Working with Switch Mode Power Supplies in Automation Applications

Power Supplies · Basics

2. Safety • Basic insulation Working with Insulation to provide basic protection against The safety of people and equipment is hazardous structure-borne currents. switch mode power always the priority. Accordingly, power • Supplementary insulation supplies in automation supplies must comply with unified regulations Protection against hazardous structure- and standards. borne currents if the basic insulation fails. applications • Double insulation 2.1 Galvanic isolation Insulation comprising both basic insulation

and supplementary insulation. A power supply has a decisive influence Galvanic isolation generally refers to the • Reinforced insulation on the availability and operational isolation between two conductive objects, Unified insulation system. Provides reliability of electrical systems. such as metal plates or electrical circuits. In equivalent protection to double insulation.

the case of electrical circuits it is Consequently, the selection of the right consequently not possible for charge carriers 2.3 Safe isolation power supply should be just as critically to flow from one circuit into another, as there and carefully undertaken as that of the is no electrically conductive connection Safe isolation according to EN 50178 is other system components. between the two. required for all interfaces between different Product electrical circuits, such as between a SELV FOCUS 1. General structure circuit and a mains circuit. In the case of power supplies this means that

Regardless of the technology employed, there is no electrical connection between the Safe isolation means that no current flow can power supplies are devices with an input side input and output sides. occur from one electrical circuit to another. and an isolated output side. This isolation has to be implemented either by 2.2 Insulation double or reinforced insulation or by means of

The different kinds of insulation are specified protective shielding. in IEC/EN 60950: Input side Output side Efficiency in Automation 2.4 Secondary grounding Cable Connectivity • FunctionalCabinet insulationControl L L+ Insulation needed for the correct operation In case of secondary grounding, the output of the equipment. side of the power supply is connected to N protective earth (PE) in order to prevent dangerous ground faults. Working with PE L– switch mode In technology terms, however, there are two different basic designs: power supplies Unregulated and regulated. in automation The regulated variants are subdivided into linear-regulated and switched-mode power applicationsPower Supplies · Basics supplies.

2. Safety • Basic insulation L L+ Working with Insulation to provide basic protection against The safety of people and equipment is N A powerswitch supply mode has a decisive power influence on the hazardous structure-borne currents. always the priority. Accordingly, power • Supplementary insulation PE L– availability and operational reliability of electricalsupplies must comply with unified regulations Protection against hazardous structure- supplies in automation Power Supply systems. and standards. borne currents if the basic insulation fails. applications • Double insulation 2.1 Galvanic isolation Insulation comprising both basic insulation Secondary grounding

Consequently, the selection of the right power and supplementary insulation. A power supply has a decisive influence Unregulated Regulated Galvanic isolation generally refers to the • Reinforced insulation supplyon the should availability be just and as operationalcritically and carefully A ground fault occurs if a current-carrying line isolation between two conductive objects, Unified insulation system. Provides reliability of electrical systems. such as metal plates or electrical circuits. In equivalent protection to double insulation. has contact to earth. In the worst case, two undertaken as that of the other system the case of electrical circuits it is simultaneous groundn f aults ca lead to a Consequently, the selection of the right components. consequently not possible for charge carriersLinear -regulated2.3 Safe isolation Switched-mode power supply should be just as critically bridging of switches and thus can start to flow from one circuit into another, as there and carefully undertaken as that of the equipment accidentally. is no electrically conductive connection Safe isolation according to EN 50178 is other system components. 1. General structure between the two. required for all interfaces between different Power failure buffering Secondary Primary electrical circuits, such as between a SELV Switched-mode Switched-mode Power Factor Correction (PFC) Regardless1. General of structure the technology employed, power circuit and a mains circuit. In the case of power supplies this means that suppliesRegardless are devices of the technology with an inputemployed, side and an there is no electrical connection between the Safe isolation means that no current flow can power supplies are devices with an input side input and output sides. isolated output side. occur from one electrical circuit to another. and an isolated output side. The key criteria in selection of a power supply 2. Safety This isolation has to be implemented either by 2.2 Insulation are: Input side:The keyOutput criteria side: in selectiondouble of aor power reinforced supply insulation are: or by means of Input side Output side The safety of people and equipment is always The different kinds of insulation are specified protective shielding. in IEC/EN 60950: the priority. Accordingly, power supplies must Input side Output side Input side: Output side: Ground fault Input voltage Output voltage2.4 Secondary grounding comply with unified regulations and standards. • Functional insulationInput voltage Output voltage L L+ InsulationPrimary needed grounding for the correctSecondary operation groundingIn case of secondary grounding, the output If secondary grounding is used, the Primary grounding Secondary grounding of the equipment. side of the power2.1 supplyGalvanic is connected isolation to occurrence of such a ground fault leads to a N Current consumption protective earthShort (PE)-circuit in order current to prevent Current consumption Short-circuit current so-called short circuit to earth which causes dangerous ground faults. PE L– Inrush current ResidualGalvanic ripple isola tion generally refers to the the fuses in the secondary circuit to trip. Inrush currentInput fuse Residual ripple Output characteristics isolation between two conductive objects, such Frequency Output current In technologyIn technology terms, terms, however,however, therethere are are two two Input fuse DC supply Output characteristics as metal plates or electrical circuits. In the different basic designs: case of electrical circuits it is consequently not different basic designs: Frequency 10 Output current Unregulated and regulated. possible for charge carriers to flow from one Unregulated and regulated. DC supply circuit into another, as there is no electrically The regulated variants are subdivided into Thelinear regulated-regulated variants and switched are subdivided-mode power into Power failure buffering conductive connection between the two. supplies. linear-regulated and switched-mode power Power Factor Correction (PFC) In the case of power supplies this means that supplies. L there is no electrical connectionL+ between the N input and output sides.

PE L– Power Supply Secondary grounding Unregulated Regulated A ground fault occurs if a current-carrying line has contact to earth. In the worst case, two simultaneous ground faults can lead to a Linear-regulated Switched-mode bridging of switches and thus can start www.lutze.co.ukequipment accidentally. Power failure buffering Lütze Limited. 3 Sandy Hill SecondaryPark, Sandy Way, Tamworth, Staffordshire,Primary B77 4DU. T 01827 313 330 F 01827 313 332 [email protected] Switched-mode Switched-mode Power Factor Correction (PFC)

The key criteria in selection of a power supply are:

Input side: Output side: Ground fault

Input voltage Output voltage If secondary grounding is used, the Primary grounding Secondary grounding occurrence of such a ground fault leads to a Current consumption Short-circuit current so-called short circuit to earth which causes Inrush current Residual ripple the fuses in the secondary circuit to trip. Input fuse Output characteristics Frequency Output current DC supply 10

Power Supplies · Basics

1. General structure circuit and a mains circuit. In the case of power supplies this means that

The different kinds of insulation are specified protective shielding. in IEC/EN 60950: Input side Output side 2.4 Secondary grounding • Functional insulation L L+ Insulation needed for the correct operation In case of secondary grounding, the output of the equipment. side of the power supply is connected to N protective earth (PE) in order to prevent dangerous ground faults. PE L–

In technology terms, however, there are two different basic designs:

Unregulated and regulated.

The regulated variants are subdivided into linear-regulated and switched-mode power supplies.

L L+ N

Product FOCUS PE L– Power Supply 2.2 Insulation Secondary groundingSecondary grounding Thanks to the housing earth, hazardous

Unregulated Regulated leakage currents can be discharged via the The different kinds of insulation are specified in AA ground ground faultfault occursoccurs ifif a current-carryingcurrent-carrying line has contact to earth. In the worst case, two structure independently of the low voltage when IEC/EN 60950: line has contact to earth. In the worst case, simultaneous groundn f aults ca lead to a interference occurs on other equipment whose Linear-regulated Switched-mode twobridging simultaneous of switches ground and thusfaults can can start lead to touchable conductive parts receive mains • Functional insulation aequipment bridging of accidentally. switches and thus can start Power failure buffering voltage. Secondary Primary equipment accidentally. Switched-mode Insulation neededSwitched for the correct-mode operation of Power Factor Correction (PFC) the equipment. Power Supplies · Basics 2.7 Protection class

• Basic insulation The standard IEC/EN 61140 defines protection 2. SafetyThe key criteria in selection of a power supply• Basicare: insulation classes for electrical equipment. The devices are

Working with InsulationInsulation to to provide provide basic basic protection protection against against Input side: Output side: classified according to the safety measures taken The safety of people and equipment is hazardous structure-borne currents. Ground fault hazardous structure-borne currents. to prevent electric shock. The protection classes switch mode power always the priority. Accordingly, power • Supplementary insulation Input voltage Output voltage If secondary grounding is used, the supplies must comply with unified regulations Protection against hazardous structure- If secondary grounding is used, the occurrence are divided into the classes 0, I, II and III. supplies in automation Primary grounding Secondary grounding occurrence of such a ground fault leads to a and standards. •borne Supplementary currents if the insulation basic insulation fails. Current consumption Short-circuit current ofso such-called a groundshort circuit fault toleads earth to whicha so-called causes short applications Inrush current Residual ripple•ProtectionDouble insulation against hazardous structure currents circuitthe fuses to earth in the which secondary causes circuit the fuses to trip. in the • Protection class 0 2.1 GalvanicInput fuse isolation Output characteristicsInsulation comprising both basic insulation

Frequency Output currentifand the supplementarybasic insulation insulation.fails. secondary circuit to trip. Apart from the basic insulation there is no A power supply has a decisive influence GalvanicDC isolation supply generally refers to the • Reinforced insulation on the availability and operational protection against electric shock. These devices isolation between two conductive objects, •Unified Double insulation insulation system. Provides reliability of electrical systems. 10 cannot be connected to electrical installations such as metal plates or electrical circuits. In equivalent protection to double insulation. the case of electrical circuits it is Insulation comprising both basic insulation and with PE. Equipment of class 0 is not allowed in Consequently, the selection of the right consequently not possible for charge carriers 2.3 Safe isolation Germany. Protection class 0 will no longer be power supply should be just as critically supplementary insulation. to flow from one circuit into another, as there and carefully undertaken as that of the considered in future versions of the standard. is no electrically conductive connection Safe isolation according to EN 50178 is other system components. • Reinforced insulation 2.5 SELV between the two. required for all interfaces between different

electrical circuits, such as between a SELV • Protection class I Unified insulation system. Provides equivalent SELV according to IEC/EN 60950 is a safety 1. General structure circuit and a mains circuit. In the case of power supplies this means that protection to double insulation. extra low voltage, which thanks to its low level In addition to the basic insulation, all electrically Regardless of the technology employed, there is no electrical connection between the Safe isolation means that no current flow can and insulation offers better protection against conductive parts of the housing are connected power supplies are devices with an input side input and output sides. occur2.3 fromSafe oneisolation electrical circuit to another. and an isolated output side. electric shock than higher-tension circuits. to PE. This guarantees that no electric shock This isolation has to be implemented either by 2.2 Insulation can occur in the event of an insulation failure. doubleSafe isolation or reinforced according insulation to EN 50178 or by ismeans of Power supplies generating SELV, for example,

The different kinds of insulation are specified protectiverequired f orshielding. all interfaces between different must be designed to prevent shorting between in IEC/EN 60950: • Protection class II Input side Output side electrical circuits, such as between a SELV the primary and secondary windings and their

2.4circuitSecondary and a mains grounding circuit. Protection against electric shock is not only • Functional insulation connections. The windings can only be overlaid L L+ based on the basic insulation. The housing is Insulation needed for the correct operation InSafe case isolation of seco meansndary that grounding, no current the flow output can if double or reinforced insulation is placed of the equipment. side of the power supply is connected to between them. This isolation is termed galvanic equipped with reinforced or double insulation. N occur from one electrical circuit to another. protective earth (PE) in order to prevent isolation. If the housing is made of electrically conductive dangerousThis isolation ground has to faults. be implemented either by PE L– material, no direct contact between the housing double or reinforced insulation or by means of Grounding of the secondary side is not required and current-carrying parts is possible. The protective shielding. but permitted. housings of class II devices are not equipped In technology terms, however, there are two The peak value must not exceed 42.4 V in case with a PE connection. It is important to note different basic designs: 2.4 Secondary grounding of AC voltages and 60 V in case of DC voltages. that the PE connection is not only used for Unregulated and regulated. In case of secondary grounding, the output side the grounding of housings but also to connect of the power supply is connected to protective 2.6 PELV filters for EMC measures (electromagnetic The regulated variants are subdivided into earth (PE) in order to prevent dangerous ground PELV according to IEC/EN 60950 is a protective compatibility) to ground. linear-regulated and switched-mode power faults. supplies. extra low voltage with safe isolation. In case of This is why even devices of which the housings PELV, the electrical circuits are grounded and are completely made of plastic material can be L L+ (like SELV) safely isolated from circuits of higher equipped with a PE connection. voltages. N • Protection class III PE L– The voltage limits are identical to SELV. The device is operated with safety extra-low Power Supply PELV is used where active low-voltage voltage (SELV) and thus does not require any Secondary grounding conductors or the equipment structures have to protection measures. Power supplies are Unregulated Regulated be grounded for operational reasons. That is the A ground fault occurs if a current-carrying line usually class I or II equipment. case, for example, where potential equalisation has contact to earth. In the worst case, two simultaneous ground faults can lead to a is required to prevent sparking inside vessels Linear-regulated Switched-mode bridging of switches and thus can start and explosive rooms. equipment accidentally. Power failure buffering Secondary Primary Switched-mode Switched-mode Power Factor Correction (PFC) www.lutze.co.uk Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected]

The key criteria in selection of a power supply are:

Input side: Output side: Ground fault

Product FOCUS

2.8 Degree of protection PROBLEMS DUE TO NETWORK VOLTAGE We prefer to indicate 120 - 230Vac and related VARIATIONS current values, as these voltages are used by a According to DIN EN 60529, electrical wider number of countries and users than 100 equipment is classified using so-called IP Any power supply is defined by three main - 240Vac. codes. IP stands for “International Protection” parameters: or “Ingress Protection”. The IP code consists The manufacturer must give the final user Input rated voltage of two figures: The first digit specifies the a clear indication on the min-max allowed protection against accidental contact and Output rated voltage input voltage limits of the power supply, and against ingress of solid foreign bodies; the Output rated current must indicate clearly if there are any output second digit specifies the protection against performance limitation related to input voltage ingress of water. About input voltage of power supplies variations allowed by IEC-EN, eg a certain output current limitation at 90Vac input voltage. Since power supplies are mostly installed inside IEC and EN standards accept network voltage For international IEC-EN-UL standards, any cabinets, their typical degree of protection is IP variations within ± 10% of the rated value, power supply, as any other device, must work 20. which varies among the countries that have within ±10% min-max variations of its rated subscribed IEC-EN standards, as indicated in voltage. 3 Input voltage ranges the following table: But as there are some technical difficulties in 3.1 Wide-range input World Wide network voltages acc. engineering a switch mode power supply that Wide-range input means that the device can be to IEC-EN gives the same output performances within operated with any voltage within the specified a very wide input voltage variations, such as limits. Lütze devices operate in the single-phase Single Phase Network between 90 to 264Vac, the manufacturer is range from AC 90V to AC 264V or DC 110V to Rated Voltage min-max voltage allowed by IEC-EN-UL to reduce the output DC 370V and in the three-phase range from performances at the limit conditions, eg when Europe 230Vac ±10% 207 - 253Vac AC 340V to AC 576V or DC 480V to DC 820V. input voltage is 90Vac. There is no loss of power, i.e. the device is able England- UK 240Vac ±10% 216 - 264Vac The manufacturer must communicate to the to deliver the specified rated power over the USA 120Vac ±10% 108 - 132Vac end user any performance reduction, with entire input voltage range. clear technical information on product, or on Japan 100Vac ±10% 90 - 110Vac data sheets or instruction manuals, about 3.2 Autorange conditions or limitations to be applied to rated 3 Phase Network Power supplies that are equipped with performance, also called performance derating. Europe 400Vac ±10% 360 - 440Vac autorange behaviour perform an internal Generally: the higher voltage stresses the measurement of the applied supply voltage USA 480Vac ±10% 432 - 528Vac isolation values of isolating materials, creepage and automatically switch between the available and clearance distances on air and on PCBs, USA 207Vac ±10% 186 - 228Vac input voltage ranges. and isolation between primary and secondary Canada 575Vac ±10% 517 - 632Vac coils of transformers. 3.3 Manual range selection The lower voltage causes a current increase In case of manual range selection, the housing Rated voltage indicated on the label of a power on the input stage to keep the same output of the device is equipped with a selector switch supply: power, thus losses increase which overheats for manual input voltage range selection. Lütze components and stresses the temperatures offers devices permitting operation at AC 115V IEC, EN, UL standards allows manufacturers limits. or 230V. to indicate the rated voltage of a power supply in many different ways, but always requires to If the manufacturer does not give any specific The operating voltage range is then refer indicated current absorbed by the input different information on performances derating AC 90 V to AC 132 V; AC 185 V to AC 264 V or to the rated voltage indicated on the label. This regarding either voltage, operating ambient DC 300 V to DC 370 V. is fundamental technical information for an temperature or both, when the mains voltage accurate choice of connecting wire gauge and rises to the maximum allowed value eg. 264Vac overcurrent protection fuses on AC line by the or when mains drops to 90Vac, a power supply end user. So if the label gives 100-240Vac, the with an input range of 90-264Vac the device current absorbed by the input must be related has to provide rated performances. to 100Vac and 240Vac. If the label indicates 120-230Vac, absorbed currents are related to 120 and 230Vac.

www.lutze.co.uk Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected] Product FOCUS

If input voltage rises over the maximum allowed Figure 1 How to solve the problem value : over maximum allowed voltage limit, the Use a 3 phase primary // single phase input stage might be damaged depending on secondary transformer to provide isolation and the value reached by the voltage and depending voltage reduction to get a single phase 120 or on its duration ; if a 100-240Vac input power 230Vac from a 400 or 480Vac 3 phase line and supply is fed with 400Vac for more than a few do not connect the secondary to ground. ms, a failure on input stage is unavoidable. Use a 3 phase power supply, where What fails in this case? If the input of a power 340-550Vac is the operating voltage. supply is fed with a voltage higher than the maximum allowed for more than a few ms, the Use a super wide range power supply with an immediate consequence is the short circuit operating input voltage range of 90-550Vac ; of the overvoltage input protection Varistor this new technology allows the power supply connected between L and N on single phase to continue to work even if It is connected to models, between L1-L2-L3 on 3 phase models, a single phase line that rises to 500Vac when and consequently it explodes or burns. When there is a failure somewhere in the system. the varistor is shorted, the AC line overcurrent Typical application with three-phase network protection switches off. If the operator tries to and neutral. The latter is used to obtain a If mains voltage drops under the minimum switch on the protection, it switches off, or if 230Vac voltage in order to supply power to rated or allowed value the fuse is replaced it blows again as the line loads (in the example, a simple lamp) and If AC line voltage drops under the minimum voltage is connected to the shorted varistor. power supplies. value allowed by IEC-EN or by the manufacturer, depending on the value reached by the drop Greater reliability on 3-phase lines Figure 2 and depending on its duration, the immediate Compared to single-phase power supplies, this consequences are: series is more reliable in industrial applications. A shut down of the power supply output The input stage uses components with 900V A high increase of input current operating voltage, which are more resistant to voltage peaks in industrial power lines, A ripple increase: the higher the load, the higher compared to components used in single- the ripple increase. phase supplies, whose operating voltage is A voltage drop of output DC voltage: the higher 550V in high-quality power supplies, but often the load, the higher the voltage drop. 400...450V in low cost products. For switch mode power supplies, the minimum Being able to work from 185 to 550Vac, these input voltage and full load are the worst working power supplies are immune to power failures. conditions. At 230Vac input (L1-N), when another device Where ripple reaches the maximum value and connected to L2-N goes short, the neutral rises DC stability is the lowest. Nevertheless, also up to approx 400Vac, and the input is supplied A simple short-circuit on the load causes a in such difficult conditions, ripple and stability phase/phase until the protection is activated, rise in the neutral’s potential, all the devices keeps normally acceptable in good quality which takes place – at best - in 300 ms. This connected to it will be powered between power supplies. is one of the most common causes of damages two phases, i.e. with a value of approx. to 230Vac single-phase power supplies in 340...400Vac instead of 230 Vac. If low AC line voltage has a long duration industrial applications. Another example the consequences are: of faults in 230Vac single-phase devices powered between phase-neutral is due to the If AC voltage drops under the minimum allowed disconnection or accidental interruption of the value eg some minutes, and if the output is panel’s neutral from the system’s neutral: failing supplying rated current, on the input stage to return to the neutral point, the neutral rises flows a current higher than rated, thus input up to phase voltage applying approx. 400Vac components overheat and this might cause to single-phase loads, inevitably damaging the a failure or an over temperature protection system. switches off if this function is included, and if it is located to detect input stage temperature.

Minimum line voltage along with maximum output load are working conditions to www.lutze.co.uk Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected] Product FOCUS be avoided. This can occur as they are What happens if a surge is higher than voltage is cut very rapidly. Whereas the use consequences of the life reduction of any 4.5kV: of conventional line protection equipment in device. If an isolation- transformer is to be the secondary circuit is very critical in any Surge currents higher than 4.5kV 8/20 adopted for other reasons, we recommend to case, the function under Hiccup mode is not. damages the varistors and often the devices. choose its secondary voltage corresponding to Electronic overload protection units such as the higher rated input voltage of the adopted Solutions: the Lütze LOCC-Box should always be used in power supply eg. 230Vac. such cases. They provide safe protection in all If frequent failures of input stages of power circumstances. AC line undervoltage definitions supply and other AC powered devices are detected, overvoltage protection devices Class U/I characteristic Undervoltage: when the voltage value is lower C, 10kV 8/20, must be connected between Lütze power supplies with a U/I characteristic than allowed by IEC, EN, UL for a long period of phases and gnd; install the overvoltage perform current limiting to typically 1.2 times time. protections where the AC line is connected to the nominal current at constant output voltage. Sag: when voltage drops to zero for some AC the AC main terminal blocks of the cabinet ; this This current is still available in case of an cycles is also required by IEC-EN EMC standards that overload or a short circuit. The voltage is slowly must be applied also to electric systems, control Flicker: low frequency modulated variations of lowered, while the output current may rise panels and cabinets. mains under rated voltage further (triangular current limiting). Since the current does not sag in case of an overload, this The above events lower quality and 4 Self-protection method enables reliable starting of high loads. performances of electric power and are very In case of overload, the power supply needs to frequent in industrial electric systems and can be switched off as quickly as possible. be dangerous for any electronic devices. A poor quality of AC voltage is very often the real cause There are basically two types outside of of the failures of AC powered electronic devices. nominal operation. Overload, which can occur sporadically or continuously, and short-circuit. Surge (high overvoltage): A high voltage Overload means that the current required by the peak, which can be single or multiple (burst) loads exceeds the nominal current of the power on AC line; surges are due to lightning strikes, supply. failures on power lines, commutations of high A short-circuit is a special form of overload. current loads, switching off of circuit breakers; Power supply protection against In this case, the outputs of the power supply when a sag occur, it’s often followed by an overcurrent and fire risk overvoltage. are interconnected at very low resistance, as a result of which the output current may assume If power supplies are not provided with How to prevent failure due to surge extremely high values. proper protection fuse, they absolutely must voltages: be protected providing external overcurrent State-of-the-art Lütze power supplies offer the protections on the AC line. As required by IEC1000…, EN61000-4- following protective functions: 2, 4 – 4 , 4 - 5, the input stage of a power 3 phase power supplies usually are not supply must withstand 2.5kV surge voltage Fold-back characteristic/Hiccup mode provided with proper internal fuses, so external protection on the AC line is absolutely between the phases, phase and neutral, and Lütze power supplies supply a current typically necessary to prevent electric shock and fire 4kV between phase to ground. The surge test up to 1.2 times the nominal output current. risk. applies pulse waveform 1.2/50 (voltage pulse) They automatically switch off if the current and 8/20 (current pulse). To withstand such consumption of the connected loads exceeds high energy pulses, input stages are usually this value or if a short-circuit occurs. After protected by varistor connected between L-N on a defined period of time, the power supply single phase power supply and between, L1- tries to restart the load. If the overload or L2-L3 on 3 phase. the short-circuit still exists, it switches off again. This procedure repeats until the fault is cleared. The power supply has “hiccups”. In applications requiring high starting currents, it must be ensured that the overload current capacity is higher than 1.2 IN. To do so, Lütze Even if the power supply is protected with also offers devices with overload capacity proper fuse, for safer working conditions it’s as of 1.5 IN featuring Hiccup mode. Another well recommended to provide external fuses or aspect is response to short-circuit. The output overcurrent switches. www.lutze.co.uk Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected] Product FOCUS

Mains cable protection NOTICE: Even if some manufacturers declare under a certain current, will not feed the operating temperatures higher than 45°C system any more, but this only happens after Even if the power supply is provided with proper (113°F) eg 60°C (140°F), we suggest this a long period of stress that shortens the power input overcurrent protection fuse, AC line information be treated as a ‘reliability or supply’s life. cables feeding the device have to be protected ruggedness’ statement, because if the device to prevent overcurrent through them if their operates for a long period of time at 60°C, this What to do when ovtp protection shuts off length is longer than 4m from the main bussbar drastically reduces the life of the power supply. the power supply (for EN standards); nevertheless, for better electric shock and fire risk prevention, external When ovtp circuit shuts off the power supply, it Power dissipated by power supplies overcurrent protection of AC line cables is indicates that working conditions are abnormal. increases surrounding air temperature always recommended. Verify that output current supplied by the power When a certain electric power is dissipated supply is not higher than rated. If protection fuse blows inside a cabinet, air temperature inside the Make sure that air temperature inside the cabinet increases compared with external air Usually the input of single phase power supply cabinet during full power operating conditions temperature. Air temperature increase gets is protected by a fuse to prevent overcurrent keeps within operating limits higher as the dimensions (or volume) of the and fire risk. Often the fuse blows as a cabinet gets smaller. Make sure that the temperature of air consequence of mains overvoltages that cause surrounding the power supply is lower than failures to input circuitry. In 99% of the cases, Operating temperature of power supplies the limit allowed by the manufacturer; usually a blown fuse is a sure sign of internal failure 45°C is the limit for continuous operating rated on input stage, and even if the fuse is replaced With 25°C (77°F) environment temperature, power. normally the power supply doesn’t work. If a generally a good and efficient power supply, power supply seems to work after the fuse feeding rated current, has a temperature If the power supply is mounted right over a replacement, it might be stressed by high increase of 25°- 35°C (77-95°F) over 25°C power device eg motor drives, inverters that current and voltage and thus no longer safe for (77°F), so it reaches 50-60°C (122-140°F) at generate heat, the power supply might be this reason, an internal protection fuse should its hottest point. heated by hot air ascending, increasing its temperature instead of being cooled. be replaced by the factory or by authorized and With 45°C (113°F) air temperature inside the skilled personnel. cabinet, the same power supply reaches 70- The power supply must have 5 cm (2 inches) 80°C (158-176°F), which is to be considered free space above and below, and 1 cm at the Rated Output Current the maximum limit for an acceptable life sides. The current that the power supply can provide duration of electronic components - eg. life of Clean the power supply from dust to assure free keeping all performances and parameters electrolytic capacitors are rated 105°C (221°F) air passages. within the manufacturer’s data sheet and operating limit temperature, reduces 50% every product approval. Rated current has to be 10°C (50°F) temperature increase), this is why Verify the efficiency of the cooling system: Fans supplied within the min - max input voltage, “the cooler the better”. efficiency, air filters efficiency etc. keeping output voltage no lower than –10% of Mains voltage has not dropped lower than the Overtemperature protection (ovtp) rated value, below which the power supply is minimum allowed by manufacturer. considered to be in “overload protection”. A circuit that prevents failure, if temperature limits of the components are overheaded; ovtp Power supplies efficiency Current and operating temperature protection is a second back up protection, that Any electric and electronic device dissipates a If an output current rating is not referred to the works when currents are higher than rated for a certain amount of total absorbed power as heat. operating temperature range at which that current long duration, but still under overload protection This increases the temperature, and therefore can be given, it is almost useless. limit, together with a high environment increases surrounding air temperature. temperature or reduced cooling conditions. Current flowing through components, conductors, A higher efficiency means a lower power PCB paths etc., causes a voltage drop. The voltage Ovtp protection can be achieved detecting the dissipation that saves on the costs of electric drop multiplied for the current flowing through temperature on a key component and setting power and reduces the temperature increase the component, gives the power that it dissipates up a point where the ovtp circuit starts limiting inside cabinets They can work inside smaller for Joule effect, that causes its temperature to output power, or shuts off the power supply. enclosures without exceeding the maximum increase above the environmental temperature. In the case of ovtp, ovtp protections that shut temperature, and finally are more reliable in Power supplies operate inside panels and off the power supply are better than ovtp that the same given operating conditions. Today’s cabinets, where the maximum allowed reduce output power. technology makes it easy to get 90% efficiency temperature is 45°C (113°F). So as a minimum on single phase power supplies and up to 94% If the power supply shuts off, it makes condition, rated current has to be referred to 45°C. on 3 phase. immediately clear that something is wrong. A power supply where ovtp limits output power www.lutze.co.uk Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected]

Power Supplies · Basics

100 up to a degree where safe operation is no 8 Line cross-section and protection 230VAC

[%] 115VAC longer guaranteed. There are a number of

techniques for protecting the power supply 8.1 Input-side protection voltage 50 against destruction due to overheating. If power supplies have their own input protection,

Output such as a safety fuse, no further protective • The maximum output power is reduced, 0 allowing the power supply to cool down. measures are necessary. However, standards stipulataet th a power supply must be capable of • The device is switched off completely and being disconnected from the supply mains by cannot resume operation until a manual external means. Line protection equipment can reset is performed. Depending on the then be used. For the relevant characteristics manufacturer, the reset is done either using refer to the LÜTZE data sheets. a corresponding switch or by disconnecting the supply voltage. 8.2 Output-side protection

Alongside the output behaviour described in • The device only switches off the output and section 4, there is a U/I characteristic with an does not switch it on until the temperature Product additional power reserve. However, all these FOCUS falls below a certain limit value. This is the output behaviour modes are ultimately not Power Supplies · Basicsmost frequently used method nowadays, suitable for safe activation of standard line and is the one used by LÜTZE. protection equipment. The reason lies in the Power dissipated by power supplies falls below a certain limit value. This is the 100 up to a degree where safe operation is no 8technical Line cross-section design of the andequipment. protection Only 230VAC 7 Generalmost frequently parameters used method nowadays, and electronic protection devices capable of A 100W output power supply with a 85% [%] 115VAC longer guaranteed. There are a number of is the one used by LÜTZE. 8.1reacting Input fast-side enough protection to overload or short- efficiency, absorbs 117.6W total input power, 7.1techniques Open circuit for protecting resistance the power supply voltage 50 circuit offer a solution. These devices also against destruction due to overheating. thus 17.6W is dissipated in heat. Manufacturers Open circuit resistant power supplies require Iffeature power asupplies high degree have tofheir repeat own inpu accuracyt protec tion, Output 7 General parameters such as a safety fuse, no further protective usually do not indicate input power, but indicate no• The minimum maximum load output in order power to isprovide reduced, a stable across the entire temperature range. With 0 the efficiency. To calculate the total power and outputallowing voltage. the power This issupply important, to coo forl down. example, measuresthe LOCC are Box necessary LÜTZE offers. However intelligent, standards DC 100 110 120 130 140 150 160 in7.1 the Open case circuit of time resistance-critical applications in stprotectionipulate tha modulest a power which supply can mus alsot be becapable of dissipated power: 100 110 120 130 140 150 160 •which The devicea load isis switchedapplied which off completely has to be and beingintegrated disconnec into fieldted f rombus tcommunicationshe supply mains by immediatelyOpencannot circuit resume suppliedresistant operation wpowerith voltage.until supplies a manual Power require exsystems.ternal means (See .also Line Electronicprotection equipmenoverload t can P dissipated in W = Pout : R − Pout 5 Influence of ambient temperature supplies which are not open circuit resistant 5 Influence of ambient temperature noreset minimum is performed. load in orderDepending to provide on the a stable tphenrotection, be used page. For ).the relevant characteristics often require up to the seconds range until an The ambient temperature has a direct influence manufacturer, the reset is done either using refer to the LÜTZE data sheets. eg: 100W (output power) : 0.85 (efficiency) = actualoutput supplyvoltage. takes This place.is important, for example, 8.3 Selectivity a corresponding switch or by disconnecting on the maximum possible output power of a in the case of time-critical applications in which 117.6W total input absorbed power The ambient temperature has a direct the supply voltage. 8.2 Output-side protection 7.2 Resistance to reverse feed Selectivity means the tripping coordination. influencepower suppl on ythe and maximum so on its possibleresponse output to short- a load is applied which has to be immediately AlongsideIn electrical the systems, output behaviourdistinction describedcan be in 117.6W (P input) − 100W (Poutput) = 17.6W powercircuit ofor aoverload. power supply and so on its • The device only switches off the output and Thesupplied resistance with voltage. to reverse Power feed supplies specifies which up sectionmade between 4, there "seriesis a U/I selectivity", characteristic which with an power dissipated in heat by the power supply. response to short-circuit or overload. does not switch it on until the temperature toare which not open voltage circuit a power resistant supply often is requireimmune up to additionalmeans that power individual reserve. fuses However, connected all thesein TemperaturesTemperatures inside cabinets may be over falls below a certain limit value. This is the against the feeding of voltages into the outputseries arebehaviour selective modes against are each ultimately other, not 60 °C as a result of internal or external themost seconds frequently range used until method an actual nowadays, supply takes Power supplies operating inside small 60°C as a result of internal or external secondary side. Such a current flow can suitableand "parallel for safe selectivity", activation which of standard means linethat influences. Power supplies still have to and is the one used by LÜTZE. influences. Power supplies still have to operate occurplace. if power supplies are operated in protectionelectrical circuits equipment. connected The reason in parallel lies inare the cabinets or enclosures operate reliably even at such high tempera- parallel or inductive consumers are technicalselective againstdesign ofeach the other.equipment. Only tures.reliably Due even to atthe such components high temperatures. used, however, 7 General parameters connected. electronic protection devices capable of The power dissipated by any electronic device, there is a point as from which the output 7.2 Resistance to reverse feed Due to the components used, however, there reactingSeries selectivity fast enough to overload or short- increases its temperature and increases the power has to be reduced. That point is 7.1 Open circuit resistance is a point as from which the output power has 7.3The Overvoltageresistance to protectionreverse feed specifies up circuit offer a solution. These devices also described by so-called derating. The temperature of surrounding air. (secondary side) Infeature case aof high series degree-connected of repeat fuses, accuracy the trip - Deltato be seriesreduced. from That Lütze point is israted described for ambient by so- Opento which circuit voltage resistan a powert power suppl suppliesy is immune require pingacross coordination the entire temperatureof fuses is considered range. With as So, if a device operates inside an enclosure, the temperaturescalled derating. up The to 70°C Delta for series example, from Lütze with is no minimum load in order to provide a stable Inagainst case theof an feeding internal of errorvoltages of the into power the selectivethe LOCC if Boxonly LÜTZE the fuse offers installed intelligent nearest DC to derating beginning at 60°C. The reduction in output voltage. This is important, for example, temperature inside the enclosure increases.100 rated for ambient110 120temperatures 130 140 150 up to160 70°C for supply,insecondary the case this side. ofprotection time Such-critical amechanism current applications flow prevents can in occur theprotection fault trips. modules Fuses which that arecan located also be nearer output power is 2.5%/°C. the occurrence of overvoltage on the example, with derating beginning at 60°C. The whichif power a loadsupplies is applied are operated which hasin parallel to be or integratedto the energy into feeding field bus point communications do not trip. This Rule : the smaller the volume of the enclosure secondaryimmediately side supplied that could with possiblyvoltage. Powerdamage systems.guarantees (See that also as manyElectronic system overload parts as reduction in output power is 2.5%/°C. inductive consumers are connected. with the power supply, the higher the increase 5 Influence of ambient temperature orsupplies even destroy which are a connected not open circuitload or resistant exceed ppossiblerotection, remain page operative). in the event of one theoften SELV require voltage up to limit. the seconds range until an single fault, resulting in an increased avail- of air temperature inside. 100 actual supply takes place. 8.3ability Selectivity of electrica l systems. 7.3 Overvoltage protection

7.4 Power failure buffering The ambient75 temperature has a direct

Practical parameter: one W dissipated inside [%] (secondary side) 7.2 Resistance to reverse feed Selectivity means the tripping coordination. out

influence on the maximum possible output 1dm³ (1 decimeter = 10cm) volume enclosure, In electrical systems, distinction can be power of a power supply and so on its PowerIn case supplies of an internal must errorbe able of theto maintain power Power The resistance to reverse feed specifies up made between "series selectivity", which increases inside temperature 10°C (50°F). response to short-circuit or overload. their output voltage for a certain time in case tosupply, which this voltage protection a power mechanism supply is prevents immune the means that individual fuses connected in 0 Temperatures inside cabinets may be over of supply voltage dips. Usually, a power -25 61 71 against the feeding of voltages into the series are selective against each other, UL508C Power Conversion Equipment standard, 60 °C as a result ofTemperature internal [oC] or external occurrence of overvoltage on the secondary secondaryfailure buffering side. timeSuch of a atcurrent least 20flow ms can is and "parallel selectivity", which means that makes performance approval tests on devices influences. Power supplies still have to aspired in order to provide buffering for one occurside that if power could suppliespossibly aredamage operated or even in destroy electrical circuits connected in parallel are operate reliably even at suchLütze high tempera- at 45°C while devices are operating inside Example:Example: Derating curvecurve ofof Lütze of DeltaDelta series cparallelaomplete connected or cycle inductive load of orthe consumersexceed mains thevoltage. SELVare Involtage the selective against each other. tures. Due to the components used, however, series semiconductorconnected. industry longer time are an enclosure with a volume that must be there is a point as from which the output limit. required. The devices must then comply with Series selectivity communicated by the manufacturer. 6power6 Thermal Thermalhas toprotection be protection reduced. That point is the7.3 requirementsOvervoltage ofprotection SEM F47. Most LÜTZE described by so-called derating. The devices7.4 (secondaryPower do so. failure side) buffering In case of series-connected fuses, the trip- When selecting a power supply, its rated current WhenDeltaWhen seriesoperating from a Lütze power is supplsupply ratedy forunderunder ambient extreme ping coordination of fuses is considered as extreme conditions for a long duration, and the current derating versus temperature, temperaturesconditions for upa long to 70°C duration, for example, e.g. in case with of InPower case supplies of an internal must beerror able of tothe maintain power their selective if only the fuse installed nearest to Rule of thumb: e.g.derating in case beginning of permanent at 60°C. operation The reduction within thein supply,output voltagethis protection for a certain mechanism time in preventscase of the fault trips. Fuses that are located nearer must be selected and calculated, considering permanent operation within the power limits or The fuses must differ by two nominal quantities poweroutput limitspower or is in 2.5%/°C. case of very high ambient the occurrence of overvoltage on the to the energy feeding point do not trip. This the final operating volume and the environment temperatures,in case of very the high power ambient supply temperatures, can heat the supply voltage dips. Usually, a power failure secondary side that could possibly damage guarantees that as many system parts as temperature of the application, and also the power supply can heat up to a degree where orbuffering even destroy time of a at connected least 20 ms load is orapplied exceed in possible remain operative in the event of one power dissipated by other devices inside the safe operation is no longer guaranteed. There thordere SELV to provide voltage buffering limit. for one complete single fault, resulting in an increased avail- 15 100 cycle of the mains voltage. In the semiconductor ability of electrical systems. same cabinet. are a number of techniques for protecting 7.4 Power failure buffering 75 [%] the power supply against destruction due to industry, a longer time is required. The devices

out

Consider also, that if a part of or all of the overheating. must then comply with the requirements of Power supplies must be able to maintain output power of the power supply feeds a load Power Semi F47. their output voltage for a certain time in case located inside the same cabinet, the power • The 0maximum output power is reduced, of supply voltage dips. Usually, a power -25 61 71 dissipated by the load must be considered as it allowing the powerTemperature suppl [oC]y to cool down. failure buffering time of at least 20 ms is increases temperature too. aspired in order to provide buffering for one Example:• The device Derating is switched curve offof Lützecompletel of Deltay and complete cycle of the mains voltage. In the seriescannot resume operation until a manual reset semiconductor industry longer time are is performed. Depending on the manufacturer, required. The devices must then comply with 6 Thermal protection the requirements of SEM F47. Most LÜTZE the reset is done either using a corresponding devices do so. Whenswitch operating or by disconnecting a power supply the unsupplyder voltage. extreme conditions for a long duration, e.g.• The in devicecase of only permanent switches operation off the output within and the Rule of thumb: powerdoes limits not switch or in case it on ofuntil very the high temperature ambient The fuses must differ by two nominal quantities temperatures, the power supply can heat www.lutze.co.uk 15 Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected] Product FOCUS

8 Line cross-section and protection Series selectivity 8.4 Connection cross-sections In case of series-connected fuses, the trip- The line cross-sections are selected dependent 8.1 Input-side protection ping coordination of fuses is considered as on the maximum output current. The following If power supplies have their own input selective if only the fuse installed nearest to table provides an overview of the current protection, such as a safety fuse, no further the fault trips. Fuses that are located nearer capacities of multi-core flexible copper cables protective measures are necessary. However, to the energy feeding point do not trip. This with different conductor cross-sections at a standards stipulate that a power supply must be guarantees that as many system parts as temperature of 30 °C and up to a nominal capable of being disconnected from the supply possible remain operative in the event of one voltage of 1000 V (to DIN 57100-523). mains by external means. Line protection single fault, resulting in an increased avail- 2 A equipment can then be used. For the relevant ability of electrical systems. Cross-section in mm characteristics refer to the Lütze data sheets. 0.75 12 1 15

8.2 Output-side protection 1.5 18 Does not trip Alongside the output behaviour described in 2.5 26 section 4, there is a U/I characteristic with Trips 4 34 an additional power reserve. However, all 6 44 these output behaviour modes are ultimately 10 61 not suitable for safe activation of standard line protection equipment. The reason lies 9 PFC (Power Factor Correction) in the technical design of the equipment. Since 1 January 2001, the European standard Only electronic protection devices capable regarding the limits for harmonic current of reacting fast enough to overload or short- emissions (IEC/EN 61000-3-2) is in force. circuit offer a solution. These devices also Rule of thumb: The fuses must differ by two This standard defines the maximum allowed feature a high degree of repeat accuracy nominal quantities intensity of harmonic currents fed back into across the entire temperature range. With the the supplying mains system. It is applicable LOCC Box Lütze offers intelligent DC protection Parallel selectivity for consuming devices with an active power modules which can also be integrated into field input between 75 and 100 W that are directly Based on the self-protection, the output voltage bus communications systems. connected to the public electricity supply. is switched off or reduced in the event of a Power supplies for industrial applications often fault. If multiple loads are carried on one power 8.3 Selectivity do not require PFC, since large installations are supply, a voltage drop will occur throughout the equipped with a central PFC, installed between Selectivity means the tripping coordination. entire application. To prevent this, protective the internal electrical system and the public In electrical systems, distinction can be made devices are installed in the individual lines to electricity supply. between “series selectivity”, which means the consumers. If a fault occurs, the protective that individual fuses connected in series are device concerned must trip fast enough so as 9.1 Passive PFC selective against each other, and “parallel to disconnect the faulty consumer reliably from selectivity”, which means that electrical circuits the rest of the system and such that the other For passive PFC, a reactance coil is connected connected in parallel are selective against each consumers remain available. to the input circuit. This reactance coil buffers other. energy from the mains and thus reduces the current pulses. The lower the pulses, the less harmonics are produced. The advantage of this solution is its easy implementation into existing circuitry. However, the drawback is that it is not able to reduce all harmonics.

9.2 Active PFC Active PFC is able to deliver considerably better results. In a very simplified consideration, one could say that the actual power supply is preceded by another power supply that performs a regulation of the current consumption from the mains. www.lutze.co.uk Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected] Product FOCUS

This consumption is oriented towards the For this the individual power supplies must be What does this mean in practice? sinusoidal supply voltage. Using this technology, isolated from each other, as one faulty power For example, if you have four branches, two it is possible to avoid the production of almost supply might impact on the other one. In the requiring 1A nominal current and two others every kind of harmonics. However, the circuitry worst case the failed power supply effects a at 3.5A each. Two fuses with 2A and two is much more complex than for passive PFC. secondary-side short-circuit, which would result with 6A would normally be chosen. In normal Lütze power supplies are all equipped with in failure of the second power supply. To isolate circumstances, 9A flows where a 10A power active PFC. the power supplies from each other, isolating supply might be chosen. diodes (so-called O-ring diodes) must be 10 Applications looped into the secondary outputs of the power supplies. They then prevent reciprocal loading. PSU 10.1 Parallel connection of power supplies This ensures an uninterruptible power supply. In for increased capacity operation the Lütze Delta series the isolating diodes are An increase of the output power can be built-in to the output. In the Compact series the diodes must be installed externally as follows: obtained by connecting power supplies in 2A 1A parallel. This can be necessary if the current Lütze offers isolating diodes up to a nominal required by the load is higher than a single current of DC50A. power supply can deliver, for example after the expansion of an existing installation. The Correct sizing of power supply and fuse following preconditions must be met when elements 6A 3.5A connecting power supplies in parallel for the Only a carefully designed power supply and purpose of increased capacity: fuse concept guarantees reliable protection. • Parallel connection is only allowed for With individually protected branch circuits as identical power supplies. 6A shown on the left side of the figure above, the 3.5A • The power supplies have to be switched on inclination is to underestimate the total power simultaneously. requirement and to choose a too small power • The following points must be observed when supply. 2A 1A connecting the power supplies in order to prevent different voltage drops on the supply –VO –VO –VO lines or at the terminals which would lead to +VO unbalanced load at the common connection +VO Rdy point: Rdy If a 3.5A group then suffers a fault or a short- • Identical lengths of the supply lines –VO circuit, the 6A fuse requires 9A to trigger. –VO • Identical conductor cross-sections of the +VO This means that, together with the other three supply lines +VO +VO branches, the power supply must be able to Rdy supply 14.5A to shut-down the faulty branch. • Terminal screws have to be fastened with Rdy the same torque to guarantee equal contact The necessary current reserve is determined resistances. Electronic fuses are usually specified precisely by the fuse with the greatest maximum ampere in the tripping current, but normally need 1.5 to value and in this case is 5.5A. In practice, a • The output voltages of the power supplies 1.8 times the nominal current for a fast tripping. 20A standard power supply would need to be should not differ by more than 50 mV in the This is an intended behaviour to avoid nuisance used in this example, even though the nominal open circuit state. Otherwise safe operation tripping in case of short peak current demands current is only 9A. cannot be guaranteed. (e.g. when a motor starts). The power supply If a plant is modified, refurbished or extended must therefore be oversized for this “extra 10.2 Redundancy during operation, there is a danger lurking here. current” which is needed for a fast tripping At this time, it is very likely that nobody would The term redundancy generally denotes the in case of a fault in the system. Otherwise, think about the required “current reserve” any existence of several objects that are identical in the protective effect and selectivity will be more, and the power supply is loaded up to functionality, content or nature. questionable. the permitted nominal current. In the case of a In industrial automation, redundancy ensures branch failure, the power supply is then limiting that in the event of failure of a power supply the current before the fuse can cut-out the another one takes over the supply, thereby faulty branch. maintaining operation of the system. www.lutze.co.uk Lütze Limited. 3 Sandy Hill Park, Sandy Way, Tamworth, Staffordshire, B77 4DU. T 01827 313 330 F 01827 313 332 [email protected]

LUK-PSUPF-Rev1 3/15