Power System Parameters
When current flows in a transmission line, the characteristics exhibited are explained in terms of magnetic and electric field interaction. The phenomena that results from field interactions is represented by circuit elements or parameters. A transmission line consists of four parameters which directly affect its ability to transfer power efficiently.
These elements are combined to form an equivalent circuit representation of the transmission line which can be used to determine some of the transmission losses. The parameter associated with the dielectric losses that occur is represented as a shunt conductance.
Conductance from line to line or a line to ground accounts for losses which occur due to the leakage current at the cable insulation and the insulators between overhead lines. The conductance of the line is affected by many unpredictable factors, such as atmospheric pressure, and is not uniformly distributed along the line.
The influence of these factors does not allow for accurate measurements of conductance values. Fortunately, the leakage in the overhead lines is
negligible, even in detailed transient analysis. This fact allows this parameter to be completely neglected.
It directly follows that the losses due to the line resistance can be substantially lowered by raising the transmission voltage level, but there is a limit at which the cost of the transformers insulators will exceed the savings.
The efficiency of a transmission line is defined as:
η = PR / PS = PR / (PR + PLoss)
- PR is the load power and
- PLoss is the net sum of the power lost in the transmission system
As the transmission dissipates power in the form of heat energy, the resistance value of the line changes. The line resistance will vary, subject to maximum and minimum constraints. in a linear fashion.
If we let R1 be the resistance at some temperature, T1, and R2 be the resistance at time T2, then:
R2 = R1 × ((235 + T2) / (235 + T1))
The capacitive reactance of a transmission line comes about due to the interaction between the electric fields from conductor to conductor and from conductor to ground. The alternating voltages transmitted on the conductors causes the charge present at any point along the line to increase and decrease with the instantaneous changes in the voltages between conductors or the conductors and ground.
This flow of charge is known as charging current and is present even when the transmission line is terminated by an open circuit.
|Title:||Losses in the transmission system and ways to reduce them – E. Benedict, T. Collins, D. Gotham, S. Hoffman, D. Karipides, S. Pekarek, and R. Ramabhadran|
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