We are preparing to do some generator and traction motor testing on our ATSF Motorcar. We have Sante Fe Rail Motor Car Bulletin M-13. "Dielectric Test", and it references a "standard insulation testing apparatus furnished by the General Electric Company as shown on diagram No. K-5086225."

Unfortunatley we don't have one of those, and other than the test voltage, we don't know what else it's properties are. BTW, this isn't just a megger. The bulletin indicates that we use this tester after we've tested the insulation.

Does anyone happen to be familiar with this tester, its testing parameters (current, AC vs dc, etc.? Or better yet, does anyone have one?

Greg

The only other information that you need is the inductance of the windings. A shorted turn will not show up in DC megger tests. Several different companies make bridges that will measure inductance. Of course you will need to know the correct inductance values for your motors and generator.

Streetcar companies often had a device that measured inductance in field coils. Electrically it was a bridge. It used a vibrator to create an AC signal and used headphones as a detector. You tuned it for minimum buzz in the headphones and then read the value off the dial. It was not calibrated in any standard units. The streetcar company posted a chart with the correct readings for all the different types of motors in use.

This is a typically a test of high voltage (greater than 1000 volts) that is used to check the insulation between 2 cables/ systems. Unless you are very familiar with working with this type of voltage, I would advise you to skip this test and rely on meggar testing on an annual basis, and build up a database of readings for each cable/ system. This will give you more information regarding when to clean your panel boards and or insulation, or in extreme cases when new cables are required. Wire insulation typically does not go bad overnight, but will deteriorate over a time period. You need to keep a log of meggar and inductance tests, these will be a great help if you need to trouble shoot your systems.
Mike Tillger

Two sources for material relating to megger testing and other forms of motor testing are IEEE and the "MEGGER" Company website. While IEEE will hit you up for a good buck for this material, there is a free download on the MEGGER site.

Another point to remember is this: While a megger test is inherently non-destructive,
the application of a high voltage test to a machine of doubtful insulation quality may render the machine unservicable. In essense, a satisfactory megger test can be considered a pre-qualification for additional testing.

A megger test is called for every 92 days on d/e locos, per CFR 229.

DPK

What specific section of CFR 229 calls for a megger test, I see a test requirement for continuity? How do others perform their continuity test? We just ascertain that current flows through out the entire system and motors and the like work correctly.
Thanks,
Mike Tillger
Excerpt from
http://ecfr.gpoaccess.gov/cgi/t/text/te ... .3&idno=49

§ 229.25 Tests: Every periodic inspection.

Each periodic inspection shall include the following:

(a) All mechanical gauges used by the engineer to aid in the control or braking of the train or locomotive, except load meters used in conjunction with an auxiliary brake system, shall be tested by comparison with a dead-weight tester or a test gauge designed for this purpose.

(b) All electrical devices and visible insulation shall be inspected.

(c) All cable connections between locomotives and jumpers that are designed to carry 600 volts or more shall be thoroughly cleaned, inspected, and tested for continuity.