Transformadores De Distribucion
Páginas: 30 (7494 palabras)
Publicado: 24 de septiembre de 2012
Shoemaker_CH15.qxd
13/07/06
11:43AM
Page 15.1
CHAPTER 15
DISTRIBUTION
TRANSFORMERS
The purpose of a distribution transformer is to reduce the primary voltage of the electric
distribution system to the utilization voltage serving the customer. A distribution transformer is a static device constructed with two or more windings used to transfer alternatingcurrent electric powerby electromagnetic induction from one circuit to another at the same
frequency but with different values of voltage and current.
Figure 15.1 shows distribution transformers in stock at an electric utility company service building. The distribution transformers available for use for various applications, as
shown, include pole-type (Figs. 15.2 and 15.3), pad-mounted (Fig. 15.4), vault ornetwork
type (Fig. 15.5), and submersible (Fig. 15.6).
The distribution transformer in Fig. 15.2 is self-protected. It is equipped with a lightning
arrester, a weak-link or protective-link expulsion-type fuse (installed under oil in the transformer tank), a secondary circuit breaker, and a warning light. The transformer primary
bushing conductor is connected to one phase of the three-phase primarycircuit through a
partial-range current-limiting fuse. The transformer tank is grounded and connected to the
FIGURE 15.1 Electric utility distribution storage yard. Forklift trucks are used
to load transformers on line trucks. Storage area is covered with concrete to provide accessibility and protect transformers.
15.1
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15.2
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Page 15.2CHAPTER 15
FIGURE 15.2 Typical pole-type distribution transformer installation with
the transformer bolted directly to the
pole. The unit is equipped with a surge
arrester, a low-voltage circuit breaker,
and an overload warning light. A partialrange current-limiting fuse is mounted
on the primary bushing, connecting it in
series with the high-voltage winding to
prevent a violent failureof the transformer if an internal fault develops.
primary and secondary common-neutral ground wire. The self-protected transformer contains a core and coils, a primary fuse mounted on the bottom of the primary bushing, a secondary terminal block, and a low-voltage circuit breaker.
Convential overhead transformers are also available. The key component distinguishing the conventionaltransformer from the self-protected transformer is the lack of internal
fusing in the conventional model. An external fuse/cutout combination is mounted between
the distribution primary and the conventional transformer. A conventional unit is depicted
in Fig. 15.3.
Pad-mounted transformers are used with underground systems. Three-phase padmounted transformers are used for commercial installations, asillustrated in Fig. 15.4, and
single-phase pad-mounted transformers are used for underground residential installations,
as described and shown in Chap. 34. Vault-type distribution transformers are installed for
commercial customers where adequate space is not available for pad-mounted transformers. The vault-type transformer (Fig. 15.5) may be installed in a vault under a sidewalk or
in abuilding. They are often used in underground electric network areas.
Submersible single-phase distribution transformers (Fig. 15.6) are used in some underground systems installed in residential areas, as described in Chap. 34. Corrosion problems
and the high cost of installation have minimized the use of submersible transformers.
Distribution Transformer Operation. The basic principle ofoperation of a transformer
is explained in Chap. 1. A schematic drawing of a single-phase distribution transformer
appears in Fig. 15.7. The single-phase distribution transformer consists of a primary winding and a secondary winding wound on a laminated steel core. If the load is disconnected
from the secondary winding of the transformer and a high voltage is applied to the primary
winding of the...
13/07/06
11:43AM
Page 15.1
CHAPTER 15
DISTRIBUTION
TRANSFORMERS
The purpose of a distribution transformer is to reduce the primary voltage of the electric
distribution system to the utilization voltage serving the customer. A distribution transformer is a static device constructed with two or more windings used to transfer alternatingcurrent electric powerby electromagnetic induction from one circuit to another at the same
frequency but with different values of voltage and current.
Figure 15.1 shows distribution transformers in stock at an electric utility company service building. The distribution transformers available for use for various applications, as
shown, include pole-type (Figs. 15.2 and 15.3), pad-mounted (Fig. 15.4), vault ornetwork
type (Fig. 15.5), and submersible (Fig. 15.6).
The distribution transformer in Fig. 15.2 is self-protected. It is equipped with a lightning
arrester, a weak-link or protective-link expulsion-type fuse (installed under oil in the transformer tank), a secondary circuit breaker, and a warning light. The transformer primary
bushing conductor is connected to one phase of the three-phase primarycircuit through a
partial-range current-limiting fuse. The transformer tank is grounded and connected to the
FIGURE 15.1 Electric utility distribution storage yard. Forklift trucks are used
to load transformers on line trucks. Storage area is covered with concrete to provide accessibility and protect transformers.
15.1
Shoemaker_CH15.qxd
15.2
13/07/06
11:43AM
Page 15.2CHAPTER 15
FIGURE 15.2 Typical pole-type distribution transformer installation with
the transformer bolted directly to the
pole. The unit is equipped with a surge
arrester, a low-voltage circuit breaker,
and an overload warning light. A partialrange current-limiting fuse is mounted
on the primary bushing, connecting it in
series with the high-voltage winding to
prevent a violent failureof the transformer if an internal fault develops.
primary and secondary common-neutral ground wire. The self-protected transformer contains a core and coils, a primary fuse mounted on the bottom of the primary bushing, a secondary terminal block, and a low-voltage circuit breaker.
Convential overhead transformers are also available. The key component distinguishing the conventionaltransformer from the self-protected transformer is the lack of internal
fusing in the conventional model. An external fuse/cutout combination is mounted between
the distribution primary and the conventional transformer. A conventional unit is depicted
in Fig. 15.3.
Pad-mounted transformers are used with underground systems. Three-phase padmounted transformers are used for commercial installations, asillustrated in Fig. 15.4, and
single-phase pad-mounted transformers are used for underground residential installations,
as described and shown in Chap. 34. Vault-type distribution transformers are installed for
commercial customers where adequate space is not available for pad-mounted transformers. The vault-type transformer (Fig. 15.5) may be installed in a vault under a sidewalk or
in abuilding. They are often used in underground electric network areas.
Submersible single-phase distribution transformers (Fig. 15.6) are used in some underground systems installed in residential areas, as described in Chap. 34. Corrosion problems
and the high cost of installation have minimized the use of submersible transformers.
Distribution Transformer Operation. The basic principle ofoperation of a transformer
is explained in Chap. 1. A schematic drawing of a single-phase distribution transformer
appears in Fig. 15.7. The single-phase distribution transformer consists of a primary winding and a secondary winding wound on a laminated steel core. If the load is disconnected
from the secondary winding of the transformer and a high voltage is applied to the primary
winding of the...
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