Instruction Guide for the Sampling of Oil from Trench COTA Bushings for DGA Forward This instruction is protected by copyright. Imparting to any third party and reproduction of any kind without written permission from Trench is strictly prohibited. Trench is not responsible for any damage or failure that would result from improper operation, customer furnished materials or failure to observe the recommendations contained in this instruction. This applies even if there is no specific instruction included for the procedures or operation for a particular bushing type. All information contained in this manual is subject to change without notice and does not represent a commitment on the part of Trench. Based on Trench's experience and industry standard practices the highest level of reliability is achieved when the recommendations, as outlined in this instruction, are followed. 1
1. Introduction Trench does not recommend taking oil samples from healthy bushings that exhibit power factor and capacitance values that are in accordance with the original commissioning tested results. This procedure must be preformed by qualified personnel, trained to handle oil samples and has read the Trench Installation Manual, Bushings, IEEE/ANSI Standard, Type COTA 150 2050, E8233.72 or latest revision. Caution: Transformer, Reactor or Oil Circuit Breaker must be deenergized and grounded following all pertinent safety procedures dictated by local requirements. Disregarding safety precautions may result in death or severe injury. The bushing to be sampled should be near to ambient temperature; it is recommended to allow 6 hours after de-energizing the transformer or reactor before taking the oil sample. Weather must be clear with a dry ambient. Trench bushings are not pressurized under normal conditions; however, pressure build up may appear as result of excessive oil gassing or temperature. As a precaution, safety glasses or goggles should be worn during this procedure. 2. General Conditions 2.1 Required equipment 2.1.1 PVC tubing, Nalgene, PU or any other gastight and oil resistant kind of plastic, equipped with connections, 500 mm long with a diameter 8-10 mm. Shorter sections of tubing are not recommended since they may accidentally drop inside the bushing. 2.1.2 50 ml glass syringes with 3-way valve. 2.1.3 Small transport case. Do not expose oil sample to sun light as UV rays will alter DGA test results. 2.1.4 Recommend ordering new sealing gaskets from Trench before sampling the oil. 2
2.2 Sample Identification (Refer to bushing nameplate). 2.2.1 Bushing type; COTA, COBA, COTC, COT. 2.2.2 Country of Manufacture. 2.2.3 Style Number, example, 650-H014-23-AG3-01. 2.2.4 Bushing outline drawing number. 2.2.5 Sampling date and location. 2.2.6 Sampler s name. 2.2.7 Reason for taking oil sample. 2.3 Oil Replacement 2.3.1 Trench bushings contain a small volume of free oil with most of the oil volume indicated on the bushing outline drawing contained in the paper insulation system. 2.3.2 When taking an oil sample it is recommended to replace the sample volume with an equal proportion of identical or compatible oil. Upon request Trench can provide new oil from our factory for a nominal fee 2.3.3 If not supplied by Trench the selected oil has to be filtered, dried and degassed to the following specifications: Oil Water Oil Cleanliness IFT Dielectric Strength Oil Condition Mineral, Corrosive Sulfur Free. < 5 PPM. ISO Code 16/14/10 or better. > 40 dyne/cm > 70 kv per 0.1 inch 3. Oil Sampling Procedure (See Figure 1) 3.1 Locate the oil fill plug on the top of the bushing head casting. Bushings that have the bolted top terminal, (Refer to Installation manual) early versions have a projection on one side designed for attaching arcing horns. This projection may 3
be covering the oil fill plug. In that case the bolted top terminal must be removed. Caution, if the transformer or reactor is under pressure or has a conservator type oil preservation system transformer oil will exit though the central tube of the bushing once the bolted top terminal is loosened. Correct this situation before removing the bolted top terminal. 3.2 Clean the surface around the oil fill plug with alcohol. 3.3 With a 6-mm Allan wrench remove the oil fill plug. 3.4 Insert the tube described in clause 2.1.1. 3.5 Connect the syringe with the 3-way valve and the tube. 3.6 Insert the tube into the head casting making sure the end of the tube is below the oil level in the head casting making sure that the syringe is below the oil level as well. 3.7 Pull the syringe piston slowly back and rotate it at the same time. 3.8 Place the 3-way value in the other position. Hold the syringe in the vertical position, nozzle upwards. Press the syringe piston in order to eliminate an air space. 3.9 Reopen the 3-way valve to the sampling position and perform clause 3.7 and 3.8 again until total suppression of the air bubbles. 3.10 Take 25 to 35 ml 3.11 Disconnect the 3-way valve from the syringe while pressing it s piston with a light pressure. Turn the syringe upside down and put its cap with oil out of the syringe. Close the syringe carefully with the cap. 3.12 Replace the volume of removed with new oil as described in clause 2.3. 3.13 Purge the gas space in the head casting with dry nitrogen several times before sealing the bushing by hand-tightening the oil fill plug to 30 in-lb. Caution: Be careful not to over tighten the plug as that may damage the sealing gasket.. Suggest ordering new gaskets from Trench before sampling the oil. 4
Figure 1 4. Evaluation of the DGA Results 4.1 Parameters measured in p.p.m. for normal conditions and bushings to be taken out of service table: D G A Measured Parameter Normal Condition Take Out of Service H 2 < 140 >1000 CO < 1000 > 1500 CO 2 < 3400 > 5000 Methane (CH 4 ) < 40 > 75 Ethane (C 2 H 6 ) < 70 >100 Ethylene (C 2 H 4 ) < 30 > 40 Acetylene (C 2 H 2 ) < 2 > 10 Water <10 >20 5
Report to Trench all bushings removed from service regardless of the state of any warranty. Provide results that led to the action of removing the bushing from service. Trench Ltd. 432 Monarch Avenue Ajax, Ontario L1S 2G7 Canada +905-426-2665 (P) +905-426-2671 (F) www.trenchgroup.com 6