Please elaborate a little on why these resistor banks needed. All new to me so just a little curious.Wound rotor or brake system.
Common mistake number 1: cleaning those “rusty” resistors. Stainless steel oxidizes to chrome oxide which is a black colored “rust”. This “rust” protects the metal from the heat. Other than blowing off dust, do not CLEAN resistors.
Common mistake number 2: a section of resistor is damaged so jumpers are added to bypass it. This causes a couple unintended consequences. In a wound rotor motor reducing resistance cuts the motor torque. So now it draws a lot more current to compensate. Also as mentioned current imbalances become a big issue. In a motor we have to derate. A 1% imbalance is acceptable. At 5% we derate by 25%! The principle is the same with resistors.
Common mistake number 3: adjusting running resistor taps to increase torque by decreasing resistance. In wound rotor motors it’s the opposite.
Lots more checking you need to do. When I do PMs on these, I test all the timing relays, aux contacts, contactor coils, contactor contact pressure, contact tips, resistor overall resistance on each phase. Even something as simple as a worn contact tip can cause a major problem.
Depends on what they are forPlease elaborate a little on why these resistor banks needed. All new to me so just a little curious.