The basics of device circuit breakers | Why device circuit breakers ?
the magnetic shutoff occurs in the event of a short circuit and ideally falls in the 3 to 5 ms range . Depending on the characteristic curve in use , up to 15 times the normal current needs to be flowing for a rapid short-circuit cutoff . If this current is not available , the entire system can be affected . The required current may be limited downstream of a switched-mode power supply unit or if the line impedance is too high . This means that the required higher tripping current may not be reached , causing the system voltage to dip . The result is that parallel loads fail .
MCBs are designed for the AC grid ( without power limitation ): miniature circuit breakers were developed for installation in buildings , and that is precisely what the currents and characteristic curves are designed for . Therefore , there are no nominal current values in the lower amp range , or a slow characteristic curve needs to be selected in order to reach the right nominal current . In principle , the characteristic curves were initially established for use only with AC voltages . If these types of fuses are used with DC voltage , a correction factor of around 1.4 must be taken into consideration in the short-circuit tripping range . Tripping therefore occurs even later , often not until a current 15 times the nominal current has been reached . Thus , in the case of a C6 quick-break cutout , a current of up to 90 A must be reckoned with for serious events . If this tripping current is not available downstream of a switched-mode power supply unit , the entire system will experience a voltage dip . The same is true for a cable that is too long . It can create a situation where the current is limited , thus preventing prompt tripping , which in turn can also lead to a voltage dip in this case .
1.3 What is a fault ?
Overload currents and short-circuit currents are usually unexpected . They cause malfunctions and interrupt the operation of a system . Production downtimes and repair costs are often the unpleasant result .
Effects of this type can be minimized by protecting individual devices separately or by logically organizing the devices in groups . Since different loads also have different nominal currents ( Fig . 1 ), it makes sense to implement separate protection for each individual circuit .
Motors 1 to 12 A
Controllers 1 to 8 A
Ideally , the nominal current selected will be close to the nominal current for the load . In this way , end devices are optimally protected against damage or destruction . System parts that are not in the affected circuit can continue to operate without interruption , provided the overall process allows it . This ensures high system availability .
Voltage dip Machines and systems for the most part operate with different supply
Sensors 0.5 to 2 A
Relays 0.5 to 5 A
Valves 0.5 to 4 A voltages . These largely range between 12 and 48 V DC . For the primary applications , 24 V DC has been the control voltage generally used for many years now . Synchronized power supply units are standard equipment in most industries for control voltages . This voltage consistently delivers high efficiency . In addition , the output current is limited . The voltage can also be maintained over great distances using DC / DC converters .
Like fuses and circuit breakers , power supplies also come with a variety of characteristic curves , allowing them to meet different system availability demands . Many power supply units use the U / I characteristic curve , for example ( Fig . 2 ). The voltage is constant , the current is variable . If the current exceeds the nominal range , or if an overload leads to a voltage dip , the connected loads fail .
If the PLC ( programmable logic controller ) fails , the only way to find and eliminate the error is through an enormously painstaking search .
Fig . 1 : Typical nominal currents of electrical loads
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