Name: reducing power loss in three-phase lines
Uploaded: 2024-07-08T13:19:58.000Z
Duration: 1 min 10 s
Channel: JoVE

חשבו על מעגל Y-to-Y מאוזן בעל שלושה חוטים המיוצג בתחום הזמן, שניתן להפוך אותו למעגל שווה ערך לכל פאזה.
ראשית, נקבע זרם הקו, ואחריו מתח הפאזה בעומס.
לאחר מכן, הכוח המסופק על ידי המקור נקבע באמצעות הערכים האפקטיביים של מתח הפאזה הסינוסואידלי וזרם הקו.
לאחר מכן, הכוח המועבר לעומס מחושב באמצעות זרם הקו והתנגדות העומס.
הכוח האבוד בקו מתקבל באמצעות זרם הקו והתנגדות הקו.
לאחר מכן, הכוח הכולל המועבר על ידי המקור התלת פאזי, הכוח הכולל שהתקבל על ידי העומס התלת פאזי, ואת הכוח הכולל שאבד בקווים נקבעים.
אחוז גבוה של כוח הולך לאיבוד בקו, אשר ניתן להפחית על ידי מזעור זרם הקו.
עם זאת, זה יפחית את זרם העומס, אשר בתורו להקטין את הכוח מועבר לעומס.
אחת הדרכים להפחית את זרם הקו מבלי להשפיע על זרם העומס היא להכניס שנאים למעגל התלת פאזי.

אובדן קו

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התצורות השונות של חיבורי עומס-מקור כוללות חיבורי wye (כוכב) ודלתא (משולש). הקשר בין מתחי קו ופאזה והזרמים משתנה בהתאם לתצורה. כאשר המקור מספק הספק, הוא מועבר דרך החוטים לעומס, ובמהלך ההעברה הזו, חלק מההספק נספג בחוטים, מה שמוביל לאובדן קו.

אובדן בקו משפיע על יעילות העברת החשמל במעגל תלת-פאזי מאוזן. הסימטריה במעגל כזה מפשטת את הניתוח בכך שהיא מאפשרת לנו לשקול רק פאזה אחת. המעגל המקביל לכל פאזה מסייע בחישוב פרמטרים שונים, כולל אובדן קו.

חישוב אובדן הספק:

ההספק המסופק לכל פאזה של העומס הוא מכפלת הריבוע של זרם הפאזה והתנגדות העומס הפאזי.
חישוב אובדן קו:
אובדן בקו עבור כל חוט מחושב על ידי לקיחת הריבוע של גודל זרם הקו והכפלתו בהתנגדות הקו.
במערכות תלת-פאזיות מאוזנות, חישוב זה מוכפל בשלוש (אחת לכל פאזה) כדי לקבל את סך אובדן ההספק. התנגדות הקו פרופורציונלית ישירות להתנגדות החומר ולאורך הקו, והפוכה לשטח החתך של המוליך. משמעות הדבר היא שאובדן הקו הוא פרופורציונלי ישירות לאורך המוליך והפוך לשטח החתך של המוליך. חברות חשמל משתמשות במוליכים עם שטחי חתך גדולים יותר כדי למזער את אובדן הקו ולהעביר חשמל במתח גבוה יותר, מה שמאפשר זרם נמוך יותר לאותה כמות הספק. הסיבה לכך היא שההספק הוא תוצר של מתח וזרם, וברמת הספק נתונה, הגדלת המתח מאפשרת הפחתת הזרם, ומצמצמת את אובדן הקו.

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חשבו על מעגל Y-to-Y מאוזן בעל שלושה חוטים המיוצג בתחום הזמן, שניתן להפוך אותו למעגל שווה ערך לכל פאזה.
ראשית, ...

Education

JoVE Core

Electrical Engineering

הנדסה חשמלית

Unit 1

יחידה 1

Three-Phase Circuits

מעגלי תלת-פאזה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

Line Loss

reducing power loss in three-phase lines

Three-phase power lines can lose energy as electricity travels from the source to the load. This line loss affects how efficiently power reaches the load. In balanced three-phase circuits, the symmetry makes the analysis easier because one phase can represent the whole system.

The source-load connection can use wye, also called star, or delta configurations. These setups change the relationship between line voltage, phase voltage, line current, and phase current. A per-phase equivalent circuit helps calculate the power delivered to the load and the power lost in the lines.

For each phase of the load, the delivered power depends on the square of the phase current and the phase load resistance. The power lost in one wire is found from the square of the line current multiplied by the resistance of that line. For a balanced three-phase system, the total line loss is three times the loss in one phase.

Line resistance depends on the material resistivity, the length of the conductor, and its cross-sectional area. As the line gets longer, resistance and line loss increase. A larger cross-sectional area lowers resistance and helps reduce loss. Power companies use larger conductors and higher transmission voltages to keep current lower for the same power level, which reduces line loss.

Reducing Power Loss in Three-Phase Lines

three-phase circuits

How Three-Phase Power Delivers Electricity

Three-phase power is a major part of AC power distribution, especially where steady and efficient electricity delivery is needed. AC systems are grouped into single-phase, two-phase, and three-phase systems. These categories help describe how power moves from the source to the load. Single-phase circuits are common in homes. They usually use a two-wire system that connects one AC source to loads. These circuits can supply everyday appliances such as lamps, televisions, and microwaves at 120 V...

generation of three-phase voltage

Three-Phase AC Generator Windings

A three-phase AC generator uses rotating magnet windings and a stationary stator to make three-phase voltage. The rotor carries a magnet that spins inside the stator. The stator holds the three-phase winding, and mutual induction creates the voltage. The stator windings are spread evenly around the inside of the stator. They are placed 120 electrical degrees apart. These windings consist of three separate coils, or groups of coils, called phases. The phases can be connected in a Y, or star,...

three-phase voltages

Three-Phase Power Connections

Three-phase power connections use balanced voltages that are equal in magnitude and separated by 120 degrees. A three-phase generator produces these voltages, and the balance helps reduce power loss while keeping energy delivery steady to connected loads. Three-phase sources can be arranged in either wye or delta form. The loads connected to the system can also use wye or delta. This flexibility gives control over how the system is designed and managed. In a wye connection, one end of each...

the y-to-y circuit

Balanced Wye-to-Wye Neutral Current

A balanced wye-to-wye circuit uses three wye-connected sinusoidal voltage sources and three wye-connected loads. A neutral wire links the neutral node of the source to the neutral node of the load. The load impedance is connected across each phase of the load. The source and load can be connected in either a four-wire or a three-wire arrangement. A three-phase system is balanced when each phase has the same load. In that case, the current flow and phase angle are uniform across the system. If...

the y-to-delta circuit

Wye Source and Delta Load Currents

A balanced wye source and delta load form a common three-phase circuit with no neutral line connection. The source is Y-connected, and the load is delta-connected. To analyze the circuit, the first step is to assume a positive phase sequence. These phase voltages are then used to find the line voltages that appear across the delta load impedances. In the wye source, the phase voltages are V an, V bn, and V cn. In the delta load, the line voltages are V ab, V bc, and V ca. These line voltages...

the delta-to-delta circuit

Balanced Delta-Delta Power Circuit

A balanced delta-delta power circuit uses a delta-connected source and a delta-connected load. The two deltas form a closed loop that creates three separate phases. In this setup, the phase voltages are the same as the line voltages. If the source is in positive sequence, the phase voltages can be written directly, and no neutral wire is needed. The delta-connected load current is found by dividing the phase voltage by the impedance of each phase. For line current, Kirchhoff’s Current Law...

the delta-to-y circuit

Delta-Wye Source and Load Connections

A balanced delta-wye circuit connects a delta-connected source to a wye-connected load. In this setup, the phase voltage of the delta source equals the line voltage of the wye load. The source also sets the line currents that flow into the load. For a balanced system, the phase difference between currents makes it possible to find one line current from the other by using the positive sequence of phases. In the wye-connected load, each phase current equals the line current from the delta source.

power in a three-phase circuit

Balanced Three-Phase Power Calculation

Balanced three-phase power calculation depends on the wye and delta connections used in the circuit. A wye, or star, configuration can use three wires or four wires. A delta configuration connects the components in a closed loop. These connection types change how voltages and currents are arranged, but both are used in three-phase systems. In a balanced three-phase system, instantaneous power is the power at one exact moment. Even though the power in each phase changes over time, the total...

power distribution in three-phase and single phase circuits

power-distribution-in-three-phase-and-single-phase-circuits

Single-Phase vs. Three-Phase Power Loss

Single-phase and three-phase circuits distribute electrical power in different ways. Single-phase power is common in homes, while balanced three-phase power is widely used in industrial settings with heavy machinery. Both systems deliver energy, but their current flow and wire needs are not the same. A single-phase circuit usually uses a two-wire system. The current depends on the power absorbed by the load and the line voltage. Because wire loss from resistance follows the square of the...

line loss

Three-phase power lines can lose energy as electricity travels from the source to the load. This line loss affects how efficiently power reaches the load. In balanced three-phase circuits, the symmetry makes the analysis easier because one phase can represent the whole system. The source-load connection can use wye, also called star, or delta configurations. These setups change the relationship between line voltage, phase voltage, line current, and phase current. A per-phase equivalent circuit...

reducing line loss

Cutting Heat Loss in Three-Phase Lines

Three-phase power systems can lose energy as heat in transmission lines because the wires have resistance. This line loss becomes important when electricity travels over a distance. A common solution is to use transformers to change the voltage and current in the system. The setup uses two three-phase transformers. A step-up transformer is placed at the source, and a step-down transformer is placed at the load. Raising the voltage at the source lowers the current in the transmission lines, and...

key terms and concepts

Learn how balanced three-phase circuits, wye and delta connections, and conductor size affect line loss, power delivery, and transmission efficiency.

Reducing Power Loss in Three-Phase Lines | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Reducing Power Loss in Three-Phase Lines

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