Overview
Installing the current transformers (CTs) correctly on a three-phase system is critical if the power zappi measurements are going to be correct.
This article provides some practical tips to get the three-phase CTs set up correctly.
Introduction
Important:
- If you have a single-phase zappi or an eddi then you will need a harvi to measure the current on all three phases - you cannot connect the three CTs from different phases directly to the single-phase zappi.
- If you have a three-phase zappi then the three CTs can be wired directly to the zappi.
In theory, it's simple:
- The CT must be clipped around the right cable (CT1 on Phase 1, CT2 on Phase 2 and CT3 on Phase 3)
- The arrow on the CT must point towards the consumer unit/fuse board
- The "phase rotation" setting on the zappi must agree with the way the three-phase wiring is connected.
- Simplest is to have zappi wired L1 - terminal 1 / L2 - terminal 2 / L3 - terminal 3 + Neutral and Earth
- This is the default setting for zappi. More information on the zappi phase rotation setting will be covered in a separate article (The zappi phase rotation setting)
Checking CT's
Start by checking the Grid CTs Make sure that any local generation (PV / wind) is turned off and that there is enough load in the house to draw at least 1A per phase.
Now look at the CT readings.
For directly connected CT these readings are on the menu:
Other Settings -> Advanced -> CT Config -> Readings...
For CT's that are connected to a harvi, the readings are on the menu:
Settings -> Advanced -> Linked Devices - Devices -> Harvi
- Each CT should read a +ve power and have a power factor close to 1.0 (at least 0.9)
- A power factor reading of 0.5 means that the CT is clipped around the wrong phase.
If it's not easy to see which CT is in the wrong phase, try the following:
- Clip all the CT's around the same wire.
- Check the CT readings.
- One CT will show a power factor close to 1.0. The others will show power factors close to 0.5
The CT with the power factor of 1.0 is in the correct phase
- Now move the other two CTs to a different wire.
- Check the CT readings. One CT will show a power factor close to 1.0, the other will show a power factor close to 0.5
The CT with the power factor of 1.0 is in the correct phase
- Now move the last CT to the remaining wire and check the CT readings again.
The CTs should now all be in the correct phase and giving the correct power reading.