PHASE DIRECTIONAL ELEMENT (67P)

5.4.3.3 PHASE DIRECTIONAL ELEMENT (67P)

The Phase directional element (67P) provides independent elements for each phase, and determines the direction of the current both in permanence and in fault condition.

Its main function is to apply a blocking signal to the overcurrent elements to prevent their operation when the current is flowing in a certain direction. In order to determine the direction of the current, the element uses phase current values as operation magnitude, and phase-to-phase voltage values as polarization magnitude. This means that in order to polarize a phase, we use the phase-to-phase voltage of the other two phases, known as crossed polarization.

The following table describes the phase directional element settings.

Table 5–41: PHASE DIRECTIONAL ELEMENT SETTINGS

Function: This setting allows enabling or disabling the corresponding directional element.

MTA: The MTA setting corresponds to the Torque angle, which is the rotation applied to phase-to-phase crossed voltage.

Direction: This setting allows selecting the area for the directional element to operate, either forward or reverse.

Block Logic: This setting allows selecting either permission or block, depending on the logic to be applied in the event of directional element block.

Polarization Voltage Threshold: This is the minimum voltage considered for the direction calculation. Under this setting, the element will be blocked.

Snapshot Events: The snapshot event setting enables or disables the snapshot event generation for the phase directional elements.

Phase directional element is an independent Protection element that provides block and Operation signals for each phase.

These signals can be monitored both through the relay HMI or using EnerVista 650 Setup at “Actual > Status > Protection

> Phase Current”

SETPOINT > PROTECTION ELEMENTS > PHASE CURRENT > PHASE DIRECTIONAL >

PHASE DIRECTIONAL 1> PHASE DIRECTIONAL 2 > PHASE DIRECTIONAL 3

SETTING DESCRIPTION NAME DEFAULT VALUE STEP RANGE

Function permission Function DISABLED N/A [DISABLED – ENABLED]

Maximum Torque Angle MTA 45º 1 Deg [-90 : +90]

Operation Direction Direction FORWARD N/A [FORWARD – REVERSE]

Block logic Block Logic PERMISSION N/A [BLOCK – PERMISSION]

Polarization voltage threshold Pol V Threshold 40 1 V [0 : 300]

Snapshot event generation Snapshot Events ENABLED N/A [DISABLED – ENABLED]

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Table 5–42: BLOCK AND OPERATION SIGNALS FOR THE PHASE DIRECTIONAL ELEMENT

Signals provided by the directional element are, block and operation signals. Signals used to block overcurrent elements are configured at Setpoint > Relay Configuration > Protection Elements.

Operation signals are active when operation and polarization magnitudes meet conditions given by the settings.

Block signals indicate blocked elements by an external block input or by polarization voltage loss. Using the “Block logic”

setting, the user can select how the directional element responds in case of a block. When the “Block” option is selected, the operational signal will not be activated in a block condition. When the “Permission” option is selected, the operation signal will be activated in a block condition.

Figure 5–7: shows the default configuration for the phase overcurrent block input. When the “Block logic” setting is set as

“Block”, this input will be active in case of a block in the directional element, avoiding any phase overcurrent trip.

When the “Block logic” setting is set as “Permission”, the phase overcurrent element is enabled to trip as the block input is not active in case of polarization voltage loss.

BLOCK AND OPERATION FOR 67P PHASE DIR1 BLOCK A

PHASE DIR1 A OP PHASE DIR1 BLOCK B PHASE DIR1 B OP PHASE DIR1 BLOCK C PHASE DIR1 C OP PHASE DIR2 BLOCK A PHASE DIR2 A OP PHASE DIR2 BLOCK B PHASE DIR2 B OP PHASE DIR2 BLOCK C PHASE DIR2 C OP PHASE DIR3 BLOCK A PHASE DIR3 A OP PHASE DIR3 BLOCK B PHASE DIR3 B OP PHASE DIR3 BLOCK C PHASE DIR3 C OP

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Figure 5–7: OVERCURRENT ELEMENTS BLOCK CONFIGURATION BY THE DIRECTIONAL ELEMENT

Directional elements can also be blocked with signals coming from other relays, PLCs, or through signals configured in the relay PLC Editor (Logic configuration tool). The signal used in that case is PHASE DIR BLK INP. Figure 5–8: shows an example of the default block configuration of directional elements by digital input. There is one block signal per input for each setting group.

Figure 5–8: DIRECTIONAL ELEMENT BLOCK CONFIGURATION BY INPUT

The main component of the phase directional element is the angle comparator with two inputs: the operation magnitude (phase current) and the polarization magnitude (phase-to-phase voltage rotated the angle set in MTA setting), which is the torque angle.

The Polarization type used in the directional element is crossed, this means that in case of a fault in phase A, the Operation magnitude will be Ia, and the polarization magnitude will be Vbc, rotated by the torque angle. In case of a fault in phase B, the operation magnitude will be Ib, and the polarization magnitude will be Vca rotated by the torque angle. Finally, in case of a fault in phase C, the operation magnitudes will be Ic, and Vab.

Table 5–43: OPERATION AND POLARIZATION MAGNITUDES FOR DIRECTIONAL UNITS POLARIZING SIGNAL VPOL

PHASE OPERATING SIGNAL ABC PHASE SEQUENCE ACB PHASE SEQUENCE

A IA angle VBC angle x 1 MTA VCB angle x 1 MTA

B IB angle VCA angle x 1 MTA VAC angle x 1 MTA

C IC angle VAB angle x 1 MTA VBA angle x 1 MTA

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The polarization diagram is as follows:

Figure 5–9: POLARIZATION DIAGRAM

The diagram shows a fault in phase A, therefore the Operation magnitude is IA, the polarization magnitude is VBC, which has been rotated the torque angle set as MTA. Positive angles are considered as counter clockwise rotations, and negative angles clockwise rotations. Direction is considered to be forward when the fault current is inside an arc of ±90º to both sides of the polarization voltage. In the directional element settings there is a Direction setting that allows to select in which area the element operation is allowed, either forward or reverse. Operation areas include a safety zone of 5º to each side of the cone. This safety cone is applied when the operation direction calculation is performed from initial block conditions. When we go from a non-trip area to a trip area, the safety cone is considered. In case we go from a trip area to a non-trip area, this cone will not be considered, and the whole area will be operative. This safety cone is located always in the operation area, both in forward and reverse cases.

NOTE: In situations where a current inversion is produced during a fault, the phase directional element will require a period of time to establish the blocking signal. This time is approximately 20 ms. Certain instantaneous overcurrent elements can be activated before receiving the blocking signal from the directional element. In cases where these situations can be expected, we recommend to add a 50ms delay to IOC elements.

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The following figure shows the logic scheme for the phase directional element.

Figure 5–10: DIRECTIONAL ELEMENT LOGIC SCHEME (A6632F3)