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DR on the GSA Williams Building Spot Network One year of Monitoring the Operation of the Interface S

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How does the DR behave under abnormal conditions? ... of the Tecogen unit during abnormal conditions, it has not been tested against model data. ... – PowerPoint PPT presentation

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Title: DR on the GSA Williams Building Spot Network One year of Monitoring the Operation of the Interface S


1
DR on the GSA Williams Building Spot NetworkOne
year of Monitoring the Operation of the Interface
System

2
(No Transcript)
3
A Quick Review of What and Why We Did a
Monitoring Study
  • The System
  • The Design
  • The IEEE Standard

4
Arrangement of Williams Building Spot Network
  • 277Y/480 volt LV supply system
  • two utility primary feeders supplying network
    transformers
  • primary feeders may have other loads
  • integrated transformer, relays, and LV air-break
    switch (network protector or NWP) in a Vault in
    the basement
  • Initial design had the protectors opening on
    reverse power flow with no time delay

5
DR on Spot Networks
  • use inverter-based generation technology so
    network protectors are not as likely to be opened
    by fault current contribution from the local
    generator or,
  • time-coordinate network protector relay with
    feeder relaying to prevent NP opening from
    generator fault current contribution

6
Network Relay Modifications
  • Electromechanical Master relay changed to a solid
    state MPCV (also a very sensitive three-phase
    reverse power relay but with the capability to
    set a low reverse power level with time delay)
  • Time delay selected was 15 cycles
  • The MPCV high reverse power setting for
    instantaneous trip was set at 50 of the
    transformers rated current

7
Adjustable Reverse -Power Characteristic
time delay for low currents
time
adjustable delay time
adjustable instantaneous trip threshold
instantaneous trip for higher currents
100
current ( of xmfr rating)
8
Also Added Network Interface Control Unit, The
CH Auxiliary Unit
 
 
  •  
  •  
  •  
  •  

9
Problems with Local Generation on Network
  • if local generation exceeds local load, even
    momentarily, network protectors open and isolate
    the network from the utility supply.
  • At very light load conditions, one of parallel
    protectors may open due to a minor change in
    feeder supply system which can lead to excessive
    cycling
  • A preventative rule of thumb is to maintain
    between 2 and 10 of transformer rated power flow
    into the network

10
DR on Spot Networks
  • limit generation to less than local load, with an
    adequate margin for sudden loss of load
    conditions, to insure no undesired reverse power
    conditions or,
  • control inverter power output with tie-line load
    control so power flow from the utility to the
    network never reverses or,

11
DG with Network UnitsAlternatives
  • trip or isolate local generation from network if
    network protector relays sense low incoming power
    flow or,
  • isolate local generation with critical loads by
    sensing reverse power from critical load bus to
    network (not an option for induction generators)

12
DR on Spot Networks
  • prevent islanding of the network trip generation
    or isolate it from the network unit with a
    circuit breaker whenever a network protectors open

13
Over and Under-power Relays Required
  •  
  •  
  •  

14
Reconnection of the DR must be blocked until
  • 1. Both protectors are closed and
  • 2. The minimum load is greater than (150 minimum
    load DR rating) and
  • 3. Each protector is supplying one half of the
    value under item 2, and
  • 4. After the minimum reconnection threshold is
    reached, a selectable time delay must pass before
    reconnection is permitted. This time delay must
    be adjustable from 1 to 300 seconds.
  •  

15
Compliance with IEEE Standard 1547-2003
  •  
  • In the clause applying directly to spot networks,
    the Standard first requires that a protector
    shall not be used to separate, switch, or act as
    a breaker failure backup, or in any manner
    isolate a network to which DR is connected unless
    the protectors are rated for such an application.
    It clear that the framers of 1547 intend that if
    all the protectors were to open, the DR must have
    already switched off the network bus.

16
Continued--Compliance with IEEE Standard 1547-2003
  • To meet the requirement that the protectors not
    act as a breaker failure backup to the DR
    breaker, the Tecogen engineers provided an engine
    kill circuit which acts in parallel with the
    tripping of the DR contactor.

17
Continued--Compliance with IEEE Standard 1547-2003
  • The second requirement in this clause of 1547 is
    that the DR cannot cause operation of a network
    protector or prevent re-closing of any of the
    protectors. It further states that this
    coordination must be accomplished without
    requiring any change to the utilitys practice
    for clearing times of the network protectors

18
Continued--Compliance with IEEE Standard 1547-2003
  • The interconnection package meets the first part
    of this requirement by the under power relay
    tripping the DR if the power level drops in
    either protector to the point that a power
    reversal might be experienced by a sudden loss of
    a block of load. The approach that, if either
    protector is open, the DR must be off the
    network, meets the requirement of not preventing
    re-closing

19
Continued--Compliance with IEEE Standard 1547-2003
  • The third requirement of the clause is that the
    DR cannot be connected to the network unless more
    than 50 of the spot network protectors are
    closed.
  •  
  • The interconnection package meets this
    requirement by the prevention of a DR connection
    unless both protectors are closed.

20
Continued--Compliance with IEEE Standard 1547-2003
  • The fourth requirement is that the DR cannot
    cause any protector cycling.
  •  
  • One of the principal missions of the under power
    relays is to prevent this condition.

21
Continued--Compliance with IEEE Standard 1547-2003
  • The fifth requirement of the clause is that by
    connecting the DR to the network bus, network
    equipment loading and fault interrupting capacity
    cannot be exceeded.
  •  
  • This requirement was addressed in the Phase I
    engineering study where no issues were
    discovered.

22
What the Captured Data Shows
  • Questions to be answered
  • Salient Events
  • Conclusions

23
Questions to be Answered
  • Time for the Tecogen unit to shut down after a
    trip signal was issued by the CH unit?
  • How often did the CH units protective function
    operate?
  • How effective was the CH unit?
  • Did the PV or Tecogen units recognized all events
    other than minimum power flow that required their
    shutdown? For example, could they detect and
    clear for faults on either of the feeders
    supplying the network units, or determine when
    one of the network units tripped, or when voltage
    went below limits?

24
Continued-Questions to be Answered
  • Did any event occur during or near minimum power
    conditions that required the present minimum
    power settings to prevent reverse power flow
    through either network protector?
  • Did protector cycling exist even with the
    presently determined minimum load?
  • If any protector cycling occurs, was it
    excessive?

25
Continued-Questions to be Answered
  • Would protector cycling be excessive if the
    minimum power settings of the auxiliary
    protection package were lowered?
  • Did the MPCV time delay of .25 seconds give an
    adequate margin of error for all feeder events?
  • Was the generation fault response characteristics
    under abnormal conditions such that time delay
    was not required?

26
Continued-Questions to be Answered
  • What does the CH unit protection package demand
    of the Tecogen (DR) unit?
  • What situations occur on the 480 volt system?
  • How close to borderline between normal and
    abnormal are the Tecogen protection settings
    operating on the system?
  • How does the DR behave under abnormal conditions?
  • Is the generator affecting voltage on the system?

27
Continued-Questions to be Answered
  • Confirm the CH units and Tecogen equipments
    clearing times are consistent with those
    demonstrated by the commissioning test. What
    happens because of the ten-cycle limit allowed by
    IEEE P1547 for the Tecogen or the PV unit in case
    of a single-line-to-ground (SLG) fault on the 480
    volt system, i.e., will there be any temporary
    overvoltages on the GSA system as a result of
    slow clearing of the DRs?
  • How many trips accurate, missed, unnecessary?
  • What caused the event?

28
Continued-Questions to be Answered
  • Under abnormal situations out on the utility
    system, how does the onsite generation respond?
    If the Tecogen system were to be as benign as
    motor loads, it would have to shut down well
    before three cycles of abnormal behavior have
    been experienced on the power system.

29
Answers Determined from Data Captured
  • The Cutler Hammer Auxiliary Protection Package
    (CH unit) performs exactly as designed to trip
    the Tecogen unit off line within 5 cycles when
    either protector experiences momentary reverse
    power.
  •  

30
Answers Determined from Data Captured
  • The CH unit holds the Tecogen off line when
    either protector is open. Since the CH unit
    tripped the Tecogen unit when under power
    occurred in either protector, initially the
    Tecogen unit was being tripped nearly every
    evening. By the time the monitoring system got
    installed, the Tecogen operator had the unit
    gracefully shut down on a time of day schedule.
    Of the 37 transient events captured, there were
    only six that resulted in the CH unit forcing the
    Tecogen unit off line.
  •  

31
Answers Determined from Data Captured
  • The CH unit underpower/overpower scheme
    functioned as designed. It blocked Tecogen
    operation when a protector was open and it
    allowed Tecogen operation even when one
    protectors net import dropped to very close to
    the under power set point (down to 64.7 kW in one
    of the example events). The trip point was set
    to 60 kW.

32
Answers Determined from Data Captured
  • Very little data was collected to show how the
    Tecogen or PV protection functions work under
    fault conditions because the CH unit operates so
    rapidly for necessary trip conditions. The only
    data that reveals something of the Tecogen units
    response is two apparent transmission fault
    events. When the Tecogen unit was on line during
    these voltage dips it did not shut down on a
    voltage trip. However, these dips last less than
    10 cycles.

33
Answers Determined from Data Captured
  • The data has not been completely screened for
    minimum load network protector non-trip
    conditions. To the extent that it has been
    reviewed, only the day that building power was
    deliberately reduced for maintenance did power
    flows on a per protector basis drop below 60 kW. 
  • No condition that suggests cycling has been
    observed.
  • With no indication of cycling, there would
    not be any excessive cycling.
  •  

34
Answers Determined from Data Captured
  • To the extent that the data has been evaluated,
    there are no data that would indicate cycling
    might be increased if a lower reverse power
    setting were applied to the CH unit at this
    installation where the MPCV relays have a low
    reverse power time delay of 15 cycles. Based on
    the frequent observation that load current
    dropped at a rate greater than voltage dips, in
    any application that does not employ a small time
    delay, a system voltage dip could result in
    cycling or total network loss if it occurred near
    the minimum loading conditions.

35
Answers Determined from Data Captured
  • The MPCV time delay of 15 cycles appears to be
    appropriate for this application
  • There is limited data that demonstrates the
    Tecogen unit increases its current output under
    fault conditions. These data alone may not be
    sufficient to draw conclusions on need for time
    delay in protector relaying because of the quick
    action of the CH unit.

36
Answers Determined from Data Captured
  • The 60 kW minimum import criteria, at least
    during the Spring months, meant that the Tecogen
    tripped off line every evening. Therefore the
    Tecogen operators installed a timed shut down
    each evening to avoid the non-graceful trip from
    the CH unit.

37
Answers Determined from Data Captured
  • Many dips greater than 3 have been recorded.
    However, they appeared to be related to
    transmission faults. Because of the high
    resistance grounding of the NSTAR network feeder
    system, single-line-to-ground feeder faults do
    not seem to cause much of a voltage dip at the
    480 volt bus.

38
Answers Determined from Data Captured
  • From the limited data collected where the Tecogen
    unit may have had time to operate before the CH
    unit forced a trip, the Tecogen protective
    settings were not sensitive enough to be of use
    in detecting faults for which they should trip.
  •  

39
Answers Determined from Data Captured
  • While we have some data on the dynamics of the
    Tecogen unit during abnormal conditions, it has
    not been tested against model data. The
    three-phase fault that occurred on April 11, 2004
    showed that the unit could feed 170 of rated
    current for two cycles when its terminal voltage
    was held at 36. The voltage dip event of
    February 2, 2004 suggested that, during
    unbalanced fault conditions, an induction
    generator might supply current long enough to
    cause network protector tripping

40
Answers Determined from Data Captured
  • The generation does not seem to be affecting the
    480 voltage, but it does seem to have noticeable
    harmonics in its current output as demonstrated
    by the difference between the average rms value
    and the average fundamental value.
  •  
  • The rapid and correct actions of the CH unit
    appear to preclude gathering much useful data on
    the trip times of the Tecogen or PV units from
    their own control actions.

41
Answers Determined from Data Captured
  • All of the trip commands issued by the CH unit
    were accurate and necessary. When the Tecogen
    unit was on line to respond to these CH unit
    required trips, the Tecogen unit appears to have
    tripped in one cycle after receiving the trip
    command as designed by Tecogen.

42
Answers Determined from Data Captured
  • All but two of the network protector trips were
    clearly caused by faults. One was a maintenance
    trip and the other was from an undetermined
    cause.
  •  

43
Answers Determined from Data Captured
  • The rapid and comprehensive action of the CH unit
    may have precluded the gathering of meaningful
    data on the nature of the Tecogens dynamic
    response during faults and the effectiveness of
    the Tecogens protective actions to integrate
    with a network without requiring a time delay in
    the protector.

44
Conclusions
  • The findings from monitoring at this site
    verified
  • The functional performance of the CH unit 
  • The need for at least 15 cycles of time delay in
    network protector with DR connected to its low
    voltage bus

45
Continued-Conclusions
  • The voltage characteristics of loads must be
    considered when determining if a low voltage
    island might be formed 
  • Network protectors can sense and clear a fault in
    less than six cycles which, given the mechanical
    nature of the switch lends credence to concern
    that network protector relays can initiate
    tripping in three cycles

46
Continued-Conclusions
  • Voltage sensing at the DR cannot be counted on
    to trip the DR in a timely manner for
    interconnections with network systems 
  • Some interfacing device must be provided to trip
    the DR when one of the protectors opens.
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