Switchgear Arrangement, Torque Requirements, Insulation Systems & Maintenance Intervals Mike Schmaderer
Questions Feel free to interrupt There are no dumb questions
Just what exactly is Switchgear?
The term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream.
Substation vs Switchgear Substation Easier to maintain Easier to modify Lower arc flash incident energy Switchgear (Substation in a box) Smaller footprint Better at keeping animals out Build off sight Out of weather (maybe)
Open Switchgear
Traditional Switchgear Breakers all in the bottom May require a ramp
Enclosure Side View
Two High Construction Takes up less space Lift is required for breakers in top row
Combination Lift is required
Typical One Line
Switchgear One Line
Laid Out to Minimize Load on the Bus
Laid Out to Meter Generation
Laid Out to Facilitate Maintenance
Laid Out to Facilitate Maintenance
Fused Switches
Outdoor Metal Clad Switchgear
Arc Resistant Designed to vent energy from an arc safely away from operators Extra support Costs about 30% more
Arc Reduction Techniques Bus Differential Protection Instantaneous Tripping With blocking Arc Relaying Strategically placed fiber Combined with overcurrent Remote Switching
Things to Consider Before Ordering Gear Number of Feeders Generators Tie(s) and Bus Tie Bus Ampacity Entrance Top Entrance Bottom Entrance Throat Connected Bastard
Things to Consider Before Ordering Gear CTs PTs For Relaying For Metering Location For Metering For Relaying For Synchronizing Location
Things to Consider Before Ordering Gear Breaker Arrangement Single high Two high Location of feeders, generators, tie Continuous Current Rating of the Breaker Interrupting Capability of the breaker Must be able to interrupt max fault current Arc Flash
Insulation Porcelain (glass) Glastic Indoor only Polymer Skirts
Breaker -Interrupters How does the Breaker extinguish the arc? Air Blast Under Oil SF6 Vacuum
Torqueing Requirements
Torque τ = torque σ y = yielding stress of material D = bolt diameter c = coefficient of friction Yield Strength (Mpa) Aluminum 241 Steel 248 Brass 200
Torque US Recommended Bolt Torque Recommended Torque Size Grade 2 Grade 5 Grade 8 18-8 S/S Bronze Brass Coarse Fine Coarse Fine Coarse Fine Coarse Fine Coarse Fine Coarse Fine #4* - - - - - - 5.2-4.8-4.3 - #6* - - - - - - 9.6-8.9-7.9 - #8* - - - - - - 19.8-18.4-16.2 - #10* - - - - - - 22.8 31.7 21.2 29.3 18.6 25.9 1/4 4 4.7 6.3 7.3 9 10 6.3 7.8 5.7 7.3 5.1 6.4 5/16 8 9 13 14 18 20 11 11.8 10.3 10.9 8.9 9.7 3/8 15 17 23 26 33 37 20 22 18 20 16 18 7/16 24 27 37 41 52 58 31 33 29 31 26 27 1/2 37 41 57 64 80 90 43 45 40 42 35 37 9/16 53 59 82 91 115 129 57 63 53 58 47 51 5/8 73 83 112 128 159 180 93 104 86 96 76 85 3/4 125 138 200 223 282 315 128 124 104 102 118 115 7/8 129 144 322 355 454 501 194 193 178 178 159 158 1 188 210 483 541 682 764 287 289 265 240 235 212
Torque Torque Values = inch-lbs Bolt Size 18-8 Stainless Steel Brass Aluminum 2024-T4 316 Stainless Steel Nylon 2-56 2.5 2.0 1.4 2.6 0.44 4-40 5.2 4.3 2.9 5.5 1.19 4-48 6.6 5.4 3.6 6.9 6-32 9.6 7.9 5.3 10.1 2.14 6-40 12.1 9.9 6.6 12.7 8-32 19.8 16.2 10.8 20.7 4.30 8-36 22.0 18.0 12.0 23.0 10-24 22.8 18.6 13.8 23.8 6.61 10-32 31.7 25.9 19.2 33.1 8.20 1/4" - 20 75.2 61.5 45.6 78.8 16.00 1/4" - 28 94.0 77.0 57.0 99.0 20.80 5/16" - 18 132.0 107.0 80.0 138.0 34.90 5/16" - 24 142.0 116.0 86.0 147.0 3/8" - 16 236.0 192.0 143.0 247.0 3-8" - 24 259.0 212.0 157.0 271.0 7/16" - 14 376.0 317.0 228.0 393.0 7/16" - 20 400.0 357.0 242.0 418.0 1/2" - 13 517.0 422.0 313.0 542.0 1/2" - 20 541.0 443.0 328.0 565.0 9/16" - 12 682.0 558.0 413.0 713.0 9/16" - 18 752.0 615.0 456.0 787.0 5/8" - 11 1110.0 907.0 715.0 1160.0 5/8" - 18 1244.0 1016.0 798.0 1301.0 3/4" - 10 1530.0 1249.0 980.0 1582.0 3/4" - 16 1490.0 1220.0 958.0 1558.0 7/8" - 9 2328.0 1905.0 1495.0 2430.0 7/8" - 14 2318.0 1895.0 1490.0 2420.0 1" - 8 3440.0 2815.0 2205.0 3595.0 1"- 14 3110.0 2545.0 1995.0 3250.0
Maintenance Cleaning Relay Testing Breakers Ductor High potential Function Testing
Switchgear Maintenance When is the last time that the bus and bus supports were cleaned Are the heaters working Do they get turned off Dirt and Moisture Most are hard to get out of service Even with generation Ethanol Plant Example
Switchgear Maintenance Moving parts seldom operate Switching load Clearing faults Generator breakers operate more often Breakers/Switches Battery Relays
Functional Trip Testing Electrical mechanical relays Spin the disk Microprocessor based relays Force a trip Inject current Through test switches Inject primary current Through the CT s
Breakers Heaters Year round Trip/Close coils Rewind motors Exercise the breaker Lubricate the Mechanism
Relays Monitor current and voltage Overcurrent Directional overcurrent Voltage Impedance Etc.
Relays Relays should be tested periodically Suggest generator and tie relays every three years Suggest feeder relays every five to six years Function of the value of the asset they are protecting Test should include a functional test of the breaker
Types of Relays Ice cube Interposing Lockout Electromechanical Solid state (Static) Microprocessor-based (Digital/Numerical)
DC/Battery System Stored Energy Battery Charger Trip coils Close coils Rewind Motors?
Battery Check it once a month Turn off AC breaker for one hour Monitor voltage drop Compare to previous months Don t let the voltage drop more than 10% DC rewind motors
Common Switchgear and Substation Issues
Mechanism gummed up Caused by dirt and inactivity Will not trip Common during the winter Especially in outdoor breakers Often causes a blown fuse or a trip coil to burn up
Rewind motor will not stop winding Broken or misaligned gear Often causes motor to burn up Pull motor rewind fuses
Rewind motor winds up, unwinds, and rewinds continuously Latch does not catch Caused by dirt and grim Common during the winter Especially in outdoor breakers Often causes motor to burn up Pull motor rewind fuses and lubricate latch
Breaker will not close after a trip Blown fuse in close circuit Burnt up close coil Lockout relay not reset Sync switch not turned on
Broken Pole or linkage One or more phases not making contact Current imbalance Voltage imbalance Hard on generators
Check voltage and current often Voltage Use voltmeter to check all three phases Use sync scope to check sync PT Current Use ammeter to check current on all three phases Multifunction meters Microprocessor based relays
Other things to consider Record faults Phase Time Weather conditions Interrupting rating Fault study Arc Flash
Once again, if you are not 100% sure, get help
Questions?