The operation of 67/51N, 67/50N can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
A070438-ANSI V1 EN
Figure 151: Functional module diagram
Level detector
The magnitude of the operating quantity is compared to the set Pickup value and the
magnitude of the polarizing quantity is compared to the set Voltage pickup value. If both
the limits are exceeded, the level detector sends an enabling signal to the timer module.
When the Enable voltage limit setting is set to "False", Voltage pickup value has no effect
and the level detection is purely based on the operating quantity. If the ENA_MULT input
is active, the Pickup value setting is multiplied by the Pickup value Mult setting.
The operating quantity (residual current) can be selected with the setting IG/I0 signal Sel.
The options are "Measured IG" and "Calculated I0". If "Measured IG" is selected, the
current ratio for IG-channel is given in Configuration/Analog inputs/Current
(IG,CT). If "Calculated I0" is selected, the current ratio is obtained from the phase-current
channels given in Configuration/Analog inputs/Current (3I,CT).
The operating quantity (residual voltage) can be selected with the setting Vg or V0 The
options are "Measured VG" and "Calculated V0". If "Measured VG" is selected, the
voltage ratio for VG-channel is given in Configuration/Analog inputs/Voltage
(VG,VT). If "Calculated V0" is selected, the voltage ratio is obtained from the phase-
voltage channels given in Configuration/Analog inputs/Voltage (3V,VT).
Example 1: IG is measured with cable core CT (100/1 A) and VG is measured from open-
delta connected VTs (20/sqrt(3) kV : 100/sqrt(3) V : 100/3 V). In this case, "Measured IG"
and "Measured VG" are selected. The nominal values for residual current and residual
voltage are obtained from CT and VT ratios entered in Residual current IG:
Configuration/Analog inputs/Current (IG,CT): 100 A : 1 A. The Residual voltage VG:
Configuration/Analog inputs/Voltage (VG,VT): 11.547 kV : 100 V. The Pickup value
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 327
Technical Manual
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