Woodward MRG3 User manual

MRG3 – Generator protection with mains
supervision, time overcurrent protection
and earth current supervision
(September 2008)
Manual MRG3 (Revision New)

Woodward Manual MRG3 GB
2 TD_MRG3_09.08_GB_Rev.New
Woodward Governor Company reserves 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 Woodward Governor Company unless otherwise expressly undertaken.
© Woodward 1994-2008

Manual MRG3 GB Woodward
TD_MRG3_09.08_GB_Rev.New 3
Inhalt
1.Overview and Application ........................................................................... 6
2.Features and Characteristics ...................................................................... 7
3.Design ........................................................................................................... 8
3.1Connections ...................................................................................................................... 8
3.1.1Connection Diagrams.................................................................................................... 8
3.1.2Analog input circuits .................................................................................................... 13
3.1.3Output relays............................................................................................................... 13
3.1.4Blocking input.............................................................................................................. 13
3.1.5External reset input ..................................................................................................... 13
3.1.6Serial interface ............................................................................................................ 13
3.1.7Auxiliary voltage supply............................................................................................... 13
3.1.8Code plugs .................................................................................................................. 14
3.1.9Low/high range of the digital inputs............................................................................. 16
3.2Front plates ..................................................................................................................... 17
3.3LEDs ............................................................................................................................... 20
4.Working Principle....................................................................................... 21
4.1Analog circuits................................................................................................................. 21
4.2Digital circuits .................................................................................................................. 21
4.3Voltage supervision......................................................................................................... 21
4.3.1Selection of star or delta connection ........................................................................... 22
4.4Principle of frequency supervision................................................................................... 23
4.5Mains decoupling ............................................................................................................ 24
4.5.1Measuring of frequency gradients ............................................................................... 24
4.5.2Vector surge supervision............................................................................................. 25
4.5.3Measuring principle of vector surge supervision ......................................................... 26
4.5.4Voltage threshold value for frequency, df/dt and vector surge measuring ................. 29
4.6Over current- and short circuit supervision...................................................................... 29
4.7Earth fault protection ....................................................................................................... 30
4.7.1Generator stator earth fault protection ........................................................................ 30
4.7.2System earth fault protection....................................................................................... 30
4.7.3Earth-fault directional feature ...................................................................................... 31
4.7.4Residual voltage.......................................................................................................... 33
4.7.5Behavior of MRG3 under different operating conditions ............................................. 33
4.7.6Blocking function set in compliance with requirements ............................................... 33
4.8Fault recorder.................................................................................................................. 34
5.Operation and Settings.............................................................................. 36
5.1Display ............................................................................................................................ 36
5.2Setting procedure............................................................................................................ 40
5.3Systemparameters .......................................................................................................... 40
5.3.1Y – Change-over switch .............................................................................................. 40
5.3.2Display of measurement values as primary quantity................................................... 40
5.3.3Setting of measured secondary values for the voltage transformers .......................... 40
5.3.4Setting of the generator’s nominal values ................................................................... 40
5.3.5Voltage transformer connection for residual voltage measuring (3pha/e-n/1:1).......... 41
5.3.6Nominal frequency ...................................................................................................... 41
5.3.7Selection between vector surge function or df/dt supervision ..................................... 41
5.3.8Display of the activation storage ................................................................................. 41
5.3.9Parameter changeover switch/external triggering of the fault recorder ....................... 42
5.4Protection parameter “Mains decoupling” ....................................................................... 43
5.4.1Parameter setting of “Over- and under voltage functions” .......................................... 43
5.4.2Number of measuring repetitions (T) for frequency functions ..................................... 43
5.4.3Threshold values of frequency supervision ................................................................. 44
5.4.4Tripping delays for the frequency elements ................................................................ 44
5.4.5Parameter setting for vector surge supervision or frequency gradient speed ............. 44
5.4.6Voltage threshold value for frequency- and vector surge measuring resp. df/dt-
measuring................................................................................................................................ 46
5.5Protection parameter “Over current” ............................................................................... 46

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5.5.1Pickup value for phase over current element .............................................................. 46
5.5.2Time current characteristics for phase over current element....................................... 46
5.5.3Trip delay or time factor for phase over current element ............................................. 46
5.5.4Reset mode for all tripping characteristics in the phase current path .......................... 47
5.5.5Pick-up value for high set element .............................................................................. 47
5.5.6Trip delay for high set element .................................................................................... 47
5.6Parameter protection earth fault supervision................................................................... 48
5.6.1Pick-up value for residual voltage................................................................................ 48
5.6.2Trip delay for residual voltage (only MRG3-IU0 and MRG3-U0) ................................. 48
5.6.3Pick-up value for earth fault element ........................................................................... 48
5.6.4WARN/TRIP changing-over......................................................................................... 48
5.6.5Time current characteristics for earth fault element (only MRG3-IE)........................... 48
5.6.6Trip delay or time multiplier for earth fault element...................................................... 49
5.6.7Reset mode for tripping characteristics in earth current path ...................................... 49
5.6.8Pick-up value for earth faults resp. earth short circuit fast trips ................................... 49
5.6.9Trip delay for earth fault s resp. earth short circuit fast trips........................................ 49
5.6.10COS/SIN-measurement........................................................................................... 49
5.7More Settings .................................................................................................................. 50
5.7.1Circuit breaker failure protection.................................................................................. 50
5.7.2Adjustment of the slave address ................................................................................. 50
5.7.3Setting of Baud-rate (applies for Modbus Protocol only) ............................................. 50
5.7.4Setting of parity (applies for Modbus Protocol only) .................................................... 50
5.8Fault recorder .................................................................................................................. 51
5.8.1Adjustment of the fault recorder .................................................................................. 51
5.8.2Number of the fault recordings .................................................................................... 51
5.8.3Adjustment of trigger occurrences............................................................................... 51
5.8.4Pre-trigger time............................................................................................................ 51
5.8.5Adjustment of the clock ............................................................................................... 52
5.9Additional functions ......................................................................................................... 53
5.9.1Blocking of protection functions and assignment of the output relays ......................... 53
5.10Indication of measuring values ........................................................................................ 55
5.10.1Measuring indication for mains decoupling.............................................................. 55
5.10.2Storage of min./max. values .................................................................................... 55
5.10.3Unit of the measuring values displayed ................................................................... 56
5.10.4Indication of values measured for over current - and earth fault protection............ 56
5.10.5Units of the measuring values ................................................................................. 57
5.10.6Indication of fault data ............................................................................................. 58
5.10.7Fault recorder .......................................................................................................... 58
5.10.8Erasure of fault storage ........................................................................................... 59
5.10.9Reset ....................................................................................................................... 60
5.10.10Delete of disturbance records.................................................................................. 60
6.Maintenance and Commissioning ............................................................ 61
6.1Connection of aux. voltage .............................................................................................. 61
6.2Testing of the output relays and LEDs ............................................................................ 61
6.3Checking the set values .................................................................................................. 62
6.4Test with transformer secondary current (Secondary injection test).............................. 62
6.4.1Equipment required to test voltage functions............................................................... 62
6.4.2Test circuit ................................................................................................................... 63
6.4.3Checking of the input circuits and measuring functions............................................... 64
6.4.4Checking the pick-up and release values for over/under voltage ................................ 64
6.4.5Checking of the tripping delay time for over/under voltage.......................................... 64
6.4.6Checking of the pick-up and release values for over/under frequency........................ 65
6.4.7Checking of the tripping delay time for over/under frequency s................................... 65
6.4.8Checking of the vector surge function ......................................................................... 65
6.5Test with transformer secondary current (Secondary injection test).............................. 66
6.5.1Equipment required to test voltage functions............................................................... 66
6.5.2Test circuit for the current function .............................................................................. 67
6.5.3Checking the input circuits and measured values ....................................................... 67
6.5.4Checking the operating and resetting values of the relay............................................ 68
6.5.5Checking of the tripping delay ..................................................................................... 68
6.5.6Checking the high set element of the relay.................................................................. 68

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6.6Example of a test circuit for MRG3-IER-relay with earth current directional feature ..... 69
6.7Checking the external blocking and reset inputs............................................................. 70
6.7.1Test of the CB failure protection.................................................................................. 70
6.8Primary injection test....................................................................................................... 70
6.9Maintenance.................................................................................................................... 70
7.Technical data ............................................................................................ 71
7.1Measuring input voltage .................................................................................................. 71
7.1.1Influences on the voltage measurement ..................................................................... 71
7.2Frequency measurement ................................................................................................ 71
7.2.1Influences on the frequency measurement ................................................................. 71
7.3Measuring input: phase current....................................................................................... 72
7.3.1Influences on the current measurement...................................................................... 72
7.4Measuring input: Residual voltage .................................................................................. 72
7.4.1Influences on the residual voltage measuring ............................................................. 72
7.5Measuring input: Earth current ........................................................................................ 73
7.5.1Influences on the earth current measuring.................................................................. 73
7.6Common data.................................................................................................................. 74
7.7Output relays................................................................................................................... 74
7.8Setting ranges and steps ................................................................................................ 75
7.8.1System parameter....................................................................................................... 75
7.8.2Parameter protection: Voltage protection, Frequency protection, Frequency gradient
77
7.8.3Time over current protection ....................................................................................... 78
7.8.4Earth fault supervision................................................................................................. 79
7.8.5Earth fault supervision with directional feature............................................................ 80
7.8.6Determination of the earth fault direction (MRG3-IER) ............................................... 80
7.8.7Residual voltage protection......................................................................................... 81
7.8.8CB failure protection.................................................................................................... 81
7.8.9Interface parameter ..................................................................................................... 81
7.8.10Parameter for the fault recorder .............................................................................. 82
7.8.11Output relay............................................................................................................. 82
7.8.12Inverse time over current protection relay ............................................................... 83
7.9Inverse time characteristics............................................................................................. 84
8.Order form................................................................................................... 87
Important Note!
The description “digital Multi-Function Relay MR” is part of the present description including those
chapters that are valid for all devices of this High Tech Line such as:
•Characteristics and features
•Technique of MR – Relays
•Operation and settings
•Housing
•Maintenance
•General technical data
Technical data subject to change without notice!

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1. Overview and Application
The MRG3 is a universal mains decoupling device that covers all the protection functions which are
required by VDEW and by most other utilities for the mains parallel operation of power stations
such as:
•over/and under voltage protection,
•over/and under frequency protection,
•extremely fast generator mains decoupling in case of vector surges or rate of change of
frequency df/dt
The MRG3 can furthermore be equipped with a multi-purpose over current time and earth fault pro-
tection re-lay and it has been designed as to be also used for grids with isolated and compensated
star points respectively. It is applicable for the mains parallel operation of power generating gen.-
sets and includes the following protection functions.
•Independent (Definite) time over current relay,
•dependent time over current relay with selectable characteristics, independent short
circuit protection
•two-element (low and high set) earth fault protection with definite or inverse time
characteristics,
•integrated determination of earth fault direction for application to power system networks
with isolated star point or earth fault compensation (ER/XR-relay type),
•two-step protection for the residual voltage
For applications where only individual protection functions are required SEG can, of course, also
offer the following MR-relays as individual devices:
•MRU3-1 four step independent over-/ and under-voltage protection (also used for
generator earth fault protection).
•MRU3-2 two step independent over-/ and under-voltage protection with evaluation
of the symmetrical voltage components.
•MRF3 four step independent over/ and under- frequency protection and two step
frequency gradient supervision df/dt.
•MRI3-I Independent (Definite) time over current relay, inverse time over current
relay with selectable tripping characteristics, independent short circuit
protection
•MRI3-E two-element (low and high set) earth fault protection with definite or inverse
time characteristics,
General Note
The description of the digital multifunction relay MR is a part of the present description and it in-
cludes technical data and details valid for most of the MR devices.

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2. Features and Characteristics
•Microprocessor technology with watchdog function.
•Effective analog low pass filter for suppressing harmonics when measuring frequency, df/dt
and vector surge.
•Digital filtering of the measured values by using discrete Fourier analysis to suppress
higher harmonics and d.c. components induced by faults or system operations.
•Integrated functions for voltage, frequency, df/dt and vector surge in one device.
•Voltage supervision each with two step under-/and overvoltage detection.
•Frequency supervision with three step under-/or over frequency (user setting).
•Completely independent time settings for voltage and frequency supervision.
•User configurable vector surge measurement 1-of-3 or 3-of-3.
•Adjustable voltage threshold value for the blocking of frequency-, df/dt or vector surge
measuring.
•Independent time over current protection.
•Selectable protective functions between:
- definite time over current relay and
- inverse time over current relay,
•Selectable inverse time characteristics according to IEC 255-4:
- Normal Inverse (type A)
- Very Inverse (type B)
- Extremely Inverse (type C)
Further characteristics:
- Long Time Inverse,
- RI-Inverse
- RXIDG characteristic
•Reset mode selectable for inverse time characteristics.
•Definite time element for short circuit fast trip.
•Two-step earth fault supervision.
•Optionally: sensitive, watt metric directional earth fault detection with measurement of the
residual voltage.
•Optionally: supervision of the residual voltage in two steps.
•Two parameter sets.
•Circuit breaker failure protection with release for subordinate protection.
•Functions for the backward blocking.
•Display of all measuring values and setting parameters for normal operation as well as
tripping via alphanumerical display and LEDs.
•Display of measuring values as primary quantities,
•Setting of the switching points for current and voltage measured in per cent.
•Voltage fail-safe storage and indication of tripping values in an error memory, 16 times
(voltage fail-safe).
•Recording of up to four fault events with time stamp in Comtrade format according to
IEC602555-25.
•For the blocking of individual functions via external blocking input, parameters can be set
according to requirement.
•Suppression of indication after completed activation (LED flash).
•Free assignment of the output relays.
•Display of date and time.
•Requirements in compliance with VDE 0435, part 303 and IEC 255.
•Possibility of serial data exchange via RS485 inter-face possible; alternatively with SEG
RS485 Pro-Open Data Protocol or Modbus Protocol.

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3. Design
3.1 Connections
3.1.1 Connection Diagrams
Figure 3.1: Connection diagram “Mains decoupling”
The measuring circuits can optionally be star- or delta connected (see chapter 4.3.1)
Figure 3.2: MRG3-I Connection diagram “Mains decoupling with time over current protection

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Figure 3.3: MRG3-I Connection diagram “Mains decoupling with time over current protection”
Figure 3.4: Connection diagram with time over current protection and earth fault protection Holmgreen circuit
This connection can be used with three existing phase current transformers when combined phase
and earth-current measuring is required. Disadvantage of the Holmgreen-circuit:
At saturation of one or more C.Ts the relay seemingly detects an earth current.

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Figure 3.5: Connection diagram with time over current protection and earth fault directional feature

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Figure 3.6: Connection diagram with time over current protection and detection of the residual voltage
For the unit version including the earth fault directional feature (ER unit type), the residual voltage
U can be generated internally in the secondary measuring circuit. The device shall then be en-
coded as described in chapter 3.1.8. Thus, star connection of voltage transformers is imperative.
For the detection of residual voltage from the open delta winding, it is possible to connect the vol-
tage transformer directly to B1 and A2. Connection of voltage transformers in iso-
lated/compensated grids is explained in chapter 4.7.3

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Figure 3.7: Connection diagram with detection of the residual voltage

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3.1.2 Analog input circuits
The protection unit receives the analog input signals of the phase currents IL1 (B3-B4), IL2 (B5-
B6), IL3 B7-B8) and the current IE (B1-B2), phase voltages UL1 (A3 - A4), UL2 (A5 - A6); UL3(A7 -
A8) and residual voltage U0(A2 – B1), each via separate input transformers.
The constantly detected current measuring values are galvanic ally decoupled, filtered and finally
fed to the analog/digital converter.
The voltage measuring circuits can optionally be star- or delta connected (see chapter 4.3.1)
For the unit type with earth fault directional features (MRG3-IER) the residual voltage UEin the
secondary circuit of the voltage transformers can internally be formed. The device shall then be en-
coded as described in chapter 3.1.8. Thus, star connection of voltage trans-formers is imperative.
For the detection of residual voltage from the open delta winding, the voltage transformer can di-
rectly be connected to B1 and A2. Connection of voltage trans-formers in isolated/compensated gr-
ids is explained in chapter 4.7.3.
3.1.3 Output relays
The MRG3 is equipped with 5 output relays. Apart from the relay for self-supervision, all protective
functions can be optionally assigned:
•Relay 1: C1, D1, E1 and C2, D2, E2
•Relay 2: C3, D3, E3 and C4, D4, E4
•Relay 3: C5, D5, E5
•Relay 4: C6, D6, E6
•Relay 5: Self-supervision C7, D7, E7
All trip and alarm relays are working current relays, the relay for self supervision is an idle current
relay.
3.1.4 Blocking input
The blocking function can be set according to requirement. By applying the auxiliary voltage to
D8/E8, the previously set relay functions are blocked (see chapter 4.8 and 5.9.1).
3.1.5 External reset input
See chapter 5.10.9.
3.1.6 Serial interface
The serial interface is an RS485 interface that is used for the parameterization of the MRG3 via
HTL/PL-Soft4 and for the sorting of recorded sequences of events. The terminal conditions are
specified in chapter 5.2 of the description MR – Digital Multifunction Relay.
3.1.7 Auxiliary voltage supply
The MRG3 is supplied with auxiliary voltage by means of the terminals C9 – D9. It has to be made
sure that the device is connected to ground by means of terminal D9.

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3.1.8 Code plugs
The measuring range of phase and residual voltage can be adjusted via code plugs. For the mea-
suring range from 0 – 150 V, the code plugs have to be adjusted to X-100V; for the measuring
range 0 – 600 V, adjust the code plugs to x_400V. the x, in this case, is used as a replacement
character for the phases L1, L2, L3 and U_E.
Encoding:
100V L1: Measuring range 0 -150V in phase U_L1
L2 100V: Measuring range 0 -150V in phase U_L2
100V L3: Measuring range 0 -150V in phase U_L3
100V U_E: Measuring range 0 -150V in phase U0
L1 400V: Measuring range 0 - 60V in phase U_L1
400V L2: Measuring range 0 - 600V in phase U_L2
L3 400V: Measuring range 0 . 600V in phase U_L3
U_E 400V: Measuring range 0 - 600V in phase U0
Based on the set value of the secondary transformers’ rated voltage, a change-over to the measur-
ing range is automatically detected by the MRG3 (refer to chapter 5.3.3). This set value determines
the secondary rated voltage of the device. If the adjusted value is lower than 138V, the MRG3 relay
recognizes the measuring range 0 – 150V; at a value of 138V and up, measuring range 0 – 600V
will be detected.
Attention:
Factory setting of the coding plugs is 400V. To avoid damage of the relay, the proper measuring
range must always be observed. The measuring range is to be set for each phase separately.
Figure 3.8: Change-over to/of measuring range for residual voltage UO

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Figure 3.9: Change over to/of measuring range for phase voltages phase l1 and L2
Figure 3.10: Change-over to/of measuring range for phase voltage Phase L3. Selection of the measuring method to
be used for residual voltage.

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There are three possibilities to measure the residual voltage:
•directly in the star point
•based on the open delta winding
•based on star-connected phase voltages
For detailed description of this function, refer to chapter 4.7.3.
For direct star point measurement as well as for the measurement out of the open delta winding,
the MRG3 is equipped with a proper measuring input. For this purpose, the code plug is set to posi-
tion “1:1”. For detection of the residual voltage based on the three star-connected phase voltages,
adjust the code plug to “3PHA”. The code plug’s default position is “1:1”.
3.1.9 Low/high range of the digital inputs
The MRG3 is equipped with a power supply unit so that the supply voltage can be freely selected.
This means, that the switching threshold of the digital inputs has to be defined dependent on the
supply voltage. It is possible to adjust two switching threshold ranges:
•a low range with a switching threshold of
U
AN >= 10 V;
U
AB <= 8 V = connector plugged; or
•a high range with a switching threshold of
U
AN >= 80 V;
U
AB <= 60 V = connector unplugged.
Figure 3.11: Selection of low/high range of the digital inputs

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3.2 Front plates
Figure 3.12: Front plate MRG3
Figure 3.13: Front plate MRG3-IE

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Figure 3.14: Front plate MRG3-IU0
Figure 3.15: Front plate MRG3-I

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Figure 3.16: Front plate MRG3-IER
Figure 3.17: Front plate MRG3-UO

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3.3 LEDs
All LEDs (except L1, L2, L3 and the clock symbol) are two colored. The LEDs on the left side, next
to the alphanumerical display light up green during measuring and red after fault messages.
The LEDs below the push button <SELECT/RESET> are lit green during setting and inquiry proce-
dure of the setting values which are printed on the left side next to the LEDs. The LEDs will light up
red during parameterizing of the setting values next to their right side.
Remarks:
Due to the fact that there are a variety of protection functions, it is not possible to assign each indi-
vidual function to one separate LED. For this reason, some of the measured values or parameters
are indicated by simultaneous flashing of several LEDs.
Example: To indicate the function of parameter U<, the LEDs next to U and 1 and < are lit up.
You can find an overall list showing the assignment of functions and LEDs in Chapter 5.1 and at
the end of this description.