ASTM D3613 for Sampling Insulating Liquids for Gas Analysis and Water Analysis
ASTM D3613 Standard Practice for Sampling Insulating Liquids for Gas Analysis and Determination of Water Content
6. Preparation for Sampling
6.1 Check for positive pressure by first observing the pressure vacuum gage, if one is present, then check for positive pressure at a sample outlet by placing a slug of insulating fluid in a piece of clear plastic tubing and attaching it to the sample outlet. While observing the slug of insulating fluid, slowly crack the sample outlet valve open. If the slug moves towards the electrical apparatus, a negative pressure exists. Sampling should be discontinued. If the slug moves away from the electrical apparatus, a positive pressure exists. Samples can be obtained safely. Extreme care should be used in performing this procedure.
6.2 Place a flush-oil container under the main drain valve and remove the security pipe plug from the drain valve. Wipe the inside of the valve and threads with a clean lint-free cloth. Drain at least 1.9 L (2 qt) of fluid into the flush oil container to flush the drain valve and drain valve extension. One of two procedures may then be used to prepare the sample outlet.
6.2.1 Procedure A - Install the sample adapter on the drain valve (suitable thread size bushing adapter IPS to 3/8 in. bayonet) with a piece of oil resistant tubing attached. Flush the valve at installed sample adapter, flushing at least one more quart of fluid into the flush oil container before collecting sample.
6.2.2 Procedure B - Install the drain valve security plug. Attach oil-resistant tubing to the sample port on the drain valve and flush at least one more quart of fluid into the flush-oil container before collecting the fluid in the sample container.
6.3 This is an alternate procedure for purging the valve when it is not practical to flush oil through the drain valve or a flush container cannot be placed below the valve.
6.3.1 Place a flush oil container under the main drain valve or use absorbent material. Remove the security pipe plug from the drain valve. Wipe the inside of the valve and threads with a clean lint free cloth. Install the drain valve security plug.
6.3.2 Attach a 60-cm (24-in.) length of poly(vinyl chloride) tubing to the sample port on the drain valve and flush a minimum 1.9 L (2 qt) of oil into the flush oil container through the sample port.
7. Sampling Considerations
7.1 When it is necessary to obtain a sample from a piece of energized equipment not hermetically sealed, under no circumstances take the sample by any other means than from an external sampling valve.
7.2 All equipment filled with insulating fluid having a specific gravity less than 1, should be sampled from the bottom valve.
7.3 All equipment filled with insulating fluid having a specific gravity greater than 1, should be sampled at the top of the tank at the 25°C (77°F) liquid level, so that a top sample of the liquid may be obtained.
7.4 Maintain the insulating fluid within the electrical apparatus being sampled at a level that will not reduce the electric strength of the insulation system. Take extreme caution when samples are drawn from electrical apparatus having a small volume of insulating fluid.
7.5 Energized electrical apparatus being sampled must have a positive pressure at the sample outlet, so as not to admit an air bubble into the apparatus during the sampling process.
7.6 Do not sample electrical apparatus if only a drain plug is provided, as it would be difficult to control the flow.
7.7 Samples shall not be taken from energized instrument transformers.
7.8 Care must be taken in drawing samples to prevent contamination and to ensure a representative sample.
7.9 Collection of samples in metal cans will result in atmospheric air contaminating the sample and the loss of gas from the oil into the atmosphere. Test Method D3612, Table 1, provides coefficients of variation for different gas-in-oil analysis from samples collected in the three containers recommended in this practice.
7.10 New oil resistant tubing shall be used for each apparatus sample port.
7.11 When collecting samples with glass syringes for the determination of dissolved gases or water, or both, the syringe should be filled 80 % full. The filled syringe should contain no air. However, gas-saturated samples will begin to release gases (bubbles) soon after sampling. Do not release any evolved gases (bubbles) since these gases must be included in the dissolved gas analysis. Package the filled syringe as soon as possible to protect the sample from light.
