Outline
The PID insulation tester (TOS7210S) is designed based on the insulation resistance tester (TOS7200) to carry out the evaluation of the PID (Potential Induced Degradation) effect of the PV module precisely and efficiently.
 Being equipped with the output ability of 2000 V and the ammeter with nA resolution as well as a polarity switching function, the TOS7210S is also applicable not only to the PID evaluation but also the evaluation of the insulators that requires a high sensitivity of measurement. The tester is equipped with the panel memory that is externally accessible and RS232C interface as standard; it can be flexibly compatible with the automated system.
PID effect
 The PID effect is a phenomenon that the amount of power generation by a cell remarkably decreases when high voltage is applied between the solar cell and the frame for long hours. It is supposed that the higher the applied voltage is and/or the higher and more humid the environment is, the further deterioration accelerates. For example, the potential difference in the string becomes extremely higher when the number of sheets that are connected in series increases even if the output voltage of the crystalline silicon solar cell module is just tens of volts. On the other hand, the grounding methods of the PCS (Power Conditioning System) that connects to the system as an AC power supply varies according to the type of PCS. In recent years, the transformerless method, where the input side is in the floating method (the negative polarity is not connected to the ground) is increasing. In this case, a high potential difference occurs between the cell and the ground. Regarding the crystalline silicon solar cell module, it is proved that the cell having a higher negative electric potential than that of the frame (ground) easily causes the PID effect. (See Fig. 1) The PV modules are currently managed with the maximum system of voltage as 600 V in Japan and 1000 V in Europe. There is a market trend that the maximum voltage of the commercial mega solar system is raised from the perspective of reducing the number of the strings and the total number of the PCS, and improving the efficiency of power generation.
 Figure 2 shows the simulation of a crystalline silicon solar cell module being exposed to a high potential difference. It is considered that, in the PID effect of the crystalline silicon solar cell module, the sodium ion in the white tempered plate glass moves to the side of the cell and then causes the deterioration. (The PID effect of the thin film solar cell module is also confirmed, however, the mechanism of the deterioration is different from that of the crystalline silicon solar cell module.) The cause of the PID effect is currently being tested with and researched by various research organizations.
Features
- Capable of arbitrary setting of the output voltage
You can set the test voltage that is appliedto the DUT within the range of 50 Vdc to 2000 Vdc(resolution 1 V). In addition, an insulation resistancetest of the electricity/electronic components orthe electricity/electronic devices is alsopossible besides the voltagespecified in JIS C 1302:1994. In the range of 50 V to 1000 V,the output properties are complied to JIS C 1302:1994.
- Polarity switching function
You can easily change the output polarityby the switch on the front panel. The PID deterioration is a reversible phenomenonthat may recover after the reverse bias voltage is applied. The polarity switching is a convenient functionthat can avoid a wiring change that connectsto the DUT. In addition, switchingby the external control throughthe RS232C interface is also possible.
- The output is floating from the ground.
The output terminal is floating from theground electric potential(*1). In addition, a shield cable is adopted as an output cable (TL51-TOS) . Therefore, it can be measured only an electric current flowingbetween test points excluding the one betweenthe DUT and the ground, and it realizes to conductthe highly-sensitiveand precise evaluation.
*1: Ground voltage of the terminal that polarity is set as an anode (± 1000 Vdc)Ground voltage of the terminal that polarity is set as a cathode (+1000 Vdc and -3000 Vdc)
- Analog output terminal
In the resistance display mode,the voltage depending on the measured resistanceis logarithmically compressed and outputwithin the range of 0 V to 4 V. In the current display mode, the current is output in a linear scale depending on the measured current andranges of measurement (4 ranges). You can analyze the changes or the deteriorationstatus of the DUT by using an external recording device such as the data logger.
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