Overrreaching distance relays Kenneth Opskar Statnett, Norway CIGR

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Overrreaching distance relaysKenneth
OpskarStatnett, NorwayCIGRÉ Study committee B5
ProtectionAutomationMember WG 16 Busbar
ProtectionMember WG 07 Line Protection
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PSRC Overrreaching distance relays

• Brief description of grid characteristics
• Relay protection requirements. Legal fundament
• Setting policy regarding overreaching distance
  relays in Norway

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• NORDIC COUNTRIES
• Peak load 69 000MW
• Installed capacity 89 000MW
• Hydro 53
• Nuclear 14
• Thermal 32
• Wind 2,6
• Norway
• Peak load 23 050MW
• Installed capacity 27 500MW
• Hydro power 99
• Population 4 million
• Norway deregulated in 1991
• TSO Statnett owns 85
• 4 TSOs
• 1 common Power Exchange (96)

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Common Nordic Power Market- with elspot areas
Hydro
FINLAND
SWEDEN
F
NORWAY
DENMARK
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Legal fundamentOverreaching distance relays

• Energy law of 1991 fundament for the TSO
• Regulations for TSO 2005
• TSO has specified guiding recommendations for
  relay protection in main and regional grid
• Considers what kind of faults and abnormal events
  that may occur in the power system
• Relay protection requirements are defined on this
  basis
• Applies to new substations or replacements that
  affect the relay protection setting

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Relay protection requirements

Relay protection requirements OK
Unit specific
Requirements that apply to unit in case of normal
fault clearance
Requirements that apply to unit in case of relay
system or breaker failure
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General requirements (not all..)
1. All short circuits on any unit should be
covered by two independent relay systems 2. All
faults should be cleared selectively.
Unselectivity is accepted in case of failure in
the relay system(s), circuit breaker, broken
conductor etc 3. The relay systems should not
trip on transient, dynamic phenomena, abnormal
situations that occur due to tripping, switching
of breakers, energizing, disconnection of load or
production 4. The owner of the unit (e.g.line,
transformer) is responsible for the requirements
regardless of the location of the relay system
(local or remote).
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Unit specific requirementsLine Protection

• Two relay systems that detects the fault and trip
• Short curcuits should be tripped within 5 cycles
• When a 1phase fault evolves into a two or three
  phase fault, the tripping should be 3 phase
• When autoreclosing onto a permanent fault, trip
  within 5 cycles
• When switching onto a permanent fault, trip
  within 5 cycles, and do not start autoreclose

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Unit specific requirementsLine Protection

• When CB fails the short circuit should be cleared
  within 15 cycles (only 1 relay system)
• High impedance faults and open-pole/broken
  conductor is tripped by zero sequence relay
• Short circuit between CB and CT should be tripped
  within
• 5 cycles for a double CB/ single CT system
• 15 cycles for a double CB/ double CT system

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Unit specific requirementsLine Protection

• Autoreclose functionality available
• Autoreclose functionality for beeing switched
  ON/OFF, and automatic blocking
• AR either 1pole, 3pole, or 13 pole
• Programmable for either 1 or several cycles
  controlled (frequency,angle,voltage etc) or
  uncontrolled.

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Unit specific requirementsLine Protection

• Small and damped power swing oscillations should
  not initiate any relay protection response
  (blocking/tripping)
• Bigger and undamped power swings should be
  detected and an adequate relay response initiated
  (blocking, tripping or other)

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Example 145 kV OH-line(compensated or isolated
system)
Short circuit current from transformers should be
disconnected asap and no later than than 2,1
seconds
Short circuit current from production should be
disconnected asap and no later than 3 seconds
SC from lines should be disconnected asap and
no later than 1,0 seconds
SC from step-down transformers Should be
disconnected asap and no later than 2,1 seconds
Main protection should trip within 400 ms (20
cycles). In some cases 700 ms is allowed (e.g.
due to selectivity)
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Relay setting requirements other units

• Production units
• Solidly grounded system
• Busbars
• Lines
• Isolated or compensated system
• Busbars
• Lines
• Transformers connected to solidly grounded system
• Transformers connected to isolated or comp.system
• Shunt reactors
• Shunt capacitors
• FACTS
• HVDC
• Autoreclose units

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Norway Relay arrangement420300 kV solidly
grounded
420300 kV Lines - 2 distance relays as main 1
and main 2 - fault clearing time 5 cycles -
autoreclose 3 phase within 20 cycles and 1 phase
within 45 cycles - dual battery system - some
differential line protection but not widespread
used 420300 kV Busbars - 1 Busbar Protection
relay - Breaker failure
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Norway Relay arrangementlt 145 kV isolated or
compensated
lt 145 kV Lines - 1 distance relay as main 1 -
fault clearing time 20 cycles - no
teleprotection - remote distance as backup for
relay and breaker failure - only 3pole
tripping - delayed autoreclose 10-30 seconds lt
145 kV Busbars - No Busbar Protection relay
(AIS) - No Breaker failure Main problem with
overreaching distance relays are on lt 145 kV
lines!
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Overreaching distance relaysSetting policy zone 2
We have a detailed model of the whole Nordic main
grid (Norway, Sweden, Finland) in all sequences
(positive, negative, zero). We use this PSS/E
model to perform short circuit calculations
considering e.g. -          maintenances -        
  contingencies -          actual power
flow -          arc resistance -          short
circuit capacity -          fault type -         
fault location  The PSS/E model is used to
determine the setting of all distance zones.
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Overreaching distance relaysSetting policy zone 2
The calculated reach based on PSS/E simulations
needs to be checked to ensure that it does not
reach beyond the zone 1setting of the next
remote line section. If dual and independent
pilot protection exists on the line to be backed
up we accept unselectivity. That is, we accept
that if both the pilot schemes fail this might
lead to cascading outages. The criterion is that
these pilot schemes have to be completely
independent of each other. If there is a single
or no pilot schemes, selectivity has to be
ensured by adding a margin of at least 20 so
that if the single pilot scheme fails, this will
not lead to unselective tripping whatsoever.
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Overreaching distance relaysSetting policy zone 2
Depending on the situation,a minimum infeed could
be accounted for, hereby allowing an extension of
the reactive setting. This benefit is considered
by the explicit PSS/E simulations. If no infeed
is unrealistic this is not used unless it
doesnt matter. These contingencies that result
in a calculated minimum could result in a very
extreme case, but however it should be a
realistic case (voltage and load/production
profile)
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Overreaching distance relaysSetting policy zone 3
Zone 3 is an internal backup for zone 12 Zone 3
is set as a forward overreaching zone Zone 3
setting depends on the remote terminal - dual
line protection - breaker failure
protection Zone 3 setting depends on adjacent
transformer impedances Zone 3 setting depends on
the load carrying capabilty
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Overreaching distance relaysSetting policy zone 3
Overreaching distance zones is to some extent
bakcup for remote transformer relays and
transformer breakers (primary side
faults) Overreaching distance zones is to some
extent backup for remote busbar protection
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Overreaching distance relayszone 3 apparent
impedance
The zone 3 reach should cover with a sufficient
margin the apparent impedance accounting for
maximum infeed when the fault is at the far end
of the longest outgoing line at the remote
terminal. In some cases the worst case is a
shorter line due to stronger infeed. The margin
should be at least 20
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Overreaching distance relayszone 3 transformer
impedance
The prerequisite is that the zone does not see
through any transformer with a margin of at least
30 with respect to the nominal transformer
impedance with the tap changer in middle
position. This margin is set due to variations in
tap changer position.
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Overreaching distance relayszone 3 loadability
If the Zone 3 setting is in conflict with the
load carrying capability, it is a requirement
that the zone should be adjusted allowing
whatever load transfer that is required. We do
not want backup functions to restrict the
loadflow in normal operational situations. We
would require the installation of local backup of
relay or breaker failure protection, or leave
those perhaps unlikely events uncovered. Or use
several parameter groups.
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Zone 3 loadability

• When we calculate the loadability we determine
  the minimum load impedance
• - Umin 0.9 pu
• - Imax 1.2xInominal CT current
• Load angle 30 degrees.
• Power factor 0.866

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Load enchroachment
20 margin against Zmin w/load angle 30 degrees
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Apparent zone 2 fault
Fault location zone1