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 temperature.

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 properties.

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 avoided.

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.

WARNING

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 4-6 precautions. Personal protective equipment, such as impermeable gloves and chemical splash goggles, are mandatory.

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 be necessary.

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 way.