MEM18102 — Fault-find, test and rectify single and three-phase transformers

Elements & performance criteria

Performance evidence

• following work instructions, standard operating procedures (SOPs) and safe work practices
• identifying and interpreting circuits, drawings and specifications relevant to the work to be undertaken
• determining the electrical and non-electrical isolation requirements to prevent the creation of hazards linked from the loss of machine/system/process control according to established procedures
• using lock out tag procedures with appropriate tags/signs
• proving electrical isolation and following established safety rules prior to working on electrical equipment or wiring
• ensuring all electrical equipment and tools are tested and tagged and up to date
• observing work health and safety (WHS) precautions and considerations when dealing with instrument transformers especially current transformers and high voltage equipment
• applying fault finding and diagnostic techniques on at least two (2) or more of the following single and three-phase transformers and their associated control circuits: - instrument - current - voltage - oil filled transformers - high voltage power transformers - low voltage power transformers - neutral - distribution: - step up - step down
• complying with the Australian/New Zealand Wiring Rules for the installation and safety requirements of transformers, including limiting the rise of touch voltages
• performing the following tests in accordance with specifications and regulatory requirements: - basic insulation resistance, continuity and winding identification tests - open and short circuit tests
• carrying out routine maintenance on transformers
• documenting all necessary repairs in accordance with SOPs

Knowledge evidence

• safe work practices and procedures and use of personal protective equipment (PPE)
• operating principles of transformers, including: - principles of mutual induction and how it relates to a transformer - phasor diagram for a transformer on no-load and the voltage and current components - factors that determine the value of induced voltage in a transformer winding - transformers ratios both voltage and current - calculate the value of output voltage given the input voltage and turns ratio of a transformer - transformer losses, including: - eddy current losses and the use of laminations to reduce this effect - hysteresis losses and core materials to reduce this effect - copper losses also referred to as primary/secondary losses or I2R losses - transformer efficiency and the effect flux leakage has on it and its related formula, i.e. transformer efficiency = - voltage regulation as applicable to a transformer and its related formula, i.e. voltage regulation = - power in a transformer, i.e. power in = power out - impedance ratio and reflected impedance - percentage impedance as applied to transformers and how its value affects the value of the available short-circuit current - calculating the percentage impedance of a transformer and determine the percentage impedance of a transformer from test results - transformer construction, including: - single and three-phase transformer cores and winding arrangements - transformer ratings, i.e. in kVA - relationship between transformer cooling and rating - methods used for natural and forced cooling of transformers - properties and tests that are conducted on transformer oil - winding polarities and polarity identification of single and three-phase transformers - four common methods of connecting the primary and secondary windings of a three-phase transformer, i.e. star-star, delta-delta, delta-star and star-delta - three-phase tertiary windings and the purpose they perform - changing transformer ratios, i.e. off-load and on-load changing - transformer auxiliary equipment and their function (bushings, surge-diverters, tap-changers, hot oil and winding indicators, breather, Buchholz relay and conservator) - application of transformers, including welders - paralleling of single-phase transformers, including: - ensuring their voltages are equal - instantaneous polarities are identical - consequences of incorrectly phased transformers - paralleling of three-phase transformers, including: - the need for paralleling - ensuring they are of equal voltages, same phase sequence and phase voltages are in step and the consequences if they are not - testing of transformers, including: - performing basic insulation resistance, continuity and winding identification tests - testing of final connections, i.e. in star, delta and open-delta configurations and transformer ratio - safe working procedures when connecting and testing transformers - open and short circuit tests - dielectric tests - special transformers, including: - potential and current transformers and the reason why they are used - construction and application of potential and current transformers - work health and safety (WHS) hazards associated with instrument transformers especially current transformers where the secondary must never be open-circuited under any circumstances as it will cause a potentially dangerous voltage to be present at the secondary terminals - instrument transformer load or burden ratings - safe working procedures of potential and current transformers - commissioning and testing instrument transformers - transformers with multiple secondaries and tapped windings - advantages and disadvantages of auto-transformers - calculate the voltage and current in the windings of an auto-transformer - high-reactance or leakage transformers - applications of auto-transformers and instrument transformers - Australian/New Zealand Wiring Rules installation and safety requirements for transformers - dangers of high voltage equipment and distribution systems, including: - step and induced voltages - sources of induced voltage and stored energy - creepage and clearance requirements - application of safe working procedures in the vicinity of high voltage equipment

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