sequence component applications in protective relays...
TRANSCRIPT
© 2019 SEL
Sequence Component Applications in Protective Relays –
Advantages, Limitations, and Solutions
Bogdan Kasztenny, Mangapathirao V. Mynam, and Normann Fischer
Schweitzer Engineering Laboratories, Inc.
Symmetrical Components Are 100 Years Old
Charles Legeyt Fortescue
XC
XB
XA
Sequence Components Transformation
X0C
X0B
X0A
X1A
X1B
X1C
X2A
X2BX2C
𝑋𝑋0𝑋𝑋1𝑋𝑋2
=13
1 1 11 𝑎𝑎 𝑎𝑎21 𝑎𝑎2 𝑎𝑎
𝑋𝑋𝐴𝐴𝑋𝑋𝐵𝐵𝑋𝑋𝐶𝐶
𝑋𝑋𝐴𝐴𝑋𝑋𝐵𝐵𝑋𝑋𝐶𝐶
=1 1 11 𝑎𝑎2 𝑎𝑎1 𝑎𝑎 𝑎𝑎2
𝑋𝑋0𝑋𝑋1𝑋𝑋2
Sequence Components Transformation
X0C
X0B
X0A
X1A
X1B
X1C
X2A
X2BX2C
XA
XC
XB
Solving Unbalanced Three-Phase NetworksRepresent Each Element With a Sequence Model
[ZABC]
[VABC]
[IABC]
I0 Z0
V0
Z1
V1
Z2
V2
I1
I2
Solving Unbalanced Three-Phase NetworksConnect Sequence Networks According to Unbalance
IAF
RFVAF IBF = 0 ICF = 0
CB
A
V0F
I0F
V1F
I1F
V2F
I2F
3RFVAF
Solving Unbalanced Three-Phase NetworksSolve a Single-Phase Network
S RF
Solving Unbalanced Three-Phase NetworksSolve a Single-Phase Network
S
V0F
V2F
V1F
R
ES ER
3RF
I0F
F
VAF
• Negative-sequence directional
• Zero-sequence directional
• Negative-sequence differential
• Zero-sequence differential
• Restricted earth fault
• Fault type identification
• System unbalance protection
• Disturbance detectors
• LOP and CT failure detection
• Distance element polarizing
• Fault locating
• Stator-field unbalance
Protection Applications of Sequence Components
Directional ElementsForward Fault
F
V2F V2REL
I2REL
Z2SYSF
F
V2FV2RELZ2SYSR
I2REL
Reverse Fault
V2FV2REVV2FWD
Protected Element
Voltage Profile𝑍𝑍2 =
𝑉𝑉2𝑅𝑅𝑅𝑅𝑅𝑅𝐼𝐼2𝑅𝑅𝑅𝑅𝑅𝑅
= −𝑍𝑍2𝑆𝑆𝑆𝑆𝑆𝑆𝑅𝑅 𝑍𝑍2 =𝑉𝑉2𝑅𝑅𝑅𝑅𝑅𝑅𝐼𝐼2𝑅𝑅𝑅𝑅𝑅𝑅
= +𝑍𝑍2𝑆𝑆𝑆𝑆𝑆𝑆𝐹𝐹
• Sensitivity• Speed of operation• Simple settings• Improved security through
limited comparator angle
Directional ElementsImpedance Plane Implementation (32Q, 32G)
Im(Z2)
Re(Z2)ZFWD
ZREV
ZSYSF
‒ZSYSR
Z2ANG
Forward Direction
ReverseDirection
• Analog relays pay a price in cost, size, and reliability when obtaining negative-sequence
• Today, with µP-based relays, application drives the selection
• Effect of mutual coupling favors negative-sequence
• Nonstandard sources favor zero-sequence
Directional ElementsZero-Sequence or Negative-Sequence?Phase RelaysIA
IB
IC
3I0
GroundCurrent Relay
To C
Ts
GroundVoltage Relay
VA
VB
VC
3V0
Ground Fault Protection
R1R2
v0FR2
R1 3I0
t
R2 R1
Restricted Earth Fault
32
Pha
sor
Filte
riA
iB
iC
IB
IA
IC
3I0
Pha
sor
Filte
rIN iN
ABC
G
IOP = INIPOL = 3I0
Negative-Sequence Differential
87Q
ProtectedApparatus
Pha
sor
Filte
riRA
iRB
iRC
IRB
IRA
IRC
IR2
Pha
sor
Filte
r
iSA
iSC
ISB
ISA
ISC
IS2
Terminal R Terminal S
iSB
ABC ABC
Q Q
IOP = | ΣI2 |
IRT = Σ| I2 |
Stator-Field Unbalance
60
Pha
sor
Filte
r
iA
iB
iC
IB
IA
IC
I2
Dou
ble-
Freq
uenc
y Fi
lterIF iF
+
SHUNT ‒
Q
ABC
• System unbalance• Open pole• Instrument transformer
errors- CT ratio errors and
saturation
- VT ratio errors, coupled signals, CCVT transients
• Breaker pole scatter• Filter transients• Asymmetrical bypass of
series capacitors
Many Events Drive Sequence Components, Not Only Faults
CT SaturationThree-Phase Fault
60
0
4020
–20–40
1050
–5–10–15
10 20 30 400
Pha
se C
urre
nt (k
A)
Spu
rious
I 0 C
urre
nt (k
A)
Time (ms)
Asymmetrical Bypass of Series Capacitors(AG Fault)
Phase Impedances
Sequence Impedances
−𝑗𝑗𝑋𝑋𝐶𝐶1 → 0 0 0
0 1 00 0 1
−𝑗𝑗𝑋𝑋𝐶𝐶3
2 −1 −1−1 2 −1−1 −1 2
Spark Gap
Controls
A A'XC
C C'XC
B B'XC
Asymmetrical Bypass of Series Capacitors(BC or BCG Fault)
−𝑗𝑗𝑋𝑋𝐶𝐶1 0 00 1 → 0 00 0 1 → 0
Phase Impedances
Sequence Impedances
−𝑗𝑗𝑋𝑋𝐶𝐶3
1 1 11 1 11 1 1
Spark Gap
Controls
A A'XC
C C'XC
B B'XC
Filter TransientsThree-Phase Balanced Fault
–2
0
2
–1 0 1 2 3 4
Time (cyc)
0
0.5
1
Cur
rent
(pu)
I 1, I 2
(pu)
I1I2
Securing Sequence Elements for CT Errors
| I1 |2 pu
0.1
| I0 |
0.1
| I2 |
0.5
3PFLT
LLFLT
–
+
–
+
–
+
–
+1 CYC
0.5 SEC
1 CYC
0.5 SEC1.5 CYC
0
0
1.5 CYC
Securing Sequence Elements for SmallSystem Unbalances and Errors
| I2 |
PKP| I2 | > PKP
| I2 || I1 |
Σ‒
a2| I1 |
IN OUT
Inverse-Time Security Counts
–+
• R2 must see the internal fault • R2 must identify the faulted phase• Can we count on 32Q, 32G, and fault type logic in R2?
Using Right Schemes for a Protection JobCross-Country Fault Example
R2R1
S RFEXT
FINT
Cross-Country Fault AnalysisOnly Forward AG Fault Present
V2 A
C
B
IZ2
V2
A
C
B
IZ2
Only Reverse BG Fault Present
• The polarizing voltage is off by 60°
• Forward or reverse direction asserted based on relative current flow
• 32Q and 32G may respond differently
• Use distance elements rather than 32Q/G
Cross-Country Fault AnalysisBoth Faults Are Present
V2
IZ2
Marginal Operation
32Q and 32G May DisagreeForward and Reverse Fault?
S R
R1 R2
• Avoid using multiple sensitive directional elements
• Use separate permissive key signals if needed
32Q and 32G May DisagreeForward and Reverse Fault?
S2 R2
VS2 VR2
strong weak
S0 R0
VS0 VR0
strongweak
R1 R2
R1 R2
• Many conditions can cause operating current
• If biased forward, 32Q/G would key on many non-fault events
• Use bias only when short-circuit studies show it is a must
32Q and 32G With Zero Polarizing VoltageAvoid Unless Necessary
Im(Z2)
Re(Z2)ZFWD
ZREV
ZSYSF
‒ZSYSR
Z2ANG
Forward Direction
ReverseDirection
Weak Infeed LogicNever Key Back if Not Sure There Is a Fault
KEYRECEIVED
ABNORMAL VOLTAGE
REVERSE DIRECTION
ECHO KEYPKP
0
Nontraditional Sources Drive Sequence Components Differently Than We Expect
WTG(Type 3)
34.5 kV 345 kV
AG
• Strong zero-sequence due to transformer ground
• Negative-sequence is low and modulated
• Inverter-based source even more difficult than WTG
AG Fault RecordC
urre
nt (A
)V
olta
ge (k
V)
0 50 100 150
200
–200
0
0
500
1000
–500
–1000
Time (ms)
Incremental Quantities-Based Relay Performs Very Well
806040
200
0
–200
0
800
–800
STARTTD32FAGFLT
–20 0 20
Cur
rent
(A)
Vol
tage
(kV
)
Time (ms)
• Responds to many types of events, not only faults• Works well for a single event• Requires proper restraining as a part of design• Calls for careful application• May face issues with nontraditional sources• Benefits from phase-based “backup”
Protection Based on Sequence Components Is Fast and Sensitive, But …