Maintaining MV Switchgear Western Mining Electrical
Association Tucson, AZ
November 15, 2007
Maintenance of MV (Above 1000V and up to 38kV) Switchgear
Keywords:SafetyDeenergize Lockout/TagoutMaintenance IntervalArc-flashGroundingInterlocksToolsBackfeed
Why Maintain Switchgear?
It’s a Hobby!!!!!!!Switchgear is new and doesn’t need maintenance!!!Short-Circuit is unpredictable so why bother?
Why Maintain Switchgear? Getting Everyone’s Attention
Every Electrical Conductor or Circuit is Considered Energized (Unsafe) Until Proven Otherwise (Innocent)
Why Maintain Switchgear?
Reduce Hazards to Life and Property that can result from Failure or Malfunction of Poorly Maintained Electrical SystemsReduce the Outages and Down timeIncrease the efficiency of work force Significant Loss of Revenue until Service is RestoredWell Maintained Switchgear will last long time, More importantly, It is the safest thing to do
Factors affecting the Electrical Safety in Coal Mines
Inadequate or Improper Training Failure to Deenergize, Lockout and TagoutFailure to ensure proper groundingFailure to recognize downstream devices (Possible back feed from downstream device) Defeating and/or Ignoring Mechanical and Electrical Safety InterlocksPoor Grounding
Factors affecting the Electrical Safety in Coal Mines
Failure to Maintain Electrical Distribution Documents (What is that?)Aging Assets (Run to Failure Approach, No one wants to spend Time and Money until it breaks down)Intrusion by Animals into Electric Supply Substations
Potential Sources of Animal Outages
Animals Percentage
90%
86%
57%
46%
Cats 43%
Mice 30%
Rats 19%
Opossums 13%
Survey of 174 Public Utilities.
114 Responded
IEEE Std 1264-1993
IEEE Guide for Animal Deterrents for Electric Power Supply Substations
Potential Sources of Animal Outages
Animals Percentage
Squirrel 90%
Birds 86%
Raccoons 57%
Snakes 46%
Cats 43%
Mice 30%
Rats 19%
Opossums 13%
Survey of 174 Public Utilities.
114 Responded
IEEE Std 1264-1993
IEEE Guide for Animal Deterrents for Electric Power Supply Substations
Interrupting Devices and Key Components of MV Mining SwitchgearStationary Mounted or Drawout Vacuum Circuit Breakers Stationary Mounted Load-break and Non Load-break Disconnect SwitchesVacuum ContactorsNeutral Grounding ResistorsSurge ArrestersCurrent Transformers (CT’s)
Interrupting Devices and Key Components of MV Mining SwitchgearPotential Transformers (PT’s)Ground Monitors & Capacitor Trip DevicesStation Service Transformers (CPT’s)FusesProtective Relays, Meters, Control Switches and Indicating Lights
Mechanical Endurance Capabilities and Maintenance
Intervals
Vacuum Circuit Breakers and Air-break Switches
Schedule of Operating Endurance Capabilities for Circuit Breakers (ANSI Std C37.06-2000)
4.76kV, 15kV 600A-2000A (up to 31.5kA SC)No. of NO Load Mechanical Operations = 10,000No. of Load (Rated Current) Operations = 1,000Inrush Current Switching = 750No. of operations Between Servicing = 2,000
One Closing+One opening = 1 Operation
Schedule of Operating Endurance Capabilities for Circuit Breakers (ANSI Std C37.06-2000)
27kV, 600A- 2000A (up to 25kA SC)No. of NO Load Mechanical Operations = 2,500No. of Load (Rated Current) Operations = 200Inrush Current Switching = 100No. of operations Between Servicing = 500One Closing+One opening = 1 Operation
Periodic Inspection of Vacuum Circuit Breakers
Maintenance Intervals are usually based on both, an elapsed time and no. of operations, whichever Occurs firstIf Short-Circuit Operation Occurs (major event) before the completion of listed operations, maintenance is recommendedAn Annual inspection for serviceability is recommended by most manufacturers
What is Recommended for Servicing Between Maintenance Interval (Breakers)
Cleaning ContactsAdjusting and Tightening ContactsLubricating and Dressing Contacts
Mechanical Endurance for MV Switches ANSI Std C37.22-1997
Load Current Switching Rating for MV Switches ANSI Std C37.22-1997
Recommended Minimum Electrical Clearances for Indoor Switches & Buss
supports (ANSI C37.32-1996)
Use Fluidized Epoxy Buss Insulation for Reducing Electrical Clearances
Epoxy Powder Aluminum
Foil Wrap
Silver Plating
Uniform coating
Fluidized Epoxy Buss
Maintenance/Inspection of Neutral Grounding Resistors
• Damage May Occur from:LighteningStormsEarthquakeWildlifeOverloadsExtended Service Life
Maintenance/Inspection of Neutral Grounding Resistors
• Periodic Inspection :• Deenergize the system being grounded and break
the connections between neutral and the grounding resistor
• An Isolation Switch may be used to break this connection
• Remove the front and rear covers for visual inspection of internal components
• Check for cracked insulators or bushings• Perform Dielectric Withstand Test (Hi-pot) to
ensure the insulation isolation
Maintenance/Inspection of Neutral Grounding Resistors
• Check the Resistive Element for continuity• Check all internal connections for tightness• Vacuum any dirt or debris from the inside of the
enclosure• Follow Manufacturer’s Maintenance Instructions
Surge Arresters - Short Cable Length
BIL Margin is Reduced Appox 1.6kV/Ft
Skirt-to-Skirt Clearance = 1”/30kV BIL
Maintain Good Ground (Inspect Grounding Connections for tightness and Absence of
Corrosion
Insulation Coordination When CT’s are Mounted on Buss
C-400 Class CT is bus mounted by using Polyester bottles with full coordination of Insulation and eliminating Corona
Disconnect Switches with Fluidized Epoxy Buss Insulation and Inter-phase Barriers
When Specifying Switchgear, Consider Unusual Service
Conditions
Application Guide For Switchgear Unless Specified, Usual Service Conditions Apply
Ambient Air Temp does not exceed –30C or + 40CAltitude does not exceed 1000m above sea levelAir is not significantly polluted (Pollution level 1 for I/D, 2 for O/D per IEEE C37.100.1)Relative Humidity (Average value) does not exceed 95% over 24h period & 90% over 30 day periodVibration does not exceed low level per IEEE- 693Solar Radiation does not exceed 1044 W/m sq (O/D Swgr only)Ice coating for exposed movable parts does not exceed 1mm (O/D only)Wind speed does not exceed 40 m/s or 90 mph (O/D)
Application Guide For Switchgear
Unusual Service ConditionsAmbient Air Temp above 40 CCan’t exceed total temp (40C + 65C Rise = 105C)Continuous current rating must be de-rated per section 8.4 of C37.20.2Ambient Air Temp below –30 CUse Thermal insulation and Space heatingAltitudeHistorically, switchgear has been successfully applied at altitudes up to 1,000 m without the use of an altitude correction factor
Application Guide For Switchgear Unusual Service Conditions (Cont)
For Altitude higher than 1 000 m, multiply the rated insulation levels at sea level by a factor Ka in accordance with Figure 1 of C37.100.1Hot and Humid ClimatesMake Fungus-resistant by means of:- Heaters & Ventilation- Fungus resistant coating for secondary wiring- Fungus and rust resistant property for paint Solar Radiation (O/D Switchgear)When Solar radiation must be considered for specific geographic location, refer to IEEE Std C37.24 for details
Maintain and Update Electrical Distribution Documentation
• Instruction Manual• One-Line Diagram• Three-Line and schematic Diagrams• Wiring Diagrams• Material List• Utilize Mimic Buss for System Representation
System Representation with Mimic Buss
Switchgear Looks Nice when it’s New
What Happens if It is not Maintained
Reward for those who Maintain MV Switchgear
Reward for Maintaining Switchgear
References
• NFPA 70B –2000 Recommended Practice for Electrical Equipment Maintenance
• NFPA 70E-2000, Electrical Safety Requirements for Employee Workplace
• IEEE Std 1264-1993, IEEE Guide for Animal Deterrents for Electric Power Supply Substations
• IEEE Std 1584-2002, IEEE Guide for performing Arc-Flash Hazard Calculations
• NFPA 70-2002, National Electric Code
Questions?
Thank you
