5-190 L90 Line Current Differential System GE Multilin5.6 GROUPED ELEMENTS 5 SETTINGS5To increase security for three phase faults very close to the VTs used to measure the polarizing voltage, a voltage memoryfeature is incorporated. This feature stores the polarizing voltage the moment before the voltage collapses, and uses it todetermine direction. The voltage memory remains valid for one second after the voltage has collapsed.The main component of the phase directional element is the phase angle comparator with two inputs: the operating signal(phase current) and the polarizing signal (the line voltage, shifted in the leading direction by the characteristic angle, ECA).The following table shows the operating and polarizing signals used for phase directional control:MODE OF OPERATION:• When the function is “Disabled”, or the operating current is below 5% CT nominal, the element output is “0”.• When the function is “Enabled”, the operating current is above 5% CT nominal, and the polarizing voltage is abovethe PRODUCT SETUP DISPLAY PROPERTIES VOLTAGE CUT-OFF LEVEL value, the element output is dependent onthe phase angle between the operating and polarizing signals:– The element output is logic “0” when the operating current is within polarizing voltage ±90°.– For all other angles, the element output is logic “1”.• Once the voltage memory has expired, the phase overcurrent elements under directional control can be set to block ortrip on overcurrent as follows:– When BLOCK WHEN V MEM EXP is set to “Yes”, the directional element will block the operation of any phaseovercurrent element under directional control when voltage memory expires.– When BLOCK WHEN V MEM EXP is set to “No”, the directional element allows tripping of phase overcurrent elementsunder directional control when voltage memory expires.In all cases, directional blocking will be permitted to resume when the polarizing voltage becomes greater than the ‘polariz-ing voltage threshold’.SETTINGS:• PHASE DIR 1 SIGNAL SOURCE: This setting is used to select the source for the operating and polarizing signals.The operating current for the phase directional element is the phase current for the selected current source. The polar-izing voltage is the line voltage from the phase VTs, based on the 90° or ‘quadrature’ connection and shifted in theleading direction by the element characteristic angle (ECA).• PHASE DIR 1 ECA: This setting is used to select the element characteristic angle, i.e. the angle by which the polariz-ing voltage is shifted in the leading direction to achieve dependable operation. In the design of the UR-series elements,a block is applied to an element by asserting logic 1 at the blocking input. This element should be programmed via theECA setting so that the output is logic 1 for current in the non-tripping direction.• PHASE DIR 1 POL V THRESHOLD: This setting is used to establish the minimum level of voltage for which the phaseangle measurement is reliable. The setting is based on VT accuracy. The default value is “0.700 pu”.• PHASE DIR 1 BLOCK WHEN V MEM EXP: This setting is used to select the required operation upon expiration ofvoltage memory. When set to "Yes", the directional element blocks the operation of any phase overcurrent elementunder directional control, when voltage memory expires; when set to "No", the directional element allows tripping ofphase overcurrent elements under directional control.The phase directional element responds to the forward load current. In the case of a following reverse fault, the ele-ment needs some time – in the order of 8 ms – to establish a blocking signal. Some protection elements such asinstantaneous overcurrent may respond to reverse faults before the blocking signal is established. Therefore, acoordination time of at least 10 ms must be added to all the instantaneous protection elements under the supervi-sion of the phase directional element. If current reversal is of a concern, a longer delay – in the order of 20 ms –may be needed.PHASE OPERATINGSIGNALPOLARIZING SIGNAL V polABC PHASE SEQUENCE ACB PHASE SEQUENCEA angle of IA angle of VBC (1ECA) angle of VCB (1ECA)B angle of IB angle of VCA (1ECA) angle of VAC 1ECA)C angle of IC angle of VAB (1ECA) angle of VBA (1ECA)NOTE
