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Summary
Pre-assessment of available quantity for park and loan is complex.
Competing needs for flexibility and contingency impact on the
operating range of linepack.
This motivates discretionary release, with appropriate incentive.
Operational Range of Linepack Flexibility
Maximum operating pressures
Contractually agreed pressures
Linepack
Flexibility
day
Demand / supply pattern
Flexibility + contingency
NTS set-up
System Flexibility
NTS has historically been built to transport gas efficiently, based on flat
supply and demand, within a range of operating pressures.
System flexibility is inherently a “by-product” of operating the NTS within a
range of pressure limits.
Current “limits” of flexibility entirely dependent on the daily NTS setup and
the supply/demand pattern and therefore quite complex to define and model
outer-boundary and maxima of available flexibility.
National Grid is incentivised to minimise day-on-day linepack changes but
has no incentive on within-day linepack ‘release’ or ‘use’
Flow Pattern Volatility – “Time of flight”
The ability to profile energy within day across a number of entry/exit points
whilst maintaining an energy balance in aggregate across the day.
Supply patterns responding to demand and market changes.
Plant issues and Portfolio balancing.
Price-responsive supplies and demands.
Supply A
Offtake
Supply B
200km50km
Flows from Supply A switch to Supply B. Linepack levels at Offtake will drop due to the inherent lag of flow from Supply B taking time to reach the Offtake
Single Entry/Exit Point Flexibility
The ability to profile an entry or exit flow above and below a flat rate.
DN offtake profiles.
Power station changes driven by electricity market interaction.
Storage and interconnector within-day switching.
Within-day entry flow fluctuations driven by demand changes and nomination changes.
Flo
w
Time
Removing Linepack from
NTS
Replenishing Linepack to
NTS
Average flow (1/24th rate)
Example: DN Offtake Flows vary within day due to domestic demand
(2) NTS Flow, Pressure & Flexibility
Time
Flo
w
Average flow (1/24th rate)
Pre
ssur
e
Time
Max Daily Pressure
Min Daily Pressure
22:0006:00Start of Day
06:00
Minimum pressure at point where depletion of
linepack ceases
Flow profile varying about the
1/24th rate
Finite limit of flexibility linked to compression/ flow rates required to return to start of day
pressure
Increases the severity of NTS pressure drop
Increasing Linepack
Usage
Replenishing Linepack to
NTS
Removing Linepack from
NTS DN Offtake
Example Day – 9th January (Actual Data)
Within day linepack movement - 9th January 2010
330
335
340
345
350
355
360
06:00
08:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
00:00
02:00
GM
T
04:00
06:00
mcm
Operational Range of Linepack Flexibility
Maximum operating pressures
Contractually agreed pressures
Linepack
Flexibility
Compressor trip risk
day
Operational Range of Linepack Flexibility
Maximum operating pressures
Contractually agreed pressures
Linepack
Flexibility
Within-day exit flexibility
Compressor trip risk
day
Operational Range of Linepack Flexibility
Maximum operating pressures
Contractually agreed pressures
Linepack
Flexibility
Within-day exit flexibility
Compressor trip risk
Within day entry flexibility
day
Within-day Linepack Utilisation
Within-day Max-Min Range of NTS Linepack
0
5
10
15
20
25
30
01
/10
/08
01
/11
/08
01
/12
/08
01
/01
/09
01
/02
/09
01
/03
/09
01
/04
/09
01
/05
/09
01
/06
/09
01
/07
/09
01
/08
/09
01
/09
/09
01
/10
/09
01
/11
/09
01
/12
/09
01
/01
/10
01
/02
/10
01
/03
/10
Date
MC
M
30 day rolling average
Operational Range of Linepack Flexibility
Maximum operating pressures
Contractually agreed pressures
Linepack
Flexibility
Within-day exit flexibility
Compressor trip risk
Within day entry flexibility
day
Information uncertainty,EOD imbalance
Day-to-day linepack change
Closing Linepack minus Opening Linepack, 01-Apr-08 to 06-Jun-10
-12
-9
-6
-3
0
3
6
9
12
01/0
4/20
08
01/0
6/20
08
01/0
8/20
08
01/1
0/20
08
01/1
2/20
08
01/0
2/20
09
01/0
4/20
09
01/0
6/20
09
01/0
8/20
09
01/1
0/20
09
01/1
2/20
09
01/0
2/20
10
01/0
4/20
10
01/0
6/20
10
mcm
Within-day PCLP swings
Predicted Closing Linepack (PCLP)Daily Range of Hourly PCLP: Monthly Maximum and Average
0
10
20
30
40
50
60
70
80
Apr
-06
Jun-
06
Aug
-06
Oct
-06
Dec
-06
Feb
-07
Apr
-07
Jun-
07
Aug
-07
Oct
-07
Dec
-07
Feb
-08
Apr
-08
Jun-
08
Aug
-08
Oct
-08
Dec
-08
Feb
-09
Apr
-09
Jun-
09
Aug
-09
Oct
-09
Dec
-09
Feb
-10
Apr
-10
mcm
monthly maximum monthly average
PCLP = Opening linepack+ System Inputs (Daily Flow Nominations and Storage Flow Nominations)– System Demand (Offtake Profile Notifications)
This graph shows ranges of hourly PCLP values during the gas day.
Operational Range of Linepack Flexibility
Maximum operating pressures
Contractually agreed pressures
Linepack
Flexibility
Within-day exit flexibility
Compressor trip risk
Within day entry flexibility
day
Information uncertainty,EOD imbalance
Supply loss risk
Example Day – 4th January (Supply Loss)
Within day linepack movement - 4th January 2010
315
320
325
330
335
340
345
350
06:0
008
:00
10:0
012
:00
14:0
016
:00
18:0
020
:00
22:0
000
:00
02:0
0 GM
T04
:00
06:0
0
mcm
4th January - Continued
Within day linepack movement - 4th January 2010
315
320
325
330
335
340
345
350
06:00
08:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
00:00
02:00
GM
T
04:00
06:00
mcm
Actual Linepack Linepack based on a Average profile
Within-day entry flexibility
Operational Range of Linepack Flexibility
Maximum operating pressures
Contractually agreed pressures
Linepack
Flexibility
Within-day exit flexibility
Compressor trip risk
Inter-Day Linepack ‘park and loan’
day
Information uncertainty,EOD imbalance
Supply loss risk