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: • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 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: • • • Disassembly Cleaning Drying • • • • • • • • • • • 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.