Application of distribution overload monitoring device ACM

Abstract: This article focuses on the principle, characteristics and main parameters of the ACM distribution line overload monitoring device, that is, by detecting the current in the distribution line, two-stage alarm is given to the line overload to avoid line protection due to overload Unnecessary loss caused by the action, and introduced the application of ACM in fire protection distribution lines and other important places.
Keywords: Fire protection overload monitoring two-stage alarm circuit breaker

1 The design of the ACM monitoring device is based on Article 4.3.5 of the "Code for Design of Low-Voltage Power Distribution" (GB 50054-95): "For a line that is suddenly powered off and has a greater loss than overload, its overload protection should be applied to the It should not be used to cut off the circuit. "The article states:" After all, the overload of the line is not short-circuited after all. Short-term overload does not immediately cause disaster. In some cases, the conductor can be operated beyond the allowable temperature, that is, sacrifice. Some service life to ensure that the power supply to certain loads is not interrupted, such as fire pumps and other loads, then protection can act on the signal. "
"Code for Electrical Design of Civil Buildings" JGJ 16-2008, Article 7.6.5, paragraph 4, stipulates that "for a sudden power failure, a line with greater losses than overload, the overload protection should act on the signal and not cut off the circuit." This is a mandatory provision and must be observed. There are two objects for overload protection: one is the fire-fighting equipment, that is, the motor; the other is the power distribution line for these fire-fighting equipment. This article mainly introduces the latter, that is, how to use ACM to realize the overload alarm function of distribution lines to meet the requirements of the mandatory provisions of the specification.
Miniature circuit breakers and molded case circuit breakers are commonly used in power distribution design. Among them, the miniature circuit breaker is mainly used for overcurrent protection in households and similar places, the rated current does not exceed 125A; most of the industrial occasions are plastic case circuit breakers. According to GB10963.1-2005, GB14048.2-2008 and above circuit breakers have their action breaking characteristics, see table 1:

Table 1 Distribution overload protection characteristics


According to Table 1, once the current in the distribution line exceeds a certain multiple, the circuit breaker will operate within the agreed time, thereby cutting off the load current. However, as mentioned above, "Sudden power failure will cause greater losses than overload" lines or motors are not allowed to cut off the power supply. Therefore, in these circuits, we need a device that can target different The tripping characteristics of circuit breakers of this type, such as detecting the overcurrent of the line through current transformers, and simulating the overload tripping characteristics of the circuit breaker as much as possible, providing an overload alarm signal to remind users that the line is overloaded, and take timely measures. On the one hand, prevent greater losses due to circuit breaker tripping to meet the requirements of the specification, on the other hand, remind people to promptly check to prevent greater failures.

2 Basic principle of ACM monitoring device
2.1 Principle of monitoring device
The ACM distribution line overload monitoring device adopts the latest 32-bit single-chip technology, which has the characteristics of strong anti-interference ability, stable and reliable work, digitalization, and networking. By detecting the current of the line, the two-stage alarm of the distribution circuit is realized. The monitoring device can have current, voltage, active power, reactive power, apparent power, power factor, leakage current measurement function, current 2-15 harmonic analysis function, built-in buzzer, indicator light alarm function, alarm event Recording, RS485 Modbus-RTU, Profibus-DP protocol communication interface, switch input, programmable relay output, DC4 ~ 20mA analog output, etc., it is convenient to form a network with industrial control equipment such as PLC and industrial control machine to realize remote monitoring of line operation . The hardware block diagram of the monitoring device is shown in Figure 1.

Figure 1 ACM hardware functional block diagram

2.2 Main functions
1) In the load current monitoring distribution circuit, the monitoring device can be used in conjunction with a miniature circuit breaker and a molded case circuit breaker (the circuit breaker at this time should be a single magnetic trip circuit breaker), and the alarm section is shown in Table 2. Taking a molded case circuit breaker as an example, when the load current exceeds the alarm 1 stage overload value 1.05In, the alarm 1 instantaneous alarm; when the load current exceeds the alarm 2 stage overload value 1.3In, in the (1.3 ~ 4) In range, the alarm delay When alarming, follow the principle of inverse time limit, the greater the load current, the shorter the alarm delay time. The time-current curve is shown in Figure 1, and the 1.3In action time can be set.

Table 2 Types of distribution line protection appliances

Figure 2 Time current curve

Table 3 Graph description


2) Leakage current monitoring By measuring the leakage current in the main loop, the leakage current is monitored, and an alarm is given through the D01 (95, 96) relay or internal buzzer.
3) The measurement function has the functions of measuring phase voltage, line voltage, phase current, overload percentage of current and rated current, active power, reactive power, power factor, frequency, leakage current and harmonics.

3 There are many applications of fire-fighting electrical equipment in fire-fighting occasions. In addition to fire-fighting water pumps, there are also fire elevators, smoke exhaust fans, and fire-proof rolling shutter doors. Some use electricity for electricity, and some belong to lighting; Some are not; some are only used for fire fighting, and some are used as fire fighting equipment for long-term use, such as exhaust and smoke exhausters, fire elevators and passenger elevators, normal lighting and emergency lighting. The nature of the load is different from the usage. For those equipment that are normally used for fire protection and their distribution lines, the most appropriate method is to adopt certain technical measures to achieve overload and cut off the power supply during normal use, and overload alarm in fire protection conditions. ACM series monitoring devices can be used:
1) When the load current exceeds a section of the alarm threshold, the monitoring device can issue an alarm indication through the indicator light, and the load current continues to increase. When the load current exceeds the second section of the alarm threshold, the monitoring device alarms through the indicator light and the buzzer;
2) Leakage current alarm function, which can perform leakage current alarm by measuring the leakage current in the line, which is also an effective method of fire monitoring;
3) The monitoring device can monitor the opening and closing status of the circuit breaker in the line through two-way switch input. In addition to the ACM monitoring device itself, it also has a programmable relay output, which can be used for one-stage alarm, two-stage alarm, and leakage current. Or the status of the circuit breaker is output, which is convenient for linkage control.
4) ACM monitoring device can have 4-20mA analog output, RS485 Modbus-RTU communication, Profibus-DP communication, which is convenient for host computer monitoring.

4 Application of ACM in practice

Figure 3 ACM3 overload monitoring device schematic

Figure 3 is a schematic diagram of the ACM distribution line monitoring device. In this figure, the ACM monitoring device is used in conjunction with a molded case circuit breaker. The molded case circuit breaker has two types of single magnetic and thermal magnetic. The single magnetic circuit breaker only has short circuit protection function and no thermal overload protection. In this case If there is an overload phenomenon in the line, the circuit breaker will not operate, and the ACM monitoring device will issue an alarm signal according to different overload levels to remind the on-site maintenance personnel, and it can also be transmitted to the control center. The thermal magnetic plastic case circuit breaker has both short-circuit protection and thermal overload protection. At this time, the ACM monitoring device can only function as an alarm function. When the detected current reaches the set threshold, the internal relay operates.
The current transformer used in the monitoring device uses Ankerui AKH-0.66 series current transformer. If the rated current of the distribution line is 32A, the transformer is AKH-0.66-60 / 5. This model has a 2In range measurement and monitoring device. The maximum continuous measurement current can reach 10A, so the device can monitor the overload current 4 times at most. For the occasions where the residual current loop needs to be monitored, the AKH-0.66L series residual current transformer must be installed. In the above figure, when the current of the distribution line exceeds the alarm threshold of stage 1, the relay (7, 8) is closed, the alarm output of stage 1, the KA1 coil is energized, and the PGR light alarm; when the load increases, the alarm threshold of stage 2 is reached, The relay (9,10) is closed, 2 alarm output, KA2 coil is energized, PG sound alarm. When the sound and light alarm release button is pressed or the load current decreases, the alarm state is released. The digital input can upload the opening and closing and tripping status of the circuit breaker to the background control center, and can also add a programmable relay relay for remote control or leakage current alarm output. For specific use, please refer to the description of the ACM overload monitoring device .

5 Conclusion
ACM series distribution line overload monitoring device is a two-stage alarm. The alarm follows the inverse time limit principle. The greater the overload, the faster the alarm speed, which meets the site conditions. At the same time, the design method of the device meets the requirements of the standard well, and it is worthy of use by electrical designers.

The article comes from: "Intelligent Building Electrical Technology", Issue 3, 2011.

references
[1] Li Binghua. On the application of new technology of building electrical [J]. Electric technology of intelligent building, 2010.6.
[2] Tang Ming. Overload protection of fire fighting equipment and its distribution lines [J]. Low-voltage electrical appliances, 2009 supplement.
[3] Wu Weiguang. Discussion on overload protection of fire-fighting electrical equipment [J]. Building Electrical, 2007-06.
[4] Yao Bo, Lu Weiqing. Design and application of an overload monitoring device for distribution lines [J]. Electrical Technology, 2010-11.

About the Author:

Yu Jing, female, undergraduate, engineer of Wuhan Ankerui Electric Co., Ltd., the main research direction is intelligent power monitoring and power management system

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