, or worse.

5.Plant restarting may be delayed because of the requirementto shut down and then restart other remote facilities thathave been affected by the loss of the main facility, beforethe main facility can be started


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Under Frequency Relay Scheme

Frequency relay sense the fault or deficiency in

generation by way of frequency . They detect

either a rapid change in frequency or gradual

frequency deterioration and initiate stagedoperation of interlocked breakers. It works in

stages i.e. it checks for underfrequency and sets

the stage for tripping after certain time dalay.


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PLC BASED LOAD SHEDDING

With a common type of PLC-based load sheddingscheme, load shedding is initiated based on the systemfrequency deviations and/or other triggers. The circuit

breaker tripping can be programmed based on thesystem loading, available generation, and otherspecific logics. Each subsystem is equipped with aPLC that is programmed to shed a preset sequence of

loads. This static sequence is continued until thefrequency returns to a normal condition.


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OUR PLANT GENERATION VS DEMAND

SCENARIO

Following are the possible plant generation and load conditions

Case 1 : 5 GTG operating in parallel with the grid and grid trips

Case 2 : 4 GTG operating in parallel with the grid and grid trips

Case 3 : 3 GTG operating in parallel with the grid and grid trips.

Case 4 : 2 GTG operating in parallel with the grid and grid trips. Case 5 : 1 GTG operating in parallel with the grid and grid trips

Case 6 : 5 GTG operating in parallel and one GTG trips.





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PLANT LOAD PROFILE

Plant load profile for the purpose of load shedding

is considered to be as per attachment 1 , wherein

total plant load for 120% send out operating

condition is indicated. C:\Documents and

Settings\bbhadauria\Desktop\Attachment1-2.xls
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LNG VAPORIZER SOURCES

For vaporization following sources are available

4 SCV where 2 SCV in hot water mode ( hot water generated bycogeneration in GTG) and 2 SCV totally in burner backup.

14 STV

1 STV with Cogeneration heat recovery mode


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HOW TO SELECT THE PRIORITY OF

VAPORIZER

SCV/STV in service are selected according to the followingpriority based on minimizing of the running cost.

1.STV with cogeneration heat recovery mode.

2.STV3.One SCV in hot water mode

4.One SCV in combined mode.

5.Additional SCV in burner mode.

Whether to switch on all the above sources or switch onsome of the sources will depend upon the send out raterequired.


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LOAD SHEDDING OPERATION:

Power available under various operating conditions ofGTG and grid is tabulated in attachment II .Loadshedding requirements is described in remarks columnof the above attachments.

For all cases wherein GTG are operating in parallelwith grid and GTG trips , the GTG load will beautomatically transferred to the grid for the shortduration of approx 5 minutes . During this time

manual adjustment will be done from the DCS to limitthe import from the grid . C:\Documents andSettings\bbhadauria\Desktop\Attachment 6.xls
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FREQUENCY PROFILE STUDY

The computer program ETAP power station (electrical transient analyzer program) version 5.5.5 cdeveloped by operation technology inc. USA has beenutilized to carry out the frequency profile study .Frequency profile study has been carried out for eachcase except for case I and VI wherein in either case ofGTG / grid tripping no load shedding is envisaged .Result of the same are enclosed herewith attachmentIII. Attachment

Load shedding operation shall take place within 300ms from the instant of loss of the generationconsidering relay operating time , circuit breakeroperation time and PLC operating time .


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LOAD SHEDDING PRINCIPLES

For load shedding purpose ABB make SPAF 340 Crelay has been utilized. This relay has four differentfrequency stages with individual rate of change offrequency feature (df/dt).

For various cases described in Attachment 2, GTG

overload is sensed by frequency relay. The loadshedding command will be issued to dedicatedredundant PLC. Tripping command will be issued bydedicated redundant PLC to trip the pre-assigned loads.

It is envisaged to utilize two stage frequency protectionalong with df/dt feature to carry out the load sheddingoperation.


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For first two stages frequency setting with individual df/dtsetting shall be used.

For Third stage only frequency setting shall be used.

If frequency does not restore even after operation of Stage1&2, then third frequency stage shall operate trippingfurther additional load. (Block A) \Frequency relay settingexc.doc
http://localhost/var/www/apps/conversion/tmp/Frequency%20relay%20setting%20exc.dochttp://localhost/var/www/apps/conversion/tmp/Frequency%20relay%20setting%20exc.dochttp://localhost/var/www/apps/conversion/tmp/Frequency%20relay%20setting%20exc.dochttp://localhost/var/www/apps/conversion/tmp/Frequency%20relay%20setting%20exc.dochttp://localhost/var/www/apps/conversion/tmp/Frequency%20relay%20setting%20exc.doc


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Load blocks

Depending upon the power deficit in case of grid / GTGtripping following load shedding blocks have beenconsidered

For Power Deficit up to 2 MW

Block A

Trip 1 No HP Pump.

Trip 2 Nos. Air heater banks.


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Load blocks contd.


Block B

Trip 2 Nos HP Pumps. Trip 2 Nos.Intank pumps.

Trip 2 Nos air heater banks

This block has presently not been utilized for load shedding.


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Load blocks contd.


Block C

Trip 3 Nos.HP Pumps. Trip 2 Nos Intank pumps.

Trip 3 Nos. Air heater banks


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Load blocks contd

Block D

- Trip 1 No HP Pump

- Trip 1 No. Intank Pump.

- Trip 12 Nos GW Pumps

- Trip 1 no. Hot Water Pump

- Trip 1 No. BOG compressor.

- Trip 7 Nos. Air heater banks.


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Flow chart of load shedding

C:\Documents and

Settings\bbhadauria\Desktop\Attachment-5.doc
http://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.dochttp://c/Documents%20and%20Settings/bbhadauria/Desktop/Attachment-5.doc


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SCHEME FOR AIR HEATER PHASE 1 , GROUP RUN SIGNAL TO AIR HEATER TO

BE TAKEN FROM DCS TO LOAD SHEDDING PLC , GROUP TRIP COMMAND TO

AIR HEATER VIA DCS


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SCHEME FOR AIR HEATER BANK II , RUN SIGNAL TO BE CONNECTED TO LOAD

SHEDDING PLC AND THE SAME TO BE SEND TO DCS VIA SERIAL LINK , LOAD

SHEDDING TRIP COMMAND TO BE HARD WIRED DIRECTLY TO LOAD

SHEDDDING PLC


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SCHEME FOR HP /INTANK PUMP


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SCHEME FOR BOG AND SCV


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ILS and its advantage over under

frequency shedding

I can draw the drawing of phase 1 and 2 load

shedding