6 December 2006
Including change 1, 7 December 2006
9-6.1.3 When transformers are installed, and before they are energized, the ground
connection must first be made to the case and to the neutral, when applicable.
9-6.1.4 When removing transformers, case and neutral grounds must be
9-6.1.5 When working on or near an energized three-phase, wye-connected
transformer or transformer bank, verify the transformer neutral is properly grounded.
9-6.1.6 Never operate no-load (or manual) tap changers when the transformer is
energized. Only load-tap-changing (LTC) type tap changers can be operated when the
transformer is energized. When reenergizing a transformer after changing the position
of manual tap changers, maintain a safe working distance with all required personal
protective equipment until it is determined the internal switching was successful.
9-6.1.7 If necessary to relieve pressure on a transformer, the pipe plug, pressure
relief device, or inspection cover plate must be loosened slowly so the internal pressure
of the transformer can dissipate gradually.
9-6.1.8 Pressure relief valves must never be opened when there is precipitation or
high humidity, except on failed transformers and when re-fusing.
9-6.1.9 Never draw an oil sample, open a pressure relief valve, or otherwise open a
transformer when there is an internal vacuum on an energized transformer. Doing so
can cause an explosion.
9-6.1.10 Transformers or tanks must not be entered unless forced ventilation or an air
supply is used to maintain a minimum oxygen level of 19.5 percent by volume in the
9-6.1.11 Energized pad-mounted transformers and associated equipment must be
locked or otherwise secured when unattended.
9-6.2.1 Voltage regulators are normally installed with bypass and disconnect
switches. Never open or close a regulator bypass switch, unless the regulator is set on
its neutral position and the control switch is open, or the automatic control feature is
inactivated in accordance with the manufacturer's recommendations.
9-6.2.2 When regulators are maintained as spares in substations, their bushings must
be short-circuited and grounded.