Explanation of the ELS G100 operation
The export power to the grid is automatically limited by adjusting power supplied to several electric heating elements which can be used for space, process or water heating. A control system that complies with the requirements set out ENA Recommendation G100, Issue 1, 2016 is used to continuously and smoothly adjust the amount of power sent to the electric heaters. The active export power is compared with the permitted limit and power sent to the electric heater is adjusted as and when necessary to prevent export exceeding the relevant limit. In the event of export exceeding the permitted limit for more than 5 seconds, the controller will isolate the generator by sending a trip signal to the G59 or generator isolation relay.
Compliance & Power Quality
A typical Export Limiting Scheme (ELS) consists of the MyEnergi ELS G100 controller and several Solid-State Relays (SSRs). The main controller utilises Vari-Sine™ technology, this technology continually adjusts the AC voltage to one of the loads on each phase. Other loads are switched on/off using SSRs, these loads are switched only when the voltage crosses zero.
This combination of Vari-Sine™ power control technology and zero-cross switching solid state relays, enables the ELS G100 to be fully EMC compliant, even when controlling large loads. Voltage flicker levels and harmonic distortion are always kept well within permissible limits.
The ELS G100 controller has several failsafe features. The trip signal to the G59 or generator isolation relay will be a DC on-signal powered by the ELS controller. This on-signal is not issued until the ELS controller has completed a full start-up test sequence and validated all input signals and all internal software functions. This means that the turbine will not be connected to the grid until the ELS controller is fully operational.
In the event of the power supply to, or in the ELS unit failing or the communication cable from the ELS to the G59/generator isolation relay being cut, this on-signal will fail naturally (because of loss of power) resulting in the G59/generator isolator relay opening.
The ELS firmware and hardware has several in-built watchdog-type failsafe features. These include any input signals falling outside the normal range. These input signals include current and voltage as well as internal and external temperature sensor signals. In addition, standard firmware watchdogs are used to determine if any internal software cycles stall or become irregular (indicating a partial component or software failure). In the event of these watchdogs detecting a fault, the on-signal to the G59/generator isolator relay will deactivate.
Load Failure/Out-of-service Compensation
In the event of partial load failure, the ELS will try to limit export using other available loads, if the export limit cannot be maintained, the ELS will failsafe, thereby isolating the generator from the grid. This intelligent function prevents unnecessary generator disconnection if the export can still be maintained, albeit not optimally. This function is important in larger export limiting schemes, as the allows for heater maintenance without the generator being shut down.