Substation Current Transformer Failure

Introduction High Voltage Current Transformers, like any power electrical piece of equipment, are designed and manufactured to operate for at least 20 years. Extensive laboratory and factory tests are performed in new equipment to ensure this. These tests have been also applied in instrument transformers retired from service.

Problems & Findings:
The current transformer used in substation for measuring the current in substation. Usually Current transformer have a long life in substation; we don’t need to change it frequently. It can work continuously up to 10 years but somehow environment condition & successive transients affect its performance. In this case, we found that CT suddenly burst out and oil spurt with fire surrounding it and the porcelain petty coat broken into pieces & whole substation needed to shut down.

Check points:

Sr No	Check points	Status
1	Checked the CT condition properly & insulation status.	Completely worst condition
2	Checked manufacturer recommended manual for CT	Every year Tan Delta Test recommended
3	Busbar protection operated	All other protection circuit checked for any other cause
4	Master relays of auto transformer operated	Master relays checked for any other abnormality
5	All other tripped feeder checked	Other tripped feeder found healthy
6	Preventive maintenance records checked	Tan Delta test annual basis record not found

Recommendations:

1. ABB current transformer recommended in place of any other because of its long term services & reliability.

2. Tan Delta test recommended annually for getting its insulation status, so that before failure of insulation, it can be replaced on time.