Howard Substation Transformers User Manual
Howard Industries, Inc.
Substation Transformer Division
INTRODUCTION
Howard medium power substation
transformers are designed and
built according to the most
exacting engineering standards to
provide many years of outstanding
performance and reliability in the
most demanding utility, industrial,
and commercial applications.
All designs incorporate the latest
advances in materials, design
techniques, and power transformer
technology veried with 2D and
3D analysis software. Howard’s
Substation Division has staffed
its operations with well-trained
engineers, winders, assemblers,
and testers, with many years of
experience in the development,
design, and manufacture of medium
and large power transformers.
Catalog Section
Medium Power
34-10
Substation Transformers
Howard’s Substation Transformer
Division also offers nationwide
delivery and the option of complete
job-site services, including unloading,
inspection, assembly, uid lling, and
testing. Field supervision is available
for customer-installed jobs.
PRODUCT SCOPE AND
APPLICATIONS
Howard Industries currently
manufactures uid-lled medium
power substation transformers with
capacities through 60 MVA (ONAN)
and primary voltage ratings through
230 kV at 900 kV BIL.
An extensive range of features and
accessories are available, including
de-energized tap changers, on-load
tap changers, forced-air cooling
systems, uid preservations systems,
and many other options to satisfy the
special requirements of virtually any
application.
Figure 1: Medium power substation transformer with forced air cooling
Howard medium power substation
transformers are suitable for a wide
range of demanding applications,
including utility substations, wind
generation sites, chemical plants, oil
and gas processing facilities, mining
operations, paper mills, steel mills,
water treatment plants, ofce and
shopping centers, internet server
facilities, and many other uses.
MANUFACTURING FACILITIES
Howard’s new 355,000 square foot
substation manufacturing facility
(Figure 2) was custom designed and
built specically for the production of
medium power transformers. Every
aspect of the facility’s design and
construction was carefully considered
to maximize its manufacturing
capabilities and provide the exibility
needed to satisfy ever-changing
Figure 2: Howard Industries Substation Plant,
Ellisville, MS
customer requirements. The facility’s
air handling systems maintain a
clean, positive-pressure environment
throughout, with temperature and
humidity controlled conditions
maintained in the insulation staging
and winding room. All oor surfaces
are sealed to help control airborne
contamination. Tank fabrication,
insulation cutting, uid storage and
Document No. 2.4.18
Revision: 2
Issued: October, 2013
Copyright © 2013 Howard Industries, Inc.
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Howard Industries, Inc.
Laurel, MS 39440
www.howardtransformers.com
34-10
Medium Power Substation Transformers
processing, and other potential
sources of contamination are isolated
from the main facility. Heavy-capacity,
high-lift gantry cranes can travel the
entire length of the manufacturing
area and beyond to the covered truck
and rail loading bay.
Production processes use the latest
available technologies to enhance
quality and efciency. Computer-
controlled coil sizing, vapor-phase
coil drying, computer-controlled
core lamination cutting (Georg) and
state-of-the-art electrical test systems
are just a few examples of leadingedge technologies that contribute to
process precision and repeatability.
QUALITY
Howard employees understand the
importance of quality, particularly
as it relates to the critical nature of
substation transformers. Emphasis
on quality begins at design and
follows throughout the manufacturing
and delivery processes. Only the
highest quality components and
materials are used in Howard
transformers. Attention to detail
and thorough inspection and testing
ensure that a high level of quality
is maintained. Continuous process
improvement is an integral part of our
design and manufacturing goals.
The Substation Transformer Division’s
quality management system is
designed to ensure that all of the
company’s products and services
meet or exceed its customers’
requirements and is certied as
being compliant with ISO-9001:2008
(Figure 3). The ISO-9001 standard
covers design, manufacturing,
and servicing systems, and is the
most stringent and comprehensive
standard in the internationally
recognized ISO-9000 series of
quality standards. This certication
is audited every six months with full
re-certication occurring every three
years.
Document No. 2.4.18
Revision: 2
Issued: October, 2013
Figure 3: ISO-9001 Certicate
Copyright © 2013 Howard Industries, Inc.
2
Howard Industries, Inc.
Laurel, MS 39440
www.howardtransformers.com
Medium Power Substation Transformers
DESIGN AND MANUFACTURING PROCESSES
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TRANSFORMER DESIGN
Howard’s design philosophy employs
technology in ways that provide a
cost-competitive transformer built
with conservative design margins, a
thorough verication of designs using
the latest computer analysis tools,
and automation of the design process
to reduce cycle time and eliminate
human error.
Our experienced mechanical
designers employ the latest available
computer-based design tools, such as
parametric 3D computer-aided design
systems (Figure 4) for both internal
and external layouts. The Anderson
2D nite element analysis program,
the Ansoft Maxwell 2D electrostatic
and magnostatic eld analysis
program, 3D ALGORE mechanical
analysis program, and others are
used in the determination of electrical
and mechanical design margins.
Howard substation transformers are
designed with conservative
mechanical and electrical margins to
withstand the harsh environments
encountered in today’s power delivery
systems. Exceptional short-circuit and
impulse strengths are hallmarks of
the Howard design. All transformer
designs are optimized to satisfy our
customers’ total cost of ownership
requirements.
General industry standards applicable
to Howard substation transformer
designs include IEEE C57.12.00
(Standard General Requirements for
Liquid-Immersed Distribution, Power,
and Regulating Transformers), IEEE
C57.12.90 (Standard Test Code for
Liquid-Immersed Distribution, Power
and Regulating Transformers and
Guide for Short Circuit Testing of
Distribution and Power Transformers),
IEEE C57.93 (Guide for Installation
of Liquid-Immersed Power Transformers), IEEE C57.98 (Guide for
Transformer Impulse Tests), and IEEE
C57.100 (Standard Test Procedure for
Thermal Evaluation of Oil Immersed
Distribution Transformers).
which have been precision slit to
width and stress-relieved by our
supplier. Core laminations are
precisely cut to length and mitered on
a computer-controlled Georg cutting
line (Figure 5).
Core laminations are carefully
stacked on precision hydraulic lift
tables to prevent misalignment when
up-righting (Figure 6).
Figure 6: Core Stacking Table
Cores are securely banded and
clamped with tie plates to ensure
stability and minimize stress on the
core. Core support blocks (Figure 7)
Figure 4: Image of 3D CAD model
The design verication process
includes:
• Validation of transient voltage
response
• Validation of short-circuit strength
• Analysis of eddy losses and hotspot
calculations
• Validation of insulation design
• Verication of loading beyond
nameplate capacity
• In-rush current analysis
• Over-voltage analysis
Howard Industries, Inc.
Laurel, MS 39440
www.howardtransformers.com
MAGNETIC CIRCUIT
Howard medium power substation
transformers employ core-type
construction and are designed with
an optimized cruciform conguration
with step-lap joints to provide
excellent mechanical strength and
magnetic performance. Core designs
use regular grain-oriented steels
Figure 5: Georg core cutter
Copyright © 2013 Howard Industries, Inc.
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Figure 7: Core support blocks
and cooling ducts are used to provide
uniform pressure across the
lamination surface. The top and
bottom core clamps are held together
by steel lock plates congured to
contain mechanical short-circuit
forces and modied as necessary
for leakage ux to limit excessive hot
spots.
Document No. 2.4.18
Revision: 2
Issued: October, 2013
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Medium Power Substation Transformers
ELECTRICAL CIRCUIT
Windings are cylindrical construction,
with concentric windings separated by
axial oil ducts (Figure 8).
Figure 8: Coil winding
The type of winding used depends
on the voltage rating. Low-voltage
windings are helical type, mediumvoltage windings are continuous disc
type, and high-voltage windings are
shielded disc. Conductor material
is C11000 grade copper, tough
pitch cast, with ASTM edge radius,
and custom tempered per design
requirements. The conductor is
insulated with thermally upgraded
crepe paper tape, wrapped in multiple
layers. Rectangular conductor or
continuously-transposed cable
(CTC) is used according to design
requirements.
Finished coils are oven dried and
accurately sized in a computer-
controlled hydraulic press (Figure 9).
Coil sizing establishes the coil’s
electrical length at a specied
pressure. Sizing pressure is
determined by design engineering,
and is sufcient to contain axial short-
circuit forces that would be generated
during throughfault conditions.
ASSEMBLY
After the coil sizing process is
completed, core and coils are
assembled together in a heavy-duty
clamping structure that produces
a rugged, stable assembly, yet
minimizes mechanical stress in the
core (Figure 10).
Figure 10: Core coil unit
High-density laminated pressure rings
transmit uniform clamping pressure
to each coil. The lead structure is
designed to provide generous
dielectric clearance and to resist
the lead forces generated by system
faults. Leads are secured using
either pressboard or kiln-dried maple
braces.
Figure 11: Mical vapor phase system
drying chamber is ooded with
transformer oil to impregnate the
insulation system fully.
FACTORY TESTING
In addition to numerous quality
inspections throughout the manu-
facturing process, nal tests are
conducted on the completed
transformer to ensure proper
function of all systems. All tests
are conducted in accordance with
applicable industry standards. Test
equipment is state-of-the-art and
capable of extremely accurate and
reliable test measurements, meeting
all the industry loss measurement
standards. (Figure 12). All test
systems are calibrated regularly
according to industry standards.
Figure 9: Coil sizing press
Document No. 2.4.18
Revision: 2
Issued: October, 2013
COIL DRYING
Core and coils are dried and oil
impregnated in a Mical automated
vapor-phase system (Figure 11).
Proper dryness is critical to maintain
the integrity and life of the insulation
system. The Mical process
automatically monitors and controls
moisture extraction in an oxygen-free
environment, producing an extremely
dry insulation system. During the nal
phase of the Mical process, the
Copyright © 2013 Howard Industries, Inc.
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Figure 12: Electrical test station
Howard Industries, Inc.
Laurel, MS 39440
www.howardtransformers.com
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