IEC TS 60034-24 pdf download – Rotating electrical machines – Part 24: Online detection and diagnosis of potential failures at the active parts of rotating electrical machines and of bearing currents – Application guide

IEC TS 60034-24 pdf download – Rotating electrical machines – Part 24: Online detection and diagnosis of potential failures at the active parts of rotating electrical machines and of bearing currents – Application guide
1 scope
This part of lEC 60034 is applicable to the on-line detection and diagnosis of failures at theactive parts of multi-phase rotating electrical machines (induction and synchronous machines)and of bearing currents.The failure analysis includes:
-interturn faults;
-phase-to-phase short-circuits;
double earth faults and single earth faults of motors with earth connection of the star-point;
static and dynamic eccentricities;
– cage imperfection or defects (e.g. broken bars or end-rings);- bearing currents.
This can be achieved by tools like search coils or other magnetic sensors or partly by theanalysis of the terminal voltages and currents.
The detection of the following effects is excluded from the scope:
– vibration (covered by Iso standards, e.g. ISO 10816 and lSO 7919);partial discharge (covered by lEC 60034-27);
– single earth-faults of motors without earth connection of the star-point;- core imperfection.
Also excluded are special methods applicable for specific applications only (e.g. turbogenerators).
Normative references
There are no normative references in this technical specification.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
distribution factor
the factor，related to a distributed winding，which takes into account the reduction in thegenerated voltage due to the phase difference between the voltages generated in the coils indifferent slots
[IEV 411-38-37]
3.2
chording (pitch) factor
the factor，related to a distributed winding， which takes into account the reduction in thegenerated voltage, when the winding pitch is not 100 %
[IEV 411-38-38]
3.3
branch factor
the factor,related to a distributed winding，which takes into account the reduction in thegenerated voltage due to the phase difference between the voltages generated in the series-connected branches
4Basis of the diagnosis
The ability of electrical machines to operate is based on the existence of a magnetic field inthe air-gap，which is looping in a cross-sectional area of the laminations of stator and rotor.Flux components in the end-portions of the machine outside the cores are of a parasiticnature. Therefore available signals suitable for the detection of potential faults originate fromthe magnetic field in the air-gap,which shall be analyzed in order to distinguish betweenthose components which occur under regular operating conditions and those componentswhich are attributed to a specific failure and which do not exist in a healthy machine.
Since the winding producing the magnetic field consists of coils distributed symmetricallyaround the circumference and since the sum of the supplying currents is usually zero, the air-gap field forms also a periodic function along the circumference.The wave of the flux densitycan be considered as the superposition of a sum of sinusoidally distributed waves, which arecharacterized by the following features:
– amplitude,
– number of pole-pairs,-angular velocity,
– phase-angle,
-type of wave (rotating or standing).
Table 1 shows the composition of the air-gap field in the case of a three-phase cage inductionmotor,which is equipped with an integral slot winding. The table can easily be extended to bevalid also for fractional slot windings.Similar tables can be developed for slip-ring motors andall kinds of synchronous machines.
5Kinds of electrical signal analysis5.1General
A valuable detection method shall be able to detect failures at an early stage. Thereforesignals disclosing a rapid change in the case of small deficiencies， are optimal for theintended purpose.By contrast signals which vary only insignificantly should not be used asthe basis of the diagnosis.
The signal processing needs the availability of appropriate electronic equipment. Although theresolution of modern devices is high, signals which do not need excessive precision should bepreferred in this respect.
5.2Stator current/voltage analysis
The analysis of the terminal voltages or currents of a rotating machine allows identification of- different frequencies,
– positive-, negative-, and zero-sequence components,- different amplitudes of the components.
ln general, all waves of induction in the air-gap field can induce voltages of certainfrequencies in the stator winding and can cause currents of the same frequencies. Theadditional current components which are generated by a specific failure are superimposed tothe supply values during undisturbed operation.All details shall be taken from the ‘relevanttable, that is Table 1 in the case of three-phase cage induction motors.
Table 1 is worded for one single supply frequency j4.However，in case of a convertersupplied machine， it is valid for each voltage/frequency component,which is contained in theoutput spectrum of the converter.
Table 1 shows the components of the air-gap field. Whether a specific component induces avoltage in the stator winding, depends on its winding factor for the number of pole pairs underconsideration.The winding factor is the product of the following terms:
– the distribution factor,
– the chording factor,
– the branch factor.