8.10
Lijnverlies
De verschillende configuraties van bron-belastingverbindingen omvatten Y- (ster)- en delta-verbindingen. De relatie tussen lijn- en fasespanningen en…
Consider a balanced three-wire Y-to-Y circuit represented in the time domain, which can be transformed into a per-phase equivalent circuit.
First, the line current is determined, followed by the phase voltage at the load.
Then, the power delivered by the source is determined using the effective values of the sinusoidal phase voltage and line current.
Next, the power delivered to the load is calculated using the line current and the load resistance.
The power lost in the line is obtained using the line current and the line resistance.
Then, the total power delivered by the three-phase source, the total power received by the three-phase load, and the total power lost in the lines are determined.
A high percentage of power is lost in the line, which can be reduced by minimizing the line current.
However, this would reduce the load current, which would in turn decrease the power delivered to the load.
One way to reduce the line current without affecting the load current is to introduce transformers in the three-phase circuit.
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Q1: How is line loss calculated in a balanced three-phase circuit?
Line loss for each wire is calculated by squaring the line current and multiplying it by the line's resistance. For balanced three-phase systems, this calculation is multiplied by three to account for all three phases. The total line loss represents power absorbed by the transmission wires during power distribution in three phase and single phase circuits.
Q2: What factors affect the amount of power lost in transmission lines?
Line loss is directly proportional to conductor length and inversely proportional to the conductor's cross-sectional area. Line resistance depends on material resistivity, conductor length, and cross-sectional area. Increasing the conductor's cross-sectional area or reducing line length minimizes power loss during transmission.
Q3: Why does reducing line current help minimize power loss without affecting load power?
Line loss depends on the square of line current, so even small reductions significantly decrease power loss. Transformers can reduce line current while maintaining the same load current and power delivered to the load. This allows power companies to transmit energy efficiently over long distances without compromising load power delivery.
Q4: How does voltage transmission strategy reduce line losses?
Power companies transmit power at higher voltages to reduce line losses. Since power equals voltage multiplied by current, increasing voltage allows current to decrease for the same power level. Lower current dramatically reduces line losses because loss is proportional to the square of current.
Q5: What is the relationship between line current and power loss in three-phase systems?
Power loss in transmission lines is proportional to the square of the line current multiplied by line resistance. A high percentage of power can be lost in lines when current is large. Minimizing line current is the most effective strategy for reducing power loss in three-phase transmission systems.
Q6: How does a per-phase equivalent circuit help analyze line loss?
The per-phase equivalent circuit simplifies analysis of balanced three-phase systems by allowing engineers to examine just one phase. This symmetry-based approach enables straightforward calculation of line current, phase voltage, and power loss. Results from one phase are then multiplied by three to determine total system performance.
Q7: What is the trade-off between reducing line current and maintaining load power?
Directly reducing line current decreases load current, which reduces power delivered to the load. Transformers solve this problem by reducing line current while preserving load current and power. This allows power companies to minimize transmission losses without sacrificing the power available to consumers.