1. Presented by : Jayashree Behera
Regd no : 0911013030
Electrical ‘C’

2.  Power from CPP and elements in busbar protection
 Conversion by equipments :
1. Regulating Transformer
2. Rectifying Transformer
3. Rectifier Bank
 Protection of equipments
 References

3. NALCO
The Smelter Conversion Substation receives power from
Captive Power Plant at 220KV AC. It converts the
power to DC and feeds to the Potlines for electrolysis of
Alumina(Al2O3) to Aluminium metal.

4. The conversion substation performs 3 types of transformations.
 Conversion of high Voltage(220KV) to low voltage(1.1KV).
 Conversion of AC to DC.
 Conversion of Constant Voltage input(220KV) to Constant
Current(180KA) output.
Power is transmitted to smelter from CPP by 5 transmission lines
called as incomer. Then busbar protection is done by following
equipments :
 Lightning arrestor
 Current transformer
 Potential transformer
 SF6 Circuit breaker
 Semipantograph isolator

5. 1. Regulating Transformer
 The function of Regulating transformer is to step down the
voltage from 220KV to 93KV and regulate the output
voltage according to the requirement of the Potline.
 The transformer is connected in star in both windings. It is
cooled by Oil Forced Air Forced cooling.
RADIATORS
(used for cooling purpose)

6. Breather (absorb
moisture in air).

7. 2 . Rectifying Transformer
 The variable voltage output of the Regulating
Transformer is fed to Rectifier Transformer. The
primary winding is connected in extended delta while
there are two secondary windings, one is connected in
star and other in delta.
 There is 30 phase shift between star and delta
resulting in 6phase output from 3phase input.
 It also steps down the output voltage in from 82volts
to 897volts. It is cooled by oil forced-air forced
cooling.
 Rating- 83.3MVA, 3phase, 50Hz,Connection-
Extended Delta/Star/Delta, Primary-
220KV, Secondary- 8.97KV to 92.94KV .

8. RECTIFYING TRANSFORMER
CONNECTION

9. 3. Rectifier Bank
 The output of Rectifying Transformer is fed to two
rectifying bank. Each bank is connected in 3phase full
wave bridge rectifier.
 The bank reduces ripples for smoother DC. The diodes
are cooled by air forced-water forced-air forced
cooling. RC snubber circuits are provided in both AC
and DC sides to protect the Rectifier from lightning and
switching surges.
 The output of each of rectifier banks is
33KA,1100volts. This is fed to the main DC busbar
feeding to potline.
 Rating – 33KA, 1100volts, 3phase full wave bridge
rectifier.

11. 1. Regulating Transformer
Buchholz relay (makes alarm or trips during fault conditions)

12.  Two numbers of phase-fault over-current relays and one
earth-fault over-current relay is used for phase fault and earth
fault protection.
 Under healthy condition the resultant current flowing through
the secondary grounded neutral transformer will be zero. In such
a three phase system if one of the three phases gets grounded or
earthed then unbalancing of current occurs.

13. 2 . Rectifying Transformer
- Buchholz relay
- Pressure Relief Valve
An oil pressure relief valve prevents excessive oil
pressure from developing in the engine. The oil relief
valve usually contains a spring that allows just
enough oil to bypass the system and return to the
sump or oil pan.

14. 3. Rectifier Bank
A simple SNUBBER uses a small resistor(R) in series with a small
capacitor(C). This combination can be used to suppress the rapid
rise in voltage across a thyristor, preventing the turn-on of the
thyristor.
High Rupturing Capacity (HRC) Fuse
In HRC fuse, the fuse wire or element can carry short circuit heavy
current for a known time period. During this time if the fault is
removed, then it does not blow off otherwise it blows off or
melts.

15.  Datasheets of NALCO
 Y.G.Paithankar , “Fundamentals of Power System Protection”
 V.K.Mehta , Principles of Power System
 http://wiki.answers.com/Q/What_is_the_function_of_radiator
 http://www.silicagelpacks.com/Silica-gel-breather-
function.htm
 Snubber - Wikipedia, the free encyclopedia