Electrical Issues and Power Factor Correction

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Questions and Answers

What is one common cause of voltage sag?

Line-to-ground faults (correct)

De-energized capacitor units

Loose or isolated system neutral

High tap-setting of distribution transformer

Which of the following effects is associated with unbalanced voltage?

Shutdown of equipment due to zero-sequence relay (correct)

Improved efficiency of three-phase motors

Enhanced power factor

Increased voltage sag occurrence

How is the % voltage unbalance calculated?

(Maximum Deviation from the Average) / (Average Voltage) x 100% (correct)

(Nominal Voltage) - (Average Voltage)

(Average Voltage) / (Maximum Deviation from the Average) x 100%

(Total Voltage) / (Number of Phases)

Which solution is typically used to address voltage sag?

Increased size of conductors and transformers Signup and view all the answers

What is a potential consequence of overvoltage?

Equipment overheating Signup and view all the answers

Which of the following is NOT a cause of unbalanced voltage?

High primary voltage Signup and view all the answers

In the case of unbalanced voltage, what is one effective solution?

Load balancing Signup and view all the answers

What characterizes overvoltage?

A voltage above nominal for a duration exceeding 1 minute Signup and view all the answers

What is one of the typical effects of undervoltage?

Dropout of motor controllers Signup and view all the answers

Which of the following is a common cause of low primary supply voltage?

Loose connections on the primary Signup and view all the answers

The nominal voltage in voltage computation typically refers to what value?

An arbitrary standard value Signup and view all the answers

Which solution can be implemented to combat undervoltage issues?

Raising of transformer tapping Signup and view all the answers

What does the formula for computing voltage variation measure?

Percentage change from rated voltage Signup and view all the answers

In the context of undervoltage, what is meant by 'load splitting'?

Distributing loads across multiple sources Signup and view all the answers

What is a significant consequence of poor grounding related to undervoltage?

Loose connections and equipment malfunction Signup and view all the answers

What results from an overloaded transformer in the context of undervoltage?

Reduction in voltage levels Signup and view all the answers

What is a common cause of voltage problems in the customer's electrical facilities?

Loose connections Signup and view all the answers

How do capacitors affect the power factor in industrial and commercial systems?

They improve the power factor Signup and view all the answers

Which of the following is a solution for managing voltage mismatch in motors?

Install a special transformer Signup and view all the answers

What effect can voltage swell have on electronic devices?

Failure of electronic and computer devices Signup and view all the answers

What is one way to mitigate overvoltages caused by capacitors during off-peak periods?

Manually de-energize the capacitors Signup and view all the answers

What is a typical voltage fluctuation range in electrical systems?

95% to 105% Signup and view all the answers

Which issue can lead to unbalanced distribution of single-phase loads?

Improper load scheduling Signup and view all the answers

What type of controller can be installed to manage capacitor energization during specific times?

A power factor controller Signup and view all the answers

What is the allowable frequency variation in power quality standards?

59.7 to 60.3 Hz Signup and view all the answers

Which of the following is NOT a primary nominal voltage listed in power quality standards?

230 Volts Signup and view all the answers

What is the maximum allowable voltage Total Harmonic Distortion (THD) according to the standards?

5% Signup and view all the answers

From which perspective can power quality issues be viewed?

End-user Signup and view all the answers

What is the stated definition of a power quality problem?

Any power problem manifested in voltage, current, or frequency deviation Signup and view all the answers

What is a key concern for utility companies regarding power disturbances?

The origin and cause of power disturbances Signup and view all the answers

What is the acceptable voltage unbalance limit in power quality standards?

2.5% Signup and view all the answers

What aspect does electromagnetic compatibility NOT refer to?

Inducing significant electromagnetic disturbances Signup and view all the answers

Study Notes

Common Problems at the Customer Side

Voltage problems at the customer's end may arise from issues within their electrical facilities
Examples include loose connections, undersized/overloaded/overextended conductors, and unbalanced single-phase loads
To resolve these issues, correct the problem and consult an electrical consultant if necessary

Power Factor Correction Capacitors

Industrial and commercial customers commonly install capacitors to enhance their system's power factor
However, capacitors can elevate system voltage, possibly causing overvoltages during periods of light load or off-peak hours when continuously switched on
Solutions involve manually de-energizing capacitors during off-peak periods, or using voltage/power factor-based devices to selectively energize units during specific times of day

Voltage Mismatch

Some customer equipment, primarily motors, are rated for specific voltage levels (e.g., 220V or 440V)
Motors can function with supply voltages within a tolerance range (e.g., ±10% of their rating)
Supply voltages exceeding these ranges, although still permissible, might exceed the operating range of the equipment.
Solutions for customers include installing special transformers or voltage regulators for the equipment, and for utilities, adjusting source transformer tap settings after evaluating existing customer supply voltages

Voltage Fluctuation

Fluctuations in voltage are described as random changes normally between 95% and 105% of the nominal value
Solutions include correcting loose connections, upgrading conductors, and providing separate power sources for the problematic loads

Voltage Swell

Voltage swell is a sudden increase in voltage exceeding 1.1 pu (per-unit) for durations of less than one minute
Typical causes include line-to-ground faults and the switching on of large capacitor banks or the sudden dropping of large loads
Effects of voltage swell include device failure in electronic and computer equipment; shortened equipment lifespan; unwanted relay operations

Voltage Sag/Dip

Voltage sags (dips) are temporary reductions in voltage, usually lasting less than one minute, characterized by voltage variation between 0.1 to 0.9 of the nominal voltage
Possible causes include line-to-ground faults, the starting of high-inrush-current equipment (e.g., motors, arc furnaces), and loose connections
Typical solutions include using larger conductors and transformers, reduced voltage motor starters, and employing constant voltage transformers or UPS systems for sensitive loads

Unbalanced Voltage

Unbalanced voltage in three-phase systems can lead to overheating of motors and trigger the operation of zero-sequence relays, leading to equipment shutdown
Causes can include unbalanced secondary loads, loose connections, non-uniform transformer taps, large impedance differences between transformers, de-energized capacitor units, and single-phasing in open-wye/open-delta configurations
Load balancing and correcting loose connections are common solutions

Overvoltage

An overvoltage occurs when a voltage measurement surpasses the nominal value for longer than one minute
Possible causes include high tap settings on distribution transformers, high primary voltages, loose neutral grounding, inappropriate transformer connections, and single phasing issues in open-wye/open-delta systems

Undervoltage

Undervoltage happens when a voltage is consistently lower than the nominal value for more than a minute
Potential causes include load shifting issues, problems with connections, transformer tap settings, improper sizing of conductors, and de-energized capacitor banks
Solving this typically involves adjusting load distribution, repairing connections, adjusting transformer tap settings, and, in some cases, adding capacitors or voltage regulators

Low Primary Supply Voltage

Low primary supply voltage stems from problems on the primary side of electrical installations: loose connections, excessively long primary lines, insufficiently sized conductors, de-energized substation capacitor banks, faulty power transformers, and malfunctioning voltage regulators
Addressing the root cause of low voltage is vital

Sample Computations and Formulas

Methods for calculating voltage imbalance and variation are presented, showcasing formulas and example calculations using measured/given values and nominal voltages

Power Quality Parameters and Limits

Frequency, typical service voltage levels, voltage waveform distortion (THD), and voltage unbalance are key power quality parameters and their allowable ranges are described

Equipment and Utility Concerns

Equipment manufacturers focus on the compatibility of equipment, considering tolerance to power disturbances.
Utility concerns revolve around determining the source and effect of power disturbances, aiming for minimizing disturbances and maintaining the delivery of reliable power within the specified limits

End-User Concerns

End-users worry about how power disturbances affect their equipment operation and the overall impact on plant operations

Power Quality Problem Definition

A power quality problem is essentially any power issue affecting voltage, frequency, or current, leading to equipment malfunction or under performance

Electromagnetic Compatibility

Electromagnetic compatibility (EMC) is defined as the ability of equipment to function correctly in an electromagnetic environment without causing unacceptable disturbance in other devices

Other

A general overview of the concept of power quality and its importance in overall electrical system performance is provided

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Description

This quiz covers common electrical problems that customers may face, including voltage issues and power factor correction. It explores the impact of capacitors on system voltage and provides solutions for managing these challenges. Test your knowledge on troubleshooting and optimizing electrical systems.