Capacitor Banks in Power Systems

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Questions and Answers

What is the primary purpose of conducting a power factor analysis in a distribution system?

  • To identify the best location for energy storage systems
  • To establish the maximum demand during peak periods
  • To determine the overall system voltage levels during low load conditions
  • To detect areas needing capacitor banks for low power factor improvement (correct)

Which type of metering system is most relevant for tracking both energy consumption and energy fed back into the grid from renewable sources?

  • Demand Meters
  • Net Metering (correct)
  • Smart Meters
  • Prepaid Meters

Which capacitor bank type allows for flexibility in operation by being turned on or off as needed?

  • Dynamically switched capacitor banks
  • Fixed capacitor banks
  • Switched banks (correct)
  • Automatic capacitor banks with controllers

What is a primary benefit gained from implementing routine maintenance for capacitor banks?

<p>Early identification of issues and reliability in power factor correction (A)</p> Signup and view all the answers

Which of the following best describes a critical aspect of the selection process for capacitor banks?

<p>The specific requirements and characteristics of the distribution system (B)</p> Signup and view all the answers

What is characterized by a phase displacement of 120º among electrical quantities?

<p>Positive sequence impedance (D)</p> Signup and view all the answers

Which type of sequence impedance is described as having no mutual impedance between components?

<p>All sequence impedances (C)</p> Signup and view all the answers

In a power system, which sequence network is primarily used for analyzing symmetrical faults?

<p>Positive sequence network (D)</p> Signup and view all the answers

How is sequence impedance calculated in a power system?

<p>By the ratio of phase sequence voltage to phase sequence current (C)</p> Signup and view all the answers

What is the role of sequence networks in power systems?

<p>To perform load flow studies and fault calculations (A)</p> Signup and view all the answers

Which sequence component is not directly analyzed when considering positive sequence impedance?

<p>Zero sequence current (A), Negative sequence current (D)</p> Signup and view all the answers

What defines the negative sequence impedance in a power system?

<p>The impedance associated with the flow of negative sequence current (D)</p> Signup and view all the answers

What is the main benefit of using symmetrical components in power system analysis?

<p>To simplify calculations of asymmetrical fault conditions (D)</p> Signup and view all the answers

What is the effect of connecting transformers in a Delta-Star configuration regarding phase voltage?

<p>Secondary phase voltage leads primary phase voltage by 30°. (B)</p> Signup and view all the answers

Which of the following connections avoids issues with unbalanced loads and third harmonics?

<p>Star-Delta connection (C)</p> Signup and view all the answers

In an open delta configuration, what percentage of load capacity is retained when one transformer is removed?

<p>58% (D)</p> Signup and view all the answers

What is the primary factor affecting the power factor of an AC circuit?

<p>Inductive nature of the circuit (B)</p> Signup and view all the answers

What happens to the current in each winding of a V-V transformer when it operates under rated load?

<p>Current increases by √3 times. (B)</p> Signup and view all the answers

What indicates a leading power factor in a circuit?

<p>Voltage lags behind current (B)</p> Signup and view all the answers

Which type of connection provides a balanced path for the circulation of third harmonics without the use of a neutral wire?

<p>Star-Delta connection (C)</p> Signup and view all the answers

What is the term for the component of current that is in phase with voltage in an AC circuit?

<p>Active component (A)</p> Signup and view all the answers

What is primarily used to neutralize the lagging reactive component of load current?

<p>Static capacitor (C)</p> Signup and view all the answers

Which statement is true regarding the voltage relationship in a Delta-Star transformer connection?

<p>Primary line voltage is equal to √3 times the secondary line voltage. (C)</p> Signup and view all the answers

What is a key disadvantage of static capacitors regarding their lifespan?

<p>Short service life ranging from 8 to 10 years (B)</p> Signup and view all the answers

How does a synchronous condenser improve power factor?

<p>By drawing a leading current (B)</p> Signup and view all the answers

What is the typical power factor value expressed in percentage that corresponds to a power factor of 0.7?

<p>70% (D)</p> Signup and view all the answers

What defines the operation of a phase advancer in relation to induction motors?

<p>It provides exciting ampere turns at slip frequency (A)</p> Signup and view all the answers

Which of the following is NOT an advantage of using static capacitors?

<p>Long service life (D)</p> Signup and view all the answers

Why is the power factor improvement important for generating stations?

<p>Increases their kWh output delivery (D)</p> Signup and view all the answers

What is one of the main drawbacks of synchronous condensers?

<p>Noisy operation (A)</p> Signup and view all the answers

What is a significant disadvantage of phase advancers when used with motors?

<p>Not economical for motors below 200 H.P. (A)</p> Signup and view all the answers

Which of the following is a method to connect capacitors for three-phase loads?

<p>In star or delta (B)</p> Signup and view all the answers

When considering installing capacitor banks, what is NOT a benefit of their installation in a distribution system?

<p>Decreases system efficiency (B)</p> Signup and view all the answers

What is the primary difference between the positive and negative sequence networks?

<p>The negative sequence network is of opposite sign compared to the positive sequence network. (D)</p> Signup and view all the answers

What happens to the voltage and current in the negative and zero sequence networks during a balanced system?

<p>Both have zero voltage at the fault point. (D)</p> Signup and view all the answers

Which of the following statements about the Delta-Delta connection is true?

<p>An open delta configuration can supply power even with one transformer failure. (D)</p> Signup and view all the answers

What is a significant disadvantage of the Delta-Delta transformer connection?

<p>There is no neutral available for grounding. (C)</p> Signup and view all the answers

What is a primary concern with the Star-Star connection regarding load conditions?

<p>The absence of a neutral can lead to severe voltage unbalance. (B)</p> Signup and view all the answers

In a three-phase transformer with a Y-Δ connection, what is the effect on the phase voltages?

<p>There is an inherent phase shift of 90º between phases. (D)</p> Signup and view all the answers

Which configuration would typically allow third harmonics to circulate effectively?

<p>Delta-Delta (Δ-Δ) connection (B)</p> Signup and view all the answers

Which sequence network is considered to have no response during a balanced system under fault conditions?

<p>Zero sequence network (A)</p> Signup and view all the answers

In the context of three-phase transformers, what is the significance of the Thevenin equivalent circuit?

<p>It simplifies analysis by replacing each sequence network with a single voltage and impedance. (C)</p> Signup and view all the answers

What phase angle separation is typically observed between the line and phase voltage in a Star-Star (Y-Y) connection?

<p>30º (D)</p> Signup and view all the answers

Flashcards

Sequence Impedance

Describes how a power system behaves during unbalanced faults, giving the impedance to different phase sequence current components.

Positive Sequence Impedance

Impedance offered to the positive sequence current, where all quantities are equal and shifted by 120 degrees.

Negative Sequence Impedance

Impedance offered to the negative sequence current, which differs from the positive sequence.

Zero Sequence Impedance

Impedance offered to zero sequence current, a component of unbalanced faults.

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Sequence Networks

Equivalent networks that represent a power system under imagined balanced conditions that consider only one phase component simultaneously.

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Positive Sequence Network

A component of sequence networks that helps analyze balanced faults and load flow studies in the power system.

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Symmetrical Components

Mathematical tools (or technique) that break down unbalanced phases into three balanced components to make fault analysis easier.

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Unbalanced Fault

An electrical fault where the three phases have different values (or magnitude).

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Positive Sequence Network

Identical to the sequence reactance/impedance network for balanced system analysis.

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Negative Sequence Network

Similar to positive sequence, but with the opposite sign of impedance.

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Zero Sequence Network

Internal fault point-free; current flow caused by fault voltage.

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Unbalanced Power System

Power system where different phases have different magnitudes (or values) due to a fault.

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Three-Phase Transformer Connections

Ways transformers are connected to handle three-phase power. Can exist on the primary and secondary sides.

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Delta-Delta Connection

Three-phase transformer connection where all windings are in Delta configuration.

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Star-Star Connection

Three-phase transformer connection where windings are in Star configurations (both sides).

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Unbalanced Load (Star-Star)

In the Star-Star connection, without a neutral, highly unbalanced load creates significant voltage imbalances.

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Thevenin's Equivalent Circuit

Simplification of a network; all components reduced to a single Voltage and Impedance (for Sequence networks).

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Sequence Networks (simplified)

Networks used to analyze power systems during an unbalanced fault.

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Delta-Star (Δ-Υ) Connection

A three-winding transformer connection where the primary line voltage equals the secondary phase voltage, and secondary voltages are shifted 30° from the primary voltages.

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Star-Delta (Υ-Δ) Connection

A three-phase transformer connection with primary line voltage √3 times the primary phase voltage, and secondary line voltage equal to the secondary phase voltage.

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Open Delta (V-V) Connection

A three-phase transformer connection using only two transformers, reducing the bank's rating to 58%.

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Power Factor

The cosine of the angle between voltage and current in an AC circuit.

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Lagging Power Factor

When circuit current lags behind the voltage, usually in inductive circuits.

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Leading Power Factor

When circuit current leads the voltage, usually in capacitive circuits.

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Power Factor Improvement

Increasing the power factor, often by adding capacitive components to offset lagging inductive loads.

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Unbalanced Load

A load where the current in each phase is of different magnitude.

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Unbalanced and third harmonics problems

Problems which can occur in a Y-Y transformer connection, and which can be solved with a solid grounded neutral, and tertiary windings

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Power Factor Impact on Transformers

Unbalanced loads will impact current flow per phase, and can lead to overloading if current is significantly increased

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Power Factor Analysis

A method to identify areas in a distribution system with low power factor and determine capacitor bank size and placement.

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Capacitor Bank Size

The amount of kilovars (kVAR) needed to improve the power factor to the desired level.

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Fixed Capacitor Bank

A continuously connected capacitor bank.

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Industrial Metering System

Systems used to track and measure energy consumption, and power quality in industrial settings.

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Smart Meter

A digital meter providing real-time data and two-way communication for residential use.

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Power Factor Improvement

Methods to increase the ratio of real power to apparent power, usually from 0.8 to 0.9 in large generators.

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Static Capacitor

Device for improving power factor by supplying leading current.

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Synchronous Condenser

Over-excited synchronous motor acting as a capacitor for power factor improvement.

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Phase Advancer

Device providing exciting current to induction motors, improving leading power factor.

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Consumer Power Factor

Ratio of real power to apparent power for a consumer’s load.

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Generating Station Power Factor

Ratio of real power to apparent power for the station's overall output.

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Capacitor Bank Installation

Connecting capacitors to a distribution system for reactive power compensation and power factor improvement.

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Lagging Power Factor

A power factor where reactive power is larger than real power.

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Leading Power Factor

A power factor where reactive power is smaller than real power

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Power Factor Importance

Improved power factor leads to savings in electricity costs and higher capacity utilization for generating stations.

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