Current Operated Detection Elements

Phase Overcurrent

Phase overcurrent detection monitors the RMS current in each phase in order to detect single phase, phase to phase or three phase faults.

A phase detection pickup occurs when the measured current ≥ the Phase Fault Detect current x the Phase Pickup Multiplier.

The fault detect time is calculated based on the magnitude of the fault current as a multiple of the Phase Fault Detect setting.

The phase current values are updated every 5 ms and the fault detect time is continually being recalculated while the pickup is active.

Unless the fault resets, a fault detection will ensue.

Configuration options for Phase Overcurrent fault detection and reset are listed in the table below.

EF

The EF element is driven by the residual current that is the real-time vector sum of the three phase currents.

The residual or earth current is calculated by digitally summing the phase currents sampled every 5 ms.

Residual current = A phase current + B phase current + C phase current or I_e = I_a + I_b + I_c

An EF pickup occurs when the measured current ≥ the EF Detect current x the Earth Pickup Multiplier.

The fault detect time is calculated based on the magnitude of the fault current as a multiple of the EF Detect setting.

The earth current values are updated every 5 ms and the EF detect time is continually being recalculated while the pickup is active.

Unless the fault resets, a fault detection will ensue.

Configuration options for EF detection and reset are listed in the table below.

Sensitive EF (SEF)

The Sensitive EF elements are driven by measured residual current.

The residual current used for the SEF element is determined by measuring the current in the common connection between the three CT secondary currents on the PCOM board.

Residual current = A phase current + B phase current + C phase current or I_e = I_a + I_b + I_c

A sensitive EF pickup occurs when the measured current ≥ the SEF Fault Detect current x the SEF Pickup Multiplier.

The fault detect time is calculated based on the magnitude of the fault current as a multiple of the SEF Fault Detect setting.

The SEF current values are updated every 5 ms and the SEF fault detect time is continually being recalculated while the pickup is active.

Unless the fault resets, a fault detection will ensue.

Configuration options for SEF detection and reset are listed in the table below.

NPS

The NPS elements are driven by the NPS current (I₂) which is calculated in real time by digitally summing the phase currents sampled every 5 ms and applying the Fortescue formula for sequence components.

I₂ = (I_a + I_b phase shifted 240° + I_c phase shifted 120°) / 3

An NPS pickup occurs when the measured current ≥ the NPS Fault Detect current x the NPS Pickup Multiplier. The fault detect time is calculated based on the magnitude of the fault current as a multiple of the NPS Fault Detect setting.

The NPS current values are updated every 5 ms and the NPS fault detect time is continually being recalculated while the pickup is active.

Unless the fault resets, a fault detection will ensue.

Configuration options for NPS fault detection and reset are listed in the table below.

Fault Detect and Reset Configuration

The Fault Detect and Reset settings for Phase, Earth, SEF, and NPS detection elements can be configured in WSOS on the Global Settings page.

Figure 194
Fault Detection and Reset settings for Phase, Earth, SEF, and NPS elements

Broken Conductor

Open circuit faults due to broken conductors or mal operation of switchgear will not cause an increase in current and are not detected by standard over current protection.

This type of fault will cause an unbalance and produce NPS current.

The broken conductor algorithm is based on monitoring the relationship between NPS and PPS currents and is independent of load fluctuations.

Broken Conductor can only be used if it has been made available either through WSOS in Feature Selection.

Display > Configuration > Feature Selection > Detection

Or it can be made available on the operator interface.

If available it can be configured on the Broken Conductor page in the WSOS Protection menu.

Figure 195
AS Broken Conductor settings

or on the operator interface.

A description of these settings are shown in the table below:

Broken Conductor fault detection pickup will occur when the following conditions are present:

• Broken Conductor is Available.

• Broken Conductor Protection is On.

• The real time I_nps/I_pps ratio exceeds the configured I_nps/I_pps Setting Ratio.

A Broken Conductor pickup will be recorded in the Event Log.

A pickup will start the fault detect timer and if the pickup persists for the Definite Time setting, a Broken Conductor fault detection will occur.

A Broken Conductor pickup will reset if the I_nps/I_pps ratio drops to the Reset Threshold for the Reset Time. The Reset Threshold is 90% of the I_nps/I_pps ratio by default.

A Broken Conductor reset event will be recorded in the Event Log.

Configuration options for Broken Conductor fault detection and reset are listed in the table below.