Design of increased safety electrical machine: development activities and certification testing

Abstract

Electrical machines are used widely in the petrochemical industry. Most of the machines are operated in Class I hazardous locations and hence appropriate precautions must be taken to protect the machine to ensure that the explosive atmosphere cannot be ignited. There are four types of protection applicable to large machines. They are type p (purged and pressurized), type e (increased safety), type d (flameproof) and type N. Type p, type e and type d protections are permitted in Zone l o r Zone 2. In 1996 and 1999, two machines were designed and tested to meet IEC 60079-0 and 60079-7 standards regarding Exe II B 200°C ( T3 ) requirement. The machines are installed in Zone 2 locations. The paper will present the electrical and mechanical design consideration of the increased safety induction machine. Finally, the paper describes the test procedure and summarizes the results from the series of tests performed on these two machines.

Performance Analysis of Increased Safety HT Induction Motor with Higher Stator Coil Pitch for Classified Hazardous Area

“…Effective loss of motor = 0.45 core loss + stator copper loss + 0.3 rotor copper loss (7) So effective losses of 2200KW / 6.6KV / 18 pole normal motor based on Eq. (7) is = 0.45 × 6.83 + 10.53 + 0.3 × 23.06 = 20.51 KW, Similarly the effective losses of motor when coil pitch is increased is = 0.45 × 6.28 + 11.13 + 0.3 × 25.48 = 21.60 KW, As the surface area of the motor is not changed and it remains same in both the design of Ex e motors and the estimated temperature rise of the motor as per Eq.…”

“…Corona discharges and surface tracking [6] on contaminated winding can also cause sparking. The phenomenon of sparking and arcing could pose a hazard in explosive atmosphere [7]. When three-phase induction and synchronous motors are properly designed, built, installed, and maintained, uncontained sparking is not expected except at higher speeds and higher voltages [8].…”