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EUMP Distance Education Services EE532 Power System Dynamics and Transients Satish J Ranade EE532 Power System Dynamics and Transients Objectives Understand basic aspects of power-system stability with focus on Electromechanical dynamics Transient and long term stability

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ee532 power system dynamics and transients2
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

EE532 Lecture 1 (Ranade)

ee532 power system dynamics and transients3
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

EE532 Lecture 1 (Ranade)

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

Power System Transients and Dynamics

EE532 Lecture 1 (Ranade)

power system stability
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)

EE532 Lecture 1 (Ranade)

power system stability7

SPEED

VOLT.

STABLE

UNSTABLE

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

EE532 Lecture 1 (Ranade)

power system stability8

SPEED

Line Real Power P

Power System Stability

Pm Pe

Manifestations – Angle Stability

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

EE532 Lecture 1 (Ranade)

power system stability10
Power System Stability

P

Manifestations – Angle Stability

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 can’t?

Stability means returning to synchronous speed

In a multi-machine system it means settling at a common speed

SPEED

Line Real Power P

EE532 Lecture 1 (Ranade)

power system stability11
Power System Stability

P

Manifestations – Angle Stability

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

EE532 Lecture 1 (Ranade)

power system stability12
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

EE532 Lecture 1 (Ranade)

power system stability13
Power System Stability

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 significant;Issue 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

Terminology

EE532 Lecture 1 (Ranade)

power system stability14
Power System Stability

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.

Terminology

EE532 Lecture 1 (Ranade)

power system stability15
Power System Stability

Voltage Stability

Inability to maintain voltage because of reactive power deficit

Voltage Collapse

Voltage instability leading to low-voltage profile

Terminology

EE532 Lecture 1 (Ranade)

power system stability16
Power System Stability

It’s 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

Comment on Terminology

EE532 Lecture 1 (Ranade)

power system stability17
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

EE532 Lecture 1 (Ranade)

fast transients
Fast transients
  • Lightning (uS)
  • Switching (mS)
  • Abnormal (mS – S)

EE532 Lecture 1 (Ranade)

fast transients19
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

EE532 Lecture 1 (Ranade)

fast transients20
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

EE532 Lecture 1 (Ranade)

fast transients21
Fast transients

Switching

EE532 Lecture 1 (Ranade)

fast transients22
Fast transients

Design issues ( Self Restoring Insulation)

Probabilistic approach

Stress Strength

Probability of Failure

EE532 Lecture 1 (Ranade)

fast transients23
Fast transients

Design issues (Non Self Restoring Insulation)

Insulation coordination

kV

Margin

Equipment Withstand

Prospective Surge

(Limited by design,

surge arresters,…)

Time

EE532 Lecture 1 (Ranade)

slide25

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 , < 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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EE532 Lecture 1 (Ranade)