4. 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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5. 2000 - 25,000 Amp DC Power Plant
Dual Level Distribution
Shunt
-48 VDC
Return
Primary Secondary
+ + Power Bay Power Bay
1 24 1 24 600 A
Fuses “A” Power
2 23 2 23 1
Battery Battery 2
String #N “B” Power
String #1
1300 AH 1300 AH
To Equipment
11 12 11 12
Bays
Return
14
800 Amp 800 Amp
Battery Battery
Charger Charger
#1 #N
480 VAC 480 VAC
3 Phase 3 Phase
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6. Load Current
At float voltage
At end of discharge
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7. 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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9. Recharge Time
Reliability Requirements
Rundown Problem
Charger sizing
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10. Rundown Problem
The problem of more load than the
chargers will support
What 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 Amps
The MINIMUM amount of chargers must
exceed 1350A.
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11. Plant Type
Single or Dual Level Distribution
Architecture
Small plants use single level
distribution
Large plants use dual level
distribution
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12. DC Power – Single Point Ground
Minimal current in framework
Balanced distribution to cancel
fields
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13. Applicable Standards
T1.311 DC Power Systems –
Telecommunications Environment
Protection
T1.315 Voltage Levels for DC-Powered
Equipment in the Telecommunications
Environment
NFPA 70 National Electrical Code
Applicable Local Standards
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14. Allowable Plant Voltage Drop
2 volts - battery to load
0.25 volts - between battery and primary
distribution
1.0 volt - between primary and secondary
distribution
0.5 volts - between secondary distribution
and load bay
0.25 volts - allocated for fuse, circuit
breaker, and shunt loss
Other allocations are possible
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15. Battery Sizing Considerations
Average Discharge Current
Average Discharge Voltage used for
calculating Average Discharge Current
45 VDC is a good value (42-
48)/2=45VDC
If the load is 1000 ADC at Float (54
VDC), the load at 45 VDC is 1000*54/45
= 1200 ADC
USE THIS VALUE TO SIZE YOUR
BATTERY
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16. Battery Disconnect
Not 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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