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