Transformer Maintenance

By the end of the this course you will be able to:  List the essential parts of a simple transformer. State how a transformer fulfills the three requirements for electromagnetic induction. State the relationship between primary and secondary voltages and transformer turns ratio. State the relationship between primary and secondary currents and transformer turns ratio. Define the following terms: Regulation Copper losses Iron losses Eddy currents Hysteresis Demonstrate how a transformer1s turns ratio can be altered by selecting various combinations of primary and secondary taps. Define the following terms: Additive polarity Subtractive polarity List the requirements that must be satisfied when transformers are connected in parallel banks. List the advantages and disadvantages of autotransformers as compared to two-winding transformers. List four common connection schemes for three-phase transformers. Define distribution transformer. List the basic safety precautions necessary before performing maintenance on a dry-type transformer. Using data from a transformer nameplate indicate the required tap connections to maintain the rated output voltage for a given supply voltage. List the sequence of test connections for performing a ratio test on a three-phase transformer. List the necessary preparations and the connection sequence for performing an insulation resistance test on a three-phase transformer. Define wet-type transformer. Compare and contrast the safety considerations involved with the use of mineral oil and PCBs as the insulating liquid in wet-type transformers. List three tests commonly performed on wet-type distribution transformers. List the basic steps in the high-potential insulation test procedure. List the basic steps in the two-voltmeter ratio test procedure. List the basic steps in the core-loss test procedure. Define power transformer. List four typical types of transformer cooling systems and the basic components of each type. Describe four typical methods for sealing power transformers. List the typical· in-service inspection points for a forced-air/forced-oil gas seal type power transformer. List the typical tests and checks performed on power transformers that are de-energized and cleared for maintenance. State the function of a load tap changer. Define the following terms: Potential transformer Current transformer Draw a schematic of a potential transformer showing its primary connections. Draw a schematic of a current transformer showing its primary connections. Describe the safety precautions required when disconnecting the secondary of a current transformer.