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 veried 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, ofce 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 specically 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

Howard Industries, Inc.

Laurel, MS 39440

www.howardtransformers.com

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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 efciency. 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 certied 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 certication

is audited every six months with full

re-certication occurring every three

years.

Document No. 2.4.18 Revision: 2 Issued: October, 2013

Figure 3: ISO-9001 Certicate

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 verication 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 verication process

includes:

• Validation of transient voltage

response

• Validation of short-circuit strength

• Analysis of eddy losses and hotspot

calculations

• Validation of insulation design

• Verication 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 conguration

with step-lap joints to provide excellent mechanical strength and magnetic performance. Core designs use regular grain-oriented steels

Figure 5: Georg core cutter

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 congured to

contain mechanical short-circuit

forces and modied as necessary for leakage ux to limit excessive hot

spots.

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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 specied

pressure. Sizing pressure is determined by design engineering,

and is sufcient 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: Mical 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 Mical automated vapor-phase system (Figure 11).

Proper dryness is critical to maintain the integrity and life of the insulation

system. The Mical process

automatically monitors and controls moisture extraction in an oxygen-free environment, producing an extremely

dry insulation system. During the nal phase of the Mical process, the

Figure 12: Electrical test station

Howard Industries, Inc.

Laurel, MS 39440

www.howardtransformers.com

Medium Power Substation Transformers

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Transformer Class

Tests

Winding resistance

Winding insulation resistance (Megger)

Core insulation resistance (Megger)

Ratio

Polarity and phase relation

Insulation power factor

Control (auxiliary) cooling losses

Single-phase excitation tests

No-load losses and excitation current

Impedance voltage and load losses

Zero-phase sequence impedance voltage

Class I (≤ 69 kV) Class II (115-765 kV)

Standard Optional Standard Optional

• •

•

• •

Temperature rise

Low frequency dielectric tests

Low frequency dielectric tests on auxiliary devices,

control, and current transformer circuits

Lightning impulse

Front of wave impulse

Switching impulse

Partial discharge

Audible sound level

Operational tests (all devices)

Dissolved gases in oil

Leak test

• •

Howard Industries, Inc. Laurel, MS 39440 www.howardtransformers.com

Document No. 2.4.18

Revision: 2

Issued: October, 2013

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FEATURES AND ACCESSORIES

SUMMARY OF STANDARD FEATURES AND ACCESSORIES

Howard medium power substation transformers are supplied with the following standard features and accessories:

• Capacity range: Through 60 MVA

(ONAN), with high-voltage ratings

through 230 kV (900 kV BIL)

• Service location: Outdoor

• Core: Regular grain-oriented;

mitered cruciform with step-lap construction

• Coils: Cylindrical construction; all

copper windings, custom tempered

per design requirements; circular

windings with rectangular or

continuously-transposed conductor; helical low-voltage windings;

continuous disc medium-voltage

windings; shielded disc high-voltage

windings

• Conductor insulation: Thermally-

upgraded crepe paper taping

• Cooling/insulating uid: Type II

mineral oil

• Fluid preservation system: Sealed tank

• Tank: All-welded construction;

welded cover with manhole and

non-skid nish; base construction suitable for jacking, skidding, and

rolling

• Radiators: Detachable panel type with shut-off valves; mild steel

• Bushings: Oil-lled, cover-mounted,

condenser type with power factor test points

• Dial-type uid level gauge

• Dial-type uid temperature gauge

with maximum temperature drag hand

• Dial-type pressure/vacuum gauge

• Dial-type winding temperature

gauge with maximum temperature drag hand (standard on forcedcooled transformers only)

• Automatic pressure relief device

• Rapid pressure rise relay (mounted

on isolation valve)

• Fluid ll valve

• Fluid drain valve

• Diagrammatic nameplate, engraved

stainless steel

• Tank grounding pads

• Filter press connections (top and

bottom)

• Transformer lifting lugs

• Provision for cover-mounted

posttype fall-protection device

• Paint nish: Exterior polyurethane enamel, ANSI 70 gray color; interior

polyurethane enamel, white color

SUMMARY OF OPTIONAL FEATURES AND ACCESSORIES

Howard medium power transformers are available with many optional features and accessories to satisfy

a customers’ special needs for the

operation, protection, monitoring, and

maintenance of their equipment. The

following list contains the most frequently

requested options. Check with

the factory for the availability of other optional features and accessories not listed below.

• Cooling/insulating uid: Seedbased natural ester uid

• Bushing-mounted current

transformers

• Surge arresters and mounting brackets

• High-voltage and/or low-voltage

terminal compartments

• Wye-delta or series multiple

terminal connections

• Forced-air cooling with automatic

control system or provisions for forced-air cooling

• Control cabinet

• Nitrogen gas uid preservation

system

• Dial-type winding temperature

gauge (standard for forced-cooled transformers)

• Electronic temperature indicator

• Fiber-optic winding temperature

in dicator

• De-energized tap changer with padlocking provisions

Medium Power Substation Transformers

• On-load tap changer with

microprocessor-based control

• Special exterior paint color

• Galvanized or stainless-steel

radiators

• Cover-mounted fall-protection

device

INSULATING/COOLING FLUID

Power transformers are lled with Type II mineral oil that is highly rened

for excellent insulating properties and inhibited for long-term stability at elevated temperatures.

Less-ammable ester-based uids

are available as an option in the

main tank.

SELF-COOLED RATING

Power transformers rated for selfcooled operation (ONAN class) are designed to operate at rated load with

natural cooling by ambient air ow

outside the transformer and natural oil convection within the transformer

tank. Heat is radiated from the

transformer

tank and from tank-mounted

radiator panels.

FORCED-AIR COOLED RATINGS

A single-stage forced air cooling system may be supplied to increase the transformer load capacity (ONAF

Figure 13: Cooling fans and panel radiator

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Howard Industries, Inc.

Laurel, MS 39440

www.howardtransformers.com

Medium Power Substation Transformers

class) (Figure 13).

Sealed motor-driven fans are mounted on radiators to provide

increased air ow. Fan operation

may be manual or may be controlled automatically by temperature sensors mounted inside the transformer. Fans are connected to a weatherproof control box with weatherproof cable and a separable connector.

A second stage of forced-air cooling

may be used (ONAF/ONAF class) to

provide a further increase in load capacity beyond that provided by single-stage forced-air cooling. Stages one and two are operated automatically by heat sensors

mounted inside the transformer tank

and a control panel mounted inside the control cabinet.

FLUID PRESERVATION

A sealed-tank uid preservation

system is standard on all Howard

medium power transformers. The interior of the tank is sealed from the

ambient atmosphere, such that the gas-plus-oil volume remains constant throughout the range of normal operating temperatures. An automatic pressure relief device is provided to vent excessive pressure that might build up gradually during extreme overloads or fault conditions. A

pressure/vacuum gauge is provided

to measure internal pressure. Prior to shipping the gas space is pressurized

with a dry air or nitrogen blanket.

INERT GAS SYSTEM

An optional nitrogen inert-gas system provides a constant nitrogen atmosphere in the gas space of the

transformer (Figure 14). The nitrogen blanket protects the transformer uid from deterioration

that could occur from exposure to moisture or oxygen. Main system components include a nitrogen cylinder, pressure regulators, valves,

and gauges. The system also includes

provisions for various pressure

alarms. A lockable weatherproof

enclosure protects the system.

BUSHINGS

Standard bushings are oil-lled

condenser-type with porcelain

housings (Figure 15).

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Figure 16: CTs mounted under cover

SURGE ARRESTERS

Surge arresters are porcelain or polymer housed, gapless metaloxide-varister (MOV) type (Figure

17), externally mounted on heavy steel brackets. All arresters meet the requirements of IEEE C62.11.

Figure 14: Nitrogen system

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Figure 15: High voltage bushing

All bushings meet the requirements

of the IEEE C57.19 series of

standards.

CURRENT TRANSFORMERS

Current transformers (CTs) are bushing-mounted in the main tank interior (Figure 16). All CTs meet the requirements of the IEEE C57.13

series of standards.

Figure 17: Lightning arrester

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Medium Power Substation Transformers

GAUGES

All gauges are dial-type and are located for convenient viewing at

ground level (Figure 18).

Figure 18: Gauges

Fluid temperature and winding temperature gauges have resettable maximum temperature drag hands.

ELECTRONIC MONITORING

Various sophisticated electronic monitoring systems are available as options, including those that monitor oil temperature, winding temperature, pressure, moisture, gases, apparent charge, arrester surge count, and

leakage current. Contact the factory

for these and other monitoring systems that may be available.

CONTROL CABINET

The control cabinet provides a

weatherproof enclosure for accessory

items such as fan controls, OLTC controls, and terminal blocks for customer connections (Figure 19).

with three-point latch and padlock provisions. The cabinet interior is

painted white to improve visibility and

is equipped with a work light and

accessory power outlet.

PRESSURE RELIEF DEVICE

A cover-mounted automatic pressurerelief device is provided to vent excessive pressure that might build up gradually during extreme over-

loads or fault conditions (Figure 20).

Figure 20: Pressure relief device

The standard device has a 6” throat and a cracking pressure of 10 psi. Devices with other pressure and ow

characteristics are available with nonstandard operating characteristics. Options include alarm contacts,

indicating ag, and discharge diverter.

DE-ENERGIZED TAP CHANGER

A de-energized tap changer can be provided to adjust the transformer voltage ratio to meet system requirements. An external operating handle is mounted on one end of the trans-

former near ground level (Figure 21).

The handle can be locked in any

switch position and has provisions for

a padlock.

ON-LOAD TAP CHANGER

A three-phase on-load tap changer

(OLTC) provides automatic voltage

regulation in an energized trans-

former while serving load (Figure 22).

Figure 22: On-load tap changer

OLTC’s typically operate over a range of thirty-two 5/8% voltage steps,

sixteen above and sixteen below

rated secondary voltage. The total tap range is typically 20% (10% above and 10% below rated secondary voltage). Standard OLTC’s provided

on Howard transformers use vacuum interrupter technology manufactured

by Reinhausen or ABB.

The OLTC switch mechanism is sealed in an oil-lled enclosure welded to

one end of the main transformer

tank. A motor drive and switch

position indicator are housed in a weatherproof cabinet mounted below

the switch mechanism. A crank lever

is provided to operate the tap changer manually.

Figure 19: Control cabinet

The cabinet is mounted on the side of the transformer tank. Access to the

cabinet is protected by a hinged door

Document No. 2.4.18 Revision: 2 Issued: October, 2013

Figure 21: DETC handle

OLTC control panels are housed in the control cabinet (Figure 23).

A variety of microprocessor-based controls are available, including those

manufactured by Beckwith, ICMI, and

Reinhausen. In addition to the automatic regulation of secondary voltage, control systems can also be equipped to provide communication, data storage, and power quality analysis. All controls are provided with manual override capability.

Howard Industries, Inc.

Laurel, MS 39440

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Medium Power Substation Transformers

Figure 23: OLTC control

TANK

Howard transformer tanks are

rectangular all-welded steel construction and are designed for strength,

durability, and compact form. Tank

corners are folded with welds made six inches from corners (no corner

welds). Tanks are reinforced with

external enclosed-box bracing to provide the necessary strength and rigidity.

Cover-mounted lifting lugs are provided for lifting the transformer cover. Additional lifting lugs are provided for safely lifting the completely assembled transformer. Copper or stainless-steel ground

pads are located on tank sides near ground level. Transformer covers are

constructed of a heavy steel plate that is internally braced and welded

to the tank. Bolted and gasketed

manhole covers are provided to allow convenient access to the main

tank interior. Covers are supplied

with provision for a post-type fall protection device. Other fall-protection provisions or systems are available as options.

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with a durable polyurethane topcoat.

Tank interiors are painted white. Tank

covers have a slip-resistant surface

nish.

RADIATORS

Panel-type radiators provide additional cooling to supplement heat

radiation from the transformer tank (Figure 13). The number and size of

radiators is determined by the design. Radiators are typically detachable and are provided with individual shutoff valves. Standard radiators are made of cold-rolled mild steel that is

primed and nished with a durable

polyurethane top coat. Stainless steel and galvanized radiators are available as options.

OTHER FEATURES AND ACCESSORIES

Contact the factory for other features and accessories that are not discussed here but may beavailable as options.

The standard tank base is construct-

ed of a heavy plate steel that is

suitable for rolling or skidding in all directions. Jacking pads are provided on all four corners of the tank to allow for jacking of the completely

assembled transformer.

Tank surfaces are sand blasted and

coated with a rust inhibiting primer. After assembly and before shipping,

completed transformers are leak tested, washed and then nished

Howard Industries, Inc. Laurel, MS 39440 www.howardtransformers.com

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Medium Power Substation Transformers

DELIVERY AND INSTALLATION

Delivery is made by truck whenever

possible or by rail when transformer

size or weight makes truck delivery

impractical. An impact recording device is provided on all rail ship-

ments and can be provided on truck

shipments upon customer request.

Figure 24: On-site installation

Impact recorders measure and store three-axis impact data, identifying any abnormally severe impacts that might have caused damage to the transformer during transportation.

Howard Industries offers a full

complement of eld installation

services, including unloading, inspec-

tion, assembly, vacuum oil lling, and testing under the supervision of eld service technicians (Figure 24). Field

supervision is available for customerinstalled jobs. Field inspection

includes checks of bushings, gasket seals, tank pressure, tap changer operation, and controls. Tests include

turns ratio, insulation resistance, power factor, internal moisture, and oil dielectric strength.

Document No. 2.4.18 Revision: 2 Issued: October, 2013

Howard Industries, Inc.

Laurel, MS 39440

www.howardtransformers.com

Medium Power Substation Transformers

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NOTES

Howard Industries, Inc. Laurel, MS 39440 www.howardtransformers.com

Document No. 2.4.18

Revision: 2

Issued: October, 2013

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Medium Power Substation Transformers

Document No. 2.4.18 Revision: 2 Issued: October, 2013

Medium Power Substation Transformers

Catalog Section 34-10

Document 2.4.18, Revision 2, October 2013

Laurel, Mississippi

Telephone: 601-425-3151

Fax: 601-649-8090

E-mail: mkt@howard.com

Web: howardtransformers.com

www.howardtransformers.com

Howard Industries, Inc.

Laurel, MS 39440

Howard Substation Transformers User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual