Friday, July 15, 2022

Transformer Back-to-Back or Sumpner Test

Sumner's Test or Back-to-Back Test of a Transformer

A full-load test of the large transformer is needed to determine the maximum temperature rise of a transformer. This kind of Transformer test is called a back-to-back test. The back-to-back test is also known as Sumpner's test or regenerative test of transformers.


Sumner's Test Circuit Diagram of Transformer

The circuit diagram or the connection diagram to carry out the transformer Sumpner's test also known as the transformer back-to-back test is shown below. Find herewith the following connection diagram where two transformers are connected in a parallel way to supply the AC voltage V1 and the low voltage supply V2

EXCAVATIONS SAFETY IN THE WORKPLACE


How Excavations Carry on Safely in the Workplace:   

Safety for Excavation work

Excavation and trenching are among the most hazardous construction operations. The Safety and Health code should follow strictly during Excavation and Trenching in the workplace. Trenching and excavation work presents serious hazards to all workers involved. Especially in trafficked crowded city areas and moreover in the rainy season is more hazardous and much more likely than other excavation-related accidents to result in worker fatalities. Excavation in soil movement and cave-ins should take special care. Other potential hazards include falls, falling loads, hazardous atmospheres, and incidents involving mobile equipment.

Nobody should enter an unprotected trench! Trenches about 1.5 meters deep or greater require a protective system unless the excavation is made entirely in stable rock. Trenches about 6 meters deep or greater require that the protective system be designed by a registered professional engineer or be based on tabulated data prepared and or approved by a registered professional engineer.

There are different types of protective systems are available. Sloping involves cutting back the trench wall at an angle inclined away from the excavation. Shoring requires installing aluminum hydraulic or other types of supports to prevent soil movement and caverns. Shielding protects workers by using trench boxes or other types of supports to prevent soil cave-ins. Designing a protective system can be complex because you must consider many factors: soil classification, depth of cut, the water content of the soil, changes due to weather or climate, surcharge loads (eg., spoil, other materials to be used in the trench) and other operations in the vicinity.


You may have past long job experience on so many trenching, shoring, and backfilling, but it is important to approach each new job with the utmost care and preparation. Most job accidents result directly from insufficient initial planning. So pre-planning for every excavation job and taking standard safety measures can reduce accidents.

If working in or near EXCAVATIONS, Please check:


ØIs their edge protection to stop people or materials from falling?

ØExcavated spoil stored well away from the edge?

ØThe excavation sides stable before entering?

ØThe integrity of any shoring in place before entering?

ØNo site traffic travel near the edge of excavations?


ØThere is at least two ladders and a maximum of 9 meters apart? 

What is the Benefits of Bundle conductor for EHV (Extra High Voltage) Transmission Lines?


Generally, 230kV or higher system overhead transmission line uses single-stranded conductors; above this voltage system multi-stranded like two, three, or four strands with bundle conductor spacers is required.

As per the nature of current flowing on conductive materials, maximum electrons tend to flow through the surface of the conductor rather than the inner. Considering this property hollow conductor is more suitable to optimize the current flow for higher capacity power transmission in an extra-high-voltage (EHV) system.

Theoretically, the hollow conductor may be viable, but practical conductors are not economical for maintenance and erection. So, the concept of a bundle conductor is the best solution to instate a hollow conductor.

Advantages of Using bundle conductors in EHV overhead transmission system

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A bundle conductor in a transmission line is used to get the following advantages:

1.    Bundle conductor of transmission line reduces the reactance of the electric transmission line;

2.    Bundle conductor in power system also reduces corona loss, which improves the transmission efficiency as loss due to corona effect;

3.    Bundle conductor in EHV transmission system provide the higher capacitance to neutral when compared to single lines. This results in higher charging currents which helps in improving the power factor;

4.    In bundled conductor lines, as the effective GMR (geometric mean radius)  of the bundled conductor increases the conductor diameter, virtually acts like a larger diameter hollow conductor, and  the inductance per phase of the conductor decreases;

5.    The bundle conductor spacers give optimum spacing (8 to 10 times the diameter of the conductor) between sub conductors in bundled conductors that gives a minimum voltage gradient on the surface of bundle conductors;

6.    As the advantage of bundled conductors in transmission lines by reducing voltage gradient, the radio interference is also reduced or minimized;

7.    With the decrease in inductance of bundled conductors, the surge impedance of the line is also reduced, L=(u0/2π)* ln(Mutual GMD)/(Self GMD)) H/m/phase;

8.    Due to bundling the conductor uses the surge impedance reduction, so more SIL-surge impedance loading (Z=(L/C)^1/2)) of the conductor increases which increases the transmission capacity of the system.

The remarkable phenomenon of the overhead transmission system is the “Corona effect” that can be observed when the air medium present between the phases is charged up and start to ionize and acts as a conducting medium.

Primarily bundle conductor concept is employed to reduce the corona loss and radio interference of transmission lines. Especially EHV at around 400 kV or higher corona losses are very high that can reduce using bundled conductors.

To know more details about Corona Effect and Radio interference, read-

Bundle Conductor Formation

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Usually following three types of bundle conductor formation used in power transmission systems:
1.    Duplex formation;
2.    Triplex formation;&
3.    Quadruplex.

bundle conductors in overhead transmission system
Bundle Conductor in Overhead Line



bundle conductor configuration
Usually Used Bundle Conductor Formation


The geometric mean radius of a bundled conductor for a two-conductor (duplex), a three-conductor (triplex), and a four-conductor (quadruplex) arrangement is shown in Figs.

In conclusion, we can say bundle conductors are used for transmission purpose as it helps in obtaining better voltage regulation and efficiency by reducing the inductance and skin effect that are present in the power lines.