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INTRODUCTION TO SYSTEMPROTECTIONHands-On Relay School 2012
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CONGRATULATIONS
On choosing the field of system protection. It is anexciting, challenging profession.
System protection has changed considerably in thepast 20 years.
Many learning and growth opportunitieswill comeyour way in the future.
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What is SystemProtection?System protection is the art and science of detectingproblems with power system components and isolatingthese components.Problems on the power system include:
1.Short circuits2.Abnormal conditions3.Equipment failuresNERC defines the protection system as:
Current Approved Definition:
Protective relays, associated communication systems, voltage and currentsensing devices, station batteries and DC control circuitry.
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Purpose of System ProtectionProtect the publicImprove system stabilityMinimize damage to equipmentProtect against overloadsEmploy relay techs and engineers
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What Components (Equipment) Do We Protect?
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What Components (Equipment) Do We Protect?
GeneratorsTransformers, ReactorsLinesBuses
Capacitors
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What Components (Equipment) Do We Protect?
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Some Basics
Current Transformer (CT)
A device which transforms the current on the power system fromlarge primary values to safe secondary values. The secondary
current will be proportional (as per the ratio) to the primary current.
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Some BasicsPotential Transformer (PT)A device which transforms the voltageon the power system from primaryvalues to safe secondary values, in aratio proportional to the primary value.
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What Components (Equipment) Do We Protect?
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I. Generator ProtectionA. Construction & Theory of Operation C:\Documents and Settings\clh6411\Desktop\hydroturbine.jpg
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Three Gorges Dam in ChinaLargest in the world(22,000MW, 26 Generators)
C:\Documents and Settings\clh6411\Desktop\800px-ThreeGorgesDam-China2009.jpgC:\Documents and Settings\clh6411\Desktop\Three Gorges Dam-1.jpg
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What can go wrong?A.Stator Winding Problems1. Winding-winding short2. Stator ground
I. Generator Protection
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What can go wrong?A.Stator Winding Problems
I. Generator Protection C:\IPCO\SysOp\HCPR_GEN2_JAN_8_2003\Pictures\Winding damage\P1100001.JPG
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How Do We Protect the Stator?
A. Differential Protection (what goes in must come out)
1. Detects phase-phase faults
B. Stator Ground Protection
1. 59N (95% of Stator)
2. Third Harmonic Voltage Method (100% of Stator)
3. Signal Injection (100% of Stator)
Generator Protection
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Generator Protection
What can go wrong?
B. Rotor Problems
1. Loss of field
2. Field ground
a. First ground
b. Second ground
=TROUBLE
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Generator Protection E:\Picture1.jpgRotor
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Generator ProtectionHow Do We Protect theRotor?1.Loss of Fielda. Impedance
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Generator Protection
How Do We Protect the Rotor?
2. Field ground
a. DC voltage relay (64F)
The field ground relay is connected from the negative sideof the field to DC ground. Detects voltage from the field toground.
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Generator Protection
What else can go wrong?C. Abnormal Conditions1. Over/Under Frequency
2. Over Excitation3. Reverse Power4. Out of Step5. Unbalance Current
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Generator Protection
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Transformer Protection
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XFMR PROTECTIONPower transformers are expensive, and are a long lead-time item
(1 year or longer) so protection must be effective
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Transformer Protection
Construction
200681695059692
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Construction img0048Transformer Protection
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Construction image001Transformer Protection
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Transformer size and rating
. MVA: the capacity of the transformer in terms of millionvolt-amps. Size can range from less than 1 MVA to 500MVA and higher.
. Transformer rating (MVA) is determined in part by theamount of cooling employed. MVA rating increases withmore cooling. OA, FOA (stage 1), FOA (stage 2)
Transformer Protection
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What can go wrong?. Winding-to-winding faults. Winding-to-ground faults. Bushing faultsTransformer Protection
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Transformer Protection
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Protection Methods
. Fuse
. Overcurrent
. Differential
Transformer Protection
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High Side Fuse
Transformer Protection
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Sysop03Transformer Damage Curve
Transformer Protection
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Overcurrent Relays
Transformer Protection
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Differential Protection:
What goes in must come out.. P-in = P-out
Transformer Protection
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Microprocessor Relays187T1-TWraps transformer187T1-BWraps transformer and busTransformer Protection
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187 T1-TZone ofProtectionTransformer Protection
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187 T1-B
Zone of
Protection
Transformer Protection
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Some terms you will be learning about this week:
Restraint
Operate
Slope
Inrush
2nd Harmonic
Transformer Protection
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LINE PROTECTION
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Transmission LineProtection
Transmission lines can vary in length from several hundred feet to severalhundred miles, and in voltage (line-to-line) from 46KV to 750KV.
Construction can be simple, such as a single wood pole with insulatorsatop a crossarm, with little spacing between the conductors and fromthe conductors to ground. At the other end of the scale are metallattice structures with bundled conductors (2 or more conductors perphase) with large spacing between conductors and betweenconductors and ground.
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Transmission LineProtection C:\HRS\2012 HRS\Introduction to System Protection\typical_transmission_structures.gif
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Transmission LineProtection
C:\HRS\2012 HRS\Introduction to System Protection\woodtower_transmission_lines.jpgC:\HRS\2012 HRS\Introduction to System Protection\transmission_lines_onpage.gif
C:\HRS\2012 HRS\Introduction to System Protection\46kv_trans_line.jpgC:\HRS\2012 HRS\Introduction to System Protection\flooded_power_lines.jpg
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Transmission LineProtection
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Transmission LineProtection
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Transmission Line Protection
How Do We Protect Transmission Lines?A.OvercurrentB.Directional OvercurrentC.Distance (Impedance)
D.Pilot1. DCB (Directional Comparison Blocking2. POTT (Permissive Overreaching Transfer Trip)E. Line Current Differential
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Transmission Line Protection
Overcurrent Protection
Non-Directional
Relay responds to overcurrent condition
Instantaneous (IOC) device #50
No intentional time delay
Time Overcurrent (TOC) device #51
Various curve types, including inverse, veryinverse, extremely inverse
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Transmission Line ProtectionOvercurrent Line Protection
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Transmission Line Protection
C:\Projects\traning\overcurrentgndblue.bmpAC Schematic
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Time Overcurrent Curves
C:\Projects\traning\u4toccurveblue.bmpTransmission Line Protection
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Transmission Line ProtectionDirectional OvercurrentProtection
Relay responds to overcurrent condition in theforward direction only (device #67, 67N,67NT)
Will not respond to reverse faults
Compares the current in the line versus aknown reference that will always be the
same (such as a voltage or polarizing currentsource)
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Transmission Line Protection
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Transmission Line ProtectionDirectional Overcurrent Example
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Transmission Line ProtectionDistance ProtectionA distance relay measures the impedance of a line usingthe voltage applied to the relay and the currentapplied to the relay.When a fault occurs on a line, the current rises
significantly and the voltage collapses significantly.The distance relay (also known as impedance relay)determines the impedance by Z = V/I. If theimpedance is within the reach setting of the relay, itwill operate.
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Transmission Line Protection
Distance ProtectionElectromechanical distance relays use torque to restrain or operate
KD, GCY, etc. Device #21
Microprocessor distance relays use equations to restrain or operate
SEL, ABB, GE, Areva, etc. Device #11
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Transmission Line Protection
Distance Relay
CT and PT
Connections
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Transmission Line Protection
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Transmission Line ProtectionDistance Protection
Typical zone reach
settings
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Transmission Line Protection
Distance ProtectionThe most common characteristic (orprotection shape) of distance relays isthe mho characteristic, a circular type
reach characteristic.Distance relays have a settablemaximum torque angle (mta), which isthe angle of the current compared tothe angle of the voltage at which therelay is most sensitive. In the drawingon the right, the mta is approximately75 degrees.
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Introduction to System Protection
Dependability: the certainty that a protection system will operate
when it is supposed to
Security: the certainty that a protection system will not operate
when it is not supposed to
Reliability = Dependability + Security
Terminology
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Transmission Line ProtectionPilot Relaying Scheme
A protection scheme which employs communications to send asignal from one station to another to allow high speed tripping(permission) or to prevent high speed tripping (blocking).
Pilot protection allows over-reaching zones of protection toensure full protection of the line as well as high speed tripping.
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Transmission Line Protection
Pilot Relaying Scheme
Directional Comparison Blocking (DCB)
A communications based protection scheme where high speedover-reaching tripping is allowed unless a block signal isreceived.
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Transmission Line Protection
Pilot Relaying SchemePermissive over-reaching transfer trip (POTT)A communications based protection scheme where high speedover-reaching tripping is allowed only if a permissive signal is
received
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Relay
BLOCKING SCHEMEOPERATING PRINCIPLE
Relay
STATION A
STATION BTransmission Line Protection
BLOCKING SCHEME OPERATING PRINCIPLE
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RelayBLOCKING SCHEMEOPERATING PRINCIPLE
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BLOCKING SCHEME OPERATING PRINCIPLERelay
DO NOTTRIP!!!External Fault
Transmission Line Protection
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RelayPERMISSIVE SCHEMEOPERATING PRINCIPLE
Relay
STATION A
STATION B
Permissive Scheme
Transmission Line Protection
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Relay
Permissive scheme internal fault
C:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\U3WPAPQL\MCj03638360000[1].wmf
C:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\2MNXHIZG\MCj03478690000[1].wmfRelay
STATION B
STATION A
Transmission Line Protection
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Relay
C:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\U3WPAPQL\MCj03638360000[1].wmfC:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\2MNXHIZG\MCj03478690000[1].wmf
Relay
STATION B
STATION APermissive scheme internal fault
Transmission Line Protection
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Relay C:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\U3WPAPQL\MCj03638360000[1].wmfC:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\2MNXHIZG\MCj03478690000[1].wmfRelayYou Can Go Ahead
and Trip If You WantTo!
You Can Go Aheadand Trip If You WantTo!
High Speed Tripping Takes Place at Station A and BSTATION B
STATION A
Permissive scheme internal fault
Transmission Line Protection
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Relay
C:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\U3WPAPQL\MCj03638360000[1].wmfC:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\2MNXHIZG\MCj03478690000[1].wmf
Relay
STATION BSTATION A
Permissive scheme external fault
Transmission Line Protection
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Relay
C:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\U3WPAPQL\MCj03638360000[1].wmfC:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\2MNXHIZG\MCj03478690000[1].wmf
Relay
STATION B
STATION APermissive scheme external fault
Transmission Line Protection
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Relay C:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\U3WPAPQL\MCj03638360000[1].wmfC:\Documents and Settings\clh6411\Local Settings\Temporary Internet Files\Content.IE5\2MNXHIZG\MCj03478690000[1].wmfRelayYou Can Go Ahead
and Trip If You WantTo!
No High Speed Tripping Takes Place Because the Fault
Is Reverse to the Relay at Station B.
STATION BSTATION A
Permissive scheme external fault
Transmission Line Protection
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BLOCKING VS. PERMISSIVE
BlockingIncreased dependability because if the carrier fails, the protection will tripanyway.Decreased security because if the carrier fails, the protection will trip for an
out of section fault.PermissiveIncreased security because if the communication fails, the protection will nottrip high speed.Decreased dependability because if the comm fails, the protection will nottrip high speed for an in section fault.
Transmission Line Protection
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LINE DIFFERENTIAL
No fault or external fault, current at each end is balancedThe current going into the line is going out at other endTransmission Line Protection
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Line differential
Internal fault, relay trip is processed
Transmission Line Protection
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Bus Protection
Bus Differential:
Current into bus must equal current out of bus
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Bus Fault
Bus Protection
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Single bus with XFMR
Bus Protection
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Double bus,breaker-and-a-half
Bus Protection
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Double bus,double breaker
Bus Protection
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Capacitor Protection
Purpose of capacitors:Shunt capacitors raise the voltage on a bus or line to a higherlevel, thus helping keep the voltage at desired levelSeries capacitors cancel out the inductive reactance of a line,
thus making the line appear shorter increasing load flow on theline.
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Capacitor Protection
Capacitors connected in parallel add
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Capacitor Protection
Capacitors connected in series sum like they are in parallel
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Capacitor Protection
Capacitors are connected in series and parallel combination
to obtain the desired total capacitance for the bank
CDWL C131.JPG
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Capacitor Protection
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Capacitor ProtectionVoltage across cap bank is determined by current flow and impedance
(capacitive reactance) of bank.
If a capacitor fuse blows or if a capacitor shorts, the voltage drop across
the bank changes due to a change in capacitive reactance of the bank.
A voltage relay detects the higher voltage and trips the breaker
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Capacitor Protection
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Introduction to System Protection
If you are still awake, nudge your sleeping neighbor and tell him/her that
the lecture is over and it is almost time for the next lecture, which may actually
prove to be an interesting and informative lecture (unlike this one).
If you are not awake, may you dream that you are on a Hawaiian beach
And then wake up in Pullman!
????? QUESTIONS ?????
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