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Related Concept Videos

Pilot and Numeric Relaying01:21

Pilot and Numeric Relaying

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Pilot relaying is a type of differential protection used in power systems. It compares electrical quantities at the terminals of equipment via a communication channel instead of direct relay interconnection. This method is essential for transmission lines where the terminals are far apart, typically up to 80 km for lines with 69 to 115 kV ratings. Four types of communication channels are used for pilot relaying:
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Directional Relays01:25

Directional Relays

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Directional relays, essential for managing unidirectional fault currents, enhance the safety and efficiency of power systems. On power lines equipped with directional relays, faults downstream (to the right) of the current transformer typically cause the fault current to lag the bus voltage by approximately 90 degrees, known as the forward direction. In contrast, upstream (left-side) faults may result in the fault current leading the bus voltage by nearly 90 degrees, termed the reverse...
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Differential Relays01:20

Differential Relays

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Differential relays are used to protect generators, buses, and transformers by comparing electrical quantities at different points. When a fault occurs, the difference in current between the two points triggers the relay to operate, opening the circuit breaker. Under normal conditions, the current entering (i1) and leaving (i2) a generator are equal. When a fault occurs, however, these currents become unequal, and the difference current flows in the relay operating coil, causing the relay to...
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Proportional Integral (PI) controllers are a fundamental component in modern control systems, widely used to enhance performance and mitigate steady-state errors. They are particularly effective in applications such as automatic brightness adjustment on smartphones, where they excel at mitigating steady-state errors for step-function inputs. Unlike PD controllers, which require time-varying errors to function optimally, PI controllers leverage their integral component to address residual...
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Overcurrent Relays01:26

Overcurrent Relays

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Overcurrent relays, crucial for circuit protection, are connected to the secondary current of a current transformer. There are two primary types of overcurrent relays: instantaneous and time-delay.
Instantaneous overcurrent relays activate immediately when the input current exceeds a predetermined value, known as the pickup current, instantly energizing the circuit breaker trip coil. This rapid response is vital for addressing severe faults quickly.
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Line Protection with Impedance Relays01:27

Line Protection with Impedance Relays

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Coordinating time-delay overcurrent relays in complex radial systems and directional overcurrent relays in multi-source transmission loops can be challenging. Impedance relays address these issues by responding to the voltage-to-current ratio, specifically measuring the apparent impedance of a line. These relays become more sensitive during faults as current increases and voltage decreases, thereby reducing the apparent impedance.
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Related Experiment Video

Updated: Mar 13, 2026

Automated Deployment of an Internet Protocol Telephony Service on Unmanned Aerial Vehicles Using Network Functions Virtualization
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Development and Testing of a Two-UAV Communication Relay System.

Boyang Li1, Yifan Jiang2, Jingxuan Sun3

  • 1Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong, China. boyang.li@connect.polyu.hk.

Sensors (Basel, Switzerland)
|October 19, 2016
PubMed
Summary

This study developed a novel communication relay system using one quadrotor to extend the communication range for another. The system enables reliable beyond-line-of-sight (BLOS) drone operations and overcomes communication obstacles.

Keywords:
Ground Control Stationcommunication relaymission control softwaretwo-UAV system

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Area of Science:

  • Robotics and Control Systems
  • Wireless Communication Networks
  • Aerospace Engineering

Background:

  • Standard wireless modules for Unmanned Aerial Vehicles (UAVs) have limited range and are obstructed by physical barriers.
  • Effective communication is crucial for Beyond-Line-of-Sight (BLOS) UAV operations and ground control station (GCS) connectivity.
  • Existing communication solutions struggle with range limitations and signal obstruction in complex environments.

Purpose of the Study:

  • To design and evaluate a communication relay system for enhancing UAV communication range and reliability.
  • To address the limitations of conventional wireless modules in BLOS and obstacle-rich scenarios.
  • To demonstrate the feasibility of using a quadrotor as an airborne communication relay.

Main Methods:

  • Construction of quadrotor UAVs as airborne platforms.
  • Selection and integration of hardware for the communication relay system.
  • Development of software for autonomous mission control, relay control, and GCS communication.
  • In-flight and indoor testing, recording Received Signal Strength Indication (RSSI) and noise levels.

Main Results:

  • The developed system successfully extended the communication range for UAVs.
  • The relay system demonstrated effective communication establishment over obstacles.
  • Received Signal Strength Indication (RSSI) and noise measurements validated system performance in diverse scenarios.
  • Feasibility of coordinating multiple UAVs using the same relay structure was shown.

Conclusions:

  • The quadrotor-based communication relay system significantly improves UAV communication capabilities for BLOS and cross-obstacle missions.
  • The system offers a practical solution for extending drone operational range and overcoming signal blockages.
  • This approach provides a foundation for multi-UAV communication coordination and enhanced mission flexibility.