Name: voltage and current sensing in power grids
Uploaded: 2024-11-21T14:54:34.000Z
Duration: 1 min 23 s
Channel: JoVE

تشمل محولات الأدوات محولات الجهد والتيار.
عادة ما يكون للملف الأساسي للمحول الحالي دورة واحدة أو قضيب موصل ، يتم لف حوله لفات متعددة من الملف الثانوي.
يؤدي التيار العالي المتدفق عبر الملف الأولي إلى انخفاض التيار في الملف الثانوي. يتم توصيل الملف الثانوي بشكل عام في سلسلة بأجهزة قياس مقاومة الصفرية للسماح بأقصى تدفق للتيار. 
يعتمد أداء المحول الحالي على تكرار التيار الأساسي بدقة دون تشبع يسبب الخطأ. ومع ذلك ، قد تفقد المحولات الحالية بعض التيار لتحويل مقاومة الإثارة.
الآن ، ضع في اعتبارك محولات الجهد ، التي تتكون من ملف أولي يحتوي على عدد أكبر من اللفات من الملف الثانوي.
يتم توصيل الملف الثانوي بالتوازي مع جهاز استشعار الجهد عالي المقاومة ، مما يضمن نقلا دقيقا للجهد.
للحماية ، تم تصميم محولات الجهد على أنها مثالية ، مما ينتج عنه تمثيل مصغر في الطور للجهد الأساسي. 
ومع ذلك ، فإن محولات الجهد تتعرض لانخفاض صغير في الجهد وتحولات الطور.

محولات الأجهزة

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تلعب المحولات الأجهزة، التي تتألف من محولات الجهد (VTs) ومحولات التيار (CTs)، أدوارًا حاسمة في محطات الطاقة الفرعية من خلال توفير نسخ معزولة من التيار أو الجهد لأغراض القياس والحماية. تعمل محولات الجهد على تقليل الجهد الأساسي إلى مستويات مناسبة لتشغيل التتابع والقياس، بينما تعمل محولات التيار على خفض التيار الأساسي. غالبًا ما يتكون الملف الأساسي لمحول التيار من لفه واحدة، يتم تحقيق ذلك عن طريق تمرير او توصيل الموصل الأساسي لنظام الطاقة عبر قلبه، على الرغم من أن بعض التطبيقات قد تتطلب لفات أساسية متعددة.

لأغراض الحماية، تم تصميم محولات الجهد بشكل مثالي لإنتاج تمثيل مصغر ومتزامن للجهد الأساسي. يجب أن يتصل الثانوي لمحول الجهد بجهاز استشعار جهد عالي الممانعة، مما يضمن ظهور الجهد الثانوي بالكامل عبر جهاز الاستشعار. وعلى العكس من ذلك، يجب أن يتصل الثانوي لمحول التيار بجهاز استشعار تيار منخفض الممانعة، مما يسمح للتيار الثانوي بالتدفق كاملا عبر جهاز الاستشعار.


في التطبيقات العملية، قد تواجه محولات الجهد انخفاضات في الجهد واختلافات في زاوية الطور بين الجانبين الأولي والثانوي. وعلى نحو مماثل، في محولات التيار، قد يتم تقسيم بعض التيار بين جهاز الاستشعار منخفض الممانعة وممانعة إثارة على التوازى للمحول. يعتمد أداء محول التيار إلى حد كبير على قدرته على إعادة إنتاج التيار الأولي بدقة دون أخطاء كبيرة أو تأثيرات تشبع.

تعتبر هذه المحولات ضرورية للتشغيل الدقيق لمرحلات الحماية وأجهزة القياس، مما يضمن التشغيل الآمن والموثوق به لأنظمة الطاقة. من خلال خفض الفولتية والتيارات العالية، تتمكن محولات الأجهزة من المراقبة والتحكم في المعاملات او المؤشرات الكهربائية ضمن نطاقات يمكن التحكم فيها، والحفاظ على استقرار النظام وحمايته.

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تشمل محولات الأدوات محولات الجهد والتيار.
عادة ما يكون للملف الأساسي للمحول الحالي منعطف واحد أو موصل ...

Education

JoVE Core

Electrical Engineering

الهندسة الكهربائية

Unit 1

الوحدة الأولى

System Protection

حماية النظام

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

Instrument Transformers

voltage and current sensing in power grids

Instrument transformers help power substations measure voltage and current safely. They create isolated replicas of electrical signals for measurement and protection. These devices support protective relays and other monitoring equipment that keep power systems stable and reliable.

The two main types are voltage transformers, or VTs, and current transformers, or CTs. A voltage transformer reduces the primary voltage to a lower level that relays and measuring devices can use. A current transformer scales down the primary current in the same way.

A current transformer often uses a single-turn primary winding. In many cases, the power conductor is simply threaded through the core to act as that turn. Some applications need multiple primary turns instead.

For protection, a voltage transformer should produce a scaled-down secondary voltage that stays in phase with the primary voltage. Its secondary should connect to a high-impedance voltage-sensing device. That setup lets the full secondary voltage appear across the sensing device.

A current transformer works differently. Its secondary should connect to a low-impedance current-sensing device so the full secondary current flows through the device. In practice, some current can split between the sensing device and the transformer’s shunt excitation impedance. VTs can also show voltage drops and phase-angle differences between the primary and secondary sides.

Current transformer performance depends on how well it reproduces the primary current without large errors or saturation. By reducing very high voltages and currents to manageable levels, instrument transformers let engineers monitor electrical values and protect the power system.

Voltage and Current Sensing in Power Grids

voltage-and-current-sensing-in-power-grids

instrument transformers

Instrument transformers help power substations measure voltage and current safely. They create isolated replicas of electrical signals for measurement and protection. These devices support protective relays and other monitoring equipment that keep power systems stable and reliable. The two main types are voltage transformers, or VTs, and current transformers, or CTs. A voltage transformer reduces the primary voltage to a lower level that relays and measuring devices can use. A current...

overcurrent relays

Relay Settings for Circuit Fault Protection

Overcurrent relays protect circuits by sensing excess current through the secondary side of a current transformer. They are an important part of circuit protection and help keep power systems stable when a fault occurs. Two main relay types are used here: instantaneous and time-delay overcurrent relays. An instantaneous relay trips right away when current rises above the pickup current, which is the preset level that starts the relay. It then energizes the circuit breaker trip coil at once,...

radial system protection

Breaker Coordination in Radial Systems

Breaker coordination in radial systems uses time-delay overcurrent relays to limit load interruption. When a fault happens, the nearest breaker should open first. Upstream breakers stay closed because they are set with longer delays. This lets the fault be isolated while the rest of the system keeps running. If a fault is downstream of the third breaker, only the third breaker should trip. That removes power from the load beyond the fault. The second breaker keeps a longer delay setting, so...

reclosers and fuses

Fault Coordination with Reclosers and Fuses

Fault coordination with reclosers and fuses helps protect radial distribution circuits. A recloser is an automatic switch that interrupts AC power and then closes again on a preset schedule. This brief outage can clear temporary faults on overhead lines, such as those caused by tree limbs or wildlife, and it can improve overall reliability. Reclosers and their ground-level hazards also matter. Contact with a recloser or with a broken energized conductor on the ground can be dangerous. That is...

directional relays

Directional Relays in Power System Protection

Directional relays help protect power systems by telling forward faults from reverse faults. They are used when fault current flows mainly in one direction on a line. This makes the relay useful for safe and efficient fault clearing. On a protected line, a fault downstream, or to the right of the current transformer, usually makes the fault current lag the bus voltage by about 90 degrees. This is called the forward direction. A fault upstream, or to the left, may make the fault current lead...

zones of protection

Power System Protection Zones

Power system protection zones divide the network into sections so faults can be isolated quickly. These zones can include generators, transformers, buses, transmission lines, distribution lines, and motors. Each zone is shown with closed dashed lines and contains one or more components. Circuit breakers are placed at the borders where protection zones meet. If a fault happens in one zone, the related breakers open and disconnect only that section. A fault in one area, such as a kitchen in the...

line protection with impedance relays

Impedance Relays for Fault Detection

Impedance relays help protect power lines by watching the voltage-to-current ratio on a line. They measure the apparent impedance, which is the electrical opposition the relay sees at that point in the system. This makes them useful when time-delay overcurrent relays are hard to coordinate in complex radial systems and when directional overcurrent relays are difficult to use in multi-source transmission loops. These relays respond strongly during a fault. As current rises and voltage falls,...

differential relays

Differential Relay Protection in Power Systems

Differential relays protect generators, buses, and transformers by comparing currents at different points in a power system. When the currents do not match, the relay detects the difference and opens the circuit breaker. Under normal conditions, the current entering a generator, i1, equals the current leaving it, i2. If a fault occurs, these currents become unequal, and the difference current flows through the relay operating coil to trip the relay. An electromechanical differential relay is...

pilot and numeric relaying

Pilot Relays and Digital Protection

Pilot relays and numeric relays help protect power systems. Pilot relaying is a form of differential protection, which compares electrical quantities at equipment terminals through a communication channel instead of a direct relay link. It is especially useful for transmission lines with terminals far apart, often up to 80 km on 69 to 115 kV lines. Pilot relaying can use several communication channels. Pilot wires are separate electrical circuits that operate at DC, 50 to 60 Hz, or audio...

key terms and concepts

Explore how voltage transformers and current transformers scale high power-grid signals for safe measurement, relay operation, and system protection.

Voltage and Current Sensing in Power Grids | 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

Voltage and Current Sensing in Power Grids

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