Megger MIT525 – 5 kV Diagnostic Insulation Resistance Tester

Megger MIT525 – 5 kV Diagnostic Insulation Resistance Tester

The Megger MIT525 5-kV Insulation Resistance Tester is designed for high voltage diagnostic testing and maintenance of electrical equipment. The unit is capable of measuring insulation resistance to 10 TΩ as well as performing various diagnostic tests such as Polarization index, Dielectric Absorption Ratio, Step Voltage, Dielectric discharge, and ramp testing.

This new version features a tough dual-case design which provides additional protection for the unit and for users. The MIT525’s inner case is fire retardant, providing extra safety when dealing with high voltages. The outer case provides excellent protection against drops and knocks as well as environmental variables. The unit’s outer case is actually IP65 rated, meaning it is sealed tightly against dust and water. The unit also features a CATIV 600 V safety rating, good for testing at up to 3000m in altitude. Even with this tough new design, the MIT525 is actually smaller and lighter than its predecessor.

The MIT525 now comes equipped with lithium ion fast recharge batteries. These batteries require only 2.5 hours to charge to their full operating power, providing 6 hours of continuous use. In a pinch, a 30-minute charge time will provide slightly less than one hour of use. The unit can also be powered from an AC power source.

The MIT525 also has a large, clear, easy to read display, making it equally suitable for use in both bright sunlight and poorly lit environments. Important information like resistance, voltage, leakage current, capacitance, battery status and time constant is displayed on-screen. In addition, the elapsed time of the test is displayed constantly while testing, eliminating the need for separate test timer.

Additional Features:

• Large backlit LCD shows multiple parameters simultaneously.
• High quality flexible silicon insulated test leads with test clips meet IEC 61010.
• CATIV 600V rating on ALL terminals
• Easy-to-read rotary test selection button includes IR, IR(t), DAR, PI, DD, SV and Ramp Test
• Rotary switch operation for intuitive field use.

This new range of insulation resistance testers from Megger consists of three models: two 5 kV units (MIT515 and MIT525), a 10 kV unit (MIT1025), and a 15kV unit (MIT1525). Resistance measurement is available up to 10 TΩ for the 5 kV models, 20 TΩ for the 10 kV model, and 30 TΩ for the 15 kV model. The following features are specific to the MIT525, however many overlap with other models.

Five preset voltage ranges are provided in insulation test mode, plus a user-defined 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. Graphs are downloadable from the unit via USB and can be compared to example curves in IEEE 95-2002 to reveal a variety of faults which are otherwise difficult to detect. Small defects can be easily detected without the risk associated with the sudden large voltage increments produced by a Step Voltage test. Monitoring the developing graph during testing enables the operator to terminate prior to breakdown, thereby reducing the possibility of damage to already flawed insulation. The MIT525 is particularly informative on polyester, asphalt and epoxy-mica insulations. The unit can also test voltage suppression devices.

In accessing all these functions, Megger has maintained the utmost simplicity of operation. The two rotary switches (pictured above) allow users to easily switch test modes. The large backlit display enables multiple results to be displayed simultaneously.

The MIT525 supports high current up to 3mA short circuit current. The unit also features high noise immunity up to 3mA of noise rejection. The MIT525 includes a dedicated voltmeter function as well, good from 30 V to 660 V.

The MIT525 also features internal memory for logging test data. 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.

Applications

All four Megger units in this series are designed for testing the insulation of high-voltage electric equipment. Their wide voltage range also allows applications for low-voltage equipment including generators, motors, transformers, cables and switchgear.

All four instruments can test the insulation resistance of:

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

The MIT525, MIT1025, and MIT1525 can also perform spot tests, step-voltage tests, dielectric discharge tests, ramp tests, and dielectric absorption tests for the use in 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.