Appendix E: Hazards of Bypassing a Regulator off Neutral
Siemens Industry, Inc. 67
E: Hazards of Bypassing a Regulator off Neutral
Proper regulator bypassing procedure is of critical importance.
Regulators that are not in the neutral position when bypassed
frequently fail. This failure is the result of extremely high
circulating current inside the regulator caused by what is,
effectively, a short circuit being placed across the series
winding. The result of such a failure can be catastrophic.
Methods of Determining Neutral Tap Position
Since the tap changing mechanism is submerged in a tank full of
oil, some external means of determining tap position is
mandatory. Methods most commonly used include:
• The regulator tap Position Indicator provides first line
indication of the neutral position. On modern regulators,
the tap changing mechanism drives the regulator Position
Indicator through gears or flexible shafts to provide an
accurate, reliable indication of the regulator tap position.
• The MJ-5 Control Panel is equipped with a neutral
indicating light (Neutralite). A switch mounted on the tap
changing mechanism actuates the light circuit. The circuit
is activated when the regulator is in the neutral position. A
test switch on the MJ-5 Control Panel can be used to verify
proper operation of the Neutralite.
The Position Indicator and the Neutralite should all indicate
neutral before you attempt to bypass the regulator.
Methods other than the ones described above are also used;
however, the ones described above are the most common and
are recommended.
The regulator must be placed in neutral before bypassing. If
there is any doubt as to the location of neutral, the line should
be dropped before bypassing the regulator.
Deactivating the Control Panel Before
Bypassing
Consult your voltage regulator instruction manual for
bypassing instructions.
To eliminate the possibility of inadvertent (and possibly
catastrophic) tap operations during bypassing operations, it
is mandatory that you completely disable the control panel.
Disable the MJ-5 control panel as follows:
1. Disconnect the Polarized Disconnect Switch (PDS)
or
2. Remove all MJ-5 fuses (Power, Sensing, and External
Power); place MJ-5 power switch in Off position;
place Remote/Off/Manual switch in Off position; and
place the Tap Raise/Lower switch in Off position.
Operating regulator while bypassing
will result in explosion.
Will cause death, serious injury, or
property damage.
Place regulator in neutral position
before bypassing and disable control
panel.
Operating regulator while bypassing
will result in explosion.
Will cause death, serious injury, or
property damage.
Place regulator in neutral position
before bypassing and disable control
panel.
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