It corresponds to the peak value (not RMS) of the theoretical fault current. 773 0 obj <> endobj OverCurrent Protection (Over Current Protection) is the current protection device action when the current exceeds a predetermined maximum. The switch is formed by a GTO thyristor connected in series with the current limiting device. Anything less leaves the apparatus or circuit susceptible to damage or total destruction within a relatively short time. Fuseology is the study of the fuse’s fundamental operating principles. 0000036599 00000 n Circuit breakers protect transformers from overcurrent situations and short circuits. United States Patent 3895337 . Overcurrent protection devices include circuit breakers and fuses. Circuits can be designed to meet many of the automotive, military, and avionic standards including ISO 7637-2, Time-overcurrent relays are available with various timing characteristics to coordinate with other protective devices and to protect specific equipment. h�b```f``U``e``ded@ A6 ��1)e�#����"�ˉ&�3����W����7�gilq���j��y�8+�����}44s^8+Ԭ�fwV �# 0000008110 00000 n 0000036307 00000 n In many countries, the short-circuit current of the array determines the size of the overcurrent protection devices. Figure 4. A known overload condition is the only situation that permits the immediate resetting or replacement of overcurrent protective devices per OSHA. Overcurrent protection devices are meant to protect against the potentially dangerous effects of overcurrents, such as an overload current or a short-circuit current, which creates a fault current. An overcurrent protective device usually will have protection from ground fault, short circuit as well as over current. Also, the maximum array current is equal to the sum of the short-circuit currents of the strings. It needs to be large enough to prevent nuisance tripping and small enough to ensure it clears the potential fault current, as well as ensuring it is less than or equal to the maximum series fuse value specified by the manufacturer. Circuit breakers are switching or automatic overcurrent protection devices. The type of overcurrent protection system used and the maximum current passing through the circuit components determine the size of the overcurrent protection system. 0000009082 00000 n 0000035869 00000 n An overcurrent exists when current exceeds the rating of conductors or equipment. The switch is formed by a GTO thyristor connected in series with the current limiting device. An insulated case circuit breaker is one that is assembled as an integral unit in a supporting and enclosing housing of insulating material and with a stored energy mechanism. 9~$�� A���pJ nGBH�\E懍�5��]e��f�50000 ]� f)�x00���v �U 2. Overcurrent protective devices An OCPD is installed to protect against instances when the current exceeds the rating of the conductors or the equipment. In this way soft-start allows the output capacitor to charge gradually toward its final value. Overcurrent Protective Devices-8 • Making capacity: Maximum fault current that a switchgear or circuit breaker can withstand (without any damage to itself electrically and structurally) while it is being closed. Figure 5.18. Short circuit is a type of overcurrent. To protect downstream loads, the point of overcurrent protection should occur at the FET switch. Commercial, industrial, and utility applications, operating at voltages above 1000 V typically may use any of the mediums depending upon the application. Once the circuit breaker opens or "trips" due to a short circuit or some other overcurrent scenario, the circuit breaker blocks current flow to the circuit. Once the circuit breaker opens or "trips" due to a short circuit or some other overcurrent … 0000005143 00000 n ETAP Star™ overcurrent device protection and coordination evaluation software provides an intuitive and logical approach to Time-Current Characteristic curve selectivity analysis. An overcurrent protection device protects the circuit by opening the device when the current reaches a value that will cause an excessive or dangerous temperature rise in conductors. 0000002100 00000 n 0000002274 00000 n 0000001837 00000 n In a fusible switch, the overcurrent protection function is accomplished by This can provide protection against excessive module reverse currents and may also enable the use of smaller string cables. Rather, a device with an interruption rating of 10,000 amps is certified to be able to stop a … Both the phase and ground overcurrents, as well as the differential current relays, are commonly used for detecting the phase and ground faults. xref The overcurrent protection devices should be placed at the point where the string cables are combined, in order to protect them from currents flowing from wider sections or other sources. It also complements the protection for generator terminal phase faults for directly connected generators. It generally operates instantly. Magnetic circuit breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection.