Syringe Oil Sampling Procedures

Use of Glass Syringes for the Collection of Gas-in-Oil SamplesSome considerations before sampling: •Syringe should be filled to 80% full. •The handle of the nylon stopcock always points to the closed port. •DO NOT PULL BACK ON THE BARREL. This will result in bubble formation. Allow the fluid pressue to push back the barrel and fill the syringe. Apply a slight resistance to the barrel with your thumb. •Filled syringe should contain no air bubbles. However, sample will begin releasing gases soon after sampling. •Do not release any evolved gases since these gases must be included in the DGA Analysis. Refer to ASTM D3613 for complete instructions on the sampling of transformer insulating fluids.

Adjust the flow Adjust flow from sampling port for a gentle flow of fluid through the tubing and stopcock. Bleed fluid through stopcock Handle at Position 1. Fill syringe Handle at Position 2 Evacuate fluid from syringe Handle at Position 3. Repeat steps 2 & 3 three times Fill syringe to 80% full Handle at Position 2Ensure no bubles at this time. Close syringe Handle at Position 4.

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That’s it. You should now have a representative sample of the oil from within the transformer ready to be shipped to the laboratory.

Complete the information on the sample data sheet and prepare the sample for shipment. Be sure to write down all pertinent information on the sample data sheet.

Oil Sampling Procedures

Use of Metal Cylinders for the Collection of Gas-in-Oil SamplesMetal cylinders can be used effectively to collect oil samples from transformers. To obtain a representative sample it is necessary to use the proper sampling technique. Following the procedure below will ensure that the sample received by the laboratory is reflective of the oil in the main tank of the transformer. Refer to ASTM D3613 for complete instructions on the sampling of transformer insulating fluids.Hold the cylinder in a vertical position at all times. This will ensure all air bubbles rise to the top and exit the container.

Drain the Sampling Valve Stagnant oil from the lower drain valve of the transformer must be removed before the sample is collected. Also moisture that may be present in the depression of the drain valve must be removed. To achieve this, remove the plug from the drain valve and drain approximately one-half to one gallon of oil into an oil-waste container. To the drain valve, attach a plug fitted with a tubing connector and a section of clear plastic tubing. Attach the Tubing to the Container Attach the cylinder’s lower valve fitting to the tubing connected the transformer. Attach the cylinder’s upper valve fitting to the tubing discharging to the waste oil container. Open Valves in Ordered Sequence Open the valve on the transformer. Open the lower cylinder valve (A). Open the upper cylinder valve (B). Allow about 1 quart of oil to flow through the cylinder into the waste container. Tap the sides of the cylinder with a tool to dislodge air bubbles. Oil running though the tubing should be free of air bubbles. Shut Valves in Reverse Order Shut the upper cylinder valve (B). Shut the lower cylinder valve (A). Shut the transformer drain valve. Shake the cylinder then listen and feel for signs of incomplete filling. If not completely filled, redo from step 1 of Open Valves in Ordered Sequence. Re-Assemble Transformer Valve and Plug Disconnect the tubing and remove the connector from the drain valve. Replace the original plug on the drain valve. Apply pipe dope or Teflon tape on the plug threads to insure a good seal and to prevent rust.

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That’s it. You should now have a representative sample of the oil from within the transformer ready to be shipped to the laboratory.

Complete the information on the sample data sheet and prepare the sample for shipment. Be sure to write down all pertinent information on the sample data sheet.

METALS TESTING

Northern Technology & Testing began metals testing in-house in 1997. Metals testing is used to provide vital information about transformer operation and in locating potential fault sites within the transformer. Not only can the method provide information needed to pin-point fault locations but it can also detect excessive wear in oil circulation pumps. We routinely analyze for seven metals: iron, copper, aluminum, lead, silver, tin and zinc. Analysis for other metals can be done on request.

NTT has recently introduced state-of-the-art equipment to analyze your insulating fluids for metals at low concentration levels. As a result, significant price reductions are now available. As always, we provide rapid turnaround with NTT’s well-established QA/QC program.

AA Spectroscopy

High energy faults can generate metal particles, which are then dispersed in the oil. Identifying the types of metal particles and their concentrations by atomic absorption (AA) provides answers that help localize the fault within the tank.

Several methods exist for determining low concentrations of metals present in a liquid matrix such as transformer oil. Among them include electromechanical, nuclear-activation analysis, X-ray fluorescence, emission spectrometry, and atomic absorption spectroscopy (AA).

AA analysis depends on the selective absorption of discrete frequencies in the radiation spectrum by free metal atoms. During the analysis, an oil sample is burned, and the metals are turned into free metal atoms by this high-temperature incineration. During incineration, the instantaneous intensity of the radiation spectrum is measured and compared against standards to determine the presence and concentration of any free metal atoms. The most practical way to do this is to burn the oil sample in a high-temperature graphite furnace. The advantages of this method are that the oil sample can be placed directly in a disposable graphite sample tube and burned in the tube without any further preparation and, more importantly, the detection levels of this method are better able to determine lower concentrations of metals. Another, less suitable method is to dilute the oil with hexane and then burn it.

Detection Limits

Metals analysis by AA spectroscopy with a graphite furnace:

Aluminum Copper Iron Lead Silver Tin Zinc

0.3 ppb 0.01 0.1 0.01 0.01 5 0.01

Metals and their possible sources in transformers

Aluminum	Windings, corona shields, ceramic bushings
Copper	Windings, bronze & brass components
Iron	Core and tank
Lead	Solder joints
Lead, Tin, Silver, Zinc	Connectors, lugs, bolts and peripheral components