(i) Insulation Resistance Test
This test most often conducted to determine the quality of High voltage bus duct insulation is the insulation resistance test. It is performed as a routine maintenance test for bus ducts already in service or as an acceptance test for new bus ducts. DC over potential testing is another way of testing bus duct insulation. This test is performed primarily on medium and high voltage bus ducts to test their dielectric strength and is not recommended for routine maintenance testing of low voltage bus ducts. It is a simple, quick, convenient and nondestructive test that can indicate the contamination of insulation by moisture, dirt or carbonization. Before testing any bus duct, the circuit must be de-energized. Once that is done, it is usually best to isolate the bus duct in order to test only the bus duct, and to avoid error due to leakage across or through switchboards or panel boards. For an acceptance test, bus duct less than or equal to 300 V may be tested at 500 V and bus duct greater than 300 V but less than 600 V may be tested at 1,000 V. For a routine maintenance test, test voltage should be restricted to 80 percent of the factory test voltage. The test voltage should be applied from phase to ground on each conductor with the shielding tapes and metallic jackets also connected to ground. While no general standard exists for minimum acceptable insulation resistance values for bus ducts in service, a “rule-of-thumb” of one mega ohm of resistance (minimum) per 1,000 V of applied test voltage is accepted.
(ii) High Potential Test
The objective of the test is to ensure the insulation level of bus duct. For conducting the test any Two Phase are short using connecting probe and it is earthed, another one terminal is connected to the test kit , Form the test kit one terminal is connected to the earth. Before conducting the test Insulation Resistance test has to be conducted to ensure the insulation resistance of the bus duct In the DC test, the voltage is quickly raised from zero to the specified level. The test is usually held for one minute. The current is measured in mill amperes. The reading of current is provided so that the person running the test can determine if the particular test set has sufficient capacity for the task at hand. If the bus duct withstands the one minute application, the test has been passed. Failure results in short circuit and a ruined portion of the bus duct. The test set is designed to trip off immediately upon detection of the fault current. After conducting the HIPOT test, the bus duct has to be re-checking the Insulation Resistance; to confirm the bus duct has no damage due to HIPOT test.