Visit to 11KV/415V

Substation of BSES Rajdhani

Power Ltd.

REPORT
Submitted By
Name :- ATUL KUMAR
Course :- PGDC RE&GIT

Submitted To :
Dr. Vatsala Sharma
Director NPTI Badarpur
Date :- 29th November 2024
 Table Of Contents
Introduction To Sub Station
Key Components :-
 Feeders
 Ring Main Unit (RMU)
 Air Circuit Breakers
 Transformers
 Oil Type Plinth Mounted (630KVA)
 Dry Type (990 KVA)

 Aerial Bunched Cables

 Fault Detection Cell
 New Technologies Undertaken
Conclusion

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Introduction to a Substation: -

The 11kV/415V Sukhdev Vihar indoor substation is a

crucial component in the electrical distribution
network for the Sukhdev Vihar locality in Delhi,
India. It is designed to step down the 11kV medium
voltage supply to 415V, suitable for residential,
commercial, and industrial consumption. The
substation integrates multiple electrical components
to control, protect, and monitor the distribution of
power. This report covers key components and
technologies commonly found in such substations,
including Feeders, Ring Main Units (RMU), Air
Circuit Breakers (ACB), Transformers (oil and dry
type), Aerial-bundled cables (ABC), and Fault
detection cells etc.

Key Components :-

I. Feeders
 Feeders are crucial elements of a substation. They are required
for the transmission of electrical power from the substation to
distribution lines. Feeders link a sub-station with the
consumers.

 Types of Feeders:

o Radial Feeders: In a radial feeder system, power flows in

one direction from the substation to the consumers. These

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 are simple to design but can lead to more downtime if
faults occur.

o Ring Feeders: In a ring feeder system, the power supply

can come from two directions, offering better reliability.
Ring feed systems help isolate faults and minimize
outages by rerouting power when necessary.

 Applications: Feeders in an 11 kV substation connect the

substation to various outgoing lines, including the main
feeders, which supply electricity to local transformers, and
branch feeders, which supply specific areas.

Advantages:

o Flexibility: Ring feeders offer higher reliability than

radial feeders as they allow alternative power supply
routes.

o Minimized Downtime: Fault isolation and restoration

are quicker with a ring feeder system.

o Efficient Distribution: Feeders help evenly distribute

power to multiple sectors of a city or industrial area.

II. Ring Main Units (RMU)

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 A Ring Main Unit (RMU) is an essential component used in
electrical distribution networks, particularly in 11kV and lower voltage
systems. The RMU provides an efficient and flexible method of
isolating and protecting sections of the power distribution network,
improving reliability, and minimizing downtime.

 Purpose and Function: The RMU is used to manage and

control power distribution in a ring system, where the supply to
consumers can come from two directions, offering backup in
case of faults.

 Design: RMUs are typically housed in compact, weatherproof

enclosures and feature several key elements, including circuit
breakers, switches, fuses, and isolators. They are designed to
operate in indoor or outdoor environments.

 Types of RMUs:

o Gas-insulated (GIS): These units use SF6 (sulfur

hexafluoride) gas as an insulating medium. They are often
used in areas with space constraints.

o Air-insulated (AIS): These units rely on air as the

insulating medium and are more common in less space-
constrained environments.

Advantages of RMU:

o Improved Reliability: Ring circuits ensure multiple

power supply paths, enhancing reliability.

o Compact Design: RMUs are space-efficient and cost-

effective, making them ideal for urban and residential
areas.

o Easy Fault Isolation: RMUs allow easy identification of

faults and enable efficient isolation of affected areas
without affecting the entire distribution network.

III. Air Circuit Breakers (ACB)

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 The Air Circuit Breaker (ACB) is used in substations to protect
electrical circuits from overcurrent and short-circuit conditions. It is
designed to operate under normal and fault conditions to isolate faulty
sections of the circuit.

 Working Principle: The ACB uses air as the arc quenching

medium. When a fault occurs, the breaker interrupts the current
flow, and the arc formed is extinguished by the natural
ionization of air.

 Applications: ACBs are typically used for medium voltage

circuits, providing protection for transformer feeders, busbars,
and outgoing lines. They can be operated manually or
automatically, depending on the setup.

Advantages of ACB:
o High Current Interrupting Capacity: ACBs can
interrupt high fault currents effectively.

o Reliable Protection: They provide reliable protection for

the electrical system and equipment.

o Adjustable Settings: Many ACBs offer adjustable trip

settings for overload and short-circuit protection, offering
flexibility in the protection scheme.

IV. Transformers
i. Oil-immersed Transformers (630 KVA)

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  Construction: These transformers are filled with mineral oil, which
serves as both an insulating and cooling medium. The oil dissipates
the heat generated during operation and prevents electrical
breakdown of the transformer windings.

Advantages:

o Higher Cooling Efficiency: The oil provides better cooling,

allowing for higher current ratings.

o Longer Lifespan: Oil-immersed transformers generally have a

longer operational life due to better heat dissipation.

o Widely Used: These are the most common transformers in

substations due to their high efficiency and reliability.

ii. Dry-type Transformer (990KVA) :-

 Construction: These transformers use air as the cooling medium,

with insulation typically provided by non-flammable materials like
epoxy or silicone.

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  Applications: Dry-type transformers are preferred in indoor
applications where oil leakage could pose a risk, such as in high-rise
buildings, hospitals, or critical infrastructure.

Advantages:

o Safety: No risk of oil leaks or fire hazards.

o Environmentally Friendly: Because they do not use oil, dry-

type transformers are considered more environmentally
friendly.

o Lower Maintenance: Less maintenance is required compared

to oil-immersed transformers.

V. Aerial-Bundled Cables (ABC)

Aerial-bundled cables (ABC) are used for medium and low-voltage

overhead power distribution. Unlike traditional open-wire systems, ABC
consists of multiple insulated conductors twisted together, providing
enhanced safety and reliability.

 Components: ABC typically consists of several conductors with

insulation, a central core for mechanical strength, and an outer
sheath for protection against environmental factors.

Advantages:

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 o Improved Safety: The insulated design helps prevent electrical
accidents such as short circuits and electrocution.

o Reduced Maintenance: Due to their durability and resistance

to environmental factors, ABCs require less maintenance than
traditional overhead lines.

o Cost-Effective: ABCs are cheaper to install and maintain

compared to traditional systems

VI. Fault detection cells

A Fault Detection Cell (FDC) is an important part of the substation

automation system that detects faults in the electrical network and
triggers appropriate actions for fault isolation. These cells are
typically integrated into the control system of the substation.

 Function: The FDC monitors parameters such as current,

voltage, and frequency. When it detects anomalies like
overloads, short circuits, or voltage drops, it initiates corrective

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 actions, such as tripping breakers or sending alarms to the
control center.

 Types:

o Overcurrent Protection: Detects excess current that

may indicate a fault or overload condition.

o Differential Protection: Compares the current entering

and leaving a section of the circuit to detect any
imbalance that could indicate a fault.

o Distance Protection: Measures the impedance to detect

faults based on the distance from the substation.

Advantages:

o Real-Time Monitoring: Provides real-time monitoring

and control to ensure minimal downtime.

o Automated Fault Isolation: Reduces manual

intervention by automatically isolating faults and
protecting equipment.

o Enhanced System Stability: Contributes to the stability

and reliability of the power system by minimizing the
impact of faults.

VII. New Technologies Undertaken

BSES Rajdhani Power has been doing innovation to solve

problems faced in the daily life by the officials such as

Thefts of Electricity, Maintenance issues, Rising Demand of
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Load and Consumer related Issues. Some new technologies
are being incorporated including:

1) Fault Location Cell (FLC) – BSES Officials have taken up this

technology for Fault detection in Underground Cables.

2) All Aluminium Alloy Conductors (AAAC) — It is used in

Overhead Cables, as aluminium proves as a great conductor of
electricity.

3) Dry-Type Transformers

4) Smart Meters

Conclusion
Overall, the visit gave me the exposure of real life
engineering problems and as an Engineering Student I must
know the difficulties that an Engineer faces and how they
solve them.

It was a wonderful learning experience at Sukhdev Vihar

11KV/415V indoor sub station operated and maintained by
BSES. The friendly welcome from all the employes is
appreciating. They shared their experience and knowledge
which they have gained in the long journey of their work. I
hope this experience will help me in future and also in my
career.

So, at last I would like to thank Dr. Vatsala Sharma ,

Director, NPTI(NR), BADARPUR, Deputy Director Shri

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Rajesh Shukla sir for coordinating and organizing this visit
and BSES Rajdhani Power Ltd. employees who gave
guidance to me regarding Power Distribution & Protection.

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