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Related Concept Videos

Zones of Protection01:16

Zones of Protection

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In power systems, the entire setup is divided into protective zones to isolate faults and protect the rest of the network. These zones include generators, transformers, buses, transmission lines, distribution lines, and motors. Each zone can be visualized as a separate room in a house, with each room protected by its own circuit breaker.
Protective zones are defined by closed dashed lines, containing one or more components. A key characteristic of these zones is the strategic placement of...
300
Fault Types01:18

Fault Types

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When analyzing a single line-to-ground fault from phase A to ground at a three-phase bus, it is important to consider the fault impedance. This impedance is zero for a bolted fault, equal to the arc impedance for an arcing fault, and represents the total fault impedance for a transmission-line insulator flashover. To derive sequence and phase currents, fault conditions are translated from the phase domain to the sequence domain.
For line-to-line faults occurring between phases B and C, the...
119
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.
Under normal conditions, low load currents keep the measured...
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Heating and Cooling Curves02:44

Heating and Cooling Curves

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When a substance—isolated from its environment—is subjected to heat changes, corresponding changes in temperature and phase of the substance is observed; this is graphically represented by heating and cooling curves.
For instance, the addition of heat raises the temperature of a solid; the amount of heat absorbed depends on the heat capacity of the solid (q = mcsolidΔT). According to thermochemistry, the relation between the amount of heat absorbed or released by a substance, q, and its...
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Multimachine Stability01:25

Multimachine Stability

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Multimachine stability analysis is crucial for understanding the dynamics and stability of power systems with multiple synchronous machines. The objective is to solve the swing equations for a network of M machines connected to an N-bus power system.
In analyzing the system, the nodal equations represent the relationship between bus voltages, machine voltages, and machine currents. The nodal equation is given by:
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Power System Three-Phase Short Circuits01:21

Power System Three-Phase Short Circuits

140
Determining the subtransient fault current in a power system involves representing transformers by their leakage reactances, transmission lines by their equivalent series reactances, and synchronous machines as constant voltage sources behind their subtransient reactances. In this analysis, certain elements are excluded, such as winding resistances, series resistances, shunt admittances, delta-Y phase shifts, armature resistance, saturation, saliency, non-rotating impedance loads, and small...
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Related Experiment Video

Updated: Aug 30, 2025

Design and Application of a Fault Detection Method Based on Adaptive Filters and Rotational Speed Estimation for an Electro-Hydrostatic Actuator
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A holistic sequential fault detection and diagnostics framework for multiple zone variable air volume air handling

Narges Torabi1, Huseyin Burak Gunay1, William O'Brien1

  • 1Department of Civil and Environmental Engineering, Carleton University, Ottawa, ON, Canada.

Building Services Engineering Research & Technology : BSER & T
|September 2, 2022
PubMed
Summary

This study introduces a hierarchical fault detection and diagnostics (FDD) framework for air handling unit (AHU) and variable air volume (VAV) systems. It prioritizes system-level and hard faults to accurately identify root causes and minimize false alarms in commercial buildings.

Keywords:
Fault detection and diagnosticshard faultshierarchical frameworkmultiple-zone VAV AHU systemssequencing logic faults

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Area of Science:

  • Building Systems Engineering
  • Fault Detection and Diagnostics
  • HVAC Systems

Background:

  • Existing fault detection and diagnostics (FDD) methods often overlook system- and zone-level fault dependencies.
  • This limitation can lead to false alarms and masked faults in complex HVAC systems.
  • A holistic approach is needed to address interactions between system- and zone-level devices.

Purpose of the Study:

  • To propose a holistic hierarchical framework for FDD in Variable Air Volume (VAV) Air Handling Unit (AHU) systems.
  • To integrate the detection and diagnosis of control hardware and sequencing logic faults.
  • To address detectability and significance issues in FDD for VAV AHU systems.

Main Methods:

  • Developed a sequential hierarchical FDD framework prioritizing hard faults over sequencing logic faults.
  • Prioritized system-level faults over zone-level faults for accurate root cause isolation.
  • Fault detection achieved by visualizing discrepancies between expected and measured operational behavior of AHUs and VAV boxes.

Main Results:

  • The framework successfully diagnoses faults by addressing hard faults in AHUs, hard faults in VAV zones, sequencing logic faults in AHUs, and sequencing logic faults in VAV zones.
  • Demonstrated effectiveness using data from 10 different VAV AHU systems.
  • The method helps facilities management experts identify and rectify faults on-site.

Conclusions:

  • The proposed hierarchical FDD framework effectively detects and diagnoses faults in VAV AHU systems.
  • Prioritizing fault types and levels enhances accuracy and significance in fault management.
  • Visualizing operational biases provides actionable insights for facilities management.