ent
2006 Power Systems Conference & Exposition
Wednesday November 1, 2006
1 The Modeling Requirements for Short-Term
Voltage Stability Studies
John Diaz de Leon II
Bud Kehrli
2 Loadflow PV and VQ Curves
Loadflow PV and VQ Curves
3 Typical Loadflow Base Case
Typical Loadflow Base Case
Sub B
Sub C
Sub A
138 kV
Load represented on the
transmission bus, typically
as constant MVA.
Good representation for
loads if voltage stays
within +/- 10% of unity.
4 Voltages Vary >
+/- 10% of Unity
115 kV
Sub B
Detailed Loadflow
Necessary Detail that Needs to be
Added to the Loadflow Base Case
Necessary Detail that Needs to be
Added to the Loadflow Base Case
Sub B
Sub C
Sub A
138 kV
Small Motors
Large Motors
Discharge Lighting
Constant Power
Remaining
13 kV
13 kV
Distribution
Capacitor
Banks
46 kV
Sub-Transmission
System
Sub 1
Sub 2
Sub 3
Dist. Transformer
and Dist. Line Z
The transmission flows
and voltages between
the loadflows should
not change.
5 Before
After
Small
Motors
Large
Motors
Discharge
Lighting
Remaining
Load
Constant
Power
Distribution
Capacitors
Distribution
Transformer
and
Distribution
Feeder
The transmission flows
and voltages between
the loadflows should
not change.
So What Makes Up the Detailed Loads?
So What Makes Up the Detailed Loads?
6 Calculated
Industrial
Commercial
Agriculture
Residential
Residential
Industrial
Commercial
Agriculture
5.0
5.0
10.0
65.0
7.3
4.5
41.5
0
19.5
4.5
20.0
10.0
26.8
4.1
3.7
0
Remaining
Constant
Power
Discharge
Lighting
Large
Motor
Percentage of:
Customer class:
For a Dynamic Voltage Study, We Need to
Determine the Load Makeup to be Modeled
For a Dynamic Voltage Study, We Need to
Determine the Load Makeup to be Modeled
This table shows typical peak load splits for each of the major customer classes.
LOAD BREAKDOWN BASED UPON LITERATURE REVIEW AND HEURISTICS
From WPS/PTI
Power Factor
90.0%
92.8%
88.7 %
15.0
46.7
45.0
64.4
Small
Motor
82.0 %
7 Example Data
Example Data
The load splits can be made by area, by zone, or by bus.
It all depends on the type of data that is available.
Normal Load Split 45% 15% 20% 5% 15%
% SM
% LM
% DL
% MVA
% REM
Residential
64.4
0.0
3.7
4.1
27.8
Agriculture
45.0
10.0
20.0
4.5
20.5
Commercial
46.7
0.0
41.5
4.5
7.3
Industrial
15.0
65.0
10.0
5.0
5.0
Motor
Area Zone Residential
Agriculture Commercial
Industrial
Total
Totals
% SM
% LM
% DL
% MVA
% REM
Total
North
1
36
5
36
23
100
61.1
45.7
15.5
19.6
4.5
14.8
100.0
2
32
7
39
22
100
60.3
45.3
15.0
21.0
4.5
14.3
100.0
3
38
6
41
15
100
58.9
48.6
10.4
21.1
4.4
15.5
100.0
4
39
3
36
22
100
61.2
46.6
14.6
19.2
4.5
15.2
100.0
East
1
34
10
37
19
100
59.9
46.5
13.4
20.5
4.5
15.2
100.0
2
22
5
41
32
100
61.7
40.4
21.3
22.0
4.6
11.7
100.0
3
38
6
33
23
100
61.6
46.0
15.6
18.6
4.5
15.4
100.0
4
38
6
30
26
100
62.6
45.1
17.5
17.7
4.5
15.3
100.0
South
1
39
3
34
24
100
61.8
45.9
15.9
18.6
4.5
15.1
100.0
2
40
2
33
25
100
62.3
45.8
16.5
18.1
4.5
15.2
100.0
3
42
2
30
26
100
63.0
45.9
17.1
17.0
4.5
15.6
100.0
4
36
4
39
21
100
60.4
46.3
14.1
20.4
4.5
14.7
100.0
West
1
40
5
37
18
100
60.2
48.0
12.2
19.6
4.4
15.7
100.0
2
33
6
40
21
100
60.0
45.8
14.3
21.1
4.5
14.4
100.0
3
31
4
38
27
100
61.5
43.6
18.0
20.4
4.5
13.6
100.0
4
38
6
32
24
100
61.9
45.7
16.2
18.3
4.5
15.3
100.0
Overall Load Split
61.1
45.7
15.5
19.6
4.5
14.8
8 IPLAN Programs
Voltage Collapse Base Case Builder
IPLAN Programs
Voltage Collapse Base Case Builder
9 IPLAN Programs
Voltage Collapse Loadflow Builder Base Assumptions
IPLAN Programs
Voltage Collapse Loadflow Builder Base Assumptions
10 Use Them
Use Them!!!
Use the Best Information Available
Use the Best Information Available
Distribution transformers impedances
Amount of distribution capacitors on a
substations network
Two Key Assumptions
11 Why go through all of this
work to model the load?
Next a Question!
Next a Question!
12 You Cant Determine If You Have a Problem Without It!
You Cant Determine If You Have a Problem Without It!
Voltage In Per Unit
ZIP Load Models
Time In Seconds
0
3
13 Compare ZIP Models and Detailed Models!
Compare ZIP Models and Detailed Models!
Voltage In Per Unit
Time In Seconds
Detailed Load Models
0
3
14 /
/ CIM5ZN - Motor Models
/
71,'CIM5ZN','SM',2,0.0369,0.1318,2.396,0.0645,0.0415,0.0489,0.3210,1,0.06,1.2,0.6,0,1.2,0.6,0,0,0,1,0,/ SM PTI
72,'CIM5ZN','LM',2,0.0138,0.0830,3.000,0.0550,0.0530,0.0115,0.0550,1,0.06,1.2,0.6,0,1.2,1.0,0,0,0,1,0,/ LM PTI
/
/ CLODZN - Discharge Lighting, Transformer Exciting Current, Constant Power Loads, and Remaining Loads
/
73, 'CLODZN','DL', 0,0, 0,100, 0, 0,0,0 / Discharge Lighting
74, 'CLODZN','CP', 0,0, 0, 0,100, 0,0,0 / Constant Power Loads
75, 'CLODZN', 'IZ', 0,0, 0, 0, 0,1.5,0,0 / Remaining Loads
/
The distribution load data in the loadflow was designed to fit with the above
dynamic load models. Each distribution bus has its load split into the
above five zones. In the stability simulation, the load in that zone will then
take on the characteristics of that type of load.
PSS/Es Dynamic Load Models
PSS/Es Dynamic Load Models
15 Voltage In Per Unit
Time In Seconds
CLOD
Voltage In Per Unit
Time In Seconds
CLOD
Voltage In Per Unit
CIM5
Time In Seconds
Why use the PSS/E CIM5 Motor Model
Instead of the PSS/E CLOD Motor Model?
Why use the PSS/E CIM5 Motor Model
Instead of the PSS/E CLOD Motor Model?
Sensitive to changes in
frequency and
voltage
.
The PSS/E
CIM5
series
and GE motor models
simulate both the rotating
load dynamics and the
motor electromagnetic
dynamics.
0
3
16 Why use the PSS/E CIM5 Motor Model
Instead of the PSS/E CLOD Motor Model?
Why use the PSS/E CIM5 Motor Model
Instead of the PSS/E CLOD Motor Model?
Voltage In Per Unit
Time In Seconds
CLOD
CIM5
The PSS/E CLOD model
does not have these
capabilities.
Use the
CIM5
model.
Without using it, youll
miss the problem!
0
3
17 Amount of Motor Load
Amount of Motor Load
Voltage In Per Unit
Time In Seconds
50%
50%
60%
60%
70%
70%
60%
60%
Voltage recovery
or collapse is
influenced by the
percentage of
motor load.
0
4
18 Distribution Impedances
Distribution Impedances
Voltage In Per Unit
Voltage stability
problems show
a lower voltage
a slower recovery
even a collapse
with
HIGHER
distribution
impedances.
Time In Seconds
8%
8%
12%
12%
13.5%
13.5%
15%
15%
18%
18%
10%
10%
8%
8%
12%
12%
13.5%
13.5%
15%
15%
18%
18%
10%
10%
The distribution impedances include the distribution transformer and
distribution lines
.
0
3
19 Circuit Breaker Clearing Times
Circuit Breaker Clearing Times
Voltage In Per Unit
Similar to angular
stability problems,
voltage stability
problems are
improved with
FASTER
breaker
clearing times.
Time In Seconds
3
3
5
5
6
6
7
7
8
8
4
4
3
3
5
5
6
6
7
7
8
8
4
4
0
3
20 IPLAN Programs
Voltage Collapse Checker
IPLAN Programs
Voltage Collapse Checker
21 IPLAN Programs
Voltage Collapse Checker Clearing Times for Breaker Openings
IPLAN Programs
Voltage Collapse Checker Clearing Times for Breaker Openings
Plus MUST Contingency Lists
! Estimated Clear Times for different types of elements
TCPcleartime = 7.0/60.0 ! TCP - Transmission Capacitor Bank 7.0 Cycles
DCPcleartime = 6.0/60.0 ! DCP - Fused Sub Distribution Cap Bank 6.0 Cycles
GSUcleartime = 8.0/60.0 ! GSU - Generator Step-up XFMR 8.0 Cycles
DXFcleartime = 7.0/60.0 ! DXF - Distribution XFMR 7.0 Cycles
DBScleartime = 15.0/60.0 ! DBS - Distribution Buses and Feeders 15.0 Cycles
! TLN, TXF, BUS - Transmission Lines, XFMRS, Buses (From bus is fault bus and sets clearing time)
Cleartime345 = 4.0/60.0 ! 345 kV and above 4.0 Cycles
Cleartime230 = 4.5/60.0 ! below 345 kV to 230 kV 4.5 Cycles
Cleartime138 = 5.0/60.0 ! below 230 kV to 138 kV 5.0 Cycles
Cleartime115 = 6.0/60.0 ! below 138 kV 6.0 Cycles
22 Contingency
List
Monitor
List
Inputs
Level 1
All Results
Level 2
Summary of
The Problems
Voltage
Stability Plots
Outputs
IPLAN Programs
Voltage Collapse Checker Input and Output Files
IPLAN Programs
Voltage Collapse Checker Input and Output Files
23 1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.10.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0
Time
(Seconds)
Transmission
Voltage
(P.U.)
0.5 Seconds
After Fault Clearing
1.0 Seconds
After Fault Clearing
Fault
Clearing
Po
or
The longer the voltage
recovery takes,
the more
likely that loads will trip off
line, motors will stall
(especially residential air
conditioners),
and a
voltage collapse event will
occur.
Ide
al
Ad
equ
ate
Voltage Recovery Criteria
Impact on Distribution System Loads
Voltage Recovery Criteria
Impact on Distribution System Loads
24 0%
10%
20%
30%
40%
50%
60%
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00
Post Fault Transmission Voltage Recovery Time (Seconds)
to Recover to 90% Voltage
Percentage of
Contingenc
ies Studied
Voltage Stability Results
For Recent Voltage Stability System Scans
Voltage S