| With the power innovation going further, a more strict operation management of the 10kV medium voltage distribution network is required. The distribution power network management system, including the distribution automation, remote metering, load management and the demand side management is being applicable and engineering practicable. On of the technical bottlenecks constraining the development of distribution power network management system is the absence of a data exchange platform with higher ratio of performance to cost. Power line communications use the power network as a transmission channel to realize the data transmission and information exchange. As a more competitive information exchange platform of the distribution power network management system, power line communications take many advantages on the economic transmission channel and network coverage. Nevertheless, the traditional power network serves for the energy transmission and distribution of the mains frequency and exhibits a typical bus structure. For high-frequency communicating signal transmission, such structure and the existence of load of mains frequency result in a hostile environment for signal transmission. Such a hostile channel makes the research of power line communication being more challenging.This paper mainly focuses on the channel characteristics of the 10kV medium voltage power network. On the basis of empirical data obtained from two representative 10kV medium voltage power networks, and with the support of laboratory experiments, the basic channel characteristics are examined, including noise, impedance and transmission properties of the 10kV medium voltage power networks over the frequency ranging from 40kHz-2MHz. Some meaningful conclusions are exposed, and the corresponding channel model is established. The main studies include:(1)Based on the topology and some fundamental properties of the 10kV power line channel, a basic model representing the physical properties of the 10kV power line channels is proposed. Furthermore, the parameters describing the channel properties and practical research methods are discussed. The methods for measuring the channel parameters are examined. And a new approach which uses the electrical loop wires to directly measure the channel transfer function H(f)and obtains the amplitude response and phase response, is provided to deal with the direct measurement of phase response for a line of long length. This problem has puzzled the researchers for a long time. Also, the method of moving the reference plane of the network analyzer is used for the first time. This method can efficiently eliminate the impacts on measuring the practical channel parameters introduced by the auxiliary equipments such as coupling devices, which will improve the measurement efficiency and accuracy of the data process.(2)A relatively deep research on the noise characteristics on the 10kV power network is carried out. The noise level of the 10kV power networks depends on the power network structure, configuration, and loads. It is often higher than that of the low voltage power networks. The noise power spectrum density usually follows the exponential distribution. However, if the power lines cross with the lines of higher voltage class power networks, the distribution is impacted by the noise from the higher voltage power network. On the 10kV power line, the noise at the power supply side (head side) is a little higher than that at the receiving end (tail side). Whereas, the noise distributes uniformly. The system impedance at the busbar absorbs some noise power. The noise level of phase to phase coupling is usually lower than or at least not greater than or even much lower than those of the related two single phase to ground coupling, respectively.(3) The background noise is statistically analyzed and corresponding statistical models are established in the time domain and the frequency domain respectively. And the Pearsonχ2 test is used to estimate the model's application. In the time domain, the background noises on the 10kV power network follow different statistical distribution. At lower frequencies and a broad band, both the white noise and colored noise follow the Nakagami-m distribution which is different with the commonly assumed Gaussian noise. Only at frequencies on the order of tens of megahertz, the noise distribution obeys Gaussian. In the frequency domain, even there are distinct functions to fit the spectrum profiles of different power networks, their parameters, however, still follow the Nakagami-m distributions.(4) The impedance characteristics of the 10kV power network are studied. The impedance characteristic is in correlation with the power system structure and its configurations. Below 1MHz, the dynamic range of the input impedance is from several tenths of ohms to several hundreds of ohms. The dynamic range is becoming narrower with frequency and tends to the order on several tenths of ohms at last, where it exhibits pure resistance. The input impedances at each network node are different but their characteristic impedances are the same. The input impedance of the 10kV power network is greatly steady and scarcely varies with the loads working at mains frequency. The capacitor group connected to the bus has no influence on the input impedance. The input impedances in differential mode and common mode coupling are almost symmetric. The impedance value in differential mode coupling is higher than that in common mode coupling. However, the dynamic range of the former one is larger.(5) A pilot study on the transmission characteristics of the 10kV power line channel is carried out. A 10kV power line channel has the characteristics of a typical multi-path propagation. The channel frequency response attenuates with oscillations. If there are no branches and distribution transformers between TX/RX, the power attenuation is about 10-20dB/km in phase to ground coupling.The corresponding phase response is linear. The narrowband fading follows Nakagami-m distribution. And the fading depth is 3-10dB. In general, the time variance of the channel is weak. If the communication data rate is up to kbps, it can be regarded as a time-invariant channel. The channel is time dispersed. Both the rms delay spread and coherence bandwidth of the channel are related to the practical power network structure. The corresponding values are about ten microseconds and several tens of kilohertz respectively.(6) Based on the transmission line theorem, the path loss over the 10kV power network channel is discussed. A simple path loss model is proposed for engineering analysis. The most severe impact on the path loss depends on electrical equipments connected between TX and RX. These equipments including distribution transformers and branches introduce some drain losses. Other parts of the network have little impact on the path loss. Also, the parallel compensation capacitor groups connected to the bus have no effect on the path loss. The equivalent impedance of any component wired into the network through a branch has been smoothed by that branch. If the impedance of the equipment is lower, thus smoothness favors the reduction of the drain loss caused by the corresponding equipment. The path loss is 5-15dB lower in phase to phase coupling than that in phase to ground coupling.
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