PPT ON DC SUPPLY SYSTEM

CLICK HERE TO DOWNLOAD PPT ON DC Supply System

DC Supply System   Presentation Transcript

1.DC Supply System

2.Presentation outline
Duties
DC Loads
DC system
Types of Batteries

3.DC SYSTEM IS DESIGNED
TO SUPPLY HIGH STANDARD OF RELIABLE & SECURE DC POWER
TO PROVIDE CONTINUOUS & QUALITY POWER AS AND WHEN REQUIRED
UNDER NORMAL & ABNORMAL OPERATING CONDITIONS
ULTIMATE & FINAL DC BACK-UP POWER TO EQUIPMENT AND DC DRIVES WHEN TOTAL AC SUPPLY FAILS
HENCE THEY ARE BATTERY BACKED

4.DUTIES
TO SUPPLY EQUIPMENT WHICH REQUIRES DC DURING NORMAL CONDITIONS
TO SUPPLY STANDBY EQUIPMENT/DC DRIVES
TO SUPPLY STARTERS OF VARIOUS EQUIPMENT
TO SUPPLY EQUIPMENT WHEN AC SUPPLIES HAVE BEEN LOST

5.Types of Power Supplies In a Power Plant
11KV/3.3KV/415V AC Power Supply
415V AC Emergency Supply(DG)
DC Power Supply
UPS Supply

6.DC Power Supply
Various Critical Drives
Emergency DC Lighting
Switchgear Control Supply for closing & tripping
Control, Protection And Interlocks
Indication, Annunciation & Alarm System
Public Address System
DAS And Communication System

7.DC Supplies……………Why?
Emergency Lube Oil Pump
  Emergency Jacking Oil Pump
  Emergency Scanner Air Fan
  Emergency Seal Oil Pump
  Breaker/Unit Protections
   Emergency Lighting

8.The Ultimate Backup
In case of unit tripping / grid failure, either station changeover takes place / DG would start.
Normally, grid supply would be restored in minimum possible time and DG would shut down.
In case of DG failure, the DC backup comes in to service to facilitate safe shut down.

9.Selection of voltage -DC POWER SUPPLY
In power plant D.C. pumps, lighting require comparatively high voltage due to their high power requirement. Hence as a standard these applications are designed with 220V level.
It is desirable to have comparatively lower voltage- 24V/48V/110V for control/indications/annunciation due to safety reasons. However to avoid multiplicity of DC supplies (particularly we require two control supplies), we have adopted uniform 220V DC voltage for plant electrical systems for switchgear control, protection and interlock operation.

10.DC POWER SUPPLY SCHEME
Earlier concept;
1X100% battery bank along with its chargers for each unit with inter-unit interconnection through high capacity DC bus bar.
In view of large size of above DC loads of each unit and the large unit pitch it is necessary to provide a separate DC system (battery +chargers) to enhance the plant’s overall reliability.
2) Present concept;
In view of the reasons explained above 2x100% capacity DC system is provided for each unit and switchyard separately.
Minor DC loads of offsite areas in the plant i.e. WTP, Ash handling are fed from plant DC system as it is now restricted to limited area switchgear rooms

11.DC System
Battery
Battery Charger

12.DC SYSTEM
BATTERY CHARGERS [TWO/THREE]
BATTERY BANKS [ONE/TWO]
DC DISTRIBUTION BOARDS [ONE/TWO]
DC FUSE BOARDS
CHARGER TROUBLE, DC EARTH FAULT AND DC VOLTAGE ABNORMAL ALARMS IN UCB

13.220 V Supplies

14.Battery Capacity
Expressed in ampere hour(AH)
Duration of discharge-10 hr for Plante/5 hr for Ni-Cd
End cell voltage-1.85 volt for Lead acid plante/1.0 volt for Ni-Cd
Ambient temperature-27 deg cent.
Electrolyte specific gravity-1.2+-.005 lead acid plante cells

15.SELECTION OF BATTERY TYPE IN POWER PLANT
Power plant batteries standby duty  require high discharge performance with continuously connected on float mode operation.
Expected Life of lead acid tubular is of the order of 8-10 years so in a power plant life of 25 years minimum two replacement would be required.
Lead acid PLANTE and Ni-Cd (alkaline) have expected life of 15-20 years hence only one replacement would be required in whole plant life.
In addition lead acid plante have much better discharge performance than tubular type for the specified emergency duration.
In view of above plante type lead acid or  Ni-Cd high discharge batteries are specified for  power plant applications.