Advantages and Disadvantages of Cascade Test Transformer
1. Advantages of Cascade Test Transformer
(1) It avoids the phenomenon of excessive voltage in a single transformer, and the fabrication of insulation structure is relatively simple and convenient, with extremely low material costs. Additionally, since each individual component is relatively light overall, the test transformer as a whole does not become overly heavy, making installation and transportation extremely convenient.
(2) Wiring changes can be made to facilitate three-phase testing. Through reconnection, transformers can be connected in parallel to supply large load currents. When reconnecting for three-phase testing, the corresponding voltage can be reduced.
(3) If the required test voltage is low, only one or two of the transformers need to be used, effectively reducing the voltage without causing insufficient excitation of the power generator, and the operation is relatively simple and convenient. Moreover, with a reduction in the number of cascade transformers, the short-circuit reactance of the loop during the overall test can be effectively reduced.
(4) Due to the structural design, each transformer can also be used independently for its specific purpose, which increases the number of work sites and applications. Additionally, if one transformer fails, it does not affect the normal operation of the whole system, effectively minimizing losses.
2. Disadvantages of Cascade Test Transformer
(1) The autotransformer is the most common device in cascade test transformers, so during operation, the power of the upper-stage transformer needs to be supplied by the lower stage, resulting in low overall utilization of the device. Furthermore, during insulation operation and treatment, the excitation devices provided by the transformer to each stage also have low overall utilization due to insulation effects.
(2) The leakage reactance in the low-voltage winding and excitation winding is mostly caused by phenomena in the insulating transformer. If the number of stages increases, the total reactance will continuously increase or even intensify. Therefore, the number of cascade stages should generally not exceed four, but this is not effectively implemented in practical applications.
(3) In a cascade high-voltage test transformer, if overvoltage occurs, the transient voltage distribution among stages may be uneven, and in certain cases, insulation faults such as flashover in the excitation winding or bushing may even occur.
