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High Voltage DC Dielectric Test Sets from Megger

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article image High Voltage DC Dielectric Test Set

Megger  offers a range of high voltage DC dielectric test sets for checking the quality of various electrical components.  

Available in capacities of 70 kV, 120 kV and 160 kV, Megger’s high voltage DC dielectric test sets comprise of two modules. 

  • Control Module: Allows the operator to switch-select the appropriate current output range, adjust the output level and monitor both the applied voltage and leakage current at a safe distance from the high voltage being delivered to the load under test
  • High-Voltage Module: Featuring an air-insulated design, the module generates the DC high voltage that is delivered to the load under test.

Applications of high voltage DC dielectric test sets  

The portable dielectric test sets are used to conduct proof tests and insulation tests on electrical power cables, motors, switchgear, insulators, transformers and capacitors.  

Both types of tests are performed by applying controlled high voltages to the unit under test at or above insulation system operating level.  

Measuring the leakage current helps determine the unit’s ability to withstand over-voltages such as lightning strikes and switching surges.  

Proof Test

  • Acceptance testing of newly installed cables
  • Maintenance testing of aged and/or repaired cables
  • Unit under test will either withstand the test voltage or break down, providing the user with a ‘go/no-go’ answer

Insulation Resistance Tests  

The Insulation resistance testers must have microampere sensitivity to conduct appropriate tests on healthy insulation. Insulation resistance can be measured in at least three different ways:  

Spot check testing  

Spot check is performed by applying a predetermined voltage to the unit under test, holding it until the apparent leakage current becomes stable and recording the readings with adjustments for temperature.  

This test is especially applicable to low-capacitance units under test.  

Time-varying testing  

Time-varying tests such as the polarisation index test (PI test) are independent of temperature effects and save time. To perform this test, a predetermined test voltage is applied to the unit under test and readings are taken at 1 minute and 10 minutes. The resulting ratio is analysed to determine insulation quality.  

This type of test is especially appropriate for high-capacitance samples.  

Step-voltage testing  

The step-voltage test is independent of temperature effects and saves time. To perform this test, the output voltage is increased in even steps at regular intervals over a fixed period of time.  

As long as the resistance of the unit under test increases with time, it has high-quality insulation. This type of test is only useful for high-capacitance samples.  

Key features of high voltage DC dielectric test sets

  • Operates like a full-wave rectified unit (filtered half-wave rectification)
  • Lightweight high-voltage module
  • Complete internal guard circuit/guard
  • Connection on high-voltage output cable
  • Choice of digital or analogue metering
  • Continuously variable test voltage
  • Fast charging of high-capacitance samples
  • Negative polarity to ground
  • Strip chart recorder (optionally)
  • Standard safety features
    • Bipolar ammeter on digital models  
    • Input-supply-line circuit breaker
    • Output current overload relay
    • Zero-start interlock for high-voltage output
    • Pushbutton controls and indicating lights for high-voltage ON/OFF
    • Full circuit-breaker protection against internal damage by overloads, surges or test sample breakdown
    • Connection for external permissive and safety interlocks

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