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What is Line Regulation？

05/20/2025

Definition: Voltage regulation (or line regulation) refers to the variation in voltage at the receiving end of a transmission line when the full load at a specified power factor is removed, with the sending-end voltage maintained constant. In simpler terms, it is the percentage change in the load-end voltage when transitioning from no-load to full-load conditions. This parameter is expressed as a fraction or percentage of the receiving-end voltage, serving as a critical metric for assessing the stability and performance of electrical power systems.

The line regulation is given by the equation shown below.

Here, ∣Vrnl​∣ represents the magnitude of the receiving-end voltage at no load, and |Vrfl| represents the magnitude of the receiving-end voltage at full load.
Line voltage regulation is influenced by the load's power factor:
  • Lagging Power Factor: The sending-end voltage exceeds the receiving-end voltage at full load, resulting in positive regulation.
  • Leading Power Factor: The receiving-end voltage becomes higher than the sending-end voltage at full load, causing the line regulation to be negative (as the receiving-end voltage rises when the load is removed).

This phenomenon underscores how reactive power flow—dictated by power factor—alters voltage distribution along the transmission line.

Line Regulation for Short Lines:
For a short transmission line, the receiving-end voltage at no load ∣Vrnl​∣ equals the sending-end voltage ∣VS​∣ (assuming no significant reactive power effects). At full load,
The simplest method for measuring line regulation involves connecting three parallel resistors to the supply. Two resistors are linked to a switch, while the third is directly connected to the supply. The resistor values are selected such that the directly connected resistor has a high resistance, whereas the other two (connected in parallel via the switch) have nominal values. A voltmeter placed in parallel with each resistor measures the voltage across each line, providing data for calculating line voltage regulation.
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Basic Physics Articles

Zhejiang Vziman Electric Group Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing, and service of power electrical equipment. Committed to innovation, quality, and customer satisfaction, it supplies smart solutions for global power sectors, covering grid construction, new energy, and industrial distribution. Core Business • Switchgear (GIS, circuit breakers, Recloser, Load break switch) • Distribution equipment (transformers, RMU, smart terminals) • Power automation systems • Engineering services (installation, maintenance, consulting) Technical Strength • Provincial R&D center, multiple patents • Modern production, ISO/GB/IEC/CE/UL certified • High capacity, large-scale delivery support Market & Vision Serves State Grid, Southern Grid, and global projects (Asia, Africa, Europe, etc.). Aims to lead in smart grids and new energy, promoting sustainable energy development.

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