Howard Substation Transformers - Manual (Page 6)

Copyright © 2013 Howard Industries, Inc. Howard Industries, Inc.
Laurel, MS 39440
www.howardtransformers.com
Document No. 2.4.18
Revision: 2
Issued: October, 2013
6
Medium Power Substation Transformers
34-10
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 fluid: Type II
mineral oil
• Fluid preservation system: Sealed
tank
• Tank: All-welded construction;
welded cover with manhole and
non-skid finish; base construction
suitable for jacking, skidding, and
rolling
• Radiators: Detachable panel type
with shut-off valves; mild steel
• Bushings: Oil-filled, cover-mounted,
condenser type with power factor
test points
• Dial-type fluid level gauge
• Dial-type fluid temperature gauge
with maximum temperature drag
hand
• Dial-type pressure/vacuum gauge
• Dial-type winding temperature
gauge with maximum temperature
drag hand (standard on forced-
cooled transformers only)
• Automatic pressure relief device
• Rapid pressure rise relay (mounted
on isolation valve)
• Fluid fill 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 finish: 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 fluid: Seedbased
natural ester fluid
• 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 fluid 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 pad-
locking provisions
• 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 filled with
Type II mineral oil that is highly
refined
for excellent insulating properties
and inhibited for long-term
stability at elevated temperatures.
Less-flammable ester-based fluids
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 flow
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
FEATURES AND ACCESSORIES
Figure 13: Cooling fans and panel radiator