Current transformer for photovoltaic systems
In current measurement in PV systems, current transformers are used for recording feed-in, reference and consumption currents. Here you will learn what to pay attention to when selecting and dimensioning.
More information
Why current transformers in photovoltaic systems?
In PV systems, current transformers are used to reduce high AC and DC currents to a level that is manageable for meters, energy management systems and protective devices. Typical applications include measuring the feed-in and consumption current at the grid connection point, recording self-consumption and connecting to energy management systems that coordinate generation, consumption and storage.
What to consider when selecting
- Primary rated current: depends on the fuse or the maximum expected current on the line to be measured, not generally on the rated power of the system.
- Secondary rated current: 1 A or 5 A, depending on the input provided by the connected measuring device, meter or energy management system.
- Accuracy class: for pure consumption and generation monitoring, a general operating class is often sufficient. For billing feed-in tariffs or calibrated settlement metering, higher classes such as 0.2s or 0.5s are provided – more on this in our article on accuracy classes.
Suitable designs
Plug-on current transformer (ASK) can be retrofitted onto an existing line without having to disconnect it – practical when PV measuring technology is retrofitted in the meter cabinet or inverter connection area. Wound-type current transformer (WSK) are more suitable for smaller currents and confined spaces, as the primary winding is permanently wired. A more detailed distinction of the designs can be found in our selection guide.
Compatibility with inverters and energy management systems
Many inverter and energy management manufacturers specify concrete requirements for rated current, burden and output signal for their measuring inputs. Check these manufacturer specifications before selecting – we will be happy to advise you on which current transformer is suitable for your specific system combination.
Common sources of error
A current transformer must never be operated open on the secondary side while current is flowing on the primary side – dangerous voltages can occur at the connection terminals. An excessively generously dimensioned primary current rating also leads to lower measuring accuracy in the partial load range, which is particularly relevant with fluctuating PV feed-in.
Advice on the right PV measuring solution
Every PV system has its own requirements for current measurement. Contact us with the key data of your system – we will recommend the right current transformer type.