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Page 51

| sound levels to satisfactory levels in certain communities, are sometimes installed. |

| Connections most often are made by means of open bus work usually located above the units. The impressive but expensive and hazardous steel racks to support these connections and associated switches have given way to sleek streamlined busses mounted on unobtrusive supports of steel or concrete. Even though installed outdoors, these units often have provisions for forced air and forced oil cooling. The transformers may also be painted with light colors (often silver) to allow the unit to reflect heat from the sun's rays and to improve appearances generally. |

| Protection |

| Practically all transformer installations include some form of electrical protection for the transformer. This generally includes protection of the unit from lightning and switching surges, deenergization to prevent damage under fault or overload conditions, and means for providing safety when worked upon. The solid grounding of system neutrals and transformer cases, sometimes using two or more separate leads for this purpose, is an absolute necessity. |

| Overhead line transformers of the conventional type are protected by a lightning arrester and a primary fuse cutout, mounted separately on the pole or crossarm. |

| Arresters designed to protect substation installations generally operate on the same principle as those protecting line installations. They are specifically designed to handle larger currents and higher voltages. See Chaps. 11 and 12. |

| Self-Protected Distribution Transformers |

| In the self-protected transformer (Fig. 3-10 on page 52), a weak link or primary protective fuse link is mounted inside the tank with the transformer unit as also are two circuit breakers for protection on the secondary side of the transformer. A simple thermal device causes the breakers to open when a predetermined safe value of current is exceeded. The lightning arrester is mounted on the outside of the tank. It is apparent that the self-protected transformer makes for simpler, more economic mounting and neater appearance. What's more, it is of particular advantage for higher voltage (13.8 kV) primary distribution systems where connections and disconnections are made with the unit energized. |

| Similar protection is provided to pad-mounted transformers installed at ground level. For larger size units, station-type lightning arresters and circuit breakers may be substituted for the pole-type arrester and fused cutout. Large |

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