JD TVS are needed with modern transformers as well as pw ZWs and other older units. TVS are installed to arrest voltage spikes that can damage the locomotive's circuit boards and fragile wires. Fuses and breakers are for overcurrent surges that can damage the transformer and possibly certain of the layouts railpower wiring runs. A voltage spike will not trip the breaker or blow the fuse. High current does that, not voltage. You need TVS.