EE532 Power System Dynamics and Transients

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EE532 Power System Dynamics and Transients
EUMP Distance Education Services

• Satish J Ranade

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EE532 Power System Dynamics and Transients

• Objectives
• Understand basic aspects of power-system
  stability with focus on
• Electromechanical dynamics
• Transient and long term stability
• Voltage stability issues
• Obtain a feel for
• Stability analysis
• Interpretation of results

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EE532 Power System Dynamics and Transients

• Objectives
• Understand basics of electromagnetic transients
  with focus on
• Lightning
• Switching
• Calculation of response
• Over-voltages
• Obtain a feel for
• Insulation withstand concepts
• Standards
• Mitigation-Shielding, Line Design, Surge
  Arresters

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Power System Transients and Dynamics

• Time scale Phenomenon Result
• µS Lightning Overvoltage
• mS Switching Insulation Failure
• mS Abnormal Transient Fault
• .1 S Breaker Operations
  Instability
• 1 S Mechanical Dynamics
• Many Seconds Load Dynamics Collapse

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Power System Stability

• Definition (Ch.2)
• The ability of a power system to reach a new
  steady state or equilibrium after a disturbance.
• Interconnected synchronous generators must settle
  to a common, constant speed
• Voltages and power flow must settle to reasonable
  values ( otherwise relays will trip breakers)

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Power System Stability
A disturbance, e.g., fault causes generator
speeds, system voltages and power flow to change
over time
Stability ? post-disturbance quantities become
constant
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Power System Stability

• Manifestations Angle Stability

Pm Pe
Large System Infinite Bus Voltage and frequency
constant
V
Fault Occurs Generator Terminal voltage V goes
to zero Generator electrical real power output Pe
goes to zero Turbine is still putting out
mechanical power Pm Generator speeds up builds
up kinetic energy Fault is cleared Can generator
get back to constant --synchronous speed? Time
scale of 1-10 Seconds
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Power System Stability

• Manifestations Angle Stability

P
KE Builds up
P
Excess KE Needs to be removed
Can generator get back to constant --synchronous
speed? Only if it can get rid of excess
KE Excess KE needs to go into the infinite bus
through the line? Will it? What happens if it
cant? Stability means returning to synchronous
speed In a multi-machine system it means
settling at a common speed
SPEED
Line Real Power P
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Power System Stability

• Manifestations Angle Stability

P
KE Builds up
P
Excess KE Needs to be removed
The process of power transfer across the line to
get rid of excess KE is inherently
oscillatory The infinite bus is trying to
synchronize the generator or bring it back
into step Stability requires synchronizing
torque In addition damping torque to make
oscillation decay this comes from the machine
as well as from control systems
SPEED
Line Real Power P
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Power System Stability

• Manifestations Voltage Stability

Line Opens Load Voltage Drops Many loads keep
power constant --Current goes up Voltage drops
further Reactive power loss goes
up . Generator hits limit Generator
voltage drops Voltage collapses Time scale
of 1 seconds to minutes to hours
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Power System Stability

• Terminology

First Swing (Transient Stability) Generator
speeds swing around to common speed (Better
definition later..)Little or no control action
from exciters.. 1 Second Transient
Stability Multiple Swings 1-5 Sec Field action
most important Mid-Term Past 1 second control
action is significantIssue is oscillations and
damping. This term is not used as much any
more Long Term Past 1 second and including all
control action Includes voltage stability
effects This has become the standard study
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Power System Stability

• Terminology

Rotor Angle Stability Refers to conditions in
which generator dynamics is significant and
voltages less important Steady state
Stability Slow incremental changes that
ultimately makes the system unstable (
associated with maximum power transfer) Small
signal stability Response to small changes that
can be analyzed using linear models.
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Power System Stability

• Terminology

Voltage Stability Inability to maintain voltage
because of reactive power deficit Voltage
Collapse Voltage instability leading to
low-voltage profile
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Power System Stability

• Comment on Terminology

Its all one big ball of wax! Distinctions are
made for a number of reasons Ease of analysis
or computation To emphasize/identify
components and controls that have major
impact A systems may be more prone to one
type of stability than the other Modern
long-term stability simulations capture most of
the effects
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Power System Stability

• Purpose of Stability Study

Planning Transmission Requirements Voltage
Support ( VAR Supply) Design Controls
Excitation, Power system Stabilizers, FACTS
devices Relay Settings Load
Shedding Operations Operating Margins
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Fast transients

• Lightning (uS)
• Switching (mS)
• Abnormal (mS S)

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Fast transients

• Lightning (uS)

e
Strokes to shield Induce voltage
e
Direct stroke to phase
E ( back flashover)
Strokes to ground Induce voltage
Lightning strikes induces over voltages in a line
by several mechanisms
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Fast transients
Lightning Transmission Line Design issues
Geometry to provide Adequate insulation
Shield placement to eliminate Direct Stroke
Surge arrester
Grounding to minimize Induced voltage
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Fast transients
Switching
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Fast transients
Design issues ( Self Restoring Insulation)
Probabilistic approach
Stress Strength
Probability of Failure
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Fast transients
Design issues (Non Self Restoring Insulation)
Insulation coordination
kV
Margin
Equipment Withstand
Prospective Surge (Limited by design, surge
arresters,)
Time
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Notes Collaboration on Homework
Assignments/Projects/Summaries is permitted. Do
not provide or seek help from others on
Tests. Violation of rule 4 will result in an
automatic "F" grade and a recommendation for
suspension. GRADING POLICY Homework Assigned
each lecture, due following Monday 20 Tests 3
60 Projects 20 On Campus Students
Each unexcused absence will cost you 2 The
grading scale is absolute 90 - 100 A, 80 -
89 B, 70 - 79 C, 60 - 69 D , lt 60
F --------------------------------------------
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-------------------- Late homework Policy Unless
prior arrangements are made, Late Homework Will
Not Be Graded. However you will be given 50 of
the credit if you turn homework in prior to the
next scheduled test. -----------------------------
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