Emerson LARGE AC ELECTRIC MOTORS, 986269 manual Storage

U.S. ELECTRICAL MOTORS INSTALLATION AND MAINTENANCE

Storage

(H)All motors must have the shaft rotated a few turns once a month to maintain a lubricant film on bearing races.

3.Periodic Maintenance/ Insulation History

The only accurate way to evaluate the condition of the winding insulation is to maintain a history of the insulation readings. Over a period of months or years these readings will tend to indicate a trend. If a downward trend develops or if the resistance drops too low, thoroughly clean and dry the windings, retreating if necessary.

The recommended insulation resistance test is as follows:

(A)Using a megohmmeter, with winding at ambient temperature, apply DC voltage (noted below) for 60 seconds and take reading.

Rated Motor Voltage	Recommended DC Test Voltage
600 and less	500 VDC
601 to 1000 incl.	500 to 1000 VDC
1001 and up	500 to 2500 VDC
	(2500 VDC optimum)

(B)For comparison the reading should be corrected to a 40°C base temperature. This may be done by utilizing the following:

R40C = Kt X Rt

Where R40C = insulation resistance (in megohms) corrected to 40°C

Rt = measured insulation resistance (in megohms)

Kt = temperature coefficient (from Graph 1)

GRAPH 1

Winding Temperature °C

(ADAPTED FROM IEEE 43)

Installation Resistance Temperature Coefficient: Kt

3