This work will focus on stator ground faults and will look into different schemes currently being used to provide 100% stator ground fault protection in synchronous machines. Version 1 august 1997 1mrk 504 006uen page 6 total loop impedance, zloop. Stator earth fault protection of alternator electrical4u. This is due to generator construction imperfections and the subsequent small amounts of zero sequence current that. This is due to generator construction imperfections and the subsequent small amounts of zero sequence current that will flow in the generator ground. Mar 08, 2018 100% generator stator earth fault protection is explained in this video with its basic principle. Differential protection can be considered as the first line of protection for internal stator phasetophase or phaseto ground faults in induction and synchronous motors. Sensitivity to phasetophase and phaseto ground faults high speed fault detection. Ground fault protection the following cases describe three grounding impedance levels. Generator earthing and stator earth fault protection eep. Pdf understanding generator stator ground faults and their.
Third harmonic differential voltage and subharmonic schemes are studied in this research. Neutral overvoltage protection is the simplest method for detecting a stator windingtoground fault, but this method does. Understanding generator stator ground faults and their protection. Understanding generator stator ground faults and their protection schemes. Adaptive 100% injectionbased generator stator ground. Add the sel2664 field ground module to the sel300g or sel700g to protect all the critical components in your generator with one comprehensive relay. Sel2664s stator ground protection relay schweitzer. Dedicated stator ground fault protection is required for highimpedancegrounded machines. Description and damage mechanism ground faults in a generator stator winding can cause considerable and severe damage as the level of fault current increases. Stator earth fault protection in most countries, it is a common practice to ground the generator neutral through a grounding transformer having a loading resistor across its secondary. These exhibit sensitivity, security and clearing speed issues that may subject a generator to prolonged lowlevel ground faults that may evolve into damaging faults.
Generator stator protection, underover voltage, under. Pdf understanding generator stator ground faults and. The 100 % stator earthfault protection can even be used for generators with neutral point tuned reactor. Neutral overvoltage protection is the simplest method for detecting a stator windingto ground fault, but this method does not detect faults over the entire winding. Aug 30, 2018 stator earth fault protection of alternator august 30, 2018 february 24, 2012 by electrical4u this is to be noted that, the star point or neutral point of stator winding of an alternator is grounded through an impedance to limit the ground fault current. Because the conventional methods are unable to separate ground faults close to the neutral point of view, there should be a method to protect entire stator winding.
Here, different types of faults of alternators and possible protections by conventional means have. Step 78 underfrequency accumulation 81a rate of change of. Motor faults motor protection overview ge grid solutions. A field ground fault must be detected and removed quickly and efficiently. Mar 24, 2017 the video explains you about the two most important protection schemes of stator earth fault in a synchronous generator.
If a generator does not have the appropriate grounding, the rotor and or stator can be damaged beyond repair during a ground fault event. Neutral overvoltage various third harmonic voltagedependent schemes these exhibit sensitivity, security and clearing speed issues that may subject a generator to prolonged low level ground faults that may evolve into damaging faults 37 neutral overvoltage 59g. Moreover, the cost of fixing them in case of damage is very high. As such, a single ground fault will not generally affect the operation of a generator. The design of stator ground fault protection consists of 20 hz signal generator, band pass filter, 20. Ground fault protection methods of a generator stator przeglad. Advanced generator ground fault protections relay conference. Tuned reactors which limit the earthfault current to. A stator ground fault is the most common type of fault to which generators are subjected. Neutral overvoltage various third harmonic voltagedependent schemes these exhibit sensitivity, security and clearing speed issues that may subject generator to prolonged low level ground faults that may evolve into damaging faults. The main types of stator winding faults, in order of importance are.
The most desirable method is to use the zero sequence ct approach, which is considered the best method of ground fault detection methods due to its sensitivity and inherent noise. In this work, it is focused protection of alternators based on subharmonic injection method using low frequency band pass filter. Inter turn fault and restricted ground fault protection of. Stator ground fault traditional stator ground fault protection schemes include. A novel adaptive scheme for both methods is modelled and implemented in a comprehensive lab scale setup where a real generation unit is scaled down including all. Generator protection stator earth fault protection. Tuned reactors which limit the earth fault current to less than 1 a are also used. This is supervised by a three phase undervoltage element. Advanced generator ground fault protections a revisit with. This is one of the most important electrical protection method applied for large size generators. Pdf 100% stator ground fault protection of alternators by. Generator protection rotor earth fault protection 64r1.
This is one of the most important electrical protection. Nerc protection coordination webinar series july 15, 2010 jon. Stator ground protection transformer relay free 30day. The maximum phasetoground fault current available at the generator terminals may vary from threephase fault current levels or higher to almost zero. F relay coil of the differential protection shown in. Protection of alternators different types of fault. Protection, page 46 rotors the field circuit of a generator is an ungrounded system. These types of faults occur due to the insulation breakdown of the stator coils. Statistically, 9095% of all system shortcircuits are ground faults so this is an important topic. A comparison of 100% stator ground fault protection. Today there is a distinct trend towards providing ground fault protection for the entire stator winding 100% ground fault protection. Stator ground faults could be caused by the insulation degradation in the windings as well as environmental influences such us moisture or oil in combination with dirt which settles on the coil surfaces outside the stator slots. A low impedance grounded generator relates to a generator that has zero or minimal impedance at the wye neutral point.
The practices used in groundfault protection are described in. Numerous methods of stator winding to ground fault protection schemes are also reported in the literature. Stator earth fault protection of alternator august 30, 2018 february 24, 2012 by electrical4u this is to be noted that, the star point or neutral point of stator winding of an alternator is grounded through an impedance to limit the ground fault current. Generator protection systems understanding common faultsfailure conditions. Conference technical papers and manufacturer documents do a good job of describing the implementation and function of the various 64g element types. Conference technical papers and manufacturer documents do a good job of describing the implementation and function. What is meant by the rotor earth fault in a generator. Pdf in this paper, 100% stator ground fault protection by application of low frequency 20 hz injection for 6. This detected faults over 90 95% of the stator winding. Tripping mode conventional protection schemes for stator ground fault detection provides protection for only about 80 to 95 percent of the stator windings. Fundamental zero sequence over voltage scheme 95% stator winding. Gpm field and stator ground fault protection modules. Stator ground fault traditional stator ground fault protection schemes include neutral overvoltage and various third harmonic voltagedependent schemes. Conventional stator ground fault protection until the late 1970s, almost all stator ground fault protection for unitconnected generators involved the use of only an overvoltage relay 59g in the generator neutral that was tuned to the fundamental frequency.
Generator stator protection, underover voltage, under over. Therefore, additional protection is required in the form of thirdharmonic. Medium voltage products technical guide protection. Pop e, a comparison of 100% stator ground fault protection schemes for generator stator windings, ieee trans. In this thesis, synchronous generator stator windings to ground fault is studied as one of the most common and crucial faults in these machines. The design of stator ground fault protection consists. In that case during an earth fault at the generator hv terminals, earth current from the generator is roughly equal. The following is a circuit that could be used for field ground generator protection.
W, the fault current i f, flows through a part of the winding and neutral to ground circuit. In this paper, 100% stator ground fault protection by application of low frequency 20 hz injection for 6. Ground fault protection damage to a phase conductors insulation and internal shorts due to moisture within the motor are common causes of ground faults. Traditional stator ground fault protection schemes include. Upgrading the rotor ground fault protection on electric. The zerosequence voltage transferred to the stator circuit in. Generator protection systems article on internal faults.
Sel2664 field ground module schweitzer engineering. Differential protection can be considered as the first line of protection for internal stator phasetophase or phasetoground faults in induction and synchronous motors. Understanding generator stator ground faults and their. The degree of ground fault protection provided by these schemes is directly related to how. There are various methods used in grounding the generator. These faults occur mainly due to the insulation failure of the stator windings. Circuit breakers defend the generator rotor and stator against failure generated by a components on the load side of the. Generator protection rotor earth fault protection 64r1 64r2. Eliminate protection blind spotsdesignate up to four individual injected frequencies to ensure that the protection does not have a blind spot. Or, add the sel2664 to the sel2664s to complete ground fault protection on both the rotor and stator. Pdf 100% stator ground fault protection of alternators. The current flowing to the delta connected load thru line a is 10a. The 100% stator ground fault scheme includes a 95% uniti, which.
Medium voltage products technical guide protection criteria. Modeling and experimental verification of a 100% stator ground fault protection based on adaptive thirdharmonic differential voltage scheme for synchronous generators abstract. A strategy that is typically used to limit the level of the ground fault current is to connect an impedance between the neutral point of the motor and ground. If the ground fault is bolted and not intermittent, ground fault protection is required for highimpedancegrounded then the potential difference of the unfaulted phases increases machines. Symmetrical components example problem one conductor of a three phase line is open. The practices used in ground fault protection are described in a later section of this guide. The 889 stator differential element offers the following distinct features. Earth fault protection must be applied where impedance earthing is employed that limits the earth fault current to less than the pickup threshold of the overcurrent andor differential protection for a fault located down to the bottom 5% of the stator winding from the starpoint. The lab scale generator is used to emulate the fault characteristics of industrial generators along the stator windings. A single phase to ground fault on a field is dangerous because a second ground fault could short part of the field winding, causing damaging vibrations. Depending on the ground fault current available, the damage may be repairable or nonrepairable. The third harmonic voltage between the neutral point and earth will increase, compared to generators with earthing resistor. Pdf adaptive 100% injectionbased generator stator ground.
Simulations based on finite element analysis methods were used to design and tune the laboratory. Gpm field and stator ground fault protection modules instruction manual 7 divider output. There are several ways by which a ground fault can be detected. The principle diagram of the relay is shown in fig. Nerc protection coordination webinar series july 15, 2010. The degree of ground fault protection provided by t hese schemes is directly related to how the generator is grounded and, therefore, to the magnitude of the ground fault current available. In this paper, a novel adaptive stator ground fault protection scheme based on thirdharmonic differential voltages is implemented on a lab scale synchronous generator.
Ragek 100 % and 95 % stator abb network partner ab earth fault protection for generators. Inter turn fault and restricted ground fault protection of stator. This is very sensitive type earth fault protection but it also have some limitations. Upgrading the rotor ground fault protection on electric generators summary rotor field ground faults also referred to as earth faults can occur on electric generators without warning, causing severe damage to rotors and forcing extended outages that can be extremely costly. Gasparovsky slovak university of technology in bratislava, slovak republic this paper deals with the influence of harmonics produced by the static excitation system of generator on the rotor ground fault protection of synchronous generator. F relay coil of the differential protection shown in the figure above. Cfe generator protection guidelines for setting 40 and 64g. Modeling and experimental verification of a 100% stator. Therefore, generators must be protected against all kind of. Grounding methods are proportional to size and complexity of facility larger and more complex designs require more complex grounding circuit. The operating theory, a setting example, and field measurementsare provided for each of the three. Stator ground protection transformer relay free 30. This method of earthing is called high impedance earthing where the earth fault current is limited to 510 amps. Neutral overvoltage protection is the simplest method for detecting a stator windingtoground fault, but this method does not detect faults over the entire winding.