Utilities | RKI


March 10, 2017

Transformer Condition Tested with an H2 Gas Monitor

Application Description
Electrical utilities use large electrical transformers to drop the voltage coming from power lines. These transformers can be huge; the size of a car or greater. The transformers are sealed with an oil bath surrounding all of the electrical coils inside. This oil bath acts as both a coolant and an insulator. At the top of the transformer, there is a headspace that has no oil and instead is filled with nitrogen, generally under a slight positive pressure. For a new transformer, this nitrogen blanket will remain “clean” for a long time. As the transformer ages, and the insulation between the wire coils starts to break down, the high voltage can arc between two adjacent coils of the transformer. When this occurs, the high voltage passes through the oil blanket, and causes the oil to break down. This causes small amounts of flammable vapors to form from the oil, and rise to the top of the transformer to mix with the nitrogen blanket. These flammable vapors consist of a variety of gases, but generally hydrogen is predominant. Periodic testing of the nitrogen blanket for flammable vapors is a good indication of the health of the transformer. If the testing reveals a buildup of flammable vapors, the transformer can be removed from service in a planned manner instead of a catastrophic manner (they can blow up if undetected).


RKI’s Solution

RKI offers “Transformer Gas Testing” versions of our EAGLE portable sample drawing gas monitor for this application. These instruments have a range of 0-5% hydrogen and use a catalytic sensor. This unit also monitors Oxygen. This Eagle for transformer gas testing has two pumps. In this version the probe is connected directly to the transformer tap, and the internal pump is used to extract a sample from the transformer. A second pump is used to pull the required air through the dilution fitting. This version can also be used on transformers with positive or negative pressure. Testing frequencies vary for each Utility, but generally are between 3 to 6 months. A sudden rise of flammables over this time period is an indication of transformer trouble.


  • Available in single H2 or dual gas with H2 and O2 channels
  • Dual pump design eliminates the need for sample gas bags or dilution fittings
  • Increasing O2 alarms
  • LEL, PPM, or % vol H2 readings
  • Takes samples from positive or negative pressure transformers

Ordering Information

Single Gas H2 EAGLE
EAGLE for Hydrogen (H2), 0 – 5% volume with 2 pumps for transformer testing

Calibration kit, EAGLE, 103L cylinder of 50% LEL Hydrogen/Air, demand flow regulator, case & tubing

Dual Gas H2/O2 EAGLE
EAGLE for H2 (0 – 5%) / O2, with 2 pumps for transformer gas testing

Calibration kit, EAGLE, 103L cylinder of 50% LEL H2/Air, 103L cylinder of 100% N2, demand flow regulator, case & tubing

Cal kit, EAGLE, 34L cylinder 50% LEL H2/Air, 34L cyl 100% N2, dispensing valve, gas bag, case & tubing.

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