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Manual MRS1 GB 

Woodward 

DOK-TD-MRS1 Rev.A 

4.3  Principle of negative sequence protection 

 
An unbalanced-load can be caused due to unequal distribution of current in the grid on account of 
unequal loading, unsymmetrical line-to-line short-circuits (one phase and two phase), line interrup-
tion and also switching operations. 
 
Through the unbalanced-load, negative sequence currents occur in the stator, which cause higher 
harmonics with odd numbers in the stator winding and higher harmonics with even numbers in the 
rotor winding. The rotor is particularly endangered in this because the higher harmonics put extra 
load on the rotor winding and induce eddy currents in massive iron content of the rotor which can 
even lead to melting of the metal or to the destruction of the metal structure. 
 
An unbalanced-load is, however, permissible in certain limits and with regard to the thermal loading 
limit of the generator. In order to avoid a premature outage of the generator in case of unbalanced-
load, the tripping characteristic of the negative sequence protection should be adapted to the ther-
mal characteristic of the generator. 
 
Basically it is established that the better the cooling of the rotor, the lower are generally the per-
missible negative sequence values. This is due to the fact that with better rotor-cooling the maxi-
mum permissible symmetrical load can be chosen higher, however in relation to that, an unba-
lanced-load is permissible to a lesser extent. For turbo-generators the value of the permissible un-
balanced-load is relatively low. Usual values are approx. 10 - 15 % of the load which is permissible 
with symmetrical load. 
 
The negative sequence relay MRS1 has a large number of adjustable tripping characteristics.  
Protection of almost every type of generator is thereby possible. 
 
In case of unsymmetrical short-circuits in the grid the negative sequence protection relay normally 
also picks up. In order to ensure selectivity, to the extent the overload carrying capacity of the ge-
nerator permits it, a tripping time longer than that of the mains protection (e.g. overload protection) 
is to be selected. 
 

 

Summary of Contents for MRS1

Page 1: ...MRS1 Negative sequence relay Manual MRS1 Revision A...

Page 2: ...the right to update any portion of this publication at any time Information provided by Woodward Governor Company is believed to be correct and reliable However no responsibility is as sumed by Woodw...

Page 3: ...rip delay thermal time constant T 13 5 2 6 Rated frequency 14 5 2 7 Adjustment of the slave address 14 5 3 Indication of measuring values and fault data 14 5 3 1 Indication of measuring values 14 5 3...

Page 4: ...oice between an independent or an inverse time tripping characteristic In case of low unbalanced load a warning is given after an adjustable time delay In case of inadmissible high unbalanced load the...

Page 5: ...two change over contacts is used for tripping the other relays with one change over contact each are used for indication Tripping output relay C1 D1 E1 C2 D2 E2 Indication self supervision C7 D7 E7 Wa...

Page 6: ...constant tripping time Thermal time constant in case of INVS or tripping time in case of DEFT in seconds SELECT RESET T Function blockade EXIT until max setting value LED of blocked parameter Nominal...

Page 7: ...Green indicates measuring red fault values The LED marked with letters RS lights up during setting of the slave address of the device for serial data communication In accordance with the display 5 LED...

Page 8: ...MRS1 relay is a powerful microcontroller All of the operations from the analog digital convertion to the relay trip decision are carried out by the microcontroller digitally The relay program is locat...

Page 9: ...e generator in case of unbalanced load the tripping characteristic of the negative sequence protection should be adapted to the ther mal characteristic of the generator Basically it is established tha...

Page 10: ...tor IL3 by 120 Figure 4 1 Symmetrical components A rotating field is produced with opposite direction of rotating field If the currents of this negative sequence system are added the sum is zero in ca...

Page 11: ...ent IN of the generator K2 I2S IN This is usually given in where I2S is the continuously permissible negative sequence current b The generator constant which is dependent on design K1 K2 2 x t For gen...

Page 12: ...econdary side of the cur rent transformer amounts to I2Ssec 0 4 x 4 A 1 6 A The pickup value I2S of the negative sequence cur rents related to IN 5A can be calculated to I2S 1 6 A 5 A 0 32 The time co...

Page 13: ...delay for the negative sequence warning tW an indication value in seconds appears on the display The de sired time delay can be set with pushbuttons and in the range of 0 1 to 20 s LED tW lights up d...

Page 14: ...ed load warning LED flashes for the dura tion of the time delay and then changes over to steady light In case of a negative sequence activation the LEDs and flash for the duration of the time delay an...

Page 15: ...put circuits which can cause the tripping of the circuit breaker if the breaker operation during this test is not desired By pressing the pushbutton TRIP once the display shows you the first part of t...

Page 16: ...test circuit The figure 6 1 shows a simple example of a single phase test circuit with adjustable cur rent energizing the MRS1 relay under test Figure 6 1 Single phase test circuit 6 4 3 Checking the...

Page 17: ...three Note the difference between the operating current and the operating negative sequence current The deviation of the operating negative sequence current I2 must not exceed 5 of the set value Furth...

Page 18: ...al service for example the measured cur rent values on the MRS1 relay display may be compared phase by phase with the current indications of the ammeter on the switch board panel to verify that your r...

Page 19: ...0 ms Minimum operating time 100 ms Transient overreach at instantaneous operation 5 Influences to the negative sequence current measuring Harmonics at 20 of the third harmonic 1 2 at 20 of the fifth h...

Page 20: ...GB 20 DOK TD MRS1 Rev A 7 4 Tripping characteristic Figure 7 2 Tripping characteristic 7 5 Output contact ratings Number of relays 4 Contacts 2 change over contacts for trip relay 1 change over conta...

Page 21: ...anual MRS1 GB Woodward DOK TD MRS1 Rev A 21 8 Order form Negative sequence relay MRS1 I Rated current 1 A 5 A 1 5 Housing 12TE 19 rack Flush mounting A D Technical data subject to change without notic...

Page 22: ...t which leads to a warning x IN 0 02 tw Time delay for I2w s 0 1 I2s Continuously permissible negative sequence current x IN 0 02 CHA R Tripping characteristic DEFT T Thermal time constant of inverse...

Page 23: ...Manual MRS1 GB Woodward DOK TD MRS1 Rev A 23...

Page 24: ...ermany Postfach 10 07 55 P O Box D 47884 Kempen Germany Phone 49 0 21 52 145 1 Internet www woodward com Sales Phone 49 0 21 52 145 216 or 342 Telefax 49 0 21 52 145 354 e mail salesEMEA_PGD woodward...

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