ABSTRACT This paper describes the Power Demand Control System installed at the Lufkin Mill of

Transcription

1 ESL-E A POWER CONTROL SYSTEM FOR A PAPER MLL George H. Rchter Delbert Keenon St. Regs Paper Company - Houston, Texas Automaton, nc. - Houston, Texas ABSTRACT Ths paper descrbes the Power Demand Control System nstalled at the Lufkn Mll of Southland Dvson, St. Regs Paper Company. The system s based around a mcroprocessor unt that automcally changes the output of the generators to mantan a constant power load from the utlty company. NDRODUCTON Up untl the energy crss of 1973, the Mll used a mnmum amount of purchased power. Wth the monumental ncrease n natural gas rates, t s more economcal to purchase electrc power than to generate. However, n order to get the most for your money n purchased power t s necessary to mantan a constant pull at the set demand lmts wthout exceedng the demand lmt. Ths shown n "Economc Justfcaton for Demand Controller". MLL HSTORY The Lufkn Mll started producton n January, The frst newsprnt produced from southern pne. Power was furnshed by two (2) 2400 volt, 7.5 MVA steam turbnes. n 1948, the second newsprnt machne was added and two (2) 6900 volt, 12.5 MVA steam turbnes were added to the system. n 1956, the thrd machne was nstalled and two (2) 15 MVA, 6900 volt, steam turbne generators were added to the system. Also a 50 MVA te was completed wth the utlty, l32kv to 6900 volts. n 1968, a 18 MVA, l3.8kv gas trubne generator was added to the system. DESGN CONCEPT The basc desgn of the Demand Controller s to mantan a constant power level from the utlty. Ths can be accomplshed by turlj'4.ng loads "OFF" or "ON" to mantan the demand. However, wth n plant generaton, the demand can be mantaned by ncreasng or decreasng generaton. Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

2 ESL-E ECONOMC JUSTFCATON Power Rates $18, frst 5000 kw demand 3.60 per kw all addtonal demand $ per kw all kwh $ per kwh fuel adjustment $.014 per kwh average Cost Dfference 44,640 kw - Demand Bllng 31,130, 000 kwh - Blled kwh 44,640 kw X 744 hrs (31 days) = 33, 212,160 kwh at constant demand 33,212,160-31,130,000 = 2,082,160 kwh Addtonal kwh suppled by generators 2,082,160 kwh X 12,070 BTU/kwh X $2.39/MM BTU = Cost to Generate $60, Purchase Cost 2,082,160 X $ , Savngs per month = $30,915.00,'-, -, f.'_ " r' r: (;< Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

3 ESL-E KV 1. P &L. o/s-20.25mva 0/ 0/ ~ ~ ~42-47MVA p. 'Q ~~r""-~ ~~r""\.r'\ SYNC. BU8.6.9KV BUS :lll 6~" 14) B@ LEGEND GflJNDER NO. GENERATOR G 4000 H. CELL NO 0 REACTOR ~ t-' o ~ ~ NO.4 10% NO.3 O~o NO.S 39'0 NO.6 39'0 \:AllMVA 'T-2 A",...".~,-...~ A FOR APPROVAL B PROP. SYNC. BUS TE BY 2'78 A"D. ~Duthr(md P'AP'ER HOUSTON, T XAS C GENERAL REVSON BY 1S'781 A'PO. ONE LNE DAGRAM D GENERAL REVSON 13 Y 9 78\ CHKO. CALC. MAN POWER BUSES LUFKN MLL NO. fv$lons 1 o'."0.1 OAT orv. :l(asfd,01. O. OAT ACTON O. DATE PROPOSED NEW SYNC SUS TE CORPORATE ENG. ~~. Dele GHR 12-4'781.-r- 'ROJ 2.78.LPP 037.HT. J NO. 0: 0 ", C Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25, ".. J.,:, "''':'.:. -.

4 ESL-E The output of each generator, s controlled by a reversng D.C. motor whch s meqh ancally connected to the man stearn valve. The motor s actvated by a swtch o~ the control panel to open or close the valve as load s ncreased or decreased. KWH pulses, whch are recorded by the Power Company on magnetc tape for bllng, are ;fed nto the computer. The computer totals the pulses, look at the tme n the pero~,. and then provdes a contact closure to drve the control motor up or down to 1ncrease or decrease the generaton. The KWH pulses are receved approxmately every 3 se90nds and the contact closure to generator control s set for 2 seconds duraton. At t~e present, the Rase - Lower pulses are fed smultaneously to four (4) steam turbn~ "~,', ~.j 1 generators. 1 Durng the demand perod, the accumulated KWH pulses are dsplayed along wth theltme j n seconds left n the perod. At the end of the demand perod, a log s prntedlwhch lsts the total KWH pulses for the perod, KW load on each generator and grnders on automatc shed control. At the end of the day, a daly/monthly summary s prnte4. Hgh-low lmts are programmed for each generator. When these lmts are reached~ \ the computer wll qut sendng pulses to that generator. n addton, there s apont of mnmum generaton wth steam extracton, when the generaton reaches ths po~t an alarm wll sound, lettng the operator know he must cut extracton to further reduce generaton. EMERGENCY CONDTONS Due to the arrangement of the busses and the dstrbuton system n the Mll, t ~as decded to program emergency condtons nto the computer. Under normal operatng condtons, the generators are capable of an addtonal 20J,000 KW. However, the response tme of the generators and bolers are so slow t was necessary to shed an amount of power equal to the loss and let the operator restoje the loads manually as generaton was ncreased. One of the man problems s the Bus Te from utlty to the man sync bus. Ths ~s through breaker No. 70. Ths s a 6900 volt, 500 MVA, 2000 amp breaker, whch l~ts the power to 25,000 KW. Under some of the emergency condtons, the current throqgh ths breaker would exceed lmts and cause a trp whch would shut more equpment ldown. The emergency condtons are relayed to the computer by a contact closure whch ~ generated when a crcut breaker trps. t was mpractcal to use a contact fromthe breaker so auxlary relays were used whch parallel the trp crcut n each control panel. The trp contact for grnder shed parallels the trp crcut n each cont~ol -~ ; panel. Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25, ;

5 ESL-E EMERGENCY CONDTONS A. Total Loss of Texas Power & Lght - 50 MW 1. Results a) Hgh error sgnal b) Controller wll try to back down generators 2. Acton Requred by Controller a) Generators swtched to frequency control or manual control b) Load Shed 1. By Controller 2. Grnders 1, 14, 15, 16, 17, 18, 2, 3, 4, 19, 5, 10, 12, 7, & 8. B. Loss Sync Te Breaker No Results a) Hgh error sgnal b) Controller wll try to back down generators 2. Acton Requred by Controller a) Generators swtched to frequency control or manual control b) Load Shed nternal 1. Controller 2. Grnders 2, 3, 5, 6, 7 & 8 C. Loss of Bus V or V, Breaker 72 or Results a) Hgh error sgnal b) Controller wll try to back down generator c) Hgh current Breaker Acton Requred a) Reset demand to 35 MW D. Loss of Generator 1. Results a) Hgh error sgnal b) Controller wll ncrease load on other generators c) Hgh current Breaker No Acton Requred a) Load Shed - nternal 1. By Controller 2. Grnders on generator Bus. See Generator lst Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

6 ESL-E The grnders actually use water pressure n the pockets to force the logs aga1nst the stones. t would be better to unload the pockets,.e., take the pressure off, t~an to trp the grnders but due to the control arrangement of these grnders t was, "" decded to shut the motor off.,~ POWER DEMAND CONTROL SYSTEM The equpment selected to mplement the Power Demand Control requrements as prev ously descrbed was suppled by Automaton, nc. of Houston. conssts of the followng major peces of equpment and software: a) Man Demand Control System b) Operator Control Console c) Backup Demand Control System d} Prnter and Vdeo (CRT) Dsplay Unts e) Smulator Panel f} Relay Panels The Power Demand Control ystem g) Power Frequency Transducer h) Real Tme Executve System ) Applcaton Software MAN DEMAND CONTROL SYSTEM The Man Demand Control System s mcro-processor based and contaned n a 20-s1ot, -: chasss. The system electroncs consst of the followng prnted crcut modules Z-80 Computer Module General Purpose nput/output Module Multfuncton /O Modules Hgh Level A/D Converter Modules Power Fal Detect Module Swtchng Power Supples Ths confguraton provdes computng and logc capablty, program and data stortge, nput/output, and nterface electroncs. The mcro-processor s a Z-80 8-bt CPU~, Also ncorporated on the computer module s a math processor whch executes n patallel wth the Z-80. The math processor performs both sngle and double precson ADD,SUB, MULT, DV, Floatng Pont ADD, SUB, MULT, DV, all trgonometrc functons and exponentals. The program and data storage ncludes 10,240 bytes of Erasable Read Only Memory (trom) and 10,240 bytes of Random Access Memory (RAM). The mportant feature of the ERO~ s Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

7 that stored programs cannot be altered or lost by power falure, operator error, or ESL-E program error. All programs are stored n EROM. Data s stored n RAM. The RAM moudle s equpped wth battery backup to portect aganst loss of data durng power outages. The nput/output and AD converter modules are the means by whch contact status s read, analog data values are nput, relays are operated, and data values are ndcated on the dgtal dsplays. The vdeo dsplay and prnter are both connected va seral communcaton crcuts. The operator can both nput and receve data on the vdeo dsplay/keyboard and the prnter/keyboard. OPERATOR CONSOLE The plant operator s able to control all generators and grnders from the desk console. Generators and grnders can be put on automatc or manual control and operated from the console manually. The operator's console s a desk-type cabnet wth.a slopng nstrument panel. The console contans the followng tems: 1. Nneteen (19) grnder motor selector for automatc-off manual operaton of each grnder. 2. Seven (7) generator selector swtches for automatc-manual control of each generator. 3. Seven (7) generator manual control swtches for "Rase-Lower" KW output ';.; of each generator. 4. Annuncator wth four alarm lghts: a) Loss of 120 volt AC power b) Loss of output from computer c} Mnmum generaton d) Load shed 5. Two (2) ndcator lghts a) Rase pulses to generator b) Lower pulses to generator 6. One () key swtch to permt change of demand settng 7. Two (2) dgtal dsplays a) Dsplay counts n demand perod b} Seconds remanng n demand perod 8. Vdeo montor wth keyboard BACKUP DEMAND CONTROL SYSTEM The backup Demand Control System s dentcal to the man demand controller except that no provsons are made to dsplay or prnt operator nformaton. Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

8 ESL-E Durng normal operaton, the man demand controller performs all control functons and responds to the operator for nformaton or operator alteratons n control. The backup Demand Controller dsplays the seconds remanng n the perod and the number of ~ pulses durng ths perod. A falure of the man controller s ndcated when the: man controller's computer fals to send a pulse to the backup computer mmedately followng a KWH pulse from the demand meter. The KWH pulse s nput to both the mhn and backup demand controller smultaneously. : PRNTER AND VDEO (CRT) DSPLAY The prnter and CRT unts are the major means by whch the operator accesses nfo~ton wthn the control system. The CRT provdes the operator wth requested data wh~ the prnter s avalable at another locaton to provde the supervsor wth prnted nformaton. Essentally, the same nformaton can be requested from the prnter lor CRT. SMULATOR PANEL The smulator panel provdes a means of testng the complete control system wtho~t beng connected to the plant control actuators. The smulator panel contans two clockd to smulate the two sgnals from the KWH meter. These sgnals are the KWH pulse and the Demand Perod Reset pulse. The Demand Perod Reset pulse s a fxed clock pulse ~th an nterval of one pulse per 15 mnutes. The KWH pulse s a varable pulse rate. l To operate the panel, the plant control sgnal cable s dsconnected from the rel~y panel. A smulator Panel cable s connected to the relay panel n place of the p~ant control sgnal cable. Ths cable feeds the smulated KWH meter sgnals nto the computer as well as allows the relay contact sgnals to be fed nto the smulator panel. The controller s now able to perform demand control calculatons and output powej correctons. These power correctons, however, are fed nto the smulator panel,nd results n changng the smulated KWH clock pulse rate. n addton, ndcator lghts on the smulator panel permt vsual trackng of tu1nng on and off loads. Toggle swtches areprovded to smulate emergency condtons a~d feld contact closures. ; RELAY PANELS The purpose of the relay panels s to provde a means of controllng plant equpm~nt. The relays selected are standard DPDT DA relays wth 24V - col operaton. The ltelays are plug-n type. The relay socket feeds through the panel such that all relay ~ter- face wrng s on the rear of the panel. Feld sgnals are termnated on the front of Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25, j

9 the panel. The arrangement provdes easy access for plant mantenance. ESL-E POWER FREQUENCY TRANSDUCER Normally, the frequency s synchronzed from the te lne power frequency. However, n case of the loss of the te lne, t s necessary to mantan the frequency. The Power Frequency Transducer measures the lne frequency and compares t to an nternal reference frequency. The dfference s output as a varyng analog voltage. The varance s proportonal to the devaton from the 60 Hz reference. The controller reads the analog voltage and corrects the lne frequency by outputtng ncrease or decrease KW pulses to generators. Note that frequency control only occurs when te lne power s not avalable. Therefore, no demand control s possble. REAL TME EXECUTVE SYSTEM The control of plant processes requre responses, n tme, to a number of randomly occurrng events. The events are detected by an nterrupt nput or a tmed nterval. Thus, we have the bass for the Real Tme Executve System. The Real Tme Executve System permts the total control problem to be dvded nto a number of functons or tasks. Each of these tasks requre system resources such as central processor tme, /O, prnters, etc. The Real Tme Executve System (RTX-80) schedules and dstrbutes system resources on a prorty bass to concurrently executng tasks. Key features of the RTX-80 nclude nterrupt drven devce handlers, real tme clock control, mult-task schedulng, task stack management, and power~up ntalzaton. RTX-80 servces avalable to a task nclude task schedulng, task suspenson, task tme delay, termnate tasks, savng and.restorng the envronment, devce /O control and calendar mantenance. The current year, month, day, hour, mnutes, seconds and tenths of seconds are avalable for program use. The feld-proven RTX-80 may be confgured for 16, 32, 64, or 127 tasks. The program s wrtten to be stored entrely on PROM except for dynamcally changng schedule and control tables. The amount of memory requred s approxmately 2876 bytes ROM. APPLCATON SOFTWARE The executve for ths control system s confgured for 16 tasks. lst of these tasks: Task 1 - Power Fal Restart 2 - Debug 80 (off lne) The followng s a Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

10 ; : 3 - Spare ESL-E Operator Control 5 - Demand Reset 6 - Load Frequency Control 7 - Demand Control 8 - Supervsor Control 9 - Generator Control 10 - Grnder Control 11 - Analog Data Control 12 - Spare 13 - Alarm Task 14 CRT Dsplay Task 15 - Log Task 16 - CRT Perodc Update Task n addton to these tasks, a number of subroutnes, and a common data storage s requred. The followng s a lst of these: are,a a) Common Data Storage b) nterrupt Handler c) System Subroutnes d) Applcaton Subroutnes e) Analog Control Subroutnes f) Demand Control Subroutnes g) nput/output Subroutnes h) Prnt Subroutnes ) Arthmetc Subroutnes POWER FAL RESTART TASK When the lne voltage drops off approxmately 12%, the Power Fal Detect module g~nerates j an nterrupt. The nterrupt handler stores data, sets the power fal flag and extcutes a halt command. When power s restored, the power-on routne checks for the power fal flag and bds the power fal restart task. The Power Fal Restart Task alarms the operator of the power falure and prnts al power fal message. operaton on the system. The Power Fal Task then ntates other tasks necessary to restore Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

11 DEBUG TASK ESL-E The Debug Task provdes the programmer wth a means of trackng the nternal operaton of the system software. Debug s used only for program testng and s not permanently nstalled n the machne. Debug has functons ntated from the keyboard whch allows the programmer to alter RAM data, prnt programs and data, prnt programs and data, set breakponts n RAM-stored programs, fll RAM wth constants (.e. zero RAM area), perform nteger and hex arthmetc, move data from one locaton to another, bd a task, examne regsters, and mscellaneous othe functons. OPERATOR CONTROL TASK The Operator Control Task provdes the operator wth a way ntate control functon~ and request operatng nformaton. The operator selects the desred functon through the CRT keyboard. When a key s depressed, a message s dsplayed to dentfy the functon whch the operator has selected. The operator then follows the nstructons dsplayed on the console CRT screen. f the operator depresses a key whch does not select a functon, an "UNDEFNED" message s dsplayed. An ** ndcates the computer s lookng for an operator command. Any of the accepted functons may now be requested by depressng the approprate key. When the operator has completed all hs requests, he should depress the "0" key. Ths functon turns off the "OPERATOR CONTROL" program. The tme, date, and demand perod data s dsplayed contnuously on the CRT screen untl the operator agan requests operator functons. The followng lsts some examples of operator control functons whch have been programmed. G - D - Grnder Status Dsplay Demand Lmt, Actual Summary Dsplay K - ntalze Daly/Monthly KWH Accumulaton L - ls-mnute Generator Accumulaton Dsplay P - Generator Status Dsplay R - S - Return Demand Lmt to Normal Steam Extracton Status Dsplay T - Set Tme/Date Y - Turn on Debug o - Turn Off Operator Control Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

12 DEMAND RESET TASK ESL-E The Demand Reset Task ntalzes data for the next demand perod. n addton, th task saves the prevous demand perod data for accumulatons, dsplayng, and 10gg~9. \ Also, the backup ls-mnute + S second counter s started. The ls-mnute + S second counter s used n case of loss of the ls-mnute demand perod pulse. Ths task s ntated normally by the demand perod nterrupt. The ls-mnute + S second counter may also ntate ths task. LOAD FREQUENCY CONTROL TASK n the event of the loss of te lne power and consequently the loss of frequency synchronzaton, a separate means of controllng frequency must be ntated. The Joss of bus-te nterrupt ntates ths task. At one-second ntervals, ths task reads the devaton from 60 Hz analog sgnal. ncrease and decrease power pulses are then output n the same manner as the correc on pulses for demand control. Demand control wll not functon concurrently wth the oad Frequency Control Task. DEMAND CONTROL The prmary purpose of ths Power Demand Control System s to mantan the te lne power at a constant level. The means of control s to swng the plant generaton. As plant demand decreases, the generaton s decreased. The demand s montored by countng contact closure pulses (KWH pulses) over a ls-mlnute perod. The begnnng of each ls-mnute perod s ndcated by a second contact cl sure pulse. Each of these sgnals s generated at the power company bllng meter. Calculatons are made at each KWH pulse tme to determne f the power consumpton fate (plant demand) s above or below predefned lmts. (See demand rate curve)* f te rate exceeds the hgh lmt, generaton s ncreased. f the rate s below the low r lmt, generaton s decreased. maxmum lmt s beng exceeded. n addton, a calculaton s made to determne f/the f so, the load s trpped representng an emerge cy condton. These calculatons result n settng flags and ntatng the appropra e task to take control acton. Durng the demand perod, the accumulated KWH pulses (counts) are dsplayed along w~th seconds remanng n the perod. At the end of the demand perod, a "log s ntat~d, whch prnts a summary of the demand perod nformaton. Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25, 1979

13 ESL-E DEMAND RATE CURVE 260 CONTRACT DEMAND LMT J TARGET CONTROL LMT' ~ ~ ~ ~ / / ~V / "" ~ ~ ~V ~V ~~ 7 ~ "'/ ~ 1/.,...1 ~ \~\y' / ~~ ~ ~ \t?~~ ~~~: ~..,, tg')j' ~~'~~"J~ " ~~~ ~\y~,,,, Q~"~' ~ O\'Y"~~/'... ~~,...y~ >- ~ co t~~'/0" ~r> 1.~r/~~~oY ~~t/ra,o~ ~~~ ~~ ~\t.. '" ~ \ V ~~/~O~ o o DEMAND PEROD -SECONDS Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

14 GENERATOR CONTROL ESL-E The functon of the Generator Control Task s to ncrease or decrease the output of the generators. Ths task checks the ncrease or decrease flag to determne f or decrease relays must be pulled n. Those generators whch may be controlled sgnalled to ncrease or decrease ther output accordngly. When the relays are p lled n, a check s made va an auxlary contact to determne f the relay s controll'ng. The relays are closed for two (2) seconds. ncrease or decrease. The length of the pulse determnes KW GRNDER CONTROL TASK The Grnder Control Task turns off grnders accordng to predetermned prorty l~sts. to an nterrupt or f demand exceeds the maxmum lmt. A total of 12 dfferent ~rorty lsts are pre-programmed. The specfc lst used for dumpng load s qetermned ~y the emergency condton. Under certan crcumstances, the demand must be lowered n order to mantan good Ths task may be ntated by an emergency condton sgnal by a contact connected regulaton of generaton. Therefore, the removal of large blocks of load also re~ult n a reducton of the demand. The normal demand lmt s reset by the operator a1ter the emergency condton has been corrected. ANALOG DATA CONTROL TASK Two (2) A/D converters, each wth 16 nputs, are ncorporated nto the system. sgnals allow the system to read generator KW, frequency transducer, and the current of the te lne breaker. generator stearn extracton, the Ths task scans the analog nputs, converts the A/D counts to engneerng values, j Tllese compares the values wth hgh/low lmts, and ntates the correspondng alarm mlssages. Also, provsons are-made for the operator to change hgh/low lmts, remove ponts from scan, restore ponts to scan and dsplay the values. ALARM TASK The Alarm Task has the functon of prntng and dsplayng all alarm messages. When an alarm condton s detected by another program, the correspondng alarm messag~ s queued for later prntng. Alarm messages are output to the operator on the C T and prnter. j Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25,

15 ESL-E GEN. 1 K\~ ANALOG -STH. EXT [ NPUT GEN. 2 KW STM. EXT -- ~ GEN. 3 KW 0 \J1 STM. LXT 1-:11 REAL TME CLOCK POWER FAL/RESTART ~::~U: ~:SS LOAD 6 OFF '" GEN. 7 DOWN ~OUTPUT LOSS _all OUTPUT LOSS, ~ 1--'-~ LOAD 7 OFF, r- VDEO ~~ OUTPUT LOSS GEN. 1 GEN. 1 UP POWER LOSS.----rll OUTPUT LOSS jl KWH GEN. 1 DOWN -LOAD 1 OFF - ' 10UTPUT LOSS -tl KVAR-H ~ OUTPUT LOSS,GEN. 2 UP LOAD 2 OFF PEROD,OUTPUT LOSS -- f--o:output LOSS GEN. 2 DOWN lload 3 OFF PROM MEMORY ~tl OUTPUT LOSS u OUTPUT LOSS ---1r REVERSE POWER ~ RAM HEMORY H"-"-' DSPLAY - j LOAD 8 OFF - LOSS OF PWR. --:- ~ OUTPUT LOSS - LOSS OF OUT ALARHS 11- f- REV. PWR Gt:N. 7 KW --.:-::: f 11- MN. LOAD STM. EXTj f- LOAD SHED L TE BUS CURR. SPARE. PRNTER POWER DEMAND CONTROL SYSTEM Proceedngs from the Frst ndustral Energy Technology Conference Houston, TX, Aprl 22-25, ~.:.;,. j'" ~