IEEE 421.6-2017 pdf free download – IEEE Recommended Practice for the Specifcation and Design of Field Discharge Equipment for Synchronous Machines.
field breaker rated continuous current- The current that the main contacts of a field discharge circuit breaker should he required to carry without having the temperature of its parts exceed the values specified and guaranteed by the manufacturer
NOTE—The rated continuous curreni of a ticid circuit breaker plies to the main contacts aid not (he disclsage contacts I ifprovided).
field breaker rated control voltage. The voltage at which the mechanism of the field breaker is designed to operate when measured at the control power terminals of the operating mechanism (e.g.. trip coil) with the highesi iipcrating current flowing. Raced control voltages and their ranges for low -voltage power circuit breakers are listed in Table 23, lLLl± Std CI?. l6ru*2otJO.
field breaker rated interrupting current of discharge contaeta: The maximum value of direct currcntt that the disch.itgc contscts ditatld be tequired to internipt.
field breaker rated interrupting current of main contacts: The maximum value of direct current that the field breaker main contacts should he required to interrupt at rated maximum interrupting voltage.
field breaker rated making current oF the discharge contacts. The peak value of current that the discharge contacts should be required to close with rated maximum voltage applied across the contacts.
field breaker rated may itiiuni interrupting voltage Average value of field breaker arcing voltage during the arctng ttme when interrupting the rated interrupting current of main contacts,
field breaker rated nominal voltage class: The voltage to wInch operating and performance charactenstics should be referred, and the voltage to witich dielectric characteristics of the circuit breaker are related.
field breaker rated short-time voltage The highest voltage at which the circuit breaker main contacts should he required to interrupt exciter short-circuit current
rated interrupting current of main contacts at rated short-time voltage: The maximum value of direct- current that the main contacts of the field breaker should he required to interrupt at rated short-time voltage.
4. Field discharge equipment
The field discharge equipment plays a vital role in protecting the synchronous machine and excitation sstem. In case of a severe electrical fault iii the vicinity of the synchronous machine orexcimation system, the function of the field discharge equipment is to pros-ide a quick machine rotor flux reduction in order to limit the damages caused by the very high energy released during the fault. The field discharge equipment also has the function to limit the overvoltages between the poaitivc and negative terminals of the synchronous machine field coil. The field dtscharge equipment can physically disconnect the voltage source from the field in case of severe excitation system faults and allow discharge via the field discharge resistor. During normal shutdown, multiple strategies arc common for field discharge including implementing two power Silicon Controlled Rectifiers t.SCRvi connected in anti-parallel tcrowtmar) with a series discharge resistor across the field. At shutdown, the crowbar SCRv are gatesl (triggeresht on simnulmanerius to the field breaker tnp conirnand in order to slisclsarge the field energy through the discharge resistor. In case ofstatmc excitation, the 5CR converter bridge may have the triggering pulses blocked or foeeed to the full inversion initiated simultaneously with the field breaker tnp command.IEEE 421.6 pdf download.