Fundamentals of Distance Protection - PowerPoint PPT Presentation

View by Category
About This Presentation
Title:

Fundamentals of Distance Protection

Description:

Title: Phase Distance & Power Transformers Author: GE Consumer and Industrial Last modified by: GE Consumer and Industrial Created Date: 2/14/2006 1:57:41 PM – PowerPoint PPT presentation

Number of Views:178
Avg rating:3.0/5.0
Slides: 112
Provided by: GECon1
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Fundamentals of Distance Protection


1
Fundamentals of Distance Protection
  • GE Multilin

2
Outline
  • Transmission line introduction
  • What is distance protection?
  • Non-pilot and pilot schemes
  • Redundancy considerations
  • Security for dual-breaker terminals
  • Out-of-step relaying
  • Single-pole tripping
  • Series-compensated lines

3
Transmission Lines
  • A Vital Part of the Power System
  • Provide path to transfer power between
    generation and load
  • Operate at voltage levels from 69kV to 765kV
  • Deregulated markets, economic, environmental
    requirements have pushed utilities to operate
    transmission lines close to their limits.

4
Transmission Lines
  • Classification of line length depends on
  • Source-to-line Impedance Ratio (SIR), and
  • Nominal voltage
  • Length considerations
  • Short Lines SIR gt 4
  • Medium Lines 0.5 lt SIR lt 4
  • Long Lines SIR lt 0.5

5
Typical Protection Schemes Short Lines
  • Current differential
  • Phase comparison
  • Permissive Overreach Transfer Trip (POTT)
  • Directional Comparison Blocking (DCB)

6
Typical Protection Schemes Medium Lines
  • Phase comparison
  • Directional Comparison Blocking (DCB)
  • Permissive Underreach Transfer Trip (PUTT)
  • Permissive Overreach Transfer Trip (POTT)
  • Unblocking
  • Step Distance
  • Step or coordinated overcurrent
  • Inverse time overcurrent
  • Current Differential

7
Typical Protection Schemes Long Lines
  • Phase comparison
  • Directional Comparison Blocking (DCB)
  • Permissive Underreach Transfer Trip (PUTT)
  • Permissive Overreach Transfer Trip (POTT)
  • Unblocking
  • Step Distance
  • Step or coordinated overcurrent
  • Current Differential

8
What is distance protection?
  • For internal faults
  • IZ V and V approximately in phase (mho)
  • IZ V and IZ approximately in phase (reactance)

9
What is distance protection?
  • For external faults
  • IZ V and V approximately out of phase (mho)
  • IZ V and IZ approximately out of phase
    (reactance)

10
What is distance protection?
Intended REACH point
Z
RELAY
11
Source Impedance Ratio, Accuracy Speed
Relay
Line
System
Consider SIR 0.1
Fault location Voltage () Voltage change ()
75 88.24 2.76
90 90.00 0.91
100 90.91 N/A
110 91.67 0.76
12
Source Impedance Ratio, Accuracy Speed
Relay
System
Line
Voltage at the relay
Consider SIR 30
Fault location Voltage () Voltage change ()
75 2.4390 0.7868
90 2.9126 0.3132
100 3.2258 N/A
110 3.5370 0.3112
13
Challenges in relay design
  • Transients
  • High frequency
  • DC offset in currents
  • CVT transients in voltages

14
Challenges in relay design
  • Transients
  • High frequency
  • DC offset in currents
  • CVT transients in voltages

15
Challenges in relay design
Sorry Future (unknown)
  • In-phase internal fault
  • Out-of-phase external fault

16
Transient Overreach
  • Fault current generally contains dc offset in
    addition to ac power frequency component
  • Ratio of dc to ac component of current depends
    on instant in the cycle at which fault occurred
  • Rate of decay of dc offset depends on system X/R

17
Zone 1 and CVT Transients
  • Capacitive Voltage Transformers (CVTs) create
    certain problems for fast distance relays applied
    to systems with high Source Impedance Ratios
    (SIRs)
  • CVT-induced transient voltage components may
    assume large magnitudes (up to 30-40) and last
    for a comparatively long time (up to about 2
    cycles)
  • 60Hz voltage for faults at the relay reach point
    may be as low as 3 for a SIR of 30
  • the signal may be buried under noise

18
Zone 1 and CVT Transients
  • CVT transients can cause distance relays to
    overreach. Generally, transient overreach may be
    caused by
  • overestimation of the current (the magnitude of
    the current as measured is larger than its actual
    value, and consequently, the fault appears closer
    than it is actually located),
  • underestimation of the voltage (the magnitude of
    the voltage as measured is lower than its actual
    value)
  • combination of the above

19
Distance Element Fundamentals
XL
R
XC
20
Impedance locus may pass below the origin of the
Z-plane - this would call for a time delay to
obtain stability
21
CVT Transient Overreach Solutions
  • apply delay (fixed or adaptable)
  • reduce the reach
  • adaptive techniques and better filtering
    algorithms

22
CVT Transients Adaptive Solution
  • Optimize signal filtering
  • currents - max 3 error due to the dc component
  • voltages - max 0.6 error due to CVT transients
  • Adaptive double-reach approach
  • filtering alone ensures maximum transient
    overreach at the level of 1 (for SIRs up to 5)
    and 20 (for SIRs up to 30)
  • to reduce the transient overreach even further an
    adaptive double-reach zone 1 has been implemented

23
CVT Transients Adaptive Solution
  • The outer zone 1
  • is fixed at the actual reach
  • applies certain security delay to cope with CVT
    transients
  • The inner zone 1
  • has its reach dynamically controlled by the
    voltage magnitude
  • is instantaneous

24
Desirable Distance Relay Attributes
  • Filters
  • Prefiltering of currents to remove dc decaying
    transients
  • Limit maximum transient overshoot (below 2)
  • Prefiltering of voltages to remove low frequency
    transients caused by CVTs
  • Limit transient overreach to less than 5 for an
    SIR of 30
  • Accurate and fast frequency tracking algorithm
  • Adaptive reach control for faults at reach points

25
Distance Relay Operating Times
26
Distance Relay Operating Times
35ms
25ms
30ms
20ms
15ms
27
Distance Relay Operating Times
SLG faults
LL faults
3P faults
28
Actual maximum reach curves
29
Maximum Torque Angle
  • Angle at which mho element has maximum reach
  • Characteristics with smaller MTA will
    accommodate larger amount of arc resistance

30
Mho Characteristics
Traditional
Directional angle slammed
Directional angle lowered and slammed
Both MHO and directional angles slammed (lens)
31
Load Swings
XL
LOOKING INTO LINE normally considered forward
Reach
Load Trajectory
Operate area
No Operate area
Typical load characteristic impedance
R
32
Load Swings
Lenticular Characteristic
Load swing
33
Load Encroachment Characteristic
The load encroachment element responds to
positive sequence voltage and current and can be
used to block phase distance and phase
overcurrent elements.
34
Blinders
  • Blinders limit the operation of distance relays
    (quad or mho) to a narrow region that parallels
    and encompasses the protected line
  • Applied to long transmission lines, where mho
    settings are large enough to pick up on maximum
    load or minor system swings

35
Quadrilateral Characteristics
36
Quadrilateral Characteristics
Ground Resistance (Conductor falls on ground)
R
Resultant impedance outside of the mho operating
region
XL
37
Distance Characteristics - Summary
Mho
Quadrilateral
Lenticular
JX
R
Better coverage for ground faults due to
resistance added to return path
Standard for phase elements
Used for phase elements with long heavily loaded
lines heavily loaded
38
Distance Element Polarization
  • The following polarization quantities are
    commonly used in distance relays for determining
    directionality
  • Self-polarized
  • Memory voltage
  • Positive sequence voltage
  • Quadrature voltage
  • Leading phase voltage

39
Memory Polarization
  • Positive-sequence memorized voltage is used for
    polarizing
  • Mho comparator (dynamic, expanding Mho)
  • Negative-sequence directional comparator (Ground
    Distance Mho and Quad)
  • Zero-sequence directional comparator (Ground
    Distance MHO and QUAD)
  • Directional comparator (Phase Distance MHO and
    QUAD)
  • Memory duration is a common distance settings
    (all zones, phase and ground, MHO and QUAD)

40
Memory Polarization
Static MHO characteristic (memory not established
or expired)
ZL
Dynamic MHO characteristic for a reverse fault
Dynamic MHO characteristic for a forward fault
Impedance During Close-up Faults
ZS
41
Memory Polarization
Static MHO characteristic (memory not established
or expired)
ZL
Dynamic MHO characteristic for a forward fault
RL
ZS
Memory PolarizationImproved Resistive Coverage
42
Choice of Polarization
  • In order to provide flexibility modern distance
    relays offer a choice with respect to
    polarization of ground overcurrent direction
    functions
  • Voltage polarization
  • Current polarization
  • Dual polarization

43
Ground Directional Elements
  • Pilot-aided schemes using ground mho distance
    relays have inherently limited fault resistance
    coverage
  • Ground directional over current protection using
    either negative or zero sequence can be a useful
    supplement to give more coverage for high
    resistance faults
  • Directional discrimination based on the ground
    quantities is fast
  • Accurate angular relations between the zero and
    negative sequence quantities establish very
    quickly because
  • During faults zero and negative-sequence currents
    and voltages build up from very low values
    (practically from zero)
  • The pre-fault values do not bias the developing
    fault components in any direction

44
Distance Schemes
Non-Pilot Aided Schemes (Step Distance)
Pilot Aided Schemes
Communication between Distance relays
No Communication between Distance Relays
45
Step Distance Schemes
  • Zone 1
  • Trips with no intentional time delay
  • Underreaches to avoid unnecessary operation for
    faults beyond remote terminal
  • Typical reach setting range 80-90 of ZL
  • Zone 2
  • Set to protect remainder of line
  • Overreaches into adjacent line/equipment
  • Minimum reach setting 120 of ZL
  • Typically time delayed by 15-30 cycles
  • Zone 3
  • Remote backup for relay/station failures at
    remote terminal
  • Reaches beyond Z2, load encroachment a
    consideration

46
Step Distance Schemes
Local
Z1
BUS
BUS
Z1
Remote
47
Step Distance Schemes
Local
End Zone
Z1
BUS
BUS
Z1
End Zone
Remote
48
Step Distance Schemes
Local
Z1
Breaker Tripped
BUS
BUS
Breaker Closed
Z1
Remote
49
Step Distance Schemes
Local
Z2 (time delayed)
Z1
BUS
BUS
Z1
Z2 (time delayed)
Remote
50
Step Distance Schemes

Z3 (remote backup)
Z2 (time delayed)
Z1
BUS
BUS
51
Step Distance Protection
52
Distance Relay Coordination
Local Relay
Remote Relay
53
Need For Pilot Aided Schemes
BUS
BUS
Local Relay
Remote Relay
Communication Channel
54
Pilot Communications Channels
  • Distance-based pilot schemes traditionally
    utilize simple on/off communications between
    relays, but can also utilize peer-to-peer
    communications and GOOSE messaging over digital
    channels
  • Typical communications media include
  • Pilot-wire (50Hz, 60Hz, AT)
  • Power line carrier
  • Microwave
  • Radio
  • Optic fiber (directly connected or multiplexed
    channels)

55
Distance-based Pilot Protection
56
Pilot-Aided Distance-Based Schemes
  • DUTT Direct Under-reaching Transfer Trip
  • PUTT Permissive Under-reaching Transfer Trip
  • POTT Permissive Over-reaching Transfer Trip
  • Hybrid POTT Hybrid Permissive Over-reaching
    Transfer Trip
  • DCB Directional Comparison Blocking Scheme
  • DCUB Directional Comparison Unblocking Scheme

57
Direct Underreaching Transfer Trip (DUTT)
  • Requires only underreaching (RU) functions which
    overlap in reach (Zone 1).
  • Applied with FSK channel
  • GUARD frequency transmitted during normal
    conditions
  • TRIP frequency when one RU function operates
  • Scheme does not provide tripping for faults
    beyond RU reach if remote breaker is open or
    channel is inoperative.
  • Dual pilot channels improve security

58
DUTT Scheme

 
Zone 1
Bus
Bus
Line
Zone 1
59
Permissive Underreaching Transfer Trip (PUTT)
  • Requires both under (RU) and overreaching (RO)
    functions
  • Identical to DUTT, with pilot tripping signal
    supervised by RO (Zone 2)

60
PUTT Scheme
Rx PKP

Local Trip
Zone 2
OR
Zone 1
61
Permissive Overreaching Transfer Trip (POTT)
  • Requires overreaching (RO) functions (Zone 2).
  • Applied with FSK channel
  • GUARD frequency sent in stand-by
  • TRIP frequency when one RO function operates
  • No trip for external faults if pilot channel is
    inoperative
  • Time-delayed tripping can be provided

62
POTT Scheme

63
POTT Scheme
POTT Permissive Over-reaching Transfer Trip
End Zone
BUS
BUS
64
POTT Scheme
Remote Relay
Local Relay
65
POTT Scheme
Communications Channel(s)
POTT TX 1
A to G
POTT RX 1
POTT TX 2
B to G
POTT RX 2
POTT TX 3
C to G
POTT RX 3
POTT TX 4
Multi Phase
POTT RX 4
Local Relay
Remote Relay
66
POTT Scheme Current reversal example
Local Relay
Remote Relay
67
POTT Scheme Echo example
Open
Local Relay
Remote Relay
68
Hybrid POTT
  • Intended for three-terminal lines and weak
    infeed conditions
  • Echo feature adds security during weak infeed
    conditions
  • Reverse-looking distance and oc elements used to
    identify external faults

69
Hybrid POTT
70
Directional Comparison Blocking (DCB)
  • Requires overreaching (RO) tripping and blocking
    (B) functions
  • ON/OFF pilot channel typically used (i.e., PLC)
  • Transmitter is keyed to ON state when blocking
    function(s) operate
  • Receipt of signal from remote end blocks tripping
    relays
  • Tripping function set with Zone 2 reach or
    greater
  • Blocking functions include Zone 3 reverse and
    low-set ground overcurrent elements

71
DCB Scheme
72
Directional Comparison Blocking (DCB)
End Zone
BUS
BUS
73
Directional Comparison Blocking (DCB) Internal
Faults
Local Relay
Remote Relay
74
Directional Comparison Blocking (DCB) External
Faults
Local Relay
Remote Relay
75
Directional Comparison Unblocking (DCUB)
  • Applied to Permissive Overreaching (POR) schemes
    to overcome the possibility of carrier signal
    attenuation or loss as a result of the fault
  • Unblocking provided in the receiver when signal
    is lost
  • If signal is lost due to fault, at least one
    permissive RO functions will be picked up
  • Unblocking logic produces short-duration TRIP
    signal (150-300 ms). If RO function not picked
    up, channel lockout occurs until GUARD signal
    returns

76
DCUB Scheme

 
77
Directional Comparison Unblocking (DCUB)
End Zone
BUS
BUS
78
Directional Comparison Unblocking (DCUB) Normal
conditions
Load Current
FSK Carrier
FSK Carrier
GUARD1 TX
GUARD1 RX
Local Relay
Remote Relay
GUARD2 TX
GUARD2 RX
NO Loss of Guard
NO Loss of Guard
NO Permission
NO Permission
Communication Channel
79
Directional Comparison Unblocking (DCUB) Normal
conditions, channel failure
Load Current
FSK Carrier
FSK Carrier
GUARD1 TX
GUARD1 RX
Local Relay
Remote Relay
GUARD2 TX
GUARD2 RX
Communication Channel
80
Directional Comparison Unblocking (DCUB) Internal
fault, healthy channel
FSK Carrier
FSK Carrier
GUARD1 TX
GUARD1 RX
Local Relay
Remote Relay
GUARD2 TX
GUARD2 RX
Communication Channel
81
Directional Comparison Unblocking (DCUB) Internal
fault, channel failure
FSK Carrier
FSK Carrier
GUARD1 TX
GUARD1 RX
Local Relay
Remote Relay
GUARD2 TX
GUARD2 RX
Communication Channel
82
Redundancy Considerations
  • Redundant protection systems increase
    dependability of the system
  • Multiple sets of protection using same protection
    principle and multiple pilot channels overcome
    individual element failure, or
  • Multiple sets of protection using different
    protection principles and multiple channels
    protects against failure of one of the protection
    methods.
  • Security can be improved using voting schemes
    (i.e., 2-out-of-3), potentially at expense of
    dependability.
  • Redundancy of instrument transformers, battery
    systems, trip coil circuits, etc. also need to be
    considered.

83
Redundant Communications
End Zone
BUS
BUS
AND Channels
OR Channels
POTT Less Reliable
POTT More Reliable
Communication Channel 1
DCB More Secure
DCB Less Secure
Communication Channel 2
More Channel Security
More Channel Dependability
84
Redundant Pilot Schemes
85
Pilot Relay Desirable Attributes
  • Integrated functions
  • weak infeed
  • echo
  • line pick-up (SOTF)
  • Basic protection elements used to key the
    communication
  • distance elements
  • fast and sensitive ground (zero and negative
    sequence) directional IOCs with current, voltage,
    and/or dual polarization

86
Pilot Relay Desirable Attributes
  • Pre-programmed distance-based pilot schemes
  • Direct Under-reaching Transfer Trip (DUTT)
  • Permissive Under-reaching Transfer Trip (PUTT)
  • Permissive Overreaching Transfer Trip (POTT)
  • Hybrid Permissive Overreaching Transfer Trip (HYB
    POTT)
  • Blocking scheme (DCB)
  • Unblocking scheme (DCUB)

87
Security for dual-breaker terminals
  • Breaker-and-a-half and ring bus terminals are
    common designs for transmission lines.
  • Standard practice has been to
  • sum currents from each circuit breaker externally
    by paralleling the CTs
  • use external sum as the line current for
    protective relays
  • For some close-in external fault events, poor CT
    performance may lead to improper operation of
    line relays.

88
Security for dual-breaker terminals
Accurate CTs preserve the reverse current
direction under weak remote infeed
89
Security for dual-breaker terminals
Saturation of CT1 may invert the line current as
measured from externally summated CTs
90
Security for dual-breaker terminals
  • Direct measurement of currents from both circuit
    breakers allows the use of supervisory logic to
    prevent distance and directional overcurrent
    elements from operating incorrectly due to CT
    errors during reverse faults.
  • Additional benefits of direct measurement of
    currents
  • independent BF protection for each circuit
    breaker
  • independent autoreclosing for each breaker

91
Security for dual-breaker terminals
  • Supervisory logic should
  • not affect speed or sensitivity of protection
    elements
  • correctly allow tripping during evolving
    external-to-internal fault conditions
  • determine direction of current flow through each
    breaker independently
  • Both currents in FWD direction ? internal fault
  • One current FWD, one current REV ? external fault
  • allow tripping during all forward/internal faults
  • block tripping during all reverse/external faults
  • initially block tripping during evolving
    external-to-internal faults until second fault
    appears in forward direction. Block is then
    lifted to permit tripping.

92
Single-pole Tripping
  • Distance relay must correctly identify a SLG
    fault and trip only the circuit breaker pole for
    the faulted phase.
  • Autoreclosing and breaker failure functions must
    be initiated correctly on the fault event
  • Security must be maintained on the healthy
    phases during the open pole condition and any
    reclosing attempt.

93
Out-of-Step Condition
  • For certain operating conditions, a severe
    system disturbance can cause system instability
    and result in loss of synchronism between
    different generating units on an interconnected
    system.

94
Out-of-Step Relaying
  • Out-of-step blocking relays
  • Operate in conjunction with mho tripping relays
    to prevent a terminal from tripping during severe
    system swings out-of-step conditions.
  • Prevent system from separating in an
    indiscriminate manner.
  • Out-of-step tripping relays
  • Operate independently of other devices to detect
    out-of-step condition during the first pole slip.
  • Initiate tripping of breakers that separate
    system in order to balance load with available
    generation on any isolated part of the system.

95
Out-of-Step Tripping
The locus must stay for some time between the
outer and middle characteristics
When the inner characteristic is entered the
element is ready to trip
Must move and stay between the middle and inner
characteristics
96
Power Swing Blocking
  • Applications
  • Establish a blocking signal for stable power
    swings (Power Swing Blocking)
  • Establish a tripping signal for unstable power
    swings (Out-of-Step Tripping)
  • Responds to
  • Positive-sequence voltage and current

97
Series-compensated lines
  • Benefits of series capacitors
  • Reduction of overall XL of long lines
  • Improvement of stability margins
  • Ability to adjust line load levels
  • Loss reduction
  • Reduction of voltage drop during severe
    disturbances
  • Normally economical for line lengths gt 200 miles

98
Series-compensated lines
  • SCs create unfavorable conditions for protective
    relays and fault locators
  • Overreaching of distance elements
  • Failure of distance element to pick up on
    low-current faults
  • Phase selection problems in single-pole tripping
    applications
  • Large fault location errors

99
Series-compensated lines Series Capacitor with MOV
100
Series-compensated lines
101
Series-compensated lines Dynamic Reach Control
102
Series-compensated lines Dynamic Reach Control
for External Faults
103
Series-compensated lines Dynamic Reach Control
for External Faults
104
Series-compensated lines Dynamic Reach Control
for Internal Faults
105
Distance Protection Looking Through a Transformer
  • Phase distance elements can be set to see beyond
    any 3-phase power transformer
  • CTs VTs may be located independently on
    different sides of the transformer
  • Given distance zone is defined by VT location
    (not CTs)
  • Reach setting is in ?sec, and must take into
    account location ratios of VTs, CTs and voltage
    ratio of the involved power transformer

106
Transformer Group Compensation
  • Depending on location of VTs and CTs, distance
    relays need to compensate for the phase shift and
    magnitude change caused by the power transformer

107
Setting Rules
  • Transformer positive sequence impedance must be
    included in reach setting only if transformer
    lies between VTs and intended reach point
  • Currents require compensation only if
    transformer located between CTs and intended
    reach point
  • Voltages require compensation only if
    transformer located between VTs and intended
    reach point
  • Compensation set based on transformer connection
    vector group as seen from CTs/VTs toward reach
    point

108
Distance Relay Desirable Attributes
  • Multiple reversible distance zones
  • Individual per-zone, per-element characteristic
  • Dynamic voltage memory polarization
  • Various characteristics, including mho, quad,
    lenticular
  • Individual per-zone, per-element current
    supervision (FD)
  • Multi-input phase comparator
  • additional ground directional supervision
  • dynamic reactance supervision
  • Transient overreach filtering/control
  • Phase shift magnitude compensation for distance
    applications with power transformers

109
Distance Relay Desirable Attributes
  • For improved flexibility, it is desirable to have
    the following parameters settable on a per zone
    basis
  • Zero-sequence compensation
  • Mutual zero-sequence compensation
  • Maximum torque angle
  • Blinders
  • Directional angle
  • Comparator limit angles (for lenticular
    characteristic)
  • Overcurrent supervision

110
Distance Relay Desirable Attributes
  • Additional functions
  • Overcurrent elements (phase, neutral, ground,
    directional, negative sequence, etc.)
  • Breaker failure
  • Automatic reclosing (single three-pole)
  • Sync check
  • Under/over voltage elements
  • Special functions
  • Power swing detection
  • Load encroachment
  • Pilot schemes

111
Questions?
About PowerShow.com