This Resistors are of different rating varying from 300 Watt to 12 kilowatts and are housed in a square aluminium tank besides GTO Thyristors, diodes etc. and form a so called valve sets (Total 8 Nos. per loco i.e. Line Convertor and Motor Inverter). Some of these resistors with different combinations along with appropriate rating of capacitor in series with each configuration are used as switching surge suppression units. Rest of the resistors are used either economy or dropping resistors. Such a valve set is oil filled and cooled by forced oil circulation. So these resistors are also called as Oil Cooled Grid Resistors.