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NMTU-21C 3BSE017429R1 Input module

Where the rated c.t. current IN1 differs from the rated current IGN of the protected unit, compensating the measurement to achieve a match is recommended. This is done by correcting either the reference value of the A/D input or the setting. For example, assuming IGN = 800 A and IN1 = 1000 A, the setting to pick up at 1.5 IGN = 1200 A would be 1.2 1000A 800A 1.5 I I 1.5 N1 GN

Characteristic angle Determining the phase-angle of the current provides an additional criterion for preserving discrimination compared with nondirectional overcurrent protection. The directional sensitivity is 180° in relation to the reference voltage. This is illustrated in the following diagrams. The angles given apply for connection according to the diagram in Section 12

The function determines the power direction by measuring the phase-angle of the current in relation to the opposite phase-tophase voltage. Which current is compared with which voltage can be seen from the following table.

The voltage measurement automatically compensates the group of connection of the v.t’s. For example, the phase-to-phase values are calculated for Y-connected v.t’s (v.t. type UTS), while the input voltages are used directly for delta-connected v.t’s (v.t. type UTD).

Delay

 The delay enables the protection to be graded with other timeovercurrent relays to achieve discrimination. Its setting is thus chosen in relation to the timer settings of upstream and downstream protective devices. The zone of protection covered by this overcurrent protection extends to the next overcurrent protection device. Should in the event of a fault in the next downstream zone, the protection for that zone fail, this protection functions takes over after the time set for “Delay” and clears the fault as backup.Time allowed for a signal to be received Where directional functions are configured in both line terminals, each can send a signal from its “MeasBwd” output to the “Receive” input of the function at the opposite end of the line (e.g. via a PLC channel) when it is measuring a fault in the reverse direction. This signal prevents the respective directional overcurrent function from tripping, because the fault cannot be in the zone between them. The functions therefore have to allow time, i.e. the “wait time”, for the signal from the opposite line terminal to be received. If none is received within “tWait”, the circuitbreakers are tripped at both ends. The time set for “Delay” acts in this kind of scheme as a backup which does not rely on the communication channel. Thus when the “Receive” input is being used, the setting for “Delay” must be longer than the setting for “tWait”: “Delay” > “tWait”.