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NETWORK OPERATING DIVISION
Operating Effectiveness
Transmission Lines
Protection Overview
Operating Effectiveness
Training & Development
Transmission Lines
LH1 Protection Overview
 Hydro One Networks Inc
49 Sarjeant Drive
Barrie, Ontario
Canada, 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.
Transmission Lines Protection
Objectives
Through 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 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
Transmission Lines Protection Overview.
This presentation will cover:
LH1 configuration
Micro-wave communications
Power Line Carrier communications
Fibre-Optic Digital communications
Various types or schemes
Transmission Lines Protection Overview.
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’
Power flow
Station
‘B’
Transmission Lines Protection Overview.
In more complicated configurations there
could be:
1. Multiple terminal stations
2. Multiple tap stations
3. Combinations of both
Station
‘A’
Station
‘D’
Station
‘B’
Power flow
Station
‘F’
Station
‘C’
Station
‘E’
Transmission Lines Protection Overview.
To begin, we will look at a simple two
ended circuit
Station 'Y'
Station 'Y' is a terminal
that has two breakers on
the circuit.
Station 'Z'
Station 'Z' is also a two
breaker terminal for the
circuit.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Station 'Z'
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.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Station 'Z'
A fault could develop anywhere along the
circuit causing fault current to flow
between phases and/or to the ground.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Station 'Z'
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.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
How does the
protection system see
the fault?
Station 'Z'
Protection systems will sense the fault
and clear the circuit removing it from
service.
Transmission Lines Protection Overview.
Simple two ended circuit
There are many ways in which faults can
be detected.
For transmission circuits the most common
method is by using impedance .
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Voltage
(CVT)
Current
(CT)
Station 'Z'
At each end of the line there are both
voltage sensing devices and current
sensing devices
Transmission Lines Protection Overview.
Simple two ended circuit
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.
Transmission Lines Protection Overview.
Simple two ended circuit
The Impedance is derived by placing the
voltage and current into a ratio using
OHMS law.
Impedance =
Voltage
230,000
Current
2,000
= 115 ohms
Voltage = 230,000 volts
Current = 2,000 amps
Transmission Lines Protection Overview.
Simple two ended circuit
If a fault occurs then these quantities will
be disrupted causing the ratio to greatly
change.
Impedance =
150000
230,000
50000
2,000
115
ohms
=3
ohms
Voltage = 230,000
150,000 volts
Current = 2,000
50,000amps
amps
Transmission Lines Protection Overview.
Simple two ended circuit
The impedance is set to a certain range.
Anything outside of that set range is
considered a fault and will trip the circuit.
Impedance is outside of preset
range – Circuit will trip. 3
ohms
Trip Setting range
Normal Operating range
115 ohms50000 Amps
2000 Amps
150000
230000 Volts
Volts
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Station 'Z'
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.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Station 'Z'
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.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Z'
Station 'Y'
The settings could be set:
Too short. Under protected
Too long. Over protected
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Station 'Z'
To correct this problem, specific zones of
protection have been created.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Z'
Station 'Y'
Zone 1 – 80-85%
Zone 2 – 125-150%
Zone 1 – Is set to cover 80-85% of the
circuit and is instant.
Zone 2 – Is set to cover 125-150% of the
circuit but is generally a timed protection.
Transmission Lines Protection Overview.
Zone 1 Protection
Station 'Z'
Station 'Y'
Zone 1 – 80-85%
Zone 1 – Is set to cover 80-85% of the
circuit and is instant.
Zone 1 protection is generally known as
Direct Underreach
Transmission Lines Protection Overview.
Zone 1 Protection
Station 'Y'
This area
Instantaneous
protection from
Station 'Y' only.
There is a limit to the
protection when using
Direct Underreach
This area overlaps
and is
Instantaneous
protection from
both Station 'Y'
and Station 'Z'.
Station 'Z'
This area
Instantaneous
protection from
Station 'Z' only.
Transmission Lines Protection Overview.
Zone 1 Protection
Station 'Y'
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
Trip
Station 'Z'
Transmission Lines Protection Overview.
Transfer Trip
Station 'Y'
1
Communication is
accomplished by a
variety of media but
will not be discussed
right now.
Station 'Z'
T/T
Rx
2
Transfer Trip
At Station 'Y' both Zone 1 and Zone 2 will see the fault.
Station 'Y' Zone 1 will trip instantly and send Transfer Trip
Station ‘Z' will receive Transfer Trip and trip its terminal
breakers instantly.
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
How do we
protect this
area from
Station 'Z'?
The answer
is to limit
use another
There
is another
to the
zone
designedwhen
to reach
all the
protection
using
way
across
the circuit.
Direct
Underreach
Station 'Z'
How do we
protect this
area from
Station 'Y'?
Transmission Lines Protection Overview.
Simple two ended circuit
Station 'Y'
Zone 2
Zone 2 is set to ‘see’
125-150% of the
circuit.
Station 'Z'
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.
Transmission Lines Protection Overview.
We will look at Zone 2 independent of Zone 1
Station 'Y'
Zone 2
Zone 2 is set to ‘see’
125-150% of the
circuit.
Station 'Z'
Although Zone 2 is normally timed, there is a
need for the Zone 2 protection to be
instantaneous in order to satisfy rapid removal
of the transmission circuit in a faulted
condition.
Transmission Lines Protection Overview.
Zone 2 Protection
Station 'Y'
Station 'Z'
The rapid removal will be by using Zone 2 in a:
Permissive Overreach scheme or
Directional Comparison scheme
Transmission Lines Protection Overview.
Permissive Overreach
Station 'Z'
Station 'Y'
Zone 1 Limit
2
In Permissive Overreach each Station has a timed 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).
Transmission Lines Protection Overview.
Permissive Overreach
Station 'Z'
Station 'Y'
Zone 1 Limit
1
2
2
Permissive Signal
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 Permission to
Station 'Z' Zone 2 to trip instantly instead of timed.
Transmission Lines Protection Overview.
Directional Comparison
Station ‘Z’
Station ‘Y’
Zone 1 Limit
2
In Directional Comparison each Station has Instant 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.
Transmission Lines Protection Overview.
Directional Comparison
Station ‘Z’
Station ‘Y’
Zone 1 Limit
2
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.
Transmission Lines Protection Overview.
Directional Comparison
Station ‘Z’
Station ‘Y’
Zone 1 Limit
2
For example: The fault is located on the adjacent circuit.
Station ‘Z’ Zone 2 ‘sees’ the fault and will trip instantly
Only the circuits breakers of the faulted circuit should
trip
Transmission Lines Protection Overview.
Directional Comparison
Station ‘Y’
The OM3 will sense the fault as
well and send a block signal to
the opposite Zone 2 preventing
it from tripping instantly.
OM3
Station ‘Z’
X
2
Block Signal
To correct this a 3rd Zone is employed
This is the Directional Comparison element which employs a
relay known as an OM3 relay and is set to look backwards
If 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.
Transmission Lines Protection Overview.
Protection review
Permissive Signal
Station 'Y'
1
OM3
2
Station ‘Y’
Zone 3 OM3
Block Signal
Transfer Trip
Station ‘Z’ Zone 2
Station ‘Z’ Zone 1
Station ‘Y’ Zone 1
Station ‘Y’ Zone 2
Station 'Z'
Station ‘Z’
Zone 3 OM3
2
OM3
1
Transfer Trip
Block Signal
Permissive Signal
The
Directional
protections
Comparison
will all
have
isTimed
Instant
a Zone
1 Direct
it receives
Under
In some
cases
Zone
2 may
be is
different
in unless
each
Group,
Group
These
protections
are
referred
to
as
Groups.
Permissive
Overreach
unless
it
receives
a A
Zone
2
can
be
Permissive
Overreach
or
Each
Station
Zone
1the
send
Transfer
Trip3of
to
Each
Station
has
Zone
1generally
Direct
Underreach
aEach
reach
Block
and
Signal
Zone
from
2 awill
have
opposite
either
end
Permissive
Zone
OM3
ZoneEach
2 could
have
Permissive
Overreach
where
Group
B
Each
Group
Station
A
and
has
Group
Zone
Bwill
2
are
covering
125-150%
clones
each
other
terminal
will
have
duplication
of
each
group
Permissive
Signal
from
the
opposite
end
Zone
2could
Directional
Comparison
opposite
endwhere
station
tripping
its
covering
80-85%
of then
the
circuit.
Overreach
element
or
Directional
itas
Comparison
will
then
trip
but
timed.
not Zone
both.
havewith
Directional
Comparison
a Zone
1
Direct
Underreach
the
circuit.
and
abreakers.
similar
and
will
bewhere
known
Group
A
and
Group
B. 2.
protection
it
will
trip
instantly.
Transmission Lines Protection Overview.
Protection review
Permissive Signal
Station 'Y'
1
OM3
2
Station ‘Y’
Zone 3 OM3
Block Signal
Transfer Trip
Station 'Z'
Station ‘Z’ Zone 2
Station ‘Z’ Zone 1
Station ‘Y’ Zone 1
Station ‘Y’ Zone 2
Transfer Trip
Block Signal
Permissive Signal
This is what represents a basic line protection.
Two Zones with a dual redundancy built in.
Station ‘Z’
Zone 3 OM3
2
OM3
1
Transmission Lines Protection Overview.
Permissive
Signal
Lets look
at when
a terminal is
Out of ServiceBlock
withSignal
its line disconnect
Station 'Z'
Station 'Y'
open
Transfer Trip
Station ‘Z’
Zone 3 OM3
1
OM3
2
Station ‘Y’
Zone 3 OM3
Station ‘Z’ Zone 2
Station ‘Z’ Zone 1
Station ‘Y’ Zone 1
Station ‘Y’ Zone 2
2
OM3
1
Transfer Trip
Block Signal
Permissive Signal
The line switch at Station ‘Y’ is OPEN
As a result, Station ‘Y’ Protections no longer see the
circuit.
Transmission Lines Protection Overview.
Lets look at when a terminal is
Out of Service
Station 'Y'
Transfer Trip
Station 'Z'
Station ‘Z’ Zone 2
Station ‘Z’ Zone 1
2
1
Transfer Trip is Blocked
to opposite terminal
breakers
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’.
Transmission Lines Protection Overview.
Lets look at when a terminal is
Out of Service
‘B’ Pallets
Station 'Y'
Permissive Signal
Station 'Z'
Station ‘Z’ Zone 2
Station ‘Z’ Zone 1
2
1
Permissive Echo Signal
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 back to the sending terminal and it will then
trip instantly. This signal is keyed on at all times.
Transmission Lines Protection Overview.
Communication
Station 'Y'
1
Powerline CarrierWave Trap
Station 'Z'
Fibre-Optic
MicroWave
Digital Teleprotection
2
1
2
In order for the Protection signals to travel from one
station to another, a communications medium is
required.
There are several types used today.
Transmission Lines Protection Overview.
Station 'Y'
Micro-Wave Communication
Microwave
signals
Guard
Tones
AThe
large
microwave
are transmitted
typically
consist
transmission
towerof
is
between
points.
4built
Transfer
Trip
Tones
at each
end
of
andthe
2 Permissive
/
circuit
These are known as
Blocking Tones
Guard Tones
We will call them…
Station 'Z'
Transmission Lines Protection Overview.
Station 'Y'
Micro-Wave Communication
Transfer Trip Channel #1
Transfer Trip Channel #2
Transfer Trip Channel #3
Transfer Trip Channel #4
Permissive / Block Channel #1
Permissive / Block Channel #2
Station 'Z'
Transmission Lines Protection Overview.
Micro-Wave Communication
Station 'Y'
The question arises.
Why so many
Tones?
Here’s why….
Microwave is:
- influenced by external forces
- a line of sight communication
Station 'Z'
Transmission Lines Protection Overview.
Micro-Wave Communication
Station 'Y'
Station 'Z'
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 asMicrowave Fading
Transmission Lines Protection Overview.
Micro-Wave Communication
Station 'Y'
Distortions in the air can be
caused by changes in:
-Temperature
- Pressure
-Humidity
-Precipitation
-Fog
and many other atmospheric
factors.
Station 'Z'
Transmission Lines Protection Overview.
Micro-Wave Communication
Microwave is also a “Line of Sight”
communications
Station 'Z'
Station 'Y'
Trees
Buildings
Any type of physical obstruction
will affect the path of the signal
Transmission Lines Protection Overview.
Micro-Wave Communication
Station 'Z'
Station 'Y'
To correct for these limits.
Pathways are carefully
determined to minimize external
influences.
Transmission Lines Protection Overview.
Station 'Y'
Micro-Wave Communication
Main Pathway
Bodies of Water
Tall
Buildings
Hills and
Mountains
Another
method
secure
Pathways
will gotoaround
transmission
ofobstacles
the signal
avoiding large
is sending along redundant
pathways
Alternate Pathway
Station 'Z
Transmission Lines Protection Overview.
Micro-Wave Communication
Station 'Y'
Main Pathway
T/T ch#1
T/T ch#2
Perm#1
Bodies of Water
Tall
Buildings
Hills and
Mountains
Sometimes signals will be split.
T/T ch#3
T/T ch#4
Perm#2
2 T/T ch’s, 1 Perm on Main path
2 T/T ch’s, 1 Perm on Alt Path
Alternate Pathway
Station 'Z
Transmission Lines Protection Overview.
Power 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.
60hz Wave Trap
passes,
high hz
does not
Transmission
Circuit
CVT shunts
signal to
communications
equipment
Wave Trap
Transmission Lines Protection Overview.
Digital Tele-protection – Fibre Optic
Digital Tele-protection had
employs
oncelight
utilized
signal
injected into
microwave
tone
fibre
equipment
optic cable.
for the LH1
configuration but for the most part has since
The fibre could be buried or even in the sky wire
been replaced with all digital equipment.
of a transmission circuit.
This is a true Digital Tele-Protection scheme and
is beyond the scope of this presentation.
Fibre
Optic
Fibre
Optic
Skywire
Shield
Wires
Transmission Lines Protection Overview.
Micro-Wave Communication
Station 'Y'
Frequency Shift
T1 G1
T2 G2
T3 G3
T4 G4
T5 G5
T6 G6
Fault
TRIP
R1 G1
R2 G2
R3 G3
R4 G4
R5 G5
R6 G6
Watch carefully
how this works
Relay/Microwave buildings
Station 'Z'
Transmission Lines Protection Overview.
‘A’
Battery
DC +
‘A’
Protection
‘B’
Battery
DC +
‘B’
Protection
CH
#1
CH
#3
CH
#2
CH
#3
CH
#2
CH
#4
CH
#1
CH
#4
Permissive
‘A’ Logic
LH1
Configuration
Permissive
‘B’ Logic
Disconnect Switch ‘A’ Pallet Supervision
Click
These
Fail
Trip Guard
#1
#1
Fail
Trip Guard
#2
#2
Trip Circuit
Fail
Trip Guard
#3
#3
Fail
Trip Guard
#4
#4
Transfer Trip Channels
Fail
Perm Guard
#1
#1
Fail
Perm Guard
#2
#2
Permissive Channels
Disconnect
Switch
Close
Open
Transmission Lines Protection Overview.
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
Transmission Lines Protection Overview.
The End