Parallel operation of transformers involves connecting two or more transformers together to supply a common load. Parallel operation offers several benefits, including increased capacity, load sharing, redundancy, and improved system reliability. However, it requires careful consideration of various factors to ensure proper operation and compatibility. Here are the key aspects to be consider when parallel operating transformers:
- Ratings and Parameters: Transformers to be paralleled should have similar ratings, including voltage rating, kVA rating, impedance, and impedance voltage. It is essential to ensure that the parameters of the transformers are compatible to avoid imbalances and unequal load sharing.
- Vector Group: Transformers with the same vector group should be paralleled. The vector group indicates the phase relationship and polarity between primary and secondary windings. Paralleling transformers with different vector groups can result in circulating currents and operational issues.
- Polarity: The polarity of transformers should be checked to ensure they are in phase when connected in parallel. Transformers with the same polarity will have additive voltages when connected together.
- Voltage Ratio: The voltage ratios of the transformers should be equal or very close. If there are minor differences, voltage transformers (VTs) or potential transformers (PTs) can be used to compensate for any variations and ensure voltage equality.
- Impedance Matching: The impedance values of the transformers should be matched to minimize circulating currents. If the impedances are significantly different, additional measures, such as reactors or load tap changers, may be required to balance the load sharing.
- Cooling and Temperature Rise: The cooling methods of the transformers should be compatible. It is important to consider the cooling capacity of each transformer to prevent overheating and ensure proper cooling when operated in parallel.
- Protection and Control: The protective relays of the transformers should be coordinated to ensure selective tripping and fault detection. The control and monitoring systems should be capable of managing the parallel operation, including load sharing and voltage regulation.
- Commissioning and Testing: Proper commissioning and testing are essential before parallel operation. This includes verifying the parameters, conducting insulation resistance tests, conducting short-circuit tests, and verifying the performance under different load conditions.
- Maintenance and Monitoring: Regular maintenance and monitoring of paralleled transformers are necessary to ensure their continued reliable operation. This includes checking for any abnormalities, performing inspections, and conducting periodic tests.