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DC Power Plants for Telecommunications and Data

Thomas G. CrodaPrincipal Engineer

Presented toPresented to

INFOBATT INFOBATT 20052005

CSI Telecommunication

Engineers

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IntroductionEngineering RequirementsApplicable Standards

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Engineering Considerations

Equipment to be PoweredRequired Reserve TimeMinimum Operating VoltageSize of the Facility

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Plant Size and Design

Load current

Voltage operating range

Required reserve time

Recharge time

Battery sizing

Rundown problems

Allowable plant voltage drop

Grounded (+) conductor

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2000 - 25,000 Amp DC Power PlantDual Level Distribution

BatteryString #11300 AH

1

2

11 12

23

24

BatteryString #N1300 AH

1

2

11 12

23

24

800 AmpBatteryCharger

#1

+ +

Shunt-48 VDC

Return

480 VAC3 Phase

480 VAC3 Phase

PrimaryPower Bay

600 AFuses

12

14

800 AmpBatteryCharger

#N

SecondaryPower Bay

“A” Power

“B” Power

Return

To EquipmentBays

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Load Current

At float voltage

At end of discharge

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Voltage Operating Range

See T1.315 for new equipment (40-57 VDC)

Check specific equipment for its operating range

Float voltage

End of discharge voltage

Equalize voltage

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Required Reserve Time

Regulatory requirementsReliability requirementsEconomic issues

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Recharge Time

Reliability RequirementsRundown ProblemCharger sizing

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Rundown Problem

The problem of more load than the chargers will supportWhat happens with a 1000 Amp load at 54 VDC?Since the entire load is "constant power" the load at 40 VDC is: 54 * 1000 / 40 = 1350 AmpsThe MINIMUM amount of chargers must exceed 1350A.

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Plant Type

Single or Dual Level Distribution ArchitectureSmall plants use single level distributionLarge plants use dual level distribution

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DC Power – Single Point Ground

Minimal current in frameworkBalanced distribution to cancel fields

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Applicable Standards

T1.311 DC Power Systems –Telecommunications Environment Protection T1.315 Voltage Levels for DC-Powered Equipment in the Telecommunications EnvironmentNFPA 70 National Electrical CodeApplicable Local Standards

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Allowable Plant Voltage Drop

2 volts - battery to load0.25 volts - between battery and primary distribution1.0 volt - between primary and secondary distribution0.5 volts - between secondary distribution and load bay0.25 volts - allocated for fuse, circuit breaker, and shunt loss Other allocations are possible

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Battery Sizing Considerations

Average Discharge CurrentAverage Discharge Voltage used for calculating Average Discharge Current45 VDC is a good value (42-48)/2=45VDCIf the load is 1000 ADC at Float (54 VDC), the load at 45 VDC is 1000*54/45 = 1200 ADCUSE THIS VALUE TO SIZE YOUR BATTERY

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Battery DisconnectNot generally used in the telecom industry.If used, it should be 2-pole to completely isolate the battery.Each string should have a separate disconnect so one failure will not fail the plant.

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Questions?