Features and accessories – Howard Network Transformers User Manual

Page 5

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Catalog Section 94-10

Network Transformers

Issued: April 9, 2010

Howard Industries, Inc.

Laurel, MS 39440


Copyright © 2010 Howard Industries, Inc.


Network Transformer


Howard network transformers are available with a wide

range of features and accessories in order to satisfy the

requirements of even the most demanding applications.

Contact the factory or your area sales representative for
the availability of other design options not listed.

Standard Features and Accessories

Howard network transformers are supplied with the follow-

ing standard features and accessories:

• Self-cooled power ratings (ONAN)—300 kVA through

2,500 kVA, three-phase

• High-voltage rating—from 2.4 kV through 34.5 kV

• High-voltage taps—Per ANSI C57.12.40.

• Low-voltage ratings—through 600 Volts

• BIL levels—Per ANSI C57.12.40

• Excitation limit—Per ANSI C57.12.00

• Average temperature rise—55ºC/65ºC

• Frequency—60 Hertz

• Impedance and impedance tolerance—Per ANSI


• Audible sound levels—Per ANSI C57.12.40

• Service location—vault-type network transformers are

suitable for installation in above-ground dry vaults

where occasional submersion is possible. Subway-

type network transformers are suitable for installation

in subsurface vaults where frequent or continuous

submersion is likely. Subway type designs are suit-

able for subway or vault applications.

• Cooling/insulating fluid—Type II mineral oil with oxida-

tion inhibitor

• Fluid preservation system—sealed tank

• Main tank—copper-bearing steel construction, with

sub-base, main cover, and the following standard ac-


− Dial-type magnetic liquid-level indicator (without

alarm contacts) welded to tank

− Dial-type thermometer (without alarm contacts)

− Combination drain and bottom filter valve

− Filling plug and upper filter press connection

− Top liquid sampling plug

− Air test provision

− Grounding pad welded to tank

− Lifting provisions for complete unit

− Lifting provisions for main tank cover

− Cover-mounted, pad-lockable tap changer switch

under protective pipe cap for de-energized opera-

tion (on units supplied with high-voltage taps)

− Bolted hand hole cover

− Corrosion-resistant steel fastening hardware

− Secondary throat suitable for mounting network

protector, with mounting holes, guide pins, gas-

ket, and steel plate shipping guard

− Subway-type radiator panels (when required by


− Pressure-relief valve (subway type)

• Primary terminal chamber—sealed enclosure welded

to main tank above the primary switch chamber, with

the following standard accessories:

− Bolted cover with, gasket, guide pins, and lifting


− Drain plug

− Liquid filling plug

− Liquid level and vent plug

− Three replaceable primary bushings between

terminal chamber and switch chamber, with ter-


− Primary entrance consisting of one of the follow-

ing two methods: 1) wiping sleeves or 2) dead-

front bushing bushings

• Primary switch chamber—sealed enclosure welded to

main tank beneath the primary switch chamber, with

the following accessories:

− Bolted cover with, gasket, guide pins, and lifting


− Three-pole, three-position, 200 Ampere, non-

interrupting high-voltage switch and external

operating handle with latch

− Electrical interlock on switch

− Dial-type magnetic liquid level indicator welded to

chamber (without alarm contacts)

− Liquid filling plug

− Air test provision

− Drain valve

− Mineral oil insulating fluid

• Low-voltage termination consisting of the following:

− Three externally replaceable bushings bolted to

the tank within the secondary throat

− Three flexible connectors for electrical connection

to a network protector

− Low-voltage neutral connection welded to the


• Paint finish—catalyzed epoxy primer plus catalyzed

urethane enamel topcoat; 3.0 mils nominal dry thick-


• Nameplate—non-corrosive diagrammatic nameplate,

permanently attached with non-corrosive hardware

Features and Accessories