Basic DC Training

8/12/2019 Basic DC Training

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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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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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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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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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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.


AC

DC

DC to LoadAC Mains


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


DC to LoadAC Mains



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


AC

DCDC to LoadAC Mains



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.


AC

DCDC to LoadAC Mains



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 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 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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Basic DC Training