Howard Medium Power Substation User Manual
Page 18
Document 2.4.06, Revision 4
June 2013
Medium Power Substation Transformers
18
Transformer Cooling Fans
Optional cooling fans may be provided to increase
the transformer load capability without overheating
the transformer windings. Operation of the fans is
controlled by a contact in the fluid temperature gauge
or winding temperature gauge (when furnished) and
by an “auto/manual” control switch. Controls for the
fans are contained in a control cabinet mounted on the
transformer.
DANgER
: AlWAYS DE-ENERGIZE THE FAN
CIRCUIT WHEN INSTAllING OR PERFORMING
MAINTENANCE ON FANS. IN ADDITION, DE-ENERGIZE
THE TRANSFORMER WHEN IT IS POSSIBlE TO COME
ClOSE TO ElECTRICAllY CHARGED/lIvE PARTS.
FAIlURE TO DO SO COUlD RESUlT IN SEvERE
PERSONAl INJURY OR DEATH. FAN GUARDS ARE
FURNISHED AND INSTAllED AT THE FACTORY TO
PREvENT ACCIDENTAl CONTACT WITH ROTATING FAN
BlADES. DO NOT REMOvE FAN GUARDS OR AllOW
PERSONNEl TO REACH INSIDE A GUARD. DOING SO
CAN RESUlT IN SERIOUS PERSONAl INJURY AND
EQUIPMENT DAMAGE.
The auto/manual switch determines the mode of
operation for the fan motors. When the switch is in
the “manual” position, fans will operate continuously.
When the switch is in the “auto” position, fans will
be automatically controlled by contacts in the fluid
temperature gauge or winding temperature gauge.
Refer to the schematic wiring diagram provided with the
transformer.
Fan motors are provided with thermal overload
protection. The overload protection is usually contained
within the motor. However, if the motors are located in a
hazardous location, the overload protection device may
be located in the control box. Refer to the wiring diagram
provided with the transformer.
Fan motors have permanently sealed ball bearings
and do not normally require maintenance, except as
explained on Page 20.
When fan assemblies are installed by the user, it
is important to permanently remove the drain plug
from the motor housing of each motor. This will allow
condensation to drain from the motor housing.
De-Energized Tap Changer
The de-energized tap changer may be used to adjust the
voltage ratio of a transformer while it is de-energized.
It is intended to allow adjustment of the output
(secondary) voltage to the rated value. Do not use the
tap changer to raise or lower the output voltage to any
voltage other than that indicated on the transformer
nameplate. If the tap changer is set to provide an output
voltage different from rated voltage, a high noise level,
high core loss, and core saturation may result.
DANgER
: DO NOT OPERATE A DE-ENERGIZED
TAP CHANGER UNlESS THE TRANSFORMER IS
TOTAllY DE-ENERGIZED. FAIlURE TO DO SO WIll
RESUlT IN DAMAGE TO THE TRANSFORMER AND
COUlD RESUlT IN SEvERE PERSONAl INJURY OR
DEATH. DO NOT RE-ENERGIZE THE TRANSFORMER
UNlESS THE TAP CHANGER IS FIRMlY lOCKED INTO
POSITION.
The tap changer is operated by use of a rotating
handle located on the outside of the transformer tank.
Never operate a de-energized tap changer while the
transformer is energized. Tap changers normally have
five or seven tap positions as indicated on the tap
changer dial plate and the transformer nameplate. A
locking mechanism is provided to lock the tap changer
in position and prevent accidental operation. Do not
re-energize the transformer until the tap changer is firmly
locked into a tap position.
The transformer is shipped from the factory with the tap
changer in the rated voltage position, unless otherwise
specified by the customer.
Dual-voltage or Delta/Wye Switch
Transformers designed with dual-voltage windings or
reconnectable delta/wye windings as indicated on the
nameplate are provided with a de-energized two-position
dual-voltage or delta/wye switch. The transformer must
be completely de-energized before operating the switch.
If the transformer is not de-energized before operating
the switch, permanent damage will result.
WARNINg
: DO NOT OPERATE DUAl-vOlTAGE OR
DElTA/WYE SWITCH UNlESS THE
TRANSFORMER IS TOTAllY DE-ENERGIZED.
FAIlURE TO DO SO WIll RESUlT IN DAMAGE TO THE
TRANSFORMER AND COUlD RESUlT IN SEvERE
PERSONAl INJURY OR DEATH. DO NOT RE-ENERGIZE
THE TRANSFORMER UNlESS THE DUAl-vOlTAGE
OR DElTA/WYE SWITCH IS FIRMlY lOCKED INTO
POSITION.