MIL-HDBK-1025/10
c. When working on or in the vicinity of any three-phase wye-connected
transformer bank, check whether the transformer neutral is grounded. If not grounded
then the neutral is floating and it is possible to have full phase-to-ground voltage on the
neutral.
d. Unless transformers are load-tap-changing (LTC) type, tap changers should be
operated only when the transformer is de-energized. When re-energizing, maintain a safe
distance of at least 6 meters (20 feet) away to assure that internal switching was
successful.
e. When relieving pressure on transformers, the pipe plug, pressure relief device,
or inspection cover plate will be loosened slowly, so that the internal pressure of the
transformer will dissipate gradually. Pressure relief valves will not be opened when there
is precipitation or high humidity, except on failed transformers and when re-fusing.
f. Transformers or tanks will not be entered unless forced ventilation or an air
supply containing a minimum of 19.5 percent oxygen is present and maintained in the
work area.
g. Energized pad-mounted transformers and equipment will be locked or
otherwise secured when unattended.
h. Properly control connected leads or jumpers before transformers are raised,
lowered, or repositioned.
Voltage Regulators. Voltage regulators are installed with bypass and
6.9.2
disconnect switches.
WARNING
Never open or close a regulator bypass switch, unless the
regulator is set on its neutral position and the control switch is
open, or automatic control is otherwise inactivated in accordance
with the manufacturer's recommendations. When regulators are
maintained as spares in substations, their bushings should be
short-circuited and grounded.
Metal Clad Switchgear Safety. Metal clad switchgear is inherently safe
6.10
to maintain so long as manufacturer's instructions and the following rules are adhered to.
6.10.1 Before Circuit Breaker Drawout Requirements. Prior to the drawout
of a circuit breaker:
a. De-energize switchgear (including control power) and ground as much of the
switchgear as permitted by operating conditions.
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