Frequently Asked Question

How to measure phase voltages in 3-phase system
Last Updated a year ago

Connecting measurements to measure phase voltages in a 3-phase system inside of THCC can result in warnings when applying a straightforward approach. Without knowing the cause of behavior, it can be hard to interpret the warning that will arise when you try connecting measurements.

Consider the following case:

When trying to connect voltage measurements in such a fashion, you are met with the following warning: Undefined Basic Electrical.el_voltage_msr: Va1.Va1 inside Va1.

Inside of THCC, voltage measurement components are treated as open circuit elements. This means the circuit shown above will be equivalent to the following:

We see that the ground is essentially floating. To resolve this, the compiler will define one voltage measurement as a short circuit, so that the other two can be defined. In practice, this will be manifested as one voltage measurement always displaying 0 V, while the other two measurements will be measuring line instead of phase voltage.

There are several ways how you can approach measuring phase voltages in a 3-phase system:

- Adding another ground component at some other electrically defined point in the circuit. The two nodes that are connected to ground components are resolved as one node during the compilation process, generating a short circuit between them. This way, you will be able to provide an “electrically defined point” to your measurement circuit. You can read more about how the ground component is modeled in Typhoon Software here.

- Creating an ‘’artificial” neutral point using shunt resistors. In case you want to measure phase voltage in a 3-phase system, you can make an ‘’artificial’’ neutral point using a shunt resistor. For example, if the voltage level is 10kV, you can set Rshunt = 1e6Ω which will consume only 100W of the transferred power. The described concept is illustrated in the figure below.

- Using the Three-Phase Meter component. The Three-Phase Meter is a component located in the Microgrid Library. It has a prebuilt option of creating an artificial neutral point. The snubber resistance is defined in the General Tab of the component properties using the Snubber resistance property.

- Using line voltage measurements. In case you have available line voltage measurements, you can use them to estimate phase voltages. This can be done by means of Signal Processing, but in that case, phase measurements will be calculated with a lower resolution.

In the attachment, you can find this approach realized by using Voltage controlled voltage sources, which utilize FPGA resources for calculating phase voltages with high resolution. This approach assumes that the zero sequence of voltage is equal to zero.

Bear in mind that controlled sources must be in the same sub circuit as the components that are controlling it. In other words, they must be compiled into the same Standard Processing Core.

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