High Voltage Self Test 4 Flashcards
(20 cards)
What is the primary function of insulation?
To prevent current flow to ground or another conductor
What factors can cause insulation to deteriorate over time?
-Temperature Rise
-Moisture
-Contamination
-Chemical Changes
Is dielectric loss mainly due to AC or DC or both?
AC
What is it called when a charge can reappear on a conductor even after the conductor has been grounded?
Dielectric Absorption
List the four factors that lead to water trees in insulation?(only found 3 in book)
-Electrical field
-Time
-Water
Which causes partial discharge: electrical trees or water trees?
Partial discharge is associated with electrical trees.
List three factors that may cause partial discharge within a dielectric?
-Voids in the insulation
-Inclusions of contaminations that may cause partial discharge within a dielectric
-protrusion of copper throught the semi con into the insulation
All meggers are safe because they operate at less than 750V? T/F
False
Inuslation tester is safe to connect to an energized circuit? T/F
False
4 common environmental or operational stressors that might result in cable insulation deterioration?
-Elevated temperature
-High UV radiation
-High Humidity
-Water submersion
-Exposure to dust, dirt, and corrosive contaminants
-Lightning strikes or power system transients
-Short circuit surge current
List 3 disadvantages associated with DC hipot testing.(only found 2 in book)
-May not detect some defects such as clean cuts or voids
-Increases water tree growth when testing
-
List 2 advantages of tan delta testing methods?
-Only type 2 testing method to detect the presence of water treeing deterioration within the cable insulation
-Testing can be done on any length of cable
Describe 2 types of Type 1 Field test methods?
-AC hipot
-DC hipot
When are insualtion tests performed?
-Done after cable is installed but before any acccessories, joints, splices, or termination are installed
-Tests are intended to detect shipping, storage, installation damage that may have occured
Which testing mehod is the best at detecting water trees within cable installtion?
Tan delta
Which testing method measures and compares resistive leakage current to capacitive current?
Tan delta
To determine the degree of insulation aging in the cable, what test methof would be the most suitable?
Tan delta
Which testing method may be performed regardless of cable length?
Tan delta
PD test methods are withstand or “go/no-go” tests. T/F
False
What is the function of a guard lead on test instruments?
to divert surface leakage away from meter movement
