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. In addition, since each component is relatively light overall, the test transformer does not become excessively heavy, making installation and transportation extremely convenient.
(2) Wiring changes can be made to facilitate three-phase testing. Through rewiring, transformers can be connected in parallel to supply large load currents. When rewiring 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 voltage without causing insufficient excitation of the power generator, and operation is relatively simple and convenient. Moreover, with fewer cascade transformers, the short-circuit reactance in the total test circuit can be effectively reduced.
(4) Due to the structural design, each transformer can also be used independently for its specific purpose, increasing the number of work sites and scope. If one transformer fails, it does not affect the overall normal operation, effectively minimizing losses.
2. Disadvantages of Cascade Test Transformer
(1) Autotransformers are the most common devices 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. Additionally, during insulation operation and treatment, the excitation devices provided by the transformer to each stage 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 cascade high-voltage test transformers, if overvoltage occurs, the transient voltage distribution between stages may be uneven, and in certain cases, insulation faults such as flashover in the excitation winding or bushing may occur.
