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Page 54

| Review |

| 1. Transformer installations should provide adequate mechanical and structural support; space for access and maintenance; sufficient clearances, barriers, or signs for safety to the public and workers; means of restricting noise levels; and means for dissipating heat. They may be mounted in clusters (Fig. 3-1), directly on poles (Fig. 3-2), or on hangers and crossarms (Fig. 3-3); also on elevated platforms (Fig. 3-6), or ground level pads or in underground manholes or vaults. |

| 2. Transformers installed underground are watertight and equipped with waterproof bushings or terminal chambers filled with oil and are watertight. These units may also contain switches on either the primary or secondary sides, for grounding or disconnecting purposes; where such switches on the secondary are operated automatically, they are known as network protectors (Fig. 3-7). |

| 3. Ventilation of vaults and manholes is of special importance. Sufficient vent areas should be provided, not only for heat dissipation, but to prevent explosive mixtures of oil vapor or gasses and air to form in event of transformer failure. The greater the vent-volume ratio, the less pressure will develop in the manhole or vault and the lighter the construction necessary to withstand the force of possible explosion. |

| 4. Substation transformers may be installed indoors or outdoors (Fig. 3-8). Precautions are taken to keep failure of one unit affecting adjacent equipment, usually by installing barriers. Sumps around the transformers are often provided to collect its oil should leaks develop or the unit experience trouble. Facilities are also supplied to hold down noise (Fig. 3-9), and to provide for fans, pumps and other accessories. |

| 5. Electrical protection of transformers include lightning arresters and switches or cut-outs to disconnect them from the line either automatically or manually. These may be installed with the unit on poles, crossarm, pad, manhole or vault, or mounted on the tank or case. Solid grounding of system neutrals and transformer cases, sometimes using two or more separate leads, is an absolute necessity. |

| 6. Completely self-protected (CSP) transformer (Fig. 3-10) provide surge protection and disconnecting devices within the transformer itself, simplifying installation as only the connection from the unit to the line is necessary. |

| STUDY QUESTIONS |

| 1. What factors should be considered in the installation of overhead distribution transformers? What are some of the methods of doing so? |

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