7 - final_2011 relay fundamentals 2-23-11

8/11/2019 7 - Final_2011 Relay Fundamentals 2-23-11

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Protection Systems

es gn un amen a s

Transmission Line Protection

FRCC System Operator Subcommittee

- Spring Seminars 2011 -

Objectives

Review Definitions

Review Purpose of Relays (Protectionys ems

Review 5 Design Attributes protectionsystems

Review Types of transmission lineprotection

Review Communications Based Schemes

Review Protection Redundancy vs Backup

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Purpose of Relays (what ?)

NERC Definition of Protection System:

Protective relays, associated communication systems,vo age an curren sens ng ev ces, s a on a er es ancontrol circuitry.

Merriam- Webster definition of Relay:

an electromagnetic device for remote or automatic controlthat is actuated by variation in conditions of an electric circuitand that operates in turn other devices (as switches) in thesame or a different circuit.

ower ys em e ay ng ex oo e n on o e ay :

equipment that detect abnormal power system conditions,

and initiate corrective action as quickly as possible in order toreturn the power system to its normal state.

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Purpose of Relays (why ?) Silent sentinels that watch the power system - Relays are

continuously monitoring the system to detect abnormal condition on Power

System, and initiate corrective actions as quickly as possible in order to return

.

Minimize power system equipment damage

Minimize danger to people

Provide automatic response (no human intervention)

Remove electrical stress from other equipment

The power system one big machine electricallyconnected

Provide a quick response to remove faulted equipment Restore the power system to a normal state

Increase reliability of the overall power system

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Minimize the damage

Minimize the effects of faults

2003

Northeast

Blackout

2/26 UFLS Event- 3 phase fault

- Failed 138 kV switch in Miami

--

equipment while troubleshooting

- Led to Delayed clearing of a fault

-Fault remained on the system for:

approximately 1.7 seconds

Resulting effect on frequency


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Design Attributes of Relays

5 Attributes inherent to protection system design

Re a ty 2 components - epen a ty an secur ty

Selectivity of Relays (zones of protection)

Relay Speed

Economics/Cost

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Design Attributes of Relays(cont)

Reliability contains two components:

Dependability the degree of certainty that a relay or relay

system will operate correctly when called upon to trip

Easy to ascertain dependability by testing

Security relates to the degree of certainty that a relay or relay

system will not operate incorrectly say when there is no fault or

fault is outside the zone.

Not eas to ascertain due to wide ran e of conditions that mi ht

be presented to the relay and control systems. Cant bepredicted.

How does FRCC track and learn from occurrences ?

Misoperations !8


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Reliability of Relays

Reliabilitys 2 components:

-

increase certainty, backup, secondary, multiple redundant

schemes. Redundancy will be discussed later.

Security Two independent series systems - will not operate

incorrectly

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IMPROVE DEPENDABILITY

Primary Relay scheme is dedicated to aspecific zone of protection. A Primary relayscheme operates with no intentional time

e ay.

Redundant Relay scheme does the exactsame function as the primary and providesredundant protection

Back-up Relay Scheme is usually timedelayed. It will typically remove more of thesystem elements than required by operationof the primary relay scheme.


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Dependability: B a ck u p , p r i m a r y ,

s e c o n d a r y , r e d u n d a n c y

Security


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Selectivity Minimum system disconnection forisolation of faulted equipment - Zone of Protection

Generally a zone of protection is designed for eachsystem element. The faulted element is isolated. Somecases more than one elements is combined in one zoneof protection.

DEDICATED RELAYS FOR EACH ZONE

Transmission line Generators TransformersSubstation Bus Capacitor bank Dist. Feeder

Reactor Circuit Breaker

Combined Elements: Two or more of the above elements.13


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ZONES OF PROTECTION

Note: Not tobe confusedwithZone 1 ,Zone 2,Zone 3, tobe discussedlater

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SPEED: minimize the damage


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Speed Attribute to remove a fault as quickly aspossible


The initiating event was a three phase fault on a failed 138 kV switch at a

transmission substation located West of Miami, Florida. The disabling of all

local protective relay equipment while troubleshooting a transmission

switch led to delayed clearing of a fault that developed on the switch.

The fault remained on the system for approximately 1.7 seconds.

delayed clearing

- .

Typical local backup clearing time 0.255 seconds

The depressed voltages in the area of the fault led to protective equipment tripsof the two Nuclear generating units at Turkey Point as well as the loss of

additional fossil generation at that and other sites in the Region .

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Speed definitions


intentional time delay (inverse time delaycharacteristic)

Time Delay an intentional time delay isinserted between relay decision and operation

High-Speed relay operates in less than 50

m typ ca cyc esUltra High Speed relay operates in 4 mS or

less (non-standard but currently typical

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What designattribute is

this ?


Simplicity Fewer components and attributes in a design result in:

A system with fewer potential Human and Equipment Performance

issues

Usually more cost effective, both immediate and life-cycle

Easier to troubleshoot when issues occur

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Economics - Protection & Control systems typically rangefrom 10 15% of the cost of the equipment they protect,down from 15 20% ust ten fifteen ears a o rior touprocessor technology coming to market.

The more equipment you install the more money is required cost benefit vs dependability and security equation

You use overlapping zones /

backup protection etc.

Critical equipment you install -

Fully redundant systems21

Are we done yet ?

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Were just getting started !

Any Quest ions on Design Attribu tes


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Transmission Line Protection

R o a d M a p t o t h e En d

TLP Options:

Overcurrent relays

Instanstaneous

Time delay

Directional Overcurrent

Non-pilot

Ste -Distance Rela s

Carrier types andcommunication at a highlevel

Cover some relay types

Define

Primary Protection

Backup Protection

Zones 1, 2 & 3

Pilot Protection

Redundancy

Redundancy

Communication Outages

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The Goal of Line ProtectionTo detect transmission line faults and

initiate isolation of that line fault 3-5c cles. A fault duration of lon er time 8plus cycles) can cause instability.

Typical Transmission line

Substation A Substation B


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Only looks at line current Simple setting (normal load +25%) Does not see faults behind - no fault current

Overcurrent Protection

an coor nate w t re ays uses ownstream Add time delay Coordination for all types (10 types) of faults

becomes difficult (phase to phase, phase toground, 3 phase etc.)

Substation A Radial Load

Ohms Law:

V = I x Z

I = V/Z

Relay trip when

I = set current flow

As the protected system gets morecomplex

Distance or Impedance Relay

Available changes in configuration(network)

Changes in generating patterns Wider variation in fault current than

radial Cant just use current monitoring for

reliable protection

We need to look at current AND voltage


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Ohms Law:

Look at Current and

Voltage to detect fault= x

Z = V/I

V = 100 V

Conclusion: if we know voltage and

current we can estimate the

impedance

If we know the conductor and

construction (impedance per mile

of transmission line is fairly

THE LINE CONDUCTOR AND

CONSTRUCTION IS SAME,

cons an

We can estimate a where a fault is

based on measured voltage and

current on the line

IMPEDANCE

We know the properties of the transmission line

How to know if line has a FAULT??


Length Impedance

We know the current on the line from thesubstation

We know the voltage on the line bus at thesubstation

V = I x R or V = I x Z (for Impedance)

We can identify a set of Zs for faults and setthe relay to pick-up


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Step Distance Relaying

Its hard to pinpoint the end of the line Z use zones

Company PHILOSPHIES may vary

80%Typical setting

Zone 1

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120%

120% of combined

Zone 3

Step Distance Line Protection

why 80%, 120% etc

Create Zones of Protection

= ne mpe ance no me e ay

Z2 = 120% line impedance time delay-

Z3 = 120% line impedance and 120% ofnext zone; with a time delay backup nextzone


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Limitations of Step DistanceLine Protection

Problem: cant clear both ends of the lineinstantaneously for faults near one end

As loading increases the Z viewed by therelay may cross into the Z trip area of therelay setting

Harder to coordinate multi-terminal andparallel line

So far all information for tripping decision

has come from one substation

Provides instantaneous protection overentire line section

2 modes blocking mode (integral to line)

Pilot Protection

channel)

Communicate information from oneterminal to the other terminal (in the zoneof protection)

Communication methods: Power line carrier Microwave

Fiber optics Pilot cable

Speed up remote end clearing time


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Schemes can be classified as: Directional Comparison Phase comparison Pilot wire

Pilot Protection

Depending on type of sensing used

Further described as : Blocking Unblocking Transfer tripDepending on how transmitted signal is used

Transfer trip is further categorized as:

Direct Permissive underreaching Permissive overreaching

1. Power line carrier On/Off, FSK

Reliable, expensive, noise, freq. availability

Types of Communication Channels

2. Pilot wire dedicated 2 wire copper circuit

Expensive

3. Leased line digital or audio tone

Dedicated channel, low installation cost

Reliability, ongoing costs

4. Microwave digital or analog

apac ty, ow no se ocat on, weat er5. Fiber optic digital

Noise immunity/network delays, cost

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Current Differential

87L 87LCommunication channel

Basic End to EndCommunication Scheme

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Permissive OverreachingTransfer Trip

1. LOCAL END DETECTS FAULT, SEND PERMISSIVE TRIP

2. REMOTE END RECEIVES PT, IF REMOTE SEES FAULT, IT TRIPS

AND SENDS PT TO OTHER END3. CONSIDER FAULT INSIDE AND OUTSIDE

Directional Comparison

Blocking

1. LOCAL END DETECTS FAULT, DOES NOT SEND BLOCK TRIP2. REMOTE END SEES FAULT AND IT DID NOT RECEIVE BLOC FROM REMOTE, IT

TRIPS. ALSO, IT DOES NOT SEND BLOCK. PASSIVE PERMISSION

3. FAULT CLOSE BY AND OUTSIDE, BLOCK IS SENT AND TRIP IS BLOCKED.

4. CONSIDER FAULT INSIDE AND OUTSIDE


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Loss of Blocking CommunicationChannel To RanchExample #1 Adjacent line fault with Blocking scheme

1) No communications on Cedar- Corbett 230 kV line

3) Corbett terminal sees fault on Deltrail line (zone 2)

2) Fault on Cedar Deltrail 230 kV line (close to Cedar)

4) Corbett terminal does not receive blocking signal

5) Corbett breakers 8W45 and 8W99 trip high speed

Possible temporary

remedy: Study opening line

at a distribution sub, whichshould only allow

instantaneous zone 1 trips.

6) Both Cedar and Corbett will trip for any zone 2 fault

Loss of CommunicationChannel To RanchExample # 2 close in fault on line with blocking scheme

1) No communications on Cedar- Corbett 230 kV line

2) Fault on Cedar Corbett 230 kV line (close to Cedar)

4) Corbett terminal sees fault on zone 2 and trips high speed

5) Breakers 8W45 and 8W99 at Corbett trip

6) All faults on Cedar-Corbett line will still be cleared high speed

3) Cedar sees zone 1 fault - trips 8W62 & 8W48 instantaneously

Internal NO issue


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Communication Based Schemes

, , . ,

cover in a little bit detail, Mention DUCB, PUTT, DUTT.

Discussion / Simulation

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Road Map Continued Pilot Protection Schemes

Directional Comparison,

PUTT/DUTT

DCB

DCUB

CURRENT DIFF

POTT- next


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FRCC Handbook Procedure

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REDUNDANCY

Protection system components (below) make up aprotection system. In some cases, for redundancytwo system are provided. A complete Chain ofcomponents make up a system.

AC Current Source AC Voltage Source

Protective Relay Communication Channel -

DC Source Trip Coil

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REDUNDANCYNon-redundant system

Single DC

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Power supply

REDUNDANCY

Fully-redundant system

Diverse DC

power supply

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Typical DC Control Circuit

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Protection System Outages

If a protection system (chain of components)does not meet all of the requirements

escr e a ove, en e pro ec on sys emis not redundant.

From an operations standpoint

- is the remaining protection redundant

- Is the remainin rotection back-u

- Understand what s e c o n d a r y means

- What elements will be tripped for a fault inthe affected protection zone

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Questions ?

7 - final_2011 relay fundamentals 2-23-11

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