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 in overall weight, the test transformer as a whole does not become overly heavy, making installation and transportation extremely convenient.
(2) It allows for changes in wiring 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 in the overall test circuit can be effectively reduced.
(4) Due to the structural design, each transformer can also be used independently for its specific purposes, which increases the variety of work locations 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 efficiency. Furthermore, during insulation operation and treatment, the excitation devices provided to each stage are also affected by insulation, keeping the overall utilization rate low.
(2) The leakage reactance in the low-voltage winding and excitation winding is mostly caused by phenomena occurring in the insulating transformer. If the number of stages increases, the total reactance will continuously increase or even intensify. Therefore, under normal circumstances, the number of cascade stages should 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 between stages may become uneven, and in certain cases, insulation faults such as flashover in the excitation winding or bushing may occur.
