The electric driving motors of locomotives or railcars are designed for a far lower voltage than that present in the overhead contact wires of the tractionlines. So transformers are used to transform the voltage down to a value that the motor can take.
Temperature-dependent control of transformer cooling with AMTHF series surface-mounted thermostats
The temperature of an oil-filled transformer will vary, depending on the power consumption during vehicle operation. To counteract overheating, a temperature-dependent cooling system that can incorporate the different power levels is used. The exact switching point of the cooling system is highly significant, particularly when there are vast fluctuations in ambient temperature, (e.g. when traveling through a tunnel). AMTHF series surface-mounted thermostats monitor the oil temperature of the transformer and reliably operate the individual cooling system power levels. A further option is to use a temperature sensing element to regulate the motor power in accordance with the oil temperature, that is, to adjust the vehicle performance to the maximum operating temperature of the transfomer. The pressure in the cooling sytem can be measured with the JUMO MiDAS S19R.