E Hazards Of Bypassing A Regulator Off Neutral - Siemens MJ-4A Installation And Operation Manual

Appendix E: Hazards of Bypassing a Regulator off Neutral

E Hazards of Bypassing a Regulator off Neutral

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.
Proper regulator bypassing procedure is of critical impor-
tance. 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 posi-
tion is mandatory. Methods most commonly used include:
• The regulator tap Position Indicator provides first line
indication of the neutral position. On modern regula-
tors, the tap changing mechanism drives the regulator
Position Indicator through gears or flexible shafts to
provide an accurate, reliable indication of the regula-
tor tap position.
• The MJ-4A & MJ-4B Control Panel is equipped with a
neutral indicating light (Neutralite). A switch mounted
on the tap changing mechanism actuates the light cir-
cuit. The circuit is activated when the regulator is in
the neutral position. A test switch on the MJ-4A &
MJ-4B 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.
Siemens Energy, Inc.
DANGER
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.
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.
Disable the MJ-4A control panel as follows:
1. Disconnect the Polarized Disconnect Switch (PDS).
or
2. Remove all MJ-4A fuses (Power, Sensing, and Exter-
nal Power); place MJ-4A power switch in Off position;
place Remote/Off/Manual switch in Off position; and
place the Tap Raise/Lower switch in Off position.
Disable the MJ-4B control panel as follows:
1. Disconnect the Polarized Disconnect Switch (PDS)
or
2. Push Auto/Manual switch until Auto Disabled LED is
ON, and leave the Raise and Lower keys in Off posi-
tion.
Remove all MJ-4B fuses (Power, Sensing, and Exter-
nal Power); place MJ-4B power switch in Off position.
DANGER
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