Earth Ir Cos (Ø) Polarising

The Ir Cos (Ø) operating characteristic is used in similar situations to Wattmetric. The operating value is defined as the active component of the residual current given by:

Where Ø is the Fault Angle that is the angle between the V_ZPS and I_ZPS phasors.

This feature works in a similar manner to Wattmetric with the following differences.

The Active Current threshold is adjustable in the range 10 to 1260 A in steps of 1 A with a default value of 40 A.
Ir Cos (Ø) is the value used to determine whether a fault is present, that is the pickup value.

When Ir cos(Ø) is selected as the polarising decision for directional EFs, WSOS displays this message:

This is because the Earth Pickup Threshold (Setting Current) is now set in
Ir Cos (Ø) units as shown below.

Earth Ir Cos (Ø) Characteristic Fault Angle

When a forward EF occurs on a compensated earthing system, V_ZPS and I_ZPS are assumed to be 180° out of phase.

Therefore the Characteristic Angle for Ir Cos (Ø) is fixed at 180°.

NOTE: When the directional EF decision is Ir Cos (Ø), the Characteristic Angle is fixed and not displayed.

The Ir Cos (Ø) Fault Angle for a given fault is the Zero Sequence Current angle relative to the Zero Sequence Voltage angle V_ZPS → I_ZPS.

The Angle at Fault recorded in the Event Log is the fault angle relative to the Characteristic Angle which is fixed at 180°.

So a fault with a Fault Angle (V_ZPS → I_ZPS) = 135° would log an Angle at Trip of -45° (135°-180°) which indicates that the fault angle is lagging the Characteristic Angle by 45°.

When the Earth Tripping Direction is Trip Forward, the above fault will log the following events:

Forward Pickup Earth
Earth Directional Armed
Earth Protection Trip
Angle at Fault -45°
Quantity at trip Earth/SEF I_R Cos Ø – xx.xx A
Polarizing Voltage at trip V_ZPS
Quantity at the maximum Earth/SEF – Maximum I_R Cos Ø - xx.xx A
Polarizing Voltage at the maximum V_ZPS

Earth Ir Cos (Ø) Sector Width

The default Forward and Reverse Sector Width settings for earth protection when the Decision is Ir Cos (Ø) are both 90°. These are ± settings and equate to actual sector widths of 180°.

Sector Width settings are identical for all elements and Decision settings. For more information, refer to Sector Width.

Earth Ir Cos (Ø) Low Voltage Block

When the Earth Low Block setting is On, tripping is blocked if the polarising voltage is below the Low Threshold setting.

In this situation the ACR will still record fault resetting events when the apparent fault goes away as shown:

Fault On

Earth Directional Low V Blocked.
Polarizing Voltage Low V_ZPS

Fault Off

Quantity at the maximum Earth/SEF – Maximum Ir Cos Ø xx.xx A
Polarizing Voltage at the maximum V_ZPS

When the Low Block setting is Off, the polarising voltage is disregarded and the action is entirely based on the calculated fault angle in relative to the Earth Characteristic Fault Angle.

So if the polarising voltage is below the Earth Low Threshold setting, a protection trip will occur but no fault angle will be logged.

The Event Log will record:

Earth Directional Low V Armed
Polarizing Voltage Low V_ZPS
Earth Protection Trip
Earth Low V_ZPS
Quantity at trip Earth/SEF Ir Cos Ø xx.xx kW
Polarizing Voltage at trip V_ZPS
Quantity at the maximum Earth/SEF Ir Cos Ø xx.xx kW
Polarizing Voltage at the maximum V_ZPS

The default Earth Low Threshold setting is 500 V_ZPS configurable over the range 150...15,000 V_ZPS.

Earth Ir Cos (Ø) Voltage Memory

When Ir Cos (Ø) is selected as the Decision for directional EFs, a Voltage Memory time between 0.01 s and 10.00 s or OFF can be configured.

The default setting is 2.00 s.

Consider a reverse EF where V_ZPS and I_ZPS are in phase and V_ZPS is above the Low Threshold setting.

If the EF Tripping Direction is Trip Reverse, and the Voltage Memory setting is 2.00 s, this fault will cause a reverse pickup and Earth Directional Armed will be logged. If V_ZPS then drops below the Low Threshold setting before the switchgear trips, this will not cause a Low V condition as the controller will continue to use the last sampled value of V_ZPS that was above the threshold as the polarising voltage while the pickup is active.

If the fault persists long enough to cause a trip, the memorized voltage and corresponding fault angle displayed in the Event Log will be identified by an asterisk ‘*’.

The Event Log will report the following events:

Reverse Pickup Earth
Earth Directional Armed
Earth Protection Trip
Angle at Fault* 180°
Quantity at trip Earth/SEF Ir Cos Ø xx.xx A
Polarizing Voltage at trip* V_ZPS 514 V
Quantity at the maximum Earth/SEF Maximum Ir Cos Ø xx.xx A
Polarizing Voltage at the maximum V_ZPS 601 V

NOTE:

The Angle at Fault and Polarizing Voltage at trip events above are identified as memorized values.
The Polarizing Voltage at trip V_ZPS would be expected to be just above the Low Threshold setting (default 500 V).
The Polarizing Voltage at the maximum is not a memorized value as V_ZPS was above the Low Threshold setting when the fault first appeared.

Earth Ir Cos (Ø) Fault Hold Time

When Ir Cos (Ø) is selected as the Decision for directional EFs, a Fault Hold Time between 0.01 s and 10.00 s or OFF can be configured. The default setting is 2.00 s.

The effect of the Fault Hold Time is to pause the protection timing for a set period after a fault that caused a pickup has gone away.

When the fault hold time is 2.00 s, a forward EF with a tripping time of 3.0 s that goes away after 1.5 s for 1.0 s and then returns will cause a trip after another 1.5 s. Because the hold time, that is the time that the fault went away for (1.0 s), is a shorter duration than the Fault Hold Time (2.0 s), the pickup will remain active while protection timing is paused and the tripping time will be extended by the Fault Hold Time setting.

The Event Log will record a Paused event during the hold time. The events recorded from pickup with relevant time stamps would be:

Event	Time Stamp
Forward Pickup Earth	00:00:00.00
Earth Directional Armed	00:00:00.00
All protection elements resetting	00:00:01.50
All protection elements paused	00:00:01.50
Protection element timing	00:00:02.50
Earth Protection Trip	00:00:04.00
Quantity at trip Earth/SEF Ir Cos (Ø) xx.xx A	00:00:04.00
Polarizing Voltage at trip V_ZPS	00:00:04.00

The fault was paused during the 1.0 s hold time so never reset. When the fault returned a Protection Element Timing event was logged.

NOTE: this was not a pickup as a pickup was already active.

The time between pickup and trip would be 4.0 s that is 3.0 s tripping time plus
1.0 s hold time.