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

Appendix E: Hazards of Bypassing a Regulator off Neutral

E Hazards of Bypassing a Regulator off Neutral

Possible explosion can cause death,
serious injury or property damage.
To prevent:
The regulator must be placed in neutral
before by-passing.
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.
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• The MJ-X 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-X
Panel can be used to verify proper operation of the
Neutralite.
Siemens Power Transmission & Distribution, Inc.
DANGER
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Control
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• The MJ-X control program "dead reckoning" proce-
dure tracks the tap changer position and presents it
on the display panel.
The Position Indicator, the "dead-reckoning" tap position,
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.
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Deactivating the MJ-X
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 control panel as follows:
1. Disconnect the Polarized Disconnect Switch (PDS).
or
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2. Remove all MJ-X fuses (Power, Sensing, and Exter-
nal Power); place MJ-X
place Remote/Auto/Manual switch in Manual posi-
tion; and place Tap Raise/Lower switch in Off posi-
tion.
Before Bypassing
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power switch in Off position;
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