Helpful information. Do I need to take into account the inrush currents of LED lamps? Circuit breakers for protecting LED luminaires
Over the past five years, LED lights have gone from exotic gadgets for green lifestyle enthusiasts to everyday items. Therefore, it is not surprising that the installation of such lamps is increasingly being carried out not by top-class engineers as part of projects of national importance, but in the most ordinary offices by ordinary electricians or in general by people who have only the most basic understanding of electricity. And what a disappointment it can be when, when turning on seemingly “economical” LED lamps, a circuit breaker is triggered, chosen, it seems, in compliance with all the rules. Or a paradoxical situation arises when, when replacing fluorescent lamps with LED ones, a fuse is triggered, which previously “held” very “gluttonous” Soviet-made devices without any problems. It's time to lose faith in the efficiency of LED lamps. Problems arise because the most important parameter of any lamp is not taken into account - the inrush current value. Moreover, this approach is imposed by the lamp manufacturers themselves, who often claim that their products simply do not have inrush currents.
When an electrical device is turned on, transient processes are usually observed. In addition, starting the device may require more power than in steady state. Because of this, a phenomenon called inrush current is observed. The inrush current value is equal to the maximum input current value when the device is turned on. The inrush current is expressed either in absolute values or as a multiple of the maximum value of the input current divided by the current consumed in steady state. Another important value is the duration of the inrush current - the time during startup during which the input current of the device exceeds the current consumption in steady state.
The presence of inrush current is typical even for such an “ancient” and simple light source as an incandescent lamp. A tungsten filament in a cooled state has a resistance 10-15 times less than when heated to the temperature when it glows. Accordingly, the starting current of an incandescent lamp is 10-15 times greater than the current consumed in steady state.
This, by the way, is why incandescent lamps (and halogen lamps, which are similar in operating principle) most often fail when turned on.
In discharge light sources, upon startup, energy is spent on creating plasma between the electrodes, that is, an electrical discharge that produces a glow. Such light sources include, for example, sodium lamps, metal halide lamps and fluorescent lamps. Data on the frequency of starting currents and their duration can be found in Table 1.
Table 1. Trigger parameters for traditional light sources
The table shows that incandescent lamps and halogen lamps have the highest inrush current ratio. But transition processes occur faster in them. The start-up time of discharge lamps, especially HPS and MGL, is much longer, which forces significant current reserves to be included when calculating wiring.
Time-current characteristics of protective circuit breakers
Modern circuit breakers ensure that the circuit opens when at least one of two events occurs - a prolonged excess of current consumption I above nominal value I n and short circuit. In the first case, an inertial process of opening the bimetallic contacts occurs when heated. Opening occurs when a current of 1.13 I n more than 1 hour or current 1.45 I n less than one hour. In the second case, an electromagnet is instantly triggered, opening the contacts. Response time graph t c from the ratio I/I n called time-current characteristic.
Existing time-current characteristics are divided into three main groups: IN, WITH And D. Classification is carried out according to the relative value of the current I short, in which an instantaneous electromagnetic trip occurs, that is, when the machine detects a short circuit. For group B the value I short ranges from 3 to 5 I n, For WITH- from 5 to 10 I n and for D- from 10 to 20 I n. The lower limit corresponds to a response time of 0.1 s, the upper limit - 0.01 s. In relation to lighting systems, circuit breakers with the characteristics IN And WITH, devices with characteristic D are used to protect powerful electric motors, as well as at the input of large electricity consumers.
When designing electrical installations, reliable protection against short circuits at the ends of the wires is a prerequisite. The smaller the cross-section of the wires, the greater their resistance and, accordingly, the lower the ratio I kz / I n. At the same time, the smaller the cross-section of the wires, the cheaper they are. That is why, when designing lighting systems based on traditional sources, previously, by default, machines with the characteristic IN.
Do LEDs have inrush currents?
According to its physical principle of operation, the LED does not have any inrush currents - it begins to produce light almost immediately after electric current is applied to it, without any transient processes. This circumstance allows some manufacturers of LED lamps to claim that their products allegedly also do not have inrush currents. In fact, this is not always the case.
LED lamps built according to the so-called driverless scheme [L] really do not have inrush currents. But due to the high level of light flux pulsations, the scope of application of such lamps is limited.
To protect lighting systems based on traditional light sources, automatic machines with characteristic B were used by default
In LED lamps powered by alternating current and intended for widespread use, as a rule, a capacitor is installed to smooth out ripples. When the lamp is turned on, this capacitor is charged, causing a sharp increase in current consumption. This is how the concept of inrush currents becomes applicable to LED lamps.
Calculations show that for certain types of drivers, the circuit breaker is triggered when simply replacing fluorescent lamps with LED lamps, even if the current consumption in steady state after the replacement has become less. This problem can often be solved by replacing the machine with the characteristic IN WITH.
The same can be applied to LED retrofit lamps powered by AC power (with the exception of the simplest driverless models). If the luminaire uses a driver in the form of a separate module, the multiplicity of the starting current and the duration of the starting current are determined by this particular unit. Starting characteristics for some drivers from leading manufacturers are shown in Table 2.
Table 2. Starting characteristics of some driver models with 230 VAC input voltage
| Rated current consumption at full load, A | Starting current ratio | |||||
|---|---|---|---|---|---|---|
| For characteristic B | For characteristic C | For characteristic B | For characteristic C |
|||
| Mean Well LPC-35-1050 | ||||||
| Mean Well ELN-30-12 | ||||||
| Osram Optotronic Fit 50/220 | no data | no data |
||||
| Osram Optotronic Element LD 30/220 | no data | no data |
||||
| Philips Xitanium Constant Current Xtreme | no data | no data |
||||
The table shows that the inrush current multiplicity of LED lamps with drivers exceeds traditional lamps by one or two orders of magnitude!
The inrush current multiplicity of LED lamp drivers is several hundred due to the presence of smoothing capacitors
In addition, the duration of the starting current for LED drivers is usually determined at 50% of the maximum value. This value, as a rule, lies in the range of 100-500 µs. However, such a short pulse can trigger an electromagnetic circuit breaker, but calculating its action is not as simple as for the inrush currents of traditional light sources.
K = I nd / I p ,
Where I nd- rated current of the circuit breaker in terms of one driver, I p- driver current consumption in steady state at full load.
The less TO, the less likely it is that a situation with a false triggering of the circuit breaker will occur. Coefficient TO always more I, it depends on the characteristics of the machine. For circuit breakers with characteristic B coefficient TO higher than or equal to the coefficient for the characteristic WITH.
Now let’s find out where the situation with “knocking out traffic jams” arises when replacing, for example, fluorescent lamps with more economical LED ones. Let's assume that we are solving the problem of replacing old fluorescent lamps of the LPO 4x18 type with modern ones. We have a fluorescent lamp with steady state current consumption I l. The designers took into account the starting current multiple of 1.5, the fact that the duration of the starting current in real conditions can reach tens of seconds (for example, the lamp does not light up the first time) and took an additional safety factor of 1.25. Then the rated current of the circuit breaker will be
I nl= 1,5 1,25 I l= 1,875 I l
When replacing fluorescent lamps with LED lamps with the same luminous flux, energy consumption is reduced by approximately 2 times. This means that the current consumption of the new lamp is I s = 0,5 I l, and the rated current of the circuit breaker I ns = 0,5 K I l.
We use a lamp with a mid-price driver Mean Well LPC-35-1050. For him, when characterizing IN we have TO = 5,7.
I ns = 0,5 5,7 I l = 2,85 I l > I nl
This means the circuit breaker has tripped.
For a machine with the characteristic WITH we have TO= 3.3, then
I ns = 0,5 3,3 I l = 1,65 I l < I nl.
False activation of the circuit breaker during startup will not occur.
That is, the problem with “knocking out traffic jams” can be solved by replacing the machine with the characteristic IN for a machine with characteristics WITH and the same rated current. But at the same time, you should make sure that after replacing the machine, the short-circuit current standards for the existing wires will be observed. The specific calculation method is beyond the scope of this article; it can be found in reference books for electricians.
Leading luminaire manufacturers usually provide information on the recommended types of circuit breakers and the maximum number of devices that can be connected to one circuit breaker. If such information is not available, you should find out the model of the driver used in the luminaire and find recommendations on the driver manufacturer’s website.
If it is impossible to replace a machine with the characteristic IN for a machine with characteristics WITH and partially re-arrange the wires in order to comply with the driver (luminaire) manufacturer’s recommendations for the maximum number of devices connected to one machine.
Selecting a circuit breaker
Ideally, the manufacturer himself should indicate in the documentation for the luminaire the recommended type of circuit breaker and the maximum number of luminaires that can be connected to it in parallel. In reality, this does not always happen; moreover, as already noted, manufacturers often hide the very fact that the lamp has any inrush currents. You can ask the manufacturer for the driver model and find out the data on the website of the manufacturer of this node. Driver manufacturers are increasingly publishing this information on their websites.
The manufacturer may offer a choice of using machines with characteristics such as IN, so WITH. If the project requires connecting the maximum number of luminaires to one circuit breaker (for example, there are difficulties with laying wires or there is no space to install extra circuit breakers), then preference should be given to the characteristic WITH. But then, as already noted, it will be necessary to provide additional margin for the thickness of the wires.
If recommendations for selection are not given for an LED lamp and there is no way to obtain information about the driver model, you actually have to “play roulette” with an unpredictable result. But there are all sorts of rules of thumb, for example, do not connect more than 8 LED lamps to one machine, use machines with the characteristic WITH instead of characteristics IN and so on. These measures make it possible to ensure reliable operation of the lighting system at the cost of introducing excess technological reserves. This is why the availability of driver or luminaire manufacturer recommendations for the use of circuit breakers is an additional competitive advantage.
Combating high inrush currents
The topic of tripping circuit breakers when replacing lamps with traditional light sources with LED ones, constantly discussed in specialized Internet forums, has already attracted the attention of electronics manufacturers. Abroad, all sorts of devices have appeared on the market that, according to their manufacturers, are capable of limiting inrush currents. Typically, the operating principle of such devices boils down to the fact that during startup, a resistor is switched in series with the lamp, which reduces the starting current. As a result, the smoothing capacitor in the driver charges more slowly and the startup time increases, but this is almost imperceptible to users. The disadvantage is that such current limiters are not compatible with all drivers.
Another method, which, according to the author of the article, is more promising, is the use of drivers with a slight start delay, the time of which in the batch varies from instance to instance. The delay time for each driver during their production is set randomly or according to a certain pattern. As a result, the simultaneous launch of two or more drivers is unlikely or completely excluded. Adding such a function slightly increases the cost of the driver, but due to savings on installation work, the increase in price pays off many times over.
Literature
// Electrical market, No. 1 (73), 2017, pp. 16-20.
Alexey VASILIEV
To protect electrical circuits from overloads and short-circuit currents, automatic circuit breakers (automatic circuit breakers) are used in industry and everyday life.
They come in 3 types:
- Air - industrial use for currents of thousands of A
- Molded case - designed for a wide range of currents 16-1000A
- Modular - for domestic use
In everyday life, modular circuit breakers are used to protect electrical wiring and electrical appliances. They have a standardized width, a multiple of 17.5 mm.
Main functions of circuit breakers:
- Electrical circuit switching. Manually turns off or on an electrical circuit
- Automatically turns off when network overload occurs
- Automatically breaks the power grid when a short circuit occurs.
To choose the right circuit breaker, you need to be able to read its markings:
- At the top is the manufacturer's mark
- Catalog serial number
- Next comes the size of the rated current for which this circuit breaker is designed.
- Rated mains voltage.
- Short circuit current (Maximum breaking capacity)
- Current limiting class.
Circuit breaker device
The circuit breaker housing is made of plastic. Using terminals, the machines are mounted on a DIN rail.
The main element is an electromagnetic splitter with a metal core. When a current exceeding the norm passes through it, the core is pushed out and moves the mechanism of the splitting device - the circuit opens.
Another element with which contacts can be opened is a bimetallic plate, which acts as a heat splitter. Different metals have different melting points. Most often, circuit breakers use bimetallic plates made of steel and brass. When the load on the machine increases above normal or a short circuit current passes, the plate bends, setting the shutdown mechanism in motion. When cooled, the bimetallic plate straightens and the contacts close. The melting (distortion) temperature of the plate is calibrated according to the current rating specified on the specific circuit breaker.
The arc arrester is designed to protect other elements of the circuit breaker during heating of the bimetallic strip, since it can heat up to a very high temperature during a malfunction.
Classification of circuit breakers.
- Single pole. They are used in single-phase electrical networks. It is single-pole switches that are most often used in everyday life. Electric current is supplied to the bottom terminal, and the phase is supplied to the top. When passing an increased load, the circuit opens.
- Bipolar, which consists of two single-pole circuit breakers. The shutdown blocking is made so that the phase is turned off before zero.
- Three-pole. They are used for three-phase power supply. This is already a design of combined three single-pole circuits that are switched off simultaneously in the event of an emergency.
In the Synergy Stroy online store you can buy automatic switches from leading manufacturers for various electrical circuits. We deliver throughout Moscow; we send orders to the regions by transport companies. You can pay for your purchase using a bank card, through payment systems or in cash, in cases of self-pickup of goods from the warehouse. We work for you 6 days a week. Call, come!
Our company "Yug-Service" (Rostov-on-Don) is engaged in wholesale and retail supplies of various products related to LED lighting. In the catalog you will find circuit breakers from the Italian brand Legrand, as well as miniature surge protection modules. Automatic machines (type C) differ in current strength - from 10 to 63 Amperes. Protection modules are designed for voltages up to 1.2 kV.
Switches with surge protection
We offer Legrand MCB circuit breakers (type C) in six modifications: 10 A, 16 A, 25 A, 32 A, 40 A and 63 A. These devices provide reliable protection of electrical equipment from voltage surges, line overloads and other emerging problems . In addition, circuit breakers (type C) provide effective protection of humans from high voltage.
Protection modules are manufactured in South Korea and are intended for lighting equipment. They protect lamps of various types from voltage surges. The maximum lamp power is 15 W.
Type C modules and circuit breakers
Our company sells Italian circuit breakers (type C) only in wholesale, modules - retail sale is possible, wholesale starts from 10 units. High quality products from trusted manufacturers are offered at very competitive prices. A detailed description of the products is posted on the website, or you can consult our employees. They have an excellent knowledge of the range and are always ready to help you make a choice and purchase the best electrical equipment. We work throughout the Russian Federation, and also supply goods to the CIS countries.
Electrical switchboards and various control panels are widely used in industries, public buildings, and there are also options for use in domestic conditions. Without exception, all electrical circuit control units can be equipped with special signal lamps, control buttons and various switches. This equipment has a variety of purposes and applications, but in general it performs the function of monitoring and managing electrical circuits or monitoring the functioning of various equipment.
Electrical panels, basically, are manufactured based on the user’s wishes according to an individual order, and are equipped with various control modules. Users actually build their own electrical circuits and, to monitor and control them, use various modules for all kinds of switching and light indication for process control. All modules installed in the electrical network are divided into two types: informing and control. There are also combined versions of modules that can perform both functions.
TO informing include all kinds indicator lights, which consist of two parts, namely the module itself and the lamp for light emission, and can be installed in any electrical panel or control panel. The indicator, operating on LEDs, has a long service life of 6000 hours. All light indicators can be quickly mounted or dismantled and have a large range of colors, so the user is not limited in any way when choosing these devices. This type of device is used on switchboards and control panels in order to quickly attract the user’s attention and indicate the ongoing process in real time. Any digital sensor or measuring device needs to be constantly monitored, and the indicator light simply lights up, thereby making it clear about the status of the process.
Control modules– these are all kinds of switches, toggle switches and just control buttons. This type of module can be fixed permanently or portable. Fixed modules are used in places where the technical process does not require movement. Various toggle switches can have a varied switching range, so the user can select the module he needs.
Some buttons and switches have special protection to prevent accidental pressing, which can lead to harmful consequences. This protection includes special caps on the buttons, or even locks that are inserted into the button itself, and you need to turn the key to activate the module. There are also buttons with a large cover, they are made for emergency termination of processes. Thanks to the large button, the user can simply hit it, thereby triggering the module, this is very effective in emergency situations.
All lights, switches and various control buttons, have good protection and can be exposed to any external influences.