14 Topic: Underground Transformers (15m)
Instructions:
- Cover the following content as a group (either reading out loud or independently) then give an opportunity to answer any questions.
- Have students do the review questions independently, then take up answers.
Transformers must be square, level and at the proper grade. They must sit on the appropriate “tub or vault” and be fastened down.
The cable is coiled in the transformer well, so in the event of a termination burning off, a splice will not be necessary to allow the cable to reach the bushings.
The conductor, in a vault, is coiled in opposing direction as follows:
- Primary – clockwise direction to accommodate the primary bushings, which are on the left side of the transformer.
- Secondary – counter-clockwise direction to accommodate the primary side bushings, which are on the right side of the transformer.
The incoming line primary cable should always be installed on the H1A bushing, with the exiting (load) cable coming off the H1B.
These cables should always be labeled properly with cable markers. The cables are marked by showing the location of the apparatus attached to the opposite end of that cable.
Conductor should never be energized until it is properly terminated in the pedestals or transformers, and all workers have given clearance. The cable should be meggered to ensure it is insulated from any reference to ground. Meggering will also ensure cables are not cross-phased.
All underground cable and apparatus is subject to clearance standards. (See Section C-26-02 in the Underground Construction Standards.) Positioning this equipment without proper clearance may cause interference or hazards.
Review Questions: Transformers (15m)
- ( True / False ) Transformers must be square, level and at the proper grade.
- ( True / False ) Excess cable is not required when constructing an underground transformer structure.
- ( True / False ) Conductor should never be energized until it is properly terminated in the pedestals or transformers, and all workers have given clearance.
- ( True / False ) Primary cables are placed in a counter-clockwise direction to accommodate the primary side bushings, which are on the right side of the transformer.
- ( True / False ) Primary cables are placed in a clockwise direction to accommodate the primary bushings, which are on the left side of the transformer.
Answer Key
- T
- F
- T
- F
- T
