# On the Use of LoRa Technology for Logic Selectivity in MV Distribution Networks
## 7 Experimental Tests
### 50.S3 Poly-Phase Short Circuit (Threshold 600 A)
#### 7.2.1 Fault 50.S3 between SR and PR1  
According to the selected configuration, the correct functioning of the proposed logic selectivity system was first verified with the assumption of a fault positioned between the substation relay SR and the PR nearest to the substation, referred to as PR1. In this case, only SR detects the fault, and Figure 10 shows the message exchange between the different protections.  
In Figure 11, the digital signals acquired during one of the 1000 repeated trials are reported.  
The following events can be observed:  
* After about 33 ms from the fault event (identified by the low-high transition of the FAULT signal occurring at the time instant \(t^{r}_{FAULT}\)), the SR commands the trip of its CB to isolate the fault (high-low transition of the signal SR_CB at the instant \(t^{f}_{SR\_CB}\)) and sends the Trip message to PR1, since no Blind message has been received (SR_RxDone always low).  
Figure 9: Time–frequency diagram of a LoRa packet with a duration of 15.46 ms.  
* PR1 receives the Trip message (low-high transition of the signal PR1_RxDone at the instant \(t^{r}_{PR1\_RxDone}\)), and immediately commands the trip of its CB (high-low transition of PR1_CB at the instant \(t^{f}_{PR1\_CB}\)); moreover, PR1 transmits to PR2 the Close request for the boundary TR (low-high transition of the signal PR2_RxDone at the instant \(t^{r}_{PR2\_RxDone}\)).
* PR2 leaves its CB closed (PR2_CB remains high) and forwards the Close request to PR3, which, in turn, transmits it to the TR, which commands the closing of its breaker (low-high transition of TR_IB signal at the instant \(t^{r}_{TR\_IB}\)).  
Figure 11: Digital signals acquired during the fault 50.S3 between SR and PR1.  
Figure 10: Message exchange between protections during the fault 50.S3 between SR and PR1.  
At the end of the operations, the section between SR and PR1 affected by the fault is isolated, but the section downstream PR1 is still supplied since it is connected to the lower radial network. The powered section of the MV network is highlighted by the green arrow in Figure 10.  
The evaluation of the differences between the instants identified by the edges of the acquired digital signals provided the mean values of the time intervals of interest, which are reported in Table 11.  
The standard deviation of the 1000 repeated trials confirmed that the uncertainty is mainly determined by the resolution of 10 \(\upmu\)s of the data acquisition board, adopted for acquiring the digital signals, as would be expected considering the resolution of the ST microcontroller peripheral TIMER2 and what was reported in [40].  
As it is possible to observe, the fault is cleared in the requested time considering that from the moment in which the fault is detected to the moment in which the trip command is sent to the circuit breaker immediately upstream of the fault, the elapsed time is \(T_{SR\_TRIP}\) = 0.03297 s, which is lower than 0.03300 s. The power supply of the network downstream of the fault is restored, i.e., the **Close** message is transmitted to the TR within a time interval of \(T_{IB\_CLOSED}\) = 0.10796 from the fault detection.