Preface This is the third edition of CSA C199, Three-phase network distribution transformers. It supersedes the previous editions published in 1982 and 1970 under the title Three-Phase Network Transformers.? Scope 1.1 This Standard specifies the mechanical and electrical characteristics of three-phase network distribution transformers having rated primary voltages up to 34.5 kV and kV-A ratings of 500 to 2500. Note: It is possible that transformers complying with this Standard will, if operated by a body other than an electric utility, be subject to additional requirements imposed by the electric inspection authority having jurisdiction.? 1.2 This Standard applies only to three-phase distribution transformer units intended for use in a ventilated vault or enclosure below grade level.? 1.3 The equipment covered by this Standard is primarily intended for operation by electric utilities on effectively grounded underground distribution systems.? 1.4 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. ?