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Bas ic DC TrainingBas ic DC Training
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Basic DC TrainingBasic DC Training
DC system philosophies
Basic DC system build up Basic dimensioning
Earthing
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Basic DC TrainingBasic DC Training
DC system philosophies
Basic DC system build up Basic dimensioning
Earthing
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DC system ph ilosophyDC system ph ilosophy
principle for reliable power supply. This is achieved by usingmultiple number of rectifiers & batteries that share a common
oa . rect er a ure or attery a ure w n t s case not
cause loss of power supply.
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DC system ph ilosophyDC system ph ilosophy
Component choice
Fully automatic functions
Dimensioning with redundancy N+1
Minimum two batteries per plant
MTBF for a rectifier: at least 40 years
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DC system ph ilosophyDC system ph ilosophy
Central PowerThe traditional way to supply
power for telecommunication
Integrated PowerThe power system is completely
integrated into each cabinet
Switch Room PowerSystems that reduce costs for
installation and engineering
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Basic DC TrainingBasic DC Training
DC system philosophies
Basic DC system build up Basic dimensioning
Earthing
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Bas ic DC S stemBas ic DC S stem
AC
DC
Rectifier DC Distribution Unit
DC to LoadAC Mains
Load Disconnect Unit
Battery
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DC PowerDC Power B lock Dia ramB lock Dia ram
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Demo for DC Power in BTSDemo for DC Power in BTS
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Basic DC Sys temBasic DC Sys tem -- Rect if ierRecti f ier
Converts mains to regulated DC,ripple and noise on output must meettelecommunications specifications.Rectifiers are sized in watts or amperewith regards to output capacity.Typical rectifier sizes are from ~300W up
To ~10 kW.
Rectifier DC Distribution Unit
AC
DC
DC to LoadAC Mains
Load Disconnect Unit
Battery Connection Unit
Battery
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Basic DC Sys temBasic DC Sys tem -- DC d is t ribu t ionDC distr ibu t ion
Distributes DC to telecom equipmentVia circuit breakers or fusesFuse / circuit breaker ratings from 1A to 800 A
AC
DC
Rectifier DC Distribution Unit
DC to LoadAC Mains
Battery Connection Unit
Load Disconnect Unit
Battery
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Basic DC Sys temBasic DC Sys tem Battery connect ion un i tBat tery connect ion un i t
Connection point for batteriesFuse / circuit breaker ratings from 50 A to 800 A
Rectifier DC Distribution Unit
AC
DCDC to LoadAC Mains
Load Disconnect Unit
Battery Connection Unit
a ery
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Basic DC Sys temBasic DC Sys tem Load d isconnect un i tLoad d isconnect uni t
Disconnects the load at the end of batteryDischarge to protect the battery from deep discharge.Automatic disconnect and reconnect is achieved byutomatic disconnect and reconnect is achieved byusing contactors.Contactor ratings vary from 50A to 1200A.
Rectifier DC Distribution Unit
AC
DCDC to LoadAC Mains
Load Disconnect Unit
Battery Connection Unit
a ery
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Basic DC Sys temBasic DC Sys tem Superv is ion un i tSuperv is ion uni t
Supervises and controls system specific valuessuch as:- Float voltage
- arge vo age
- Over voltage limit- Under voltage limitSupervises and controls automatic functionssuch as;- Battery charging
- Temperature controlled charging
- Battery test
- Load disconnectAlarm loglarm log- Active alarms
- Alarm historyMeasurement and display of-
- Distribution current- Battery current
- AlarmsInterface for remote monitoring- RS 232
- TCP/IP
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Basic DC Sys temBasic DC Sys tem -- BatteryBattery
The battery is the sole source of energy when the rectifiers are
not operating due to mains failure or rectifier failure.
A battery stores energy through a chemical process. Batteries
are rated in am ere-hours Ah . Euro ean and Asian batteries are
normally rated at the 10 hour rate (C10) while American batteries
are normally rated at the 8 hour rate (C8).
C10 example
A battery rated 1500 Ah will be able to provide 150 A of constant
current or 10 ours, 150 A x 10 = 1500 Ah
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Basic DC Sys temBasic DC Sys tem -- BatteryBattery
A lead acid battery is built up of battery cells,a lead acid battery cell is always 2V.A number of battery cells are often combined 48V battery stringin a shared container, this is referred to as a battery block.Standard battery blocks are 4V, 6V, 8V, 12V 16V.A number of battery cells or blocks are connected inseries to form a battery string.
+ -+ -
6V batter block
+ -
+ - + -
+ -
+ -2V cell + -
(2V+ +2V 2V) + - + -
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Basic DC TrainingBasic DC Training
DC system philosophies
Basic DC system build up
Basic dimensioning
Earthing
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Basic Dimens ioningBasic Dimens ioning -- Rect if ierRecti f ier
Constant power rectifiers
Customer load is 150 A @ 48 V or 7200 W
We intend to use a 2900 W rectifierNumber of rectifiers will be: 7200 / 2900 = 2.5 = 3 Rectifiers
re un ancy s norma y requ re w c means a e o a
Number of rectifiers will be 3 + 1 = 4 Rectifiers
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Basic Dimens ioningBasic Dimens ioning -- BatteryBattery
Customer load is 150 A or 7200 W and the required back up time is 2 hours
Normally two battery strings or more are required for maintenance reasons
. .
End of discharge voltage is normally 1.80 V/cell (1.80 x 24 = 43.2 V)Manufactures data sheets shall always be used when dimensioning
Constant Current Method
150 / 2 = 75A (each battery string shall back-up ~75A for 2 hours)
Constant Power Method
7200 / 2 = 3600 W (each battery string shall back-up ~3600 W for 2 hours)
3600 / 24 = 150 W/cell
E RangeData Sheet
Adobe Acrobat 7.0
Document
Data SheetClick to open
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Basic Dimens ioningBasic Dimens ioning -- BatteryBattery
From the data sheet we know that an Emerson EB4 6V200Ah battery can
ac -up;
76.7 A per string for 2 hours to final voltage 1.80 V/cell
- . .
or
146 W/cell for 2 hours to final voltage 1.80 V/cell
One string can back-up 146 x 24 = 3504 W
Two strings can back-up 3504 x 2 = 7008 W (load is 7200 W)
Use 2 x 200 Ah batteries
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Basic Dimens ioningBasic Dimens ioning DC Distr ibu t ionDC Distr ibu t ion
DC distribution sizing is done according to the loads that are going to be supplied
of its rating during normal operation (~54 V).Example;
= .
8A @ 54V = 432W => 432W @ 43.2V = 10A
Telecom loads are constant power consumers which means that the current will
increase as the voltage drops (during battery discharge).
Normal float voltage is ~54VEnd of discharge voltage is 43.2 V
54/43.2 = 1.25 = ~25% higher current at 43.2V compared with 54V
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Vo ltage dropVo ltage drop
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DC Cable SizeDC Cable Size
- Voltage drop
A=IL / (KU)
A cable area (mm2),
I total current (A)L cable length (m)K the conductivity factor. Kcopper=57.
U permissible voltage drop in the cable
For the distribution safety, the voltage drop in the cables
connecting battery and load can not exceed 3.2V.
- Current density
A= I /Jj
A----- Cable area mm2
I total current (A)Jj-------Density of economic current A/mm2
Jj = 3A/mm2 (2-3.5A/mm2)
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Basic DC TrainingBasic DC Training
DC system philosophies
Basic DC system build up
Basic dimensioning
Earthing
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EarthingEarthing
All objects within a telecom site shall be bonded together to a common point, this
common point is referred to as the MET (Main Earth Terminal). The MET shall
then be connected to the earth electrode. A site with non-conforming or
non-existent bonding will be subject to large variations in the earth plane duringlightning storms and other disturbances, which can lead to equipment failure
and/or personal injury.
Earth electrode impedance shall be in accordance with local or operator rules, butnever more an o m.
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EarthingEarthing
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Earth ingEarth ing Sing le po intSing le po int
Protective Earth
Protection of eo le and e ui ment a ainst accidents like electrical shocks
and fires caused by faulty electrical tools or equipment.
Building Earth.
Protection of buildings against damage because of thunder lightning and
potential differences.
The establishment of an accurate earth plane to be used as zero signal
reference.
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hank you
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