LINKS VOLTAGE LIMITS LINE CHARGE MVAR SURVIVAL POWER LINE CURRENTS AUX POWER
Permissible Voltage Limits Max permissible Voltage at the far end of lines normally kept energized from one end Voltage Under Normal Condition Nominal (kV) Max Min kV 148 132 145 120 245 220 245 200 420 420 360 400 735/765 800 700 800
Line Charging MVAR Voltage Conductor used Line Charging MVAR 800kv Class Four Bersimis 2.91MVAR/km 400kV Twin Moose 0.555MVAR/km 220kV Zebra 0.135MVAR/km
Approximate Voltage rise at Recieving end per 100km of uncompensated line 0.75 kV for 132kV S/C panther 1.5 kV for 220kV S/C Zebra 3.0kV for 400kV Twin Moose Approx. Fault Contribution at HV Bus of GT by:- 60 MW ( Hydro) 280 MVA 120 MW (Thermal) 490 MVA 210 MW (Thermal) 735 MVA 500 MW (Thermal) 1800 MVA Approx. %Voltage rise/fall at a bus due to removal/addition of a reactor of cap. dQ MVAR = dQ*100 / Fault MVA of the Bus 300 MVAR INJECTION ON A 5000 MVA BUS WOULD CAUSE A 24 KV RISE!
Some Important and Useful Thumb Rules Approx. Line Charging MVAR 132kV Panther: 5 MVAR/100km/ckt 220kV Zebra : 14 MVAR/100km/ckt 400kV Twin Moose: 55 MVAR/100km/ckt Approx. Line Current 132kV: 4.4 A/MVA 220kV: 2.6 A/MVA 400kV: 1.4 A/MVA Approx. Voltage drop per 100kM per 100Amp flow at 0.9 p.f. Lag 5 kV for 132kv S/C Uncompensated Line 3 kV for 220kV S/C Uncompensated Line 1.5kV for 400kV S/C Uncompensated Line
SURVIVAL POWER REQUIREMENT • The survival power requirement of 120 MW unit is of the order of 250-350 KW while the requirement of 210 MW unit is of the order of 350-500 KW and for 500 MW unit, it is in the order of 1250-1500 KW. As a general rule, the survival power requirement would be around 0.25- 0.30% of the unit capacity.
AUXILLARY REQUIREMENT • The start up power is the power required for the auxiliaries while the generating unit is restored. The requirement of start up power by various units is as follows : • Nuclear & Thermal: 7 to 8% of the unit capacity • Hydro : 0.5 to 1% of the unit capacity • Gas : 1.5 to 2%of the unit capacity • The start up power requirement for starting the thermal units is considerably high as the major auxiliaries like BFP, ID Fan. FD fan, CW pumps etc. are of bigger size and the starting torque is considerable. In case of hydro units, the requirement of start-up power is not significant as there are very few auxiliaries.