AS 61869.1 pdf download

AS 61869.1 pdf download.Instrument transformers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.3.1 General definitions 3.1.1 instrument transformer transformer intended to transmit an information signal to measuring instruments, meters and protective or control devices or similar apparatus [IEV 321 -01 -01 , modified] 3.1.2 enclosure housing affording the type and degree of protection suitable for the intended application [IEV 826-1 2-20] 3.1.3 primary terminals terminals to which the voltage or current to be transformed is applied 3.1.4 secondary terminals terminals which transmit an information signal to measuring instruments, meters and protective or control devices or similar apparatus 3.1.5 secondary circuit the external circuit receiving the information signals supplied by the secondary terminals of an instrument transformer [IEV 321 -01 -08, modified] 3.1.6 section electrically conductive part of an instrument transformer insulated from other similar parts and equipped with terminals 3.2 Definitions related to dielectric ratings 3.2.1 highest voltage of a system (U sys) highest value of the phase-to-phase operating voltage (r.m.s. value) which occurs under normal operating conditions at any time and at any point in the system [IEV 601 -01 -23, modified] 3.2.2 highest voltage for equipment (U m ) the highest r.m.s. value of phase-to-phase voltage for which the equipment is designed in respect of its insulation as well as other characteristics which relate to this voltage in the relevant equipment standards [IEV 604-03-01 ] 3.2.3 rated insulation level combination of voltage values which characterizes the insulation of a transformer with regard to its capability to withstand dielectric stresses3.2.4 isolated neutral system system where the neutral point is not intentionally connected to earth, except for high impedance connections for protection or measurement purposes [IEV 601 -02-24] 3.2.5 resonant earthed system (a system earthed through an arc-suppression coil) system in which one or more neutral points are connected to earth through reactances which approximately compensate the capacitive component of a single-phase-to-earth fault current [IEV 601 -02-27] NOTE With resonant earthing of a system, the residual current in the fault is limited to such an extent that an arcing fault in air is self-extinguishing. 3.2.6 earth fault factor at a given location of a three-phase system, and for a given system configuration, the ratio of the highest r.m.s. phase-to-earth power frequency voltage on a healthy phase during a fault to earth affecting one or more phases at any point on the system to the r.m.s. value of phase-to- earth power frequency voltage which would be obtained at the given location in the absence of any such fault [IEV 604-03-06] 3.2.7 earthed neutral system system in which the neutral is connected to earth either solidly or through a resistance or reactance of sufficiently low value to reduce transient oscillations and to give a current sufficient for selective earth fault protection. a) A three-phase system with effectively earthed neutral at a given location is a system characterized by an earth fault factor at this point which does not exceed 1 ,4. NOTE This condition is obtained approximately when, for all system configurations, the ratio of zero- sequence reactance to the positive-sequence reactance is less than 3 and the ratio of zero-sequence resistance to positive sequence reactance is less than one. b) A three-phase system with non-effectively earthed neutral at a given location is a system characterized by an earth fault factor at this point that may exceed 3.2.1 1 non-exposed installation installation in which the apparatus is not subject to overvoltages of atmospheric origin NOTE Such installations are usually connected to underground cable networks. 3.3 Definitions related to current ratings See specific requirements standard. 3.4 Definitions related to accuracy 3.4.1 actual transformation ratio (k) ratio of the actual primary voltage or current to the actual secondary voltage or current 3.4.2 rated transformation ratio (k r ) ratio of the rated primary voltage or current to the rated secondary voltage or current 3.4.3 ratio error (ε) the error which an instrument transformer introduces into the measurement and which arises from the fact that the actual transformation ratio is not equal to the rated transformation ratio 3.4.4 phase displacement (Δφ) difference in phase between the primary voltage or current and the secondary voltage or current phasors, the direction of the phasors being so chosen that the angle is zero for an ideal transformer. The phase displacement is said to be positive when the secondary voltage or current phasors leads the primary voltage or current phasors. It is usually expressed in minutes or centiradians. NOTE 1 This definition is strictly correct for sinusoidal voltages or currents only. NOTE 2 Electronic instrument transformers may introduce a delay time due to a digital data transmission and by digital signal processing. [IEV 321 -01 -23, modified]