6 December 2006
Including change 1, 7 December 2006
SUBSTATIONS AND SWITCHGEAR
Purpose of Substation. A substation provides a protected area for switching
power circuits and may include transforming power from one voltage to another. For
the purposes of this UFC, substation refers to substations and switching stations. A
substation presents an inherent safety hazard because usually only some portions of
the substation apparatus can be deenergized for maintenance. For safe operation and
maintenance, a thorough knowledge of the substation, including aerial and underground
line connections, is necessary. Systems are designed to be safe to operate if
maintained properly. Operating safely requires maintenance to be done in a manner
that eliminates risks and requires knowledge of the work area, its hazards, and its
Diagrams and Schematics. Electrical diagrams and schematics of the
substations must be available and up-to-date. Diagrams and schematics must be
studied to understand the operation of the systems and the location and connections of
all circuits. Protective devices, alarms, and interlocking circuits all are intended to
protect the system. The electrical worker must understand where, why, how, and when
blocking protective devices can maintain safe working conditions.
Engineering Guidance. Diagrams and schematics must be kept up to date
under the supervision of the facility's engineering staff. Engineering staff guidance must
be sought when performing maintenance on complex systems. Engineering input is
mandatory if the maintenance work involves additions or changes to the power and
control systems involved.
System Operation. System single line diagrams must be permanently
mounted at each substation. When Safe Clearance switching operations are
performed, mimic buses on switchgear can be helpful as a visual indication of the lines
or equipment being operated.
9-1.4.1 Protective Devices. Protective devices within the system, such as relays
and fuses, must retain, respectively, their correct coordination settings or be of the
proper size and type. Always record previous data so that unintended changes in
system coordination are not made.
9-1.4.2 Alarms. System alarms, if blocked during maintenance, must be returned to
their correct operating condition at the completion of the maintenance.
9-1.4.3 Interlocking. Interlocking is used to maintain proper electrical operation in
the case of a circuit loss or switching change. Interlocking provisions must be fully