A circuit breaker is a protective device used for switching of an electrical supply to a load e.g. lighting or power circuit and a must for any and all applications. Today’s applications have shrunk themselves to your wristbands and getting smarter and connected but still require protection. Modern Circuit Protection Switches is required to perform more comprehensive function keeping the footprints down to a circuit could fit inside your watch or mobile.
Modern applications ask switches to provide simple and efficient power distribution solutions to reduce system power consumption, while providing robust protection against voltage and current surges. Designed in the smallest packages to address mobile and portable applications, they greatly reduce design complexity and time to market. Modern electrical equipment continues to increase in complexity and importance in industrial, commercial, and residential installations. This equipment is often considered critical for normal system operations. As such, the importance of circuit protection and overall equipment protection continues to increase and is a very important topic to understand. Determining whether a circuit is adequately protected can require a high-level view of the electrical distribution system, from the fault current available at the source of supply down to the end device connected in the system. Circuit protection includes protection from equipment overload conditions, under voltage and overvoltage conditions, ground faults, and short-circuits. Although mandated by code for any electrical installation, the proper implementation of circuit protection products can be confusing at times. Occasionally this confusion results in circuit protection products that are installed in circuits where their use is not appropriate. From a machinery design standpoint, system engineers and equipment designers must choose appropriate protective devices to ensure the safety and reliability of their products. Circuit protection devices protect expensive systems by rapidly disconnecting power to components in the event of an abnormal operating condition. Even though guidance exists in the form of the various electrical codes, the wide variety of product offerings can make the proper selection of circuit protection devices a challenge. An understanding of circuit types and circuit protection products is critical to ensuring their proper application.
Conceptual Reality
The increasing demand for high quality and efficiency in production is leading to the construction of increasingly complex systems. At the same time, the requirements for safety and availability are increasing because the failure of a machine or larger system parts can result in significant costs. A well-planned safety concept for the individual circuits and terminal devices of the entire system makes a significant contribution toward operational reliability. This also includes the selection of a sufficiently strong power supply and suitable protective devices that safely protect against short circuit and overload currents. It is advantageous to provide fuse protection for each piece of equipment. Then, only those circuits affected by overload shut off.
Selecting the right protective devices for protecting circuits and loads ensures the safe, optimized operation of electrical systems, even in the event of a fault. When talking about circuit breakers, it is important to note the difference between power circuit breakers and device circuit breakers. Power circuit breakers are used in the field of power distribution. They mainly protect power cables in buildings or systems that supply terminal devices, building floors or building complexes with current. However, it is not the task of the circuit breaker to protect loads and terminal devices. It is only in the event of a short circuit in a terminal device that they switch off to protect the power supply line against an overload. They have a high switching capacity of 6 kA or more. As the last protection level for terminal devices, thermo-magnetic and electronic circuit breakers offer the most effective short circuit and overload protection. Securing the individual loads or small function groups when a device is disconnected prevents the simultaneous shutdown of unaffected system parts in event of a fault. These areas can then continue working without interruption to the extent that the overall process allows. If a circuit is reinstalled, you must ensure that appropriate protection for the provided terminal device is available. During installation, cable lengths and conductor cross-sections must also be taken into account. The cables must be designed for the expected operating current, but also so that they can deal with any potential overload and short-circuit currents. Within the scope of the graded protection of system areas, the selectivity between the individual fuses and protective devices must be maintained. This also ensures higher system availability as only the faulty circuit is switched off. Device circuit breakers should be easily accessible when installed in control cabinets, so that they can be switched on again quickly, easily and without problems after tripping.
The requirements for optimum device protection vary depending on the area of application and tasks. For this reason, various device circuit breakers that work with different technologies have been developed over time. There are electronic, thermo magnetic and thermal device circuit breakers. The differences lie in the tripping technologies and shutdown behavior. Characteristic curves clearly illustrate the shutdown characteristics of the various device circuit breakers. Device circuit breakers are selected based on the nominal voltage, nominal current, and, if required, the starting current of a terminal device. In addition, the shutdown behavior of the device circuit breaker must correspond to the expected error situations. There are differences in error situations involving a short circuit and those involving an overload.
Job Profile for Switches
- Reduction of direct energy expenses: Many energy saving investments provide short ROI.
- Lower risks linked to energy: Energy price variations and availability are major concerns for sustainable operation profitability
- Improved corporate profile: Sustainable development becomes as important as quality and brands for corporate valuation by both customers and shareholders
- Legal constraints and incentives: Countries have developed comprehensive sets of regulations, incentives (taxes, tax exemptions, emissions and energy savings trade markets) and communications to enforce Kyoto protocol
- Quality, reliability and availability of energy to secure production
Overload and fault protection in motor circuits
Protection devices against electrical faults may be broadly divided into fuses or circuit breakers. In some applications, fuses are used with the circuit breakers to take over the interruption of higher short-circuit currents, particularly with the miniature or lower-rated MCCB. Often a motor is loaded beyond its rated capacity due to incorrect operating conditions. This leads to a motor overload, an increase in current flowing through the winding and an increase in the temperature of the winding. This results in a permanent damage to the motor winding and the cables. In a motor circuit, the starter overload relays, protect the motor, and the associated cables against overload and the fuses in the circuit provide the required degree of short-circuit protection. A short-circuit protection is required to protect motor conductors, overload relays, and motors from the short-circuit condition. It is achieved by using the non-time delay fuse, instantaneous trip breaker, or the inverse time-breaker. Usually, manufacturers give recommendations regarding the fuse ratings required to cope with the motor starting surges and indicate the minimum cable sizes required to achieve a short-circuit protection. In a well-designed combination, the starter itself interrupts all the overloads up to the stalled rotor condition. The fuses should only operate in the event of an electrical fault. The starter manufacturers indicate the maximum fuse rating, which may be used with a given starter to ensure satisfactory protection.
Overload and fault protection in motor circuits – This is an overload protection provided externally to the motor. It is connected in series with the motor supply. A bimetallic strip operates once the temperature exceeds predetermined limits, causing the contacts to open. After the relay has tripped and the contacts are open, the problem should be solved before pressing the reset button. The bimetal relays provide an accurate overload and an accelerated single-phasing protection for the three-phase motors. It incorporates a dual slider principle for accelerated tripping under the single-phasing protection. The bimetal relay also provides protection against severe unbalanced voltages. The bimetal relays protect themselves against overloads of up to 10 times the maximum setting. Beyond this limit, they have to be protected from short-circuits.
Phase failure relays – This protection interrupts power in all phases upon failure of any one phase. Normal overload relays or fuses may not protect the motor from damage due to single phasing. Phase-failure relay senses the negative-sequence voltage component of the supply and offers protection against phase failure, unbalanced phases, phase reversal, and under-and- over voltage faults.
Winding-protection relays – Winding – protection relays provide protection against overheating of the windings of motors, alternators, transformers, etc. Temperature is sensed with the help of a PTC thermistor embedded in the winding that gives a tripping signal when the temperature exceeds the response temperature of the thermistor. In some cases, thermocouples or RTD (resistance temperature detectors) are fitted inside the winding to accurately indicate the temperature of the winding.
Mr. James Colby, Manager, Business & Technology Development, Semiconductor Business Unit, Littelfuse
There is great technical progress being made in many different areas of the electronics market. Some examples include higher data rates (HDMI 2.0, USB 3.1, etc.) for Consumer applications, greater Broadband rate and reach (e.g. G.fast, Ethernet 2.5/5.0G, etc.) for internet access and Advanced Driver Assistance Systems to make Automobiles safer. Just as important are the improving manufacturing techniques that are being developed by IC manufacturers, as well as electromechanical suppliers (connectors, inductors, capacitors, resistors, etc.). Among these improvements is smaller size, which will facilitate the shrinking of application sizes to make the computing power almost transparent. Examples include smart watches, smart clothing, and wearable medical devices. For these applications to be attractive to end customers, they have to provide a great amount of functionality, but not require a lot of space or weight. So, in order to help these new applications remain safe and reliable, it has also been necessary for circuit protection companies like Littelfuse to improve their product capabilities. And the parameter most closely aligned with shrinking application size is package or case size of the protection devices. This has required significant investment to ensure that not only are the size targets hit, but also that the performance of protection devices is not detrimentally affected. Current capabilities include 0402 size for Multilayer Varistors (ESD), 0201 for Polymer ESD devices, 01005 for ESD Diodes, 0402 for Resettable PTCs, and 0402 for surface mount chip fuses.
Because the new wearable technologies are either worn directly by the consumer, or at least in regular contact with them, the applications are frequently subjected to static electricity. In addition, the robustness of modern ICs is decreasing, so there needs to be supplemental protection to ensure that the ICs reliably perform for the intended lifetime of the applications. To provide the greatest selection for design engineers, Littelfuse offers three different ESD protection technologies: Multilayer Varistor, Polymer ESD Devices and Diode Arrays. Multilayer varistors have been used for many years as an easy-to-use and reliable solution for ESD. They are typically discrete devices that protect a single power line or interface data line. Being discrete, they are easy to install exactly where the design engineer needs them so provide good design flexibility. The smallest size available at Littelfuse is 0402 which can be found in the MLA, MLE and MHS series. Polymer ESD devices like the PulseGuard and XtremeGuard series have extremely low levels of capacitance. So, they are often used on very high-speed digital data lines (USB 3.0/3.1, HDMI 2.0) and RF lines (Bluetooth, Near Field Communications) where capacitance must be controlled to ensure signal integrity. Their typical case size is 0402, but the new PGB2 series is available in 0201 size. In a growing number of applications, the ICs are very weak against ESD transients, so Semiconductor-based ESD Diodes are the preferred solution owing to their low clamping voltage. At Littelfuse, a wide range of 0201 products are available to cover general purpose applications (where capacitance is not a concern) as well as low capacitance solutions (< 1pF) where high speed digital or RF signals are present. Recently, two new series of products were released, in the 01005 package (0.44mm x 0.23mm). The SP1020-01WTG has 20pF of capacitance and can withstand ESD pulses up to 30kV contact discharge. The SP1021-0WTG has lower capacitance at 6pF and can withstand ESD pulse up to 12kV contact discharge. For the safety protection of the DC power buses, there are two different technologies available. Surface mount chip fuses are single-use components, and Resettable PTCs are based on a polymeric formula to allow them to protect against multiple over-current conditions. For the single-use fuses, it is important that the design is able to completely clear the over current fault without arcing so that electrical isolation is achieved. Today, this capability is available down to 0402 size. The 0435 series can be used on DC buses up to 35VDC and are available in amperage ratings from 250mA to 5.0A. Lastly, for circuits where it is preferred to have multi-use over current protection, the Resettable PTC technology is available. Typically, they are used on circuits like USB, FireWire and others where mis-wiring or defective connectors may be found. These devices re-establish the current flow after the cause of the fault has been fixed. The new LoRho series includes 0402 size PTCs that are compatible with 6V circuits and has amperage ratings from 100mA to 500mA.
