Research Article
Development of fast electronic overcurrent protection circuit using current-adjustable sensing method
Advances in Mechanical Engineering 2018, Vol. 10(4) 1–7 Ó The Author(s) 2018 DOI: 10.1177/1687814018772916 journals.sagepub.com/home/ade
Hsiung-Cheng Lin1 , Bo-Rong He2, Heng-Chuan Zo1 and Kai-Chun Hsiao1
Abstract Traditional methods to protect the electric-driven facilities from overload or short circuit usually use electronic breaker or fuse. However, the reaction time for these devices normally require more than 0.1 s that may be not sufficiently fast to disconnect the power supply for protection. For this reason, this article develops a fast and simple electronic overcurrent protection circuit based on the current-adjustable sensing method. First, the load current is sensed and converted to a voltage signal using Hall sensor. Then, the signal is amplified and compared with the predefined threshold value, that is, the maximum tolerance current, using amplifier and comparator, respectively. The timer will generate a pulse signal input to the trigger circuit for rapidly switching off alternating current power once the load current exceeds the tolerance value. The alternating current power disconnection can continue for a period of time set by the timer in advance. The experimental results prove that the proposed circuit takes less than 10 ms and it is significantly fast to react for facility protection in time. Keywords Short circuit, current sensor, overload protection, fuse, breaker
Date received: 12 April 2017; accepted: 26 March 2018 Handling Editor: Jining Sun
Introduction An increasing growth in world economics has posted a tremendous demand for electrical power. The shortcircuit fault current is, probably, the most destructive event in the power distribution systems.1 The current can abruptly rise more than 20 times the maximum nominal value. If the protection circuits work properly, it may just cause loss of service, undervoltage, or overvoltage transients, and loss of synchronization. However, in a serious case, an extreme surge of power may penetrate the equipment and sequentially cause explosion or fire. A fuse is a simple, cheap, and small-sized protective device that can be used to interrupt fault currents.2,3 However, it is unrecoverable due to being a single-use device, and its reaction time may be longer than
expected in some circumstances. The electronic breaker (EB) is known as the most widely used devices to protect the facility from overload in industry.4–7 Although EB can be reset automatically, it has a limited lifetime, number of cycles, and long reaction time.8,9 High cost to cope with the rising fault current levels is another disadvantage. Recently, a fault current limiter (FCL) 1
Department of Electronic Engineering, National Chin-Yi University of Technology, Taichung, Taiwan (ROC) 2 Aeronautical Systems Research Division, National Chung-Shan Institute of Science and Technology, Taoyuan, Taiwan (ROC) Corresponding author: Hsiung-Cheng Lin, Department of Electronic Engineering, National ChinYi University of Technology, No.57, Section 2, Zhongshan Road, Taiping, Taichung 41170, Taiwan (ROC). Email:
[email protected]
Creative Commons CC BY: This article is distributed under the terms of the Creative Commons Attribution 4.0 License (http://www.creativecommons.org/licenses/by/4.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/ open-access-at-sage).
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Figure 1. Structure of the proposed short-circuit protection circuit: (a) system block and (b) control flow chart.
has given an alternative solution.10,11 FCLs can bring in several advantages to the electrical power protection. In the event of a fault, the impedance of the FCL can rapidly increase to reduce the fault current flow so that it is able to prevent transformer damage and mitigate voltage dips on the medium-voltage bus. However, FCLs require more complex circuit design with nonlinear elements, inductive devices, semiconductor, and superconductor technologies, resulting in a high cost.12–15
Design of the proposed circuit The proposed short-circuit protection circuit is shown in Figure 1. It mainly contains four parts: (1) currentsensing circuit, (2) amplifier and comparator, (3) timer circuit, and (4) trigger circuit, where the system block is shown in Figure 1(a). The operation procedure for the proposed protection strategy shown in Figure 1(b) is described as follows. (1) Sense the load current using a Hall effect sensor that can provide an output voltage proportional to the load current. (2) Amplify the output voltage and then compare it with the reference value that is defined as the maximum tolerance load current Imax . (3) If the output voltage exceeds the reference value, the timer will generate a pulse signal and thus drive the trigger circuit for turning off the triac. On the other hand, the triac remains on if the load current is below Imax . In other words, the trigger circuit will not receive any pulse signal from the timer. The function of delay time timer(m) is defined as follows timer(m) =
1 others 0 continue for m seconds
Figure 2. Current-sensing circuit.
y(x) =
1 0 + timer(m)
x\Imax x Imax
ð2Þ
where x denotes the load current. As defined above, y(x) = 0 will continue for m seconds once x Imax ; y(x) will return to 1 after m seconds.
Current-sensing circuit ð1Þ
where m can be set by the timer in advance. The trigger signal y(x) is used to control the triac and defined as follows
The proposed current-sensing circuit shown in Figure 2 is designed to detect alternative current using Hall effect–based linear current sensor IC (ACS712), where its output voltage is proportional to the amount of load current. Two sensors are involved to measure
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Figure 3. Amplifier and comparator circuit.
alternating current (AC) 110 V/220 V current for the positive cycle and negative cycle, respectively.
Amplifier and comparator The amplifier and comparator circuit is shown in Figure 3. The input signal of amplifier (HA17358) is obtained from the output of current-sensing circuit, and it is amplified 13 times. Once the output signal of amplifier goes beyond the predefined value (reference point) of comparator (HA17393), the output signal of the comparator will change to a high voltage from a low voltage (0 V).
Figure 4. Timer circuit.
Timer circuit The proposed timer circuit is shown in Figure 4. Its input signal is connected with the output of comparator, and the output signal is connected to the trigger circuit. Once the load current is detected exceeding the predefined value, a pulse signal, known as a trigger signal, is produced by the timer (NE555) to drive the trigger circuit for interrupting the AC power supply. The pulse duration time, that is, delay time, is set as T = 1.1*R1*C1=1.1*10 K*220 uF = 2.42 s.
Trigger circuit The trigger circuit is shown in Figure 5. In a normal situation, the load can continue to work with the AC power, where the triac is kept on. In an over-current or short-circuit case, a trigger signal generated from the timer circuit will turn off the triac and then disconnect the AC supply promptly. Note that the triac (BAT41) is combined with Optoisolators Triac Driver (MOC3020).
Experimental results Setup of test platform To verify the proposed model, the test platform was set up as shown in Figure 6. Three switches are installed for testing different cases:
Figure 5. Trigger circuit.
Test 1: AC short-circuit protection test. In this test, the fuse is installed in series with the triac. When AC is short-circuited by pressing the button switch A, the triac cuts AC power instantly but the fuse does not burn out. This can prove that the triac response is faster than the fuse. Test 2: Over-current protection test. Two types of 3 and 3.4 A load currents can be selected, where 3 A is the predefined over-current value. If the switch B is pressed, the load current will change to 3.4 A immediately and thus it exceeds 3 A. At that time, the AC power will be disconnected at once for the load protection. Case 1: 3 A over-current test. Consider the predefined over-current value is set as 3 A. In a normal situation, the load current is provided 3 A continuously. When
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Figure 6. Profile of test platform: (a) the block of test platform circuit and (b) real test system.
Figure 7. The 3 A over-current waveforms: (a) protection action waveforms and (b) partial enlarged view.
the load current is switched to 3.4 A load, the AC power is disconnected immediately within 5 ms. The measured signals for load current and trigger signal are shown in Figure 7(a), where the switching duration represents the switch action time. The partial enlarged view for overcurrent transient state is shown in Figure 7(b) (blue line: load current, yellow line: trigger signal). The same depiction applies to the below results (Figures 8–10), where the current value presented is 1.5 A/grid.
Case 2: Load short-circuit test. In this test, the load is short-circuited straight away and it results in the source current largely rising up immediately, as shown in Figure 8(a). It is seen that the instant maximum current does not exceed 6 A, and the reaction time takes less than 10 ms. In another case, the power supply (12 V) of load is short-circuited directly, and the instant maximum current rises up to 7.5 A, taking only 2.5 ms to shut down the power supply, as shown in Figure 8(b). As defined above, it confirms that the proposed circuit
can carry out the sufficient load protection in time for above two cases. Note that the current value presented is 1.5 A/grid.
Direct power supply short-circuit test Consider the most severe test for power supply shortcircuited from AC 110 V and AC 220 V, respectively. Case 1: Direct AC 110 V short circuit. In this test, AC 110 V is short-circuited directly, and the instant maximum current is 3.63 A, as shown in Figure 9. It takes only 5 ms to disconnect the power completely, where the current value presented is 0.66 A/grid. Case 2: Direct AC 220 V short circuit. In this test, AC 220 V is short-circuited directly, and the instant maximum current is 9 A, as shown in Figure 10. The disconnect of the power supply takes only 10 ms to complete, where the current value presented is 1.5 A/grid.
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Figure 8. Short-circuit waveforms: (a) action waveforms with load and (b) action waveforms without load.
Figure 9. AC 110 V short-circuit test.
Practical performance To carry out the practical performance of the proposed model, the induction cooker (Kolin CS-SJ005; 1300 W) shown in Figure 11(a) was used as the load, and the practical circuit system is shown in Figure 11(b). The operation waveform of for load current is shown in Figure 12. It is noted that only about 1 A is required in the initial period due to only a cooling fan working at the beginning when the induction cooker is turned on. In the first operation test, the mode 3 is selected, demanding 11 A load current. In the second operation test, it switches to the mode 4 that demands up to 14 A; the load current thus rises rapidly beyond 12 A (defined as an over-current value) at this case. Consequently, the power supply is cut down immediately less than 5 ms. After 8 s, the power supply returns to a normal status again.
Figure 10. AC 220 V short-circuit test.
Comparison with existing devices Table 1 concludes the comparison between the commercial products and the proposed circuit from the view of size, construction, cost, and response time. Generally, it indicates that the proposed circuit is superior to existing products, particularly in response time (\10 ms) for sufficiently protecting the electrical facilities from overload or short circuit.
Conclusion The commercial fast-blown fuse can react for load protection within 50 ms so that it is still widely applied in industry. However, it is unable to recover after being burn out. Although the EB has recovery capability, but it usually takes more than 100 ms to react. This article
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Figure 11. The practical performance system: (a) induction cooker and (b) the proposed circuit.
Figure 12. The performance waveform of load current: (a) the performance waveform during three periods, (b) waveform before power shutdown, and (c) partial enlarged view when power shutdown.
has developed the fast over-current protection circuit based on current-adjustable sensing method successfully. In a predefined over-current test, the reaction
time requires only 5 ms. For the direct short-circuited situation, it can fast shut down the power supply no more than 10 ms that is still much speedier than
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Table 1. Comparison between different devices. Item
Fast fuse
Traditional breaker
The proposed circuit
Size Construction Cost Response time (ms)
Small Simple Very low ’ 50
Medium Complex Medium ’ 100
\Medium Medium \Medium \10
traditional products. In the most severe case such as direct AC 220 V short circuit, the instant maximum current does not exceed 9 A so that it can protect the facilities from damage in time sufficiently. Clearly, the practical results reveal that the proposed scheme is superior to traditional overload protection methods.
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Declaration of conflicting interests
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The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
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Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
ORCID iD Hsiung-Cheng Lin
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10. https://orcid.org/0000-0001-5531-9308
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