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 a blockcommand from external devices or can be software connected to other internalfunctions in the IED itself in order to receive a block command from internalfunctions. Through OR gate it can be connected to both binary inputs and internalfunction outputs.If the pole discordance protection is enabled, then two different criteria can generatea trip signal TRIP:• Pole discordance signaling from the circuit breaker.• Unsymmetrical current detection.6.9.7.1 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 60. After a settable time tTrip, a 150 ms trip pulsecommand TRIP is generated by the pole discordance function.6.9.7.2 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 detection isenabled to generate a trip after a set time delay tTrip if the detection occurs in the next200 ms after the circuit breaker has received a command to open trip or close and if theunbalance persists. The 200 ms limitation is for avoiding unwanted operation duringunsymmetrical 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 inputs canbe connected to terminal binary inputs if the information are generated from the field(that is from auxiliary contacts of the close and open push buttons) or may be softwareconnected to the outputs of other integrated functions (that is close command from acontrol function or a general trip from integrated protections).Section 6 1MRK 511 287-UEN ACurrent protection140Technical manual
