Introduction to PEARL Standard 2400, Revision 5
Medium Voltage Transformers
I.
Introduction
From the original power source, such as the utility generator, transformers of medium-to-high
voltage are used to step up or to step down voltage for the most efficient and cost effective
transmission of electrical energy. They can be found in utility switchyards, on power poles, in
shopping centers, schools, manufacturing and process plants, and more. Proper maintenance of
this equipment is critical and proper preparation for re-application is no less critical.
PEARL Section 2400 Medium Voltage Transformers, Dry Type reconditioning standards include:
• 2410 Medium Voltage Transformers Dry-Type
• 2420 Medium Voltage Transformers Padmount Oil Filled
• 2430 Medium Voltage Transformers Padmount Gas Filled
• 2440 Medium Voltage Transformers Power Oil Filled
II.
Components
Parts and assemblies to be reconditioned under Section 2400 Medium Voltage Transformers
include but are not limited to:
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Frame, Enclosure, Tank
Phase, through or neutral bus
Ground Bus
Ground Link, Grounding Pad
Bus Support
Tap Board
De-energized Tap Changer*
Dual Voltage switch*
Windings
Fuse Block
Core
Core Yoke
Monitor Panel
Thermostat
Cooling Fans
Control Relays
Meters, Gauges, Instruments
Arrestors, surge/lightning
Radiators
Bushings
Valves
Pressure Relief Devices*
Cutouts
Bay-O-Net Fusing*
Dead-front inserts*
Dead-front Wells*
Nameplate or Label
Terminal or polarity markings
Third Party Certification Labels or Marks
Air Terminal Chambers
III.
Testing and Inspection
The PEARL Section 2400 Medium Voltage Transformers standards begins with the definition of
the term “Reconditioning” as “the process of returning electrical equipment to safe and reliable
operating condition based upon the design of the original manufacturer at the time of
manufacturing.” This is followed by reference tables used to calculate test results and tolerances
and the necessary test equipment required by the PEARL Section 2400 Medium Voltage
Transformer Standard. The medium voltage transformer standards continue with a “Recondition
Evaluation,” which is a detailed inspection of all parts of the medium voltage transformer,
including but not limited to the components listed above.
Section I for PEARL Section 2400 Medium Voltage Transformers begins with reference table
identification and a list of required test equipment. The following test equipment is required to
perform the testing requirements of this reconditioning standard:
1. Insulation Resistance Test Set (Megohmeter) 1000 Vdc minimum
One of the following pieces of test equipment is required to perform the transformer ratio
verification testing requirements of this reconditioning standard:
1. Insulation Resistance Test Set (Megohmeter) 1000 Vdc minimum
One of the following pieces of test equipment is required to perform the turn-to-turn ratio
verification testing requirements of this reconditioning standard:
1. Turns-To-Turns Ratio Test Set
2. AC Voltage Supply and Voltmeter (+/- 0.5%)
3. Transformer Winding Resistance Test Set
One of the following pieces of test equipment is required to perform the insulation resistance
testing requirements of this reconditioning standard:
1. Power Factor Test Set
2. Dissipation Factor Test Set
One of the following pieces of test equipment is required to perform the overpotential testing
requirements of this reconditioning standard if it is required by the customer:
1. AC Overpotential Test Set
2. DC Overpotential Test Set
Section II Recondition Evaluation-Inspection and Testing identifies each component and
assembly part that must be inspected to determine the components viability and the
reconditioning steps necessary to bring the transformer back to original operating condition.
Results and notes from the pre-reconditioning inspection and test are recorded in the PEARL
Reconditioning Evaluation and Test forms that accompany each respective standard.
IV.
Reconditioning
Section III Reconditioning Procedures describes how to recondition each component and
assembly, beginning with the disassembly of the medium voltage transformer down to its major
subassemblies. Reconditioning for medium voltage transformer standards includes:
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Disassembly
Cleaning
Drying
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Re-Gasketing or Re-Sealing
Deoxidizing
Removal of corrosion
Degreasing
Plating
Painting
Lubricating
Adjusting
Filtering
Add or replace oil
Add gas
Assembly of the reconditioned components and subassemblies is followed by final inspection and
testing. As with all testing, inspection, and reconditioning operations, final inspection and test
results are recorded onto the Evaluation and Test forms included with the standard. If a PEARL
certified technician follows the reconditioning standard, the medium voltage transformer assembly
is eligible for a Blue PEARL Reconditioned Quality Seal.