Archives for 2022

Deenergized stator inductance is a valuable tool in identifying the internal magnetic condition of your electric motor. It is important to know that inductance measurements can be influenced by the running characteristics and power supply of the motor before it was shutdown. A three phase balanced power supply on a healthy motor is generally expected to produce a balanced three phase inductance measurement. However, an unbalanced three phase power supply like a single phase incident will often result in a large inductance imbalance when measured after the incident. The same is true for popular post repair tests that are often performed on a motor at the motor repair facility. Quarter voltage, growler, magnetic particle, and core loss testing are examples of shop tests that will have a residual effect on the stator inductance and could mislead an analyst into thinking there is a stator or rotor anomaly. It is highly recommended to run a motor on a balanced three phase power supply following a repair or refurbishment before performing acceptance testing. If you are requiring inductance testing as a new motor or post repair acceptance criteria, make sure you are working with your motor shop to make them aware of the correct test sequence when performing inductance testing.

For more information about Inductance testing with the MCEMAX® technology visit our website at https://pdma.com/products/mcemax/

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While the use of oil seals to retain lubrication in rotating machinery is common, bearing isolator labyrinth seal technology is often selected to protect bearings and lubrication. Manufacturers, repair facilities and users often select bearing isolators for use in harsh applications where conditions such as contamination, shaft misalignments and equipment vibrations are a concern to avoid frequent replacement. Bearing isolators can provide improved reliability and protection of the bearing and extend the mean time between failure (MTBF) of equipment. In a time when facility managers are focused on maintaining costs and limiting production losses due to downtime or unplanned outages is critical, bearing isolator labyrinth seals offer several benefits.

Benefits of Bearing Isolators

Bearing isolator labyrinth seals are used to protect the bearings and bearing lubrication in rotating equipment—such as electric motors, gearboxes, pumps and split pillow block bearings. In simple terms, a bearing isolator consists of a stationary component (stator) and a rotary component (rotor). The assembly of these components creates a narrow labyrinth path through the seal. This design prevents ingress of contaminants into a bearing arrangement.

In many instances, bearing isolators can fit in the same space as an oil seal without requiring modifications to the geometry of the seal location. There are several reasons why a bearing isolator would be selected as an OEM option or as a retrofit in existing equipment. Bearing isolators provide several benefits, including long service life and a noncontact seal configuration that will not damage shaft surfaces.

Contact lip oil seals are a simple solution to retain lubrication in rotating machinery. However, there can be limitations in performance and reliability. Initially, an oil seal can provide adequate sealing characteristics, but over time operating conditions, configuration and condition of the machine can contribute to wear—and eventual failure—of the seal. The average life of a commercial oil seal can be around 1,500 hours depending on application variables. A relatively clean application that meets or exceeds recommended operating parameters for the seal will likely allow for longer service life, compared to applications with harsh environments and increased misalignments, operating temperatures and shaft speeds. The good news is that the MTBF of rotating equipment can be improved and unscheduled shutdowns can be minimized with the use of a bearing isolator, potentially lasting the life of the equipment.

To read the rest of the article, please visit: https://www.pumpsandsystems.com/how-extend-equipment-life-bearing-isolator-labyrinth-seals 

Copyright: EASA

Some important things to consider when a motor is operating in environments with higher-than-normal temperatures (>40 degrees C) such as kilns or ovens:

1. Use high temperature grease (many synthetic greases have 30 degrees C higher rating than mineral greases);
2. Use C4 bearings (greater internal clearance than the usual C3 bearings);
3. Use only open bearings (no shield or seal);
4. Be sure to specify “heat stabilized bearings” — different bearing manufacturers have their own unique designation. There are bearings capable of operating at considerably higher temperatures than normal;
5. Consider running an air line from a compressor to “pipe in” dry compressed air to cool the motor. In kiln applications, it is effective to run a ¼” copper line through a solenoid and tap the end bracket to inject cool air into the motor enclosure when it is running. If practical, insulate the air line to provide the coolest air possible.

To minimize the risk of being in the vicinity of high voltage when testing your electric motors, your electric reliability team or plant safety management may have opted to install a test access panel. This allows you to test your critical electric motors while running without opening a single cabinet. Although the large majority of these Motor Test Access Panels (MTAP’s) are installed without a problem, always test after installation to insure everything is connected properly. Here are a few tips from the field to validate your installation.

·    Verify the voltage input to the MTAP matches the voltage rating of the MTAP. There are four possible  MTAP voltage ratings (120v, 240v, 480v and 600v). Under sizing the MTAP voltage rating will saturate the MTAP isolation transformer, resulting in excessive current that will open safety fuses on the MTAP. The most common mistake is installing a 120v MTAP designed for a medium voltage 2-PT open delta secondary into a 3-PT secondary which delivers a 240v signal to the MTAP. 

·    Verify the output of the MTAP makes sense for voltage and current phase relationships. The MCEGold^® Phasor diagram is the best source for this. I1 should be lagging V1 for a standard induction motor by an angle relative to the motor load. The higher the load the lower the angle between voltage and current. The same applies for phases two and three.

·    If connecting a MTAP to a synchronous motor, the current may actually lead the voltage if the synchronous motor field excitation is increased.

·    The MTAP current input is looking for a voltage (333mV/amp) from a Current Transformer (CT) with a load resistor. Do not connect a metering CT with a 1-5 amp output directly to the MTAP. If you only have two available current sources to connect the MTAP CT’s to, make sure you select “Missing Current” in the test setup to properly calculate the missing phase current.

·    Phase leads are often swapped at the starter or in the motor connection box to reverse the rotation of the motor. This can make connecting the correct current and voltage phases more difficult. If necessary connect one phase at a time and retest until you are able to tell which phase of voltage goes with which phase of current. 

Credit: PdMA Corporation