Posted: June 25th, 2022

NNM7005 Power Quality And Harmonics

Question:

Demonstrate deep understanding of voltage-sag calculations, and also describe five short problems.

Answer:

How can we effectively calculate the Dip Duration of Voltage Sag?

It is more difficult to measure the sag length than it appears to be for the rest of the world.

The sag duration can be recorded, which is easy enough. However, it is difficult to determine the sag duration using the automated way to monitor power quality.

Although the threshold values will vary for each monitor, the most common values are close to 90% of the normal voltage (Deepa & Rajapandian 2010, 2010).

The power quality monitor calculates the rms value for every cycle.

Although the post fault sag may last for several seconds, it is not as long as the original sag.

The sag duration should not exceed the time it takes to clear fault.

The distribution system’s main protection is simply pass the current protection technique. This requires a certain amount of time grading to increase the fault clearing time. However, there is often an exception in the whole system where the current limiting fuse is used for better functioning.

How to Accurately Calculate the Dip Magnitude Of Voltage Sg?

The rms value is used to determine the magnitude of the voltage-sag determination. Therefore, the rms is calculated in a sliding one cycle window.

The finite measurement of the window is what causes the voltage. This is often used to calculate the rms value.

Because the process of sagging is not constant, the value of rms can be calculated during the sag. Also, the voltage doesn’t immediately recover from faults.

The rms voltage can be used to calculate the magnitude of the sag (“Effects on Transformer Connection on Voltage Sag Characterization” 2016).

The event’s power quality determines the power consumption of the monitors. Normally, the sags will have a constant rms value. This is usually the deepest part of the sag.

How to Calculate the Phase Angle Jump

A short circuit occurs in the power system. This is not only in the case where the voltage sag happens, but it also affects the phase angle.

A phase angle jump is a sudden change in the phase angle.

The phase angle jump at the PCC will not occur if the impedance of the source and feeder is equal.

This holds true for fault transfer in transmission systems, as faults in these are usually not responsible for faults in the distribution system. (Heffernan, Watson, & Watson, 2014.

These analyses can be quite complex for voltage sag if there are multiple unsymmetrical faults.

Unsymmetrical faults can lead to a single phase load experience with a phase angle jump equal to the X/R of the source or feeder impedance.

Explain the Preparation Of Voltage Dip Coordinating Chart

It is essential that all customers have a good knowledge of the equivalent system, or immunity process for voltage dips. This will allow them to make the most of the magnitude plot.

These can be plotted for different voltage dip magnitudes to create the voltage tolerance curve, which highlights the customers’ immunity to voltage dips (Jowder 2009).

According to the magnitude duration window, the rectangle represents the community. It starts at the bottom right corner.

Equipment is most likely to suffer severe damage from the events that fall within the rectangle. Those that occur outside the rectangle are safe.

The voltage tolerance curve provides more detailed information about the creation and interpretation.

Describe How the Graphical Presentation of Calculation Results Is Made For Voltage Dip

The graphical presentation of all calculated dips is not enough to give a complete picture of the voltage dip situation.

Mat lab analysis software can be used to create scatter plots, as well as other voltage dip density charts and voltage dip coordination charts (Martinez, & MartinArnedo 2006).

Simply by using the voltage tolerance curve, the voltage dip coordination chart can be used to estimate the severity of a dip situation for many customers.

The cumulative chart and voltage dip density charts can be used to create a visual representation of power quality according to the requirements.

What is Voltage Sag?

The term voltage sag refers to a reduction in rms current for a short time. This can easily be caused by overloading the electric motors, or short circuits.

Voltage sag is a condition in which the rms voltage drops from 10 to 90% of its normal voltage for longer than one-half cycles. This is roughly one minute (Md.

There are many references that describe the length of the sag, from the point half cycle to a few seconds to the longer duration of low voltage sections that are known as sustained sag.

What causes Voltage Sag?

Voltage swag can be caused by a variety of factors, including motor starting, electrical heaters when turned on, short circuit, or an increase in impedance. This is usually caused by loose connections.

Voltage swells can be caused by a sudden decrease in circuit load, and this is also due to a poor or damaged voltage regulator (Shamsul Azim Zulkifli. 2005).

Voltage swag may also be caused by natural loose connections or damage.

What are the Different Factors That Affect Voltage Sag?

Many factors can affect the voltage sag and swell.

Below are the key factors responsible for the process.

The tolerances of the Power Distributor are not appropriate for sensitive voltage equipment.

All three layers of the layered phase system are subject to unbalanced loads

The transformer is located at a long distance with interposed loading.

Remote rural location away from power source (T, & M,2015)

Grid system that is not reliable

Inaccessible equipments are not available in the area.

Switching the Heavy Loads

What are the Different Methods of Dealing with The Voltage Sag Phenomenon

There are many ways to deal with the sags or swells. All the factors that support each method are discussed below.

The constant voltage transformer is also known as ferroresonant.

Transformer that includes a tap changer

Large loads can be connected to the point of coupling

Equipment should be selected with dip resiience

Massive electronic equipments with soft starters (Tanaka & Sakashita 2010, 2010).

Switch mode power supply

Voltage stabilizer with servo-controlled

Economic Implications Does Voltage Sag have?

Modern business environments require that all equipment used must be resilient to supply defects. In this instance, the equipment will be removed from the shelves.

This is the best way to reduce the cost of correction.

Although some equipment manufacturers can recognize the problem, it is not common for them to do so in today’s highly competitive market.

Refer to

Voltage Sag Characterization: Effects of Transformer Connectivity

Performance of heat-pump: Voltage dip/sag. Under-voltage. Over-voltage.

The Journal Of Engineering.

Analysis and design of a dynamic voltage restorer to compensate for harmonic compensation and deep voltage sag.

Voltage Sag Studies in Distribution Networks – Part III: Voltage Sag Index Calculation.

Simulation of voltage sag mitigation with D-STATCOM (1st Ed.).

Simulation of linear feedback control for D-STATCOM voltage sag mitigation (1st Ed.).

Voltage Swell Compensation/Voltage Swell Compensation and Harmonic Distortion Using Dynamic Voltage Restorer.

The use of recorded sag data to estimate the system voltage sag profile.

Voltage Boosting and Restitution Voltage Sag with the use of DVR