Post on 12-Mar-2018
Important Considerations for Specifying MV Mining
Switchgear Western Mining Electrical
Association Edmonton, Canada
June 13, 2008
Specifying MV Mining Switchgear (Above 1000V and up to 38kV for Surface Mining)
Key Components of Specification:
Scope Applicable StandardsService ConditionsRatings ConstructionTestsQuality Assurance System
Specifying MV Mining Switchgear Scope
Scope of workDefine what is required
Example:This specification defines requirements of one (1) 69kV-25kV, 60Hz, 15 MVA mine-duty skid mounted portable substation with primary structure, transformer, neutral grounding resistor and secondary switchgear, close coupled to transformer.
Applicable Standards (For illustration only)
• IEE Std C37.20.3-2001 Metal-Enclosed Interrupter Switchgear
• IEEE Std C37.06-2000 AC HV Circuit breakers• IEEE Std C37.22 MV Switches used in indoor
Metal-Enclosed Switchgear• NFPA 70E-2000, Electrical Safety Requirements
for Employee Workplace• IEEE Std 1584-2002, IEEE Guide for performing
Arc-Flash Hazard Calculations• NEC, National Electric Code
Types of Switchgear Assemblies Defined by IEEE Standards
SWITCHGEAR ASSEMBLIES
METAL-ENCLOSED POWER SWITCHGEAR
METAL-ENCLOSED BUS C37.23
CONTROL SWITCHBOARDS C37.21
LOW-VOLTAGE POWER CIRCUIT BREAKER (LV)
C37.20.1
METAL-CLAD (MC) C37.20.2
METAL-ENCLOSED INTERRUPTER (MEI)
C37.20.3
NON-SEGREGATED PHASE
SEGREGATED PHASE
ISOLATED PHASE REQUIREMENTS AND
GUIDE FOR CALCULATING LOSSES
VERTICAL (OPEN OR ENCLOSED)
DUAL
DUPLEX
CONTROL DESKBENCHBOARD
DUPLEX BENCHBOARDFIXED RACK CABINET
SWING RACK CABINET
METAL-ENCLOSED POWER SWITCHGEAR
METAL-ENCLOSED POWER SWITCHGEAR
METAL-CLAD (MC) C37.20.2
METAL-ENCLOSED INTERRUPTER (MEI)
C37.20.3
NON-SEGREGATED PHASE
METAL-ENCLOSED BUS C37.23
METAL-ENCLOSED BUS C37.23
GUIDE FOR TESTING MVME SWITCHGEAR FOR
INTERNAL ARCING FAULTSC37.20.7-2001
Specifying MV Mining Switchgear Service Conditions
Usual Service ConditionsThe equipment shall be designed for the following service conditions:
1. The temperature of the cooling air surrounding the enclosure of the switchgear is within the limits of -30 C and +40 C
2. The altitude of the installation does not exceed 1000 m (3300 ft)
3. The effect of solar radiation is not significant
Specifying MV Mining Switchgear Unusual Service Conditions
Or you may list:1. The equipment shall be suitable to operate within
the limits of -30 C and +50 C (require either de- rating or select next higher ampacity rating)
2. The altitude of the installation does not exceed 1500 m (5000 ft), (require either de-rating or use higher insulation level
3. The effect of solar radiation shall be considered per IEEE Std C37.24
Specifying MV Mining Switchgear Altitude Correction Factors
Switchgear that depends on air for an insulating and cooling medium will have a higher temperature rise and a lower dielectric withstand capability when operated at higher altitudes
The following Table shows historical altitude correction factors for dielectric withstand voltage and continuous current
Specifier may refer to Annex B of IEEE PC37.100.1 for additional guidance
Effect of Solar Radiation is Normally Insignificant Monthly Normal Max Temp in US & Canada
See IEEE Std C37.24-2003 for Ref
Station June July AugustPhoenix 39.7 C/103.5 F 41.1 C/106 F 39.8 C/103.6 F
Las Vegas 37.9C/100.2F 41.1C/106F 39.6C/103.3F
Sheridan 24.9C/76.8F 30.1C/86.2F 29.6C/85.3F
Evansville 30.1C/86.2F 31.7C/89F 30.7C/87.3F
Fairbanks 21.2C/70.2F 22.4C/72.3F 19.1C/66.4F
Edmonton 20.9C/69.6F 22.5C/72.5F 21.8C/71.2F
Temperature rise of about 15 C may be expected on the conducting parts due to solar radiation
Specifying MV Mining Switchgear Ratings
Ratings of SwitchgearDesignations of Operating Limits under Specified Conditions
1. Rated maximum voltage2. Rated power frequency3. Rated insulation levels4. Rated continuous current5. Rated momentary withstand current6. Rated short-time withstand current
Specifying MV Mining Switchgear Example – 25kV Dual VCB House w/o NGR
Ratings of Switchgear1. Rated maximum voltage = 27kV rms2. Rated power frequency = 60Hz3. Rated insulation levels: Power frequency withstand
voltage = 60kV rms; BIL = 125kV peak4. Rated continuous current = 1200A5. Rated momentary withstand current = 43kA
peak(10 Cy)6. Rated short-time withstand current = 16kA (2 s)
Bkrs have SC interrupting rating, switches do notSwitches do have fault close rating
Specifying MV Mining Switchgear Example – Neutral Grounding Resistor
Ratings of NGR1. 23.9kV L-L, 13.8kV L-N, 60 Hz2. Resistance @ 25 C = 552.0 Ohm3. Current = 25A4. Duty/Max Temperature rise = Extended/610 C 5. Finish = Mill galvanized6. Enclosure type = Outdoor7. IEEE Std 32-1972, reaffirmed 1990
Specifying MV Mining Switchgear Neutral Ground Monitoring if applicable
Specify1. Neutral ground monitoring device2. Sensing resistor3. Current transformer
Specifying MV Mining Switchgear 25kV Junction box
Ratings of Switchgear1. Rated maximum voltage = 27kV rms2. Rated power frequency = 60Hz3. Rated insulation levels: Power frequency withstand
voltage = 60kV rms; BIL = 125kV peak4. Rated continuous current = 600A5. Rated momentary withstand current = ??kA
peak(10 Cy)6. Rated short-time withstand current = ??A (2 s)
Specifying MV Mining Switchgear Associated Major Components
Ratings of major components should also be listed in specification
1. Vacuum circuit breakers 2. Disconnect switches (specify load-break or non
load-break)3. Instrument transformers (CT’s, PT’s & CPT’s)4. Lighting arresters (MCOV for grounded or
ungrounded system)5. Ground monitor6. Metering, controls, relays and ground monitors7. Power transformers and primary structures for
portable substations
Specifying MV Mining Switchgear Construction Considerations for Rugged Mine Duty
SwitchgearSkid (shall be fabricated using the following structural members)
• Wide flange I-beams for cross members• Heavy duty structural steel channels for runners• 18”-26” Wide runners with 3/8” steel plates on bottom• ¼” Thick steel deck and belly plates• ¾ -1” Thick steel wear plates under runners• 1 ½” X 10” X 30” steel towing eyes with 3” eye• Towing eyes at 45 degree angle to facilitate lifting with
slings• 1” Diameter steel J-hooks for tying off the cables
Specifying MV Mining Switchgear Construction Considerations for Rugged Mine Duty
Switchgear
Enclosure (shall be fabricated with)• 11 Gauge steel with seam welded construction• Stainless steel hinges and door hardware• Galvanized steel slide-bolt latches with provisions for
padlocking• Double flange door construction with drip shield• Nema 3-R construction with door stops and gaskets • Viewing windows for disconnect switches• Adequate cable termination height• 3/8” Steel plates for blast protection of transformers
Specifying MV Mining Switchgear Construction Considerations for Mine Duty Switchgear
Enclosure Finishes • After the enclosure fabrication all welds and hard to
reach areas shall be cleaned with steel wire brush and power grinder to remove any corrosion, weld splatter and scale
• All enclosures shall be cleaned with high pressure phosphatizing solution to clean and etch the surfaces
• Enclosure shall be painted with a minimum of 1.5-2.0 mil high-solids primer and 2.0-3.0 mil acrylic enamel top coat
• Electronic paint gauge may be used to assure uniform quality finish
• Exterior paint shall withstand 2000 hours of exposure to a 5% salt spray
Steel FabricationWelds are cleaned with a steel wire brush
Power grinder is used to remove any corrosion, scale and weld splatter
Steel Fabrication
High pressure cleaning with phosphatizing solution, rinsing and air drying of sub-assemblies and assemblies
Construction Two-Coat Paint System
Primer: Alkyd high-solids universal primer
Finish Coat: Acrylic enamel, high-solids semi-gloss finish
2000 Hrs of salt spray withstand, resistant to chalking, peeling, and UVR
Specifying MV Mining Switchgear Blast Protection of transformers
3/8” Steel Plates11 Ga Seam welded construction
Optional top lifting structure for crane handling
Specifying MV Mining Switchgear Wiring
Control and secondary wiring• Wiring shall be rated for 600V, and 90 C, and
shall be flame-retardant. Wire shall be type SIS as listed in the NEC.
• Wiring across a hinge shall be flexible to withstand repeated door movement without sustaining damage to wire strands or insulation
• Wire size shall be suitable for the maximum steady-state load
• Wire shall be No. 14 AWG and larger
Insulation Coordination When Cables are ran through neutral CT
CT’s are properly spaced and air gaps are sealed with RTV to eliminate corona
Specifying MV Mining Switchgear Production Tests
Production tests made for quality control shall be performed to assure that product meets the design specifications and applicable standards
1. Power frequency (60Hz) dielectric tests2. Mechanical operation tests (Functioning of operating
mechanisms, interlocks, door locks etc)3. Grounding of instrument transformer cases (Metal case
design only)4. Control wiring continuity check (Operational check)5. Polarity verification (To ensure correct connections between
instrument transformers and meters)6. Request test data for power transformer if applicable
Specifying MV Mining Switchgear Quality Assurance
• Vendor shall be certified to ISO-9001 Quality Management System
• Vendor shall provide MSHA certified field service technicians when required