Electrical Insulation Testing
Why perform electrical insulation testing?
Electrical insulation starts to age as soon as it is made. Harsh environments, especially those with extreme temperature changes and/or chemical contamination, cause further deterioration of the insulation (power cord).
As a result, personnel safety (electrocution/shock) and power reliability can suffer resulting in higher operating cost and maintenance.
What is Insulation Resistance Testing
Insulation resistance testing applies a regulated stabilized high voltage (Figure 20), typically 500 VDC or greater across a dielectric (power cord). Measuring the amount of leakage current fl owing through the dielectric will yield a resistive measurement in megohms.
Insulating Material Testing
To verify the integrity of the pump's insulating material (power cable) it will be necessary to perform an electrical insulation test. Any electrical insulation must have the opposite characteristic as the conductor: it should resist the fl ow of current, keeping it within the conductor.
To measure the IR (current x resistance), the use of an IR tester must be employed.This IR tester is a portable device that is a resistance meter (ohmmeter) with a built in DC generator that develops a high DC voltage.
The high DC voltage from the IR tester is usually 500 VDC or more.This voltage, when applied causes a small current to flow through and over the insulation's surfaces.The tester provides a direct reading of IR in megohms.
Ahigh resistance reading would indicate a "good" insulation, meaning very little current is escaping through the insulation. While a relatively low resistance reading would indicate a poor insulation, meaning a signifi cant amount of current may be leaking through and along the insulation.
MAINTENANCE
NOTICE
Insulation resistance is moisture and temperature sensitive. When temperature increases, insulation resistance decreases, and vice versa.
When performing this test measurement, perform the test using the same test parameters as used in the initial testing. Contact an authorized Multiquip service center if the measured cable insulation is 10 megohms or less.
20M | POWER CABLE |
| INSULATION |
M |
|
V |
|
OFF |
|
| |
K SET | GROUND WIRE |
UP |
|
(GREEN) | |
| |
MEGGER™ |
|
500 VDC INSULATION |
|
TEST METER |
|
SUBMERSIBLE
PUMP
Figure 20. Insulation Tester Application
DANGER
Read and follow the manufacturer's user's manual prior to operating insulation tester (megaohm meter). This meter generates a test voltage of 500 volts or greater. Only qualifi ed and trained personnel should
use this equipment. The possibility exists of severe electrical shock, electrocution even death, when using insulation tester.
PAGE 24 — ST4125G/ST6125G SUBMERSIBLE PUMP • OPERATION MANUAL — REV. #0 (11/18/10)
