What are the recommended values to high and very high capacitance alarm?

Capacitance

The IEEE C57.19.100-1995 standard states that, in case of an increase of more than 5% in the initial capacitance of the bushing, it is necessary to assess whether the item remains fit for service. We recommend that this value is configured for the very high capacitance alarm, where the bushing must be removed from service. However, before that, we also have the recommendation for the high capacitance alarm as 3%. When reaching it, we suggest scheduling a programmed shutdown to carry out offline tests.

• High Capacitance: 3 %;

• Very High Capacitance: 5 %;

Delta Tangent 

Based on the IEC 60137-2017 standard, which has a value of 0.350% as the initial tangent delta of a typical bushing, the minimum value for the high tangent delta alarm is recommended as 0.7% (Absolute - when in manual mode) or 100% (twice the initial value - when in automatic mode), since values lower than this can generate undue alarms due to natural variations in the calculation of the tangent delta.

Keeping consistency and proportionality, it is advised the minimum value for the very high tangent delta alarm as 1.05% (Absolute - when in manual mode) or 200% (triple of the initial value - when in automatic mode).

• High delta tangent: 0,7 % (absolute);

• High delta tangent : 100 % (relative);

• Very High delta tangent : 1,05 % (absolute);

• Very High delta tangent : 200 % (relative);

Leakage current

As with tangent delta, leakage current alarms can be set manually or automatically. The automatic values are proportional to the average leakage current value obtained during the equipment learning process. In this case, for the high leakage current alarm the recommendation is 15% and for very high leakage current the recommendation is the value of 25%.

• High leakage current: 15 %;

• Very High leakage current: 25 %;