operate time, the OPERATE output is activated. If the fault disappears before themodule operates, the reset timer is activated. If the reset timer reaches the value setby Reset delay time, the operation timer resets and the START output is deactivated.The timer calculates the start duration value START_DUR, which indicates theratio of the start situation and the set operation time. The value is available in themonitored data view.Blocking logicThere are three operation modes in the blocking functionality. The operation modesare controlled by the BLOCK input and the global setting "Configuration/System/Blocking mode" which selects the blocking mode. The BLOCK input can becontrolled by a binary input, a horizontal communication input or an internal signalof the IED program. The influence of the BLOCK signal activation is preselectedwith the global setting Blocking mode.The Blocking mode setting has three blocking methods. In the "Freeze timers"mode, the operation timer is frozen to the prevailing value. In the "Block all"mode, the whole function is blocked and the timers are reset. In the "BlockOPERATE output" mode, the function operates normally but the OPERATE outputis not activated.4.3.4.5 ApplicationIn solidly earthed systems, the restricted earth-fault protection is always deployedas a complement to the normal transformer differential protection. The advantageof the restricted earth-fault protection is its high sensitivity. Sensitivities of close to1.0 percent can be achieved, whereas normal differential IEDs have their minimumsensitivity in the range of 5 to 10 percent. The level for HREFPDIF is dependent ofthe current transformers' magnetizing currents. The restricted earth-fault protectionis also very fast due to the simple measuring principle as it is a unit type of protection.The differences in measuring principle limit the biased differential IED'spossibility to detect the earth faults. Such faults are then only detected by therestricted earth-fault function.The restricted earth-fault IED is connected across each directly or to low-ohmicearthed transformer winding. If the same CTs are connected to other IEDs, separatecores are to be used.1YHT530004D05 D Section 4Protection functions615 series 433Technical Manual
