435.6 MW

CONCEPT

The maximum power transfer capacity of the transmission line is given by

Where,

|Vs| is sending end voltage of transmission line

|Vr| is receiving end voltage of transmission line

X is the series reactance of transmission line

Calculation:

Given 

V_s = V_r = 132 kV

X = 40 Ω

The capacity of the line P

P = (132 × 10³)² / 40 = 435.6 MW

Therefore, the capacity of the line is 435.6 MW

Greater than natural load

Economic load dispatch:

• The economic load dispatch means the real and reactive power of the generator varies within certain limits and fulfills the load demand with less fuel cost.
• The economic load dispatch problem involves two separate steps: the unit commitment and the online load dispatch.
• The unit commitment selects that unit that will anticipate the load of the system over the required period at minimum cost.
• In unit commitment, the criterion for the most economical division of load within a plant is that all the units must operate at the same incremental fuel cost. 
• The online load dispatch distributes the load among the generating unit which is parallel to the system in such a manner as to reduce the total cost of supplying.
• While supplying power, the most economic load on an overhead line is greater than the natural load.

Differential relay:

• Differential relay operation depends on the phase difference of two or more electrical quantities.
• It works on the principle of comparison between the phase angle and the magnitude of the same electrical quantities.
• The differential relay is used for the protection of the feeder, large busbars, etc.

Differential protection for feeders consist of

1) Voltage balance differential relay

2) Current balance differential relay

NOTE:-

Generally Translay relay is used for feeder protection

• The translay relay is a differential relay
• The arrangement is similar to overcurrent relay, but the secondary winding is not closed on itself
• These types of relays are used in the feeder protection and the scheme is called Translay scheme
• In this scheme, two such relays are employed at the two ends of feeder as shown in the Fig

• The secondaries of the two relays are connected to each other using pilot wires
• The connection is such that the voltages induced in the two secondaries oppose each other
• The copper coils are used to compensate the effect of pilot wire capacitance currents and unbalance between two currents transformers
• Under normal operating conditions, the current at the two ends of the feeder is same
• The primaries of the two relays carry the same currents inducing the same voltage in the secondaries
• As these two voltages are in opposition, no current flows through the two secondaries circuits and no torque is exerted on the discs of both the relays
• When the fault occurs, the currents at the two ends of the feeder are different, hence unequal voltages are induced in the secondaries
• Hence the circulating current flows in the secondary circuit causing torque to be exerted on the disc of each relay
• But as the secondaries are in opposition, hence torque in one relay operates to close the trip circuit while in other relay the torque just holds the movement in unoperated position
• The care is taken that at least one relay operates under the fault condition