|PART 21 - FAILURE OF SIZE 1 AND 2 FREEDOM SERIES AUXILIARY CONTACTS
The following is a summary of information received from Paragon Energy Solutions:
DUKE Harris Nuclear Plant (HNP) has identified instances where Size 1 and 2 Eaton Freedom Series starters have failed to function as expected in assemblies that were originally supplied by NLI. The auxiliary contacts have degraded prematurely and have failed to change state when the starter was energized which has affected indication and other controlling actions within the circuit.
The premature degradation of the auxiliary contacts with the old model NLI special coil, part number: 057018-COIL-1/2, has occurred on size 1 and 2 contactors that were continuously energized with significant run time after approximately 3 to 5 years of service time. HNP has provided information to manage the known degradation. The auxiliary contacts should be replaced at an increased frequency until new auxiliary contacts are installed along with the new design NLI special coil, part number: 057018-COIL-1/2-M.
The nature of the defect is the pre-mature aging of the component within the auxiliary contact mechanism that is adjacent to the operating coil. The starter coil is potentially being subjected to voltages of a nature that elevates the temperature within the starter adjacent to the auxiliary contacts.
It is recommended that the starters and coils be replaced in the applications where the units are being operated in a continuous duty application. It is also recommended that the control transformer be replaced with a true 4:1 ratio transformer. Paragon/NLI has developed a true 4:1 ratio transformer that will provide additional mitigation of this potential over-voltage condition. Replacing the transformer with a true 4:1 ratio reduces the control voltage that is being applied to the control circuit in a manner that will not prevent the unit from providing a sufficient voltage during a degraded voltage condition, and also will not subject the components to a voltage above the ratings when the supply voltage is operated above the nominal 480 VAC bus voltage.
Paragon has no other recommendations as the accelerated aging of the components and the expected life based on the additional heat the units have been subjected to is unknown.
Should you have any questions regarding this matter, please contact:
Chief Nuclear Officer
Paragon Energy Solutions