The High Voltage DC Dielectric Test Sets (70, 120 and 160kV) provide the most dependable, portable dc high voltage sources for checking the quality of electrical power cables, motors, switchgear, insulators, transformers and capacitors. Each portable set (heaviest is 73 lb, 32.8 kg) is comprised of two separate modules:
This module allows the operator to switch-select the appropriate voltage 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. No voltage higher than input ac power is present in the control module.
High Voltage Module
An air-insulated design receives its instructions from the control unit. It generates the dc high voltage that is delivered to the load under test. Although a different control module is used with each of the three models, they are all the same size and weight. Each high-voltage module is a different size and weight to accommodate the rated output voltage.
- Lightest weight available in air-insulated high-voltage model.
- Advanced performance with long-term reliability provided by filtered half-wave rectification.
- Designed for maximum operator safety.
The Biddle dc dielectric test sets are used to make proof tests and insulation tests on:
- Electrical power cables.
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 under test’s ability to withstand overvoltages such as lightning strikes and switching surges. The three models described cover a range of output voltages that meet the most commonly specified ratings in 5-kV to 69-kV class cable. All are suitable for testing power cable, switchgear and rotating machinery in accordance with IEEE, IPCEA, NEMA and ANSI guidelines.
Proof testing is used for acceptance testing of newly installed cable and maintenance testing of aged and/or repaired cable. For the proof test, the unit under test will either withstand the test voltage or it will “break down,” providing the user with a go/no-go” answer. This is essentially the same as the proof test performed by Megger impulse generator systems, within voltage limitations.
Insulation Resistance Tests
To make appropriate tests on healthy insulation, the test instrument must have microampere sensitivity. Insulation resistance can be measured in at least three different ways:
The insulation resistance test is often referred to as a “spot check,” and 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 tests such as the polarization 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 analyzed to determine insulation quality. This type of test is especially appropriate for high-capacitance samples.
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.
When modified for use with Biddle accessory impulse generators, the dc dielectric test sets provide an economical means of locating faults.