Solar (PV) String Ground Fault Finder

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Solar (PV) String Ground Fault Finder

Finding the ground fault location in a solar panel string

The ground fault point can be probed by measuring the voltage of a string's disconnect switch in which insulation failure is found.
This function can find a ground fault in a string of solar panels connected in series.
Simply measure voltage at three points of the string.

Locate ground-faulted solar panel from the poorly insulated string

Features

Simply measuring the voltage of the string reveals the ground fault location

At the junction box, measure the insulation resistance of each string's circuit breaker to check the insulation condition. When you find that the insulation of the string is too low, it means that one of the solar panels in the string has a ground fault. To repair this, it is necessary to determine which solar panel has a ground fault.

This is where the Solar (PV) String Ground Fault Finder function comes in handy.

Locate ground-faulted solar panels from string found to be poorly insulated

At first, disconnect the main switch in the connection box, then the disconnect switch of the string.

Only the following voltages need be measured. The feature of this function is that the ground fault point can be probed by measuring the voltage of a string's disconnect switch in which insulation failure is found.

The open circuit voltage of the string $V_{oc}$ (between P and N)
The voltage between the positive conductor and ground $V_{PE}$ (between P and E)
The voltage between the negative conductor and ground $V_{NE}$ (between N and E)

If no information is added by the user (total panel number or open circuit voltage of one solar panel), the test result will be a percentage. In this case, the number of all solar panels is considered 100%. The output represents the percentage to this total number of solar panels from either the positive or negative side in which a ground-faulted solar panel is located.

Notation

This function is available only when the string has poor insulation. Check the insulation resistance before use.
Disconnect the main switch of the connection box and the string's disconnect switch to measure the voltage. If they are left "on," the location cannot be determined correctly.
If there are multiple solar panels with ground fault, it cannot be determined correctly.

Locating the grounded panel

Entering one of the following parameters will tell you which panel is grounded, rather than a % indication.

The number of solar panels that make up the string
The open circuit voltage of one solar panel

Estimates the location of ground-faulted solar panel simply by measuring voltage

The calculation method behind the Solar (PV) String Ground Fault Finder

Suppose that in a string consisting of n solar panels, the mth solar panel from the positive side has a ground fault. Here, the voltages at the following three points are measured.

The open circuit voltage of the string $V_{oc}$ (between P and N)
The voltage between the positive conductor and ground $V_{PE}$ (between P and E)
The voltage between the negative conductor and ground $V_{NE}$ (between N and E)

By measuring the voltage at three points, the location of the ground fault point can be calculated.

Suppose all solar panels output comparable voltages. By calculating the ratio of the voltage across the string $|V_{oc}| \simeq |V_{PE}|+|V_{NE}|$ to the voltage between the positive side and the ground fault point $|V_{PE}|$ , the location of the ground faulted solar panel can be estimated.

Panel number method

The ratio for the location of the ground-faulted solar panel from the positive side is as follows

$\displaystyle{\frac{m}{n}=\frac{|V_{PE}|}{|V_{PE}|+|V_{NE}|}}$

Multiplying this ratio by the number of solar panels per string $n$ , gives the solar panel number at ground fault, counting from the positive side.

$\displaystyle{m=\frac{|V_{PE}|}{|V_{PE}|+|V_{NE}|}\times n}$

Voc (1 panel) method

To calculate from the open circuit voltage of one solar panel $V_{oc-each}$ , first calculate the number of solar panels $n$ in the string from the following equation.

$\displaystyle{n = \frac{V_{oc}}{V_{oc-each}}}$

Then the following equation shows the solar panel number at ground fault, counting from the positive side.

$\displaystyle{m=\frac{|V_{PE}|}{|V_{PE}|+|V_{NE}|}\times n}$

Specifications

Number of simultaneous instrument connections	1
Display of ground fault location	% display The position of the ground fault is displayed as a percentage of the number of solar panels in a string, where 100% is the total number of panels. Formula for % display from the positive side: $\frac{\|V_{PE}\|}{\|V_{PE}\|+\|V_{NE}\|} \times 100 [\%]$ Formula for % display from the negative side: $\frac{\|V_{NE}\|}{\|V_{PE}\|+\|V_{NE}\|} \times 100 [\%]$ Rounded to the nearest whole number and expressed as a percentage Can switch between % display from the positive side and negative side Panel number method Enter the number of solar panels in the string to calculate the location of the grounded panel, output as the panel-number from one of the pole-sides (+/-) Enter the number of solar panels in the string $n$ Formula for counting from the positive side: $\frac{\|V_{PE}\|}{\|V_{PE}\|+\|V_{NE}\|} \times n$ Formula for counting from the negative side: $\frac{\|V_{NE}\|}{\|V_{PE}\|+\|V_{NE}\|} \times n$ Rounded to the nearest whole number Can switch between displaying the number of pannels from the positive side and negative side Voc (1 panel) method Enter the open circuit voltage of one solar panel $V_{oc-each}$ to calculate the location of the ground-faulted panel, output as the panel-number from one of the pole-sides (+/-) Enter the open circuit voltage of 1 solar panel $V_{oc-each}$ Foumula for the number of solar pannels in the string: $n = \frac{V_{oc}}{V_{oc-each}}$ Formula for counting from the positive side: $\frac{\|V_{PE}\|}{\|V_{PE}\|+\|V_{NE}\|} \times n$ Formula for counting from the negative side: $\frac{\|V_{NE}\|}{\|V_{PE}\|+\|V_{NE}\|} \times n$ Rounded to the nearest whole number Can switch between displaying the number of pannels from the positive side and negative side The open circuit voltage for each panel must be comparable
Measured values	Display refresh interval: approx. 1 s Maximum number of displayed channels: 1
Manual input mode	Measured values are input using the numeric keypad instead of from a measurement instrument