Guide to Construction of ArTu switchgear - Abb

8 Protection against the effects of short-circuit8.1 Checking short-circuit withstandGENERALSTANDARDS ANDCHARACTERISTICSVERIFYING THEOVERTEMPERATURESPROTECTION AGAINSTSHORT-CIRCUIT ANDELECTRIC SHOCKSPRACTICAL INDICATIONSCERTIFICATION ANDCONSTRUCTIONThe electric switchgear must be constructed to resist the thermal and dynamic stresses causedby a short-circuit current up to the assigned values. Furthermore, the switchgear must be protectedagainst short-circuit currents by means of circuit-breakers or fuses which can either beinstalled in the switchgear or on its supply side.At the time of ordering, the user must specify the short-circuit conditions at the point of installation.This chapter considers the following aspects:- the need or not to carry out the check on the short-circuit withstand of the switchgear.- suitability of the switchgear for a plant according to the prospective short-circuitcurrent of the plant and the short-circuit parameters of the switchgear.- suitability of a busbar system according to the short-circuit current and to theprotection devices.8.1 Checking short-circuit withstandThe short-circuit withstand check is dealt with by the IEC 60439-1 Standard, and the cases wherethe check must be carried out and the different types of checks are specified in particular.Checking the short-circuit withstand is not necessary in the following cases:• for switchgear which has a rated short-time withstand current or rated conditionedshort-circuit current not exceeding 10 kA• for switchgear protected by current limiting devices with a peak limited current not higherthan 17 kA in correspondence with the maximum admissible prospective short-circuitcurrent at the terminals of the incoming circuit of the switchgear• for the auxiliary circuits of switchgear provided to be connected to transformers whoserated power does not exceed 10 kVA with a rated secondary voltage which is not lessthan 110 V, or which does not exceed 1.6 kVA with a rated secondary voltage of lessthan 110 V, and whose short-circuit voltage is not less than 4% in both cases.• for all the parts of the switchgear (main busbars, main busbar supports, connectionsto the busbars, incoming and outgoing units, protection and operating apparatus, etc.)which have already undergone type tests valid for the existing conditions.The need to check the short-circuit withstand can therefore be seen in the following way:10 kA switchgear Icwor10 kA conditioned switchgear IccYESYESThe peak current is limited by the protection device,in correspondence with the prospective short-circuit current,at the following value: Ip 17 kANOCERTIFICATESChecknot requiredCheckrequiredWith regard to the details regarding execution of the short-circuit test, we recommend you referdirectly to the IEC 60439-1 Standard.DECLARATION OFCONFORMITY44 ABB SACEGuide to Construction of ArTu switchgear