Correct Installation of Current Transformers (CTs) in a Three-Phase System

Introduction

For single-phase and three-phase systems, the installation of CTs differs slightly:

• Single-phase zappi or eddi:

  • Requires a harvi to measure the current on all three phases.
  • It is not possible to connect three CTs from different phases directly to a single-phase zappi.

• Three-phase zappi:

  • The three CTs can be directly wired to the zappi.

Key Considerations

1. The CTs must be clipped onto the correct cables:

   • CT1 on Phase 1, CT2 on Phase 2, and CT3 on Phase 3.

2. Ensure the arrow on each CT points towards the consumer unit or fuse board.

3. The phase rotation setting on the zappi must align with the three-phase wiring configuration.

   • The simplest and default wiring setup for zappi is:
     • L1 → Terminal 1
     • L2 → Terminal 2
     • L3 → Terminal 3
     • Neutral and Earth appropriately connected.
   • More information about phase rotation settings is covered in a separate article.

Checking the CTs

To verify the CTs are correctly installed, follow these steps:

1. Initial Setup:

   • Turn off any local generation sources (e.g., PV or wind).
   • Ensure the household load is sufficient, drawing at least 1A per phase.

2. Access CT Readings:

   • For CTs directly connected to zappi:
     • Navigate to Other Settings → Installer Settings → CT Config → Readings.

1. • For CTs connected via a harvi:
     • Navigate to Settings → Installer Settings → Linked Devices → Devices → harvi.

2. Evaluate Readings:

   • Each CT should display a positive power value with a power factor close to 1.0 (at least 0.9).
   • If a CT shows a power factor around 0.5, it is likely clipped onto the wrong phase.

Identifying and Correcting Misaligned CTs

If it is unclear which CT is misaligned, use the following method:

1. Clip all CTs around the same wire.

2. Check the CT readings:

   • One CT will show a power factor close to 1.0 (correct phase).
   • The others will show power factors near 0.5 (incorrect phases).

3. Relocate the CTs as follows:

   • Step 1:
     • Identify the CT with a power factor of 1.0.

1. • • Leave it on its current phase.
   • Step 2:
     • Move the other two CTs to a different wire.
     • Check the readings again.
     • One will show a power factor close to 1.0 (correct phase), and the other will show a power factor near 0.5.
   • Step 3:
     • Move the final CT to the remaining wire.
     • Confirm the readings.

2. Repeat until all CTs are correctly aligned with their respective phases.

Final Validation

Once all CTs are correctly installed:

• The power readings should align with expected values.
• All CTs should show a positive power value with a power factor close to 1.0.

If you encounter issues or require further assistance, contact our support team for guidance.