When connecting a bidirectional power flow device such as an ESS (Energy Storage System) and an RCCB (Residual Current Circuit Breaker), the problem that occurs when the power side (Line) and the load side (Load) are connected in reverse, and a countermeasure that considers the bidirectional power flow characteristics of the ESS to solve this problem

1. Problem of RCCB reverse wiring when using ESS bidirectional power

ESS is characterized by bidirectional power flow, receiving power from the grid (charging) or supplying power to the load or the grid (discharging). Reverse connection of RCCB causes the following problems in this environment:

• Overvoltage/overcurrent protection interference :

• The ESS inverter changes the current direction during charging/discharging, and if the RCCB is reversed, the circuit breaker's differential current detection circuit may detect abnormal current flow, causing malfunction (unnecessary tripping) or loss of protection function. For example, when current flows from the ESS to the power grid during discharging, the RCCB may mistake it for leakage current.

• Increased video current :

• When the phase imbalance between the N-phase (neutral line) and the R-phase (phase line) occurs due to reverse wiring, the zero-phase current (I₀) increases. The high-speed switching inverter of the ESS generates harmonics, which further amplifies the zero-phase current and may cause the 51N (zero-phase overcurrent) relay to malfunction.

• Compatibility Issues :

• The Power Conversion System (PCS) of ESS requires precise protection settings to manage bidirectional current flow. RCCB reverse wiring can conflict with the protection algorithm of PCS and compromise the stability of the entire system.

• Risk of fire and equipment damage :

• If the arc extinguishing performance of the RCCB is reduced due to reverse wiring, the arc will not be properly extinguished in the event of a short circuit in the high current environment of the ESS, increasing the risk of fire. In addition, it may lead to damage to the ESS battery or inverter.

2. RCCB response plan when using ESS bidirectional power

Countermeasures to prevent reverse wiring and ensure correct installation for stable interconnection of ESS and RCCB.

(1) Pre-installation inspection

• Comply with manufacturer's manual :

• The line and load sides of the RCCB must follow the arrow directions indicated in the manufacturer's manual. When connecting to an ESS, make sure that the RCCB is a model that supports bidirectional current flow (e.g., IEC 61009-1 compliant, bidirectional current sensing model).

• Phase order verification :

• In a 3-phase system, the order of phases N1, N2, N3 and N is checked using a phase sequence tester. Since the PCS of the ESS is sensitive to phase imbalance, prevent incorrect wiring through a preliminary check.

• Check ESS compatibility :

• Check the technical specifications of the ESS manufacturer (e.g. Tesla, LG, Samsung SDI) to check whether the rated current, breaking sensitivity (e.g. 30 mA, 100 mA), operating time, etc. of the RCCB are compatible with the current characteristics of the ESS.

(2) Installation and wiring

• Bidirectional current design :

• Considering the charge/discharge mode of ESS, RCCB is designed to operate stably even in bidirectional current flow. Some modern RCCBs provide dedicated models (e.g. Type B RCCB) that support bidirectional current, which are suitable for ESS and solar systems.

• Applying harmonic filters :

• Install a harmonic filter or EMI filter to suppress the increase in zero-phase current due to harmonics of the ESS inverter. This is effective in reducing the malfunction of the RCCB.

• Neutral wire (N phase) management :

• In ESS systems, the neutral wire is important to maintain the current balance between the power grid and the PCS. To prevent miswiring or grounding of the neutral wire, measure the voltage and current with a multimeter after wiring.

(3) Test drive and testing

• Self-diagnosis test :

• Press the TEST button on the RCCB to check the self-diagnosis function. In the ESS environment, perform tests in each of the charge/discharge modes to check whether the RCCB operates normally when the current flows in both directions.

• Simulated load testing :

• Connect a simulated load in the ESS charge/discharge mode to measure the RCCB's breaking sensitivity and operating time. For example, artificially generate a 30mA leakage current and check whether the circuit breaker trips within 0.1 second.

• Image current monitoring :

• Monitor the zero-phase current (I₀) during ESS operation using a current clamp meter or zero-phase current measuring equipment. If it exceeds the normal range (e.g. less than 10 mA), suspect and check for wiring errors or harmonic problems.

(4) Operation and maintenance

Regular maintenance :

• Regularly check the wiring status of ESS and RCCB, especially to see if the operation of RCCB is affected after PCS software update.

Utilizing Smart RCCB

• The latest smart RCCBs provide remote monitoring and diagnostic functions, which can be used to analyze the current flow data of the ESS in real time and detect abnormal signs early.

• Emergency Response Plan : Establish an emergency protocol to immediately shut down the PCS of the ESS in the event of an RCCB trip or malfunction. This will minimize battery damage and fire risk.

(5) Compliance with standards and certifications

Compliant with IEC and national standards :

• ESS and RCCB must comply with IEC 61009-1, KS C IEC 61009, or UL certification. In particular, for Type B RCCBs supporting bidirectional current flow, select models designed in accordance with IEC 62423.

Manufacturer Partnership :

• Work with technical support teams from ESS and RCCB manufacturers (e.g. Schneider Electric, ABB) to determine the optimal wiring method for system integration.

3. Cases and References

• Domestic industrial site case in 2021 :

There was a case where the MV circuit breaker linked to the ESS was tripped due to a misconnection in the NR phase, and the zero-phase current increased to 214% of the normal value. This was analyzed to be the result of a combination of RCCB reverse connection and ESS harmonics. The solution was to install Type B RCCB and add a harmonic filter.

• Technical Recommendations :

ESS manufacturers and electrical installation experts strongly recommend pre-construction phase sequence verification and commissioning tests to prevent RCCB reverse wiring in bidirectional current flow environments.

4. Conclusion

In the bidirectional power flow environment of ESS, reverse wiring of RCCB can cause loss of protection function, malfunction, fire risk, and violation of specifications. To avoid this:

• Strict adherence to manufacturer manuals and specifications.

• Utilizing a phase sequence verifier and harmonic filter.

• Use a bidirectional current supporting model such as Type B RCCB.

• Ensure system stability through test runs and regular inspections.