Frequently Asked Questions

What is the National Electricity Market of Singapore?

The National Electricity Market of Singapore, or NEMS, is a spot market that was established in 2003 for the trade of electricity. NEMS is established under the authority of the Electricity Act (Chapter 89A) and is governed by the Singapore Electricity Market Rules. There are separate Energy, Reserve, and Regulation markets which transact in 30 minute trading intervals.

What is the Reserve Market within the National Electricity Market of Singapore?

Reserve capacity is traded in the Reserve market and represents unutilised capacity that is available on a stand-by basis to supply energy during contingency events. Reserve may be arresting a fall in the system frequency, restoring the system frequency, or replacing energy as a result of the tripping of a generation facility. Typically, this capacity must be able to be brought into production within a short timeframe. 

What is Interruptible Load?

Historically, reserve has been provided by generators alone where imbalances between demand and supply due to a loss of generation have been restored by increasing the output of other generators in the power system. Interruptible Load was introduced in NEMS in 2004 to also restore this imbalance by allowing electricity consumers to voluntarily curtail their consumption by a pre-determined quantity. In NEMS, Interruptible Load is traded in the Reserve market. Interruptible Load is a form of Demand Response.

What is an Interruptible Load Aggregator?

An Interruptible Load Aggregator manages and trades Interruptible Load in the NEMS as a Market Participant. An Interruptible Load Aggregator requires a Wholesaler (Interruptible Load Service) electricity license issued by the EMA which is granted under the Electricity Act (Cap 89A). Diamond Energy is the first Wholesaler to trade Interruptible Load in NEMS and was licensed by the EMA in 2005. Diamond Energy is the Pioneering Interruptible Load Aggregator in NEMS and has been an active market participant since 2006. Interruptible Load Aggregators compete with generators to provide reserve.

How is Interruptible Load activated and how long will the activation event typically last?

For a designated load providing Primary Reserve, the under-frequency relay, when armed, will automatically curtail the designated load when the system frequency falls below 49.4 Hz. For Secondary Reserve, the under-frequency relay, when armed, will automatically curtail the designated load when the system frequency falls below 49.7 Hz and remains at or below that level for 30 seconds. For Contingency Reserve, the Power System Operator issues an Activation Order and the designated load must be curtailed within 10 minutes. A Restoration Order is issued when the designated load can be brought back to normal operation. Due to the dynamic nature of the power system, there is no typical duration time for a Contingency Reserve activation. In 2013, there were 20 activation events for Contingency Reserve in NEMS. The average duration from the time the Activation Order was issued and when the Restoration Order was issued was approximately 53 minutes.


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