network operating division operating effectiveness transmission lines protection overview

NETWORK OPERATING DIVISION

Operating Effectiveness

Transmission Lines

Protection Overview

Transmission LinesLH1 Protection Overview

Operating Effectiveness

Training & Development

Hydro One Networks Inc49 Sarjeant Drive

Barrie, OntarioCanada, L4N 4V9

Phone (705) 719-3528

Revised: November 4, 2008

The information in this document is for reference and is to be used as a guide only. The OE Training Section makes no representation or warranty, expressed or implied, that the information contained within is current. The information included is subject to change. It is solely your responsibility to ensure that you are using up-to-date documents, prints and information. Please notify the HONOC Operating Effectiveness Training Section of required updates and/or modifications.

ObjectivesThrough the use of this presentation

participants will learn and understand Transmission Lines Protection.

Emphasis is on:– Functionality– Limitations– Instructions and Procedures– Support Services.

Cont…

Transmission Lines Protection

Transmission Lines Protection Overview.

This presentation will cover:

What transmission line protection is,

Why the need for line protection

Principles of Operation ( Impedance),

Different Operational zones

Various types or schemes

Exceptions and Anomalies

Transfer Trip Channels

Permissive Echo


This presentation will cover:

LH1 configuration

Micro-wave communications

Power Line Carrier communications

Fibre-Optic Digital communications

Various types or schemes


We first must understand what a transmission line is.

A transmission line is a high voltage circuit designed to carry a high amount of power over great distances between points.

In some cases, this could be simply between two points as shown.

Station ‘A’

Station ‘B’

Power flow


In more complicated configurations there could be:

1. Multiple terminal stations

2. Multiple tap stations

3. Combinations of both

Station ‘A’

Station ‘B’

Power flow

Station ‘C’

Station ‘D’

Station ‘E’

Station ‘F’


To begin, we will look at a simple two ended circuit

Station 'Z'Station 'Y'

Station 'Y' is a terminal that has two breakers on

the circuit.

Station 'Z' is also a two breaker terminal for the

circuit.


Simple two ended circuit


The circuit that travels between Station 'Y' and Station 'Z' is a high voltage open air

transmission line and as such is vulnerable to external influences.




A fault could develop anywhere along the circuit causing fault current to flow between

phases and/or to the ground.




If there is no way of removing this faulted equipment from service, it will remain faulted

eventually causing danger to the public, damage to equipment or even lead to a system

wide disturbance.




Protection systems will sense the fault

and clear the circuit removing it from service.

How does the protection system see the fault?



There are many ways in which faults can be detected.

For transmission circuits the most common method is by using impedance .




At each end of the line there are both voltage sensing devices and current sensing devices

Voltage (CVT)

Current (CT)



These sensing devices monitor line voltage and line current on a continuous basis.

Under normal circumstances, the current will be at expected normal values and the voltage

will be at the system normal.



The Impedance is derived by placing the voltage and current into a ratio using OHMS

law.

Impedance =Voltage

Current

Voltage = 230,000 volts

Current = 2,000 amps

230,000

2,000= 115 ohms




If a fault occurs then these quantities will be disrupted causing the ratio to greatly change.

Impedance =150000

50000



230,000

2,000= 115 ohms= 3 ohms


Trip Setting range

Normal Operating range



The impedance is set to a certain range.

Anything outside of that set range is considered a fault and will trip the circuit.

230000 Volts

2000 Amps

115 ohms

150000 Volts

50000 Amps

3 ohms

Impedance is outside of preset range – Circuit will trip.




The idea is to set the impedance such that for any fault on the line, the protections will see the changes in voltage, current and the ratio between them, covering 100% of the circuit.




With this type of impedance detection, it would be very difficult to set the range to exactly

cover 100% of the circuit due to tolerances in measuring equipment.




The settings could be set:

Too short. Under protected

Too long. Over protected




To correct this problem, specific zones of protection have been created.




Zone 1 – Is set to cover 80-85% of the circuit and is instant.

Zone 1 – 80-85%

Zone 2 – Is set to cover 125-150% of the circuit but is generally a timed protection.

Zone 2 – 125-150%


Zone 1 Protection


Zone 1 – Is set to cover 80-85% of the circuit and is instant.

Zone 1 protection is generally known as Direct Direct UnderreachUnderreach

Zone 1 – 80-85%


Zone 1 Protection


This area Instantaneous

protection from Station 'Y' only.

This area Instantaneous

protection from Station 'Z' only.

This area overlaps and is

Instantaneous protection from

both Station 'Y' and Station 'Z'.

There is a limit to the protection when using Direct Direct

UnderreachUnderreach


Zone 1 Protection


If a fault occurs here, ‘Y’ Zone 1 will see it and

send a trip signal called…

To overcome this limit communication is used between

ends.

Transfer Transfer TripTrip


Transfer TripTransfer Trip


At Station 'Y' both Zone 1 and Zone 2 will see the fault.

Station 'Y' Zone 1 will trip instantly and send Transfer TripTransfer Trip

Station ‘Z' will receive Transfer TripTransfer Trip and trip its terminal breakers instantly.

1

2

T/T Rx


Communication is accomplished by a

variety of media but will not be discussed right

now.




How do we protect this area from Station 'Z'?

How do we protect this area from Station 'Y'?

There is another limit to the protection when using

Direct UnderreachDirect Underreach

The answer is to use another zone designed to reach all the

way across the circuit.




The protection will overlook into adjacent zones and could cause erroneous trips for faults outside of the zone.

To prevent this Zone 2 protection is generally made to be timed.

Zone 2 is set to ‘see’ 125-150%125-150% of the circuit.

Zone 2Zone 2


We will look at Zone 2 independent of Zone 1


Although Zone 2Zone 2 is normally timed, there is a need for the Zone 2Zone 2 protection to be instantaneous in

order to satisfy rapid removal of the transmission circuit in a faulted condition.

Zone 2 is set to ‘see’ 125-150%125-150% of the circuit.

Zone 2Zone 2


Zone 2 Protection


The rapid removal will be by using Zone 2 in a:

Permissive OverreachPermissive Overreach scheme oror

Directional ComparisonDirectional Comparison scheme


Permissive OverreachPermissive Overreach


In Permissive OverreachPermissive Overreach each Station has a timedtimed Zone 2.

If a fault occurs outside of Station 'Z' Zone 1 as shown above, only the Station 'Z' Zone 2 will see it.

When the Zone 2 ‘sees’ the fault it starts a timer (400ms).

2

Zone 1 Limit


Permissive OverreachPermissive Overreach


At Station 'Y' both Zone 1 and Zone 2 will see the fault.

Station 'Y' Zone 1 will trip instantly

Station 'Y' Zone 2 will see the fault and will send PermissionPermission to Station 'Z' Zone 2 to trip instantly instead of timed.

1

2

2

Permissive SignalPermissive Signal

Zone 1 Limit


Directional ComparisonDirectional Comparison

Station ‘Z’Station ‘Y’

In Directional ComparisonDirectional Comparison each Station has InstantInstant Zone 2 coverage.

If a fault occurs outside of Station ‘Z’ Zone 1 as shown above, only the Station ‘Z’ Zone 2 will see it.

When the Zone 2 ‘sees’ the fault it will trip instantly.

2

Zone 1 Limit




This Instantaneous tripping, however, could pose a problem if the fault is outside of the protected circuit, but still inside the Zone 2 reach.

The fault will be seen by the Zone 2 protection and will cause the circuit to erroneously trip for this out of zone fault.

2

Zone 1 Limit




For example: The fault is located on the adjacent circuit.

2

Station ‘Z’ Zone 2 ‘sees’ the fault and will trip instantly

Only the circuits breakers of the faultedfaulted circuit should trip

Zone 1 Limit




To correct this a 3rd Zone is employed

2

This is the Directional ComparisonDirectional Comparison element which employs a relay known as an OM3 OM3 relay and is set to look backwardsIf a fault occurs out of zone it trips its local breakers.

The Zone 2 at Station ‘Z’ will also see the fault and try to trip its breakers instantly.

Block SignalBlock Signal

OM3

The OM3 will sense the fault as well and send a block signal to the opposite Zone 2 preventing it from

tripping instantly.

X

In some cases Zone 2 may be different in each Group, Group A Zone 2 could have Permissive Overreach where Group B could have Directional Comparison

Each Station has a Zone 1 Direct UnderreachDirect Underreach covering 80-85% of the circuit.

Each Station Zone 1 will send Transfer Trip Transfer Trip to opposite end station tripping its breakers.

Each Station has Zone 2 covering 125-150% of the circuit.

Zone 2 can be Permissive OverreachPermissive Overreach or Directional ComparisonDirectional Comparison

Permissive Overreach Permissive Overreach is Timed unless it receives a Permissive SignalPermissive Signal from the opposite end Zone 2

protection where it will then trip instantly.

Directional ComparisonDirectional Comparison is Instant unless it receives a Block Signal from the opposite end Zone 3 OM3 element

where it will then trip timed.

The protections will all have a Zone 1 Direct Under reach and Zone 2 will have either Permissive Overreach

or Directional Comparison but not both.

These protections are referred to as GroupsGroups. Each terminal will have duplication of each group and will be

known as Group AGroup A and Group BGroup B.Each Group AGroup A and Group B Group B are generally clones of each other with a Zone 1 Direct Underreach and a similar Zone 2.

Station ‘Y’ Zone 2

Station ‘Z’ Zone 2


Protection review


1

2

2


1OM3OM3




Station ‘Y’ Zone 3 OM3





Station ‘Z’ Zone 3 OM3




Protection review


1

2

2


1OM3OM3










This is what represents a basic line protection. Two Zones with a dual redundancy built in.





1

2

2


1OM3OM3









The line switch at Station ‘Y’ is OPEN

As a result, Station ‘Y’ Protections no longer see the circuit.


Lets look at when a terminal is Out of Service with its line disconnect open


Transmission Lines Protection Overview.Lets look at when a terminal is

Out of Service


2

1


If a fault occurs within the Zone 1, both Zone 1 and Zone 2 protections will see the fault and the Zone 1 will high speed trip the terminal at Station ‘Z’.


Transfer Trip is Blocked to opposite terminal

breakers


Transmission Lines Protection Overview.Lets look at when a terminal is

Out of Service


2

1


If a fault occurs outside of Zone 1, only Zone 2 protections will see the fault and will timed trip the terminal at Station ‘Z’.

To correct this, the Permissive Signal is returned or Echoed Echoed back to the sending terminal and it will then trip instantly. This signal is keyed on at all times.


Permissive Echo SignalPermissive Echo Signal

‘B’ Pallets


Communication


2

1

In order for the Protection signals to travel from one station to another, a communications medium is required.

There are several types used today.

1

2

Powerline Carrier- Powerline Carrier- Wave TrapWave Trap

MicroWaveMicroWaveFibre-Optic Digital Fibre-Optic Digital

Tele-protectionTele-protection


Micro-Wave CommunicationStation 'Z'Station 'Y'

A large microwave transmission tower is

built at each end of the circuit

Microwave signals are transmitted between

points.

These are known as Guard Tones

The Guard Tones typically consist of 4 4 Transfer Trip TonesTransfer Trip Tones and 2 Permissive / Blocking 2 Permissive / Blocking

TonesTones

We will call them…



Transfer Trip Channel #1Transfer Trip Channel #1




Permissive / Block Channel #1Permissive / Block Channel #1

Permissive / Block Channel #2Permissive / Block Channel #2

Transmission Lines Protection Overview.Micro-Wave Communication

Station 'Z'Station 'Y' The question arises.

Why so many Tones?Why so many Tones?

Here’s why….

Microwave is:- influenced by external forces

- a line of sight communication



Microwave is a radio signal and uses air to travel through.

When the air changes properties, it distorts the path of the microwave.

This is known as-

MicrowaveMicrowave FadingFading


Station 'Z'Station 'Y' Distortions Distortions in the air can be caused by changes in:

-Temperature

- Pressure

-Humidity

-Precipitation

-Fog

and many other atmospheric factors.


Micro-Wave Communication Station 'Z'

Station 'Y'

Microwave is also a “Line of SightLine of Sight” communications

Any type of physical obstruction will affect the path of the signal

BuildingsTrees


Micro-Wave Communication Station 'Z'

Station 'Y'

To correct for these limits.

Pathways are carefully determined to minimize external influences.


Micro-Wave Communication Station 'ZStation 'Y'

Bodies of Water Hills and Mountains

Tall Buildings

Pathways will go around avoiding large obstaclesAnother method to secure

transmission of the signal is sending along redundant

pathways

Main PathwayMain Pathway

Alternate PathwayAlternate Pathway


Micro-Wave Communication Station 'ZStation 'Y'

Bodies of Water Hills and Mountains

Tall Buildings

Sometimes signals will be split.

2 T/T ch’s, 1 Perm on Main path

2 T/T ch’s, 1 Perm on Alt Path

Main PathwayMain Pathway

Alternate PathwayAlternate Pathway

T/T ch#1 T/T ch#2 Perm#1

T/T ch#3 T/T ch#4 Perm#2


Transmission Circuit

Power Line Carrier - PLCPower Line Carrier - PLC

Power Line Carrier employs a high frequency signal injected into the transmission circuit.

At each end of the circuit, wave traps are employed which are tuned to trap the frequency and shunt it away to communications equipment.

Wave TrapWave Trap Wave TrapWave Trap

CVT shunts signal to communications

equipment

60hz passes, high hz does not


Digital Tele-protection – Fibre OpticDigital Tele-protection – Fibre OpticDigital Tele-protection employs light signal injected into fibre optic cable.

The fibre could be buried or even in the sky wire of a transmission circuit.

Fibre Fibre OpticOptic Fibre Fibre

OpticOptic

SkywireSSkywireShield hield WiresWires

Digital Tele-protection had once utilized microwave tone equipment for the LH1 configuration but for the most part has since been replaced with all digital equipment.

This is a true Digital Tele-Protection scheme and is beyond the scope of this presentation.



T1 G1 T2 G2 T3 G3

T4 G4 T5 G5 T6 G6

R1 G1 R2 G2 R3 G3

R4 G4 R5 G5 R6 G6

TRIPTRIP

Frequency ShiftFrequency Shift

FaultFault

Relay/Microwave buildings

Watch carefully how this works

Trip #1

Guard #1

CH #1

Fail

Trip #2

Guard #2

CH #2

Fail

Trip #3

Guard #3

CH #3

Fail

Trip #4

Guard #4

CH #4

Fail

CH #2

CH #1

CH #3

CH #4

‘A’ Battery DC +

‘B’ Battery DC +

‘A’ Protection

‘B’ Protection

Guard #1

Fail

Permissive ‘A’ Logic

Fail

Permissive ‘B’ Logic

Perm #2

Guard #2

Transfer Trip ChannelsTransfer Trip Channels

Perm #1

Permissive ChannelsPermissive Channels

Disconnect Disconnect SwitchSwitch

CloseClose

Open

Disconnect Switch - ‘A’ Pallet Supervision

Trip CircuitTrip Circuit


LH1 LH1 ConfigurationConfiguration

Click TheseClick These

To conclude you learned:• What a circuit is• What circuit protections are and why they are needed• The different zones of protection and how they work• Transfer Trip, Permissive & Block signals• Microwave, Power Line Carriers and Fibre-Optic Digital Tele-

Protections communications• LH1 configuration for protection tripping


The End


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