It supersedes the first edition, published in 1976.

1 Scope

1.1 This Standard covers the features of single-phase submersible transformers rated 25 to 333 kV.A. Note: For details not covered herein, reference should be made to CSA C2.1.

1.2 This Standard applies only to single-phase distribution transformer units intended for use in a ventilated vault or enclosure below grade level, with all terminations and accessories cover mounted, or nearly so, for operation above grade. It does not apply to (a) directly buried transformers in contact with the earth; (b) permanently submerged transformers; or (c) network-type transformers.

1.3 The transformers covered by this Standard are intended only for operation by electrical utilities on effectively grounded underground distribution systems having primary voltages up to and including 16.0/27.6 kV grounded Y. Note: The operation of transformers complying with this Standard by other than an electric utility may be subject to additional requirements by the electrical inspection authority having jurisdiction.

1.4 The equipment covered by this Standard typically has dual high-voltage bushings designed for circuit loop feed within the transformer tank. High-voltage fuse protection normally connected between this internal loop feed element and the transformer high-voltage winding is not covered by this Standard and specified by the purchaser.

1.5 In CSA Standards, "shall" is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the standard; "should" is used to express a recommendation or that which is advised but not required; "may" is used to express an option or that which is permissible within the limits of the standard; and "can" is used to express possibility or capability. Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material. Notes to tables and figures are considered part of the table or figure and may be written as requirements. Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application.