As a result, PJM’s spot wholesale electricity prices have soared past $1,000 per megawatt hour this week in areas where power line congestion has constrained the flow of electricity. Turbulence on power lines and related equipment also can lead to small, controlled blackouts, which can spread if the issues are not addressed. This week, PJM issued five warnings to utilities about potential small power cuts related to transmission line problems. The turmoil extends a pattern that began to take shape late last week, PJM data shows. PJM predicts electricity demand will rise to 148 gigawatts on Friday, setting an all-time record for winter.