Calgary-based TransAlta is reporting major second-quarter losses.  Severe weather, low prices, higher-than-expected maintenance costs and plant power outages are said to have contributed to the drop in revenues.  TransAlta's lossed amount to $797-million, or $3.51 a share, compared with profits of $12-million, or a nickel a share.  President and CEO Dawn Farrell is calling it an "event" and not a "trend".  She says they may have to delay a "big investment" for a couple of years, referring to their Sundance 7 facility.  On the other hand, Farrell says the company is pleased with its second-quarter power generation performance.