Routine Operations Of General Household Technology Essay Example

frequent problem in power quality jobs, impacting the wave forms of the system's electromotive force. This can lead to a decline or variation in desired power output. Power converters, also referred to as power supply units (PSUs), are essential in addressing these detrimental effects. PSUs not only deliver energy from an electrical outlet to electronic appliances but also assist in regulating the current to meet device or machine specifications.

Nowadays, most advanced electronic devices feature an embedded power supply unit (PSU) that regulates the current. These power supplies, known as switched mode power supplies (SMPS), incorporate a high-speed circuit to stabilize the electric current and voltage at the desired level. The stabilized current is then supplied to the device. SMPS are popular among consumer devices due to their convenient, lightweight design, and cost-effectiveness. However, some reviews consider them as inexpensive alternatives that have the potential to worsen efficiency and performance issues. Additionally, SMPS often generate high levels of noise and can lead to a poor power factor (Power Converter).

Power inverters are growing in popularity for everyday household devices as they convert DC to AC. Both inverters and converters are utilized to create usable power from electricity that is otherwise unusable. Converters come in two types: AC-to-DC and voltage converters. In the USA, AC-to-DC converters are typically unnecessary since most devices already work with it, but voltage converters prove highly beneficial, especially when traveling internationally or using foreign devices.

Plugging a 220-volt device into a 110-volt outlet or vice versa can result in blown fuses, fire hazards, or electric shocks. To mitigate this risk, voltage converters are recommended (Wilson). Although power surges and commercial power supplies are often

blamed for failures in computer power systems, it should be noted that SMPS can also contribute to these issues. SMPS devices make up approximately half of the power usage in an average office (What is Harmonic Distortion?) and fall under the field of power electronics, which specializes in power conversion and motor drives.

Motor drive systems are also known as power converters or electrical-mechanical converters. The advancements in converters' context make it easier to design switched control in motor drives. The similarities between converters and motor thrust concepts suggest that a designer should be knowledgeable in both converter and circuit theory, especially when creating a motor-drive system. Motor drivers are typically inverters, but this does not diminish the importance of converter theory. Ultimately, it all revolves around the mechanism of switched current control (Feucht).

Another commonly used technology in motor thrust and 3-phase power transmission applications is PWM-VSI. It has a significant impact on the efficiency of the inverter, the quality of the waveform, and the uniformity of the electromotive force (Hava 1998, p. 2). For a long time, the constant frequency and magnitude AC power was considered the dominant source of power generation and distribution. However, it is now recognized as inadequate for both industrial and residential applications.

In response to the increased demand for power transition and conditioning devices, efficient semiconductor power switches, advanced power converter circuit topologies, and intelligent control algorithms have been introduced. This has led to the successful implementation of effective power converter circuits in numerous industrial and household applications, connected to the AC power line. Not only are these circuits relatively affordable, but they also improve performance and reliability (Hava 1998, p.

2).

Among the various power converters available today, the most popular is the VSI (Voltage Source Inverter). Its purpose is to convert a fixed DC electromotive force into three-phase AC voltages that can be controlled in terms of frequency and magnitude. This converter ensures reliable and high-quality bidirectional power flow. While the main circuit topology of the VSI is relatively simple, a modern PWM-VSI drive requires a significant amount of engineering and intelligence (Hava 1998, p. 3). It is evident that the field of inverter drives has made great strides, and this innovation has brought about significant advancements in industrial processes (Hava 1998, p.

70) Rectifiers can use either thyristors or rectifying tubes to convert alternating current (AC) into direct current (DC) and regulate the voltage output. While diodes are simpler and do not require any control, the output voltage depends on the input voltage. In contrast, thyristors can generate controlled output voltage, but they require additional controls. Rectifying tubes are preferred in AC drives because of their low cost and ability to generate a fixed output voltage without the need for regeneration.

The most commonly used rectifier circuit in 3-phase AC drives is a 6-pulse rectifying tube span. Despite being simple and low-cost, it produces a large amount of low order harmonics and has minimal smoothing induction (Guide to Harmonics with AC Variable Frequency Drives).

Causes of Current Distortion:

Harmonics primarily stem from or can be considered as a byproduct of all major modern electronic appliances, particularly those powered by SMPS (also known as non-linear loads). These appliances generate the very harmonics they are sensitive to and account for a significant portion of the electrical non-linear burden in most

systems.

The currents generated by nonlinear loads flow from the load towards the power source along the paths of least electrical resistance. According to computer power system studies, computers typically experience current distortions ranging from 100% to 140%. Two types of loads exist: single-phase loads, which are commonly found in modern office buildings, and three-phase loads, which are prevalent in factories and industrial plants (Ramos, 1999). Nonlinear power supplies generate current fluctuations that result in significant distortions.

The deformation in the form of electrical current and voltage wave-shape is known as harmonic deformation. It is measured through Total Harmonic Distortion (THD). This deformation can affect other equipment connected to the same power source and can have negative impacts on the performance, efficiency, and longevity of electrical and power equipment. SMPS systems often produce continuous deformation of the power source.

Harmonics are typically not a problem for any building or office where SMPS or non-linear loads do not exist (Ramos 1999). Harmonics are generally measured as the multiples of the basic frequency of an electrical power system. For example, if the primary frequency is 60 Hz, then obviously the fifth harmonic would be five times and seventh harmonic would be seven times the primary frequency and so on. Harmonics are referred to in terms of current or voltage (Fuhr 2001, p.2). The term "power quality or dirty power" is used when harmonic currents flow in a power system.

Other causes encompass transient effects such as spikes and surges. Harmonics are regarded as a continuous cause of poor power quality since they recur on each particular cycle. Appliances or equipment that produce non-linear currents when subjected to a direct voltage generate

harmonics. Typically, this occurs with devices that convert alternating current (AC) to direct current (DC). Such devices employ power electronics such as silicon-controlled rectifiers (SCRs), rectifier tubes, and thyristors, which constitute a larger share of the load, particularly in industrial systems where a 6-pulse converter is commonly utilized.

Harmonics are commonly produced by most loads as a steady-state phenomenon. To determine if an operating burden is generating harmonics, a snapshot reading can be taken. Each burden typically exhibits a specific harmonic spectrum. For instance, a switch-mode power supply (SMPS) used in personal computers typically generates uneven harmonics, with the largest being the 3rd, followed by the 5th and 7th (Fuhr 2001, p.3). A bar chart can be used to represent the profiles of harmonic current and voltage.

These charts visually represent the harmonic components of the entire voltage or current, and are commonly referred to as Harmonic Spectrum. They show the amplitude of each harmonic order in relation to its frequency, typically displayed as a bar graph (Fuhr 2001, p.4). The amount of harmonic currents in an individual non-linear load is influenced by the overall effective input reactance, which includes both the source and added line reactance.

The harmonic spectrum of the input current in a 6-pulse rectifier with DC bus capacitance can be determined based on the input reactance. The initial reactance is inversely proportional to the harmonic content, meaning that higher harmonic content corresponds to lower initial reactance (Performance of Harmonic Mitigation options). Electrical waveforms can be categorized into two types: linear (sinusoidal) and non-linear (non-sinusoidal). One simple method for calculating Total Harmonic Distortion (THD) is by adding up all the individual harmonics. Any periodic function

can be represented by combining waves with different amplitudes and frequencies (Lemerande 1998).

The field of harmonics is currently receiving a high level of attention. Understanding the effects of harmonics and calculating increased eddy current losses has become a major focus. Additionally, hot spot temperature is an important performance parameter as it determines the lifespan of equipment. This is especially problematic for dry-type transformers. In the past, the results produced by commercially certified and advanced computer applications were more accurate than the initial mathematical or flux plot-based approaches. Now, methods have been developed to calculate electrical fields and eddy current losses in transformers.

These computer-based methods have the capability to produce elegant plots, where accuracy is a major concern (Cendes 1999). Traditional parallel mode meters have failed to accurately determine the rms value of non-linear loads, although harmonic analyzers are recognized as an effective tool for determining wave-shapes and multiple frequency platforms. The simplest harmonic measuring tools typically measure individual phase harmonic voltage and current, resulting in harmonic spectra. Harmonic analyzers are also effective in measuring power factor. 3-phase harmonic analyzers are proficient at measuring harmonic characteristics of three phases and neutral as well.

Moreover, they can create visual representations of deformation fluctuations using clip. Additionally, harmonic analysers have the ability to determine power, power factor, and temporary perturbation factors, allowing for an overall assessment of power quality. Harmonic analysers can also calculate total harmonic distortion (THD) according to professional standards such as IEEE and IEC. However, it is important to assess the voltage and current transformers connected to the analyser based on their acceptable higher frequency response level beforehand.

The text explains that in most cases, there is

a predetermined moderate degree of implementation that fails to achieve higher success. The text also mentions the use of an oscilloscope for troubleshooting electrical and electronic circuits. In the past, older parallel oscilloscopes were not as effective in dealing with high frequency features compared to recent digital storage oscilloscopes. The newer oscilloscopes not only perform their traditional tasks well but also have the ability to store signals and perform mathematical computations when needed. Additionally, the data can be easily transferred to computer systems.

Current Harmonics effects:

The main issue with harmonics is the deformation of waveforms. Electronic equipment generates multiple harmonic frequencies, known as ‘Triplen Harmonics'. These harmonics not only distort voltage waveforms, but also lead to overheating of building wirings, nuisance tripping, overheating of transformer units, and failure of end-user devices. Harmonics can cause overload of conductors and transformers, as well as overheating of utilization equipment such as motors. Triplen harmonics specifically cause overheating of neutral conductors in three-phase, four-wire systems. Even under normal conditions, neutral current levels can increase, resulting in circuit overloading.

This additional burden leads to increased heat, which can cause the insulation of the impersonal music director to break down, potentially resulting in fire or a significant shock (Michaels 1999). When it is determined that harmonics are present in a circuit or electrical system, it is important to determine their extent, magnitude, and type. Harmonic voltages and currents themselves may not be noticeable, but they have critically adverse effects on any application or system. The creation of harmonics and the extent of their effects depend on factors such as electrical burden, temperature zone, location, and installation patterns. This

means that the same magnitude of harmonics can have different destabilizing or distorting effects on two different installations.

Some of the symptoms include excessive temperature, shaking, unbearable noise, large impersonal currents, and equipment malfunction. Harmonics change rms and mean values of the electrical system and distort its waveforms (Sankaran 1996). Harmonics have been present since the beginning, even when the first AC generator came online approximately 100 years ago.

Although at that time they were negligible and had no harmful effects according to observation (Sankaran 1999). In an operational AC machine, both the winding distribution and magnetic field are not standardized, resulting in deformations that are generally around 1-2% during production. However, these deformations create a periodic function that deviates from a pure sine wave, indicating the presence of harmonics (Sankaran 1999). Pure sine waves are observed in cases where voltage and current follow each other without any deformations, such as in resistive heaters and synchronous motors.

These loads are referred to as additive loads. On the other hand, loads that cause current fluctuations during each half cycle unreasonably are called nonlinear loads, such as battery chargers, variable frequency drives, SMPS, etc. Typically, voltage distortions are caused by current distortions; however, this is not a problem when there is a strong sinusoidal voltage source (Sankaran 1999). When nonlinear currents flow through an electrical system, additional voltage distortions are created due to the impedance associated with the electrical network.

According to Sankaran (1999), it appears that the equipment is functioning satisfactorily. However, there is a possibility that the impact of harmonics is greatly increased, leading to destructive outcomes in specific circumstances. To power electric motors, variable frequency drives (VFDs) are

commonly utilized. It is important to note that the voltages and currents transmitted by VFDs typically contain harmonic frequency components. As a result, this establishes a magnetic field within the motor's core, resulting in iron losses in its magnetic structure.

Other important aspects of Fe losses negotiations regarding eddy current losses (which vary as the square of the frequency) and hysteresis (relative to frequency). These cause an increase in operating temperature and distortions in the core. In the case of non-sinusoidal voltages and currents being applied to produce magnetic fields, air gap magnetic fields are generated. There is also the production of rotor current, which is a major factor contributing to harmonic frequency components. Harmonics can be classified into the following categories:

• Positive (+): These harmonics, similar to the fundamental frequency harmonic, create magnetic fields and currents that rotate in the same direction.
• Negative (-): Unlike positive harmonics, these create magnetic fields and currents that rotate in the opposite direction.
• Zero (0): These harmonics do not produce usable torque but lead to additional losses.

It is crucial to perform harmonic assessments before installing VFD motors in order to identify and measure their impact in advance (Sankaran 1999). Interestingly, the effects of voltages and currents on transformers are often overlooked until an actual failure is detected, sometimes only when reconfigurations are made.

At the terminal of the transformers twists, a higher concentration of eddy current can be observed. This is an important harmonic load that transformers provide. When harmonics cause an increase in eddy current losses, it significantly affects

the operating temperature of transformers. However, this loss or danger can be reduced by using larger size weaving conductors or multiple twisted conductors. In such cases, k factor rated transformers are usually the safest option as they also have an inbuilt neutral terminal to address the issue of triplen harmonic currents (Sankaran 1999). Capacitors are also widely used to compensate for the impact caused by low power factor. However, in power systems, capacitor banks characterized by high voltage or current harmonics have also experienced failures. Capacitor banks are vulnerable and attract harmonic currents.

Another important characteristic is the creation of resonating conditions when the inductive and capacitive reactances are equal in electrical applications. If the amplitude of the offending frequency is high during resonating conditions, major harm can occur. It is crucial to ensure that properly rated cables are used for proper current flow, as harmonic currents can easily flow through a conductor (Sankaran 1999). The definition of the point of common yoke (PCC) is strongly relied upon in the IEEE 519-1992 standard. From the perspective of the power utility and considering the IEEE 519-1992 standard, the PCC (point of common coupling) is typically the point where metering is done.

In the context of electrical power systems, IEEE 519-1992 establishes that the Point of Common Coupling (PCC) serves as a crucial connection between additive and non-linear loads within an industrial setting. According to IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, it is widely recognized by designers, engineers, and industry leaders that keeping harmonic levels below or at an acceptable level within the local area is highly important to prevent any catastrophic or

undesirable situations. Implementing mitigation strategies for harmonics at the point where non-linear loads are connected to the power system not only addresses the overall issue but also reduces downtime, costs, and prolongs the lifespan of equipment. Compliance with the guidelines outlined in IEEE 519-1992 is of utmost significance to both facility managers and equipment suppliers in ensuring effective harmonic mitigation.

Therefore, to ensure a standardized procedure and consistent reading, it is necessary to properly identify PCC. If this is not done, most providers will follow PCC regulations in terms of utility metering, which is fine for utility purposes but not ideal for installations (Swamy 2005).

Current Harmonics Filtering Methods: Harmonic filters are effective for limiting and reducing distortion. There are two types:

• Centralized harmonic filters: These include active harmonic filters and filtered automatic power factor correction units. They are connected to the main bus of the equipment and designed to address harmonics caused by operations.
• Localized harmonic filters: These can be achieved through drive filters or active filters at the harmonic generating loads. They are connected close to the source of the harmonics, with one filter per harmonic generator (Harmonic Filtering Techniques).

Passive filtering type: A line reactor helps make the current waveform less discontinuous, resulting in lower current harmonics. As the reactor resistance increases with frequency, it provides more resistance to higher order harmonic currents. By knowing the input reactance value, the expected current harmonic distortion can be estimated.The input reactance is determined by the series combination of the electric resistance of the AC reactor, input transformer (building/plant incoming-feed transformer), and power overseas cable.

The reactor next to electrically isolates the DC bus voltage from the AC source so

that the AC source is not connected to the DC bus voltage during diode conduction. This feature reduces distortion of the AC voltage waveform caused by many Variable Frequency Drives (VFDs) when operated with weak AC systems. However, introducing AC induction between the rectifier input terminal and the AC source causes voltage drop due to the series resistance offered by the inductance. The fundamental frequency voltage drop increases with load and results in lower available DC bus voltage. Therefore, caution should be taken not to add excessive amount of line inductance to prevent low voltage condition at the input terminals of the VFD (Swamy 2005).

The presence of AC inductance in a three-phase rectifying tube rectifier system leads to the convergence of conductivity between the surpassing rectifying tube and the incoming rectifying tube. This convergence phenomenon further results in a decrease of the average DC coach electromotive force. The extent of this decrease depends on the duration of convergence in electrical grades, which is determined by the value of the intervening induction used and the current amplitude. The duration of convergence in electrical grades is usually denoted by "?". However, higher values of external inductive reactance increase the overlap angle, which in turn reduces the average output electromotive force, as observed from the equation mentioned above.

It is important to note that the VL-L voltage is the value at the input terminals of the rectifier, not before the AC inductance. The voltage drop across the AC inductance should be subtracted from the actual value of the AC supply to obtain the correct voltage available at the input terminals of the rectifier (Swamy 2005).

DC Link Choke

Placing an inductance

of equal value between the AC source and the DC bus capacitance of the VFD will help make the input current waveform more continuous. Therefore, a DC link choke, which is positioned after the rectifying diode bridge and before the DC bus capacitance, can be used to reduce the input current harmonic distortion. The DC link choke operates similarly to a three-phase line inductance.

However, when analyzing the behavior of the DC nexus choking coil, it becomes evident that it behaves similarly to the input AC line inductance in terms of current deformation, but it has a different impact on the overall electromotive force (Swamy 2005). One important difference is that a three-phase rectifier's output contains a significant DC component, meaning there is no voltage drop as observed in three-phase AC line inductances. Additionally, the DC nexus choking coil is positioned after the rectifying tube rectifier block and does not contribute to the convergence phenomenon discussed earlier in relation to external AC input reactors. Therefore, unlike with AC input reactors, using a DC link choking coil does not result in a decrease in DC bus voltage. Instead, it increases the duration of rectifying tube conductivity. There is a critical induction value for the DC nexus choke that leads to complete 60-degree conductivity of a rectifying tube pair.

Any DC link inductance value beyond the critical value is not important and a large DC link inductance will only have marginal benefits. A higher inductance value will only help reduce the fluctuations in DC current but will also cause a higher voltage drop due to increased resistance. This can result in slightly higher power loss without significantly affecting the

average output DC voltage. The critical DC link inductance value depends on the load condition, frequency of the input AC supply, and the peak value of the input AC line-line voltage, Vm.

It is important to note that the critical DC inductance value for a 240V system is 1/4th the value for a 480V system (Swamy 2005).
Bacillus: Capacitor based Passive Filters
One way to reduce harmonics generated by non-linear loads is to introduce a series passive filter in the incoming power line. This filter provides high resistance to the flow of harmonics from the source to the non-linear load. The series passive filter is tuned to a specific frequency and only offers high resistance at that frequency. Series passive filters are commonly used in single-phase applications to reduce the third-harmonic component. These filters are typically designed to have low resistance at the fundamental frequency.

A major disadvantage of this attack is that the filter components must be designed to handle the rated burden current. Additionally, one filter division is not enough to reduce the entire harmonic spectrum present in the input current of a non-linear system. Multiple divisions may be necessary to achieve satisfactory results, making them large and costly (Swamy 2005).

Shunt Passive Filter The shunt passive filter is positioned across the incoming line and is designed to provide very low electrical resistance to current components matching its tuned frequency.

Energy flows into the shunt passive filter at its fundamental frequency, while energy at the filter's tuned frequency flows out. This is because the shunt filter offers lower electrical resistance for the flow of energy at its tuned frequency compared to its source. The energy flowing into the shunt

filter at the fundamental frequency is responsible for removing VARs, but it can also cause over-voltage at the filter terminals. This can be problematic for VFDs that are sensitive to higher than normal voltage levels, especially under light-load conditions where over-voltage trips can occur. Similar to a series tuned filter, the shunt-tuned filter is only effective at and around its tuned frequency. A single section of the filter is insufficient to provide all the necessary harmonic energy for a typical non-linear load like a VFD. As a result, multiple sections are required, making them bulky and expensive.

If attention is not taken, the shunt filter may become overloaded and damaged if unprotected as it tries to provide the necessary harmonic energy for all non-linear loads connected to it. To avoid importing harmonics, it is important to use AC line inductors in series with the shunt sections of tuned filters. By adding extra line inductance, the size and cost of the filter section increase, but it prevents the flow of harmonic energy from other sources into the shunt tuned filter sections (Swamy 2005).

The Low Pass Broad Band Filter

The filtering performance is improved by replacing the inductance Ls with Lf and removing the series inductance with Cf. This changes the filter configuration from tuned type to broadband type.

The low base on balls, broadband harmonic filter has the advantage of not needing to be configured in multiple phases or subdivisions like the shunt and series type filters, according to Swamy et.al in 1994. Additionally, autotransformers have this advantage.