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IEICE Electronics Express, Vol.xx, No.xx, xx-xx

LETTER Reduction of Trip Operating Time of Electronic Type ELCB to 9 mili-Seconds for Safety Improvement of Electrical Facility Juchul Kim 1a), and SangJoong Lee 2

Abstract ELCB(Earth leakage circuit-breaker) is a used electrical circuit to provide electric shock protection and in a low-voltage AC() electrical circuit to provide electric shock protection and to prevent fires from current leakages. prevent fires from current leakages. ELCB is also called Trip operating time of ELCB depends on the magnitude of leakage “Circuit-breaker incorporating residual current current and the duration time of leakage accident. In this paper, the circuit and electrical signal after ZCT(Zero-sequence Current protection” in IEC60947-2 or a “Residual current ) output terminal of existing ELCBs are analyzed. As a operated circuit-breakers with integral over current result of measurement, electronic trip type ELCBs in present market protection for household and similar uses(RCBO)” in have shown up to 27ms of self-trip operating time under 30mA of leakage current. This 27ms of time delay is due to the problem that the IEC61009-1. It is also referred to as a “Ground-fault IC in electronic circuit detects only the reverse-half cycle of sinusoidal circuit-interrupter (GFCI)” in UL943 [2-3]. leakage current. In this paper, the authors design a new electronic circuit that minimizes the delay factors of existing circuits. And as a To protect human body from electric shock, result of an experiment, the trip operating time could be shortened minimizing the leakage trip operating time(TOT from within 9ms. Shortened trip operating time implies reduction of shock now on) of ELCB is very important [1,3]. TOT of ELCB duration of leakage current. Since the electric shock to human body and the outbreak possibility of fire are inversely proportional to square root is defined by the time elapsed from the instant leakage of shock duration, faster trip operation of ELCB proposed in this paper accident occurs until the time ELCB completely turns off will contribute to providing shock protection to human body and preventing fires from current leakages. the power source. In IEC 61009-1 standard, the TOT of key words: ELCB, TOT(Trip Operating Time); Electrical Shock; ELCB is set to less than 30ms [4-8]. Shock Duration; Rated Sensitivity Current ㎳ Classification: Power devices and circuits Leakage TOT below this time level(i.e., 1~29 ) is not described anywhere in this standard [9-13]. There are two types of trip mechanism for an ELCB. 1. Introduction One is the electronic trip type(electronic type ELCB from now on) and the other is the ZCT trip type(ZCT With increase of power consumption according to type ELCB from now on). economic growth, importance of electrical safety and the Electronic type ELCBs shown in Fig 1. detect and role of ELCB are becoming a major concern. As amplify the leakage current of ZCT output by electronic buildings are becoming larger, not only increased use of circuit and transmit a trip signal to ELCB trip coil when but also increased number of the electric the magnitude of the leakage current is larger than branch circuits is threatening the electrical safety [1-3]. A threshold value. recent analysis shows that electric shock accidents are more common at low voltage rather than at high voltage and the number of deaths has also been on the rise. ELCB is a circuit breaker used in a low-voltage AC

1 Dept. of Electrical , Seoul National University of Science and Technology, Seoul, Korea 01811 2 Seoul National University of Science and Technology, Seoul, Korea 01811 Fig 1. Electronic type ELCBs. a) [email protected]

DOI: 10.1587/elex.16.20190465 ZCT type ELCBs shown in Fig 2. and Fig 3. receive Received July 21, 2019 the leakage current and amplify it by the turn ratio of its Accepted August 26, 2019 Publicized September 17, 2019 1 Copyright © 2019 The Institute of Electronics, Information and Communication

IEICE Electronics Express, Vol.xx, No.xx, xx-xx own winding without electronic circuit to directly actuate Therefore, it is necessary to re-design the ELCB circuit the trip bar of ELCB. in order to detect the full-wave of the leakage current. ZCT type ELCB is more surge-free in general This paper presents a new electronic circuit structure compared to electronic type ELCB because it has no to reduce the TOT of electronic type ELCB and the electronic circuit inside. ZCT type ELCB, however, performance is tested for a prototype circuit. shows longer trip operating time in general when the magnitude of leakage current is relatively small. 2. Full-wave detection of leakage current

2.1 TOT of existing ELCBs

An experiment has been performed for seven existing ELCBs. A leakage current has been supplied for every 0.5 second with 220V, 60Hz sinusoidal AC. And the longest TOT out of 30 times of the tests has been Fig 2. ZCT type ELCB. recorded. Fig 4. illustrates the sequence diagram of the ELCB trip operation.

L N

ZZCCTT Leakage ELCB Trip Current Current By Amplifier Conversion Magnetic by ZCT Ratio Energy

Fig 3. Trip mechanism of ZCT type ELCB.

Further reduction of trip operating time of electronic type ELCBs is possible using today‟s advanced circuit design technology, which significantly can improve the Fig 4. Sequence diagram of ELCB trip operation electrical safety. Longer TOT of ELCB may cause a big property loss by fire or a dangerous electric shock to human body. The ELCBs selected for the test are the models The shortest TOT of most electronic type ELCBs in specifically designed for human protection from electric present market exceeds 20ms. 20ms corresponds to about shock and the rated sensitivity current are all 30mA. one and half cycle for 60Hz AC [14-24]. Electronic type ELCBs which are triggered by the This implies that the shock current flows through reference set on IC began to actuate in the range of 21.5 human body for at least one cycle or more, which may to 24.5mA [25-30]. result in a fatal damage as the case may be. Therefore, Under 30mA of rated sensitivity current, the maximum shortening the TOT of the ELCB is essential because it TOTs of existing electronic type ELCB showed 27ms directly reduces the duration of current flow through [3,25-30]. The shortest TOT for electronic type ELCB is human body. However, existing ELCBs detect only the 15ms or longer in general despite increase of leakage reverse half cycle of the leakage current inside IC, which current. makes operation time longer.

It is difficult to shorten the TOT by 15 ms or shorter even though the internal delay factors are optimized. 2

IEICE Electronics Express, Vol.xx, No.xx, xx-xx 2.2 Half-wave and full-wave detection

EIC-6PIN_MODULE VCC_ARROW Full-wave 발생누전제어 회로 Os latch PORT-C R16 22.5mA_SET circuit Q4 Shortened leakage TOT implies reduction of shock R T NPN Q3 VCC_A VCC_A VCC_A NPN

U5A 8 Nr 3 R6 D3 1 duration of the leakage current, which means reduction + 1 D6 2 - R11 C7

LM2904 R10

4 2 C3 R8 R4 R12 of electric shock to the human body and livestock. TEST-BOTTON 1pin R2 1 2 Q2 TEST-PIN C4 Q1 Electronic trip type ELCBs in present market have C1 R1 Cx R15 TEST-WIRE X 1Turn ZCT U6B

8 C6 LM2904 R9 R3 5 R7 D5 shown up to 27ms of self-TOT under 30mA of leakage 22.5mA + 7 22.5mA 2pin 6

C2 - 4 current. This 27ms of time delay is due to the problem R5 R11 that the IC in electronic circuit detects only the reverse- C5

VCC21V_PIN6 L1 half cycle of sinusoidal leakage current. RT1 3.0K 1/2W MORS TRIP-COIL If the ELCB can detect the full-wave(entire interval RW1 Q1 - +

MOV1 (1)~(4) in Fig 5-2) of the sinusoidal leakage current, BD1 R14 D5

TOT of ELCB considerably can be reduced. SCR C9 MOV2 ZD1

PORT-C In this paper, an electronic circuit by which the full- ZD2

C8

1 1 wave leakage current signal is measurable to reduce TOT J1 J2 of ELCB is developed. In Fig 5, ELCB trip operation Fig 6. ELCB circuit with two Op-Amps. time is shortened through full-wave detection, which is New circuit consists of two Op-Amps. #1 Op-Amp possible by re-design of the electronic circuit of ELCB Receives and amplifies leakage current signal from ZCT with two Op-Amps. output. #2 Op-Amp receives the same leakage current

signal that #1 Op-Amp receives but reverses its phase Existing ELCBs New ELCB angle by 180° and again amplifies it. Both #1 and #2 Detection of Leakage Signal Detection of Leakage Signal from ZCT from ZCT amplifiers adopt a filter circuit that eliminates high-

Sine wave Sine wave frequency noise as shown in Fig 6. IC latch circuit compares the amplified leakage signal with preset Amplifier by IC Amplifier by IC threshold value to actuate the trip circuit of ELCB.

(1) (2) (3) (4) t t Existing electronic type ELCBs detect only one half HalfHalf-wave - wave detectable detection Full - Full-wavewave d detectableetection

No No cycle (about 8.3ms) of the leakage signal from ZCT Reference Set Reference Set output. Therefore, the TOT may exceed 30ms-standard in Yes Yes Convert to Square Convert to Square case signal detection fails within first reversed-half cycle. Wave Wave However, the IC latch output proposed in Fig 6. No No 1nd Delay 1nd Delay always can be operated within 8.3ms because two bi-

Yes Yes directional IC inputs always enable successful detection Latch Voltage Latch Voltage Output Output of the first half cycle of sinusoidal wave.

No Full-wave detection function of new ELCB trip circuit 2nd Delay 2nd Delay No proposed in this paper has shown a stable trip operation Yes Yes SCR Turn-on SCR Turn-on without failure within the range of 9ms. Prototype ELCB circuit made by the authors is shown in ELCB Trip ELCB Trip Fig 7.

1. Half-wave detection 2. Full-wave detection Fig 5. Wave detection

2.3 New ELCB with full-wave detectable circuit The authors designed a new circuit that can detect full- wave of leakage current signal as shown in Fig 6 and Fig

7. Fig 7. PCB layout of new ELCB circuit

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IEICE Electronics Express, Vol.xx, No.xx, xx-xx The electronic used for prototype ELCB is SCR BT169G (Manufacturer: Philips). Gate controlled turn-on time of BT169G is approximately 2 micro-second and commutated turn-off time is approximately 100 micro-second[31] that can be ignored compared to ToT of ELCBs.

3. Analysis Fig 8. Test number vs TOT

The authors made two prototype ELCB circuits(New- ELCB1 and New-ELCB2 in Table 1) with two bi- As we see in Table 1, the mean value of TOT for new directional IC inputs. A test has been performed to ELCB1 was measured at 6.9ms at 22.5mA and new measure the TOT and the results have been compared ELCB2 was measured at 6.0ms at 21.3mA. with two existing ELCDs in the current market. These imply that the TOT of existing ELCBs can be (Existing-ELCB1 and Existing -ELCB2 in Table 1) reduced almost to 1/3(≒three times faster) with newly- designed ELCBs. Though the proposed electronic-type ELCB with full- Table 1. Test results of ELCB TOT wave detection can drastically reduce ToT, however, we

Sensiti Test number and TOT [ms] can imagine the following disadvantages.

vity 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Firstly, additional OP-amp for full-wave detection ELCB Curre R may increase production cost of ELCB electronic circuit. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 nt Secondly, additional OP-amp circuit for full-wave

New- 22.5 8 8 4 8 4 7 9 8 8 8 9 7 9 9 9 detection may results in narrower layout space in PCB. 6.9 5 ELCB1 mA 5 6 5 7 8 4 4 5 6 7 8 8 4 8 8 Thirdly, electronic circuit of ELCB may become

New- 21. 8 4 8 6 6 7 4 8 8 5 7 4 6 4 5 vulnerable to attack of external surge or noise due to 6.0 5 ELCB2 3mA 4 4 5 8 9 8 6 4 6 4 8 4 5 9 5 cramped layout space.

Existing 22.7 24 25 12 23 14 20 19 21 20 22 22 24 26 20 22 The authors tested a prototype ELCB including „Surge 19.8 15 -ELCB1 mA 20 16 24 12 15 27 14 25 21 19 16 21 23 14 13 Immunity Test‟ and „Test of Immunity to conducted disturbances induced by radio-frequency fields‟ and „Test Existing 21.6 17 16 14 22 18 27 24 22 18 16 25 21 16 13 16 18.3 15 of Radiated, radio-frequency electromagnetic field‟ at an -ELCB2 mA 14 22 18 22 15 17 17 12 13 24 19 24 14 12 21 authorized testing institute[32], which showed no

malfunction or other unusual behavior of prototype

ELCB. Detailed test items of prototype ELCB is listed in We can see in Table 1 that 19.8ms of existing TOT of Appendix. existing ELCBs can be reduced to 6.0ms with new

ELCBs with two OP-amps. Trip operation time of two existing ELCBs was measured from a minimum of 12ms 4. Conclusion to a maximum of 27ms.(Range of measurement=15ms)

Trip operation time of two new ELCBs was measured TOT of ELCB depends on the magnitude of leakage from a minimum of 4ms to a maximum of 9ms.(Range current and the duration time of leakage accident. of measurement=5ms) Existing ELCB1 was measured at The ICs in electronic type ELCB of present market are 19.8ms at 22.7mA and existing ELCB2 was measured operated only within the reverse half cycle of sinusoidal at 18.3ms at 21.6mA. Fig 8. illustrates the graph of test leakage current. For fundamental reduction of TOT of number vs TOT of ELCBs. ELCB, however, it is essential for the ICs to be able to

detect the full-wave input signal.

The authors in this paper developed an electronic circuit in which the delay factors are optimized and by 4

IEICE Electronics Express, Vol.xx, No.xx, xx-xx which the full-wave leakage signal is measurable to and Electrical Installation Engineers, vol 26, No 12, (2012) pp.44- obtain minimum TOT. 49. As the result of experiment, the longest TOT of [5] Korea Electric Association: “Technical guideline on the Low- existing ELCBs was 27ms under 30mA of rated voltage electric circuit ground fault protection,” Korea Electric sensitivity current while the longest TOT of newly Technology Standards Committee, Korea Electric Association, developed ELCB showed 9ms, which implies TOT of KECG 9101-2003, (2003), pp.34-36. ELCB can be improved three times faster. Needless to [6] IEEE Std 80-2000(Revision of IEEE Std 80-1986), IEEE Guide say, the faster the TOT of ELCB, the less the electrical for Safety in AC Substation Grounding, Sponsor Substations damage to human body. Committee of the IEEE Power Engineering Society, Approved 30 Faster trip operation of ELCB proposed in this paper (2000). will contribute to preventing property loss by fire and [7] IEC 61200-413 : Electrical installation guide - Part 413: electric shock to human body from current leakages Protection against indirect contact Automatic disconnection of accidents. supply, Table A, (2007). In particular, it would significantly improve the [8] Korea Electric Association: “A study on the Installation Guide of electric safety in wet areas such as a swimming pool, the Residual Current Protective Devices for Protection Against medical institutions and welfare facilities for children Electric Shock on the Human Body,” Seoul National University of and the aged. Science and Technology, Korea Electric Association, Ministry of Knowledge Economy, pp.67-68, (2002). [9] Mitsubishi Electric Advance: “Latest Low-Voltage Circuit Acknowledgement Breakers,” (2011), https://www.mitsubishielectric.com/en/about/rd/advance/pdf/vol1 This study was supported by the Korea Institute of 33/133_complete.pdf Evaluation and Planning. Ministry of Commerce, Industry and Energy. (Project No. [10] Fuji Electric: “Molded case circuit breaker/earth leakage circuit 20182220200550) breakers,” (2019), https://www.fujielectric.com/products/mccb_elcb/ [11] Fuji Electric: “Miniature circuit breakers: BE1 series,” (2019), Conflicts of interest http://www.fujielectric.com/products/mccb_elcb/mcb_be1.html [12] LSIS: “Case Circuit Breakers / Earth Leakage Circuit Breakers,” The authors declare no conflict of interest. (2019), http://www.lsis.com/ko/search/?k=elcb [13] EL-PRO-CUS: “Difference Between MCB, MCCB, ELCB, RCCB And Its Characteristics,” (2019), References https://www.elprocus.com/difference-between-mcb-mccb-elcb- rccb/ [1] Charles F. Dalziel, and W. R. Lee: "Reevaluation of Lethal [14] Cornel Stanca, Lia Elena Aciu: "Aspects Regarding the Electric Currents" IEEE Transactions on industry and general Performance of Differential Current Measurement," TEM Journal. applications, vol. IGA-4, no. 5, (1968), pp.467-475. Volume 6, Issue 4 (2017), pp.810-816. [2] Mitsubishi Electric: “Moulded Case Circuit Breakers”, “Earth [15] Yan Zhou, Hui Li: "Analysis and Suppression of Leakage Current Leakage Circuit Breakers”, Technical Notes, pp.98-116. in Cascaded-Multilevel-Inverter-Based PV Systems," IEEE [3] Ju-Chul Kim, Moon-Soo Seo, Dong-Suk Jang, Sook-Hyun Cho, TRANSACTIONS ON , Vol.29, No. 10, Yoon-Tak Han, Sang-Joong Lee: “Improvement of Leakage Trip (2014), pp.5265-5277. Operation Time through Electronic Circuits Analysis of the [16] Yongzhe Shi, Jianyuan Xu, GuannanWu: “Research on Rural Circuit-Breakers for Human Body Protection Against Electric Indoor Cable Leakage Detection and Localization,” CICED 2016 Shock”, Journal of the Korean Institute of IIIuminating and Xi‟an, (2016), pp.10-13. Electrical Installation Engineers, vol 30, No 8, (2016) pp.60-66. [17] Mohamed Youssef Tarnini, Nabil Abdel-Karim, Khaled Chahine: [4] Ju-Chul Kim, Sang-Joong Lee: “Improvement of Circuit-Time “Simulation of Leakage current and THD Compensation in a Product through Analysis of Operating Time of Earth Leakage Large PV system,” International Journal of Applied Engineering Circuit-Breakers”, Journal of the Korean Institute of IIIuminating Research ISSN 0973-4562 Volume 12, Number 19, (2017), pp.8602-8608. 5

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