BASE POINT DEVIATION DURING
SCED SHORTENED INTERVALSPRESENTATION TO SEWG
Jim Galvin- Chair, Settlements and Extract
Working Group 9/20/2010
BACKGROUND
Market trials settlement review of Base Point
Deviation has identified an anomaly in the Base
Point Deviation (BPD) settlement algorithm
 Current algorithm calculates BPD correctly when
SCED intervals are 300 seconds (5 min) in
duration
 For SCED intervals less than 5 min, it is possible
for a BPD to be calculated when a resource
follows all instructed Base Points and ramping
conditions
 Goal in this presentation is to raise issue and
discuss possible long term correction and interim
consideration

BPD- ALGORITHMS
Under-generation
$
Base-Point
Deviation Charge
= Max (0,
(BPDAMT q, p, r)
$/MWh
RT Settlement
Point Price
) x Min (1,
(RTSPP p)
MW
Adjusted
Aggregate BasePoint
(AABP q, p, r)
x¼(
)), ¼(
MW
Adjusted
Aggregate BasePoint
(AABP q, p, r)
-
Coefficient applied
to SPP for UnderGeneration
Cahrge, 1.0
(KP)
MW
MW Tolerance for
Under-Generation,
5MW
(Q2)
)]-
) x Max{0,{Min[((1MWh
Time-Weighted
Telemetered
Generation
(TWTG q, p, r)
%
Tolerance for
Under-Generation,
5%
(K2)
)
}}
Over-generation
$
Base Point
Deviation Charge
(BPDAMT
= Max(0,
q, p, r)
MW
Adjusted
Aggregated Base
Point
(AABP q, p, r)
$/MWh
RT Settlement
Price Point per
Settlement Point
(RTSPP p)
),(
) x Max [0,(
MW
Adjusted
Aggregated Base
Point
(AABP q, p, r)
+
MW
The MW
Tolerance for Over
Generation, 5MW
(Q1)
MWh
Time-Weighted
Telemetered
Generation
(TWTG q, p, r)
)))]
Where:
MWh
Time-Weighted
Telemetered
Generation
(TWTG q, p, r)
= (
y
MW
Average
Telemetered
Generation
(ATG q, p, r, y)
x
Seconds
Duration of SCED
Interval
(TLMP y)
/ 3600 )
- ¼ x Max(((1 +
%
The Percentage
Tolerance for Over
Generation, 5%
(K1)
)x
FOCUS ON AABP
Identified issue focuses on the calculation of the
Adjusted Aggregate Base Point (AABP)
 Base points are issued based on resource
ramping capabilities
 Calculation for AABP is:

Base Point for the interval (y)
 Base Point for previous interval (y-1)
 {y + (y-1)/2} * TLMP/900
 TLMP is total seconds for the SCED period which is
divided by the total of 900 seconds in a 15-minute
settlement interval

EXAMPLE
Base Point Y (Current
SCED)
Base Point Y-1
(Previous SCED)
Telemetered Gen
100
100
100
y1
150
100
125
100
150
y2
175
150
150
125
150
y3
200
175
200
150
300
y4
250
200
220
200
120
y5
250
250
250
220
180
SCED Int
Telemetered Gen Previous
SCED
SCED Int (seconds)
1. Resource has a 10 MW per minute ramp rate and is sitting at 100
MW prior to dispatch for the next interval
2. SCED dispatches the unit (red line) with desired BP of 150 MW
3. SCED interval is shortened to 150 seconds (2.5 minutes) and unit
follows ramp and reaches 125 MW (orange line)
4. Next SCED interval considers ramp rate and telemetered
generation and sets next base point to 175 MW (green line)
5. Over the course of the 15-min interval, 5 total SCEDs are run and
the resource follows its ramp in trying to reach the desired BP
EXAMPLE
SCED Int
y1
y2
y3
y4
y5
Base Point Y (Current
SCED)
100
150
175
200
250
250
Base Point Y-1
(Previous SCED)
100
100
150
175
200
250
Telemetered Gen
100
125
150
200
220
250
Telemetered Gen Previous
SCED
SCED Int (seconds)
AABP
TWTG
100
125
150
200
220
150
150
300
120
180
20.83333
27.08333
62.5
30
50
4.6875
5.729167
14.58333
7
11.75
900
190.4167
43.75
RTSPP
Bandwidth
% Tolerance
MW Tolerance
$100
0.05
180.8958
185.4167
KP
5
MWH
BPD Undergen
$147.40
1. Settlements calculates an Aggregate Adjusted Base Point using the
algorithm on previous page or 190.4 MW
2. Time Weighted Telemetered Generation (TWTG) is calculated at
43.75 MWh for the 15-min interval, or 175 MW (Under-generation)
3. Tolerance band is the % tolerance (5%) or 180.9 MW (45.22 MWh)
4. ERCOT will calculate a BPD Charge of 45.22 MWh – 43.75 MWh
multiplied at the RTSPP of $100, or $147.4
1
45.22396
EXAMPLE- OVER-GENERATION
Base Point Y
(Current
SCED)
200
175
150
100
100
Base Point Y-1
(Previous SCED)
250
250
200
175
150
100
Telemetered Gen
250
225
200
150
130
100
Telemetered
Gen Previous
SCED
SCED Int (seconds)
AABP
TWTG
250
225
200
150
130
150
150
300
120
180
37.5
33.33333333
54.16666667
16.66666667
23
9.895833333
8.854166667
14.58333333
4.666666667
5.75
900
164.6666667
43.75
RTSPP
Bandwidth
% Tolerance
MW Tolerance
BPD Overgen
$100
0.05
172.9MWh
169.6666667
KP
5
$52.50
1. Example shows resource ramping down with same 10 MW per
minute ramp rate
2. Unit follows its ramp and desired BP each SCED period
3. Resource is charged a BPD charge over the tolerance of 172.9 MW
(43.22 MWh) and the TWTG of 43.75 MWh at the RTSPP of $100,
for a charge of $52.50
1
43.225
QUESTIONS