Download HI-102 Guide for the Installation, Operation, and Maintenance of

Technical Product Guide
Document: 2.4.50
Revision: 3
February 20, 2009
Authorized By: RSS
HI-102
Guide for the Installation, Operation, and Maintenance
of Pole-Mounted Distribution Transformers
Transformers covered by these instructions should be operated and serviced only by competent
personnel familiar with good safety and technical practices. These instructions are written for such
personnel and are not intended as a substitute for adequate training and experience in equipment of this
type.
Inspection
Howard Industries distribution transformers are normally shipped completely assembled, oil filled, and
ready to install. It should not be necessary to inspect the transformer internally or examine the insulating
oil unless the unit has been damaged during shipment. Immediately upon receipt of the transformer,
examine it for any damage that may have occurred during shipment. The transformer should be checked
electrically for voltage rating, voltage output, open or short, etc. before installation. If any damage or
rough handling is evident, file a damage claim with the transportation company immediately and notify
your Howard Industries sales representative. Check the material against the bills of lading to ascertain
that the correct equipment has been received.
Handling
Lifting provisions are provided for lifting the transformer. Always lift the transformer by the main lifting
lugs, using a sling and spreader of adequate capacity.
Storage
Transformers should always be stored with the tank sealed and filled with oil to the proper level.
Adequate care should be taken to protect the transformer against damage during storage.
Installation
Transformers should be lifted by the lifting lugs only. The transformer bushings should not be used for
lifting the transformer into position. Support lugs for direct pole mounting on overhead transformers are
provided in accordance with ANSI standards.
Connections
WARNING! Do not change connections while a transformer is energized.
CAUTION! Before removing any covering, shipping plate or other device, vent the tank to atmospheric
pressure by use of the venting device provided on the transformer. Refer to the transformer nameplate
for the kVA rating and permissible connections. No connections other than those shown on the
nameplate should be made.
WARNING! The tap changer on the dual voltage switch must not be operated while the transformer is
energized. Provision is made for grounding the tank by means of a tapped pad. On single bushing
transformers, it is advisable to connect the tank and the low voltage neutral to the system neutral through
conductors of adequate capacity before voltage is applied to the transformer. Connections should then
be made to the low voltage and finally to the high voltage. When disconnecting the transformer, all high
voltage connections, including those to protective devices, should be opened first. These instructions are
not intended to relieve the customer of his responsibility for using safe and technically sound utility
operating practices.
Protective Devices
Transformer protection against overloads and over-voltages may be obtained by suitable devices applied
in the field to conventional transformers, or by the use of protected (Howard Industries CSP types)
transformers as supplied from the factory.
Howard Industries, Inc. / P.O. Box 1588 / Laurel, MS 39441-1588 USA / www.howardtransformers.com
Technical Product Guide
Document: 2.4.50
Revision: 3
February 20, 2009
Authorized By: RSS
Fuses—High-voltage fused cutouts are recommended for protection of conventional transformers
against overloads and to protect the line against outages.
On Howard Industries CSP transformers, a fusible protective link, mounted inside the tank, is
provided in series with each HV terminal. In case of internal failure of the transformer, the protective
link disconnects the transformer from the line without affecting line fuses or breakers.
Lightning Arresters—Conventional transformers should be protected by properly rated lightning
arresters. Ground connections on the arresters should be made before connection to the highvoltage line is made.
On Howard Industries CSP transformers, lightning protection is normally provided by lightning
arresters bolted to mounting pads welded to the tank wall. For externally gapped arresters, an
adjustable electrode on the top terminal of the arrester is provided for obtaining the proper gap setting
to the bushing electrode. The bottom of the arrester is permanently grounded to the tank wall.
Before the transformer is put into service, the arrester gap should be checked for alignment and
adjusted to the spacing marked on the arrester electrode.
If specified, a direct connected arrester will be provided.
Secondary breaker—Howard Industries CSP transformers are protected against secondary overloads
and short circuits by an internally mounted circuit breaker. The breaker tripping mechanism is
governed by a bimetal element that trips the breaker at short circuit or any degree of overload
consistent with safe winding temperature.
The breaker operating mechanism is designed to be operated by a lineman’s hot stick. To open the
breaker, raise the handle until its pointer coincides with the line of the breaker nameplate marked “O”
(open). To close, lower the handle until its pointer coincides with the line marked “C” (close). To
reset the breaker after it has tripped from overload, move the handle until the pointer coincides with
“R” (reset), then move it to the “C” (close) position.
Some breakers are provided with a signal light. When the signal light is energized, it indicates that
the hot spot of the winding has reached its maximum rated value for continuous full load operation.
The light will remain on until it is reset. To reset the signal light, without disconnecting the load from
the transformer, move the handle until the pointer coincides with “L” (light). The signal will go out.
Then move the handle back to “C” (close) position. If the overload conditions still exist, the light will
quickly come on again.
Some breakers are provided with an emergency overload adjustment. The handle for this device is
located close to the main operating handle. When shipped from the factory, the emergency handle of
the breaker has a meter seal attached to assure that emergency overloads are not inadvertently
permitted. If, prior to the installation, emergency overloads are anticipated, the meter seal should be
cut free. If sustained overloads should trip the breaker, and it is desired to maintain service in spite of
the overload, the emergency setting may be adjusted to an intermediate or extreme value. The
higher the setting, the greater the loss of transformer life during the emergency setting, because of
the greater than normal temperatures. It is recommended that the emergency handle be returned to
the normal position at the earliest possible opportunity.
The breaker is a thermal protective device for the transformer. It is not recommended that the
breaker be used for routine disconnect operations.
Howard Industries, Inc. / P.O. Box 1588 / Laurel, MS 39441-1588 USA / www.howardtransformers.com
Technical Product Guide
Document: 2.4.50
Revision: 3
February 20, 2009
Authorized By: RSS
Distribution transformers equipped with a combination cutout and lightning arrester are shipped with the
fuse and flipper removed and the fuse contact rotated toward the transformer. Loosen the locking nut
and rotate the contact so that the open end is away from the transformer. Adjust electrode gap to the
spacing shown on the electrode. Retighten the locking nut.
Assemble the rod end of the flipper into the high voltage bushing cable clamp, with the open side of the
contact end away from the lightning arrester.
The standard fuse has a pointed ring attached to one lead and a round ring on the other lead. Insert the
fuse lead with the pointed ring into the “V” of the flipper contact. Bend the flipper toward the arrester and
insert the fuse lead with the round ring into the “V” of the arrester contact fork.
Operation
This transformer has been designed to carry rated load with a temperature rise equal to or less than the
value shown on the nameplate. The coil insulation has been carefully selected and made with thermally
upgraded materials to ensure long life at the rated temperature and 30 ambient. Overloads in excess of
the rating can be tolerated if accompanied by longer periods of light loading. Severe and prolonged
overloads will result in overheating and accelerated aging of the insulation, which may lead to premature
failure. For more information about the relationship between loading and insulation life, refer to the
applicable ANSI Loading Guide.
Transformers should be protected from transient voltages, fault currents, and severe overloads. Some
transformers are equipped with lightning arresters, fuses, and circuit breakers to provide this protection;
the operation of these accessories is described in the preceding section. If this transformer is not so
equipped, refer to the Howard Industries office for specific recommendations.
If a three-wire low-voltage connection is used on a single-phase transformer, the loads connected from
line to neutral should be as nearly equal as possible and should not exceed one-half the rated kVA for
prolonged time periods.
Maintenance
Renewal parts may be acquired by ordering them from Howard Industries by describing the part and
giving the serial number on the transformer. If your Howard Industries transformer needs repair that is
beyond the capability of the user’s repair facilities, contact the local Howard Industries representative.
Howard Industries, Inc. / P.O. Box 1588 / Laurel, MS 39441-1588 USA / www.howardtransformers.com