Tough insulation resistance testers

Electrical Power & Protection

April 2014 Electrical Power & Protection

The MIT515 (5 kV), MIT525 (5 kV) and MIT1025 (10 kV) are the newest in Megger’s line of insulation testers over 1 kV. These instruments are based on Megger’s extensive knowledge of insulation testing – over 100 years of exper-ience – as well as feedback from actual end-users. Megger has taken the best insulation testers in the world and added functionality to make them easier to use and transport. They include Megger’s patented digital/analogue display with real-time pointer movement, a CATIV safety rating at all terminals and a unique dual-case design.

The new range of insulation resistance testers consists of three models: two 5 kV units (MIT515 and MIT525) and a 10 kV unit (MIT1025). Resistance measurement is available up to 10 T for the 5 kV models and 30 T for the 10 kV model. The new instruments are smaller and lighter than previous models yet offer advanced features and rapid charge capability. A key productivity feature is the ability to take measurements when connected to line power or 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. High reliability and safety are built in; all models are safety rated to CATIV 600 V and are double insulated.

Five pre-set 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 polarisation index (PI), dielectric absorption ratio (DAR), dielectric discharge (DD), step voltage (SV) and ramp test. Graphs can be compared to example curves in IEEE 95-2002 to reveal a variety of faults otherwise difficult to detect. Small defects can be easily detected without risking the sudden large voltage increments produced by a step voltage test.

Monitoring the developing graph during the test enables the operator to terminate prior to breakdown, thereby reducing the possibility of damage to an 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 type B USB device interface is used for safe transfer of data to Megger’s PowerDB asset management software. Typical end users include electrical contractors, testing and service companies, wind farm and solar generation operators, power generation and distribution companies, as well as industrial and rail companies.

For more information contact Stuart Ashton, Surgetek, +27 (0)11 792 1303, [email protected], www.surgetek.co.za

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Tough insulation resistance testers

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