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What are the short circuit withstand levels for 400kV, 220kV, and 132kV transformers? Ans: 400 kV transformers must withstand 63 kA for 1 second. 220 kV transformers must withstand 50 kA for 1 second and 40 kA for 3 seconds. 132 kV transformers must withstand 40 kA for 1 second and 31.5 kA for 3 … Read more
Type Tests for above 33KV up to 220KV XLPE Copper Cable Tests on Conductor Tests on Insulation 3. Measurement of Thickness of Insulation4. Measurement of tensile strength and elongation at break5. Thermal ageing in air oven6. Hot set test7. Shrinkage test8. Void and contaminants test Tests on semiconductive layers of the insulation 9. Resistivity test … Read more
A Milliken conductor is a specialized type of stranded electrical conductor. We primarily use this type of conductor in high-voltage (HV) and extra-high-voltage (EHV) power cables. Its design reduces the skin effect and, the proximity effect. Therefore, it improves current distribution in large cross-sectional conductors, typically those exceeding 800 mm² (e.g., 1000, 1200, 1600, 2000, … Read more
Before discussing the types of sheath bonding used in high voltage cable let us recall our knowledge regarding sheath and cause of induced voltage and current in the sheath of a HV cable. Actually, all types of bonding are used to limit the unwanted, induced voltage and current in a cable sheath. What is a … Read more
Sheath Voltage Limiters (SVL) As I have already told, in high-voltage cables, the metallic sheath plays an important role in protecting the conductor from external physical, environmental and electromagnetic influences. But due to electromagnetic induction of the current flowing through the main conductor, a voltage is developed along the sheath, especially in long cable runs. … Read more
Test and enhance your electrical engineering knowledge with this interactive Electrical Engineering Quiz. The quiz randomly selects 20 multiple-choice questions from a large database of topics such as circuit breakers, transformers, lightning arresters, insulators, and power systems. You can choose between:All-Subject Mode – mix of questions from all topicsSubject-Wise Mode – focus on one subject … Read more
The Earth Continuity Conductor or ECC provides an alternate fault current path in EHV installations, limiting dangerous sheath voltage and safeguarding cable insulation. Sometimes, we also call it Earth Continuity Cable. We most commonly use single-core cables for underground high-voltage transmission systems. This is because 3-core high-voltage transmission cables, mainly above 33kV, are not easily … Read more
Single Bus System with Bus Sectionalizer Often, engineers adopt a single bus bar with a sectionalizing arrangement. Because it is cheap and simple. The figure just below shows a single bus bar with a sectionalizing arrangement. The scheme works best when the incoming and outgoing circuits are distributed evenly across the sections. When a single … Read more
The Selective DC Scheme in circuit breaker control circuits is a specialized design used to enhance reliability and ensure fail-proof operation in power system protection and control. In a Selective DC Scheme, multiple (normally two) DC supplies are taken to ensure that control circuit of CB remains functional even if one of the supplies fails. … Read more
Spring-spring mechanism is the most commonly used circuit breaker operating mechanism today. It offers many advantages. Manufacturers use this as the simplest and most economical mechanism in circuit breakers. It also provides high reliability. This mechanism is much more compact than hydraulic or pneumatic mechanisms. Previously, engineers widely used spring-spring mechanisms for 11 kV indoor … Read more
In electrical power systems, circuit breakers play a crucial role in protecting equipment and ensuring the stability of the grid. However, improper operation of breakers can lead to major faults and unsafe conditions. One critical issue in breaker operation is multiple closing attempts before clearing a fault. This can occur due to a continuous closing … Read more
Before entering the minimum oil circuit breaker (MOCB), let us recall our knowledge about the older version of the oil circuit breaker and which is the bulk oil circuit breaker. In a bulk oil circuit breaker,(BOCB) we use oil as the insulating medium. Also, we use oil as the arc-quenching medium. So, to serve both … Read more
A critical component of a CT is its magnetic core, which significantly influences its performance, accuracy, and efficiency. Accuracy is the most essential property of a current transformer. Traditionally, Cold-Rolled Grain-Oriented (CRGO) silicon steel has been the material of choice for these cores. Nowadays, a superior alternative is available on the market—nanocrystalline core material. In … Read more
We are going to discuss here in this article a clear idea about SOTF Protection. Sometimes it becomes necessary to open a circuit breaker just after closing. This is due to the presence of a fault during the closing of the circuit breaker. This type of condition may arise due to different reasons. Such as … Read more
Nowadays, SF6 gas-filled current transformers become popular modern type of CT used in high-voltage substations. It uses SF6 gas as its internal insulating medium instead of conventional insulating oil. We normally install SF6 CTs in voltage levels above 132 kV. A typical SF6 CT is a single-unit, live-tank type instrument transformer. Because it contains pressurized … Read more
A Circuit breaker is an essential component in electrical power system. It is designed to interrupt fault currents and hence protect equipment from damage. A crucial aspect of their performance is the duty cycle. The duty cycle defines the operational requirements and limitations of the breaker in terms of repeated opening and closing operations. Whenever … Read more
Type Tests of Clamp Connectors The tests are performed as per IS: 5561. Type tests are performed on 3 samples of same item Routine Tests on Clamp Connectors Acceptance Tests on Clamp Connectors as per IS: 5561 The number of samples for acceptance tests will be 0.5% (or as the nearest whole number) of the … Read more
In the early days, less 1910 or the early 20th century, most utilities used a bulk oil circuit breaker (BOCB) for high-voltage switching during that time. Earlier air circuit breakers served the purpose of switching high voltage and very high voltage current. But after the 19th century, engineers realized that mineral oil, or specially treated … Read more
Each high-voltage equipment requires adequate insulation to operate safely, reliably, and efficiently. Rated insulation levels indicate the amount of stress the insulation can handle during lightning strikes, sudden electrical surges, or power overloads. The IEC and Indian Standards (IS: 13118) have established clear global rules for these insulation levels to ensure consistent operation. Actually, an … Read more