Elsevier

Electric Power Systems Research

Volume 131, February 2016, Pages 139-146
Electric Power Systems Research

Nuisance tripping of residual current circuit breakers in circuits supplying electronic loads

https://doi.org/10.1016/j.epsr.2015.10.012Get rights and content

Highlights

  • RCCBs are used to provide protection against indirect contacts.

  • Nuisance tripping of RCCBs often occur in circuits that feed electronic loads.

  • Phase currents suffer high peak values that may also trip the circuit breaker.

  • Voltage disturbances in circuits feeding electronic loads cause RCCBs to trip.

Abstract

Residual current circuit breakers (RCCBs) are often used to provide protection against indirect contacts in a grounded electrical installation. However, there are situations where the use of RCCBs presents certain problems. In circuits that feed electronic loads RCCBs often cause nuisance tripping. This article discusses the reasons why RCCBs trip in this type of circuit based on a previous case studied by the authors at ‘La Fe’ hospital in Valencia (Spain) and several tests performed in a power flexible laboratory. A theoretical circuit used to explain the phenomena is also presented.

Introduction

Nuisance tripping of residual current circuit breakers (RCCBs) is often related to the presence of electronic loads, especially computers [1]. In some facilities, a common solution is to install immunised residual current circuit breakers (known as SI RCCBs following the commercial acronym for an improved type A RCCB—such those as manufactured by Schneider Electric). However, SI RCCBs are much more expensive than type A or AC standard residual current circuit breakers (A RCCBs or AC RCCBs).

Among the possible causes of random tripping, the presence of harmonic currents is often cited [2], [3], [4], [5], [6], [7]. Recently, an interesting work [1] analysed the influence of harmonics on the value of the current that produces RCCB tripping. The influence of the time constant of an aperiodic current following an earth fault and the response of RCCBs to current pulses were also analysed [2], [8].

In currents with the presence of low-order harmonics, the minimum tripping current varies with harmonic content, as well as the phase angle of the harmonic component [1], [2]. RCCB tripping is primarily determined by the peak value of the current. Low-order harmonic components with angles that increase the peak value of the current facilitate RCCB tripping. In contrast, a desensitisation of the RCCB is produced by the presence of high-order harmonics and the minimum tripping current generally increases with increasing harmonic frequency [1].

Low-order harmonics with small values can vary the value of the leakage current that forces the RCCB trips. However, this change is small and it is very improbable that it can explain the tripping of an AC RCCB. Moreover, higher order harmonics (frequencies up 1 kHz), or the fast transient connection or disconnection of some devices, rarely causes RCCB tripping [1], [2].

Thus, a current containing a high component of harmonics, as in circuits that feed electronic loads is not a cause of nuisance tripping. However, this type of circuit often suffers this problem. An explanation is presented in this paper.

In computer rooms RCCBs sometimes trip when the computers are running, and even when they are turned off. Therefore, the type of load present in a circuit should be considered because the load may increase the transient current, raising the neutral-earth voltages and leakage currents, and so increasing the frequency of trip events.

This article presents an investigation into the causes of RCCB nuisance tripping in circuits supplying electronic loads. Section 2 summarises the detected phenomena in a previous work at ‘La Fe’ hospital. Test results obtained in a laboratory with circuits feeding computers are discussed in Section 3. Section 4 details a theoretical circuit that explains the detected phenomena. Finally, some conclusions are drawn in Section 5.

Section snippets

Detected phenomena in a previous work

The detected phenomena in a facility with RCCB nuisance tripping was analysed by the authors in a previous work [1]. The nuisance tripping occurred in a large hospital which became operational in February 2011. During the first days of use there were many RCCB incidents. Given the need to find an urgent solution, maintenance staff began replacing AC RCCBs by SI RCCBs and the number of trips was reduced to a normal number in one or two days. More than 2000 RCCBs were replaced at a significant

Tests performed in circuits feeding electronic loads

Several tests were performed in a laboratory to study the influence of electronic loads in RCCB nuisance tripping. These tests were performed under the Transnational Access to the Flex Power Grid Lab Research Infrastructure at DNV KEMA (a Dutch business and technical consultancy that tests, inspects, certifies, and verifies the energy value chain) under the DERri project and supported by the European Commission under FP7 [9].

Many tests were performed and the specific single-line set-up diagram

Equivalent circuit for theoretical explanation

In this section, a simplified equivalent electrical circuit of the data measured in the hospital (Section 2) is presented (Fig. 8) to obtain just the main data related to the phenomenon. The circuit is obtained as an equivalent circuit of a T–T three phase system and uses a Norton equivalent model to represent the nonlinear behaviour of the loads. This circuit enables the authors to further analyse the results and theoretically explain the phenomena.

In the electrical diagram the variables are

Conclusion

Current in circuits supplying electronic loads presents a high component of harmonics but these are not the cause of nuisance tripping of residual current circuit breakers. Circuits feeding this type of load in situations when there are supply voltage disturbances, suffer current surges magnified by the electronic loads and discharge currents to ground that cause RCCBs to trip. Disturbances produce leakage currents by capacitive effect and varistor discharges in electronic equipment. These

Acknowledgments

This research work has been made possible with the support of the Programa de Apoyo a la Investigación y Desarrollo (PAID-06-12) de la Universitat Politècnica de València (Spain), the GV/2015/068-Ayudas para la realización de proyectos de I + D para grupos de investigación emergentes and the Flex Power Grid Lab Research Infrastructure at DNV KEMA, the Netherlands under the European FP7 project—DERri (grant agreement 228449).

References (9)

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