Nowadays, large power systems are facing new challenges gifted from emerging and renewable energy resources. This is even worse in developing countries where load is growing rapidly and power systems are relatively weak. With more complex power systems occurrence of a contingency such as unexpected demand during extremely-hot summer days or transient heat waves may lead to voltage drops, cascaded trips and catastrophic wide area blackouts. A few solutions have been proposed, amongst which demand response is known as an effective tool. Demand response programs (DRPs) are implemented on residential, commercial and industrial loads to economically optimize energy systems, improve overall efficiency and reliability, and enhance their stability margins. This paper presents three demand-side management strategies implemented on Iran’s commercial and industrial sectors. Operational reserve programs, incentive-based reduction or disruption of electricity demand during on-peak time intervals, and replacement of traditional lamps with energy efficient ones are applied as three strategic DRPs on industrial and commercial sectors. Three cost-effective solutions are provided for participation of industrial customers in summer peak clipping programs: (a) Transferring the weekend from Friday to one of midweek days, (b) Transferring a part of each co-operated consumer from on-peak demand hours with high electricity tariffs to off-peak time intervals with lower energy prices, (c) DSM by annual overhaul and work suspension. In case of 100 kW power consumption at medium-peak load hours, commercial customer must
at least reduce 10% of this amount at on-peak demand time interval. Economic and environmental benefits obtained from numerical studies are comprehensively provided. It is found that the total asynchronous demand reduction after participation of 287 commercial centers in demand side management programs is equal to 10.187 MW. Total industrial load reduced after implementation of disruption strategy at annual on-peak day (July 20) is equal to 743 MW.