Preface
This is the third edition of CSA C227.4, Three-phase, pad-mounted distribution transformers with separable insulated high-voltage connectors. It supersedes the previous editions published in 2006 and 1978.
The major changes in this edition include the following:
a) expanded scope to include 34.5 kV system nominal voltage, and discontinued use of the terms insulation class and preferred voltages;
b) updated references to other industry standards;
c) clarified requirements with off-circuit voltage taps and added informative note on dual-voltage transformers with taps;
d) added requirements to the optional load break switch ratings since previous IEEE references are obsolete;
e) modified and clarified requirements with the two-fuse system, also removing tables with manufacturer specific part numbers;
f) improved routine test requirements to better align with IEEE. For example, no-load losses and exciting current will be at 100% rated voltage instead of 105%;
g) added no internal fuse warning markings;
h) clarified and expanded additional optional items in Clause 10. For example, routine partial discharge testing has been added based on the experience and procedures of users;
i) the continued inclusion of the electrical characteristics that apply to the transformers covered by this Standard, which were previously provided in CAN/CSA-C2; and
j) added Clause B.5.3.1.1 to explain the removal of fusing tables.
This Standard has been developed in compliance with Standards Council of Canada requirements for National Standards of Canada. It has been published as a National Standard of Canada by CSA Group.
Scope
1.1
This Standard specifies the requirements for three-phase, pad-mounted distribution transformers, consisting of a transformer and a cable entrance compartment with provision for separable insulated high-voltage connectors, intended primarily for operation by electric utilities on three-phase underground distribution systems having primary voltages as shown in Clause 4.6.
1.2
This Standard applies to three-phase, 60 Hz, pad-mounted, liquid-filled distribution transformers, rated at 3000 kVA or below, up to 34.5 kV system nominal voltage, and with separable insulated high-voltage connectors. The transformers are suitable for mounting outdoors on pads without additional protective enclosures.
1.3
This Standard includes voltage ratings, kVA ratings, certain mechanical characteristics, and test procedures. The Standard also includes the following performance characteristics: energy efficiency (in accordance with CAN/CSA-C802.1), temperature rise, loading capabilities, audible sound level, and radio influence voltage (RIV).
1.4
When this equipment is intended for operation by other than an electric utility, it is the purchaser’s responsibility to ensure that the unit meets the requirements of the appropriate electrical inspection authority.
1.5
This Standard allows for the interchangeability of a dead-front, pad-mounted unit by another of the same basic physical size from a different manufacturer for transformers rated 125 kV BIL and below, without modifications to cables or pad. This Standard covers terminal arrangements for both radial and loop-feed systems, including certain minimum dimensions and certain specific dimensions.
1.6
In this Standard, 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; and may is used to express an option or that which is permissible within the limits of the Standard.
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.
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