Section 4 1MAC309294-MB FProtection functions214 RER620Technical ManualTimerOnce activated, the timer activates the PICKUP output. The time characteristic isaccording to DT. When the operation timer has reached the value set by Operate delaytime, the OPERATE output is activated if the overvoltage condition persists. If the negativesequence voltage normalizes before the module operates, the reset timer is activated. If thereset timer reaches the value set by Reset delay time, the operate timer resets and thePICKUP output is deactivated.The timer calculates the pickup duration (PICKUP_DUR) value which indicates the ratioof the pickup situation and the set trip time. The value is available through the Monitoreddata view.Blocking logicThere are three operation modes in the blocking functionality. The operation modes arecontrolled by the BLOCK input and the global setting “Configuration/System/Blockingmode” which selects the blocking mode. The BLOCK input can be controlled by a binaryinput, a horizontal communication input or an internal signal of the relay program. Theinfluence of the BLOCK signal activation is preselected with the global setting Blockingmode.The Blocking mode setting has three blocking methods. In the “Freeze timers” mode, thetrip timer is frozen to the prevailing value. In the “Block all” mode, the whole function isblocked and the timers are reset. the “Block TRIP output” mode, the function operatesnormally but the TRIP output is not activated.4.3.5.5 ApplicationA continuous or temporary voltage unbalance can appear in the network for variousreasons. The voltage unbalance mainly occurs due to broken conductors or asymmetricalloads and is characterized by the appearance of a negative-sequence component of thevoltage. In rotating machines, the voltage unbalance results in a current unbalance, whichheats the rotors of the machines. The rotating machines, therefore, do not tolerate acontinuous negative-sequence voltage higher than typically 1-2 percent x V n.The negative-sequence component current I2 , drawn by an asynchronous or a synchronousmachine, is linearly proportional to the negative-sequence component voltage V 2. WhenV2 is P% of V n, I 2 is typically about 5 x P% x In.The negative-sequence overcurrent 46 blocks are used to accomplish a selective protectionagainst the voltage and current unbalance for each machine separately. Alternatively, theprotection can be implemented with the 47 function, monitoring the voltage unbalance ofthe busbar.If the machines have an unbalance protection of their own, the 47 operation can be appliedas a backup protection or it can be used as an alarm. The latter can be applied when it isnot required to trip loads tolerating voltage unbalance better than the rotating machines.If there is a considerable degree of voltage unbalance in the network, the rotating machinesshould not be connected to the network at all. This logic can be implemented by inhibiting
