# Design and Application of a Distribution Network Phasor Data Concentrator
## 2 DPDC Application Requirements Analysis
### Application Requirements  
In addition to the different networking structures compared with the PMU-PDC in the transmission network, the \(\upmu\)MPMU connected to the DPDC is different from the traditional PMU in terms of function, quantity, and communication method [3]. To meet the application requirements in the active distribution network, the \(\upmu\)MPMUs have the functions of power distribution terminals, and the corresponding DPDCs also need to have certain functions of the distribution station. The DPDC can be used for data collection, and the collected \(\upmu\)MPMUs data is sent to the main station, and the control commands from the main station are forwarded to the \(\upmu\)MPMU. The DPDC can also directly have the monitoring function. By analyzing the data of \(\upmu\)MPMUs, the DPDC controls \(\upmu\)MPMUs to complete fault location, isolation, restore power to non-faulty areas, the DPDC then reports the processing results to the main station. Thereby the feeder automation is implemented. To make the problem that DPDC needs to solve more clear, PMU and \(\upmu\)MPMU, PDC and DPDC are compared from various aspects, and the comparison contents are shown in Table 1.  
Through the comparison in the table, the following conclusions can be drawn regarding the application requirements of DPDC:  
1. The number of \(\upmu\)MPMUs is large and the number of points may increase as the number of important local nodes increases. A DPDC as the substation/node PDC should be able to connect more than 20 \(\upmu\)MPMUs [17], and the dynamic data files can be stored for 14 days, and the transient data files more than 1000 pieces. Commercial PDCs can connect hundreds of PMUs, but their prices are thousands of dollars or more, and there is no price advantage in promoting them in the distribution network;
2. The installation locations of \(\upmu\)MPMUs are scattered and the working environment is diverse. Compared with the traditional PMU, the \(\upmu\)MPMU may face the problem of communication interruption and clock loss [11]. The DPDC needs to be able to correctly assemble the data and not discard the clock abnormal data, and also has the function of reconnecting the \(\upmu\)MPMU;
3. The communication modes adopted by \(\upmu\)MPMU are various, and the delay of different communication methods is different. Wireless communication may have an unstable connection  
Figure 1: \(\upmu\)MPMU-DPDC networking structures. (**a**) centralized in the station; (**b1,b2**) wired distributed; (**c**) wireless distributed. under different meteorological or spatial conditions, so in the case of using a synchronous time signal, the data frames of the same timestamp produced by different \(\upmu\)MPMU may arrive at the DPDC at different times, after experiencing a significant delay. The DPDC should be able to tolerate a large arrival time difference of the same timestamp data between the \(\upmu\)MPMUs, that is, to correctly collect data of different delays. Reference [18] summarized the delay of wireless communication, and reference [9] also introduced the delay of PMU data transmission using 4G LTE, at an average of 70 ms, and even 1 s in certain cases. This paper defines DPDC's ability to tolerate data time differences as time difference tolerance, with a reference value of 150 ms;
4. Considering the versatility of the \(\upmu\)MPMU, the main tasks performed by different \(\upmu\)MPMUs may be different, and different applications have different data delay requirements, ranging from 100 ms to 5 s [19]. The classification and priority transmission of data are helpful for increasing DPDC ability and improving communication efficiency. Traditional phasor transmission such as protocol IEEE C37.118.2-2011 [20] and GB/T 26865.2-2011 [21] cannot meet the requirements, and DPDC needs to support the extended protocol. IEEE C37.118.2-2011 is an internationally popular synchronous phasor transmission protocol. GB/T 26865.2-2011 is a synchronous phasor transmission protocol used by China's power system, and the contents are mostly the same.