oil. In large transformers. the tanks have external tubes
or external radiators through which the oil circulates
by natural convection caused by the differences in oil
The liquid-immersed water-cooling transformer is
sometimes used where a plentiful supply of cool water
is available. In this type, a coil of copper or brass pipe is
installed near the top of the tank in the cooling oil.
Water is circulated through this coil and carries away
the heat from the oil as it rises in the tank.
Insulating liquids have high-insulating qualities
and serve two purposes: first. they insulate the coil, and
second. they help dissipate the heat generated by the
resistance of the windings and eddy currents in the iron
core. If this heat were not removed. the transformer
would operate at excessively high temperatures,
which. in turn, would damage or destroy the insulation
on the coils.
Two common types of insulating liquids are
mineral oil and Askarel®. Mineral oil is a nontoxic
insulating liquid. It is used in different types of high-
voltage electrical equipment, such as circuit breakers,
switches. and transformers. Mineral oil must be kept in
an airtight container, or else sludge will form. This
sludge will settle in the bottom of the tank and slow the
natural transfer of heat. Also the longer mineral oil is
left exposed to air, the greater the loss of insulation
Askarel® is a synthetic, nonflammable insulating
liquid. It has other trade names, such as Pyranol®,
Inerteen®, Chlorexirol®, and Asbestol®. This liquid
must be handled with care because of its toxic chemical
properties. Askarel® is used in special transformers
for applications where flammable liquids must be
Askarel® may have an irritating effect upon the
skin. eyes, nose, and lips. It also may irritate skin
abrasions or tender areas between the fingers.
Askarel® may contain polychlorinated biphenyls
(PCBs): a toxic, carcinogenic oily liquid.
Transformers tested and found to be contaminated
with PCBs should have labels on the outside of the
transformer warning of this hazard.
If assigned to work on a transformer
known to be contaminated with PCBs,
see your supervisor for a Material Safety
Data Sheet (MSDS) for hazards and
precautions. Personal protective
equipment, such as impermeable gloves
and chemical splash goggles, are
Avoid prolonged skin contact and
wash thoroughly after use.
Avoid breathing vapors.
When removing transformer oil,
wear respiratory protection. If you
discover PCB transformer oil spilled on
soil, immediately notify your supervisor
who must notify environmental
authorities and summons a trained
hazardous material spill clean-up team.
To protect yourself when handing Askarel®, wear
impermeable gloves. Also wear splashproof goggles.
Whenever liquid comes in contact with the skin, wash
it thoroughly with warm water and soap.
Ensure that the work space is properly ventilated
before working on transformers containing Askarel®.
Avoid breathing Askarel® vapors. Wear an
approved organic vapor cartridge respirator when
vapors are present. When removing Askarel® oil
which is contaminated with PCBs, air respirators may
If a blueprint of a particular transformer
installation is available to you, your job will be
comparatively easy. All construction and electrical
specifications will be worked out for you beforehand,
and all you have to do is convert this information into a
finished product. However, in some instances, a
blueprint will not be available. Then it will be up to you
to determine the location and size of the transformer
and install it according to the latest specifications. You
should be familiar with the rules and requirements of
the most current electrical codes. Be sure to carefully
study any applicable code requirements before
installing a transformer.
Transformers are mounted on poles in various
ways, such as suspended on a bracket bolted to the
pole, suspended from a crossarm with brackets, or set
on a platform mounted on an H-frame.
Single-phase transformers are usually hung with a
through-bolt type of bracket or a cross-arm type of
bracket. Figure 4-6 shows a single transformer hung
with cross-arm brackets. Figure 4-7 shows a bank of
three transformers of 25 kVA capacity hung the same