SDG&E Feeder Protection Philosophy: Reliability Without Compromising Safety Karl Iliev System Protection and Control Engineering (SPACE) SDG&E 1
SDG&E Distribution System 22,000 miles of lines 60% underground and 40% overhead Reactively Grounded Three wire (Grounded) and Four wire systems Nominally 12kV and 4kV Distribution >160 distribution substations >700 medium power transformers (138/12kV & 69/12kV) 2
Traditional Distribution Circuit (Simplified) R Tie SUBSTATION
Distribution Circuit of Today (Simplified) R IR R IR R F6 SUBSTATION R AE R IR PME 10 F6 R IR R F6
Distribution Circuit of Today (Simplified) PV LINE MONITOR RECLOSER RECLOSER Zone 3 Zone 2 TRAYER Vz N.O. Vy Vy Vz VOLTAGE REG Zone 1 Vv IR Zone 4 CB SUBSTATON 5
System Protection is a Balancing Act SPEED SENSITIVITY SELECTIVITY SECURITY SIMPLICITY FAST TO MINIMIZE DAMAGE RELAY SEES FAULT REMOVE FAULTED ELEMENT ONLY DO NOT TRIP FALSELY SIMPLE CONTROL SCHEMES
Protection Philosophy: Non traditional layers of protection: FCP Falling Conductor Protection detects break in conductor Speed Trips before the fault Coordination FCP should be first SGF Sensitive Ground Fault detects high impedance ground fault Slow 3.5 to 5.5 seconds Coordination between devices is unlikely Could Trip on Load Advanced SGF More sensitive than SGF using adaptive set point, spike counting, and/or harmonics (Cooper DCD, SEL ArcSense, or IR algorithm) Slower > 5 seconds Coordination between devices is unlikely Could Trip on Load and external faults or other system conditions Operational Changes: Reclosing Policy Changes (Disable reclosing during elevated fire risk) Eliminate Fuse Saving Schemes Pulse Closing Devices HLT Hot Line Tag allows fast trip, does not protect from contact Profile 3 Fast and Sensitive for safety during high risk fire conditions Fast cycles Coordination between devices is unlikely
Falling Conductor Protection (FCP) Phase Angle Comparison Requires PMUs and high speed communication Detection Methods dv/dt (change Detection) V0 & V2 magnitude V0 & V2 angle Synchrophasor Data Visualization Source 1 2 3 4 Source 2 1 PMU1 PMU2 PMU3 PMU4 FC 1 not aligned with the other PMUs Source 1 3 4 Source 2 1 2 PMU1 PMU2 PMU3 PMU4 1 and 2 aligned with each other 3 and 4 aligned with each other FC Sequence Components Analysis 8
High Impedance Faults Random and Dynamic Requires Advanced Strategies because they are NOT like conventional (3P, PP and LG) faults. High Impedence Faults can be exhibit near zero fault current. We typically see 5 50 amp events
Sensitive Ground Fault (SGF): T SGF Element GROUND Similar to conventional ground protection element but is set more sensitively with a longer time delay to detect high impedance faults. The setting is fixed and typically 5 30A higher than neutral current trending on PI seen by the recloser for one year. Challenge is distinguishing Low Current Faults vs Load Imbalance I
SGF Pickup Setting vs. Neutral Load Current Neutral: 0 25 A
High Impedance Faults Cannot detect ½ cycle spiking with conventional SGF definite time elements.
Advanced SGF Introduces innovative logic to increase sensitivity Spike detection and accumulator algorithms to address both random, intermittent spiking and sustained low level ground faults Adaptive set point control to continuously adjust the spike pick up setting based on average neutral current loading Harmonic spike detector for arcing faults Optimizes sensitivity across the load range Reduces the need for field setting revisions due to system changes Each vender has different technology and algorithms
Advanced SGF Cooper DCD
Advanced SGF Intelliruptor Fault Starts - 01:54:05 (0 sec) Final Reset - 01:54:46 (40 sec) Trip - 01:55:27 (82 sec) 45 40 35 30 25 20 15 10 5 0 seconds si nce begi nni ng of event
Ground Spike Duration IR Data Fault Starts - 01:54:05 (0 sec) Final Reset - 01:54:46 (40 sec) Trip - 01:55:27 (82 sec) 80 70 69 # of pickup events 60 50 40 30 20 10 0 20 2 3 4 2 0 < to.25.25 < to.50.50 < to.75.75 < to 1.0 1.0 < to 5.0 5.0 < # Spikes & Duration, sec (Max = 6.9 sec) Avg Drop Out = 0.046 sec
Advanced SGF SEL ArcSense Complex algorithms independent of neutral current Uses SDI (sum of difference current) calculations of odd harmonics between each successive cycle. Uses adaptive learning of circuit history and trending to fine tune sensitivity.
Profile 3/Hot Line Tag (HLT) Time Profile 3 PHASE GROUND Profile 1 Current
Intellirupter (IR) PulseClosing SDG&E Implemented to increase SCADA penetration in backcountry Multiple IRs on Circuits Unique PulseClosing Technology Confirms there s no fault on the line before initiating point on wave closing Reduction in fire risk due to reduced arcing produced Conventional reclose results in 170ms of fault current Pulseclose results in only 5ms of fault current 19
Protection Philosophy: Continuous Improvement Undesirable Feeder Operations (UFO) Cross departmental team to investigate UFOs with a charter to review outages where the unexpected protection device or more than on device, isolates the circuit fault. Essential to understand impacts caused by the ever increasing feeder complexity. Increases awareness and improve operating procedures. Balances risk, reliability, and cost
Undesirable Feeder Operation (UFO) Team Year Investigated UFOs UFO % of Total 2015 73 59 2.95 2016 55 48 2.07 2017 65 18 0.94 Completed UFO Initiatives Include: Expand high impendence fault detection (Advanced SGF) through various vender technology (e.g. SEL, S&C, Cooper) Enable Autosectionalizing switch positions that were previously disabled Reprogram of all Trayer Switches for better protection coordination (Trayer Switches were operating faster than expected, not allowing time for fuses to operate) Redefined Fuse Sizing Criteria to determine fuse sizes based on historical load as opposed to connected KVA 21
Multiple Adjacent Recloser Staggering (MARS): SGF settings currently set with 5 sec delay. Poses issues when multiple reclosers in series. Settings to be staggered by 0.5 sec. R1 R2 R3 SGF Time Delay: 5.5s SGF Time Delay: 5.0s SGF Time Delay: 4.5s SGF Time Delay: 4.0s
Example #1: Profile 3 Success UFO: Yesterday we had an outage with no cause determined. Today, we had another outage, currently patrolling again. Same devices tripped with profile 3 enabled. Outage Cause: Broken strand of AWAC Isolation Devices: R1 & R2 Investigation: Both R1 and R2 tripped and saw targets on A & B. Both devices were set to profile 3 and the fault current for A & B was greater than 400A UFO: No 12kV Sub R1 R2 2 65A 2 25A
Example #1: Profile 3 Success
Example #2: Profile 3 Frustration UFO: SCADA Device tripped on unbalance. Grid reports TL tripped open at same time. Full patrol will have to wait for daylight. Outage Cause: Phase Ground Fault on 69kV System Isolation Devices: R1 & R2 Investigation: Both R1 and R2 tripped on unbalance UFO: Yes 69/12kV Sub R1 R2
Example #2: Profile 3 Frustration 26
Example #3: Advanced SGF Frustration Investigation: Feeder tripped via electromechanical relays and locked out (went through it s full reclosing cycle). At the same time, neighboring circuits saw outages: R1 and R2 tripped and locked out on Advanced SGF targets due to bus voltage fluctuations. These reclosers were downstream of the fault. The cause of the outage was bad tees in a man hole, which all three circuits share in common. Reclosers tripped on DCD (fundamental frequency and THD). Outage Cause: Bad Tees Isolation Devices: Feeder CB, R1, R2 UFO: Yes R1 Sub MH R2
Example #3: Advanced SGF Frustration Fault location R2 R1 Cir1: 9.1% OH / 89.9% UG Cir2: 22.3% OH / 77.7% UG Cir3: 40.0% OH / 60% UG
Example #3: Advanced SGF Frustration
Example #3: Advanced SGF Frustration
Example #3: Advanced SGF Frustration
Example #3: Advanced SGF Frustration
Example #4: Falling Conductor Protection Investigation: FCP trip occurred. It was raining at the time and this is suspected to be related. ETS patrolled and no damage was found. Comm was noticed to be going in and out. There were data gaps but not during the event. The cause appears to be a faulty voltage sensor that reported a sharp change in voltage. Outage Cause: FCP Trip on V0 Faulted Sensor Isolation Devices: CB, R1 Follow Up: Short term solution is to raise the voltage threshold(s) in the field. Long term we will need to get a better sensor. UFO: Yes
Example #4: Falling Conductor Protection PV LINE MONITOR RECLOSER RECLOSER Zone 3 Zone 2 TRAYER Vz N.O. Vy Vy Vz VOLTAGE REG Zone 1 Vv IR Zone 4 CB SUBSTATON 34
Example #4: Falling Conductor Protection No high current change fluctuation was detected at any of the SCADA devices that could have caused the sudden drop in voltage on B phase
Example #4: Falling Conductor Protection Voltage differences between line and load sensors for reclosers, including a drop on B phase on the z side of R
Example #4: Falling Conductor Protection The drop in the voltage on B phase at recloser 1 caused the zero sequence voltage to trip above the pickup value of 400V
Example #4: Falling Conductor Protection Voltage on multiple MVRs in area show similar issues during rain.
Elimination of ALL risk is impossible Selectivity Security Adv.SGF Multiple SRs AE FCP IT FLISR Speed Profile 3/HLT SGF TCC Sensitivity Simplicity 39