IEEE 400.1-2018 pdf free.IEEE Guide for Field Testing of Laminated Dielectric, Shielded AC Power Cable Systems Rated 5 kV to 500 kV Using High Voltage Direct Current (HVDC).
3.1.1 Temperature
The dielectric strength 01’ some cable insulations is reduced at elevated temperatures. This necessitates a reduction in the test voltages at higher temperatures. Temperature gradients in the cable insulation, caused by heat dissipation from the conductor, can result in abnormal voltage distribution upon application of a high direct voltage. For these reasons, high voltage direct current (FIVDC) tests should be made with the cable at ambient temperature if possible.
3.1.2 Atmospheric conditions
High humidity and conditions favoring condensation on exposed surfaces can affect test results to a marked degree. Contamination of termination surfaces can greatly increase conduction or leakage current and reduce flashover levels. Relative air density affects the flashover voltage of cable terminations. At elevations higher than 1000 m (3280 II), additional insulation and clearance may be required to withstand the prescribed test voltage. If excessive corona or air discharges exist during a test, a reduced test voltage may result and high leakage current readings will be present.
3.1.3 Extraneous electric fields
Although field tests on cable are otlen made in the vicinity of energized equipment. extraneous electrical fields usually will have little influence on direct voltage test results as long as the voltage measurement circuit is well shielded. A simple test to see the influence can be made by ungrounding the test system prior to encrgization and observing any indications on the test system instrumentation on the lowest metering range. Ii is always important to maintain adequate clearances for the dc test voltages anticipated also taking into consideration the recommended clearance for the energized adjacent circuits.
A well-stabilized power source for the HVDC power supply (dc generator) is essential. Minor variations in the mains voltage or the test voltage supply can cause major variations in the output current indication. The test voltage should remain stable to within 3% during the test time.
3.2.3 Discharge resistor
A resistor with a resistance not less than 5000 1JkV of test voltage is recommended to be used to discharge the cable system after testing. This resistor should be designed to withstand the full test voltage without flashover and to handle the discharge energy without overheating. An insulating grounding stick rated for the full test voltage and a flexible conductor should be provided to connect the resistor across the cable circuit and ground. Remote control grounding devices that avoid operator intervention are preferred over manual grounding devices.
The following precautions should be considered when pcrlbrming tests with HVDC in the field:
—All components require dc-energizing and solid grounding before testing. Checking with a reliable ro!tagc indicator that responds to alternating current (ac) and dc voltage is recommended. While the indicator is in contact with each component and indicates no voltage, a ground connection should be applied to the component and remain attached at all times except when the test voltage is being applied. All unenergized metallic parts in the vicinity of the high-voltage connections should always remain grounded.
— All cable termination ends as well as all connecting leads of components being tested require guarding from accidental contact by such means as barriers, enclosures, or a watchman at all points. The cable ends require separation from all elements not to be subjected to test and by distances at least 0.25 cm! kV (0.1 in!kV) of test potential for voltages up to 100 kV and at least 0.5 cm!kV (0.2 in!kV) for higher test voltages. Please note that the lest electrode geometry has a great influence on the safety clearances. The values recommended in this paragraph arc only for conditions where high-voltage and ground electrodes are smooth and uniform and where high-voltage connections are made with round conductors of adequate size to avoid corona. lithe test connections arc not smooth, larger clearances should be provided.
— The test lead itself as well as the entire measuring circuit should be corona-free. If a bare conductor is used, it should be of a suflicient diameter to reduce corona discharges (streamers) from its surface. A general guideline of 2.5 cm (I in) conductor diameter for every 100 kV of test voltage is usually sullicient for smooth conductors and cable terminations with stress relief electrodes. If a shielded insulated conductor with the shield grounded is used to connect from the test source to the cable being tested, that insulated conductor and its terminations must be rated for the maximum test voltage. Unshielded high voltage cables may be used provided that they do not create corona discharges during the test at maximum operating voltage.
— Breakdown or terminal flashover may generate traveling waves up and down the cable that can be of a magnitude great enough to cause degradation of the insulation of the cable or accessories or breakdown of the cable insulation or the test source. A damping resistor or energy absorbing resistor in series with the output of the dc test source rated for the reflected test voltage and energy stored in the cable if a flashover occurs should be installed to isolate the dc test source from the test load. This resistor, if properly sized, may protect the test source from overvoltages by absorbing the energy in the test circuit and can reduce the oscillation amplitude of the traveling wave.IEEE 400.1 pdf download.