PowerNex Associates Inc.

PowerNex Associates Inc. Module 3 Transmission and Distribution www.pnxa.com

Module 3Transmission and Distribution Learning Objectives: To gain an understanding of the following: • Transmission system overview (4A) • Components • Types of transmission limits • Major transmission limits in Ontario • Protection Control and Metering (4B) • Concepts of Special Protection Systems (4C) • Distribution (4D) • How it’s different to transmission

Module 3ATransmission

Module 3ATransmission What will be covered • Basic Transmission Components • Overview of Transmission System • Limits - where do they come from & why do we need them • Internal Key Interfaces and effects on Generation • Normal, High Risk and Emergency Operation • Ontario Interconnections • Transmission Impactive Outages

Transmission • Basic Transmission Components • Overview of Transmission System • Limits - where do they come from & why do we need them • Internal Key Interfaces and effects on Generation • Normal, High Risk and Emergency Operation • Ontario Interconnections • Transmission Impactive Outages

TransmissionThe Single Line Diagram • The Single Line Diagram is a simple representation of the power system or a portion of it. • It shows the system as only one phase rather than three. • Its purpose is to show the power system with minimum detail, ie an overview of what’s connected to what.

TransmissionBasic Transmission ComponentsSingle Line Diagram

SF6 Circuit Breaker Transmission

Air Blast Circuit Breaker Transmission

Bulk oil circuit breaker Transmission

Disconnect switch Transmission

Transmission • What happens when a disconnect switch is used instead of a circuit breaker? • Not pretty!

A 3 phase Transformer Transmission

TransmissionPower Transformer

Transmission • Transmission Lines in parallel, if lose one, flow is redistributed • Generally not so for Distribution lines (radial) • Parallel lines lower the impedance, the more parallel lines the higher the reliability and the lower the losses (I2R) • The higher the voltage, the greater the power carrying capacity (proportional to V squared) • Maximum power carrying ability at Surge Impedance Loading (when reactive inductance and reactive capacitance of line are equal and thus cancel each other, leaving only the resistance).

Transmission Typical Power Grid System

Transmission

TransmissionElectrical Equivalent to Water Analogy Generator (tap - water supply) -Provides Energy (MW), voltage support, &frequency support Electrical Bus (Bucket) -Critical Voltage, Current, Frequency & Short Circuit Level Transmission Lines (Pipes) Impedance (Fixed Resistance to Flow) Variable Loads (tap - water removal) Absorb MW and Voltage Support, Critical Voltage and Frequency Levels

Transmission • Typical Surge Impedance Loadings • 500 Kv - 1,000 Mw • 230 Kv – 200 Mw • 115 Kv – 50 Mw • Ontario System made up of 500 Kv, 230 Kv, 115 Kv. • Distribution voltages < 50 Kv

Double circuit EHV Transmission line Transmission

TransmissionHistorical Note 1965 Northeast Blackout • One 230 kV circuit at Beck (Q29BD) tripped • Four other circuits at Beck cascade trip within 2.7s • 1700 MW power surge into New York causing a wide-spread blackout • NPCC formed to ensure utilities in the northeastern part of North America adopt practices to prevent another blackout

Transmission

Transmission • Three basic types of limits: • Thermal • Voltage Decline/ Rise • Stability • Also Short Circuit limits

Transmission Thermal Limits • Lines designed to operate to specific “ground” clearance and maximum conductor temperature • Line clearance reduced as conductor temperature rises (sag) • Ground clearance decreases as • Current flow increases • Ambient temperature rises • Wind velocity decreases • Sunlight increases Safe Ground Clearance

Transmission Thermal Limits – Limited Time Ratings

Transmission Thermal Limits also apply to equipment other than lines • For example: Transformers • Rated in MVA • Require sufficient cooling to dissipate heating • Hot spot and oil temp limits • As with lines, limited time ratings

Transmission Voltage Limits • Must be able to sustain Voltage levels both pre and post contingency • Low or high voltages can cause equipment damage to Hydro One or Generator assets and also customer equipment • Under normal conditions, continuous voltages are to be maintained within predefined levels. • For example: • 115 Kv voltage must be between 127* Kv and 113 Kv • 230 Kv voltage must be between 250Kv* and 220 Kv • 500 Kv must be between 550 Kv and 490 Kv * In Northern Ontario 132 Kv and 260 Kv

Transmission Voltage Limits • Transformer Voltages • Steady State Ratings, Maximum Acceptable Levels • 110% of Input Winding Rating, • 105% of Output Winding Rating at Full Load

Transmission Stability Limits • These are the most complex limits • Instability can cause cascading outages • Affects generators, they go out of synchronism, “pole slipping”, “out of step” are terms used. • Stability usually a problem on a system with long transmission lines • If the receiving end voltage “angle” lags the sending end voltage “angle” by 90 or more degrees, then unstable

TransmissionStability

TransmissionSummary ofSecurity Criteria • Voltage Levels,meet customer and equipment voltage limits • Stability, acceptable damping • Element Loading, operate to appropriate thermal rating of equipment • Short Circuit, breakers have capability of clearing worst short circuit condition

Transmission“Bad Things happen” • What bad things can happen? • Virtually anything, but must be practical and reasonable. • Following 1965 Blackout NPCC developed a practical list of “bad things” • All members of NPCC must operate their systems by being able to recover from events on this list without having adverse effects on the systems of other members. • This costs money due to congestion. But the costs of a cascading blackout far outweigh the congestion costs.

TransmissionRecognized “Bad Things” (Contingencies) - NPCC Criteria • Permanent 3-Phase fault (worst kind of fault) – with normal fault clearing • Simultaneous permanent phase to ground faults on adjacent circuits (same tower) – with normal fault clearing • Permanent phase to ground fault on any generator, circuit, transformer or bus section - with delayed fault clearing (Breaker Failure) • Loss of any element without a fault • Permanent phase to ground fault on circuit breaker - with normal fault clearing • Failure of a circuit breaker, associated with a Special Protection Scheme, to operate

TransmissionHow are limits developed? • Limits are developed using computerised simulation studies. • A data base representing all of the power system components, their electrical characteristics and their connectivity has been developed and is constantly being updated when new equipment is added to the system. • This data base also includes data on interconnected systems (electrically it’s all one big system) • Application software is used by engineers to run fault simulation studies and test the operation of the system following a particular fault. • From the results of these studies operational security limits are produced.

TransmissionHow are limits developed? Thermal Limits • Fairly simple • Off line load flows predict the change in flows on remaining elements post contingency, ie distribution factors • In real time these distribution factors are used to predict change in loading on the remaining elements following a contingency • Thus the operator can determine pre-contingency loading on other lines

TransmissionHow are limits developed? Voltage Limits • Developed by off line simulation studies • Use NPCC criteria to “throw” faults at the system • Calculate the post contingency effects on voltage • Are post contingency voltages within limits? If OK move on to next simulation. If not OK then reduce pre contingency loadings (by redispatch) in the simulation until can meet post contingency voltage criteria. • This then becomes the Operating Security Limit. • Pre-contingency loadings not to exceed these.

TransmissionHow are limits developed? Stability Limits • Developed by off line simulation studies, simulating the system dynamics • Use NPCC criteria to “throw” faults at the system • Calculate the post contingency effects on stability • Is the system stable pre contingency, during the contingency and post contingency? If OK move on to next simulation. If not OK then redispatch system to reduce pre contingency loadings in the simulation until post contingency stability achieved. • This loading limit becomes the Operating Security Limit. • Pre-contingency loadings must not exceed these.

TransmissionHow are Limits Developed? • Some notes re simulation studies performed: • time consuming • only study a limited number of contingencies and system conditions (eg winter peak, summer minimum, summer peak) • study conditions set up for most severe contingency usually at peak power transfers • successful study results reduced (nominally10%) to provide acceptable margins • results simplified for easier computer monitoring

TransmissionOperating Security Limits System needs to be secure • Pre-contingency • Post-contingency • Stable During Contingency (Transient Stability-non faulted generators not removed from system, acceptable equipment operation during/immediately after fault clearing, non cascading outages)

TransmissionInternal Ontario Key Interfaces • Because of the dynamic nature of the power system and its multiple parallel paths, limits generally are not expressed in terms of individual line loadings (other than some thermal limits) • Rather, limits are expressed in terms of interface flows and are called Operating Security Limits. • An interface is defined as a group of Transmission lines and the limit is expressed as the sum of the flows on this group of lines.

TransmissionInterface Limit Characteristics • ‘Base’ limit • All transmission facilities are in-service • Directional • Certain outages result in a penalty in MW • Some limits simple constants; • others more complex, and have multiple parameters including other limits!

TransmissionHistorical Flows

Transmission The End

Module 3BProtection, Control and Metering

PowerNex Associates Inc.