Intelligent Isolation and Re-Configuration Examples

The following examples describe the operation of Intelligent LA with Timer and Message Tie Control when a fault occurs between a Feeder (F1) and a Mid-Point ACR (MP1) on the network configuration shown below.

The configuration as shown consists of two feeders connected by a normally open Tie device.

The feeder from substation CB1 has one Feeder and two Mid-Point devices.

The feeder from substation CB2 has one Feeder and one Mid-Point device.

Intelligent LA Example with Timer Tie Control

The fault between F1 and MP1 causes the Feeder ACR overcurrent protection to trip F1. This may initiate an auto reclose sequence but because the fault is a permanent one, F1 will eventually go to lockout.
When F1 goes to lockout it will send a trip request to its downstream device (MP1) according to ILA RULE A. At the same time, LA Activation Timers will start to run in the controllers for MP1, MP2 and the Tie device due to a loss of supply.
Mid-Point device MP1 will change to its reverse protection group, turn Auto Reclose Off when its LA activation delay timer expires according to Classic LA RULE B and trip providing it has received a trip request from F1.
Mid-Point device MP2 will also change to its reverse protection group and go to single shot mode that is Auto Reclose Off when its LA activation delay timer expires according to Classic LA RULE B.
The Tie may also change its Protection Groups depending on which side the supply was lost (source or load) and goes to single shot mode when its LA activation delay timer expires then closes according to Classic LA RULE C regardless of whether it received a close signal or not. Refer to ILA RULE E.
The faulted section of feeder between F1 and MP1 has been isolated. All healthy sections of the feeder now have supply.
Intelligent LA was able to achieve isolation of the fault and re-configuration of the network without any device closing onto a fault as is necessary in the same scenario when Classic LA is used.

Intelligent LA Example with Message Tie Control

The fault between F1 and MP1 causes the Feeder ACR overcurrent protection to trip F1. This may initiate an auto reclose sequence but because the fault is a permanent one, F1 will eventually go to lockout.
When F1 goes to lockout it will send a trip request to its downstream device (MP1) according to ILA RULE A. At the same time, LA Activation Timers will start to run in the controllers for MP1 and MP2 as well as the Tie due to a loss of supply.
Mid-Point device MP1 will change its active protection group and go to single shot mode when its LA activation delay timer expires and also trip providing it has received a trip signal from F1. It will then send a message back to Feeder device F1 to confirm that it has tripped.
Mid-Point device MP2 will also change its active protection group and go to single shot mode when its LA activation delay timer expires.
When F1 receives confirmation from MP1 that it has tripped it sends a close message to the Tie according to ILA RULE D. The Tie LA activation delay timer must be still running when the close message is received. When the timer expires, the Tie device may change its active protection group, depending on which side the supply was lost (source or load), go to single shot mode and close.
The faulted section of feeder between F1 and MP1 has been isolated. All healthy sections of the feeder now have supply.
Intelligent LA was able to achieve isolation of the fault and re-configuration of the network without any device closing onto a fault as is necessary in the same scenario when Classic LA is used.

Fault between CB1 and F1 – Intelligent LA

If the Tie Control is Timer, Intelligent LA will isolate the detected fault and restore supply in the same way as Classic LA.

If the Tie Control is Message, the Feeder ACR F1 will send a close request to the Tie after its LA Activation Delay timer expires. The Tie will only close after its LA Activation Delay timer expires if it has already received a close request.

Fault between MP1 and MP2 – Intelligent LA

If the Tie Control is Timer, MP1 will trip due to protection and send a Trip Request message to MP2. Having received the Trip Request message, MP2 will trip when its LA Activation Delay timer expires. The Tie ACR will close according to RULE C but will not close onto the detected fault because the fault has been isolated by MP2.

The fault is isolated and supply restored to the section between MP2 and the Tie.

If the Tie Control is Message, when MP1 goes to lockout it will send a Trip Request to its downstream device MP2 and a Close Request to the Tie.

MP2 changes protection groups, sets single shot and trips. The Tie changes protection groups if required, sets single shot mode and closes to energize the non-faulted section between it and MP2.