Part 1 - Dc Power Principles Part 1.pdf

1. Introduction to Eltek
Power Systems
DC Power Principles – Part 1
P Massey
Security level: Internal use

2. Why -48Vdc?
27 July 2022
Slide 2
• Safety – Less than 60Vdc is considered as SELV (Safety Extra Low Voltage)
• Distance – Telecom equipment is powered by -48Vdc from our power systems in the exchange.
Distances between the exchange and consumers can be kilometres. Therefore -48V is considered
the best compromise for safety, distance and cable size.
• Wire corrosion – It was found in the early days that when telephone wires were run in the ground
using negative earth (+48Vdc), if there was a break in the insulation, then the copper wire would
corrode due to electrolysis. By moving the earth to the positive (-48Vdc), corrosion by electrolysis
was prevented.

3. DC Power system overview
27 July 2022
Slide 3
BATTERY
DC OUTPUT
~ =
AC INPUT
Under normal conditions the power system provides DC power
to the load and charges the batteries.

4. 27 July 2022
Slide 4
DC Power system overview
BATTERY
DC OUTPUT
~ =
When the AC mains fails, the battery discharges and supplies
the load.
AC INPUT
X

5. DC Power system overview
27 July 2022
Slide 5
BATTERY
DC OUTPUT
~ =
AC INPUT
Under normal conditions the power system provides DC power
to the load and charges the batteries.

6. DC Power system overview
27 July 2022
Slide 6
BATTERY
DC OUTPUT
~ =
AC INPUT
The system also filters out noise and disturbances from the AC
mains.
~
~
~

7. DC Power system overview
27 July 2022
Slide 7
BATTERY
DC OUTPUT
~ =
AC INPUT
The system also monitors and controls the power output and
provides alarms to external monitoring systems

8. Types of converters
27 July 2022
Slide 8
DC OUTPUT
AC INPUT
RECTIFIER
~ = Converts AC into DC
DC/DC CONVERTER
DC OUTPUT
DC INPUT
= =
Converts one DC voltage to
another DC voltage
INVERTER
AC OUTPUT
DC INPUT
= ~ Converts DC into AC

9. Components of a UPS
27 July 2022
Slide 9
A DC UPS is made up of :-
- A rectifier
- A battery
For a AC UPS we add an inverter
Battery
DC
UPS
AC INPUT
~ =
AC OUTPUT
= ~

10. Types of converters
27 July 2022
Slide 10
BATTERY
DC OUTPUT
AC OUTPUT
=
~
~
AC INPUT
Rectiverter – Combines the functions of a rectifier and an inverter
in one. Under normal conditions the rectiverter supplies the AC
and DC output and also charges the battery.

11. Types of converters
27 July 2022
Slide 11
BATTERY
DC OUTPUT
AC OUTPUT
=
~
~
AC INPUT
Rectiverter – When the AC mains fails the battery supplies the
DC load and the rectiverter which then converts the DC to AC
to continually supply the AC load.
X

12. DC power system components
27 July 2022
Slide 12
G
DIESEL
GENERATOR
AC Input
AC Input: Typically AC Mains between 110-480V, However other sources of supply can include
generators ,UPS etc.

13. DC power system components
27 July 2022
Slide 13
OVP
MAINS
FUSES
Input Protection: Can be provided by either fuses, breakers or other such devices.
G
DIESEL
GENERATOR
AC Input

14. DC power system components
27 July 2022
Slide 14
OVP
MAINS
FUSES
G
DIESEL
GENERATOR
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
Rectifier: A power supply which converts Alternating Current to Direct Current; typically for
Telecoms output below 60V

15. DC power system components
27 July 2022
Slide 15
OVP
MAINS
FUSES
G
DIESEL
GENERATOR
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
CONTROLLER
Monitor & Control unit (Controller): Monitors the system and generates alarms if an event occurs and
can control the charging of the batteries. outside of normal operation.

16. DC power system components
27 July 2022
Slide 16
OVP
MAINS
FUSES
G
DIESEL
GENERATOR
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
CONTROLLER
BATTERY
STRING
BATTERY
STRING
Battery Bank/String: A battery bank is 1 or more strings. A battery string is a number of batteries
connected in series to provide the required operating voltage.

17. DC power system components
27 July 2022
Slide 17
OVP
MAINS
FUSES
G
DIESEL
GENERATOR
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
CONTROLLER
BATTERY
STRING
BATTERY
STRING
LVBD
Low Voltage Battery Disconnect: To prevent deep discharging of the batteries. Operated by the
controller when a user-configured low battery voltage point is reached.

18. DC power system components
27 July 2022
Slide 18
OVP
MAINS
FUSES
G
DIESEL
GENERATOR
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
CONTROLLER
BATTERY
STRING
BATTERY
STRING
LVBD
LVLD
Low Voltage Load Disconnect: Reduces the drain on the batteries by non-priority loads. Operated
by the controller when a user defined low battery voltage point is reached.

19. DC power system components
27 July 2022
Slide 19
OVP
MAINS
FUSES
G
DIESEL
GENERATOR
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
CONTROLLER
BATTERY
STRING
BATTERY
STRING
LVBD
LVLD
BATTERY
DISTRIBUTION
Distribution: System hardware for distributing the DC power to the load. Hardware can include;
battery breakers, MCB’s or blade fuses.

20. DC power system components
27 July 2022
Slide 20
OVP
MAINS
FUSES
G
DIESEL
GENERATOR
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
CONTROLLER
BATTERY
STRING
BATTERY
STRING
LVBD
LVLD
BATTERY
DISTRIBUTION
NON -
PRIORITY
LOAD
PRIORITY
LOAD
Load - Any equipment connected to the output distribution of the DC system.

21. DC power system components
27 July 2022
Slide 21
OVP
MAINS
FUSES
G
AC Input
Rectifier
#1
Rectifier
#2
Rectifier
#n
REDUNDANT
RECTIFIER
SYSTEM
AC/DC
Rectifier
#n
CONTROLLER
DIESEL
GENERATOR
NON -
PRIORITY
LOAD
LVBD
BATTERY
DISTRIBUTION
BATTERY
STRING
LVLD
PRIORITY
LOAD
BATTERY
STRING
Complete system - However some components such as LVLD for example, are optional.

22. Experience the power.
Experience the power.
Experience the power.