While carrying out the testing work the Testing Engineer will fill all the necessary test formats. If the slop of the curve starts increasing, it indicates that magnetizing induction becomes low and total primary current is utilized in exciting the core alone. Measurement of power‐factor values in the factory is useful for comparison with field power‐factor measurements and assessing the probable condition of the insulation. IR is proportional to the leakage current through/over the insulation after capacitive charging and absorption currents become negligible on application of DC voltage. Larger transformers have to be dispatched with bushings, a conservator and cooling equipment and all minor accessories have to be disassembled. Safety requirements tools such as safety shoes, safety helmet, safety glasses, fluorescent vest, and safety gloves to ensure maximum ability of safe work and dust mask when require. To ascertain whether the polarity markings are correct or not as per drawing. From the curve it can be implied that up to rated KPV (Knee Point Voltage), the VI curve should be almost a straight line. Unpacking and inspection of accessories to be carried out taking all precautions so that the tools used for opening do not cause damage to the contents. Depending on the size of the unit and on the transport conditions, the transformer may be dispatched completely or partly assembled. During pre‐commissioning this test is required to ascertain that transformer active part has not suffered any severe impact/ jerk during transportation. POWER TRANSFORMER - STANDARDISATION MANUAL 183 Chapter - 5 Transportation, Erection, Testing and Commissioning Working Group Members Mr. S. K. Negi - GETCO Mr. Gautam Mazumdar - CGL Mr. Umapathi - Voltech Mr. Y. V. Joshi - GETCO Mr. D. C. Patel - J. H. Parabia Mr. N. G. Patel - GETCO Ms. Asha Agravatt - GETCO. Insulation resistance is commonly measured in megohms, (MΩ). Ensure all concerned personals shall use PPE and all other items as required. Determining the connection group is valid only in three phase transformers. Core Insulation Test shall be carried out to check insulation between core and ground. The connections about the alternating current method are detailed in standards. Measurement of turn ratio is based on, applying a phase voltage to one of the windings using a bridge (equipment) and measuring the ratio of the induced voltage at the bridge. The test is conducted with the help of mega‐ohmmeter. If oil traces are found on the surface of CT, the same should be cleaned by Methyl Alcohol only. Insulation resistance tests are performed, The significance of the power factor figure is still a matter of opinion. Measure the voltage at the both Primary and Secondary termination at all the phases. Let’s start with transformer pre-commissioning checks and tests and later on with after-receipt checks: This test is performed to check the insulation between core and ground. There should be no joints in testing cables. The ratio of the primary to the secondary currents should approximate closely to that stamped under CT identification plate. After receiving the accessories at site same should be inspected and kept ready for immediate erection: If erection work can not start immediately due to some reasons, then accessories should be repacked into their own crates properly and packing list should be retained. Megger provides thoughtfully equipped transformer test instruments for routine screening needs. – Connect the “R” phase of the Primary winding and “R” phase of the Secondary winding (Short R phase of Primary and Secondary termination). Simultaneous readings of current and voltage are taken. – Apply 3 phase supply voltage (415 V AC) across the 1U & 1V and measure the Corresponding Voltage for 1U-1V, 1V1W & 1U1W. There are some sampling techniques better suited for certain types of oil tests than others. All materials and relevant documentation to this testing works shall be checked by the responsible personnel prior to the commencement of testing activities. Inclusion as part of an in‐house quality assurance program, like verifying electric continuity within a. To assess the mechanical integrity of the transformer. For example, unless there is reason to be concerned about winding deformation, a leakage reactance test is probably not necessary. section a - customer data. (not applicable for air core reactors). Increase voltage in secondary up to rated KPV/ ISF and by recording Primary Voltage, compute ratio of V1/ V2. A thermo vision Camera determines the temperature distribution on the surface of the tank as well as in the vicinity of the Jumper connection to the bushing. The test shall be performed before winding resistance measurement. IR measurement should be carried out preferably in dry and sunny weather. Learn about power engineering and HV/MV/LV substations. Is there any amendment for knee point definition. Warning signs and safety barriers should be positioned. Before any Item of equipment is accepted for testing a visual inspection will be carried out on that equipment. All the personnel involved should be thoroughly apprised about the safe procedures to be adopted while performing various activities including carrying out tests in the switchyard. The phase relationship test should also be carried out. Common Pre-commissioning Tests of Transformer Insulation resistance values of various winding should be checked. Following points to be checked after receipt of the transformer / reactor at site: N2 pressure and Dew point to be checked after receipt of transformer at Site. 2) validate that the transformer tests the same as it did when last tested at the manufacturer’s facility,
Knee Point Voltage is normally defined as the voltage at which 10% increase in the applied voltage causes 30 to 50% increase in secondary current.