CU3 (KV10) Main Generator Power Regulator & CU6 (KV10) Heating & Rad Fan Generator Voltage Regulator

Each Class 50 is fitted with 2 KV10s. One designated CU3 regulates the main traction generator output power. The other, CU6 regulates the voltage output from the Electric Train Heating (ETH) generator. This generator provides power to the train for lighting and heating and the main radiator cooling fan. At diesel set tick over (450rpm) the voltage will be 650V, and as the engine speed rises to 850rpm the CU6 prevents the ETH generator output voltage rising above 970V. The original design of KV10 used thyristors to switch on the current to the generator field. There was then a complicated, and not always very reliable, piece of electronics that forced the thyristor to turn off. By varing the gap between turn on and turn off the current in the field was controlled and thereby the generator output was controlled. When the turn off circuit failed this caused the thyristor to “lock on”. This can be quite damaging to the generators and the surges that result can be alarming if you are trying to control the locomotive. An ex-British Rail engineer has taken both a CU3 & CU6 and modified them by combining some new high power technologies with a control board that he designed and was used very successfully on Railfreight Class 47s. This does away with the thyristors and instead uses a IGBT. These devices require a simpler and more reliable control circuit to turn them off. This will reduce the chances of “lock-on” and thereby reduce the chance of generator damage and power surges. Both of the redesigned units have been proved on other Class 50s including one that has fairly regular use on the mainline. It is intended as money and time permits to fit these units on to all our fleet.