|
|
|
Distribution Transformers |
|
Industrial, Substation & Distribution Tfr. Upto 10 MVA, Upto
33kV, ONAN A poly phase Distribution Transformers design is
presented in which transformer output pores are accurately
constructed in both voltage magnitude and relative phase
angle. The design incorporates both main and auxiliary
transformers that are used in unison to produce the
accurately constructed phases. The main transformer permits
rough phase adjustment to be made with the auxiliary
transform permitting phase fine tuning. Such a design is
particularly suitable in transformer approaches that require
output phases that are of a number not evenly divisible by
three. |
| |
|
| |
A distribution transformer
is a transformer that provides the final voltage
transformation in the electric power distribution system,
stepping down the voltage used in the distribution lines to
the level used by the customer. The invention of a practical
efficient transformer made AC power distribution feasible; a
system using distribution transformers was demonstrated as
early as 1882.
If mounted on a utility pole, they are called pole-mount
transformers. If the distribution lines are located at
ground level or underground, distribution transformers are
mounted on concrete pads and locked in steel cases, thus
known as pad-mount transformers.
Distribution transformers normally have ratings up to 200
kVA, although some national standards can describe units up
to 5000 kVA as distribution transformers. Since distribution
transformers are energized for 24 hours a day (even when
they don't carry any load), reducing iron losses has an
important role in their design. As they usually don't
operate at full load, they are designed to have maximum
efficiency at lower loads. To have a better efficiency,
voltage regulation in these transformers should be kept to a
minimum. Hence they are designed to have small leakage
reactance.
Distribution transformers are classified into
different categories based on certain factors such as:
• Mounting location - pole, pad,
underground vault
• Type of insulation - liquid-immersed
or dry-type
• Number of Phases - single-phase or
three-phase
• Voltage class
• Basic impulse insulation
level (BIL).
Distribution transformers are normally located at a
service drop, where wires run from a utility pole or
underground power lines to a customer's premises. They are
often used for the power supply of facilities outside
settlements, such as isolated houses, farmyards or pumping
stations at voltages below 30 kV. Another application is the
power supply of the overhead wire of railways electrified
with AC. In this case single phase distribution transformers
are used.
The number of customers fed by a single distribution
transformer varies depending on the number of customers in
an area. Several homes may be fed off a single transformer
in urban areas; rural distribution may require one
transformer per customer. A large commercial or industrial
complex will have multiple distribution transformers. Pad
mount transformers are used in urban areas and neighborhoods
where the primary distribution lines run underground. Many
large buildings have electric service provided at primary
distribution voltage. These buildings have customer-owned
transformers in the basement for step-down purposes. In a
secondary network system as used in urban areas, many
distribution transformers may be connected in parallel, each
equipped with its own network protector circuit breaker to
isolate it from the secondary network in case of a fault.
Distribution transformers are also found in the power
collector networks of wind farms, where they step up power
from each wind turbine to connect to a substation that may
be several miles (kilo meters) distant.
|
|
