Notes on security assessment

1
Notes on security assessment

• James D. McCalley

2
Types of security violations consequences
Security
Overload Security
Voltage Security
Dynamic Security
Xfmr overload
Line overload
Low Voltage
Unstable Voltage
Early-swing instability
Oscillatory instability (damping)
Large-disturbance instability
Small-disturbance instability
Cascading overloads
Fast voltage collapse
Slow voltage collapse
3
Types of security violations consequences
Overloaded xfmr/line has higher tripping
likelihood, resulting in loss of another element,
possible cascading, voltage or dynamic insecurity
Dynamic security can result in loss of
generation growing oscillations can cause large
power swings to enter relay trip zones
Security
Overload Security
Voltage Security
Dynamic Security
Low voltage affects load and generation
operation. Voltage instability can result in
widespread loss of load.
Xfmr overload
Line overload
Low Voltage
Unstable Voltage
Early-swing instability
Oscillatory instability (damping)
Large-disturbance instability
Small-disturbance instability
Cascading overloads
Fast voltage collapse
Slow voltage collapse
4
Traditional assessment decision

• The NERC Disturbance-Performance Table
• DyLiaccos operational decision paradigm
• System operating limits

5
NERC Disturbance-Performance Table
6
NERC Disturbance-Performance Table, cont
7
NERC Disturbance-Performance Table, cont
8
One Element Out of Service
Normal
Two of More Elements Out of Service
Extreme Events (Two or More Elements Out of
Service)
Single Contingency (Category B Event) B
B Single Line Ground (SLG) or 3-Phase (3Ø) Fault,
with Normal Clearing on 1. Generator 2.
Transmission Circuit 3. Transformer Or loss of an
element without a fault. 4. Single Pole Block,
Normal Clearing of a DC Line
Category C event A first contingency,
followed by adjustments, followed by a second
contingency)
9

Extreme Events (Two or More Elements Out of
Service)
One Element Out of Service
Two of More Elements Out of Service
Normal
Multiple Contingencies Category C Event C1-8
10
DyLiaccos operational decision paradigm
Normal (secure)
11
System operating limits (SOLs)

• The value (such as MW, MVar, Amperes, Frequency
  or Volts) that satisfies the most limiting of the
  prescribed operating criteria for a specified
  system configuration to ensure operation within
  acceptable reliability criteria. System Operating
  Limits are based upon certain operating criteria.
  These include, but are not limited to applicable
  pre- and post-contingency
• Facility Ratings
• Transient Stability Ratings
• Voltage Stability Ratings
• System Voltage Limits

There is a subset of SOLs that are known as
Interconnection Reliability Operating Limits
(IROL). IROLs are defined as, The value (such as
MW, MVar, Amperes, Frequency or Volts) derived
from, or a subset of the System Operating Limits,
which if exceeded, could expose a widespread area
of the Bulk Electric System to instability,
uncontrolled separation(s) or cascading outages.
12
Cascading outages the public perception.
13
Transmission loading relief

• Review of TRL levels and procedures
• (Standard IRO-006-1 Reliability Coordination
  Transmission Loading Relief)

14
(No Transcript)
15
(No Transcript)
16
Appendix A of IRO-00601
TLR3b
In compliance with the Transmission Service
Provider tariffs, Interchange Transactions using
Non-firm Point-to-Point Transmission Service are
curtailed first (TLR Level 3a and 3b), followed
by transmission reconfiguration (TLR Level 4),
and then the curtailment of Interchange
Transactions using Firm Point-to-Point
Transmission Service, Network Integration
Transmission Service and service to Native Load
(TLR Level 5a and 5b).
TLR1
TLR2
TLR4
TLR3a
TLR5b
TLR4
TLR6
TLR5a
17
Congestion on Transmission Lines Has Increased
Dramatically
2005
2004
2003
2002
2000
2001
2006
1999
1998
Source NERC Transmission Loading Relief
Procedure Logs
18
System operating limits
Question 1 Is it secure?
Bus 2
300 MW
X231
X121
900 MW
X131
Bus 1
1200 MW
Bus 3
Question 2 What is maximum cct 1-3 flow such
that reliability criteria is satisfied?
19
Treating power as if it is current.
A very basic relation for power system engineers
expresses the real power flow across a
transmission circuit as (1)
Here, f is the angle by which the voltage leads
the current and is called the power factor angle.
If we assume that electric loads are purely
resistive, so that only real power flows in the
network, then f0 (f will not be exactly zero
because of line reactance). In this case, eq. (1)
is (2)
20
Treating power as if it is current.
A basic fact of power system is that the voltages
usually do not deviate significantly from their
nominal value. Under a system of normalization
(called per-unit), where all voltages are
normalized with respect to this nominal voltage,
it will be the case that Vk1.0. As a result,
eq. (2) becomes (3)
In other words, the numerical value of the real
power flowing on the circuit is the same as the
numerical value of the current magnitude flowing
on that circuit (under the system of
normalization). If, again, the electric load is
purely resistive, then all currents will have
almost the same angle, and one can treat the
current magnitude as if it were the current
phasor. Useful conclusion If we assume voltage
magnitudes are all unity, and all loads are
purely resistive, then whatever rules we have of
dealing with currents also work with real pu
power flows! (or Sbasepu pwr flws)
21
Two good approximations for parallel flows
1. Current division For 2 parallel paths A and
B, power flows on path A according to
Bus 2
X231
X121
900 MW
X131
Bus 1
900 MW
Bus 3
22
Two good approximations for parallel flows
1. Current division For 2 parallel paths A and
B, power flows on path A according to
300 MW
Bus 2
X231
X121
X131
Bus 1
300 MW
Bus 3
23
Two good approximations for parallel flows
2. Superposition Results of 2 independent
calculations will add
Bus 2
Bus 1
1200 MW
Bus 3
24
System operating limits
Bus 2
300 MW
Lose Cct 2-3!
900 MW
Bus 1
1200 MW
Bus 3
25
System operating limits
Bus 2
300 MW
900 MW
Bus 1
1200 MW
Bus 3
Question 2 What is maximum cct 1-3 flow such
that reliability criteria is satisfied?
?Depends on how flow is increased assume stress
direction of Bus1/Bus3. ?Desire precontingency
limits to reflect postcontingency effects
26
System operating limits
Question 2 What is maximum cct 1-3 flow such
that reliability criteria is satisfied?
Bus 2
Bus 1
1300 MW
Bus 3
27
System operating limits
Bus 2
300 MW
Lose Cct 2-3!
1000MW
Bus 1
1300 MW
Bus 3
28
System operating limits
Bus 2
300 MW
900 MW
Bus 1
1200 MW
Bus 3
Question 2 What is maximum cct 1-3 flow such
that reliability criteria is satisfied?
29
Illustration of real-time calculation of
operating security limits w/ DTS (15 mins)

• What is dispatcher training simulator?
• PTDF and OTDF
• Automatic calculation of SOL
• Sample system

30
What is the DTS?

• An off-line environment that
• Emulates an energy control center's EMS
• Simulates the physical power system
• DTS uses the same interfaces and is composed of
  much of the same software as the real-time EMS

31
PTDF and OTDF
Power transfer dist. factors
Outage transfer dist. factors
32
PTDF and OTDF
Power transfer dist. factors
Outage transfer dist. factors
We will later show how to compute SOL using PTDFs
ali and LODF dl,k
33
Automatic calculation of SOLs

• More than identifying contingencies that result
  in violations, it identifies the LIMIT
• Overload security only
• Uses PTDFs, OTDFs, stress direction
• SOL for each cct computed as most restrictive of
• Normal condition, using continuous rating or
• All contingencies, using emergency rating
• Embedded in Arevas DTS
• Updates SOL for all circuits every 8 sec

34
Outaged Line
Monitored Line
Outaged Line
35


More than identifying contingencies resulting in
violations, it identifies LIMITS
36
More than identifying contingencies resulting in
violations, it identifies LIMITS
37
More than identifying contingencies resulting in
violations, it identifies LIMITS
38
More than identifying contingencies resulting in
violations, it identifies LIMITS
39
More than identifying contingencies resulting in
violations, it identifies LIMITS
40
(No Transcript)
41
Computing SOL using PTDFs ali and LODF dl,k