Rogowski Coils (CTs) for the Lunar System (Rev 1)

Rogowski Coils (CTs) for the Lunar System

Summary

Rogowski Coils, referred to as Coils in this Application Note, are flexible, air-core sensors designed to measure alternating current (AC) by detecting the rate of change of current in a conductor. These current transformers (CTs) provide accurate, non-intrusive current measurements and transmit this telemetry to the Lunar System. The integration of Rogowski Coils within the Lunar System enables the following functionalities:

● Partial Home Backup: Monitoring energy usage of non-backup loads connected to an upstream panelboard.

● Power Control System (PCS): The Lunar System, which includes the Lunar Battery (ESS), Lunar Bridge and optional Rogowski Coils (CTs), have been certified to both UL 1741 PCS CRD and UL 3141.

Installation Requirements

Compatible Coils

Only install Rogowski Coils sourced directly from Lunar Energy. The Lunar System uses the Magnelab RCT-120L Series Coils. Two Rogowski Coils along with the field applied labels are included in the Rogowski Coils kit (90-06789A). The datasheet for the Magnelab RCT-120L Coil is available here.

Coils Installation at Main Panel

The latch end of the Coils are typically installed on the service disconnect for a residential home.

Location: The Coil must be installed on the conductors in series between the Lunar Bridge and the grid. Clasp: Ensure the Coil clasp is fully engaged by performing a gentle tug test to confirm it is secure.

Coil Installation at Lunar Bridge

Terminating the Coil leads to the labeled terminals Coil 1A/1B and Coil 2A/2B in the Bridge as shown in Figure 1.

If a drain wire is present, do not splice or connect it to any conductor or terminal.

When extending the length of the Coil free-end wires, splice the wires using 12-24 AWG shielded, twisted or untwisted wires. Note that the maximum length of spliced wire is 100 feet.

Coil Phase & Polarity

To verify the correct phase (L1 versus L2) and polarity (positive current vs negative current) of the Coils, please follow the guidance in the Lunar Installer App.

Metering Verification Test

The Installer App uses the factory-installed Bridge Current Transformers (CTs) to compare the measured current from the Coils with that of the Bridge CTs, ensuring accurate Coil installation. This verification process requires the installer to adjust which loads are on or off in the home.

The Installer App will prompt the installer to:

1. Turn off all non-backup loads.
2. Turn on the backup loads fed from the Lunar Bridge, ensuring that the following conditions are met ○ Both AC L1 and AC L2 must have at least 2A of measured current. ○ There must be at least 2A of imbalanced current between AC L1 and AC L2 (i.e., one line must have at least 2A more measured current than the other).

The Installer App will display a green checkmark confirming the coil installation only when the required conditions are met. If the conditions are not met, the app will prompt users with the necessary actions to take, as outlined in the Table 1 below.

Table 1. Common Meter Configuration Issues and Resolutions

Adjusting Coil Phase & Polarity

The easiest method to adjust Coil phase or polarity is to adjust the wiring terminations at the Bridge, rather than adjusting the clasp end of the Coil.

● Coil Phase is flipped by swapping the terminations of Coil 1A and Coil 1B with Coil 2A and Coil 2B. ● Coil Polarity is flipped by swapping the terminations of Coil 1A with Coil 1B, and similarly, swapping the terminations of Coil 2A with Coil 2B.

Coil Indicator Arrow & Wire Termination

Each Coil has an arrow indicator intended to point toward the load. However, in the Lunar System, the Coil arrow may be pointed in either toward the Load or to the Grid, as long as the arrow indicator directions are consistent with the coil A/B wiring terminations, as shown in Table 2.

Table 2. Coil arrow directions and their permissible wiring terminations.

Installing Coils on Branch Circuit Wires

When direct Coil installation on service conductors is not feasible due to physical limitations, such as a 4-wire main breaker, it is allowed to bundle branch circuit wires instead.

Please make sure to bundle all non-backup load feeders AND the Lunar Bridge feeders within the Coils.

1. All L1 conductors should be bundled together and be inserted through Coil 1.
2. All L2 conductors should be bundled together and be inserted through Coil 2.
3. All wires must be oriented so that the current flow direction to or from the grid is the same.

Revision History