15th Tcc / 16th srpc meeting
Venue: GOA
Date: 29th / 30th April 2011
POWER SYSTEM OPERATION CORPORATION LIMITED
SOUTHERN REGIONAL LOAD DESPATCH CENTER
BANGALORE
1
NEW PROJECTS OF NTPC, NLC, NPCIL & UMPP
SL NO 1 OF TCC
NTPC SIMHADRI STAGE - II
(2 X 500)
SL NO 1.1 OF TCC
NTPC SIMHADRI STAGE - II
• MoP conveyed the allocation of Power from Simhadri Stage II to beneficiary
states.
• Units I test synchronised in March 2011 & COD yet to be declared.
• Units II likely to be commissioned by June 2011
• Scheduling of Simhadri Stage II will be done by SRLDC w.e.f COD
• Data / Speech communication to SRLDC is made operational & under testing
• Till the date of COD of Simhadri Stage – II
• Simhadri shall regulate infirm power injection as per SRLDC instruction on
real time basis
NPCIL KUDANKULAM STAGE 1
(2 X 1000)
SL NO 1.3 OF TCC
NPCIL–KUDANKULAM STAGE I
•
NPCIL informed that for Kudankulam all equipment's are in place at site and the
commissioning activities are in full flow.
•
Units I & II are likely to be commissioned by June 2011 & March 2012.
•
In Special TCC held on 3rd Jan 2011. NPCIL Informed Reactor of 1st Unit was likely to go critical
by March 2011and generation was expected from April 2011
•
SPS & Speech facilities to be provided
SRPC
TN REPLY
- Permission given by TN for placing MUX
- SRTS -2 to confirm the status / probable date of completion
•
SEM & SCADA Data Validation to be done by NPCIL – Observed error of 16kV between Field
and Scada data at Kudankulam bus
•
Commissioning of Bus Reactor at Kudankulam is essential for ensuring availability of reliable
start up supply.
•
The parallel closing of second line between Tirunelvelli – Kudankulam will be at 410 kV and
Opened at 425 kV
VALLUR JOINT VENTURE BETWEEN NTPC & TNEB
( 3 X 500)
SL NO 1.4 OF TCC
VALLUR JOINT VENTURE BETWEEN NTPC & TNEB
(3X500)
• Unit sizes of 500 MW.
• TANTRANSO had informed that commissioning of the 1st unit could be delayed
by 2-3 months because of issues regarding the coal handling plant.
• MoP vide letter dated 28th September 2010 had communicated the allocations
to the beneficiaries states as given:
Nellore – Allmatty
D/C Study Results
Nellore – Allmatty
D/C Study Report
Allocation:
AP: 178.8 MW
KAR: 111.5 MW
KER: 49.9 MW
TN: 1040.6 MW
Pondy: 6.7 MW
Unallocated: 112.5 MW
JOINT VENTURE OF NLC& TNEB AT TUTICORN
(2 X 500)
SL NO 1.5 OF TCC
Joint Venture of NLC & TNEB at Tuticorin
• NLC had informed that orders had been placed on M/s BHEL and civil works had
commenced.
• MoP had communicated allocations to the beneficiary States.
• NLC had informed that with the action plan given by M/s BHEL, Units I & II were
scheduled to be commissioned during August 2012 & October 2012 respectively.
KAYAMKULAM
1950 MW/ 1950 MW
SL NO 1.6 OF TCC
KAYAMKULAM 1950 MW/1050 MW PLANT
•
Feasibility report for the project had been finalized by NTPC.
•
Pipeline from Kochi Terminal to Kayamkulam was being developed by M/s GAIL.
•
GoI had circulated drafts on price pooling mechanism. Price of LNG was linked with
prices of crude oil. The unit rate was likely to be Rs. 3.75 - Rs. 4.00 per unit in the
present scenario where crude oil prices ranging between $ 70-80/barrel.
•
Requisition from KPTCL & KSEB received by NTPC.
•
Conditional consent communicated to NTPC by APTRANSCO.
•
TANTRANSCO & Puducherry – Presently price pooling mechanism not very clear, would
be interested in case tariff was advantageous.
NLC NEW THERMAL POWER PROJECT
(2X 500)
SL NO 1.7 OF TCC
Neyveli New Thermal Power Project (2x500 MW)
•
Director (Power ),NLC had informed that the project was likely to take 40 months after PIB
approval and was targeted to be commissioned in 2014. PIB approval was likely in the next
six months.
•
MOP vide letter dated 29th October 2010 had communicated allocation of power from this
project
•
PGCIL informed NLC had applied for connectivity. NLC had been requested to apply for LTA
also to take up planning of evacuation scheme
•
Tamil Nadu had informed that this being a replacement project since Tamil Nadu was loosing
600 MW , entire 1000 MW from the new project to be allocated to them.
Neyveli New Thermal Power Project (2x500 MW)
• TNEB’s share was 100% in Neyveli Stage 1.
• Old plant was commissioned in 1962.
• Present Evacuation Plan is at 230/110kV
• Designed for evacuating 600MW.
• Since 2 x 500MW plant is coming up, inter connection to 400kV is desirable.
• Wheeling issue
KRISHNAPATTANAM UMPP(3960 MW)
SL NO 1.8 OF TCC
KRISHNAPATTANAM UMPP(3960 MW)
Madugiri
KRISHNAPATTINAM
UMPP
TN UMPP
Cochin
400kV D/C
QUAD MOOSE
765 KV
KRISHNAPATTANAM UMPP(3960 MW)
• The unit configuration had been finalized as 6 x 660 MW and CERC had been
approached for revised configuration, clearance awaited.
• CMD, APTRANSCO had informed that about Rs. 300 Crores had already been
invested and progress was their in all the fronts.
• Project is being developed by Reliance Power Limited.
• The plant may come up beyond 2014.
Schedule Date of Commissioning of the Central Sector/JV Projects
Station
Unit
Installed Capacity
(MW)
Original date of commissioning
Revised date of
commissioning
Simhadri Stage - II
I,II
500, 500
11th Plan
Mar-11, June-11
Kayamkulam
I, II & III
1050/1950
11th Plan
12th Plan
Vallur JV with TNEB
I
II
III
500+
500+
500+
11th Plan
Oct-11
Dec-11
Dec-12
Neyveli – II (Exp)
I
II
250
250
2006 – 07
Mar-11
Jun-11
Tuticorin JV with TNEB
I
II
500
500
11th Plan
Aug-12
Oct-12
Sirkalli TPP
I,II,III
3 X 660
52 Months, 58 Months,
64 Months from GOI approval
Kaiga
IV
220
Sep – 07
Nov-10
Kudankulam Stage – I
I
II
1000
1000
Dec – 07
Dec – 08
Jun-11
Mar-12
Kalpakkam (PFBR)
I
500
2010 – 11
Mar-12
Krishnapattanam
I
VI
4000
11th Plan
June 2013
Feb 2015
4000
2015 – 17
2015-17
Cheyyur
PAYMENT OF CHARGES OF TNEB OWNED
TRANSFORMERS AT SRIPERUMBUDUR & SALEM
SL NO 2 OF TCC
PAYMENT OF CHARGES OF TNEB OWNED Xmers AT
SRIPERUMBUDUR & SALEM
1. Discussed in 13th Commercial Sub-Committee meeting held on 19th July 10
whereas PCKL had agreed to put up a draft computation for the tariff.
2. In the 14th SRPC meeting, it was noted that TCC had agreed that the proposal
prepared by PCKL be deliberated in details by the Special Commercial Committee
before being put up to TCC/SRPC.
3. Matter was further deliberated in the Special Commercial Sub-Committee meeting
held on 29th Sep 10 wherein it was noted that proposal from PCKL was awaited,
while APTRANSCO had also submitted their proposal on the issue.
4. Outcome of the 14th commercial Sub – Committee meeting
•
TNEB would compute the charges for the period from 1.4.1991 to 31.12.2011 in line with
norms prevailed during the period and the Commercial Sub-Committee would validate
the same for subsequent approval of TCC/SRPC.
MAINTENANCE OF MARCONI MAKE SDH
EQUIPMENT
SL NO 3 OF TCC
MAINTENANCE OF MARCONI MAKE SDH EQUIPMENT
1. TN to Expedite Commissioning of their system to Coincide with SR2,
PowerGrid Plan
Wide band
Failure
Microwave
Details
Minutes
12th Jan 10
EXISTING WIDEBAND NETWORK UNDER SOUTHERN REGION ULDC PROJECT
Ramagundam
Peddapally
Durshed
Jammikunta
Shapur Nagar
Warangal Sub-LDC
36
134
Ch. Gutta
Vidyut Soudha
Hydearbad SLDC
147
(400)
46
Tallapally
99
12
217
63
N’ Sagar PH
17
104
Vijayawada Sub-LDC
66
Kakinada
Bommur
Bhimadole
VTPS
Somayajula Pally
76
Gooty
58
Ananthapur
98
Muddanur
57
Chinakam Pally Sub-LDC
(Cuddaph)
302
Davanger Sub-LDC
Kumbalagodi
CHENNAI SLDC
Somanhally
Sriperabudur
B’LORE RSCC
181
Salem 400
Salem 230
30
S.P. Koil
Villianur
111
64
Neyveli-I
Pondicherry SCC
Kozhokode B
Panruti
93
Erode Sub-LDC
Chidambaram
Trichur North
31
140
Ingur
Myladuthurai
Chalakudy
Trichy
230
130
Pongalur
Kovilvenni
26
Udumalpet
Kalamassery SLDC
Thiruvarur
Adankottai
Orthanadu
Vaikkam
Thirumayam
Pallom
Pudukottai
Kayamkulam
Karaikudi
Madurai
400
Kundara
Sivaganga
Paripally
Madurai Sub-LDC
Trivandrum North
Kannur Sub-LDC
87
Visakapantam SWS
20
Hubli Sub-LDC
KPTCL SLDC
147
Ghanapur
Srisailam
LBPH
Srisailam
PH
Karnool
Gazuwaka
11
19
156
Vidyuthi Bhavanam Sub-LDC
CORPORATE LD&C DEPT.
LEGENDS:
RSCC
SLDC
Sub-LDC/ SCC
RTU / Wideband location
Repeater Station
F. O. Link (ULDC)
F. O. Link (APTRANSCO)
M.W. Link (ULDC)
M.W. Link (TNEB)
VSAT link (KPTCL)
Colour Code
C.S. links (ULDC)
Constituents links (ULDC)
APTRANSCO links
Proposed Solution for replacement of Existing Microwave Links installed under
Southern Region ULDC Project
Ramagundam
Ch. Gutta
Durshed
Shapur Nagar
147
99
147
12
Srisailam PH
217
Vijayawada
Sub-LDC
Gooty
58
302
KPTCL SLDC
19
Erode
Sub-LDC
Ingur
31
130
Udumalpet
26
Kalamassery
SLDC
Pallom
Kayamkulam
30
Salem 400
156
S.P. Koil
Pondicherry SCC
Neyveli-I
140
Villianur
Myladuthurai
Trichy 230
Thiruvarur
Pudukottai
Madurai
Sub-LDC
Kundara
Trivandrum
North
Vidyuthi Bhavanam
Sub-LDC
Madurai 400
Total OPGW = 1214kms
Total UGFO = 210 kms
LEGEND
RSCC
SLDC
Salem 230
64
Chalakudy
CHENNAI SLDC
181
B’LORE
RSCC
93
Bhimadole
VTPS
Ananthapur
98
Muddanur
57
Chinakam Pally Sub-LDC
(Cuddaph)
Somanhally
Sriperabudur
Trichur North
Bommur
Somayajula Pally
Davanger Sub-LDC
Kozhikode B
87
66
Visakapantam SWS
Kakinada
20
76
111
N’ Sagar PH
17
104
Hubli Sub-LDC
Kannur Sub-LDC
63
Tallapally
Srisailam
LBPH
Karnool
11
Ghanapur
46
Hyderabad
SLDC (400)
Gazuwaka
Warangal SubLDC
134
36
Vidyut Soudha
Sub-LDC/ SCC
RTU / Wideband location
F.O Link (ULDC)
F.O. Link (APTRANSCO)
OPGW Link (existing)
Proposed UGFO link
Proposed OPGW link
Karaikudi
Proposed Radio link
VSAT LINK (KPTCL)
Constraints In SR System
SL NO 4 OF TCC
KOODANKULAM
NLMNG
UNIT 1- JUN 11
UNIT 2- MAR 12
CHITOOR
HOODY
KOLAR
ALMATHI
HASSAN
SP-BUDUR
NLY-2 EXPN
S’HALLI
HOSUR
UNIT1- MAR 11
KALIVENDAPATTU
UNIT-2 JUN 11
MYSORE
BAHOOR
KOZHIKODE
SALEM
NEYVELI
NLY-EXP
ARASUR
NLY2-EXP
PUGALUR
THRISSUR
UDUMALPET
TRICHY
KARAIKUDI
COCHIN
MULTI-CIRCUIT
TOWER ON 220
EDAMON
KV EDAMONKAYATHAR
CORRIDOR
EDAMON-TNVL
WOULD BE AT
220 KV TO
BEGIN WITH
MADURAI
TIRUNELVELI
TRIVANDRUM
KOODANKULAM
TRANSMISSION SYSTEMS IN SR
IN PROGRESS
400 KV D/C MYSORE-KOZHIKODE
a) Reduce losses by ~ 8MW
b) Enhance margin across constrained S1-S2 corridor.
c) Enhanced reliability for N. Kerala (an issue at present)
d) Relief for Thrissur(Madakathara) transformer ( Fully loaded)
e) Relief on loading of Idukki-LP-Madakathana 220 KV lines
g) Enhanced transfer capability to Kerala, opportunity to conserve hydro.
400 KV D/C MYSORE-KOZHIKODE STUDY
1.
2.
WITH OUT KOZHIKODE-MYSORE D/C
GEN AT IDDUKKI ABOUT 520MW
NELAMANGALA
MYSORE
173 MWx2
227x2 MW
HOOTAGALLY
Losses 830.4MW
191 MW
13 MW
KADAKOLA
KOZHIKODE
TK HALLI
104 MW
KANIYAMPET
48 MW
72 MW
HORAHALLI 105 MW
KANAKPURA
AREACODE
173 MW
106 MW
NALLALAM
139 MW
SOMANAHALLI
111 MW
TRICHUR
KANJIRODE
Coal Stock Position
SL NO 5 OF TCC
DC vs Actual
Normative Vs DC
Coal Stock Position
( As on 27-Apr-11)
DAILY LINKAGE IN 1000
OF TONNES
ACTUAL IN 1000 OF
TONNES
IN DAYS
APTRANSCO
VTS
26
127
5
KTS
18.9
301
16
RYTPS
16.5
97
6
SIMHADRI
23.1
164
7
KAKATIYA
5.8
109
19
38.1
535
14
52
417
8
ISGS
RSTPS
TALCHER
KPCL
RTPS
25.1
404
16
BTPS
8.7
52
6
TNEB
ETPS
6.9
14
2
MTPS
13.6
73
5
NCTPS
10.4
59
6
TTPS
18.5
49
3
Issues Related to Transmission Schemes Agreed
in Standing Committee
SL NO 6 OF TCC
HOSUR-ELECTRONIC
400KV D/C
D/C TRANSMISSIN
HOSUR-ELECTRONIC CITY
CITY 400KV
TRANSMISSIN LINE
LINE
400kV lines
400kV lines
In standing
committee meeting it is
In 28th standing committee meeting it is
proposed to Utilise the ROW of 220kV
proposed to Utilise the ROW of 220kV
Yerandahalli-Hosur line for 400kV
Yerandahalli-Hosur line for 400kV
Hosur-Electronic City D/C line
Hosur-Electronic City D/C line
KPTCL Director
(Transmission) had stated
that KPTCL would
examine some alternate
transmission system for
Electronic city
city. to avoid
ELECTRONIC CITY
ELECTRONIC CITY
ROW problems
SOMANAHALLI
SOMANAHALLI
YERANDAHALLI
YERANDAHALLI
KPTCL had been requested to explore possibility of
establishing 400kV S/S at their existing 220kV S/S at
Yerandahalli to solve the ROW problem.
KOLAR
KOLAR
HOSUR
HOSUR
400 KV D/C HOSUR-ELECTONIC CITY
• PGCIL to do joint survey with KPTCL, if necessary latest stringing
methodology would be adopted.
• KPTCL informed that critical RoW issues existed at two locations.
• CE (Trans.) Bangalore had been nominated from KPTCL side for
joint survey.
• APTRANSCO had requested to furnish cost implication on account
of adoption of unconventional technology.
Transmission Capability of
HVDC Back to Back stations
SL NO 7 OF TCC
Transmission Capability of
HVDC Back to Back stations
• In 57th OCCM of SRPC, SRLDC had clarified that it would not be able to
certify the past cases as PDO was in service during that period and
constituents had to take a decision in this regard
ULDC Requirements Beyond 2011
SL NO 8 OF TCC
LTSA FOR SR –ULDC SCHEME
• Maintenance for comprehensive software and hardware maintenance support
for EMS/SCADA system supplied under SR-ULDC scheme with two year
extension is going to expire on 31-12-2011.
• As the upgradation process will take quite a time, as per the request of
constituents SRLDC has obtained the quote from M/s GE for extending the AMC
by one year with a provision for one more year for further extension if required.
• SRLDC seeks approval of constituents to go ahead with the proposal with
negotiation as the rate quoted by M/s. GE was 30% (Approx) higher than the
present AMC charges
AMC CHARGES OF SR ULDC SCHEME FOR THE PRESENT AND
PROPOSED BY M/S GE
Sl.No. Constituent Present Total AMC in Rs. Proposed Total AMC in Rs.
1
RSCC
1,67,38,566
2,23,21,282
2 APTRANSCO
1,73,11,346
2,30,81,561
3
TNEB
1,48,71,391
1,98,26,621
4
KPTCL
1,35,55,653
1,80,80,357
5
KSEB
1,47,70,742
1,96,95,948
6 PUDUCHERRY
1,18,34,589
1,57,87,645
Price Break Up Details for AMC OF SR ULDC SCADA
PROPOSED AMC COMBINED
ON SHORE AND OFF SHORE
PRESENT AMC VALUE
ONSHORE
Sl.No Constituent
1 RSCC
Software Support for RSCC
Hardware Support for RSCC
Sub-Total
2 APTRANSCO
Software Support for APSEB
Hardware Support for APSEB
Sub-Total
3 TNEB
Software Support for TNEB
Hardware Support for TNEB
Sub-Total
4 KPTCL
Software Support for KEB
Hardware Support for KEB
Sub-Total
5 KSEB
Software Support for KERALA
Hardware Support for KERALA
Sub-Total
6 UT PONDY
Software Support for UT PONDY
Hardware Support for UT PONDY
Sub-Total
Grand Total (INR)
OFFSHORE
TOTAL
TOTAL
Per Annum
INR
Per Annum
INR
Per Annum
INR
Per Annum
INR
4,977,295.00
3,979,507.00
8,956,802.00
4,324,307.54
3,457,456.14
7,781,763.68
9,301,602.54
7,436,963.14
16,738,565.68
12,499,918.00
9,821,364.00
22,321,282.00
5,147,620.00
4,115,687.00
9,263,307.00
4,472,299.79
3,575,738.88
8,048,038.67
9,619,919.79
7,691,425.88
17,311,345.67
12,925,674.00
10,155,887.00
23,081,561.00
4,422,084.00
3,535,598.00
7,957,682.00
3,841,967.58
3,071,741.52
6,913,709.10
8,264,051.58
6,607,339.52
14,871,391.10
11,102,908.00
8,723,713.00
19,826,621.00
4,030,841.00
3,222,786.00
7,253,627.00
3,502,020.41
2,800,005.91
6,302,026.32
7,532,861.41
6,022,791.91
13,555,653.32
10,125,000.00
7,955,357.00
18,080,357.00
4,392,152.00
3,511,666.00
7,903,818.00
3,815,960.19
3,050,963.37
6,866,923.56
8,208,112.19
6,562,629.37
14,770,741.56
11,029,731.00
8,666,217.00
19,695,948.00
3,519,072.00
2,813,611.00
6,332,683.00
3,057,395.80
2,444,509.84
5,501,905.64
6,576,467.80
5,258,120.84
11,834,588.64
8,841,081.00
6,946,564.00
15,787,645.00
47,667,919.00
41,414,366.97
89,082,285.97
118,793,414.00
Note : The above prices does not include taxes and duties.
Automatic Data Reading (AMR) /Collection
SL NO 10 OF TCC
Analysis
Details
IEGC RELATED ISSUES
SL NO 11 OF TCC
RGMO
SL NO 11.1 OF TCC
RGMO
Description
Units Mandated on RGMO as per IEGC
Telemetry Status
Hydro
Thermal
total
Avaialble
Not available
Total
No of units
194
59
253
231
22
253
Installed capacity
10888
15600
26488
25996
492
26488
No information
with RLDC for
status
Total
Status of RGMO in SR
Confirmation
for participation
Excemption/
Extention
requested to
CERC
Offer received from
OEM/Implementation
Unit Not
participating in
RGMO as declared
by the constituents
No of units
9
52
64
36
95
256
Installed
capacity
4310
6185
8855
1771
5367
26488
RGMO
RGMO analysis:
1.Droop >30% considered as non response for RGMO
2. Ramagundam Unit #5, 6, & 7 generation is in the range of 102 to 105%
2. On all instances Idukki, Varahi, Nagjhari, Lower Sileru, Sharavati, Sengulam, Kundah
–I,II,III are responding for immediate increase and decrease. (Units already in FGMO)
3. In adequate response from thermal generating units
4. Mostly hydro generating units responded (which is under FGMO)
5. In adequate response leading to system insecurity Hence petition will be filed by
SRLDC to CERC during next month
Mandated And
Declared Summary
Case Study
Summary
Response
Summary
Automatic Demand Management Scheme
SL NO 11.2 OF TCC
Automatic Demand Management Schemes
Extracts from IEGC dated 28th April 2010
Clause 5.4.2 (d)
Quote:
The SLDC through respective State Electricity Boards/Distribution
Licensees shall also formulate and implement state-of-the-art demand
management schemes for automatic demand management like rotational load
shedding, demand response (which may include lower tariff for interruptible
loads) etc. before 01.01.2011, to reduce overdrawl in order to comply para
5.4.2 (a) and (b) . A Report detailing the scheme and periodic reports on
progress of implementation of the schemes shall be sent to the Central
Commission by the concerned SLDC.
Unquote:
All the Constituents are requested to Operationalize
Status
Automatic Load Shedding Scheme for Overdrawing
Constituents at frequency less than 49.5Hz
SL NO 11.3 OF TCC
• In the 14th SRPC Meeting held at Cochin, Constituents had agreed to
Implement the Load Shedding Scheme for over drawing constituents to avert
frequency falling below 49.5 Hz with the following quantum
•
APTRANSCO had been identified 800 MW and tested for remote tripping.
•
TANTRANSCO had been identified 647MW and made operational
•
KSEB had identified 125 -250 MW
•
KAR had identified 384MW ( Max)
•
PONDY to furnish the feeder details.
Excel Computation
• The Quantum of Load relief through Radial feeder is due for revision.
Status
Arranging Interruptible Loads in four groups
SL NO 11.4 OF TCC
Extracts from IEGC dated 28th April 2010
Clause 5.4.2 (e)
Quote:
In order to maintain the frequency within the stipulated band
and maintaining the network security, the interruptible loads shall be
arranged in four groups of loads, for scheduled power cuts/load
shedding, loads for unscheduled load shedding, loads to be shed
through under frequency relays/ df/dt relays and loads to be shed under
any System Protection Scheme identified at the RPC level. These
loads shall be grouped in such a manner that there is no overlapping
between different Groups of loads. …………………...
Unquote:
• AP & Kerala had completed the exercise
• KPTCL, Pondicherry & Tamil Nadu had initiated the exercise
Status
Demand Estimation
SL NO 11.5 OF TCC
Extracts from IEGC dated 28th April 2010
Clause 5.3 (e)
Quote:
While the demand estimation for operational purposes is to be
done on a daily/weekly/monthly basis initially, mechanisms and facilities
at SLDCs shall be created at the earliest but not later than 1.1.2011 to
facilitate on-line estimation of demand for daily operational use for each
15 minutes block.
Unquote:
Constituents are furnishing the block wise forecast
Status
UFR
SL NO 11.6 OF TCC
AUFR settings and Quantum Implementation Status
• Pondicherry – To confirm the status
• UFR Quantum is due for revision
Status
Pending Field Inputs
SL NO 11.7 OF TCC
Pending as on
20.04.11
Year wise comparison
Constituent
Mar2008
Mar2009
Mar2010
Mar2011
APTRANSCO
KPTCL
KSEB
TNEB
SR 1 (POWERGRID)
SR 2 (POWERGRID)
618
800
0
400
3
205
541
693
0
138
4
411
640
766
25
129
26
729
484
334
18
106
6
173
Apr2011
(20/04/11)
410
332
24
105
17
174
56
16
32
16
22
16
35
16
31
16
40
61
40
61
45
64
61
61
63
37
17
1
2217
13
1
1950
30
1
2493
77
0
1371
57
0
1266
NTPC
RSTPS
RGCCP(Kylm)
NPCIL
KAIGA
MAPS
NLC
NLC TS 2
NLC TS 1 EXP
TOTAL
Details
TRANSMISSION SYSTEM FOR EVACUATION OF POWER
FROM SIMHADRI-II TPS (2x500 MW) OF NTPC
SL NO 12 OF TCC
TRANSMISSION SYSTEM FOR EVACUATION OF SIMHADRI-II
IN 28TH STANDING COMMITTEE MEETING, IT
WAS DECIDED THAT IN STEAD OF NEW 400KV
SIMHADRI-GAZUWAKA D/C LINE, 400KV
GAZUWAKA-VEMAGIRI D/C LINE LILOed AT
SIMHADRI
MALKARAM
PRESENT 400KV VEMAGIRINUNNA AP LINES WILL BE
CONNECTED TO
NARSARAOPET BY
DISCONNECTING FROM
NUNNA
GAZUWAKA
SIMHADRI
NARSARAOPET
VEMAGIRI
VTS
LILO OF 400KV NUNNA-VTS
DC LINE AT NARSRAO PET
400KV GAZUWAKA-VEMAGIRI D/C
LINE LILO AT SIMHADRI FOR
EVACUATION OF SIMHADRI-II
(2x500) POWER
SIMHADRI – II TPS EVACUATION
•
APTRANSCO had accorded concurrence for Open Access for a period of 5 years.
•
Further extension of Open Access would be reviewed w.r.t transmission availability.
•
APTRANSCO had informed that the charges had been worked out on ARR. The other
constituents may like to take up the matter with APERC.
•
In the 13th & 14th SRPC meeting, it was noted that since the Regulations on the use of
intervening system were likely to be notified by CERC, so there may be not be necessary
for approaching APERC in the present scenario.
•
Since Kundankulam & NLC generation has not yet came so if
Simhadri II Generation comes up, SR import capability will be
reduced to that extent.
Allocation:
AP: 384.4 MW
KAR: 176.4 MW
KER: 80.9 MW
TN: 197.7 MW
Pondy: 10.6 MW
Unallocated: 150 MW
OPERATION OF TALCHER-KOLAR HVDC TRANSMISSION
SYSTEM IN GROUND RETURN MODE
SL NO 13 OF TCC
PRDC REPORT EXCERPTS
• GRM OPERATION IS NOT POSSIBLE WITHOUT BLOCKING DEVICES AT LARGE
NUMBER OF LOCATIONS
• BLOCKING DEVICES SHIFT THE DC NEUTRAL CURRENT TO A DIFFERENT
LOCATION
• INVESTIGATE THOROUGHLY ELECTRODE DESIGN AND LOCATION
• GRM TO BE LIMITED TO 150 MW
• BLOCKING DEVICES TO BE PROVIDED AT KOLAR, DB PURA AND BIAL 220KV
STATIONS
• TRIP SINGNAL LOGIC NEEDS MODIFICATION?
CEA Letter
13.08.09
KPTCL Letter
12.11.09
GRM
DETAILS
Sudden Flow Reduction due
to High ambient temp @ Tal
& Low Volt @ Kolar
SPS 1000 &
450
APPENDIX-IV
PROGRESS OF BUS /LINE REACTORS TO BE
COMMISSSIONED IN SR
SL NO 14 OF TCC
BUS / LINE REACTORS COMMISSIONING BY SR CONSTITUENTS
•
•
•
S. No
Bus Name
Bus /
Line
Reactor
Original
Target
Revised
Target Date
1*
Ramagundam
Bus
Feb-11
Aug-11
2
Simhadri
Bus
Nov-10
Mar-11
3
Neyveli – Expn.
Bus
Apr-11
Feb-11
4
Neyveli TS-II
Bus
Apr-11
Apr-11
5
Raichur TPS
Bus
Dec-10
Dec-11
6
Talaguppa
Bus
Jun-10
Mar-12
7
Guttur
Bus
Jun-10
Mar-12
8
Nelamangala
Bus
Jun-10
Mar-12
9
Hoody
Bus
Jun-10
Mar-12
10
Hyderabad
Line
Apr-11
Jun-11
11
Kurnool
Bus
Apr-11
Jun-11
12
Vizag
Bus
Apr-11
Jun-11
Voltages
The Bus reactor at NTPC Ramagundam have to be connected to Bus section 1 or 2
instead of Bus section 4
Guttur Line Reactor to be commissioned in addition to Guttur Bus reactor
Commissioning of Bus Reactor at Kudankulam is essential for ensuring availability of
reliable start up supply
IDENTIFICATION OF STRETCHES IN THE STATE SECTOR
WHERE INSULATORS ARE TO BE REPLACED DUE TO
POLLUTION/FOG/SEA WATER
SL NO 16 OF TCC
HIGHLY SENSITIVE AREA
(FREQUENT TRIPPING DUE TO POLLUTION/FOG/SEA WATER)
• Kali Complex in Karnataka.
• Tuticorin Area in Tamil Nadu.
TTPS
• Coastal Area around Kalpaka in Andhra Pradesh.
• Tripping in Raichur Switch yard due to tracking of Insulators.
RTPS
• All Constituents to take up replacement of Insulators in prone area as well as
cleaning up of Insulators in Switch yard which are prone to pollution.
PCC Meeting
OPERATIONALISING OF
CHIKKODI-KOLHAPUR 220 KV LINE
SL NO 19 OF TCC
OPERATIONALISING OF
CHIKKODI-KOLHAPUR 220 KV LINE
• Any of the planning issues relating to Operationalizing of Chikkodi –Kolhapur
220 kV line
like seeking exemption from CERC on Inter Regional ATC
computation etc have to be done by SRPC Secretariat directly .
SHUT DOWN OF INTER REGIONAL LINKS
SL NO 20 OF TCC
SHUT DOWN OF INTER REGIONAL LINKS
• Talcher – Kolar S/D to be availed only during July – December along with S/D
of Talcher Stage II Units
• Concurrence of NLDC & the connected region to be taken for planned
outage of IR links
• Annual Outage Plan of IR links to be concurred by NLDC & Concerned region
SHUT DOWN OF 400 KV VIJAYAWADA- NELLORE D/C LINE
SL NO 21 OF TCC
BEFORE S/D
AFTER S/D
AP LETTER
SCHEDULING OF TALCHER STPS STAGE II
SL NO 23 OF TCC
Scheduling of Talcher Stg II
• Committee recommended that the scheduling of Talcher STPS-II be
continued to done by SRLDC, as the clauses in the IEGC allow the same
and change is not called for.
Scheduling of Talcher stg II
Clause 6.4 of IEGC
• The national interconnected grid is divided into control areas, like Regional ISTS,
States, DVC, etc. where the load dispatch centre or system operator of the
respective control area controls its generation and/or load to maintain its
interchange schedule with other control areas whenever required to do so and
contributes to frequency regulation of the synchronously operating system. The
Load Despatch Centre of a control area therefore is responsible for coordinating the
scheduling of a generating station, within the control area, real time monitoring the
station’s operation, checking that there is no gaming (gaming is an intentional misdeclaration of a parameter related to commercial mechanism in vogue, in order to
make an undue commercial gain) in its availability declaration or in any other way
revision of availability declaration and injection schedule, switching instructions,
metering and energy accounting, issuance of UI accounts within the control area,
collections/disbursement of UI payments, outageplaning etc.
.
Control area definition in IEGC:
An electrical system bounded by interconnections (tie lines) , metering and
telemetry which controls its generation and/or load to maintain its interchange
schedule with other control areas whenever required to do so and contributes to
frequency regulation of the synchronously operating system.
Why SRLDC ?
• Minimal to and fro co-ordination between RLDC’s and SLDc’s in case of
scheduling process involving surrender ,recall etc.
• Less time in to and fro communication
• Right from planning to implementation Talcher II is apart of SR system.
Only geographically located in ER system
• SR boundary is upto Talcher AC I/C & Jeypore end of Gazuwaka line
• In analogy to 6.4.2c(iii) of IEGC and SoR of IEGC 2010 in para 41.13, the
control area jurisdiction of Talcher-II shall be with SRLDC as more than 50%
share is to SR constituents.
• In case of Open Access transaction also the nodal RLDC is that of importing
region. On same Anology SRLDC is nodal agency for Talcher-II
Continued
• It plays a vital role in the LGBR of SR
• AOH coordination by SRPC OCC
• SPS already in place for eventualities like unit /pole tripping.
• Present system is working fine for over 8 years.
Extracts from SoR on IEGC dt.18.06.2010
41. Demarcation of responsibilities( Regulation 6.4 of draft grid code regulations)
41.13 This has been done to ensure certainty in the demarcation of responsibilities.
The IPP with their business strategy would decide quantum of power to be sold
through long term, Medium term and short terms. The connectivity to ISTS and
STU system indicates that generator wants to avail this flexibility. As the
customer of this type of generator would be in more than one region, RLDC
through its communication system would be able to coordinate with more than
one regions and also RLDC would be aware of system operating conditions like
transmission constraints, Voltage conditions etc and would be in better position
to ensure that scheduling to various consumers of the IPP is done optimally on
day to day basis. Hence, we have decided that if the host State has more than
50% share of power, then that generating station shall be under the jurisdiction
of SLDC, else it shall be under RLDC. Regarding the apprehension of some
stakeholders on frequent toggling of control area jurisdiction, it is clarified that
the control area jurisdiction is decided on the basis of permanent share of the
host State, which will not change frequently, hence frequent toggling would not
be there. Moreover, initially when one or two units/ stages of the project will
come under commercial operation, the jurisdiction would be more likely with
SLDC depending on the share of the host State. On the progressive
commissioning of units/ stages, it is more likely that the share of the host State
would decrease and become equal to or less than 50%, resulting in shifting of
control area jurisdiction from SLDC to RLDC. In future also, when more units
are commissioned, it is more likely that the control area jurisdiction will remain
with RLDC and there would not be frequent toggling. Regarding the
apprehension of some stakeholders about the problem in metering during due
to this toggling, it is clarified that the interface meters at CTU and STU
interfaces shall be installed as per the CEA regulations on metering. It is
further clarified that as switchover of control area would be done expeditiously
after the change w.e.f. the next billing period i.e. next week UI accounting there
shall not be any problem in energy accounting as anticipated by SLDC,
Maharashtra. For inter-State energy accounting, it shall be as per CERC ABT
mechanism.
LOW FREQUENCY OPERATION
SL NO 24.3 OF TCC
ABC & 12%
SCH VS DRW
FLOW GATE
VIOLATION
FREQUENCY SPECTRUM OF SOUTHERN REGIONAL GRID
(APRIL’09 TO 27th APR’11)
FREQUENCY (Hz)
MONTH
Apr-09
May-09
Jun-09
Jul-09
Aug-09
Sep-09
Oct-09
Nov-09
Dec-09
Jan-10
Feb-10
Mar-10
Apr-10
May-10
Jun-10
Jul-10
Aug-10
Sep-10
Oct-10
Nov-10
Dec-10
Jan-11
Feb-11
Mar-11
Apr-11
MAX
MIN
AVG
< 48.5 HZ
50.93
51.03
50.41
50.48
50.25
50.68
50.85
50.57
50.38
50.47
50.27
50.2
50.56
48.53
48.56
48.97
49.04
48.98
48.82
48.57
48.58
49.2
49.18
49.08
48.78
48.57
49.39
49.72
49.57
49.66
49.52
49.72
49.53
49.77
49.75
49.76
49.59
49.39
49.45
0
0
0
0
0
0
0
0
0
0
0
0
0
MAX
MIN
AVG
< 48.5 HZ
50.88
50.67
50.69
50.54
50.57
50.66
50.97
50.97
50.99
50.93
50.82
50.86
48.58
48.56
48.92
48.7
48.84
49.24
48.88
48.96
49.22
48.83
48.81
48.81
49.84
49.81
49.85
49.81
49.92
49.91
49.99
49.92
49.82
49.7
49.61
49.65
0
0
0
0
0
0
0
0
0
0
0
0.00
% OF TIME WHEN FREQUECY WAS BETWEEN
48.5 TO
49.0 TO
49.2 TO
49.5 TO
50.0 TO
49.0 HZ
49.2 HZ
49.5 HZ
50.0 HZ
50.3 HZ
6.7
13.88
39.66
36.65
3.68
1.86
2.52
18.32
51.31
21.41
1.35
3.8
32.5
51.91
9.64
0.08
0.96
21.11
65.01
11.74
0.77
3.15
34.34
58.18
3.31
0.02
0.32
11.53
69.93
15.82
1.57
4.23
37.14
47.45
8.21
0.06
0.19
4.35
76.25
18.12
0.04
0.15
7.48
70.9
20.7
0.06
0.24
6.34
74.6
17.42
0.46
2.39
20.32
71.33
5.29
2.91
9.07
50.78
35.53
1.59
2.83
7.19
40.91
45.55
3.27
48.5 TO
49.0 HZ
0.28
0.83
0.03
0.04
0.06
0
0.03
0
0
0.07
0.17
0.33
49.0 TO
49.2 HZ
0.25
1.04
0.16
0.17
0.25
0
0.07
0.03
0
0.42
0.78
1.46
49.2 TO
49.5 HZ
2.45
3.88
1.27
3.52
1.33
0.21
0.54
0.75
1.43
7.91
18.27
20.10
49.5 TO
50.0 HZ
71.97
73.81
82.36
77.64
64.25
71.15
55.03
67.24
79.97
85.73
78.63
69.77
50.0 TO
50.2 HZ
19.26
14.52
12.13
13.39
26.49
21.47
28.53
22.33
15.04
4.95
1.77
6.97
> 50.3 HZ
0.44
4.58
0.8
1.1
0.25
2.38
1.4
1.02
0.73
1.34
0.23
0.12
0.24
> 50.2 HZ
5.79
5.92
4.05
5.24
7.62
7.17
15.8
9.65
3.56
0.92
0.38
1.37
HIGH FREQUENCY OPERATION
SL NO 24.4 OF TCC
GRAPHS & MSGs
Staggering of loads in a co-ordinated manner have to be done
during change over by Constituents. Staggering to be reviewed
Major Events
SL NO 24.6 OF TCC
MAJOR EVENTS
Hydro Availability
SL NO 24.7 OF TCC
Reservoir Position
Full
Reservoir
Level
LEVEL IN MTS
Last 9 Years
Correspondi
ng Monthly
Average
Level
LEVEL
LEVEL
April
27/Apr/
2010
27/Apr
/2011
Last 9
Years
Correspon
ding
Monthly
Average
MU's
ENERGY
ENERGY
Shortfall (-ve) / Rise
(+ve) IN MU w.r.t Last
Year Same Day
Shortfall (-ve) / Rise
(+ve) w.r.t 9 years
Corresponding
Monthly Average
April
27/Apr/
2010
27/Apr
/2011
MU
%
MU
%
JALAPUT
838.40
834.61
822.17
835.24
246
83
402
319
384
156
63
SRISAILAM
270.70
263.65
247.86
247.53
---
---
---
---
---
---
---
N’SAGAR
179.90
164.82
157.34
168.71
---
---
---
---
---
---
---
LINGANMAKKI
554.50
549.29
540.21
541.75
1143
1287
1515
228
18
372
32
SUPA
564.00
546.38
527.89
529.21
788
748
805
57
8
17
2
IDUKKI
732.43
721.53
708.94
713.50
601
595
837
242
41
236
39
KAKKI
969.80
974.23
958.89
959.90
318
333
350
17
5
32
10
NILGIRIS
---
---
---
---
534
491
191
-300
-61
-343
-64
3631
3537
4100
563
16
470
13
TOTAL
Reservoir Level Graph
Reservoir levels in Mu as on last day of the month for the years
2007-08, 08-09, 09-10,10-11
14000
12000
4100 MU on
27th Apr 2011
Energy in Mu
10000
8000
6000
4000
2000
2007-08
Month
2008-09
2009-10
31st Mar
28th Feb
31st Jan
31st Dec
30th Nov
31st Oct
30th Sep
31st Aug
31st July
30th June
30th Apr
31st May
0
2010-11
Reservoir levels in % as on last day of the month for the years
2007-08, 08-09, 09-10,10-11
100.0
31.99% on
27th Apr 2011
90.0
80.0
60.0
50.0
40.0
30.0
20.0
Month
2007-08
2008-09
2009-10
2010-11
31st Mar
28th Feb
31st Jan
31st Dec
30th Nov
31st Oct
30th Sep
31st Aug
31st July
30th June
31st May
10.0
30th Apr
Energy in %
70.0
Grid Voltage
SL NO 24.8 OF TCC
Voltages
Vemagiri MOM
Vemagiri Tap
Change
Installation of Bus reactor at Vemagiri complex may be considered to
address the high voltage problem at vemagiri
VAR Absorption/Injection by
Generators within Capability Limits
SL NO 24.9 OF TCC
Graphs
Operation of Talcher – Kolar HVDC Link
in extended mode of operation
SL NO 27 OF TCC
Report
CRISIS MANAGEMENT PLAN
SL NO D 2.1 OF TCC
PROGRESS
Closing of 220/230 kV Inter State Lines
Supp Agenda 2 Point 4 OF TCC
VARIOUS MEETINGS WHERE ISSUE OF CLOSING AP-TN, AND INTER REGIONA LINKS WERE TAKEN UP
Sr.No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Date
06-Jun-08
13-Aug-08
18-Oct-08
11-Nov-08
Meeting
6th TCC
28th OCC
7th TCC
29th OCC
Point Discussed
RADIALISATION OF CHIKKODI ON N-E-W GRID THROUGH CHIKKODI – KOLHAPUR LINE
RADIALISATION OF CHIKKODI ON N-E-W GRID THROUGH CHIKKODI – KOLHAPUR LINE
RADIALISATION OF CHIKKODI ON N-E-W GRID THROUGH CHIKKODI – KOLHAPUR LINE
STATUS REVIEW ON RADIALISATION OF CHIKKODI ON N-E-W GRID THROUGH CHIKKODI –
KOLHAPUR LINE (DISCUSSED IN 28TH OCCM)
10-Dec-08 30th OCC STATUS REVIEW ON RADIALISATION OF CHIKKODI ON N-E-W GRID THROUGH CHIKKODI –
KOLHAPUR LINE (DISCUSSED IN 29TH OCCM)
05-Mar-09 8th TCC
RADIALISATION OF CHIKKODI ON N-E-W GRID THROUGH CHIKKODI – KOLHAPUR LINE
10-Jul-09 37th OCC OUTAGE OF 220KV CHITTOR - THIRUVALEM LINE SINCE 10TH FEB 09 – PROGRAMME FOR
PUTTING LINE BACK INTO SERVICE
10-Jul-09 37th OCC CLOSING OF SULURPET-GUMMDIPOONDI FOR REDUCING OVERLOADING OF NEYVELI - S P
BUDUR LINE
09-Sep-09 39th OCC PROLONGED OUTAGE OF CHITTOOR-THIRUVELAM SINCE 10TH FEB 09 15:20 HRS
13-Oct-09 40th OCC PROLONGED OUTAGE OF CHITTOR – THIRUVALEM LINE SINCE 10TH FEB 09 15:20 HRS
12-Nov-09 41st OCC PROLONGED OUTAGE OF CHITTOR – THIRUVALEM LINE SINCE 10TH FEB 09 15:20 HRS
12-Nov-09 41st OCC PROLONGED OUTAGE OF SULURPET –GUMMUDIPOONIDI SINCE 24 /10/09 22:40 HRS
11-Dec-09 42nd OCC TN TO EXPEDITE SYNCHRONISATION OF CHITTOR-THIRUVALEM LINE
11-Dec-09 42nd OCC REVIEW OF SULURPET – GUMMIDIPOONDI O/L TRIPPING SETTINGS
08-Jan-10 43rd OCC TN TO EXPEDITE SYNCHRONISATION OF CHITTOR-THIRUVALEM LINE
08-Jan-10 43rd OCC REVIEW OF SULURPET – GUMMIDIPOONDI O/L TRIPPING SETTINGS
03-Feb-10 8th PCC
TN TO EXPEDITE SYNCHRONISATION OF SULURPET – GUMMIDIPOONDI & CHITTORTHIRUVALEM LINE
11-Feb-10 44th OCC TN TO EXPEDITE SYNCHRONISATION OF CHITTOR-THIRUVALEM LINE
11-Feb-10 44th OCC REVIEW OF SULURPET – GUMMIDIPOONDI O/L TRIPPING SETTINGS
09-Mar-10 45th OCC TN TO EXPEDITE SYNCHRONISATION OF CHITTOR-THIRUVALEM LINE
25-Jun-10 48th OCC TN TO EXPEDITE SYNCHRONISATION OF CHITTOR-THIRUVALEM LINE
14-Jul-10 49th OCC CHITTOR-THIRUVALAM LINE CHARGED ON 28.06.10
08-Oct-10 52nd OCC TN TO EXPEDITE SYNCHRONISATION OF SULURPET – GUMMIDIPOONDI LINE
10-Dec-10 54th OCC SYNCHRONISED THE 230 kV SULURPET – GUMMIDIPOONDI LINE ON 04.12.2010
10-Jan-11 55th OCC RESTRICT THE LINE LOADING TO < 100 MW ON SULURPET – GUMMIDIPOONDI LINE
08-Feb-11 56th OCC TN TO EXPEDITE SYNCHRONISATION OF SULURPET – GUMMIDIPOONDI LINE
09-Mar-11 57th OCC TN TO EXPEDITE SYNCHRONISATION OF SULURPET – GUMMIDIPOONDI & CHITTORTHIRUVALEM LINE
Operation of 400 kV Lines Upto SIL
derived steady State limit
Supp Agenda 2 Point 2 OF TCC
PPT
REPORT
Automatic Data Reading (AMR) /Collection
• To avoid all the data related delays and fulfill the deadlines set by IEGC,
SRLDC had proposed to adopt AMR scheme in SR. In SR, there are about
600 SEMs installed in about 100 locations. Scheme may be implemented by
PGCIL at an estimated cost of about Rs. 1.5 Crores which can be recovered
through tariff in the same way as the cost of SEMs is being recovered.
•
Outcome of the 14th commercial Sub – Committee meeting
 Committee in principle agreed the proposal.
 SRLDC suggested that cost may be recovered through tariff.
Proposal for automatic data reading
(AMR) /collection (to be implemented by POWERGRID):
To avoid delays in SEM data transmission to SRLDC it is proposed to adopt AMR scheme in SR
at an estimated cost of Rs.1.5Crores.Schematic representation of AMR is as below.
Hardware required for each location:
Modem-1 no, Data Concentrator Unit-1 no
Local Computer- 1 no., Remote Computer at SRLDC – 1 no.
Cost of Communication on GPRS mode : as per actual.
Bill Of Quantities
Sl.
No.
Description
Qty.
*
Unit
Rate Rs
**
Amount
Rs.
A
For S/S with meters located in Control Room (Aprox. 120 S/S) #
1)
All required hardwares i.e. Meter Interfacing Unit/Protocol Comnverter/Optical Probe/
Connectors / Cable for data transfer between meters and Data Concentrator etc.
700
Per SEM
6602
4621400
2)
Data Concentrator Unit/Data Accumulator (one No. at each location)
120
No.
22000
2640000
3)
GPRS Modem (One No. at each location)
120
No.
6500
780000
B
Common for total Scheme
1)
Meter Data Acquisition & Analysis software (For all Data Concentrator Units/Data
Accumulators (Approx. 120 Nos.) and Servers at SRLDC (2 Nos.).
1
Lumpsu
m
1000000
1000000
2)
Training to personnel posted at all S/S where scheme will be commisioned and SRLDC.
(10 Trainings with a batch of 20-30 participants)
10
No.
3)
Installation, Testing & Commissioning/Customization cost
700
Per SEM
2112
1478400
C
CENTRAL LOCATION (AT SRLDC & 6 SLDCs)
1)
Central server (Including cost of required RDBMS & OS)
7
No.
175000
1225000
2)
UPS (2 KVA)
7
No.
30000
210000
3)
GPRS/GSM Modems
7
No.
6500
45500
D
Wararnty / AMC
1)
Warranty for 1 year
2)
AMC for 1st year after Warranty
700
Per SEM
806
564480
3)
AMC for 2nd year after Warranty
800
Per SEM
853
682667
4)
AMC for 3rd year after Warranty
900
Per SEM
894
804414
5)
AMC for 4th year after Warranty
1000
Per SEM
929
929032
Total
15180893
200000
NIL
Minutes of 14th NRPC meeting
reg. AMR scheme implementation
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