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Emergency Power Systems
Scott Thomas
Director - Application Engineering
Cummins Southern Plains
Agenda
Generator Application Considerations
– Ratings
– Diesel vs Natural Gas
– Common Design Challenges
• Packaging – Enclosures and Fuel Tanks
– Emissions
– Common Generator Failures
– Maintenance Recommendations
Automatic Transfer Switches
– Basic Functionality
– Open and Closed Transition
– ATS Types
Question and Answer
Generator Ratings
ISO 8528-1 Sect. 13 defines these ratings:
Emergency Standby power (ESP)
Limited Time Prime Power (LTP)
Unlimited Time Prime Power (PRP)
Continuous Operating Power (COP)
Any manufacturer can go above and beyond
the ISO ratings definitions
Definitions
Standby rating 2750 kW
Max avg. load in 24h period (70%): 1925 kW
200h/year
Unlimited Time Prime Power Rating 2500 kW
Max avg. load in 24h period (70%): 1750 kW
Unlimited Hours with Variable Load
Limited Time Prime Power 2500 kW
Max load is (100%): 2500 kW
500h/year with constant load
Continuous Operating Power 2100 kW
Max load is (100%): 2100 kW
Unlimited Hours with Constant Load
Rating Example 2750kW DQLF
Fuel Selection
Diesel Generators
Local Fuel Source
Better Transient Response
Lower Cost >150 kW
Natural Gas Generators
Unlimited Fuel Source – Outage Risk?
Slight Cost advantage <150 kW
Larger Footprint >150 kW
Emissions
Common Design Challenges
Sound – Contact city to verify sound requirement at property line
Fuel Tanks – Contact Fire Marshall for fuel storage requirements
Clearances
– Recirculation of radiator discharge air
– Proximity to ATS - Transformer
Natural gas supply piping
Generator Sizing
– Fire Pumps
– WWTP/LS/PS
– VFD’s - HarmonicsCummins Confidential
Sound Attenuation
Sources of Sound
– Engine noise
• 100 -110dB(A)@1m
– Cooling fan noise
• 100-105dB(A)@1m
– Alternator noise
• 80 – 90dB(A)@1m
– Structural/mechanical noise
• Vibration, Gears etc.
– Un-silenced engine exhaust
• 120-130dB(A)@1m
Contact City to understand local requirement based on zoning
of property – field testing requirements.
Increase distance from receiver (Property Line)
– Sound pressure drops ~6 dBA at 2x distance
Insert high mass, absorptive barriers – Enclosure Baffles
Watch for reflective surfaces
– Perceived sound pressure increases 3dBA due to a reflective
surface; 5dBA for two reflective surfaces
Direct noise away from sensitive locations
– Radiator discharge turning vanes (Scoop)
– Engine Exhaust elbows
Sound Attenuation Strategies
Sound Attenuation Strategies
Sound Attenuation Strategies
Installation Review: Airflow Restriction
Installation Review: Airflow Restriction
Installation Review: Airflow Restriction
Installation Review: Accessibility
Ease of Access
– Fuel Fill
– Load Bank Connections
Weather Events
– Snow Loading / Plowing
– Flood Plain
Proximity to Occupied Facilities
– Windows/Doors
– Ventilation Intakes
Location Considerations: Outdoor
Location Considerations: Indoor
Safety
– Dedicated space
– Working space (36” or 1 m minimum)
– Working height
Future Planning
– Additional equipment space
– Future genset capacity
– Replacement parts access
Diesel Fuel Systems
Tank size
– Contact Fire Marshall for volume, tank construction
expectations, and field testing requirements
– Access and filling for rooftop installations
– Actual run time required/desired
Fuel temperature concerns
– Cold - Waxing point of particular diesel blend on-site
– Warm – Fuel return temperature in small tanks
Tank ventilation (Discharge to exterior)
Special requirements for onsite testing, alarms,
remote fill stations
Diesel Fuel Tanks
Diesel Fuel Tank Notes
UL 142 and UL 2085 listing requires pressure/leak testing
prior to shipment
Common Options:
– Overfill protection valves (OFPV)
– Spillboxes
– Fuel level alarms
– Polishing systems
– Remote Fill Stations
– Elevated Vents
Be weary of additional control/breaker handle height with
subbase tanks
Day Tank Notes
2 to 4 hour run time
One day tank for each generator set
As close to the generator set as possible
Automatic filling control
Ability to return fuel back to bulk tank
– Auxiliary pump or gravity return
Manual filling provision
Options:
– Utilize genset subbase tank with additional ports
– Standalone day tank from 3rd party supplier
Size Lines for Flow, NOT Consumption
Route for Lowest Restriction
– Limit fittings, bends, and length of runs
Diesel Fuel System Piping
EPA Emissions Tables
CI NSPS Stationary Emissions - Diesel engines
EPA SI NSPS Final Rule
Stationary Emergency Engine Designated Use for NSPS and RICE NESHAP
Unlimited use during emergencies
– Utility failure, transformer, UPS, circuit breaker, ATS
– Document issue as a part of record keeping requirement
100 hours per year allowed for:
– Maintenance and testing
– Emergency Demand Response (EDR) programs (May 1st 2016 EDR Revision)
– 50 hrs/year (of the 100hrs/yr) for non-emergency operation allowed (if there is no financial arrangement*)
• e.g.: storm avoidance
Generator Maintenance
Common Generator Failures
– Dead Batteries (Redundant Battery String & BBS)
– Battery Charger Failure (Redundant Battery String & BBS)
– Fuel Quality (Fuel Filtration Systems, Fuel Maintenance Program)
– Low Coolant Levels (Periodic Inspection – Alarm)
– Control not in Auto (Remote Annunciator – SCADA Alarm)
– Circuit Breaker Open (Remote Annunciator – SCADA Alarm)
Maintenance Recommendations
Cummins recommendations for Annual Maintenance
– Quarterly Inspections
– Annual Oil/Filter Change
– Annual Supplemental Load Bank Testing
• In addition to any building load tests throughout the year.
– Battery Replacement
• Per NFPA 110, batteries to be replaced in standby generator sets every two
years.
– Annual Fluid Sampling
• Fuel/Oil/Coolant Analysis
– ATS Inspections
• Operate with load at least once per year
A device that transfers
electrical loads between two
sources of power by using
either automatic or manual
controls
ATS monitors utility voltage and frequency
On utility failure generator starts and accelerates to rated speed and voltage
ATS senses source available
Time delay on transfer
What is a Transfer Switch?
Utility
Transfer
switch
Generator
Transition Types and Applications
Open Transition (In Phase or Time delayed /
Programmed Transfer)
Closed Transition
To Loads
!
From
Utility
Open Transition – Utility to Genset
Utility Power
Fails
Generator Starts
Gen Source
Available
Load Transfers
to Generator
!
From
Utility
To Loads
Open Transition – Genset to Utility
Utility Power
Returns
ATS retransfers
load to Utility
ATS removes gen
run command
From
Utility
To Loads
Load (Residual) Voltage
Utility/Genset Voltage
Time Delayed Transition
INDUCTIVE
LOAD
UTILITY UTILITY UTILITY
LO
AD
VO
LTA
GE
Pre-determined delay
allows the residual
voltage to decay
TIME
INDUCTIVE
LOAD
INDUCTIVE
LOAD
Time Delayed Transition
Closed Transition
From
Utility
To Loads
LOAD
UTILITY
LOAD
UTILITY
LOAD
UTILITY
TIME
LO
AD
VO
LTA
GE
Up to 10s of power interruption
Full power outage cycle (utility drops out)
LOAD
UTILITY
LOAD
UTILITY
LOAD
UTILITY
TIME
LO
AD
VO
LTA
GE
Up to 100ms of
paralleled operation
Return to Normal Power (After Outage)
Closed Transition Risks
Why do breakers trip during closed transition transfer?
– Current flow between sources caused by a difference in instantaneous
voltage between sources at the instant of closure
What causes the difference in voltage?
– Phase angle difference between sources
– Difference in RMS voltage between sources
– Transient condition on one of the sources
• Motor stops/starts
• VFD ramps/down
Closed Transition is not a substitute for a UPS
Closed Transition might result in disturbances on transfer
– Frequency and Voltage shift due to less than perfect synchronization
– Current spike may result due to voltage difference
– Disturbances minimized by Load sequencing
Closed transition adds cost due to requirements for protective relays
Closed transition systems can result in project delays due to additional utility regulations
Closed Transition Considerations
Allows service of ATS without disrupting power to critical loads.
By having two transfer switches
connected in parallel, the bypass transfer
switch adds redundancy to the system
Applications:
– Critical power and maintenance requirements,
including data centers,health care, and waste
water treatment facilities
Bypass Isolation Switches
ATS Bypass N
L
E
Bypass Transition Switch
ATS BypassN
L
E
ATS BypassN
L
E
ATS BypassN
L
E
Connected Test Isolated
Normal Operation
Bypass open
Bypass closed
No power across ATS
No loss of power to loads
when to Bypass to same
source
ATS retains sensing and
operating functionality
Functional testing without
load interruption
Bypass carries load
ATS removed for service
or replacement
• Manual transfer to
emergency power
Isolation Bypass Positions
Be careful about size and access requirements for bypass
switches
A switch in the bypass mode is not automatic
– Remote monitoring of “Switch not in auto”
No power interruption required to service ATS
– Non Load break
Bypass Isolation Considerations
Normal ATS with a circuit
breaker on the utility side
– The breaker is a UL listed over-
current device
Meets NEC requirements for a
Service Entrance equipment
Advantages:
– Saves space and cost for a
separately mounted circuit breaker
Service Entrance Transfer Switch
Breaker Pair Transfer Switch
Breaker Pair Transfer Switch
Transfer mechanism is made of two power circuit breakers
– Integral over current protection
– Draw out capability (easier to service)
Benefits:
– Closed transition with soft loading (option)
– Can be also offered as a Service Entrance switch
– Facilitates selective coordination - can withstand fault current up to 60
cycles
– High level of serviceability