generators revisited

8/8/2019 Generators revisited

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GeneratorsPresentation byScott Martin


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Considerations for Selecting &Sizing A Backup Generator


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Power Output Quality

All Generators are NOT Created Equal

AC Power is represented as a sine wave. The smoother

the curve, the more stable the power.Utility Power = 120/240V, 60 Hz, Sine Wave

Voltage Regulation Method Determines Power Output Quality

Fluctuations in power can cause equipment to shut down or evendamage the appliance.

More of an issue with portable generators


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Voltage Regulation Methods

There are several different ways to regulate the voltage on agenerator:

Brushless

Brushless generators are among the most commonin the industry because of their inexpensive construction,

but have the least reliable voltage control. Brushless generatorscan't react to a changing load, either producing low power (abrownout) or high power. Fluctuations of this nature can cause

equipment damage.


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AVR (Automatic Voltage Regulator)

Many generators feature an AutomaticVoltage Regulator, or AVR, designed to consistently

control voltage. The AVR keeps the output voltagemore constant, regardless of the load. This means nospikes or brownouts.


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Inverter

Inverters produce the cleanest power of all.These units are ideal for sensitive electronics, suchas computers.

Inverter generators offer a number of other benefits, including lessnoise, lower weight, and greater fuel efficiency as compared totraditional models.


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Portable vs Stationary

Is Natural Gas or Propane available at the site?

If not what would the cost be to install PropaneTanks? Is that acceptable to you?


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Portable Less expensive than Stationary models Unit is Portable and may be used for other purposes in other

locations Must Wheel Outside and Setup During Power Outage Fill with Gasoline Manual Transfer Switch

Manual Start (some have remote start)

Manually Connect to House Fuel Storage Issues Refueling/Runtime Issues Lower power ratings than Stationary models Power Quality Issues more likely than with Stationary models


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Stationary More expensive than portable models

Need Suitable Permanent Location Outside House Automatic Self Test Automatic Transfer Switch

Automatic Startup during power outage No Fuel Storage Issues No Refueling/Runtime Issues Less likely to have power quality issues


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Connecting the Generator toYour Home

Improper connection can pose safety issues for lineworkers and may damage your equipment

Back Feeding 240V Dryer Plug (not recommended)Extension Cords Limits which appliances can bepowered and can be a tripping hazard. Must also

leave a door or window open for cord to passthrough.


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Install a Transfer SwitchA transfer switch is a sub-panel to which you canwire the appliance circuits you wish to powerwith your generator during a utility outage.

With a transfer switch you can power hard-wiredloads such as your furnace or well pump.

There are both Manual and Automatic TransferSwitches.

A transfer switch should be installed by a

licensed electrician.


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Manual Transfer SwitchesLess Expensive/Less Convenient

Manual Transfer from Utility Powerto Generator Power by throwing aswitch

Manual Connection of Generator

Manual Load Management


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Automatic/Intelligent Transfer SwitchesMore expensive/More Convenient

Automatic Transfer from Utility to Generator andBack Again when Power is Restored

Some Models like this APC Universal TransferSwitch offer Intelligent Automatic Load

Management and allow you to Prioritize YourLoads

This model can also be used with a secondpower source such as Wind or Solar ElectricSystems


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Generator Sizing


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Determine your Critical Loads andTheir Power Requirements

Sump Pump3 or 4 LightsWater Heater

Garage Door OpenersMicrowaveWell Pump

Radio/TelevisionRefrigeratorFurnace/Boiler


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Create a Loads List

Laptop PCDesktop PC15 Watt CFL60 Watt IncandescentWashing MachineGarage Door OpenersLCD Television

RadioMicrowaveRefrigeratorSump PumpElectric Water Heater

Well PumpWood Pellet StoveFurnace Motor

Surge 3xPower FactorApparent Power (VA)Real Power (W)Device


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Use a Power Meter to MeasureAppliance Power Requirements

Can measure 120 Volt Loads up to approximately 15 ATo measure hard wired appliances use a whole house electrical monitor like TheEnergy Detective (T.E.D.), eMonitor or Blue Line Innovations Power Cost Monitor.

Nameplate ratings on motors or appliances, or appliance power estimation chartsmay also be used to estimate power requirements, but actual measurements arepreferred whenever possible.

Kill A Watt P4300 * Kill A Watt P4460 EZ Watts Up Pro


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Enter Appliance PowerMeasurements in Loads List

0.882522Laptop PC0.949993Desktop PC0.68221515 Watt CFL1.00606060 Watt Incandescent0.501000500Washing Machine

Garage Door Openers0.975957LCD Television

0.6764Radio1200Microwave

3x0.93176163RefrigeratorSump Pump

145004500Electric Water Heater

3xWell Pump0.51197100Wood Pellet Stove

3xFurnace MotorSurge 3xPower FactorApparent Power (VA)Real Power (W)Device


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Understanding Power MeasurementsWatts (W), Volt Amps (VA) and Power Factor (PF)

Power Factor =

Real Power (Watts) / Apparent Power (Volt-Amps)

Resistive Loads - Power Factor = 1

Inductive Loads - Power Factor < 1


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Example of a Resistive Load

60 Watt Incandescent Bulb

P3 Kill A Watt Measures 60 Watts, 60 Volt AmpsPower Factor = 60 Watts / 60 Volt Amps = 1

Current Draw on Generator =

60 Volt Amps / 120V = .5 Amps


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Example #1 of an Inductive Load

Wood Pellet Stove

P3 Kill A Watt Measures 100 Watts, 197 Volt AmpsPower Factor = 100 Watts / 197 Volt Amps = .51


197 Volt Amps / 120V = 1.64 AmpsNOT

100 Watts / 120V = .83 Amps


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Example #2 of an Inductive Load

Washing Machine

P3 Kill A Watt Measures 500 Watts, 1000 Volt AmpsPower Factor = 500 Watts / 1000 Volt Amps = .50


1000 Volt Amps / 120V = 8.33 AmpsNOT

500 Watts / 120V = 4.17 Amps


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Power Measurement Summary

Use Volt Amp rather than Watt Measurement whenEstimating Loads

Measure Loads Whenever PossibleUse Appliance Tag or Contact the Manufacturerwhen Measurement is not possible

Applying a Power Factor of .85 to a Group of Loadsis a Reasonable Rule of Thumb

i.e. Total Watts / .85 = Estimated Total Volt Amps


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Environmental Factors

Elevation

A generators power rating is based on its operation at sealevel. Generator engine power decreases as altitude increases

(thinner air), and the generators maximum electrical outputdrops accordingly.

A power loss of about 3.5% per 1,000 feet of elevation gain istypical for gasoline-, diesel-, or propane-fueled generators

Natural gas-fueled generators may suffer a power loss of about5% per 1,000 feet.

Additionally, the generators carburetor may need to bemodified for high-altitude operation, even to achieve the

reduced power rating.


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Environmental Factors

Temperature

Ambient temperature is a related complication, as typical power derating is about 1to 2% for each 10F above its nominal rating.

Combining the conditions of high altitude and high temperature may requirespecifying a generator with a higher continuous rating.

For example, say youre in Denver, Colorado (elev. 5,000 ft.), and need a propanegenerator to deliver 4,300 VA during the summer days with temperatures at 90F.

Compensating for altitude would result in a 17.5% loss. (3.5% x 5 = 17.5%)If a generators full power specification is based on an ambient temperature of60F, then available output can be expected to decrease by about 3% at 90F[(90F - 60F) 1% 10F].

So the actual rating needed would be about 5,400 VA.


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Surges

Generator power specifications also emphasize their Surgecapacity, or the VA that can be delivered for 30 minutes or less.

The Surge Rating is typically about 20% higher than a generators

continuous VA rating.For Example: A 5,400 VA requirement may necessitate a generatorwith a surge rating of about 6,500 VA.

This surge capacity is useful when starting motorized loads, whose

start-up surge current is often several times the normal runningcurrent specification. So even starting with a 3,600 W load, its notunusual to need a generator rated for at least 6,500 VA, especially ifthe loads have low power factors and are operated at high elevation.


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Summary

Understanding how to accurately estimate powerrequirements, accounting for environmental factors, andunderstanding generator ratings can help ensure that agenerator can provide the power needed for youressential loads. A little up-front research and a fewsimple calculations will save you money (and

headaches) in the long run and ensure that you makean educated purchase.

Cost vs Convenience

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