# 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)
#### 7.2.2 Fault 50.S3 between PR2 and PR3  
The proposed system was assessed also with a fault located between PR2 and PR3, as schematized in Figure 12. In this case, the fault is detected by the protection relay in PR2, as well as by the relay in SR and PR1.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Interval** & **Measurement Method** & **Max Value [s]** & **Measured Value [s]** \\ \hline \(T_{SR\_TRIP}\) & \(t_{SR\_CR}^{f}\)-\(t_{FAULT}^{r}\) & 0.03300 & 0.03297 \\ \(T_{PR\_TRIP}\) & \(t_{PR\_CR}^{f}\)-\(t_{FAULT}^{r}\) & - & 0.05146 \\ \(T_{PR\_R\_R}\) & \(t_{PR\_R\_Dome}^{f}\)-\(t_{FAULT}^{r}\) & - & 0.06969 \\ \(T_{PR\_R\_R}\) & \(t_{PR\_R\_Dome}^{f}\)-\(t_{FAULT}^{r}\) & - & 0.08824 \\ \(T_{IB\_CLOSED}\) & \(t_{TR\_IB}^{r}\)-\(t_{FAULT}^{r}\) & - & 0.10796 \\ \hline \hline \end{tabular}
\end{table}
Table 11: Estimated time intervals during the fault 50.S3 between SR and PR1.  
Figure 12: Message exchange between protections during the fault 50.S3 between PR2 and PR3.  
In Figure 13, the recorded digital signals acquired during one of the 1000 repeated trials are reported.  
The following steps can be recognized:  
* As soon as the fault event is detected, PR1 transmits a Blind message to the SR and, at the same time, PR2 transmits the Blind message to PR1.
* SR and PR1 receive the Blind message after about 18 ms (low-high transition of the SR_RxDone and PR1_RxDone signals, respectively, at the instants \(t^{\prime}_{SR\_RxDone}\) and \(t^{\prime}_{PR1\_RxDone}\)).
* After about 33 ms from the fault event, PR2, which has not received any Blind messages (PR2_RxDone always low), commands the trip of its CB (high-low transition of the signal PR2_CB at the instant \(t^{\prime}_{PR2\_CB}\)) and sends the Trip message to PR3.
* PR3, once it has received the Trip message (low-high transition of the signal PR3_RxDone at the instant \(t^{\prime}_{PR3\_RxDone}\)), also commands the trip of its breaker (high-low transition PR3_CB at instant \(t^{\prime}_{PR3\_CB}\)), isolating the faulty line section. PR3, moreover, transmits the Close request to the TR, which then commands its IB (low-high transition of TR_IB signal at the instant \(t^{\prime}_{TR\_IB}\)).  
As a final result, the line section between PR2 and PR3 (i.e., the section affected by the fault) is isolated, the section between SR and PR2 is supplied by the upper primary substation, and the section between PR3 and TR is fed by the lower primary substation. In Figure 12, the powered sections are highlighted by green arrows.  
The measured time intervals are reported in Table 12.  
As it can be appreciated, the fault is cleared before the time limit expires, considering that from the moment in which the fault is detected to the moment in which the circuit breaker immediately upstream of the fault is commanded, the time elapsed is \(T_{PR2\_TRIP}\) = 0.03296 s, which is lower than 0.03300 s. The Close message is, instead, transmitted to the TR within a time interval \(T_{IB\_CLOSED}\) equal to 0.07085 s after the fault detection.  
Table 13 summarizes the interval values measured in the two cases taken into account.  
Figure 13: Digital signals acquired during the fault 50.S3 between PR2 and PR3.  
As it can be seen from Table 13, the experimental results meet the theoretical assumptions. In particular, the two considered cases highlight the main advantage of the logic selectivity approach: the time required for fault clearing is always the same and does not depend on the position of the fault.  
On the other hand, the position of the fault influences the time required for closing the Tie recloser. Since the Close message starts from the PR immediately downstream of the fault and is forwarded up to the TR, the time required for repowering the healthy line downstream of the fault is dependent on the fault position.