Transcript Rockwell Automation External LTS Template

ELECTRICAL SAFETY
Introduction and Overview of
Safety
Clayton H. Reid
September, 2010
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ELECTRICAL HAZARDS
• Electrical shock
• Electrical arc-flash
• Electrical arc-blast
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ELECTRICAL SHOCK
(part one of two)
• Body resistance
• Wet or dry skins are major factors of resistance
• Circuit voltage
• Amount of current flowing through the body
• Current through the body
• Area of contact
• Duration of contact
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ELECTRICAL ARC-FLASH
Arco electric-flash
Burn Injury - Probability of
Survival
100
90
80
70
60
50
40
30
20
10
0
• Body Burn
2029.9
3039.9
4049.9
5059.9
Age range years
Anos de edad
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25% Body Burn
50% Body Burn
75% Body Burn
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What is an Arc Flash?
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ELECTRICAL Arc-Blast
• Rapid expansion of the air caused by an electrical arc, referred to as an
electrical arc-blast or explosion
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CONTRIBUTING FACTORS TO ELECTRICAL ACCIDENTS
• Faulty Insulation
• Intentional use of obviously defective
and unsafe tools
• Improper grounding
• Loose connections
• Use of tools or equipment too close to
energized parts
• Defective Parts
• Tools left in electrical cubicle
• Ground faults in equipment
• Unguarded live parts
• Failure to de-energize electrical
equipment when it is being repaired or
inspected
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PREVENTING ELECTRICAL ACCIDENTS
• Largely preventable through safe work practices
• Examples of some safe work practices
– De-energizing electrical equipment for inspection and repair
– Keeping electrical and equipment properly maintained
– Exercising caution when working near exposed energized lines or equipment
– Using appropriate personal protective equipment and insulated tools
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ELECTRICAL SAFETY
• ENVIRONMENT, SAFETY AND HEALTH PRINCIPLES
(used by DOE)
• Plan Work
• Analyze Hazards
• Control Hazards
• Perform Work
• Feedback and improve
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ELECTRICAL ACCIDENTS CAUSED BY ONE OF THE FOLLOWING
• Unsafe work practices
• Unsafe equipment or installation
• Unsafe environment
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REQUIREMENTS
• Knowledge/Familiarity
• Mechanical Interlocks
• Electrical Interlocks
• Bus Transfer Procedures
• Lock, Tag and Try Procedures
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REQUIREMENTS
• Workers: Trained and Qualified
• One Line Diagrams: Up- to- date and attached to procedures
• Test Equipment: Good working condition and calibrated
• PPE( Personal Protective Equipment) Good Working Condition and
tested per standards
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SAFETY INTERLOCKS IN MEDIUM VOLTAGE STARTERS
• Protective Barriers for Safe Operation of MV Starter Isolating Switches
• Design And Function Of Safety Interlocks
• Maintenance of Safety Interlocks in MV Starters
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Power Cell Compartment
3 Pole, Non-Load Break
Isolation Switch
3 Current Limiting Power Fuses
(Clip-On or Bolted Type)
3 Bar Type
Current Transformers
3 Phase Vacuum Contactor
Control Power Transformer
is located behind the contactor
1 High MV Cell
Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
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Power Cell Compartment
• The power cell is designed to
allow easy access without the
need to remove components.
1 High MV Cell
Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
15
Power Cell Compartment
• The power cell in a Two High
structure includes, as standard,
a swing-out Low Voltage panel,
allowing for increased working
area.
Two High MV Cell
Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
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Low Voltage Compartment

The standard components
housed in the panel are:





Normal-Off-Test selector
switch
Male test power
receptacle
Rectifier Bridge
CR1 and CR2 control
relays
Motor protection relay(s)
Copyright © 2007 Rockwell Automation, Inc. All rights reserved.
17
Non-load Break Isolation Switch
When in the “OFF” position
the isolation switch is
connected to “Ground
Potential” via grounding
pins.
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18
Non-load Break Isolation Switch
• It is mechanically and electrically
interlocked with the contactor to
ensure it can’t open or close
when the contactor is closed.
• It is also mechanically
interlocked with the power cell
door.
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Maintenance Aids
• Voltage detectors
• Viewing windows
• Infrared sight glass
• Grounding balls
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Voltage Checking Devices
• Non Contact Voltage Detectors (NCVD)
• Voltage Indicator (low and high voltage)
• Voltmeters
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Voltage Detectors
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Voltage Detectors
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Voltage Detectors
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Voltage Detectors
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Grounding Balls
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Grounding Cable
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Infrared Sight glass
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Infrared Scanning
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ArcShield Two-High: Top Cable Entry/Exit
New plenum
design enables
top cable/conduit
connections!
1512B
1512B
1512B
1512A
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1591A
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ArcShield Overview
• Arc vent on the unit roof
– Aluminum plate designed to open
under high pressure associated with
arc flash conditions
– Offset to rear of structure (allows
use of LV wireways)
– Installers must not step on this area
(suitable warning label is provided)
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Unusual Electrical Events
• Unusual Electrical Events
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CASE HISTORY #1
• MCC starter unit
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CASE HISTORY #2
• The Reluctant Skip
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CASE HISTORY #3
• Incorrect testing with a multimeter
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CASE HISTORY #4
• Travelling arc and amperes gone beserk
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CASE HISTORY #5
• Mystery of the missing fishtape
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