Megger MIT525 Insulation Resistance Tester

The Megger MIT525 insulation resistance tester is a 5kV unit with a resistance measurement up to 10TΩ. A key productivity feature is the ability to take measurements when connected to line power/mains with a dead battery. Intelligent battery charging ensures the optimum charge rate as a function of battery level, resulting in minimum charge times.

The rugged, unique dual case design provides the ultimate protection for a portable instrument and a clip-on lead pouch ensures that leads remain with the instrument at all times. The case lid is removable for improved terminal access. IP rating is IP65 with the case closed preventing water/dust ingress. High reliability and safety are built in; all models are safety rated to CATIV 600V and are double insulated.

Five preset voltage ranges are provided in insulation test mode, plus a user settable lock voltage range. Any selectable test voltage may be locked and restored via the selector switch, thereby increasing efficiency of commissioning and repetitive tests. Preconfigured diagnostic tests include Polarization Index (PI), Dielectric Absorption Ratio (DAR), dielectric discharge (DD), Step Voltage (SV) and ramp test.

The ramp function gradually increases voltage up to a selected level while graphing current vs. voltage (graph downloadable). Graphs can be compared to example curves in IEEE 95-2002 to reveal a variety of faults difficult to detect otherwise. Small defects can be easily detected without risking the sudden large voltage increments produced by a Step Voltage test. Monitoring the developing graph during test enables the operator to terminate prior to breakdown, thereby reducing the possibility of damage to already flawed insulation. These units are particularly informative on polyester, asphalt and epoxy-mica insulations. They can also test voltage suppression devices.

Simplicity of operation is achieved with two rotary switches and the large backlit display enables multiple results to be displayed simultaneously.

Advanced memory storage includes time/date stamping of results, logging of data and recall of results to screen. A fully isolated USB device interface (type B) is used for safe transfer of data to Megger's PowerDB asset management software.

The MIT525 tests the insulation resistance of:

• High-voltage power cables and high-voltage buses
• Large motor/generator windings
• Line and substation transformers

The MIT525 also performs spot tests, step-voltage tests, dielectric discharge tests, ramp tests, and dielectric absorption tests for the following applications:

• Acceptance testing at installation to check conformance to specifications
• Routine preventive/predictive maintenance testing after installation
• QA testing as part of the manufacturing process
• Diagnostic testing to isolate faulty components for repair