Sakis Meliopoulos (Georgia Tech) - ecedha

1 2
System Protection
Out of Step (Transient Stability)
Illustration of Two Power System Swings:
(a)Stable – Out of Step Relay Should not Operate
(b)Unstable – Out of Step Relay Should Operate
Special Protection Schemes
Special Protection Schemes are Protective
Relaying Functions Concerned with the
Protection Against Special System Conditions
that May Lead to Catastrophic Results.
These System Conditions are Determined
with Extensive Studies of Specific System
Behavior. Using this Information a SPS is
designed that monitors the System and When
the Special System Conditions Occur
(Recognition Triggers) the System Operates
(Automatically or with Operator Review and
Action)
Transient Voltage Collapse
Reactance Grounded Gen
G
800 MVA-15 kV
X1=15.5%,X2=18%,X0=9%
Va = 8.400 kV
SOURCE-A
Va = 63.01 kV
BUS10
1 2
Va = 42.02 kV
BUS-MID
Reactance Grounded Gen
800 MVA-15 kV
X1=15.5%,X2=18%,X0=9%
Va = 61.99 kV
BUS20
Va = 8.238 kV
BUS30 G
Generator Angle 2x47.4 mile 115 kV Transmission Line
52 Degrees Generator Angle
-49 Degrees
Illustration of Voltage Collapse Near the Center of
a Stable System Swing
Voltage Transitions Are Slow – Undervoltage
Protection Should not Operate
Load Shedding – Frequency / Voltage
A System Disturbance May Create Generation-Load Imbalance
Leading to Sustained Frequency Decline. This Condition, if not
Corrected, May Lead to Equipment Damage. The Condition Can be
Temporarily Corrected by Load Shedding Until Additional Generation
can be Dispatched.
Similarly, a Disturbance May Create Sustained Voltage Problems.
These problems Can be Also Corrected by Load Shedding
NSF/ECEDHA Education Workshop
Georgia Tech GLC, Atlanta, Georgia, July 9-12, 2011
1.11