Many service centers are unable to perform full-load testing of large DC machines. The good news is that there are specific tests that can be performed on a DC motor to verify the integrity of windings, the correct relative polarity of armature to interpoles, and proper running performance. This article explains specific tests that can help ensure a motor operates properly when the motor is installed. 

Muchos centros de servicio no pueden realizar pruebas a plena carga en máquinas de corriente continua grandes, sin embargo, la buena noticia es que existen pruebas específicas que permiten verificar la integridad de los devanados, la polaridad relativa correcta entre la armadura y los interpolos, y el adecuado funcionamiento del motor. Este artículo explica pruebas específicas que pueden ayudar a garantizar que el motor funcione correctamente una vez instalado.

This video will walk you through how to check the relative polarity of DC machine interpoles and the armature and correct it if necessary using a simple interpole polarity test.

High-potential (hipot) testing is a critical method used to evaluate the ground insulation of AC stator windings. This testing is performed during various stages, including in-process, after rewinding, and post-delivery. The primary objective of hipot testing is to ensure the insulation's adequacy against breakdown under normal operating conditions. The paper discusses the differences between AC and DC hipot testing, emphasizing the importance of sizing AC test sets appropriately when testing large windings. It also covers relevant standards, the communication of test requirements, the timing and levels of testing, and the evaluation of results.

Traditional rotor bar defect detection systems are often insufficient in sensitivity, record-ability and numerical analysis of test results. Many means of rotor defect detection require the motor to be fully assembled with a functional stator. These limitations have laid the groundwork for the development of a new rotor defect detection technique.

When considering building a large growler for testing armatures and rotors, the initial decision typically is to select a kVA rating. A primary reason for this is that the growler will need to be connected to a power supply of sufficient ampacity at the supply voltage. To help simplify a complex design process, four kVA ratings have been selected for this article.

Cuando se considera la construcción de un gran growler para probar rotores y armaduras, la decisión inicial típica es seleccionar la potencia en kVA. La razón principal para esto es que el growler necesitará ser conectado a una fuente de alimentación que tenga suficiente amperaje. Para ayudar a simplificar el complejo proceso de diseño, en este artículo hemos seleccionado cinco potencias expresadas en kVA.

In a previous article in Plant Engineering ("A systematic approach to AC motor repair," Plant Engineering, April 2015), EASA highlighted the good practices for electrical repair found in ANSI/EASA Standard AR100 Recommended Practice for the Repair of Rotating Electrical Apparatus, and the significant impact they can have on motor efficiency and reliability. But that was only part of the story, because mechanical repairs—and even documentation, cleaning, and inspection—can also markedly affect motor reliability and efficiency.

The intent of this article is to provide an overview of the more common techniques used for dissolved gas analysis (DGA) of mineral oil. Types of gases created during transformer faults. There are several key gases produced during transformer faults. The type of gas and the quantity depends on the materials involved in the fault, the energy dissipated at the fault location and the solubility of the gases in oil.

Topics covered include:

• Types of gases created during transformer faults
• Methods of analysis and interpretation
• Dornenburg ratios
• Rogers ratios
• Key gas method
• Gas limits
• Duval triangle
• Analyzing other gases
• Factors affecting gas concentrations and diagnosis

The paper "Electrical Testing of Three-Phase Motors" by Tom Bishop, presented at the EASA Convention 2011, provides a comprehensive guide to electrical testing of three-phase squirrel cage induction motors in the service center. The paper covers various tests performed at different stages of motor repair, including incoming tests, post-disassembly tests, in-process tests, pre-assembly tests, and post-assembly tests. These tests are categorized as routine, optional, or conditional, depending on their necessity and the specific conditions of the motor.