The motor with commutator brushes pair is widely used in industrial equipment. During operation, the brush and commutator of the motor will wear out, especially in humid tropical monsoon conditions. The commutator brushes pairs operate in both loading conditions: Mechanic and Electric. The temperature, velocity, spring pressure, current, material, and environmental conditions, especially high humidity of ambient air, directly affect the wear of commutator brushes pair. This paper presents studying results on the wear behavior of graphite brushes when used in conditions changes as relative humidity and current. Initial experimental results showed that relative humidity had influenced brush wear. The wear rate increases by 1.8 to 2 times when humidity increases from 51% to 99%. The wear graphs of the brushes depend on current more than relative humidity with tropical climate characteristics. The specific wear rate changed about 2.88 times in this study.

Wear behaviour determines the service life and reliability of the motor's commutator and Brush, including mechanical and electrical wear. The temperature and relative humidity, especially humid tropical climate conditions, significantly affect the wear behaviour of commutator brushes. The traditional life tests are often manual and time-consuming due to a long expected life. This paper presents study results on the service life and reliability of graphite brushes when the temperature, relative humidity, and current change. The calculation method of service life and reliability depending on wear testing was used to evaluate the service life characteristics. The experimental results, service life, and reliability calculations showed that the service life and reliability of the graphite brushes were influenced clearly by current, temperature, relative humidity, and the probability of failurefree operation. It depends on the current more than relative humidity and temperature. In the range of changing current in this study, the service life: TP(99%) ~ 0.54*TP(50%), TP(95%) ~ 0.62*TP(50%), and TP(90%) ~ 0.68*TP(50%).