RED670熔丝熔断监视功能(英文).doc

2.1 IntroductionThe aim of the fuse failure supervision function (FSD) is to block voltage measuring functionsat failures in the secondary circuits between the voltage transformer and the IED in order toavoid unwanted operations that otherwise might occur.The fuse failure supervision function basically has two different algorithms, negative sequenceand zero sequence based algorithm and an additional delta voltage and delta current algorithm.The negative sequence detection algorithm is recommended for IEDs used in isolated orhigh-impedance earthed networks. It is based on the negative-sequence measuring quantities, ahigh value of voltage 3U2 without the presence of the negative-sequence current 3I2.The zero sequence detection algorithm is recommended for IEDs used in directly or low impedanceearthed networks. It is based on the zero sequence measuring quantities, a high value ofvoltage 3U0 without the presence of the residual current 3I0.A criterion based on delta current and delta voltage measurements can be added to the fuse failuresupervision function in order to detect a three phase fuse failure, which in practice is moreassociated with voltage transformer switching during station operations.For better adaptation to system requirements, an operation mode setting has been introducedwhich makes it possible to select the operating conditions for negative sequence and zero sequencebased function. The selection of different operation modes makes it possible to choosedifferent interaction possibilities between the negative sequence and zero sequence based algorithm.2.2 Principle of operation2.2.1 Zero sequenceThe function can be set in five different modes by setting the parameter OpMode. The zero sequencefunction continuously measure the internal currents and voltages in all three phases andcalculate: the zero-sequence voltage 3U0 the zero-sequence current 3I0.The measured signals are compared with their respective set values 3U0.The function enable the internal signal FuseFailDet if the measured zero sequence voltage ishigher than the set value 3U0, the measured zero sequence current is below the set value 3I0 at the same time as parameter SealIn = On the latched signal is sealed in.It is recommended to always set SealIn to On since this will secure that no unwanted operationof fuse failure will occur at closing command of breaker when the line is already energized fromthe other end. The system voltages shall be normal before fuse failure is allowed to be activatedand initiate block of different protection functions.If the latched signal is set and all three phase voltages are below the setting UPh the outputsignal 3PH will be activated (set to 1). Also the output signals BLKU and BLKZ will be activeas well.The output signal BLKU can also be activated if any phase voltage is below the setting UPhfor more than 60 seconds at the same time as the latch or seal in signal is set for more than5 seconds (that is fuse fail is detected), all phase currents are below the setting IDLD (operatelevel for dead line detection) and the circuit breaker is closed (input CBCLOSED is activated).This condition covers for fuse failure at open breaker position.Fuse failure condition is unlatched when the normal voltage conditions are restored(STUL1N = STUL2N = STUL3N = 0).Fuse failure condition is stored in the non volatile memory in the IED. In the new start-up procedurethe IED checks the 3PH (STORE3PH) value in its non volatile memory and establishesthe corresponding starting conditions.Input and output signalsThe output signals 3PH, BLKU and BLKZ can be blocked in the following conditions: The input BLOCK is activated The input BLKSP is activated at the same time as any of the internal signalsStartFusefail3Ph, StartFusefailRestr or StartFusefailGen are present The operation mode selector OpMode is set to Off. The IED is in TEST status (TEST-ACTIVE is high) and the function has beenblocked from the HMI (BlockFUSE=Yes)The input BLOCK signal is a general purpose blocking signal of the fuse failure supervisionfunction. It can be connected to a binary input of the IED in order to receive a block commandfrom external devices or can be software connected to other internal functions of the IED itselfin order to receive a block command from internal functions. Through OR gate it can be connectedto both binary inputs and internal function outputs.The input BLKSP is intended to be connected to the trip output at any of the protection functionsincluded in the IED. When activated for than 20 ms, the operation of the fuse failure is blockedduring a fixed time of 100 ms. The aim is to increase the security against unwanted operationsduring the opening of the breaker, which might cause unbalance conditions for which the fusefailure might operate.The output signal BLKZ will also be blocked if the internal dead line detection is activated. Theblock signal has a 200 ms drop-off time delay.The input signal MCBOP is supposed to be connected via a terminal binary input to the N.C.auxiliary contact of the miniature circuit breaker protecting the VT secondary circuit. TheMCBOP signal sets the output signals BLKU and BLKZ in order to block all the voltage relatedfunctions when the MCB is open. The additional drop-off timer of 150 ms prolongs the presenceof MCBOP signal to prevent the unwanted operation of voltage dependent function due to nonsimultaneous closing of the main contacts of the miniature circuit breaker.The input signal DISCPOS is supposed to be connected via a terminal binary input to the N.C.auxiliary contact of the line disconnector. The DISCPOS signal sets the output signal BLKU inorder to block the voltage related functions when the line disconnector is open. The impedanceprotection function is not affected by the position of the line disconnector since there will be noline currents that can cause maloperation of the distance protection. If DISCPOS=0 it signifiesthat the line is connected to the system and when the DISCPOS=1 it signifies that the line is disconnectedfrom the system and the block signal BLKU is generated.The output BLKU can be used for blocking the voltage related measuring functions (undervoltageprotection, synchro-check etc.) except for the impedance protection.The function output BLKZ can be used for blocking the impedance protection function.If the fuse failure condition is detected for more then five seconds and at least one of the phaseshas a low phase to earth voltage, then the fuse failure condition is latched: signal BLKU is turnedhigh, if there is no dead line condition also BLKZ is high; if all the three phases have no voltage(STUL1N = STUL2N = STUL3N = 1) then the output signal 3PH is turned high.The output signal 3PH is high if the fuse failure condition is detected for 5 seconds and all thethree measured voltages are low. The three phase criterion will also set the output BLKU andBLKZ. The BLKZ will only be activated if not the internal dead line detection is activated at thesame time.The fuse failure condition is unlatched when the normal voltage conditions are restored(STUL1N = STUL2N = STUL3N = 0).2.2.2 Negative sequenceThe negative sequence operates in the same way as the zero sequence, but it calculates the negativesequence component of current and voltage i.e.: the negative sequence current I2 the negative sequence voltage U2The measured signals are compared with their respective set values 3U2.The signal STZERO is set to 1, if the negative sequence measured voltage exceeds its setvalue 3U2 and if the negative sequence measured current does not exceed its pre-setvalue 3I2.2.2.3 du/dt and di/dtThe current and voltage is continuously measured in all three phases and the following quantitiesare calculated: The change of voltage U/t The change of current I/tThe calculated delta quantities are compared them with their respective set values DI.The delta current and delta voltage algorithm, detects a fuse failure if a sufficient negativechange in voltage amplitude without a sufficient change in current amplitude is detected in eachphase separately. This check is performed if the circuit breaker is closed. Information about thecircuit breaker position is brought to the function input CBCLOSED through a binary input ofthe IED.There are two conditions for activating the internal STDU signal and set the latch: The magnitude of U is higher than the corresponding setting DU and I is belowthe setting DI in any phase at the same time as the circuit breaker is closed(CBCLOSED = 1) The magnitude U is higher than the setting DU and the magnitude of I is belowthe setting DI in any phase at the same time as the magnitude of the phasecurrent in the same phase is higher than the setting IPh.The first criterion requires that the internal signal STDUDI shall be activated in any phase at thesame time as circuit breaker is closed. Open circuit breaker at one end and energizing the linefrom other end onto a fault could lead to wrong start of the fuse failure function at the end withthe open breaker. If this is considering to bee an important disadvantage, connectthe CBCLOSED input to FALSE. In this way only the second criterion can activate the signalSTDUDI.The second criterion means that detected fuse failure in one phase together with high current forthe same phase will set the latch. The measured phase current is used to reduce the risk of falsefuse failure detection. If the current on the protected line is low, a voltage drop in the system (notcaused by fuse failure) is not by certain followed by current change and a false fuse failure mightoccur. To prevent that the phase current criterion is introduced.If the latch is set and if all measured voltages are low (lower than the setting Uph) the output3PH will be activated indicating fuse failure in all three phases. The output BLKU and BLKZwill be activated as well.If the voltage is low in any phase for more than 5 seconds (STUL1N, STUL2N or STUL3N=1),the STDUDI signal is sealed in.2.2.4 Operation modesThe fuse failure supervision function can be switched on or off by the setting parameter Operationto On or Off.Negative and zero sequence algorithmFor increased flexibility and adaptation to system requirements, an operation mode selector, Op-Mode has been introduced to make it possible to select different operating modes for the negativeand zero sequence based algorithm. The different operation modes are: OpMode = Off; the negative and zero sequence function is switched off OpMode = UNsINs; Negative sequence is selected OpMode = UZsIZs; Zero sequenc