Presented by : Jayashree Behera Regd no : 0911013030 Electrical ‘C’
Power from CPP and elements in busbar protection Conversion by equipments : 1. Regulating Transformer 2. Rectifying Transformer 3. Rectifier Bank Protection of equipments References
NALCOThe Smelter Conversion Substation receives power fromCaptive Power Plant at 220KV AC. It converts thepower to DC and feeds to the Potlines for electrolysis ofAlumina(Al2O3) to Aluminium metal.
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
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)
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 .
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.
1. Regulating TransformerBuchholz relay (makes alarm or trips during fault conditions)
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.
2 . Rectifying Transformer- Buchholz relay- Pressure Relief ValveAn oil pressure relief valve prevents excessive oilpressure from developing in the engine. The oil reliefvalve usually contains a spring that allows justenough oil to bypass the system and return to thesump or oil pan.
3. Rectifier BankA 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) FuseIn 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.
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