Procedure For Eliminating The Magnetized State Of A Transformer; Parameters For Demagnetizing - Raytech WR14 Instruction Manual

PROCEDURE FOR ELIMIN ATING THE MAGNETIZED STATE OF A
TRANSFORMER
One option to safely re-energize a transformer back on line and avoid a dangerous and damaging
situation is to apply an AC voltage source and increase the voltage level to the operating voltage level
then decrease the voltage level to zero. Under controlled conditions this is possible. However, this
undertaking may not be theoretically possible when energizing a transformer on site. Equipment
required to fully demagnetize a transformer in this manner is large and expensive.
A better solution is the Raytech Winding Resistance Meter, WR-Series.
These easy-to-use systems are recognized throughout the world for precision winding resistance
measurements. A unique and new feature built into the WR-series is the ability to automatically
demagnetize a transformer core on site.
Avoid unnecessary damage and unsafe conditions when energizing a transformer; use one of the
Raytech WR-series instruments.

PARAMETERS FOR DEMAGNETIZING

The WR series utilizes the reverse Current reduction method with additional techniques to De-
magnetize a transformer.
The WR series test systems have different levels for the Demagnetization of Windings:
Fast, Course, Medium, Fine and Superfine.
Fast: Basic Demagnetization cycle. Selected to just quickly remove residual magnetization.
Course: Reduced Demagnetization cycle. Normally selected if the transformer is to be re-energized.
Medium: Average number of Demagnetization cycles. Selected if further testing is to be done.
Fine: High number of Demagnetization cycles. Selected if Medium Demagnetization cycle mode did not
fully De-magnetize the transformer. This mode takes several minutes to complete.
Superfine: Ultra High number of Demagnetization cycles. Selected if Fine Demagnetization cycle mode
did not fully De-magnetize the transformer. This mode takes the longest to complete.
Note: Running a Demagnetization mode twice can be helpful. For example, running Medium twice can
be as effective as running the longer interval Fine mode; the advantage could be reduced time.
The optimal Demagnetizing Current selected is the same as the Measuring Current used during the
Winding Resistance measurement or the maximum allowed for the nominal Current level of the High
Voltage Winding.
The Current of the WR series test system should be applied on the High Inductive or High Voltage side
of the transformer with the Potential cables from Channel 1 also connected.
For Delta Wound High Voltage Windings: Connect the Current Leads and Channel 1 Potential Leads to
the Center Phase or Limb on the High Voltage side.
For Wye Wound High Voltage Windings: Connect the Current Leads and Channel 1 Potential Leads then
short two of the Phases. For example: For example place a short between H1 and H2. Place +Current
lead on H1 and -Current lead on H3. Channel +1 on H1 and Channel -1 on H3.
Note: Do not run Demagnetization mode from a single phase to Neutral on a Wye winding.
Summary:
Demagnetize on the Primary or High Voltage side.
Delta wound: Use the center phase to demagnetize
Wye wound: Short two of the phases. For example place a short between H1 and H2. Place +Current
lead on H1 and -Current lead on H3. Channel +1 on H1 and Channel -1 on H3.
Note: Do not run Demagnetization mode from a single phase to Neutral on a Wye winding.
Version 3.03 WR14 / WR50-12/13 Winding Resistance Meter Instruction Manual 110