Mod ule 7 P o w e r Sy S y s t em e m R ev e v i ew ew C o u r s e P r o t e c t io i o n & C o o r d i n a t io io n B y : D r. H am a m i d J a f far fa r i
Fuse
Transformer
T y p i c a l D is i s t r i b u t i o n S y s t em em 7500 KVA OA 9375 KVA(125%) FA 10,000 KVA (135%) FOA
7500 KVA OA 9375 KVA(125%) FA 10,000 KVA (135%) FOA
P r o t e c t io io n & C o o r d i n at i o n
System Protection Instrumentaion
Principals of Protection
Protection Devices (Circuit breakers, Reclosers, Fuses) Principals of Coordination Coordination Coordination Study Fuse-Fuse Coordination Recloser-Recloser Coordination Recloser-Fuse Coordination Relay-Recloser-Fuse Coordination
Power System Review
Sy s t em Pr o t ec t i o n Components
Instrument Transformers PTs CTs
Circuit Breakers & Relays Mechanical Digital
Reclosers
Fuses
Power System Review
Protectiv e Devic es Ch aracteris tics
Breaker:
Distribution Class 12 kA
50 kA Extinguishing arc by means of:
Recloser:
Oil, air blast, sulfur hexafluoride gas (sF6), vacuum, or simple arc chutes
4 kA< Isymmetrical Rating<12 kA Interrupting occurs in Oil or vacuum Designed to “reclose” after fault is cleared
Sectionalizers:
interrupting capability<10KA Master minded by Reclosers
Power System Review
Protectiv e Devic es Ch aracteris tics
Expulsion Fuses:
Typically 8 kA to 16 kA Subject to X/R (interrupting capability decreases as ↑ X/R )
Power Fuse are generally available for Operating Voltage <169KV with 15KA
less accurate, inexpensive, but effective.
Current limiting fuses (CLFs) As much as 50 kA May have minimum interrupting capability, additional protection may be needed
Oil switches:
limited current interrupting capability. Power System Review
Fau l t c al c u l at i o n s
Note: I-fault drops off as inverse of Distance 1/d Power System Review
P r in c i p al s o f P r o t e c t i v e D ev i c es
Definition of Protective Devices: Protective Devices have Time-Current, Time-Voltage, or Time-Frequency Characteristics Protective Devices are responsible for removing undesired conditions: Voltage Current Frequency
Power System Review
W h at i s t h e p u r p o s e?
Clear Temporary faults and restore power when possible.
Interrupt Permanent Faults and Lock Out
Interrupt Faults in Proper Sequence
Remove undesired power conditions to maintain: Steady State Stability
Power System Review
EPRI Fau lt Stu d y Faults
Percentage
Phase-to-Ground
65%
Phase-to-Phase
11%
Phase-Phase to Ground
2%
Three Phase
2%
One Phase on the Ground
15%
Two Phase on the Ground
2%
Others
3%
Power System Review
Pr o t e c t io n & C o o r d i n at i o n
What is Coordination?
Definition: Proper trip sequencing of protective devices to isolate the fault and minimizing outage. This means proper coordination between time and current curves during power system abnormal conditions.
Coordination is : 1/3 Science 1/3 Art 1/3 Luck
Coordination
Protective Devices with Time-Current characteristics are:
Relays, Reclosers, Fault Interrupters, and Fuses.
How about Sectionalizers?? Device
Relay
Recloser
FI
Fuse
Relay
Relay-Relay
Relay-Recloser
Relay-FI
Relay-Fuse
Recloser
Recloser-Relay
Recloser-Recloser
Recloser
Recloser-Fuse
FI
FI-Relay
FI-Recloser
FI-FI
FI-Fuse
Fuse
Fuse-Relay
Fuse-Recloser
Fuse-FI
Fuse-Fuse
Fuse-Fuse Coordination
Fu s e S el ec t i o n P r o c es s Fuse
Type/Class Expulsion(Dist, Substation, etc) CLF Voltage Class Fuse Isymm interrupting capability rating X/R ratio Fuse continuous current rating i.e. K(150%), T(150%), QA(100%)
Fu s e A p p l ic a ti o n Fuses are generally:
CLF-used for short-circuit protection Non-CLF or Expulsion Fuse is used for Overload protection Selection Criteria: Non-CLF: 140% of full load CLF: 150% of full load
Ex p u l s i o n Fu s e Fuse Clearing Time @1/2 cycle Zero Crossing CT = MT+ Arcing Time
Transient Voltage @ Clearing time
I sc I full load x
100 Z %
C u r r e n t L i m i t i n g F u s e(C L F ) 60,000 A
7,400 A
B Curtsey of w w w . l i t t l e f u s e . c o m
Fu s e Ty p es & P o r p er t i es
Fuse has two TCC curves Minimum Melting Total Clearing
Common fuse types through 27kV are: Slow: T Fast: K
Avoid mixing different type fuses for better coordination Skip at least a size in each fuse class (K, T, H, C, etc) for better coordination between two fuses(i.e. 20K, 40K, 65K, etc)
Power System Review
Fu s i n g Ph i lo s o p h y
Lateral tap fuse selection Criterion: I lateral= 2x ILoad Cold load Daily/monthly/Seasonal cyclic Load Peak load
Transformer Fuse Selection Criterion: Minimum Fuse Size= I rated x 1.2 Cold Load Inrush Current Operational Limits
Power System Review
Fu s e Sp e ed & C o n t i n u o u s R at i n g Fuse
Allowable Continuous current Rating(%)
K-tin
150%
K-silver
100%
N
100%
T
150%
QA
100%
S
150% Fuse speed from fast to slow
→
N>QA>K>T>S
Power System Review
Fu s i n g D is t r i b u t i o n Tr an s f o r m er s
Why? In order to protect the transformer against internal faults, downstream bolted faults, high impedance secondary faults. Fuse must withstand transient surge currents caused by lightening, XFMR magnetizing inrush current, and cold-load pickup. Therefore, fuse must be capable of handling: Cold Load Pickup Inrush Current
Power System Review
Dist Transformer using…continued
Steps to select XFMR fuse size:
1. Calculate Cold Load Pickup withstand level: 1. I
= 3 x I (full load for 10 seconds)
cold-load
2. Calculate Inrush Current withstand limits: 1. I
= 12 x I (Full Load for 0.1 seconds) 2. I inrush= 25 x I (full load for .01 seconds) inrush
3. Select the nearest primary fuse rating that: 1.
Starts with 120% of XFMR rated load: Minimum Fuse Size = IRated x 1.2
2.
Meets the Cold load & Inrush Requirements (Steps 1 &2)
4. Select the Fuse type (K, T,H, QA,etc) and coordinate it
with upstream & downstream fuses in service. Note: Using EEI-NEMA type K, T, and T Fuses Provides protection between 200% to 300% of Rated Load
Power System Review
Transformer Fusing…continued
Example: Determine the minimum size fuse for a 300 KVA, 13.8kV/277/480 volts XFMR using “K” type fuse? I full load
300 KVA 3 x 13.8kV
300 23.9
12.55 Amp
I Cold load @ 10Sec 3 x12.55 37.65 Amp I Inrush @ 0.1Sec 12 x12.55 150.6 Amp
I inrush@ .01Sec 25 x12.55 313.75 Amp Minimum Fuse : 15 K (120%) ? OR 20K (160%) ? Power System Review
Transformer Fusing…continued Problem Area
Power System Review
Su b s t at i o n Tr an s f o r m er P r o t ec t i o n
Plot XFMR operational limits: Thermal & Mechanical limits (Damage Curve). Use FA Rating for XFMR Damage Curve Plot XFMR Inrush &Cold-Load pickup.
Apply applicable NEMA & IEEE Standards: IEEE C57.109-1993 oil immersed XFMR IEEE C57.12.59-2001 dry-type XFMR
Example: 22.86 kV / 4.16 kV Z 6%
7500 KVA OA 9375 KVA(125%) FA 10,000 KVA (135%) FOA
Power System Review
T r an a n s f o r m e r O p e r at a t i n g L i m i t at at i o n s t(sec)
FLA
200
Thermal 2
I t = 1250
(D-D LL) 0.87
Infrequent Fault (D-R LG) 0.58
Frequent Fault
Mechanical
2
2
K=(1/Z) t Inrush
2.5
Isc
I (pu) 25
Power System Review
Devices’ Damage Curves t Time
2
It
I 2t
I2t
I22t
Motor
Xfmr
Cable
Gen
I2t
I-Current =Let-through Energy
Power System Review
T r an a n s f o r m e r P r i m F u s e Pr P r o t ec ec t i o n
C ap ap a c i t o r F u s i n g
Capacitor fuse must be between 135% to 165% of its full load current rating depending on manufacturer. Capacitor Fuse Fuse Ful Full l Load x 1.35 or Capacitor Fuse Fuse Ful Full l Load x 1.65
Example: Find appropriate fuse size for a 1800 KVAR cap bank installed on a 22.86kV line. I full ful l load
1800 KVAR KVAR 3 x 22.86k V
1800 39.6
45.5 Amp Amp
Note: Check fuse continuous/overload c ontinuous/overload capability (100%-150%)
Capacitor Fuse Fuse *1.5 45.5 *1.35 Fuse Fuse 40.5 Amp Amp Select 50 K or 60QA Fuse Fuse
Fu s e-F u s e C o o r d i n a ti o n Time A
Source
B
Fault
Fuse Fuse
MT of A
Load
Fuse A (75% of MT) Current coordination limit
CT of B
Fuse-fuse coordination must follow the following rule: Time Ratio of
CTof A
CT (down stream fuse) MT (upstream fuse)
75%
Desirable coordination: Time Ratio of two fuses Must Not Exceed the 75% Ratio
t CT ( down stream fuse) t MT (upstream) * 0.75 Power System Review
Fu s e-Fu s e C o o r d i n a t io n
Example: What is the minimum size fuse that coordinates with 50K lateral tap fuse if calculated fault current is 1000Amp at point B? MT( A Fuse)=0.051 sec for Fault Current @ 1000 Amp CT (down stream fuse B) MT (upstream fuse A)
0.75
50 K
A CT (down stream fuse B) .051
0.75 CT 0.75 x0.051
B
? K 26amp
I G 1000 amp
CT 0.038sec
Power System Review
50K Fus e-20K Fus e Coo rd in atio n 50 K
A
B
I G
20 K 26 amp
1000 amp
Coordination Limit
Fu s e-Fu s e C o o r d i n a ti o n
Example: Select a fuse size at point C That can achieve proper coordination with upstream fuses.
I fault Max 2000 amp
A 90amp
100 K 65 K 80amp
B I
fault Max
1500 amp
C 35amp
? K I
fault Max
Power System Review
1000 amp
Fu s e -Fu s e c o o r d i n a t io n
I fault Max 2000 amp
A 90 amp
100 K 65 K 80amp
B I
fault Max
1500 amp
C 35amp
? K I
fault Max
1000 amp
R ec lo se r -F us e Coordination
Recloser
Defined in ANSI/IEEE C37.60
Settings Require Selecting:
Minimum Pick up or Coil size
Curve Selection:
Fast Curve
Slow Curve
Operating Sequence:
Number of Fast Curve shots
Number of Slow Curve shots
Shots to lockout
Reset time
Power System Review
Recloser
Two Types: Hydraulic
Electronics
Minimum Pickup is done by selecting appropriate rating for Series Coil inside the tank TCC Curve Selection & Settings are done inside the tank Minimum Pickup: Trip Resistors TCC Curves and Timing plugs are done at the front panel
Control Hydraulic Solid State Microprocessor
Power System Review
E lec t r o n i c R ec l o s e r S et t i n g s
TCC Curve Curve Selection/Type Settings:
Min Trip Setting Phase & Ground Instantaneous Trip Setting Phase & ground Constant Time Adder Amp Multiplier
Reclosing Operation Setting Typically Two Fast/Two Delay 0.5 sec
Power System Review
E lec t r o n i c R ec l o s e r S et t i n g s
Phase Trip Setting Minimum Trip= (Range of 2 to 2.5) x Max Load Current This facilitates cold load pick up & load growth
Ground Trip Setting Minimum Trip= (Range of 0.3 to 0.5)x Phase Minimum Trip Min trip setting helps to protect against high impedance faults
Instantaneous Setting Trip Setting= (Range of 4 to 16)X Minimum Trip
Power System Review
Hyd raulic Reclo s er Phase Trip -Settin g
Estimate the Peak load Determine the Coil Size: Inrush Current dictates the coil rating selection Coil Size(Amp)=1.25 x Peak Load
Calculate the Minimum Phase Trip Setting: Minimum Trip(Amp)=2 x Peak-Load Some utilities use factor of 2.5 or 3.0
Example (W type Hydraulic Recloser; coil sizes are 100, 140, 200, 280, 400, and 560): Assume Peak Load= 150A Coil Size= 1.25 x 150= 187.5→ Thus select 200 A Minimum Trip= 2x150= 300A→ Select 400A Min Trip Level
(Note: 200A Coil has Minimum Trip Rating of 400A) Power System Review
H y d r au l i c R ec l o s e r G r o u n d T r i p -S et t i n g
Steps:
1. Calculate the Normal Load Unbalance I grou nd MinTrip I 1( Normal Load Unbalance) I 2( Load Unbalance Created by the LargestSingle Phase Device)
I 1 I Normal Load Unbalance 10% of Peak Load I 2 I Largest Load Unbalance Largets Tap Fuse(Amp)
2. Calculate the end-of-line minimum fault current level. The Iground-Trip must be bellow Imin-Fault. I ground MinTrip I End of Line Min fault
3. Estimate the Ground Minimum Trip Level.
I Unbalance
( I 1 I 2) I gro un d
Lo ad
Min Trip
Power System Review
I End
of Line Min fau lt
TC C C o o r d i n a t io n T i m e M ar g i n s
Recloser-Reloser Hydrolic Reclosers:
Min Trip and continuous current are both dependent of the coil size Reclosing intervals are 1, 1.5, and 2 seconds Small Reclosers have Series coil : H, VH, L, and E series TCC Curve Separation >12 Cycles (0.2 sec); typically 0.25-0.30 sec Large Reclosers have High-Voltage solenoid : D, V, W, VW series TCC Curve Separation > 8 Cycles(0.133 sec); typically 0.2 sec
Electronic Reclosers:
Unlike Hydraulic recloses, Min Trip is independent of the Recloser’s continuous rating Reclosing intervals are 2, 5, and 15 seconds Min Trip selection must allow for the cold-load pick up & load growth TCC Curve Separation > 0.30 Sec 0.30 Sec=0.22 sec (CT saturation& errors)+0.08 sec (Breaker Opening time)
TC C C o o r d i n a t io n T i m e M ar g i n s
Electronic Recloser to Hydraulic Recloser: TCC Curve Separation > 0.2 Sec; typically 0.25 sec
Recloser-Fuse Methode#1: Use K factor for Recsloser: Range of 1.25
Methode#2: ADD Recloser Cumulative Times Add the cumulative reclose interval for a 2A-2C recloser sequence and coordinate with Fuse Minimum Clearing curve x 0.75
Power System Review
R ec lo s er -F us e C oo r d i na ti o n R ec l o s er C u m u l at i v e Ti m e M et h o d R
Time
Fuse
'
a
'
B'
Temp Fault: Recloser operates; Fuse is saved.
Permanent Fault: Recloser operates first, then fuse blows
2 A 2 B
B delay A' 2 A A(Fast) ' ' a a b b
Current
75% of fuse MT curve (fuse damage curve)
Power System Review
R ec lo s er -F us e C oo r d i na ti o n K -F ac to r M et ho d '
a
Refer to Manufacturer’s
Time
Supplied Tables
Extract applicable K-Factor
B K (Time Multiplier ) * Curve B
Multiply Curves by K-Factor
B delay
Note: K-factor is a t-Multiplier
A K (Time Multiplier ) * Curve A
A(Fast) ' ' a a b b
Current
75% of fuse MT curve (fuse damage curve)
Power System Review
C o o p er R ec l o s er s K -Fac t o r Table Below -Curtsey of Cooper Power Systems
•What is K-Factor? •K-Factors are Time multiplying factors for various Reclosing Intervals. K-Factor shifts the curves up increasing the time value by K-Factor for the same current value.
Power System Review
S o u r c e Fu s e -R ec l o s e r C o o r d i n a t io n R
5000 KVA
Phase Trip Setting Steps:
3 - Fault
5000 22.86 3
126.3 A
I sec
5000 4.16 3
- G Fault
1. Calculate Full Load I prim & Isec Iprim
FUSE
Z 6%
R
I
4500A
3800A
400A(Peak)
RX Recloser
694 A
22.86 kV / 4.16 kV
2A & 2C g 1 A2 & 1E
2. Select an Appropriate Fuse size Fuse Size: 1.5x126.3A=189.5A → Select 200K
3. Select an Appropriate Recloser Coil Size: Calculate Coil Size: 1.25x400=500A Select Coil size: 560A
End of Line FAULT
3 - Fault
1500A
G Fault 175 A
4. Desired Minimum Phase Trip= 2.5 x Peak Load to override the Inrush I Phase 2.5 x 400 1000 A Note: Cooper W & RX type Recloser Ratings: Coil Size Min Trip Rating Interrupting Rating 560 A 1120 A 10,000 A
S o u r c e Fu s e-R ec l o s e r C o o r d i n a t io n
Ground Trip Setting Steps: 1. Estimate Normal Load unbalance: 10% of Peak-Load Example: Iunbalance= 10% of Peak Load Iunbalance-Normal= 0.1 x 400=40A
2. Estimate the load unbalance created by the largest single-phase device: Example: Assume the largest single phase Load is 90A Fuse. Iunbalance-Load=90A
3. Calculate Unbalanced downline Ground Current:
I Ground I unbalance Normal I unbalance Load I Ground 90 40 130 A
4. Select Minimum Ground Trip: Ig Min Trip 140 A I G Unbalanced (130A) I Ground Setting (140A) I Min Fault (175A)
S o u r c e S i d e Fu s e -R ec l o s e r C o o r d i n a t io n
Reclo ser-Fus e (L o ad Sid e) Coo rd in ation •Determine an appropriate Fuse size @ Point B •Which fuse coordinates the best (100K or 140K?) • Answer 140K; Why? 5000 KVA
FUSE
Z 6%
R 400 Amp
R
RX Recloser
22.86 kV / 4.16 kV
2 A2C
B
90 Amp
FAULT
Power System Review
G
1900 A
Min Fault
600 A
R ec lo s er -F us e (L o ad S id e) C oo r d i na ti o n
5000 KVA
FUSE
Z
R
6%
3 - Fault
4500A
- G Fault 3800A
R
I
400A(Peak)
RX Recloser
22.86 kV / 4.16 kV
B
2 A & 2C
g 1 A2 & 1E
End of Line FAULT 3 - Fault
1500A
G Fault 175 A
3 - Fault
1500A
G Fault 175 A
Fuse
Coordination Limit
100 K
1112 A
140 K
2380 A
Relays Mechanical & Digital
Pr o t ec t i o n Sy s t em El em en t s
Protective relays Circuit breakers Current and voltage transducers Communications channels DC supply system Control cables
Thr ee-Phase Diag ram o f th e Pro tectio n Team CB
CTs
+
Protected Equipment
Control
SI DC Station Battery
Relay
Relay Contact
SI
Relay 52a 52 TC
VTs –
Circuit Breaker
Red Lamp
M o s t Co m m o n Pr o t ec t i v e Rel ay s
Protection Principles for Transmission & Distribution Lines: Overcurrent
(50, 51, 50N, 51N) Directional Overcurrent (67, 67N) Distance (21, 21N) Differential (87)
Circu it B reak er Selec tio n
Relay (The Brain) CT Ratio PT or VT Ratio
Interrupting Cycle
Voltage Class
K rating=(VMAX/Vmin)
BIL rating
Power System Review
Relay -Circ u it B reak er Operation A B C
Ground relay Phase relays
Circuit Breaker
In
CTs Ia
IbIb
Ic
I n
I a I b
I c Ic
Load LOAD Load
Ib Power System Review
Ia
In d u c tio n -Typ e Relay s
Power System Review
Relay Clas s ification
Overcurrent
Overvoltage
Undervoltage
Differential
Directional
Under Frequency
Distance
Power System Review
Relay s fo r Ph as e Fau lts Time overcurrent
51
Instantaneous & time overcurrent Directional Time Overcurrent
50/51 67
Instantaneous & directional time over current
50/67
Directional Instantaneous Overcurrent
67
Step Time Overcurrent
51
Directional Instantaneous and directional
67
Zone Distance
21
Power System Review
R el ay s f o r G r o u n d F au l t s Time Overcurrent
51N
Instantaneous & Time Overcurrent
50N/51N
Product Overcurrent
67N
Instantaneous and Product Overcurrent
67N/50N
Directional time overcurrent
67N
Instantaneous and directional time overcurrent 67N Directional Instantaneous Overcurrent
67N
Three-zone distance system
21N
Power System Review
Tr an s f o r m er P ro t e c t io n
O p e n -P h as e C o n d i t i o n A B C 400 a
0a
CT Ratio
400 a
120
I a
I n
Ia Ib Ic Ia Ic
I n
In I n
3.3330, Ib
0, Ic
3.333 120
3.333 1.667 j 2.886
1.666 j 2.886
3.33360
In
I n 3.33360
CTs=600/5 3.30
Ia
0
Ib
3.3 120
Ic
I n
I a 0
I c In
Ic
Ia Open
G r o u n d R el ay C o u l d P i c k u p
Sin g le-Phase to Gro u n d Fault A CT Ratio 120 B I a 500, Ib 3.333 120 Ic 3.333 120 C I n Ia Ib Ic 400 a 400 a I n 50 1.667 1.667
I SC
I n 46.6660
In
I n 46.70
CTs=600/5 I a 500
Short
I SC 6,000a
3.3 120
3.3 120
Ic In Ib
Ia
L i n e -t o -L i n e t o G r o u n d Fau l t
I SC
I SC
A B C 400 a
CT Ratio 120 I a 500, Ib 50 120 Ic 3.333 120 I n Ia Ib Ic I n 50 25 j 43.301 1.667 j 2.886 In 23.333 j 40.415 I n 46.67 60
In
I n 46.7 60
CTs=600/5 I a
Short
500
I a
50 120
I b
3.3 120
I C
6,000a
Ic Ia
Ib In
Three-Phase to Gro u n d Fault A B C I a 12,000
I SC
I a 12,000
CT Ratio 120 I a 1000, Ib 100 120 Ic 100 120 I n Ia Ib Ic
I a 12,000
I SC
I SC
I n 0
I n 0
In CTs=600/5 I a 1000
I b
100a
2
I c
100a
Ic I a 12,000
I b 12,000
I c 12,000
Ib Short
Ic
Ia Ib
Ia
Relay Settin g s Two Settings:
1. Time Overcurrent 2. Instantaneous Instantaneous Setting Time Overcurrent pickup must be capable of & time setting must be handling: capable of handling: XFMR Inrush Peak Load Capacitor Inrush Cold-Load Pickup Asymmetrical Faults Motor starting
Safety factor=1.2xSymm Fault
Power System Review
Relay Settin g s
Phase Time Over Current (TOC) Setting
Phase pick up: Method 1: 2xImax < I Pick up < I Min (phase-phase Fault current)
Note: Ensure I Min-Fault ≥ 2 x I Peak- Load I Min=Iphase-to-Phase=0.866 x I Three-Phase fault
M e th o d 2 : 25% Margin ; IPickup= Ifull-load /0.80
Ground Time Over Current (TOC) Setting
Ground Pick up: Method 1: 2xI Normal ground Current < I Pick up< I Min Ground Fault Current
Where; Normal Ground Current Range: 10% to 20% of Load Current
M e t h o d 2 : Ipickup=(0.40 to 0.75)x I peak-Load
Power System Review
In s t an t an eo u s R el ay s P ic k u p Settings
Instantaneous Pickup Range: 2 x I Phase Pickup I ins tan tan eous 10 x I Phase Pickup Typical Instantaneous Phase & Ground Pick up= 2x Time Over Current relay pick ups
Power System Review
H o w t o d et er m i n e Pi c k u p & Tim e Dial?
Step 1: Calculate Short Circuit Current @ each Bus ( usually Phase-Phase Fault)
Step 2: Identify CT Ratio & Breaker Interrupting Cycles at each Bus Step 3: Calculate Relay Minimum Pickup for each Device Step 3: Starts with the last relay and apply Time Margin of 0.3 to 0.4 sec (ANSI/IEEE Std-242 )between Relays: o CB’s operating time (5 cycles): o Relay Over travel time: o Safety factor (CT saturation, Errors): Total
Power System Review
0.08 sec 0.1 sec 0.22 sec 0.4 Seconds
Relay-Relay Setting
0.4 Sec
Power System Review
TC C C o o r d i n at i o n Ti m e Margins
Relay-Fuse TCC Curve Separation Rule:
Mechanical Relay requires minimum time margin of 0.3 sec time interval Digital Relay requires minimum time margin of 0.2 sec time interval
Relay-Relay (Mechanical) TCC Curve Separation Rule:
According to ANSI/IEEE Std-242:1986, the rime interval between two relays in series must be 0.3 to 0.4 seconds. This time interval components are: Circuit Breaker Operating Time(5cycle): 0.08 sec Relay Overtravel Time: 0.1 sec Safety factor for CT Saturation & errors: 0.22 sec
Power System Review
TC C C o o r d i n a t io n Ti m e M ar g i n s
Relay-Relay (Digital)TCC Curve Separation:
Time margin between series Relays must be minimum of 0.25 sec. This time separation consists of the following:
5 Cycle Breaker (0.08 sec)
Relay Accuracy (0.04 sec) Safety factor & CT Ration (0.13 sec)
Relay-Recloser Time Margin between Mechanical Relay & Hydraulic Recloser must be minimum of 0.28-0.30 sec Time Margin between Mechanical Relay & Electronic Recloser must be minimum of 0.25 sec
Power System Review
Relay-Recloser-Fuse Coordination
In the following CKT coordinate Breaker B1, Cooper Form-4C Recloser, ABB PCD2000 Reclsoer, and 100K Tap Fuse. B2 Load
231A
2
3 Cooper
25 MVA
115kV / 22.86kV
BUS
PCD2000
Form 4C Load
115 kV
1
ABB
400A
B1
Load
300A
R
Load
FAULT @ Bus3
FAULT @ Bus2
3
3
6000 A
Φ N
2000 A
200A
3000 A
Min Fault 443 A
Min Fault 1000A
Power System Review
100 K
FAULT @ Bus1 3
4000A
L1
R3
L2
L3
Relay -Rec los er-Fus e Coo rd ination
Relay settings: Phase setting: PU=2.4 x 400=960A Ground setting: PU= 960/2=480 A
Cooper Recloser Form 4C settings: Phase setting: PU=2x300=600A Ground setting: 160A
ABB Recloser Model PCD2000 settings: Phase setting: PU=2x200=400A Ground setting: 140A<(PU=150 A)<443
Power System Review
Relay -Rec lo s er-Fus e Coo rd ination
Over Vo ltag e Protectio n
Insulation Voltage Class
Basic Impulse Level (BIL)
Nameplate Rating
Surge arrestors.
Power System Review
O v e r v o l t ag e Pr o t ec t i o n
Sources of Overvoltage: Ferroresonance Low Order Hormonics Voltage Regulation (XFMR LTC Malfunction) Transients caused by:
Lightning surge Switching operations Line-to-Ground faults
Capacitor Bank Switching
Protection methods: Surge Arresters(ANSI C62.1-1981) Static Wires
Us efu l IEEE/A NSI Stand ard s
Graph of Curves can be found in ANSI/IEEE Standard C37.91-1985, “Guide for Protective Relay Applications to Power Transformers,” ANSI/IEEE C57.109-1993, “Guide for Transformer Through-Fault Current Duration.”
IEEE/ANSI Standards 141&242
IEEE Std 242 – Buff Book
IEEE Std 141 – Red Book
IEEE Std 399 – Brown Book
•IEEE C37.90 – Relays
IEEE C37.91 – Transformer Protection
IEEE C37.102 – Guide for AC Generator Protection
References 1. J.D. Golver, M.S. Sarma, Power System Analysis and design, 4th ed., (Thomson Crop, 2008 ). 2. M.S. Sarma, Electric Machines, 2 nd ed., (West Publishing Company, 1985). 3. A.E. Fitzgerald, C. Kingsley, and S. Umans, Electric Machinery, 4th ed. (New York: McGraw-Hill, 1983). 4. P.M. Anderson, Analysis of Faulted Power systems( Ames, IA: Iowa Satate university Press, 1973 ). 5.W.D. Stevenson, Jr., Elements of Power System Analysis, 4 th ed. (New York: McGraw-Hill, 1982 ).
