Reed Electric

Waster of Energy and Destroyer of Motors

Not all power applied to an electric motor is converted to work. Principal sources of waste include winding (I²R) loss, windage, friction, stray load loss and loss in stator, rotor and armature cores. "Core" refers to a stacked assembly of thin plate of special steel around which the copper wire is wound. The Core reacts with the Winding. Studies have shown that, depending on load, core loss is the first or second leading cause of energy waste in rewound motors, and can account for 25% or more of motor inefficiency.

Lexseco determined that the most important indication of core steel condition is the watts of electrical energy lost per pound (kilogram) of core steel when the core is excited to operating conditions. Common electrical grades of core steel have inherent Epstein test rated watts per pound (kilogram) losses ranging from 1 to 2 watts per pound (kilogram) depending upon application. This value is increased by as much as a factor of 1.5 to 2 once this steel is punched and assembled into motor cores. This increase may be attributed to a combination of the following: Lamination punching or stamping burrs, lamination thickness, lamination clamping pressure, type of insulation coating used on the steel, heat treatment process used on punched laminations, lamination assembly method, silicon content and hardness of the steel, and heavy welds across the back of the core stacking.

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Vertical Vertigo: Hollo-Shaft Horrors

Why a little known change causes headaches.

Vertical Hollo-Shaft Motors in the 150Hp and above built on the 444 Frame size have "an issue".
Gone are the easy days when you could merely count on matching the frame size, horsepower, and speed to replace your pump drive motor.

We've come to learn (the hard way), that the premiere Vertical Hollo-Shaft manufacturer - US Motors, has made a serious change in a dimension critical to the pump head shaft (shaft that connects the motor to the pump impeller(s)).

Referring to the dimension drawing examples below, pay attention to the "CD" dimension differences between the "OLD 444 frame" and the "NEW H444 frame".

Click HERE for OLD 444 frame
Click HERE for NEW H444 frame

As you can see, there now is a dimensional difference which effects the pump head shaft. In the examples to the right, the NEW 444 frame is 2.28 inches longer in the area where the head shaft locknut threads would normally have been protruding to screw the locknut onto. Sometimes the CD dimension is shorter on the NEW style motor replacement.

Read more: Vertical Vertigo: Hollo-Shaft Horrors

Size Matters !

When it comes to new or replacement motors, a common mistake that creates a lot of headaches is OVERALL SIZE of the motor. Such a basic common-sense factor as available space for where the motor is installed gets overlooked routinely.

Our own industry may be the cause for this mistake of assuming a motor will fit.

Why?

One Frame Fits All – Nope!

Decades ago, our industry did both a good and bad thing. The industry group (NEMA) set up a size standard called "Frame Size". As can be seen in the dimension drawings from all manufacturers, this standardization was very specific in MOST dimensions. The output shaft diameter (U), the shaft height (D), the mounting feet bolt-hole pattern are all standard no matter which manufacturer. These are standardized by the NEMA frame call-out. This accomplished the very good goal of making motors from many different manufacturers very interchangeable. The standard also helped keep the various manufacturers competitive with each other and helped improve ready availability.

Read more: Size Matters !

Metallizing Miracle: Saving Your Shaft

When electric motors come in for repair the bearing fits on the shaft are often worn too small to hold a bearing any more. This wear can be the result of:

    pulling the bearing off too many times for bearing changes
    the extreme pressure of carrying the load on the shaft
    from bearing failure

When a bearing fails it can create a significant amount of heat; enough heat to cause the inner race of the bearing to 'grow' too large for the shaft due to thermal expansion. The inner race then begins to spin on the shaft. The result can be a shaft many thousandths of an inch too small to hold a new bearing. In some cases the inner race will actually weld to the shaft and create straight 'threads' locking the inner race onto the shaft.The inner race must then be cut off of the shaft with a cutting torch using a scarfing technique.

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Shaft Current Horrors !

Veiled in the shadows deep within the bowels of your motor, lurks an unknown evil.

This strange beast goes by the name “Shaft Currents”.

Shaft Currents are phenomena that are not fully understood and have come out into the light more in recent years – especially with the growth of Variable Frequency Drives controlling motors. Reed has seen a steady increase in the damage from shaft currents. What this weird monster does is eat up bearings. A variety of sources induces a voltage to flow from the motor shaft to ground. And when this current flows through the vulnerable bearings a destructive arcing occurs between the bearing races and balls. (The same effect can even occur in sleeve bearings.)


The photo below and those within the Service Bulletin show you what a bearing ruined by Shaft Currents look like. Black fluting divots (similar to Electro Discharge Machining or etching machines used to print on metal) in a regular pattern can be seen on the raceways (where the balls ride) of the bearings. The balls will have either a frosted or pitted look. You or your repair facility should always be looking at the worn bearings at servicing to detect this event.

Read more: Shaft Current Horrors !

Mystery of the Missing Fan

A costly problem we run across occasionally involves a missing part. Some Reliance and GE 2-pole (3600RPM) TEFC (totally-enclosed fan-cooled) motors have very long stator designs. This length puts the drive-end bearing far away from the air stream of the cooling fan. To cool the drive-end bearing, these designs incorporate a small, thin fan mounted on the drive-end with a flat sheet metal guard.
 
This design works rather well… until…..
 
Because the fan is small and fragile, they occasionally get broken or lost over the years. And when they are not replaced, it is difficult to visually detect that these fans were originally installed on the motor. These small odd drive-end fans are nothing like the big Main Motor Cooling fans that are always on a TEFC motor.

 What then happens is the drive-end bearing runs much hotter and has a shortened life. A motor that had provided successful service for years, suddenly just doesn’t seem to hold up like it used to. And the culprit is a $50 to $100 Missing Fan.

Read more: Mystery of the Missing Fan

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Reed Electric - LA
5503 S. Boyle Avenue, Los Angeles, CA 90058
Ph: 323-587-2284 / Fax: 323-587-2142

Reed Electric - Reno
5375 Louie Lane, Reno, NV 89511
Phone: 775-824-7333 / Fax: 775-824-7344