AS Operation

Fault Detect and Pickup Multiplier Settings

The Phase, Earth, SEF, and NPS elements each have Fault Detect and Pickup Multiplier settings as shown:

For the settings shown above, the pickup values for the individual detection elements would be:

Fault Detection Reset

A fault detection that leads to a supply interrupt that in turn leads to a sectionaliser trip will reset when the AS switchgear trips as the current would have dropped to zero.

A Protection Resetting event would be recorded in the Event Log followed by a Max Current event that is the maximum current value sampled between fault pickup and reset.

Not all pickups result in a supply interrupt or even a fault detection. They may reset earlier if the fault current falls to a value determined by the Reset Threshold Multiplier for the Fault Reset Time.

There are separate Reset Threshold Multiplier settings for each overcurrent element and a common Fault Reset Time setting.

In the example shown below for the NPS element, pickup would occur when the NPS current reached 80 A (40 A x 2.0).

If the fault current then dropped to below 90% of 80 A = 72 A, the Event Log would record a Protection Resetting event and start the Fault Reset timer.

If the NPS current stayed below 72 A for 50 ms the fault would reset and the Event Log would record a Max Current event.

A 90 Amp NPS fault that caused a pickup before the NPS current fell to 70 A 10 s later would record the following events.

Fault Reset and Definite Time

If the picked up element has a Definite Time setting, the Definite Time timer will start at pickup and continue to run even if the fault current drops below the Reset Threshold providing the fault doesn’t reset.

If the fault current rises back above the pickup value before the Definite Time timer expires, a fault detection will occur when the timer expires.

If the fault current is above the Reset Threshold but below the pickup value when the Definite Time timer expires, no fault detection will occur.

A fault detection will occur immediately if the fault current rises above the pickup level anytime later without the fault resetting.

Sequence Reset Operation

The Sequence Reset timer is used to reset the supply interrupt counters to zero so that the next supply interrupt will cause the count to start from one.

Some important points to note regarding the operation of the Sequence Reset timer:

• The timer starts when the supply interrupt count is incremented.

• If fault detection pickup occurs while the Sequence Reset timer is running, it will be reset to zero and held there until the next supply interrupt occurs.

• When the Sequence Reset timer expires, a Sequence Reset event is recorded in the Event Log.

Ideally the sequence reset timer in the AS must be coordinated with the sequence reset timer in the upstream ACR. In practice this is difficult to always achieve because it can’t be know when a fault that started a sequence will clear and the ACR is likely to have different Reclose Times configured for each trip.

Detection Groups

There are up to 10 groups of detection settings (referred to as Detection Groups A, B, C, D, E, F, G, H, I, and J). Each Detection Group can have different settings. Users can nominate which one of the 10 detection groups is active.

Normally only one detection group can be active at one time. The exception is when Directional Detection is on. Directional detection uses two detection groups, one for forward faults and one for reverse faults. If Directional Detection is on, the user must choose between five pairs, A/B, C/D etc. where the first group in the pair is the forward group and the second group is the reverse group.

If less than ten detection groups are required, the controller can be configured for a lower number. The only way to change the number of configured detection groups in a controller is to change the setting in the WSOS off-line file and do a Write Switchgear Settings to the Switchgear with the Detection tick box selected.

The Write Switchgear Settings command will replace all the detection settings in the controller with those in the off-line file.

Fault Flags

Fault flags indicate which elements detected a fault during the most recent fault sequence.

Fault flags for the elements described in the table below are displayed:

The fault flags can be viewed in WSOS by going to

Display > Fault Flags.

Figure 181
AS Fault Flags Display

Fault Flags are also displayed on the operator interface.

Fault Flags Example

An example of how the fault flags might be displayed by the AS in service is shown in the figure below.

Figure 182
AS Fault Flags Example

The fault flags as shown indicate:

• The Phase Fault element was the only element to detect a fault during the last fault sequence. There have been two phase faults since this counter was last reset. They may not have both occurred during the last sequence. The last phase fault detected was between A and B phases.

• The EF element has detected one fault since the last time this counter was reset. This fault did not occur during the most recent fault sequence.

• There have been no SEF or NPS faults detected since the counters were last reset.

Detection Off

When Detection is Off, the Fault Flags are replaced by Pickup Flags. Pickups occur as normal when Detection is Off but do not trigger fault detect timing so cannot lead to a fault being recorded.