36
Maintenance or Test
Recommended Interval
Reference
Review equipment ratings
5 years
NERC Planning Standard
Infrared scan
Annually
NFPA 70B, 18-17
Power factor test if oil-filled
3-6 years
FIST Volume 3-30
Dissolved gas analysis if
oil-filled
oil-filled
Annually
Reclamation
Recommended Practice
Recommended Practice
Instrument transformers convert power-system level voltages and current to
levels safe to feed meters and other low voltage and current devices. Voltage or
potential transformers generally have output in the 240/120-Vac range, while
current transformers have output in the 2.5- to 5-ampere range. Voltage
transformers may be integral to other equipment or stand-alone. Typically,
current transformers are integral to other equipment (circuit breakers,
transformers) but occasionally may be stand-alone (e.g., 500-kV switchyard at
Grand Coulee).
levels safe to feed meters and other low voltage and current devices. Voltage or
potential transformers generally have output in the 240/120-Vac range, while
current transformers have output in the 2.5- to 5-ampere range. Voltage
transformers may be integral to other equipment or stand-alone. Typically,
current transformers are integral to other equipment (circuit breakers,
transformers) but occasionally may be stand-alone (e.g., 500-kV switchyard at
Grand Coulee).
Over the course of time, instrument transformers (particularly current
transformers) may become overburdened with the addition of more devices in the
secondary circuit. This may lead to saturation during a fault which may cause the
relay to misoperate. Periodically measuring secondary burden and comparing it to
the transformer rating will indicate if this is a problem.
transformers) may become overburdened with the addition of more devices in the
secondary circuit. This may lead to saturation during a fault which may cause the
relay to misoperate. Periodically measuring secondary burden and comparing it to
the transformer rating will indicate if this is a problem.
Instrument transformer secondary wiring should always be checked for integrity
after any work that may have disrupted these circuits.
after any work that may have disrupted these circuits.
Maintenance or Test
Recommended Interval
Reference
Review equipment ratings
5 years
NERC Planning Standard
Burden measurements
5 years
FIST Volume 3-8
Power factor test
5 years
Reclamation
Recommended Practice
Recommended Practice
Visual inspection
Annually
Reclamation
Recommended Practice
Recommended Practice
Infrared scan
Annually
NFPA 70B, 18-17