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The Dielectric Discharge (DD), sometimes called re-absorption current, test is performed during the discharge cycle after the test. There are three components of current (charging, polarization and leakage currents) present during a standard insulation test, which make it difficult to determine the dielectric discharge.
Rather than measuring the polarization current during an insulation test, the DD test looks at the de-polarization and capacitive discharge currents at the conclusion of the insulation test.
The device under test (DUT) must be charged for an adequate amount of
time to be stabilized therefore, the only remaining current component is
leakage current. The DUT is then discharged at the completion of the
insulation test and the current flow is measured during a standardized time
of one minute. This current is dependent on the overall capacitance and the ending test voltage.
Dielectric discharge is calculated as:
Dielectric Discharge = I (after 60
seconds) / Volts x Capacitance
The DD test can identify excess discharge currents that happen when a layer of multi-layer insulation is damaged or contaminated. This condition will be missed by both the spot test and the Polarization Index test. Discharge current will be higher, for a known voltage and capacitance, if an internal layer is damaged. The time constant of this individual layer will differ from the other layers, causing a higher current than for insulation that is good.
Homogenous insulation will have a DD value of 0 while good multi-layer insulation could have a value as high as 2.
Source: http://www.aemc.com/
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What is dielectric test in transformer?
why need dielectric test for transformer
Which is another name for dielectric strength test?
ASTM D149 - 09 Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies
What is BDV test for distribution transformer?
When you say BDV you might mean the dielectric strength of transformer oil. A new transformer oil should have at lest a dielectric strength of 39 KV. from a British standard.Transformer oils used are normally tested using ASTM D877-82 with the KV strength tester using 1" electrodes spaced 0.1" apart and the test voltage increased at 3,000 volts/min until it breaks down. The average Kv obtained after 8 trials is considered the Oil dielectric strength.Using this test method,dielectric strength at 30 kv and above is considered good. Dielectric strength between 23 to 29Kvis considered usable, but requires filtering. Below 23 kv, the transformer oil should be replaced.Another method ASTM D18747-82 uses the small radius electrodes but spaced only .o4 inches. The test voltage is 500volts/min and increased until breakdown. The dielectric strength is still the average Kv obtained in 8 trials. The dielectric strength of 28-29Kv is considered good. Below 28 kv, the transformer oil is usable but requires filtering. The latter method is considered a better test method
What does kv stand for in a dielectric test?
Kilovolt or 1000 volts. 1KV is 1000 volts, 2KV is 2000 volts. Kilo stands for 1000.
What is the sodium hypochlorite dielectric constant?
dielectric constant for sodium Hypochlorite
What is dielectric test in transformer?
why need dielectric test for transformer
What is Dielectric test?
The Dielectric Discharge (DD), sometimes called re-absorption current, test is performed during the discharge cycle after the test. There are three components of current (charging, polarization and leakage currents) present during a standard insulation test, which make it difficult to determine the dielectric discharge. Rather than measuring the polarization current during an insulation test, the DD test looks at the de-polarization and capacitive discharge currents at the conclusion of the insulation test. The device under test (DUT) must be charged for an adequate amount of time to be stabilized therefore, the only remaining current component is leakage current. The DUT is then discharged at the completion of the insulation test and the current flow is measured during a standardized time of one minute. This current is dependent on the overall capacitance and the ending test voltage. Dielectric discharge is calculated as: Dielectric Discharge = I (after 60 seconds) / Volts x Capacitance The DD test can identify excess discharge currents that happen when a layer of multi-layer insulation is damaged or contaminated. This condition will be missed by both the spot test and the Polarization Index test. Discharge current will be higher, for a known voltage and capacitance, if an internal layer is damaged. The time constant of this individual layer will differ from the other layers, causing a higher current than for insulation that is good. Homogenous insulation will have a DD value of 0 while good multi-layer insulation could have a value as high as 2. Source: http://www.aemc.com/
How does a capacitor discharge if there is dielectric material separating the two plates?
The capacitor can discharge over the connecting wires; i.e., outside the capacitor. Some discharge can also occur over the dielectric, since it will not insulate completely.
Best dielectric material for corona discharge?
Mica sheet
Which is another name for dielectric strength test?
ASTM D149 - 09 Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies
How often do you need a Dielectric test on bucket trucks?
Annually
What does guaiac mean?
Guaiac-positive discharge means that there was blood in the discharge. This test may be used for breast discharge.
How can you test the dielectric strength of oil of transformer?
dielectric strength is tested by transformer dielectric strength oil testing machine. at first, oil which is to be tested is pour near the two electrode. both the electrode should be dipped in oil . then adjust the distance between the electrode .now start the machine.when a sound came from machine then note down the dielectric strength of the oil.
Why the top of a lightning rod is made sharply pointed?
to concentrate the electric field there, making it easier to breakdown the air dielectric and discharge accumulated atmospheric electric charge.
For an insulating material dielectric strength and dielectric loss should be respectively?
For an insulating material dielectric strength and dielectric loss should be respectively
What is dielectric constant in chemical terms?
dielectric constant
What is BDV test for distribution transformer?
When you say BDV you might mean the dielectric strength of transformer oil. A new transformer oil should have at lest a dielectric strength of 39 KV. from a British standard.Transformer oils used are normally tested using ASTM D877-82 with the KV strength tester using 1" electrodes spaced 0.1" apart and the test voltage increased at 3,000 volts/min until it breaks down. The average Kv obtained after 8 trials is considered the Oil dielectric strength.Using this test method,dielectric strength at 30 kv and above is considered good. Dielectric strength between 23 to 29Kvis considered usable, but requires filtering. Below 23 kv, the transformer oil should be replaced.Another method ASTM D18747-82 uses the small radius electrodes but spaced only .o4 inches. The test voltage is 500volts/min and increased until breakdown. The dielectric strength is still the average Kv obtained in 8 trials. The dielectric strength of 28-29Kv is considered good. Below 28 kv, the transformer oil is usable but requires filtering. The latter method is considered a better test method
