P345 20Hz Stator Earth Fault Application Guide

Generator Protection MiCOM P345

Stator-Earth Fault Protection via 20 Hz low frequency injection method

Setting guideline, examples and commissioning

CONTENTS 1

INTRODUCTION......... INTRODUCTION........................... ................................. .............................. ................................. ............................... .................... ....... .3

2

SETT SETTIN ING G GUI GUIDE DELI LINE NES S FOR FOR 100% 100% STAT STATOR OR EARTH EARTH FAULT FAULT PROTE PROTECT CTION ION 4

3

GENE GENERA RATO TOR R EART EARTHE HED D VIA VIA PRI PRIMA MARY RY RES RESIS ISTO TOR R IN GENE GENERA RATO TOR R STARPOINT ................................... .................................................... .................................. ................................. ................................ ................ .7

3.1

Setting Setting example example with with generator generator earthe earthed d via a primary primary resisto resistorr in generato generatorr starpoint starpoint ... 9

4

GENERA ERATOR EAR EARTHED VIA EAR EARTHIN THING G TRANSFORMER......................... 11

4.1

Setting Setting example example with with genera generator tor earthe earthed d via earthin earthing g transforme transformerr and secon secondary dary resistor at the starpoint of the generator ......................................................................13

4.2

Setting Setting example example with with genera generator tor earthe earthed d via earthin earthing g transforme transformerr and secon secondary dary resistor at the terminals of the generator .....................................................................15

5

METH METHOD ODS S TO TO EST ESTAB ABLI LISH SH THE THE SER SERIE IES S IMP IMPED EDAN ANCE CE SETT SETTIN INGS GS FOR FOR 64S 64S ...................................... ................................................... ............................... ................................. .............................. ................................. ..................... ... . 17

5.1

By Calculati Calculation on ........................ ...................................... ............................ ............................ ............................. ............................. ............................ ..............17 17

5.2

By Measurem Measurement ent ........................ ...................................... ........................... ........................... ............................ ............................. ..........................1 ...........17 7

6

COMMISSIONING COMMISSIONING .................................. ................................................... ............................... .............................. ......................... .......... 18

6.1

Connec Connectt the the test circuit circuit ........................ ...................................... ............................ ............................ ............................. ............................. ...............18 .18

6.2

Check Check the pick-up pick-up settings settings ......................... ...................................... ........................... ............................ .............................. ........................18 ........18

6.3

Perform Perform the timing timing tests ......................... ....................................... ............................ ............................ ............................. ...........................1 ............19 9

6.4

Perform Perform the the 100% 100% stator stator earth earth fault fault supervi supervision sion test ............ ......................... ............................ ..........................2 ...........21 1

6.5

64S Calibrat Calibration ion procedur procedure................... e............................... ............................ ............................. ........................... ............................ .................22 ...22

6.6

Angle Angle compe compensatio nsation n setting setting (64S Angle Angle Comp) Comp) ......................... ....................................... ............................ ...................23 .....23

6.7

Series Series resista resistance nce settin setting g (64S (64S Series Series R) R) ................. ............................... ............................ ........................... ........................23 ...........23

6.8

Calibrati Calibration on at at the 64S 64S alarm alarm and and trip trip settings settings ...................... .................................... ............................. ..........................2 ...........23 3

6.9

Parallel Parallel Conducta Conductance nce (64S Parallel Parallel G) ................ ............................ .......................... ............................. ............................. ...............24 .24

6.10 Checking with other resistance values................... .................... .......... ..................... ...................... ..................... ............24 ..24 6.11 Testing the 100% stator stator earth fault protection on the the generator ........................ ............ ...................... .......... 24 6.12 Start-up tests............... tests... ........................ ...................... .................... ..................... ..................... ...................... ............ ............ ............ .......25

Protection & Control place country-regionGermany country-regionGermany

1

Introduction The 100% stator stator earth fault protection protection using using a low frequency frequency injection injection technique technique detects earth faults in the entire winding, including the generator neutral point. If an earth fault in the generator starpoint or close to the starpoint is not detected the generator is effectively running with a low impedance earth bypassing the high impedance impedance earth typically used on large machines. A second earth f ault can then cause a very high current to flow which can cause a lot of damage to the machine. This is why 100% stator earth fault protection is a common requirement for large machines. The low frequency injection technique can be used to provide protection for 100% of rd the stator winding compared to only 20-30% of the winding using the 3 harmonic technique. Also, the low frequency injection technique provides protection when the machine is stopped and running and also when the machine is running up and down. rd The 3 harmonic technique has to be blocked or is not operational when the machine is stopped and when the machine is running up and down. Also, some machines only rd rd produce a low level of 3 harmonic voltage (<1% Vn) and for these machines the 3 harmonic method of 100% stator earth fault protection can not be used. So in these applications only the low frequency injection method can provide 100% stator earth fault protection. 100% stator earth fault protection can be provided by injecting an external low frequency alternating voltage into the starpoint or the terminals of the machine. Under normal healthy conditions conditions only a very small current flows via the stator earth capacitance due to the high impedance of this path at low frequencies (Xc = 1/2 πfc). In the event event of an earth earth fault the measured measured current current increas increases es due to the smaller smaller impedance of the earth fault path. From the injected voltage and the fault current the relay can determine the fault resistance. The protection can also detect earth faults at the generato generatorr terminals terminals includin including g connected connected componen components ts such as voltage voltage transformers. A loading device with a low frequency generator is required for implementation. implementation. The output of the low frequency signal generator (approx 25V) is connected via a bandpass bandpass filter in parallel with a loading resistor to a neutral transformer at the generator starpoint or an earthing (broken delta) transformer at the terminals of the generator. The loading resistor is connected in parallel with the low frequency generator to generate a defined neutral current in normal healthy conditions. The voltage to be injected into the generator starpoint depends on the driving 20 Hz voltage (voltage divider, load resistor and bandpass), and on the transformation ratio of the neutral or earthing transformer. To prevent the secondary load resistance from becoming too small (it should be > 0.5Ω where possible to minimise measurement errors) a high secondary voltage, such as 500V, should be chosen for the neutral or earthing transformer. It is important that the earthing transformer never becomes saturated otherwise ferroresonance may occur. It is sufficient that the transformer knee point voltage be equal to the generator rated line voltage. The low frequency voltage is fed to t he relay via a voltage divider and the low frequency measuring current is fed via a miniature current transformer. All interference deviating from the nominal low frequency signal is filtered out. The 100% stator earth fault protection can also be applied with a primary loading resistor. The 20Hz voltage is connected via a voltage transformer and the neutral starpoint current is directly measured via a CT. From the measured measured current current and voltage vectors the complex complex impedance impedance can be calculated and from this the ohmic resistance is determined. This eliminates disturbances caused by the stator earth capacitance and ensures high sensitivity. ,

The relay algorithm can take into account a transfer resistance 64S Series R, that may be present at the neutral or earthing voltage transformer. An example of the series resistance is the total leakage resistance of the earthing or neutral transformer, through which the injected voltage is applied to the g enerator neutral. The algorithm can also account for parallel resistance, 64S Parallel G (G = 1/R), such as an additional earthing transformer connected on the LV side of the step-up transformer. Other error factors can be taken into account by the angle error compensation, compensation, 64S Angle Comp. The relay includes a 20Hz overcurrent element which can be used as a back-up to the 20Hz under resistance protection. The overcurrent element is not as sensitive as the under resistance elements as it does not include any transfer resistance compensation or any compensation for capacitance affects. In addition to the determination of the earth resistance, the relay also includes 95% stator earth fault protection as a back-up to the 100% stator earth fault protection. The neutral voltage protection from the measured earthing/neutral transformer or calculated neutral voltage from the 3 phase voltage input can be used to provide 95% stator stator earth fault protection protection and is active during the run-up run-up and run-down run-down of the generator. The 100% stator earth fault protection includes 2 stages of under resistance protection for alarm and trip and an overcurrent protection stage, with each stage having a definite time delay setting. The protection includes a supervision element to evaluate a failure of the low frequency f requency generator or the low frequency connection.

2

Setting Setting guidel guideline ines s for for 100% 100% stato statorr earth earth fault fault prot protecti ection on The 100% stator earth fault protection element can be selected by setting the 64S 100%St EF cell to Enabled. The 64S R Factor is set as described in section 3 and 4. The under resistance alarm threshold, 64S Alarm Set, must be set below the level of resistance present under normal conditions. This resistance can be determined by viewing the 64S R cell in the MEASUREMENTS 3 menu. A t ypical value for the primary fault resistance alarm setting is between 3-8kΩ . The under resistance trip threshold, 64S R<2 Trip Set, must be set below the level of resistance present under normal conditions. This resistance can be determined by viewing the 64S R cell in the MEASUREMENTS 3 menu. A typical value for the primary fault resistance trip setting is between 1-2kΩ . The overcurrent trip threshold, 64S I>1 Trip Set, must be set above the 20Hz level of current present under normal conditions. This secondary current can be determined by viewing the 64S I Magnitude cell in the MEASUREMENTS 3 menu. The P345’s 64S protection has a very powerful band pass filter tuned to 20Hz. The band pass filter is designed with an attenuation of at least -80db for frequencies less than 15Hz and greater than 25Hz. -80db is equivalent to a noise rejection capability with a noise-to-signal ratio of 10000 to 1. However, it is not possible for the filter to reject all the ‘noises’ around 20Hz. When the power system frequency is at 20Hz, the relay will not be able to distinguish the power system frequency signal and the injected signal. Under no fault conditions, the influence of the 20Hz power system components is practically negligible. So there is no risk of relay mal-operation under system frequency conditions, from 0Hz to 70Hz. The current measured will effectively be the capacitive current plus the current through the parallel resistance. resistance. The 64S I>1 should be set higher than this quiescent current. For earth faults occurring 0 - 15Hz and 25 - 70Hz at any point on the stator windings both the under resistance (64S R<) and overcurrent protection (64S I>) work correctly under these power system frequency conditions due to the relay filtering. The power


system frequency components will be removed by the band pass filter and will have no influence on the protection measurements. The influence of the power system signals depend on the position of the fault. At the star point, the influence is negligible. Therefore, both the under resistance (64S R<) and overcurrent protection (64S I>) work correctly under the complete range of power system frequencies from 0 to 70Hz when the f aults occur at the star-point. For faults not at the star point where the power system frequency signals are at or around 20Hz the power system 20Hz signals become more and more dominant as the fault position moves towards the terminal of the generator. For these faults there is a possibility the R< elements can overreach. In most cases the current is 180 out of phase with the voltage. The 64S current (I 64S(P345) ) under fault conditions consists of two components, the 20Hz current component from the 20 Hz injection system, (I 64S(20)) and the 20Hz current component produced by the neutral displacement voltage, (I 64S(G)). At or around 20Hz, the I 64S(G) cannot be filtered off and thus contributes in magnitude to the I64S(P345), which improves the fault detection capability of the 64S I>1 protection function. Thus, the 64S I> element can be used to t o provide back-up protection for faults that occur when the machine is running at 20Hz. The I64S I>1 Trip can be set as a backup element 15-25Hz to the 64S R<1/R<2 elements by setting a longer trip time. If required the R<1 and R<2 protection can be blocked at around 20Hz. The 64S F Band Block (operates when the measured frequency is in the range 15-25Hz) and can be used to inhibit/block the 64S R<1, R<2 protection. A time delay for these elements can be set in the 64S R<1 Alm Dly, 64S R<2 Trip Dly and 64S I>1 Trip Dly cells. The default time delays provide typical values. If the 20 Hz voltage drops below the voltage supervision threshold, 64S V<1 Set and the 20Hz current remains below the current supervision threshold, 64S I< Set, there must be a problem with the 20 Hz connection. The default settings for 64S Supervision element, 64S V<1 Set (1V) and 64S I<1 Set (10 mA) will be adequate for most applications. Where the loading resistor is less than 1 Ω, the supervision voltage threshold, 64S V<1 Set, must be reduced to 0.5 V, the supervision current threshold, 64S I<1 Set, can be left at 10 mA. The Comp Angle setting is used to compensate the angle errors between the CT and earthing or neutral transformer. The setting can be f ound from primary testing. The 64S Series R setting is used to account for the transfer resistance of the earthing or neutral voltage transformer. The default setting will be zero as the resistance of the voltage transformer is normally negligible. The resistance of the voltage transformer is not negligible if the low frequency voltage is fed to a primary side resistor via the voltage transformer. The setting can be estimated from calculation or from primary testing, see section 6. In large power units with a generator generator CB, application applications s can be found where there is some additional loading equipment such as an earthing transformer on the low voltage side of the unit transformer to reduce the influence of zero sequence voltage when the generator CB is open. If the low frequency source is connected via the neutral transformer in the generator starpoint, when the generator CB is closed the protection measures the loading resistance on the unit transformer side which can be mistaken for an earth resistance. °

The 64S Parallel G setting can be used to account for this additional parallel loading resistance. The default setting is 0, no additional loading loading resistor. The neutral transformer-resistor at the star point should produce a resistive current equal to the capacitive current for an earth fault at rated voltage. The transformer, resistor and injection devices should withstand this condition f or 10 seconds. To prevent the secondary load resistance from becoming too small (it should be > 0.5Ω where possible to minimise measurement errors) a high secondary voltage, such as 500V, should be chosen for the neutral or earthing transformer. It is important that the earthing t ransformer never becomes saturated otherwise ferroresonance may occur. It is sufficient that the transformer knee point voltage be equal to the generator rated line voltage. For a generator earthed with a primary resistor in the generator g enerator starpoint the lead resistance between the earthing transformer and the 20Hz generator/bandpass filter can have a significant affect on the accuracy of the measured resistance by the relay. So if the 20Hz generator and bandpass filter are mounted in the protection cubicle the loop lead resistance should ideally be kept below 0.5 Ω. If the 20Hz generator and bandpass filter are mounted near the earthing transformer then this will keep the errors to a minimum. The lead resistance from the 20Hz generator/banpass filter to the relay does not significantly affect the accuracy of the measured resistance. resistance. For configurations with an earthing transformer and secondary loading resistance the lead resistance does not have a significant affect on the measured resistance by the relay. Note, other earth fault protection functions such as residual overvoltage, earth fault or sensitive earth fault protection can be connected in parallel or series with to the 100% stator earth fault protection measurement inputs to provide back-up to the 100% stator earth fault protection. ,

There will be some measurement of the injected 20Hz injected and circulating current under normal healthy conditions on the VN1/2, I Sensitive and IN inputs used by these protection functions. For most applications under no fault conditions the 20Hz voltage measured by therelay across the potential divider in the external filter box and loading resistor will small and be much less than 5% of rated voltage. The 20Hz current under normal conditions should be very close to zero. So settings can be used to protect 95% of the stator winding in most applications. When commissioning the relay the level of 20Hz neutral voltage or earth current should be checked to make sure it is less than half the setting value of any protection enabled to provide stability under normal operating conditions. There will be some fluctuation of the 20Hz neutral voltage and earth current measured by the VN1/2, ISensitive and IN inputs under no fault conditions due to the 50/60Hz frequency tracking of these inputs. It is not recommended recommended that the 3rd harmonic harmonic method of 100% stator earth fault protection is used in parallel with the 20Hz injection method as there will be some measurement of the 20Hz signal by the VN1 input used by the 3rd harmonic protection which could interfere with the correct operation of this sensitive function.


3

Genera Generator tor earth earthed ed via via prima primary ry resist resistor or in in gener generato atorr starpoi starpoint nt In some power systems the generators have a load resistor installed directly in the generator generator starpoint starpoint to reduce reduce interfere interference. nce. The following following diagram shows shows the connection of the 20 Hz generator, band pass filter and protection device.

20Hz Source

Vn s rt

: 500V 500V:200V

RL

P 45

V64S

1:1 CT

164S

100% Stator Earth Fault with Primary Earthing Resistor Arrangemen t

Where RL V64S I64S

loading resistor displacement displacement voltage at the protective relay measuring current at the protective relay

Figure 1:

64S Connection for Generators earthed via primary resistor

The 20 Hz voltage is injected into the generator starpoint via a powerful voltage transformer across the primary load resistor. In the presence of an earth fault, an earth current flows through the CT in the starpoint. The protection detects this current in addition to the 20 Hz voltage. A two pole isolated voltage transformer must be used with low primary/secondary primary/secondary impedance. impedance. This applies for t he 20 Hz frequency. Primary vo voltage: Vn,Generator />3 (non-saturated up to Vn ,Generator ) Secondary voltage: voltage: 500 V Type and class: Uk<10% (50 Hz or 60 Hz); VA rating according to manufacturer Primary/secondary Primary/secondary impedance at 20Hz(Zps) Zps < RL (Zps<10000).

According to IEEE part II - Grounding of Synchronous Synchronous Generator Systems – the earth fault current usually is limited to 10A depending upon the generator size and voltage level. Sufficient damping to reduce transient overvoltages to safe levels can be achieved with a properly designed resistor. This condition can be met by making the value of the resistor in Ohm equal or less then the ohmic value of the three phase capacitance to earth.

The CT is installed directly in the starpoint on the earth side, downstream of the load resistor. Type: 15VA 5P10 or 5P15 Rated secondary current: 1A Transformation Ratio: 1 (1A/1A) As the t he transformation ratio is 1:1, a current transformer with a maximum number of ampere windings must be chosen. Note, the linear range of the 100% stator earth fault input is up to 2In. So if the earth fault current is limited to <2A then the 100% stator earth fault 1A input can be used. For earth fault currents 2-10A the relay 5A current input can be used. Note, for the 5A inputs the 64S I Magnitude measurement in the Measurements 3 menu will show 5 times lower current than being injected. There is no CT ratio setting for the 100% stator earth fault current input, however the resistance measurement and 64SR<1/2 protection can be compensated by the 64S R Factor setting if the 5A input is used by multiplying the CT ratio by 5 in the formula for the R factor. If the 64S I>1 protection is used then the setting needs to be divided by a factor of 5 when using the 5A input. During the primary test the correction angle (64S Angle Comp) and the ohmic transfer resistance (R factor) of the voltage transformer must be determined and set. The primary resistance and conversion factor for the resistance (R Factor) is calculated as follows:

R Pr

=

imary

∗

VTRatio

VDivider R atio

CTR atio

∗ R Secondary

Where the VT ratio is

VTRatio =

Vn Pr imary imary

3

V n Secondary Using the data shown in figure 1 as an example and assuming the 5A rated current input is used,

R Pr imary Pr imary

Vn

=

(

∗

3

500

)

5 2∗ 5

∗ R Secondary

Therefore,

R Factor

=

(

Vn

3

5 )∗ 500 10

Note:

Due to the transfer resistance, there may not be an ideal transformation ratio of the voltage transformers. For this reason major deviations of the ‘R Factor’ can occur. It is recommen recommended ded to measure measure the transforma transformation tion ratio with 20 Hz infeed infeed when when the machine is at standstill. This value should then be set.

R

=


3.1 Setting Setting exam example ple with with generat generator or earthe earthed d via a primary primary resi resisto storr in generator starpoint Voltag tage tr transfor former ra rating:

19kV/ >3 >3/500V, 0V, 15 1500VA 0VA Uk Uk<10 <10% (non-saturated up to Vn,Generator ) non-saturated up to 1.1 x Vn,Generator 5:2 1A/1A, 15VA 5P10

Insulation requirement: Voltage divider: Current transformer:

The maximum primary earth fault current should be limited by the primary resistor to <10A. According to IEEE part part II, as mentioned above, above, the resistor RL, which is used for the earthing of the starpoint has to be smaller or equal to the ohmic value of the capacitive reactance to earth of all three phases. In others words, the resistive component of fault current should not be less then the residual capacitive current. current. This is a basis to design the primary earthing resistor. Assumption: Capacitive reactance reactance to earth of all three phases C 0 = 0.8837uF

X cg

=

1

2 ∗ π ∗ ∫ ∗ C0

=

1

=

3602Ω

100 ∗ π ∗ 0.8837 µF

RL :≤ 3602Ω RLselected = 3600Ω If the effective earthing resistor is made equal to the total residual capacitive impedance of 3600 0 then, with a generator terminal fault at normal voltage, the neutral current is:

In

=

19kV / 3 3600Ω

=

3A

The actual fault current will contain equal resistive and capacitive components. Note, the linear range of the 100% stator earth fault input is up to 2In. So if the earth fault current is limited to <2A then the 100% stator earth fault 1A input can be used. For earth fault currents 2-10A the relay 5A current input can be used. Note, for the 5A inputs the 64S I Magnitude measurement in the Measurements 3 menu will show 5 times lower current than being injected. There is no CT ratio setting for the 100% stator earth f ault current input, however the resistance measurement and 64SR<1/2 protection can be compensated by the 64S R Factor setting if the 5A input input is used by multiplying the CT ratio ratio by 5 in the formula for the R factor. If the 64S I>1 protection is used then the setting needs to be divided by a factor of 5 when using the 5A input.

Factor

(

5 19kV 3 )∗ = 11 500 2∗5


Typical trip and alarm settings for the 100% stator earth fault under resistance elements are: Trip stage: primary 2 kΩ secondary 182 Ω Alarm stage: primary 5 kΩ secondary 455 Ω Voltage across the resistor during an earth fault is 19kV/ √3 = 10.9kV and with the factor of 1.1 for transient overvoltages at earth faults 1.1 x 10.9kV = 12kV. So, 12kV insulation will be satisfactory. But according to VDE an insulation level of minimum 19kV is needed.

Summary of components: Voltag tage transfor former rating: 19 kV/ √3/500 V (non-saturated up to Vn ,Generator ) Insulation requirement: non-saturated up up to to 1.1 x Vn Vn,Generator The transforme transformerr VA rating rating is: is: 1500VA 1500VA Uk<10% Uk<10% (e.g. Ritz Messwand Messwandler) ler) Primary/secondary Primary/secondary impedance at 20Hz < 10000. Voltage divider: Current transformer: Loading Resistor:

5:2 (included in 20Hz Filter) 1A/1A, 15VA 5P10 3600 Ω (3A, for short time operation of 10s or 20s)

Additional Remarks: The IN current input used by the stator earth fault protection can also be connected to the earth CT to provide back-up stator earth fault protection for the generator. To provide 95% stator earth fault protection IN>1 Current = 0.05 x 5A = 0.25A The VN1 voltage input used by the residual overvoltage/NVD overvoltage/NVD protection can also be connected across the voltage divider to provide back-up stator earth fault protection for the generator. The voltage divider in the f ilter device can be used to provide a 5:1 divider to connect 100V rated voltage to t he VN1 input (Vn=100/120V). Connections 1A1-1A2 on the filter provides a 5:1 divider to connect 100V rated voltage to the VN1 input.

2


4

Gene Genera rator tor earth earthed ed via via Eart Earthi hing ng Tran Transf sform ormer er With this arrangement, the injected voltage is applied through the secondary of the earthing transformer, which can either be a transformer located at the neutral of the generator, or a three single-phase, single-phase, five limb limb voltage transformer with with the secondary windings connected connected in broken delta. A five limb voltage transformer is only possible for small generators connected to the grid via a cable.

Where RL V64S I64S

loading resistor displacement displacement voltage at the protective relay measuring current at the protective r elay

Figure Figure 2:

64S 64S Conn Connect ection ion for genera generator tors s eart earthed hed via earthin earthing g tran transfo sforme rmer r

The current is also measured on the secondary transformer circuit. Therefore the relay is measuring the secondary fault resistance reflected through the earthing transformer. The primary fault resistance is related to the t he secondary resistance based on the following relationship:

R Primary R Secondar y

VPrimary =

VSecondary²2


It is also necessary to take into account the potential divider and the CT ratio. Therefore, the primary resistance is calculated from the secondary resistance as follows:

R Pr

VPrimary 2 VDivider Ratio ( ) ∗ VSecondary CTR atio

=

imary

∗ R Secondary

Vn Primary VPrimary

Where

=

VSecondary

1

3

∗

3 Vn Secondary

for the open-delta VT,

3 Vn Primary or,

VPrimary

3

=

Vn Seconda y

VSecondar

for earthing transformer connected at the generator

r

y

neutral. Note, the linear range of the 100% stator earth fault input is up to 2In. So if the earth fault current is limited to <2A then the 100% stator earth fault 1A input can be used. For earth fault currents 2-10A the relay 5A current input can be used. Note, for the 5A inputs the 64S I Magnitude measurement in the Measurements 3 menu will show 5 times lower current than being injected. There is no CT ratio setting for the 100% stator earth fault current input, however the resistance measurement and 64SR<1/2 protection can be compensated by the 64S R Factor setting if the 5A input input is used by multiplying the CT ratio by by 5 in the formula for the R factor. If the 64S I>1 protection is used then the setting needs to be divided by a factor of 5 when using the 5A input. Using the data shown in figure 2 as an example and assuming the 1A rated current input is used,

R Primary

=

(

Vn

3

500

)2

∗

5

5 400

∗

2

Therefore,

R Factor

=

(

Vn

500

3

)2 ∗

∗

5

5 400

2

∗

R Secondary

2


4.1 Setting example example with generator generator earthed earthed via earthing earthing transfo transformer rmer and secondary resistor at the starpoint of the generator Vol Voltage tage trans ransfo form rme er ra ratin ting: 19 kV/ kV/ >3/ >3/5 500 V (non (non-s -sa atura turate ted d up up to to Vn Vn,Generator ) Insu Insula latio tion n req requi uire reme ment nt:: nonnon-sa satu tura rate ted d up up to to 1.1 1.1 x Vn Vn,Generator Voltage divider: 5:2 Current transformer: 200/5 The transformation ratio of the miniature CT 400:5A can been halved to 200:5A by passing the primary conductor twice through the transformer window. The maximum primary earth fault current should be limited by the secondary resistor to <10A. The resistive component of fault current should not be less then t he residual capacitive current. Assumption: Capacitive reactance reactance to earth of all three phases C 0 = 0.8837µF

X cg

=

1

1

=

2 ∗ π ∗ ƒ C0

=

3602Ω

100 ∗ π ∗ 0.8837 µF

∗

RL : ≤ 3 6 02 Ω RLselected primary = 3600 Ω If the effective earthing resistor is made equal to the total residual capacitive impedance of 3600 0 then, with a generator terminal fault at normal voltage the neutral current is:

In

=

19kV / 3 3600Ω

=

3A

The actual fault current will contain equal resistive and capacitive components. The equivalent resistor is equal to the earth f ault capacitance of 3600 The secondary circuit load resistor is therefore:

0.

Vn Pr im

ary

R Pr imary imary R Secondar y

=

VPrim

ary

2

VSecondary²

wher e

VPrimar

=

y

VSecondar

3

Vn Secondary

y

Secondary Load Resistor: R L = 3600 ×

   

3 × 500V   ² 19kV

 

= 7.48Ω

Voltage transformer secondary maximum earth fault current is 66.85A so with a 200:5A CT the secondary current at the relay is 1.67A.

=

I

Secondary earth fault current:

=

sec

500V

=

66.85 A

7.48 Ω

Note, the linear range of the 100% stator earth fault input is up to 2In. So if the earth fault current is limited to <2A then the 100% stator earth fault 1A input can be used. For earth fault currents 2-10A the relay 5A current input can be used.

R Facto

r

19kV ( 500 V

3

)

2

∗

5

5 200

= 30

∗

2

Typical trip and alarm settings for the 100% stator earth fault under resistance elements are: Trip stage: primary 2 kΩ secondary 67 Ω Alarm stage: primary 5 kΩ secondary 167 Ω The transformer VA rating is 1.1 x 3A x 19000V/ >3= 36kVA (for short time operation of 10s or 20s). The 1.1 take account for transient overvoltages at earth faults. Summary of components: Volt Voltag age e tra trans nsfor forme merr rati rating ng:: 19 kV/ kV/ >3/5 >3/500 00 V (non (non-s -sat atur urat ated ed up to Vn Vn,Generator ) Insula Insulatio tion n requ require iremen ment: t: non-s non-satu aturat rated ed up to 1.1 x Vn Vn ,Generator The transformer VA rating is 36kVA (for for short time operation of 10s or 20s) Voltage divider: Current transformer: Loading Resistor:

5:2 (included in 20Hz Filter) 400/5, 5VA, class 1 7.48Ω (67A, for short time operation of 10s or 20s)

Additional Remarks: The VN1 voltage input used by the residual overvoltage/NVD protection can also be connected across the voltage divider to provide back-up stator earth fault protection for the generator. The voltage divider in the filter device can be used to provide a 5:1 divider to connect 100V rated voltage to the VN1 input which is typically rated for 100/120V. Connections Connections 1A1-1A2 on the filter provides a 5:1 divider to connect 100V rated voltage to the VN1 input.


4.2 Setting example example with generator generator earthed earthed via earthing earthing transfo transformer rmer and secondary resistor at the terminals of the generator Voltage tr transformer ra rating:

19 kV/>3 / 500/3 V (non-saturated up to Vn,Generator ) Insulation requirement: non-saturated up to 1.1 x Vn,Generator Voltage divider: 5:2 Current transformer: 200/5 The transformation ratio of the miniature CT 400 A:5 A can been halved to 200:5A by passing the primary conductor twice through the transformer window. The maximum primary earth fault current should be limited by the secondary resistor to <10A. The resistive component of fault current should not be less then t he residual capacitive current. Assumption: Capacitive reactance reactance to earth of all three phases C 0 = 0.8837uF

X cg

1

=

=

2 ∗ π ∗ f ∗ C0

1

=

3602Ω

100 ∗ π ∗ 0.8837 µF

RL ≤ 3602Ω RLselected primary = 3600Ω If the effective earthing resistor is made equal to the total residual capacitive impedance of 3600 0 then, with a generator terminal fault at normal voltage the neutral current is:

In

=

19kV /

3600Ω

3

=

3A

The actual fault current will contain equal resistive and capacitive components. The equivalent resistor is equal to the earth f ault capacitance of 3600 The secondary circuit load resistor is therefore:

0.

The 1/3 takes into account, that the primary fault current in the t he neutral is three times higher than the fault current at the secondary side of the transformer in one phase. Of course the transformation ratio should be noted.

=

Voltage transformer secondary maximum earth fault current is 66.85A so with a 200:5A CT the secondary current at the relay is 1.67A.

I

Secondary earth fault current:

=

sec

500V

=

66.85 A

7.48 Ω

Note, the linear range of the 100% stator earth fault input is up to 2In. So if the earth fault current is limited to <2A then the 100% stator earth fault 1A input can be used. For earth fault currents 2-10A the relay 5A current input can be used.

R Facto

r

19kV ( 500 V

3

)

2

∗

5

5 200

= 30

∗

2

Typical trip and alarm settings for the 100% stator earth fault under resistance elements are: Trip stage: primary 2 kΩ secondary 67 Ω Alarm stage: primary 5 kΩ secondary 167 Ω Assuming the transformer transformer is from 3 single phase phase transformers: The total transformer VA rating is 1.1 x 3A 19000V = 63kVA (for short time operation of 10s or 20s). I The 1.1 take account for transient overvoltages at earth faults. In case of an earth fault the VA rating is separated on two transformers. This means the VA rating of every transformer is 63kVA / />3 = 36kVA For a 3 phase transformer (five/four limb) the VA rating is 3 times higher, 109kVA for short time operation of 10s or 20s. Summary of components: Volt Voltag age e tra trans nsfor forme merr rati rating ng:: Insulation requirement: The transfo transforme rmerr VA ratin rating g is Voltage divider: Current transformer: Loading Resistor:

19 kV/ kV/ >3/5 >3/500 00 V (non (non-s -sat atur urat ated ed up to Vn Vn,Generator ) non-saturated up up to to 1.1 x Vn Vn,Generator 36kVA 36kVA (for (for shor shortt time time opera operatio tion n of 10s 10s or or 20s) 20s) (3single phase Transformers) 5:2 (included in 20Hz Filter) 400/5, 5VA, class 1 7.48 Ω (67A, for short time operation of 10s or 20s)

Additional Remarks: The VN1 voltage input used by the residualovervoltage/NVD protection can also be connected across the voltage divider to provide back-up stator earth fault protection for the generator. The voltage divider in the filter device can be used to provide a 5:1 divider to connect 100V rated voltage to the VN1 input which is typically rated for 100/120V. Connections Connections 1A1-1A2 on the filter provides a 5:1 divider to connect 100V rated voltage to the VN1 input.

5

Methods Methods to estab establis lish h the the serie series s imped impedanc ance e settin settings gs for for 64S 64S The series resistance ‘64S Series R’ is normally set as the total leakage resistance of the earthing transformer, through which the injection equipment is connected. It can either be set by calculations calculations based on the transformer t ransformer parameters, or by measurements during commissioning. The P345 measurements feature will be able


to assist for the latter. For further informations see the Commissioning chapter, P34x/EN CM.

5.1 By Ca Calcu lculatio tion Given that the per unit quantity of the total leakage impedance of the transformer is Rpu+jXpu, the transformer resistance parameters can be calculated as f ollows. For the open-delta 3-phase voltage transformer connected at the generator terminal:

For an earthing transformer connected to the generator neutral and for generator earthed via a resistor,

5.2 By Me Measureme ement After the angle compensation setting has been set, the t he series resistance R S can be established by applying a short circuit fault at the generator star point. With the ‘64S Series R’ setting originally set to zero, t he relay is now measuring the resistance due to the earthing t ransformer and its connecting cables. In order to compensate for this extra resistance of the circuit, the value read from the ‘64S R Primary’ measurement should be entered into the ‘64S Series R’ setting. After the setting has been entered, the ‘64S R Primary’ measurement measurement should now read zero.

6

Commissioning The 100% stator earth fault protection function via low frequency injection (64S) should be tested in the P345. The T he 100% stator earth fault protection via low frequency injection includes an overcurrent trip (64S I>1) an under resistance trip (64S R<2) and an under resistance alarm (64S R<1) element. It is only necessary to test the elements being used. To avoid spurious operation of any other protection elements all protection elements except the 100% stator earth fault protection should be disabled for the duration of the 100% 100% stator earth fault tests. This is done in in the relay’s CONFIGURATION column. Make a note of which elements elements need to be re-enabled re-enabled after testing.

6.1 6.1 Conn Connec ectt the the test test cir circu cuit it Determine which output relay has been selected to operate when a 64S I>1 Trip (DDB 756) and 64S R<2 Trip (DDB 757) and 64S R<1 Alarm Trip (DDB 382) occurs by viewing the relay’s programmable programmable scheme logic. The programmable scheme logic can only be changed using the appropriate software. If this software is not available then then the default output relay allocations allocations will still be applicable. If the 64S protection signals are not independently mapped directly to an output relay in the programmable scheme logic, output relay 3 and 4 (L5 - L6 and L7 – L8 in the P345) could be used in the default PSL to check the operation of the protection protection functio functions. ns. In the default default PSL relay relay 3 is the designated designated protectio protection n trip contact and 64S I>1 Trip (DDB 756) and 64S R<2 Trip (DDB 757) are assigned to this contact. In the default PSL relay 4 is the designated general alarm contact and 64S R<1 Alarm Trip (DDB 382) is assigned to this contact. Note, in the default PSL relay 3 is set to operate the Any Trip signal (DDB 626) which initiates the trip LED. The associated terminal numbers can be found from the external connection diagrams in section P34x/EN IN. Connect the output relay so that its operation will trip the test set and stop the timer. Connect a 20Hz current output of the test set to the ‘I 100% STEF’ current transformer input of the relay (terminals F12 – F11 ( 1A), F10 – F11 (5A)). Note, for the 5A inputs the 64S I Magnitude measurement in the Measurements 3 menu will show 5 times lower current than being injected. Connec Connectt a 20Hz voltage voltage output output of the test set to the ‘V 100% 100% STEF’ voltage voltage transformer input of the relay (terminals F21 – F22). To simulate a generator standstill condition there should be no signal injected into the 3 phase voltage and current inputs. Ensure that the timer will start st art when the current and voltage is applied to the relay.

6.2 Chec Check k the the pick pick-u -up p set settin tings gs Ensure that the following following settings [GROUP 1 100% STATOR EF, 64S R Factor = 1, 64S Series R = 0, 64S Parallel Parallel G = 0, 64S Angle Angle Comp = 0, 64S R<1 Alarm = Disabled, Disabled, 64S R<2 Trip = Disabled, 64S Supervision = Disabled, VN 3rd Harmonic = Disabled.] If three LEDs have been assigned to give the 64S alarm and trip information, 64S I>1 Trip (DDB 756), 64S R<2 Trip (DDB 757) and 64S R<1 Alarm Trip (DDB 382), these may be used used to indicate correct correct operation. If not, monitor options will need to be used - see the next paragraph.


Go to the COMMISSION TESTS column in the menu, scroll down and change cells [0F05: Monitor Bit 1] to 756, [0F06: Monitor Bit 2] to 757 and [0F07: Monitor Bit 3] to 382. Cell [0F04: [0F04: Test Port Status] will now appropriately appropriately set set or reset the bits that now represent 64S I>1 Trip (DDB 756), 64S R<2 Trip (DDB 757) and 64S R<1 Alarm Trip (DDB 382), with the rightmost bit representing 64S I>1 Trip. From now on you should monitor the indication of [0F04: Test Port Status]. Slowly increase the 20Hz current to the I 100% STEF input F12 – F11 (1A), F10 – F11 (5A) until the 64S I> 1 element trips. (Bit 3 of [0F04: Test Port Status] is set set to 1). Record the 20Hz 20Hz current magnitude magnitude and check that it corresponds to the 64S 0>1 Trip Set ±5%. Note, for the 5A inputs the 64S I Magnitude measurement in the Measurements 3 menu will show 5 times lower current than being injected. Switch OFF the test and reset the alarms. Set 64S R<2 Trip = Enabled and 64S R<1 Alarm = Disabled and 64S Overcurrent = Disabled. Set the 20Hz voltage to the V 100% STEF input, F21 – F22, to 20V angle 0. Slowly increase the 20Hz current, angle 0, to the I 100% STEF input, F12 – F11 (1A), F10 – F11 (5A) until the 64S R<2 element trips. (Bit 2 of [0F04: [0F04: Test Port Status] is set to 1). Record the 20Hz 20Hz current and and voltage magnitude and check that the resistance (R = V/I) corresponds to the 64S R<2 Trip Set ±5%. Switch OFF the test and reset the alarms. Set 64S R<1 Alarm = Enabled and 64S R<2 Trip = Disabled and 64S Overcurrent = Disabled. Set the 20Hz voltage to the V 100% STEF input, F21 – F22, to 20V angle 0. Slowly increase the 20Hz current, angle 0, to the I 100% STEF input, F12 – F11 (1A), F10 – F11 (5A) until the 64S R<1 element trips. (Bit 3 of [0F04: Test Port Status] is set to 1). Record the 20Hz current and voltage magnitude and check that the resistance (R = V/I) corresponds to the 64S R<1 Alm Set ±5%. Switch OFF the test and reset the alarms.

6.3 6.3 Perf Perfor orm m the the timi timing ng test tests s Ensure that the timer is reset. Set 64S R<2 Trip = Disabled and 64S R<1 Alarm = Disabled and 64S Overcurrent = Enabled. Apply a 20Hz current of twice the setting in cell [3C44: GROUP 1 100% STATOR EF, 64S 0>1 Trip Set] to the relay and note the time displayed when the timer stops. Check the red trip led and yellow alarm led turns on when the relay operates. Check ‘Alarms/Faults Present - Started Phase N, Tripped Phase N, 100% 64S Start I>1, 100% 64S 64S Trip I>1’ is on the display. display. Reset all alarms. alarms. Note, in the default PSL relay 3 is set to t o operate the Any Trip signal (DDB 626) which initiates the trip LED.


Check that the operating time recorded by the timer is within the range, 64S 0>1 Trip Dly setting ±2% or 1.2s whichever is greater with the P345 bandpass filter enabled and ±2% or 0.22s whichever is greater with the P345 bandpass filter disabled. The P345 bandpass filter is automatically enabled when the system frequency is <45Hz or it can be permanently permanently enabled using DDB 561, 64S Filter On. Allowance Allowance must also be made for the accuracy accuracy of the test equipment equipment being used. Ensure that the timer is reset. Set 64S R<2 Trip = Enabled and 64S R<1 Alarm = Disabled and 64S Overcurrent = Disabled. Apply a 20Hz voltage of 20V, angle 0 and a 20Hz current, angle 0 to give half the setting in cell [3C2C: GROUP 1 100% STATOR EF, 64S R<2 Trip Set] to the relay and note the time displayed when the timer stops. Check the red trip led and yellow alarm led turns on when the relay operates. Check ‘Alarms/Faults Present - Started Phase N, Tripped Phase N, 100% 64S Start R<2, 100% 100% 64S Trip R<2’ is on the display.. display.. Reset all alarms. Note, in the default PSL relay 3 is set to operate the Any Trip signal (DDB 626) which initiates the trip LED. Check that the operating time recorded by the timer is within the range, 64S R<2 Trip Dly setting ±2% or 1.2s whichever is greater with the P345 bandpass filter enabled and ±2% or 0.22s whichever is greater with the P345 bandpass filter disabled. The P345 bandpass filter is automatically enabled when the system frequency is <45Hz or it can be permanently enabled enabled using DDB 561, 64S Filter On. O n. Allowance Allowance must also be made for the accuracy accuracy of the test equipment equipment being used. Ensure that the timer is reset. Set 64S R<2 Trip = Disabled and 64S R<1 Alarm = Enabled and 64S Overcurrent = Disabled. Apply a 20Hz voltage of 20V, angle 0 and a 20Hz current, angle 0 to give half the setting in cell [3C20: GROUP 1 100% STATOR EF, 64S R<1 Alm Set] to the relay and note the time displayed when the timer stops. Check the yellow alarm alarm led turns on when the relay relay operates. Check ‘Alarms/Faults Present -100% 64S 64S Alarm R<1’ is on the display. display. Reset all alarms. alarms. Check that the operating time recorded by the timer is within the range, 64S R<1 Alm Dly setting ±2% or 1.2s whichever is greater with t he P345 bandpass filter enabled and ±2% or 0.22s whichever is greater with the P345 bandpass filter disabled. The P345 bandpass filter is automatically enabled when the system frequency is <45Hz or it can be permanently enabled enabled using DDB 561, 64S Filter On. O n. Allowance Allowance must also be made for the accuracy accuracy of the test equipment equipment being used. Ensure that the timer is reset.


6.4 Perfor Perform m the 100% 100% stato statorr earth earth fault fault super supervisi vision on test test Set the 64S Supervision = Enabled, Set 64S R<2 Trip = Enabled and 64S R<1 Alarm = Enabled and and 64S Overcurrent Overcurrent = Enabled. In the default PSL the 64S Fail (DDB 1076) supervision signal is connected to the 64S Fail Alarm (DDB 383) signal. The 64S Fail signal is an output from the 64S supervision element and the 64S Fail Alarm signal triggers the alarm led and alarm message. For applications where the 20Hz generator is powered by the VT it may be desirable not to alarm every time the generator is off line so the supervision element and alarm have separate DDBs. The 64S Fail signal is also connected to the 64S I>1 Inhibit, 64S R<1 Inhibit and 64S R<2 Inhibit in the t he default PSL. If an LED has been assigned to give the 64S Fail Alarm or 64S Fail information, 64S Fail Alarm (DDB 383), this may may be used to indicate indicate correct operation. operation. If not, monitor options will need to be used - see the next paragraph. Go to the COMMISSION TESTS column in the menu, scroll down and change cells [0F08: Monitor Bit 4] to 383 and and cell [0F09: Monitor Bit 5] to 1076.. 1076.. Cell [0F04: [0F04: Test Port Status] will now appropriately set or reset the bit that now represent 64S Fail Alarm (DDB 383) and 64S Fail (DDB 1076. From now on you should monitor the indication of [0F04: Test Port Status]. Apply a 20Hz current current and 20Hz voltage above the settings in cell [3C50/54: [3C50/54: GROUP 1 100% STATOR EF, 64S 0<1 Set, 64S V<1 Set] but below the 64SI>1 Trip, 64S R<2 Trip and 64S R<1 Alarm settings. Set the voltage to half the 64S V<1 Set and the current to half the 64S I< Set and check the 64S Fail Alarm and 64S Fail operates and that there is no operation of the 64SI>1 Trip, 64S R<2 Trip and 64S R<1 Alarm elements. (Bit 4 and 5 of [0F04: T est Port Status] is set to 1 and bits 1, 2, 3 = 0) Check the yellow alarm alarm led turns on when the relay relay operates. Check ‘Alarms/Faults Present – 64S Fail Alarm’ Alarm’ is on the display. display. Reset all alarms. alarms. Check that the operating time recorded by the timer is within the range, 64S Superv’n Dly setting ±2% or 1.2s whichever is greater with the P345 bandpass filter enabled and ±2% or 0.22s whichever is greater with the P345 bandpass filter disabled. The P345 bandpass filter is automatically enabled when the system frequency is <45Hz or it can be permanently enabled enabled using DDB 561, 64S Filter On. O n. Allowance Allowance must also be made for the accuracy accuracy of the test equipment equipment being used. Upon completion of the tests any protection elements that were disabled for testing purposes must have their original settings restored in the CONFIGURATION column.

p R

f

R


6.5 64S 64S Calib Calibra ratio tion n proc procedu edure re The 100% stator earth fault protection can be calibrated with the machine at standstill, because the measuring principle for t he earth resistance calculation is independent of whether the machine is at standstill, rotating or excited. A prerequisite is, however, that the 20 Hz generator must be supplied with a DC voltage or an external ac voltage source depending on the application, (see the connection diagrams in P34x/EN/IN). Ensure that the cell [0F0D: COMMISSIONING TESTS, Test Mode] is set to ‘Contacts Blocked’. This blocks the operation of the Trip Contacts. Check the Out of Service LED is on and the alarm message ‘Prot’n Disabled’ is given. The following measurements are available in the Measurements 3 column. All measurements are based on the 20Hz components extracted from the voltage and current signals. A magnitude threshold level of 0.05V and 0.1mA for the voltage and current is implemented, below which the associated measurements display zero. The 64S R is the compensated resistance in both primary and secondary quantities. The resistance measurement displays a significantly large number t o indicate an invalid measurement measurement if either the t he voltage or the current magnitude is below the threshold. The 64S Voltage signal is used as the phase reference for the 64S current signal. MEASUREMENTS 3 64S V Magnitude 64S I Magnitude 64S I Angle 64S R secondary 64S R primary

The purpose of the 64S calibration procedure is to establish the correct settings for the angle compensation (‘64S Angle Comp’), the Series Resistance (‘64S Series R’) and the parallel conductance (‘64S Parallel G’). They are required so that the relay can calculate more accurately the value of the fault resistance Rf based on the equivalent circuit as shown below.

Figure 3:

Calibration model for the 64S

To obtain the correct results, it is essential that the ‘64S R Factor’ should have already been established and has been entered into the relay. The ‘64S Angle Comp’, ‘64S Series R’ and ‘64S Parallel G’ settings should all be set to 0 initially.

As the calibration procedure requires f ault resistance to be applied to the star point of the generator which is on the primary circuit, it is better to proceed with the calibration based on primary settings and measurements. Therefore in the


Configuration column, the ‘Setting Values’ should be set to ‘Primary’. For the ‘64S R’ measurement, the primary value should also be used. Caution: Dangerous high voltages may be present at the generator terminals if the 20Hz injection voltage is not removed when the generator is taken out of service.

If the 20Hz injection voltage generator receives power from the generator terminal voltage, then the 20Hz injection voltage generator will be automatically switched off whenever the generator terminal voltage is not present.

6.6 Angle Angle compe compensa nsatio tion n settin setting g (64S (64S Angl Angle e Comp) Comp) The angle compensation setting is used to remove any phase error caused by the internal and external CTs associated with the 64S current measurement. To establish this setting, it is necessary to remove any parallel earthing point such as an addition additional al earthing earthing transforme transformerr which which may contribute contribute to the presenc presence e of the parallel resistance Rp in Figure 4. Under no fault condition, the relay should only see the lumped capacitance Cg on the system. The I64S should be capacitive and should lead the voltage V64S by +90 . The ‘64S Angle Comp’ setting should be adjusted so that the +90 is achieved. The measurement ‘64S I Angle’ displays the angle of I’64S with respect to V64S and can be used to assist with this setting adjustment. °

°

6.7 Series Series resista resistance nce setting setting (64S (64S Seri Series es R) R) After the angle compensation setting has been set, the series resistance RS can be established by applying a short circuit fault at the generator star point. With the ‘64S Series R’ setting originally set to zero, t he relay is now measuring the resistance due to the earthing t ransformer and its connecting cables. In order to compensate for this extra resistance of the circuit, the value read from the ‘64S R Primary’ measurement should be entered into the ‘64S Series R’ setting. After the setting has been entered, the ‘64S R Primary’ measurement measurement should now read zero.

6.8 Calibr Calibratio ation n at the the 64S 64S alarm alarm and trip setting settings s The above calibration procedures are performed under no fault and short-circuit fault conditions. In order to provide a better match of the relays ‘64S R Primary’ meas measure ureme ment nt to the the appl applie ied d faul faultt resi resist stan ance ce acro across ss the the whol whole e rang range e of faul faultt resistance it may be necessary to re-adjust the ‘64S Angle Comp’ setting and ‘64 Series R’ setting at the ‘64S R<1 Alm Set’ and ‘64S R<2Trip Set’ points. Apply a fault resistance equal to the ‘64S R<2 Trip’ setting and adjust the ‘64S Angle Comp’ and the ‘64S Series R’ settings for a closer match to the relays measured resistance resistance ‘64S R Primary’ if required. Repeat the process with a fault resistance equal to the ‘64S R<1 Alarm’ setting. In general it is recommended that the ‘64S Series R’ setting should only be used to provide minor adjustments of a few ohms and is more appropriate for trip or alarm threshold of less than a few hundred ohms. To provide a closer match of the relays ‘64S R Primary’ measurement to the applied fault resistance at higher settings it is more effective to adjust the ‘64S Angle Comp’ setting.


Since

the

resistance

measured

by

the

relay

is

effectively

equal

to

V64S I64S * cos( θI'64S

−V

64S

)

,

if the measure measured d resist resistanc ance e is less less than than expect expected ed,, the ‘64S ‘64S Angle Angle Comp’ Comp’ settin setting g should be adjusted such that the current vector will be rotated in the anti-clockwise direction. If the ‘64S Angle Comp’ (0c) was originally set as a negative value (i.e., the current vector was rotated clockwise by | 0c| ), it should be set less negative so that the I64S*cos( 0I’64S-V64S) denominator decreases in value. The reverse logic should be applied if t he measured resistance is more than expected. °

Finally apply various fault resistances, re-check the short-circuit condition and the no fault condition to ensure that the results are satisfactory. This whole process may need to be re-iterated to ensure the most desirable match.

6.9 Paralle Parallell Conduc Conductan tance ce (64S (64S Para Parallel llel G) After the above settings have been finalised. re-connect re-connect any parallel earthing point of the system, then apply a no fault condition to the generator. The ‘64S R Primary’ measured by the relay will be the parallel resistance Rp. It’s reciprocal should then be applied to the ‘64S Parallel G’ setting.

6.10 Checking with other resistance values After the above calibration procedure, apply different fault resistance to the star point of the generator so as to obtain a complete set of measurements from the relay.

6.11 Testing the 100% stator earth fault protection on on the generator Insert on the primary side a resistance which corresponds corresponds to about 90 % of the resistance for the alarm stage, ‘64S R<1 Alm Set’ and check that the ‘64S R<1 Alarm’ is operated after the delay time ‘64S R<1 Alm Dly’ (default setting 1.00s). Further reduce the earth resistance to 90 % of the trip stage pickup value ‘64S R<2 Trip Set’ and check that the ‘64S R<2 Trip’ is operated after the delay time, ‘64S R<2 Trip Dly’ (default setting 1.00 sec). Also, Also, if used check that the ‘64S I>1 Trip’ is operated after the delay delay time, ‘64S I>1 Trip Dly’ (default setting setting 1.00 sec). Reset all alarms. Remove the test resistor. If the 100% stator earth fault protection is blocked with the DDBs 64S I> Inhibit (558) or 64S R<1 Inhibit (559) or 64S R<2 Inhibit (560) using an opto-isolated input, the functioning of the input should be checked. Switch off the voltage supply for the 20 Hz generator, or energise the block binary input. Check the yellow alarm led turns on and check ‘Alarms/Faults Present - 64S Fail Alarm’ is on the display (assuming the 64S Fail Alarm (DDB 383) is connected to the 64S Fail signal signal (DDB 1076) 1076) in the PSL). Switch on the 20Hz generator generator or remove the block and reset all alarms. If this alarm indication already occurs with the 20 Hz generator in operation, the monitoring threshold, 64S V<1 Set, should be reduced. This can be the case if the loading resistance is very small (< 1 Ω).

Protection & Control place country-regionGermany country-regionGermany Note: Note:

If the external band pass filter accessory is to be checked as well, short-circuit the earthing or neutral transformer on the secondary side with the machine at standing still, and switch the 20 Hz generator on. Multiply the operational measured value ‘64S I Magnitude’ with the CT ratio of the miniature CT (e.g. 400 A/ 5A). The flowing current must be greater than 3 A. If the current is significantly less, the resonance frequency of the bandpass has changed. It can be better matched by adding or removing removing capaci capacitors. tors. Finally, Finally, remove remove the shorting shorting link link and check the the galvanic galvanic isolation with the measured value ‘64S V Magnitude’.

6.12 Start-up tests Ensure that the cell [0F0D: COMMISSIONING TESTS, Test Mode] is set to ‘Contacts Blocked’. This blocks the operation of the Trip Contacts. Check the Out of Service LED is on and the alarm message ‘Prot’n Disabled’ is given. The 20Hz generator and bandpass filter accessories of the protection device must be operational. Start up the generator and excite it to maximum generator voltage. Check the protection does not pick up. Check that the resistance values, ‘64S R< primary/secondary’, in the Measurements 3 menu are well in excess of the trip and alarm settings, ‘64S R<1 Alm Set/64S R<2 Trip Set’ and the current value, 64S I Magnitude, is at least half the overcurrent setting, 64S I>1 Trip Set’. Shut down generator. If the 100% stator earth fault protection operates during the generator start up there may be some zero sequence voltage being produced by the machine, depending on the type of starting, which could be superimposed superimposed on the 20Hz voltage causing incorrect measurements. The P345 100% stator earth fault protection includes a low pass filter and a bandpass filter which will filter signal frequencies 0-15Hz and >25Hz. DDB 1075 64S F Band Block operates between 15-25Hz and can be used in the Programmable Scheme Logic to block the 100% stator earth fault protection via the inhibit signals, DDBs 558 - 64S I> Inhibit, DDB 559 - 64S R<1 Inhibit, DDB 560 - 64S R<2 Inhibit. Ensure that the cell [0F0D: COMMISSIONING TESTS, Test Mode] is set to ‘Disabled’. Check the Out of Service LED is off and the alarm message ‘Prot’n Disabled’ is reset. Upon completion of the tests any protection elements that were disabled for testing purposes must have their original settings restored in the CONFIGURATION column.

P345 20Hz Stator Earth Fault Application Guide

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