Power stations generate electric power. Electrical power transmission lines transmit the generated power to far places. The resistance and reactance of the line cause a voltage drop in the power. The Voltage Regulation of Transmission Line is the change in voltage between the sending and receiving ends.
What is Voltage Regulation?
We express the Voltage Regulation as the change in receiving-end voltage from no-load to full-load condition. We represent it as a percentage of full-load voltage.
When a line does not carry any load, the voltage at the receiving end is almost equal to the sending-end voltage. (Here, we have considered that there is no charging current in the transmission line. Although in a practical line there is a capacitive charging current even when the load is not connected to the line.) However, when the load is connected, the current starts flowing through the line. The transmission line has its own impedance. So, the voltage drops due to that impedance. As a result, the voltage at the receiving end decreases.
Mathematically, it is given by:\[\text{Voltage Regulation} = \frac{V_s – V_r}{V_r} \times 100\%\] where, \(V_s\) = Sending end voltage, \(V_r\) = Receiving end voltage at full load. A good transmission line should have low voltage regulation. In other words, the voltage drop between the sending and receiving ends should be small.
Importance of Voltage Regulation of Transmission Line
Voltage Regulation of Transmission Line is a very important factor. It is essential for maintaining a stable voltage at the consumer ends. If the regulation is high, the voltage at the consumer end will fall when the load increases. We normally refer to the high voltage regulation as poor voltage regulation. Poor regulation can cause poor performance of electrical equipment. Therefore, engineers always design transmission lines with proper regulation. Meaning they try to maintain the voltage at the receiving end nearly constant under different loading conditions.
Expression for Voltage Regulation
First, we consider a short transmission line. Here, we can neglect the line capacitance. Now, we can write the relation between sending and receiving end voltages as \[V_s = V_r + I (R + jX)\]Also, we can expand the phasor equation to find the magnitude of sending-end voltage: \[|V_s| = \sqrt{(V_r \cos \phi + IR)^2 + (V_r \sin \phi + IX)^2}\]Where,
- \(I\)= Load current,
- \(R\) = Resistance of line,
- \(X\) = Reactance of line,
- \(\phi\) = Load power factor angle.
Then, Voltage Regulation of Transmission Line is \[\text{Voltage Regulation} = \frac{|V_s| – V_r}{V_r} \times 100\%\]
This formula helps in calculating the voltage drop for given line parameters and load conditions.
Factors Affecting Voltage Regulation of Transmission Line
Many factors affect the Voltage Regulation of Transmission Line. There are four most important factors.
- Line Impedance: All transmission lines have resistance R and reactance X. The voltage drop depends on both. Higher R and X cause a higher voltage drop.
- Power Factor of Load: The power factor of the load greatly affects the regulation. For a lagging power factor (inductive load), the voltage drop increases. For the leading power factor (capacitive load), the voltage drop decreases. Sometimes, the voltage at the receiving end becomes higher than the sending end.
- Length of Transmission Line: As the line length increases, the voltage drop also increases. Because long transmission lines have higher impedance.
- Current Flow: The voltage drop increases with current. When the load current increases, the regulation becomes poorer.
Voltage Regulation in Different Power Factors
The value of Voltage Regulation of Transmission Line changes with the nature of the load.
- Lagging Power Factor (Inductive Load): Voltage drop increases because current lags behind voltage. Hence, voltage regulation becomes positive.
- Unity Power Factor (Purely Resistive Load): Voltage drop is smaller, and regulation has a moderate value.
- Leading Power Factor (Capacitive Load): Voltage at the receiving end may rise instead of drop. In this case, regulation becomes negative.
Thus, the load power factor has a strong influence on the regulation value.
Methods to Improve Voltage Regulation
Good regulation ensures the stable operation of transmission systems. It increases the efficiency of the transmission system. We can improve Voltage Regulation of Transmission Line using the following methods
- Use of Capacitors or Reactors: We can install shunt capacitor banks for lagging loads. Also, we can install shunt reactors for leading loads. Obviously, these balance the reactive power and reduce voltage drop.
- Voltage Compensating Devices: We can use devices like tap-changing transformers and automatic voltage regulators to adjust voltage according to load variations.
- Increase in Conductor Size: We can use thicker conductors. A thicker conductor reduces resistance and reactance, which minimizes voltage drop.
- Power Factor Improvement: Also, we use power factor correction capacitors to improve the load power factor near unity. This reduces voltage regulation.
By combining these methods, engineers can achieve better voltage stability in transmission systems.
Significance in Power System Operation
Voltage Regulation of Transmission Line directly affects the performance of power systems. On the other hand, good regulation keeps the system voltage within permissible limits even when load changes suddenly. Thus, proper design, regular testing, and control equipment are essential for maintaining efficient transmission and a reliable power supply to consumers.