One of the cool things about the EMPATH Electrical Signature Analysis (ESA) system is the ability to look at watts losses by defect. Normally our case studies relate to AC machines, but the concept is just as applicable in DC machines. In this case the EMPATH system picked up a DC drive defect, so we looked at the conditions for what it called out as a bad card. This resulted in a 4.98 kW loss due to the defect, which was feeding the armature and commutator of a 500 hp tandem motor as shown in Figure 1.
The simple tightening of a connection would result in a reduction in consumption to ~0.5 kW (Figure 2 at equivalent load from outer motor), or an approximate reduction of 4.5kW in the motor, and significantly more under heavier loads and speeds.
As we know this is the minimum, if we apply this to the average operation of 4,400 hours, then we have 4.5kW * 4400hrs = 19,800 kWh, or 19.8 MWh. At $0.10/kWh and 0.707 Tonnes CO2/MWh, this would be $1,980 in energy costs and 14 Tonnes CO2/year (minimum, it will be substantially more). In addition, the stress on the armature winding and SCRs is very high and reduces the reliability of the machine and will eventually fail the drive or armature. All for the want of a Phillips head screwdriver (small one).
