Load Limiting Pilot (FW v0.12.11) Release Notes

The new Load Limiting feature allows a customer to program a SHYFT Smart Transfer Switch to disconnect from a mains power source (grid or generator) when the power output from the STS has exceeded a defined threshold. This functionality will not require additional hardware for sites with an STS, and instead would be achieved with software and firmware upgrades.

The current release represents a pilot implementation of the Load Limiting feature. The core functionality of this feature set has been developed and can be deployed to specific pilot sites. Configuration and remote management of the feature is limited to the SHYFT team's backend access, and therefore will be performed at the request of the customer until it can be made available for direct management within the SHYFT Connect web application.

The Load Limiting Feature implements the following key functionality:

1. A Load Limit threshold can be configured per SHYFT STS device. The default value set for this limit is currently 6 kW.
   • While Load Limiting is Enabled this Load Limit value defines the power threshold above which the SHYFT STS device will disconnect power. 
   • When the Load Limit threshold has been exceeded for 2 minutes the device will then initiate a Disconnect Period, in which the system disconnects mains power (Grid or Gen) from the Load and stays in the Off position (no mains power) for a defined reset period interval.
2. The length of the Disconnect Period is determined by the number of times in a row that the SHYFT STS device has triggered the disconnect (based on the Load Limit).
   1. The first Disconnect Period will last 5 minutes, the second will last 10 minutes, then 30 min, 1 hr, 2 hr, and 6 hrs. The Disconnect Period will then continue at a maximum of 6hrs per disconnection as long as each time the system returns to supplying power it continues to be above the Load Limit.
   2. The Disconnect Period pattern will be reset back to the initial 5 minute timing if the Load being supplied is reduced to below the Load Limit, or if the Load Limiting feature is disabled. 
   3. After each Disconnect Period has elapsed, the SHYFT STS device will clear the power disconnect setting and perform a system reset. Upon resetting, typical switching logic will apply. This means that if there is Grid available, the system will switch to the Grid source. If there is no Grid available, but the system is in ATS Mode, the Gen will be started to supply power.
   4. Once power is supplied to the Load once again, if the Load Limiting feature is still Enabled then the system will start checking the Load against this value again and the above pattern will repeat until the Load being powered from the SHYFT output is reduced to below the Load Limit threshold, or the Load Limiting is Disabled.
3. For the current pilot deployment - the Load Limiting feature will automatically be applied only when the device is operating in Smart Mode. The Load Limiting feature will not apply when the device is operating in ATS Mode. This will create a natural restriction of the Load Limiting functionality to periods during which continuous, peak power is not required at the site, since there is already an automated schedule in place controller the STS Mode according to contracted hours.

The Load Limiting Pilot Release also includes the following configuration functionality:

1. The Load Limit feature can be Enabled or Disabled through remote access from SHYFT's backend software platform.
2. When the Load Limiting feature is Disabled, power will be restored to the Load within seconds (if power is available).
3. Similarly, if the STS device is currently within a Disconnect Period at a time when the Mode of the STS device is changed such that the Load Limiting feature should no longer apply (for instance at the start of a business day when a customer's contracted hours are beginning) then the Disconnect Period will end and the system will begin to supply power.
4. The Load Limit can be remotely configured at the request of the customer through SHYFT backend software platform.
5. The Mode Configuration of the Load Limiting feature can be adjusted such that the Load Limit will be applied to any of Smart Mode, ATS Mode and Hybrid Mode, however, this configuration is not recommended during the pilot period to achieve the desired results at pilot sites.

The following edge cases / additional measures have been considered in the implementation:

• The Load Limit will not be applied to trigger the disconnection of power if the SHYFT STS system is currently offline. This is to prevent a scenario in which the Load Limiting feature has disconnected power but the site requires power and remote commands are unable to override the Load Limit disconnection.
• If the system has been placed in Maintenance Mode, and the Load Limit threshold is exceeded, the system will not be able to automatically disconnect the mains power source. Instead, the SHYFT system will generate an alerting event sent to the SHYFT backend database. Upon registering this event, the SHYFT team will notify the customer within 1 business day.
• When the Load Limit has been activated and the system has been disconnected from power, a message will be displayed on the Smart Transfer Switch display screen which reads "OVER LOAD LIMIT" This message will serve to alert any on-site staff to the state of the system and indicate that Loads must be reduced in order to allow the system to supply steady power.