Protection Overview

1
Universal Relay Family

• Protection Overview

2
Contents...

• Configurable Sources
• FlexLogic and Distributed FlexLogic
• L90 Line Differential Relay
• D60 Line Distance Relay
• T60 Transformer Management Relay
• B30 Bus Differential Relay
• F60 Feeder Management Relay

3
Configurable Sources
Universal Relay Family
4
Concept of Sources

• Configure multiple three phase current and
  voltage inputs from different points on the power
  system into Sources
• Sources are then inputs to Metering and
  Protection elements

5
Sources Typical Applications

• Breaker-and-a-half schemes
• Multi-winding (multi-restraint) Transformers
• Busbars
• Multiple Feeder applications
• Multiple Meter
• Synchrocheck

6
Sources Example 1 Breaker-and-a-Half Scheme
7
Sources Example 1 Traditional Relay Application
8
Sources Example 1 Inputs into the Universal
Relay
9
Sources Example 1 Universal Relay solution using
Sources
10
Sources Example 2 Breaker-and-a-Half Scheme with
3-Winding Transformer
11
Sources Example 2 Inputs into the Universal
Relay
12
Sources Example 2 Universal Relay solution
using Sources
Universal Relay
13
Sources Example 3 Busbar with 5 feeders
Multiple Feeder Busbar
14
Sources Example 3 Inputs into the Universal
Relay
15
Sources Example 3 Universal Relay solution
using Sources
16
FlexLogicTMDistributed FlexLogicTM
Universal Relay Family
17
Universal Relay Functional Architecture
18
Distributed FlexLogic Example 1 2 out of 3 Trip
Logic Voting Scheme
19
Distributed FlexLogic Example 1 Implementation
of 2 out of 3 Voting Scheme
20
Distributed FlexLogic Example 2 Transformer
Overcurrent Acceleration
Animation
Substation LAN 10/100 Mbps Ethernet (Dual
Redundant Fiber)
Transformer IED IF Phase or Ground TOC pickup
THEN send GOOSE message to ALL Feeder
IEDs. Feeder IEDs Send No Fault GOOSE if no
TOC pickup ELSE Send Fault GOOSE if TOC
pickup. Transformer IED If No Fault GOOSE
from any Feeder IED then switch to accelerated
TOC curve.
21
FlexLogic Benefits

• FlexLogic
• Tailor your scheme logic to suit the application
• Avoid custom software modifications
• Distributed FlexLogic
• Across the substation LAN (at 10/100Mpbs) allows
  high-speed adaptive protection and coordination
• Across a power system WAN (at 155Mpbs using SONET
  system) allows high-speed control and automation

22
L90Line Differential Relay
Universal Relay Family
23
L90 Current Differential Relay Features

• Protection
• Line current differential (87L)
• Trip logic
• Phase/Neutral/Ground TOCs
• Phase/Neutral/Ground IOCs
• Negative sequence TOC
• Negative sequence IOC
• Phase directional OCs
• Neutral directional OC
• Phase under- and overvoltage
• Distance back-up

24
L90 Current Differential Relay Features

• Control
• Breaker Failure (phase/neutral amps)
• Synchrocheck Autoreclosure
• Direct messaging (8 extra inter-relay DTT bits
  exchanged)
• Metering
• Fault Locator
• Oscillography
• Event Recorder
• Data Logger
• Phasors / true RMS / active, reactive and
  apparent power, power factor

25
L90 Current Differential Relay Overview
Direct point-to-point Fiber (up to 70Km)
(64Kbps)
- G.703 - RS422
OR
- G.703 - RS422
Via SONET system telecom multiplexer (GEs FSC)
(155Mbps)
FSC (SONET)
FSC (SONET)
26
L90 Current Differential Relay Line Current
Differential

• Improved operation of the line current
  differential (87L) element
• dynamic restraint increasing security without
  jeopardizing sensitivity
• line charge current compensation to increase
  sensitivity
• self-synchronization

27
L90 Current Differential Relay Traditional
Restraint Method

• Traditional method is STATIC
• Compromise between Sensitivity and Security

28
L90 Current Differential Relay Dynamic Restraint

• Dynamic restraint uses an estimate of a
  measurement error to dynamically increase the
  restraint
• On-line estimation of an error is possible owing
  to digital measuring techniques
• In digital relaying to measure means to calculate
  or to estimate a given signal feature such as
  magnitude from the raw samples of the signal
  waveform

29
L90 Current Differential Relay Digital Phasor
Measurement

• The L90 measures the current phasors (magnitude
  and phase angle) as follows
• digital pre-filtering is applied to remove the
  decaying dc component and a great deal of high
  frequency distortions
• the line charging current is estimated and used
  to compensate the differential signal
• full-cycle Fourier algorithm is used to estimate
  the magnitude and phase angle of the fundamental
  frequency (50 or 60Hz) signal

30
L90 Current Differential Relay Digital Phasor
Measurement
Sliding Data Window
present time
waveform
magnitude
31
L90 Current Differential Relay Digital Phasor
Measurement
Sliding Data Window
waveform
magnitude
32
L90 Current Differential Relay Goodness of Fit

• A sum of squared differences between the actual
  waveform and an ideal sinusoid over last window
  is a measure of a goodness of fit (a
  measurement error)

33
L90 Current Differential Relay Phasor Goodness
of Fit

• The goodness of fit is an accuracy index for the
  digital measurement
• The goodness of fit reflects inaccuracy due to
• transients
• CT saturation
• inrush currents and other signal distortions
• The goodness of fit is used by the L90 to alter
  the traditional restraint signal (dynamic
  restraint)

34
L90 Current Differential Relay
Operate-Restraint Regions
ILOC local current IREM remote end current
35
L90 Current Differential Relay Dynamic Restraint

• Dynamic restraint signal
• Traditional restraint signal Error factor

Imaginary (ILOC/IREM)
OPERATE
Error factor is high
Real (ILOC/IREM)
REST.
Error factor is low
36
L90 Current Differential Relay Charge Current
Compensation

• The L90 calculates the instantaneous values of
  the line charging current using the instantaneous
  values of the terminal voltage and shunt
  parameters of the line
• The calculated charging current is subtracted
  from the actually measured terminal current
• The compensation reduces the spurious
  differential current and allows for more
  sensitive settings

37
L90 Current Differential Relay Charge Current
Compensation

• The compensating algorithm
• is accurate over wide range of frequencies
• works with shunt reactors installed on the line
• works in steady state and during transients
• works with both wye- and delta-connected VTs (for
  delta VTs the accuracy of compensation is limited)

38
L90 Current Differential Relay Effect of
Compensation
Local and remote voltages
Voltage, V
time, sec
39
L90 Current Differential Relay Effect of
Compensation
Traditional and compensated differential currents
(waveforms)
Current, A
time, sec
40
L90 Current Differential Relay Effect of
Compensation
Traditional and compensated differential currents
(magnitudes)
Current, A
time, sec
41
L90 Current Differential Relay
Self-Synchronization
t0
Forward travel time
tf
t1
Relay turn-around time
ping-pong
t2
Return travel time
tr
t3
42
L90 Current Differential Relay Ping-Pong
(example)
Relay 1
Relay 2
Initial clocks mismatch1.4ms or 30
0
Send start bit Store T1i-30
Communication path
Send start bit Store T2i-30
0
8.33 ms
Capture T2i-22.3
5.1
2.3
Capture T1i-25.1
8.33 ms
8.33
Send T1i-25.1

8.33
Send T2i-22.3
Store T1i-25.1
8.33 ms
13.43
10.53
Store T2i-22.3
8.33 ms
Send T1i-116.66
16.66
16.66
Send T2i-116.66
8.33 ms
Store T1i-18.33 Capture T2i18.96
21.76
18.96
Store T2i-18.33 Capture T1i21.76
T2i-30 T1i-25.1 T1i-116.66 T2i18.96
a25.1-05.1 b218.96-16.662.3 ?2(5.1-2.3)/2
1.4ms (behind)
T1i-30 T2i-22.3 T2i-116.66 T1i21.76
a12.3-02.3 b121.76-16.665.1 ?1(2.3-5.1)/2
-1.4ms (ahead)
Speed up
Slow down
30
0
t1
t2
43
L90 Current Differential Relay Ping-Pong
(example cnt.)
Relay 1
Relay 2
33.32
Store T1i-333.32
33.32
Store T2i-333.32
8.52 ms
Capture T2i-235.62
38.28
35.62
Capture T1i-238.28
8.14 ms
41.55
41.55
Send T1i-238.28

Send T2i-235.62
8.52 ms
Store T1i-238.28
Store T2i-235.62
8.14 ms
Send T1i-150.00
50.00
49.93
Send T2i-149.93
8.52 ms
53.16
54.03
Store T1i-150.00 Capture T2i53.16
Store T2i-149.93 Capture T1i54.03
8.14 ms
T2i-333.32 T1i-238.28 T1i-150.00 T2i53.16
a238.28-33.324.96 b253.16-50.003.16 ?2(4.96-3
.16)/2 0.9ms (behind)
T1i-333.32 T2i-235.62 T2i-149.93 T1i54.03
a135.62-33.322.3 b154.03-49.934.1 ?1(2.3-4.1)
/2 -0.9ms (ahead)
Speed up
Slow down
0
30
19.5
t1
t2
44
L90 Current Differential Relay Digital
Flywheel
Virtual Shaft
clock 1
clock 2

• If communications is lost, sample clocks continue
  to free wheel
• Long term accuracy is only a function of the base
  crystal stability

45
L90 Current Differential Relay Peer-to-Peer
Operation

• Each relay has sufficient information to make an
  independent decision
• Communication redundancy

L90-2
L90-1
L90-3
46
L90 Current Differential Relay Master-Slave
Operation

• At least one relay has sufficient information to
  make an independent decision
• The deciding relay(s) sends a transfer-trip
  command to all other relays

L90-2
L90-1
L90-3
Data (currents)
Transfer Trip
47
L90 Current Differential Relay Benefits

• Increased Sensitivity without sacrificing
  Security
• Fast operation (1?1.5 cycles)
• Lower restraint settings / higher sensitivity
• Charging current compensation
• Dynamic restraint ensures security during CT
  saturation or transient conditions
• Reduced CT requirements
• Direct messaging
• Increased redundancy due to master-master
  configuration

48
L90 Current Differential Relay Benefits

• Self-Synchronization
• No external synchronizing signal required
• Two or three terminal applications
• Communication path delay adjustment
• Redundancy for loss of communications
• Benefits of the UR platform (back-up protection,
  autoreclosure, breaker failure, metering and
  oscillography, event recorder, data logger,
  FlexLogicTM, fast peer-to-peer communications)

49
D60Line Distance Relay
Universal Relay Family
50
D60 Line Distance Relay Features

• Protection
• Four zones of distance protection
• Pilot schemes
• Phase/Neutral/Ground TOCs
• Phase/Neutral/Ground IOCs
• Negative sequence TOC
• Negative sequence IOC
• Phase directional OCs
• Neutral directional OC
• Negative sequence directional OC

51
D60 Line Distance Relay Features

• Protection (continued)
• Phase under- and overvoltage
• Power swing blocking
• Out of step tripping
• Control
• Breaker Failure (phase/neutral amps)
• Synchrocheck
• Autoreclosure

52
D60 Line Distance Relay Features

• Metering
• Fault Locator
• Oscillography
• Event Recorder
• Data Logger
• Phasors / true RMS / active, reactive and
  apparent power, power factor

53
D60 Line Distance Relay Stepped Distance

• Four zones of stepped distance
• individual per-zone per-element characteristic
• dynamic memory-polarized mho
• quadrilateral
• individual per-zone per-element current
  supervision
• multi-input phase comparator
• additional ground directional supervision
• dynamic reactance supervision
• all 4 zones reversible
• excellent transient overreach control

54
D60 Line Distance Relay Zone 1 and CVT transients

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

55
D60 Line Distance Relay Zone 1 and CVT transients
Sample CVT output voltages (the primary voltage
drops to zero)
Illustration of the signal-to-noise ratio
56
D60 Line Distance Relay Zone 1 and CVT transients

• CVTs 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

57
D60 Line Distance Relay Zone 1 and CVT transients
Estimated voltage magnitude does not seem to be
underestimated
2.2 of the nominal 70 of the actual value
58
D60 Line Distance Relay Zone 1 and CVT transients
Impedance locus may pass below the origin of the
Z-plane - this would call for a time delay to
obtain stability
59
D60 Line Distance Relay Zone 1 and CVT transients

• Transient overreach due to CVTs - solutions
• apply delay (fixed or adaptable)
• reduce the reach
• adaptive techniques and better filtering
  algorithms

60
D60 Line Distance Relay Zone 1 and CVT transients
Actual maximum reach curves
61
D60 Line Distance Relay Zone 1 and CVT transients

• D60 Solution
• Optimal signal filtering
• currents - max 3 error due to the dc component
• voltages - max 0.6 error due to CVT transients
• Adaptive double-reach approach
• the 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

62
D60 Line Distance Relay Zone 1 and CVT transients

• 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

63
D60 Line Distance Relay Zone 1 and CVT transients
64
D60 Line Distance Relay Zone 1 and CVT transients
Multiplier for the inner zone 1 reach, pu
Elements Voltage, pu
65
D60 Line Distance Relay Zone 1 and CVT transients

• Performance
• excellent transient overreach control (5 up to a
  SIR of 30)
• no unnecessary decrease in speed

66
D60 Line Distance Relay Zone 1 Speed
67
D60 Line Distance Relay Zone 1 Speed
68
D60 Line Distance Relay Pilot Schemes

• Pilot Schemes available
• Direct Underreaching Transfer Trip (DUTT)
• Permissive Underreaching Transfer Trip (PUTT)
• Permissive Overreaching Transfer Trip (POTT)
• Hybrid Permissive Overreaching Transfer Trip (HYB
  POTT)
• Blocking Scheme

69
D60 Line Distance Relay Pilot Schemes

• Pilot Schemes - Features
• integrated functions
• weak infeed
• echo
• line pick-up
• basic protection elements used to key the
  communication
• distance elements
• fast and sensitive ground (zero- and negative
  sequence) directional IOCs with
  current/voltage/dual polarization

70
D60 Line Distance Relay Benefits

• Excellent CVT transient overreach control
  (without unnecessary decrease in speed)
• Fast, sensitive and accurate ground directional
  OCs
• Common pilot schemes
• Benefits of the UR platform (back-up protection,
  autoreclosure, breaker failure, metering and
  oscillography, event recorder, data logger,
  FlexLogicTM, fast peer-to-peer communications)

71
T60Transformer Management Relay
Universal Relay Family
72
T60 Transformer Management Relay Features

• Protection
• Restrained differential
• Instantaneous differential overcurrent
• Restricted ground fault
• Phase/Neutral/Ground TOCs
• Phase/Neutral/Ground IOCs
• Phase under- and overvoltage
• Underfrequency

73
T60 Transformer Management Relay Features

• Metering
• Oscillography
• Event Recorder
• Data Logger
• Phasors / true RMS / active, reactive and
  apparent power, power factor

74
T60 Transformer Management Relay Restrained
differential

• Internal ratio and phase compensation
• Dual-slope dual-breakpoint operating
  characteristic
• Improved dynamic second harmonic restraint for
  magnetizing inrush conditions
• Fifth harmonic restraint for overexcitation
  conditions
• Up to six windings supported

75
T60 Transformer Management Relay Differential
Signal

• Removal of the zero sequence component from the
  differential signal
• optional for delta-connected windings
• enables the T60 to cope with in-zone grounding
  transformers and in-zone cables with significant
  zero-sequence charging currents
• Removal of the decaying dc component
• Full-cycle Fourier algorithm for measuring both
  the differential current phasor and the second
  and fifth harmonics

76
T60 Transformer Management Relay Restraining
Signal

• Removal of the decaying dc component
• Full-cycle Fourier algorithm for measuring the
  magnitude
• Maximum of principle used for deriving the
  restraining signal from the terminal currents
• the magnitude of the current flowing through a CT
  that is more likely to saturate is used

77
T60 Transformer Management Relay Operating
Characteristic

• Two slopes used to cope with
• small errors during linear operation of the CTs
  (K1) and
• large CT errors (saturation) for high through
  currents (K2)

78
T60 Transformer Management Relay Operating
Characteristic

• Two breakpoints used to specify
• the safe limit of linear CT operation (B1) and
• the minimum current level that may cause large
  spurious differential signals due to CT
  saturation (B2)

79
T60 Transformer Management Relay Magnetizing
Inrush
Sample magnetizing inrush current
Second harmonic ratio
80
T60 Transformer Management Relay Magnetizing
Inrush

• New second harmonic restraint
• uses both the magnitude and phase relation
  between the second harmonic and the fundamental
  frequency (60Hz) component
• Implementation issues
• the second harmonic rotates twice as fast as the
  fundamental component (60Hz)
• consequently the phase difference between the
  second harmonic and the fundamental component
  changes in time...

81
T60 Transformer Management Relay New Inrush
Restraint
Solution
82
T60 Transformer Management Relay New Inrush
Restraint
3D View
Inrush Pattern
83
T60 Transformer Management Relay New Inrush
Restraint
3D View
Internal Fault Pattern
84
T60 Transformer Management Relay New Inrush
Restraint

• Basic Operation
• if the second harmonic drops magnitude-wise below
  20, the phase angle of the complex second
  harmonic ratio is close to either 90 or -90
  degrees during inrush conditions
• the phase angle may not display the 90-degree
  pattern if the second harmonic ratio is above
  some 20
• if the second harmonic ratio is above 20 the
  restraint is in effect, if it is below - the
  restraint and its duration depend on the phase
  angle

85
T60 Transformer Management Relay New Inrush
Restraint
New restraint characteristic
The characteristic is dynamic
86
T60 Transformer Management Relay New Inrush
Restraint
87
T60 Transformer Management Relay New Inrush
Restraint
Effective restraint characteristic time
(cycles) the restraint is kept vs. complex
second harmonic ratio
88
T60 Transformer Management Relay New Inrush
Restraint
Effective restraint characteristic time for
which the restraint is kept vs. complex second
harmonic ratio
3D View
89
T60 Transformer Management Relay Benefits

• Up to six windings supported
• Improved transformer auto-configuration
• Improved dual-slope differential characteristic
• Improved second harmonic restraint
• Benefits of the UR platform (back-up
  protection,metering and oscillography, event
  recorder, data logger, FlexLogicTM, fast
  peer-to-peer communications)

90
B30Bus Differential Relay
Universal Relay Family
91
B30 Bus Differential Relay Features

• Configuration
• up to 5 feeders with bus voltage
• up to 6 feeders without bus voltage

92
B30 Bus Differential Relay Features

• Protection
• Biased differential protection
• CT saturation immunity
• typical trip time lt 15 msec
• dynamic 1-out-of-2 or 2-out-of-2 operation
• Unbiased differential protection
• CT trouble

93
B30 Bus Differential Relay Features

• Metering
• Oscillography
• Event Recorder
• Data Logger
• Phasors / true RMS
• active, reactive and apparent power, power factor
  (if voltage available)

94
B30 Bus Differential Relay CT saturation problem

• During an external fault
• the fault current may be supplied by a number of
  sources
• the CTs on the faulted circuit may saturate
• Saturation of the CTs creates a current unbalance
  and violates the differential principle
• The conventional restraining current may not be
  sufficient to prevent maloperation
• CT saturation detection and other operating
  principles enhance the through-fault stability

95
B30 Bus Differential Relay DIF-RES trajectory
DIF differential RES restraining
External fault ideal CTs
96
B30 Bus Differential Relay DIF-RES trajectory
External fault ratio mismatch
97
B30 Bus Differential Relay DIF-RES trajectory
External fault CT saturation
98
B30 Bus Differential Relay DIF-RES trajectory
Internal fault high current
99
B30 Bus Differential Relay DIF-RES trajectory
Internal fault low current
100
B30 Bus Differential Relay DIF-RES trajectory
External fault extreme CT saturation
101
B30 Bus Differential Relay Operating principles

• Combination of
• Low-impedance biased differential
• Directional (phase comparison)
• Adaptively switched between
• 1-out-of-2 operating mode
• 2-out-of-2 operating mode
• by
• Saturation Detector

102
B30 Bus Differential Relay Two operating zones

• low currents
• saturation possible due to dc offset
• saturation very difficult to detect
• more security required

103
B30 Bus Differential Relay Two operating zones

• large currents
• quick saturation possible due to large magnitude
• saturation easier to detect
• security required only if saturation detected

104
B30 Bus Differential Relay Logic
DIF1
DIR
SAT
DIF2
105
B30 Bus Differential Relay Logic
106
B30 Bus Differential Relay Logic
DIF1
DIR
SAT
DIF2
107
B30 Bus Differential Relay Directional principle

• Internal faults - all currents approximately in
  phase

108
B30 Bus Differential Relay Directional principle

• External faults - one current approximately out
  of phase

109
B30 Bus Differential Relay Directional principle

• Check all the angles
• Select the maximum current contributor and check
  its position against the sum of all the remaining
  currents
• Select major current contributors and check their
  positions against the sum of all the remaining
  currents

110
B30 Bus Differential Relay Directional principle
111
B30 Bus Differential Relay Directional principle
112
B30 Bus Differential Relay Directional principle
113
B30 Bus Differential Relay Logic
DIF1
DIR
SAT
DIF2
114
B30 Bus Differential Relay Saturation Detector

• differential-restraining trajectory
• dI/dt

115
B30 Bus Differential Relay Saturation Detector
Sample External Fault (Feeder 1)
116
B30 Bus Differential Relay Saturation Detector
Analysis of the DIF-RES trajectory enables the
B30 to detect CT saturation
117
B30 Bus Differential Relay Saturation Detector
Sample External Fault (Feeder 4) - severe CT
saturation after 1.5msec
118
B30 Bus Differential Relay Saturation Detector
dI/dt principle enables the B30 to detect CT
saturation
119
B30 Bus Differential Relay Saturation Detector
120
B30 Bus Differential Relay Saturation Detector

• Operation
• The SAT flag WILL NOT set during internal faults
  whether or not the CT saturates
• The SAT flag WILL SET during external faults
  whether or not the CT saturates
• The SAT flag is NOT used to block the relay but
  to switch to 2-out-of-2 operating principle

121
B30 Bus Differential Relay Benefits

• Sensitive settings possible
• Very good through-fault stability
• Fast operation (less than 3/4 of a cycle)
• Benefits of the UR platform (back-up
  protection,metering and oscillography, event
  recorder, data logger, FlexLogicTM, fast
  peer-to-peer communication)

122
B30 Bus Differential Relay Extensions
6 feeders
6 feeders
6 feeders
123
F60Feeder Management Relay
Universal Relay Family
124
F60 Feeder Relay Features

• Protection
• Phase/Neutral/Ground IOC TOC
• Phase TOC with Voltage Restraint/Supervision
• Negative sequence IOC TOC
• Phase directional supervision
• Neutral directional overcurrent
• Negative sequence directional overcurrent
• Phase undervoltage overvoltage
• Underfrequency
• Breaker Failure (phase/neutral supervision)

125
F60 Feeder Relay Features

• Control
• Manually Control up to Two Breakers
• Autoreclosure Synchrocheck
• FlexLogic
• Metering
• Fault Locator
• Oscillography
• Event Recorder
• Data Logger
• Phasors / true RMS / active, reactive and
  apparent power, power factor, frequency

126
F60 Feeder Relay Phase Directional Element

• Directional element controls the RUN command of
  the overcurrent element (emulation of torque
  control)
• Memory voltage polarization held for 1 second

127
F60 Feeder Relay Neutral Directional Element

• Single protection element providing both forward
  and reverse looking IOC
• Independent settings for the forward and reverse
  elements
• Voltage, current or dual polarization
• Fast and secure operation due to the energy based
  comparator and positive sequence restraint

128
F60 Feeder Relay Ground Directional Elements

• Limitations of Fast Ground Directional IOCs
• Spurious zero- and negative-sequence voltages and
  currents may appear transiently due to the
  dynamics of digital measuring algorithms
• Magnitude of such spurious signals may reach up
  to 25 of the positive sequence quantities
• Phase angles of such spurious signals are random
  factors
• Combination of the above may cause maloperations

129
F60 Feeder Relay Ground Directional Elements
Sample three-phase fault currents
130
F60 Feeder Relay Ground Directional Elements
Sample three-phase fault currents (phasors)
Fault phasors (symmetrical)
Imaginary
Pre-fault phasors (symmetrical)
Real
131
F60 Feeder Relay Ground Directional Elements
Sample three-phase currents (symmetrical
components)
Positive Sequence
Zero Sequence
Negative Sequence
132
F60 Feeder Relay Ground Directional Elements

• Solutions to the problem of spurious zero and
  negative sequence quantities
• do not allow too sensitive settings
• apply delay
• new approach
• energy based comparator
• positive sequence restraint

133
F60 Feeder Relay Ground Directional Elements

• Operating power is calculated as a function of
• magnitudes of the operating and polarizing
  signals
• the angle between the operating and polarizing
  signals in conjunction with the characteristic
  and limit angles
• Restraining power is calculated as a product of
  magnitudes of the operating and restraining
  signals

134
F60 Feeder Relay Ground Directional Elements

• The powers are averaged over certain short
  period of time creating the operating and
  restraining energies
• The element operates when
• Both forward and reverse operating energies
  are calculated
• The factor K is lower for the reverse looking
  element to ensure faster operation

135
F60 Feeder Relay Ground Directional Elements
Forward looking element
Restraining Energy
Reverse looking element
Operating Energy
Operating Energy
Despite spurious negative sequence neither the
forward nor the reverse looking element maloperate
Restraining Energy
136
F60 Feeder Relay Ground Directional Elements

• Positive Sequence Restraint
• Classical Negative Sequence IOC
• Positive Sequence Restrained Negative Sequence
  IOC
• K1 1/8 for negative sequence IOC
• K1 1/16 for zero sequence IOC

137
F60 Feeder Relay Negative Sequence Directional
Element

• Single protection element providing both forward
  and reverse looking IOC
• Independent settings for the forward and reverse
  elements
• Mixed operating mode available
• Negative Sequence IOC / Negative Sequence
  Directional
• Zero Sequence IOC / Negative Sequence Directional
• Energy based comparator and positive sequence
  restraint

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139
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