The BLOCK signal is a general purpose blocking signal of the pole discordanceprotection. It can be connected to a binary input in the IED in order to receive ablock command from external devices or can be software connected to otherinternal functions in the IED itself in order to receive a block command frominternal functions. Through OR gate it can be connected to both binary inputs andinternal function outputs.If the pole discordance protection is enabled, then two different criteria cangenerate a trip signal TRIP:• Pole discordance signaling from the circuit breaker.• Unsymmetrical current detection.7.6.7.1 Pole discordance signaling from circuit breakerIf one or two poles of the circuit breaker have failed to open or to close (polediscordance status), then the function input EXTPDIND is activated from the polediscordance signal in figure 98. After a settable time tTrip, a 150 ms trip pulsecommand TRIP is generated by the pole discordance function.7.6.7.2 Unsymmetrical current detectionUnsymmetrical current indicated if:• any phase current is lower than CurrUnsymLevel of the highest current in thethree phases.• the highest phase current is greater than CurrRelLevel of IBase.If these conditions are true, an unsymmetrical condition is detected. This detectionis enabled to generate a trip after a set time delay tTrip if the detection occurs in thenext 200 ms after the circuit breaker has received a command to open trip or closeand if the unbalance persists. The 200 ms limitation is for avoiding unwantedoperation during unsymmetrical load conditions.The pole discordance protection is informed that a trip or close command has beengiven to the circuit breaker through the inputs CLOSECMD (for closing commandinformation) and OPENCMD (for opening command information). These inputscan be connected to terminal binary inputs if the information are generated fromthe field (that is from auxiliary contacts of the close and open push buttons) or maybe software connected to the outputs of other integrated functions (that is closecommand from a control function or a general trip from integrated protections).1MRK 502 034-UEN - Section 7Current protection191Technical Manual
