3. INTRODUCTION
Magnetic oil level gauge (MOG) or A liquid level indicator is
provided to aid in the systematic inspection of the transformer
under load. It consists of a float-arm inside the tank, an
indicating pointer and a magnetic coupling between the two
across a liquid-tight separation. The gauge may be furnished
with SPDT (Single Pole Double Throw) alarm contacts to give a
remote annunciation of low liquid level.
Magnetic oil level gauge-This is a mechanical device used to
indicate the position of transformer insulating oil level in the
conservator tank of a transformer.
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4. MAINLY PARTS
These parts are
• A float.
• Bevel gear arrangement (magnetic coupled linked to the pointer ).
• An indicating dial ( pointer movement by magnetic field )
incorporate with mercury switch.
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5. OPERATION PRINCIPLES
•Float Bevel gear Indicating dial Mercury switch
• (Alarm)
Movement Gear rotation Movement
by oil level (magnetic coupled) by pointer
expansion
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6. CONSTRUCTION
•A ball or drum type float is attached to the bevel gear which is
magnetically coupled with the pointer. The movement of the
float is associate with the rotation of the bevel gear and the
pointer due to the rise and fall of the insulation oil in the
transformer conservator tank.
•The magnetic field between the bevel gear and the pointer
initiate the rotation of the pointer (clockwise or anti-clockwise)
•along the dial.
•The dial has a scale from EMPTY, ¼, ½, ¾, and FULL.
•The prescribed oil level at either 30 oC or 35 oC ambient
temperature may also be indicated on the dial (filling level).
•The mercury switch is fixed with the pointer which when rotates
,the alignment of the mercury switch also changes to energized
an alarm during empty indication.
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7. WORKING PRINCIPLE
Electrical power transformer is incorporated with conservator
tank for expansion and reduction of insulation oil due to
temperature rise and fall during it working time.
Power transformer s are provided with a magnetic oil level
gauge. In the conservator tank, a light weight hollow ball or
drum floats attached to the bevel gear arm. The position of the
float goes up and down depending on the level of oil in the
conservator tank. The bevel gear rotates and transmitted to the
pointer outside the conservator tank , as this pointer is
magnetically coupled with the bevel gear. The pointer is also
incorporate with a mercury switch. When the pointer reaches
empty on the dial of MOG, this switch closes and actuate an
alarm for attention for topping up oil in the power transformer
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9. WHY TEMPERATURE DEGREE
INDICATOR SHOWN ON MOG ?
• The oil levels are generally indicated on the MOG dial as
‘Empty’, 1/4, 1/2, 3/4 and ‘Full’. But in between these levels
usually 300C temperature indication is also shown. This is
because oil level in the conservator tank changes according to
the ambient temperature. The hotter the temperature, the
more will be the oil level in the conservator tank due to
expansion and vice versa. So, as the oil level depends on the
ambient temperature, we must have an indication to what
level the oil is to be filled at a certain temperature. This is why
the level is indicated in temperature degrees so that when
the ambient temperature is same as the temperature
indicated on that MOG dial, the oil level should reach that
mark to ensure that the Transformer has sufficient oil level in
the conservator.
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10. ADVANTAGES
• Continuous oil level monitoring – with ease in reading at men
height.
• Magnetic couplings ensures a reliable movement transmission
between float arm and pointer avoiding leakages through
conservator wall.
• Initiate alarm at EMPTY oil level.
• Adjustable value settings for switches at ambient
temperature.
• No printings neither stickers on the view glass: temperature
indication is directly marked on the plate behind the view
glass.
• Modern technology MOG are equipped with data
downloading device.
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11. LIMITATIONS
• MOG is not incorporated with tripping relay.
• MOG is used only for measuring oil level in the conservator
tank.
• It is not a fault detecting device.
• MOG may loss is reading vision on aging transformer due
weather changes.
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12. REFERENCES
• PRINCIPLE OF POWER SYSTEM BY V.K. MEHTA.
• 33/11KV, 3X15MVA INJECTION SUBSTATION OGUDU, IKEJA
ELECTRIC LAGOS.
• www.electrical4u.com
• www.wikipedia.org
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