Individual Circuit Level Applications
Load shedding, defined as “the act or process of disconnecting the electric current on certain lines when the demand becomes greater than the supply”, is a very important element of implementing emergency backup generator and peak shaving programs. Backup generator power transfer (cutover) and peak shaving both create a number of negative unintended consequences, all of which can be overcome with controlled shut-down and sequential restart at the individual circuit level.
Who needs to load shed or peak shave?
Stand by generator owners
In a standard emergency generator installation an automatic transfer switch (ATS) is responsible for sensing a commercial power failure, starting the generator and transferring the electrical loads to the generator to restore electrical power. During this transfer to emergency power two undesired side effects may occur. Either a large inrush current demand or excessive continuous current demands can exceed the capacity of the standby generator.
Load shedding by individual electrical circuit allows for a controlled shut down of selected circuits followed by a stepped or sequenced restoration of power to high inrush loads like air conditioning compressors. Simultaneously, you can “lock out” non-essential loads like pool pumps and electric water heaters for the duration of the standby generator’s required run time.
There are many other benefits to load shedding circuits behind a standby generator. Turning off secondary electrical loads allows a generator to be sized to power only primary or critical loads. The decision to select a smaller generator can also mean less fuel required, installation space, reduced overall project costs and outside noise levels.
Industrial and Commercial Properties Peak Billing
Many commercial electrical customers are billed based on the single highest electrical demand during the billing period. This is referred to as Peak Billing. You can lower your electric bill by Peak Shaving; this can be accomplished two ways:
- First, by shutting down high inrush circuits and then sequentially bringing them back online as power is returned to commercial power. This spreads out the electrical inrush and reduces the peak demand benchmark.
- Turning off non-essential loads is a second tool to limit peak energy consumption during high demand periods, and thereby smoothing peak energy electrical charges. Controlling loads at the circuit level can reduce peak demand without affecting critical loads or processes.
In most climates peak usage coincides with the hottest hours of the hottest days of the year. Controlling secondary loads during these times can help avoid high peak usage charges and control energy costs.
The Combined Benefits of Load Shedding
Extend generator run time by reducing electrical load
- Turning off or shedding individual electrical loads lowers generator fuel consumption rates. This saves fuel expenses and extends generator running time for tank fed generators.
Reduce generator and fuel supply sizing.
- By turning off or shedding individual loads generator size can be reduced allowing smaller fuel supply requirements, generator capacity and installation costs.
Reduce starting load surge demand from generator.
- Removing circuits from the starting load surge avoids excessive current inrush thereby lessening the risk of nuisance trips and blown electronics downstream. Circuits can remain off or be sequenced back on after the generator has stabilized.
Reduce utility company peak billing rate.
- High current inrush during the transition back to commercial power is often responsible for setting your peak billing rate. You can lower your utility rates by cutting down on the inrush associated with transferring back to commercial power.
Sequence restart of high demand loads to avoid overloads.
- Standby generator designers will oversize a generator to meet the high current inrush that occurs for the few milliseconds after the ATS transfers to emergency power. This added expense, for the added capacity, can be avoided by installing automatic restart sequencing that steps electrical loads on after the ATS transfer.
How to control loads at the circuit level
The most appropriate place to add individual circuit control to help reduce generator inrush and shave peak current demand is at the circuit breaker panel after the Automatic Transfer Switch (ATS). Circuit control devices like remote controlled circuit breakers or relays can be incorporated with ATS switch contacts to control circuit restarting, or lock out secondary circuits, while the standby generator is providing power. This can be accomplished in either of the following ways:
- Through the installation of an intelligent remote controlled breaker panel (e.g. the LynTec RPC Motorized Circuit Breaker Panel). Motorized remote controlled circuit breakers incorporate overcurrent protection and an on / off switch in a single device.
- By installing a smart relay panel in between your breaker panel and ATS (e.g. the LynTec RPCR Relay Panel). In retrofit installations latching relay panels will add on / off control to existing circuits.
Regardless of the control platform selected, the controller must have the following features:
Onboard brownout sensing – Intelligent controls sense voltage sags or brownouts and turn off circuits powering sensitive equipment. When stable power is restored intelligent controls automatically sequence on the circuits that were disconnected for protection. You cannot load shed prior to power transferring to the generator without this feature.
Adjustable automatic restart – This is the feature that provides the ability to select which circuits remain off when needed, or sequence back on after the power is transferred. More advanced intelligent controls offer the ability to modify which individual circuits are switched off during brownouts or generator operation using an ordinary web browser. No wiring reconfiguration is required.
IP accessible web server for setup and control – This feature provides the platform for quickly determining which circuits are shut down, stay down or sequence back to life after power transfer. New smart control platforms have simple browser based interfaces with check boxes that make moving breakers in and out of status preferences a snap.
Using the three features together, you can:
Learn more about intelligent motorized circuit breaker panels at:
Learn more about smart relay panel options at:
