New challenges in relay testing

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Advanced Distance Relay Modeling and Testing

• New challenges in relay testing
• More complex impedance relay characteristic
• More complex differential relay characteristic
• No more than 8 words per line
• Increased number of functions to test
• New IEDs require a more accurate simulation of
  the electrical phenomena

Author Name Country Session .. Paper ID
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Distance relay modeling

• Unlike old relays, new impedance characteristics
  are more complex
• The test engineer must deeply know all relay
  features

• The new Toshiba GRZ100 has a very challenging
  impedance characteristic

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• The relay characteristic is not just a series of
  lines and arcs
• It is the intersection of different comparators

A characteristic like this Is the result of an intersection
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• In RIO format, that shape is defined as
• LINE 7.212389, 0.7926472, 75
• ARC 2.588202, 9.659244, 10, 32.45674, 56.51973
• LINE 8.1047, 18, 180
• ARC 2.588191, 9.659257, 10, 123.4804, 165
• LINE -7.071067, 12.24745, -60
• LINE 0, 0, -10
• ARC 2.58819, 9.659258, 10, 265, 297.5433
• It is evident it is not something that can be
  easily done by hand.

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The importance of a library...

• For this reason, several relay test set
  manufacturers offer a library
• The purpose is to automatically define that
  sequence of arcs and lines which depends on the
  extension of the circular characteristic
• And until now, nothing new

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New ways to define the characteristics

• The characteristic is always defined as a result
  of the intersection of different comparator.
• The result is a series of line and arcs
• And it represents just one single
  characteristic...
• But what if we use two characteristics to
  represent one ?

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Use the same (almost) method of the relays...

• As we already said...
• So that we can say, if that is zone 1
• Zone 1 Z1MHO n Z1QUAD

A characteristic like this Is the result of an intersection of 2 characteristics
This MHO
And this poligonal
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• So that if the draw two simple char
• Zone 11 MHO
• Zone 12 Poligonal
• The nominal char can simply been calculated as
• Znom Min (Zquad, Zmho)

• The testing software must simply evaluate 2
  impedance values and take the minimum

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In the same way...

• A Characteristic like the SEL321 will be union of
  2 shapes
• In this case
• Zone 1 Z1MHO U Z1QUAD
• and ...
• Znom Max (Zquad, Zmho)

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This is very useful in many cases

• ... Like in the general fault criteria and the

General fault criteria Load encroachment
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Conclusion for part 1

• This approach will enhance the productiveness of
  the technicians
• But it will change the method of exporting the
  impedance relay nominal characteristic
• formats like the actual RIO would be insufficient
  
• In fact, although it makes possible to define
  whatever number of zones, it is not giving
  information whether a single zone is the
  combination of more shapes.

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Getting close to a real fault simulation

• Modern protective relays implement special
  algorithms to enhance the relay operating time in
  zone 1.
• A trip time below 1 cycle is required for EEHA
  lines.
• To work properly, the currents seen by the relay
  must have a smooth change from pre-fault to fault

Good simulation Bad simulation
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The DC offset

• It is not easy to have this simulation at any
  time
• It requires the software or hardware to evaluate
  this equation at every transition
• Where
• I1 RMS value of the fault current
• I0 instantaneous value of the current just
  before the fault
• Time constant
• t Time in seconds, fault occurs at t0

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This can be done with Comtrade files ?

• It is a strategy to perform a single shot test,
  but...
• A total of
• 6 channels
• With fault duration of 1.2 s
• sampled at 1 kHz
• 2 bytes per sample
• Requires a file of 720 kB to be uploaded
• With a 10 Mbps or 100 Mbps this can be uploaded
  very quickly, therefore it might not be a problem

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But what about developing faults ?

• A developing fault is a sequence of states where
  every state depends on what happened in the
  previous state
• Due to this, a Comtrade has the limitation that
  the exact time of transition between states is
  not certain
• The exact time of transition determines the DC
  offset of the currents in the following state

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The DC offset calculated on the fly

• Due to this, the DC offset must be evaluated by
  the hardware itself
• The firmware of the equipment must be able to
  elaborate, at high speed, this formula
• Since the sampling rate of the genaration must be
  kept relatively high, 10 to 20 kHz, for all
  current involved in the test

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• Failing to do that, a simulation like the
  following would become impossible

A simulation like this Will appear like this
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Conclusion for part 2

• Nowaday, testing a relay is not simply a
  characteristic check
• Smarter relays require smarter test equipments
• Smarter test equipment require high speed
  dedicated processors
• We have answers to all testing problems may arise
  in the field.

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Thanks very muchfor your attention

• Mauro Borrielli
• Doble engineering company
• Client support engineer
• Email mauro.borrielli_at_doble.no
• Web www.doble.com