International District Energy Association’s
24th Annual Campus Energy Conference
Presented
Presentedby:
by:
Massachusetts Institute
Technology
RMFof
Engineering,
Inc.
& RMF Engineering, Inc.
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21 MW Cogeneration System
6 Boilers, 556,000 PPH
14 Chillers, 33,800 Tons
2 Satellite Plants
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Chartered in 1861
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168 acres, 100 Buildings
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Electrical Demand of 27 MW
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Majority of Campus is Served from the Central Utility Plant
Background Information:

MIT was informed of a significant reduction in the utility
company’s available fault current levels
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MIT’s electrical system is well maintained and well
documented

A Campus-Wide Arc Flash Analysis was commissioned
to maintain OSHA compliance, update the safety
program, and provide warning labels on equipment

Air Becomes the Conductor

35,000°F Arc Temperature
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Molten Metal > 1800°F

Hot Air > 500°F

Intense Pressure > 2000 lb/psf
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Sound Waves > 140db
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Shrapnel > 740 mph
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Intense Light
www.osha.gov - Safety Training for the Focus Four
Hazards in the Construction Industry
Compliments of Salisbury Electrical Safety L.L.C.

Dust, Impurities, Corrosion, Condensation, Animals

Spark Discharge from:
- Accidental Touching
- Dropping Tools
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Over-voltages Across Narrow Gaps
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Failure of Insulating Materials
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Equipment Failure
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Majority of Electrical Injuries are Burns (~80%), Not Shocks

Arc Flash Hazards Must be Identified as Part of the
Employer’s Safety Program (OSHA / NFPA 70E)

NFPA 70E Currently Allows Two Methods of Arc Flash
Hazard Analysis:
- Incident Energy Calculations – Recommended Method
- Hazard Risk Category (HRC) Tables – Limited Application,
Prone to Misinterpretation

Site Specific Incident Energy (Arc Flash) Calculations Will
Soon Be A Requirement of NFPA 70E
IEEE Std 1584-2002
IEEE Guide for Performing
Arc-Flash Hazard Calculations
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Enforced by OSHA
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Specifies Requirements for
Employer’s Safety Program
Empirically Derived Model Based on
Statistical Analysis and Curve
Fitting Programs
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Extensive Test Data Gathered from
Several Laboratories
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Provides Incident Energy Equations
for use by Software Manufacturers
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Includes Incident Energy Equations
for 208V – 15kV, Ibf = 700A – 106kA
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
Includes Incident Energy
Equations for 600V and Below
(Conservative)
References IEEE Std 1584
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System Conditions
- Available Short-Circuit Current
- X/R Ratio
- Prefault Voltages
- Loading
Protective Devices (Time-Current
Characteristics)
- The First Upstream Device
- The Second Upstream Device
System Grounding
Electrodes and Potential Arc
Lengths
- Spacing Between Phases
- Spacing Between Phases and
Ground
- Orientation
- Insulated Versus Noninsulated
Size and Shape of Enclosures
 Atmosphere Conditions
- Ambient Temperature
- Barometric Pressure
- Humidity
 Arc Conditions
- Randomness of the Arc
- Interruption of the Arc
- Arc Plasma Characteristics
- Other Unidentified Factors
 Dissipation of Energy
- Heat
- Latent Heat of Vaporization
- Light
- Sound
- Pressure Wave
 Other Miscellaneous Factors
Electrical Arcing Phenomena – R.A. Ammerman, P.K. Sen, J.P. Nelson
13.8kV
2.4kV
4.16kV
480V
Time OC
Electromech. Bus Diff.
Directional OC
Solid State Line Diff.
Electronic Fuses
Motor Protect.

Extensive Equipment Survey (Access Database)
 Record Nameplate Data
 Record all Overcurrent Protective Device Types and Settings
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Build a Power System Software Model
Run Baseline System Studies
 Short Circuit
 Coordination
 Load Flow (Voltage Drop, Circuit Capacity)
 Arc Flash
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Identify and Analyze Hazards
 Fault Duty Issues (None Found)
 Arc Flash Hazards (Several Found)
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Adjust Overcurrent Devices to Reduce Arc Flash Hazards
Incident Energy at Each Bus - Existing Conditions
80
Reactors In Service
Reactors Bypassed
70
Incident Energy (cal/cm2)
60
50
40 cal/cm2 (HRC 4)
High Risk of Physical Trauma
Above This Line
40
30
8 cal/cm2 (HRC 2)
Target Conditions
Below This Line
20
10
0
13.8kV
4.16kV
2.4kV
Bus Name
480V
Incident Energy at Each Bus - Recommended Settings
80
Generator Off
Generator Running
70
Incident Energy (Cal/cm2)
60
50
40
30
20
10
0
13.8kV
4.16kV
2.4kV
Bus Name
480V
480V Switchgear
Available Primary Fault
Current =12,000A
Available Primary Fault
Current = 13,700A
%Z = 6.36
%Z = 6.21
Identical
Settings
Secondary Fault
Current = 22,700A
Incident Energy
= 580 cal/cm2
Extremely
Dangerous
Motor
Contribution
= 3,300A
Motor
Contribution
= 3,000A
Secondary Fault
Current = 24,400a
Incident Energy
= 16 cal/cm2
Workable with
Adequate PPE
CURRENT IN AMPERES
CURRENT IN AMPERES
1000
1000
85% Arcing Current
11,030 Amps
85% Arcing Current
11,739 Amps
100% Arcing Current
12,976 Amps
100
100% Arcing Current
13,810 Ampus
100
Breaker Trips in 15.9s
IE = 580 cal/cm2
48XAM - Phase
NOT
WORKABLE
EXTREMELY
DANGEROUS
1
10
48XBM - Phase
Breaker Trips in 0.33s
IE = 16 cal/cm2
WORKABLE
USING
ADEQUATE
PPE
1
0.10
0.10
27484 A
26031 A
0.01
0.01
1K
10K
48XAM.tcc Ref. Voltage: 480V Current in Amps x 1
100K
1K
10K
48XBM.tcc Ref. Voltage: 480V Current in Amps x 1
100K
TIME IN SECONDS
TIME IN SECONDS
10
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Design Factors
- Divide and Conquer (Modular Design) – Use multiple, smaller
-
-
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transformers/substations instead of one big one. Segregate “process”
loads into modular units to facilitate shutdowns.
Electric Room Design – Provide ample space in front and in back of
switchgear.
Equipment – Use metal-clad switchgear, specify insulated bus, and
utilize remote racking mechanisms. Provide infra-red windows for
“closed door” thermo scans. Arc resistant switchgear is an option.
Overcurrent Protection - Apply differential relaying schemes (for MV) and
zone-interlocking (for LV). Provide arc flash maintenance settings inside
protective relays (for MV), and arc flash maintenance switches (for LV).
Apply Impedance-Grounding Techniques – Stop the arc before it starts
Operations & Maintenance Considerations
- Update arc flash studies and warning labels every 5 years (NFPA 70E
requirement)
- Provide a comprehensive safety program (employer)
Expected
Phase – Ground Fault Current Flow
Central Utility Plant
Cogen Plant
13.8kV, 30MVA
791Ω, 10A
10 Sec,
Neutral
Grounding
Resistor
10A
Utility Distribution Substation
Intertie
Breaker
XFMR
Secondary
Breaker
Closed
Closed
Closed
Closed
Closed
Closed
Closed
Closed
10,000A
Closed
Ground Fault Current
Contribution = 10A
10A
Substation XFMR
115kV – 13.8kV, 34MVA
10,000A
Ground Fault Current
Contribution = 10,000A
XFMR
Primary
Breaker
Actual
Phase – Ground Fault Current Flow
Central Utility Plant
Intertie
Cogen Plant
Breaker
13.8kV, 30MVA 850A
850A
1700A
791Ω, 10A
10 Sec,
Neutral
Grounding
Resistor
Utility Distribution Substation
XFMR
Secondary
Breaker
Closed
Closed
Closed
Closed
Substation XFMR
115kV – 13.8kV, 34MVA
850A
850A
XFMR
Primary
Breaker
Closed
Closed
10,000A
Closed
1700A
Ground Fault Current
Contribution = 1700A
Closed
10,000A
11,700A
11,700A
Ground Fault Current
Contribution = 10,000A
Closed
Actual
Phase – Ground Fault Current Flow
Central Utility Plant
Intertie
Cogen Plant
Breaker
13.8kV, 30MVA 1,500A
3,000A
791Ω, 10A
10 Sec,
Neutral
Grounding
Resistor
Utility Distribution Substation
XFMR
Secondary
Breaker
1,500A Closed
Closed
Closed
Closed
Substation XFMR
115kV – 13.8kV, 34MVA
1,500A
1,500A
3,000A
Closed
1,500A
4,500A
Open
Open
1,500A
Closed
XFMR
Primary
Breaker
4,500A
Open
Actual
Phase – Ground Fault Current Flow
Central Utility Plant
Cogen Plant
13.8kV, 30MVA
Utility Distribution Substation
XFMR
Secondary
Breaker
Intertie
Breaker
Substation XFMR
115kV – 13.8kV, 34MVA
XFMR
Primary
Breaker
Open
Open
10A
Open
Open
791Ω, 10A
10 Sec,
Neutral
Grounding
Resistor
Open
Open
10A
10A
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Flash Protection Boundary
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Limited Approach Boundary
-
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Minimum Distance from Live
Parts for “Unqualified Persons”
Restricted Approach Boundary
-
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Incident Energy ≤ 1.2 cal/cm2
outside this boundary
To be Entered by “Qualified
Persons with Documented Plan
and Appropriate PPE
Prohibited Approach Boundary
-
Considered the Same as Making
Contact with Live Parts
Presented By:
Richard Lucas
Ben Standish
MIT - Utilities
(617) 324-6801
rlucas@plant.mit.edu
RMF Engineering, Inc.
(800) 938-5760
bstandis@rmf.com