Transcript Instructions

October 16, 2012 MWG Meeting
Topics for Discussion
Topics for discussion:
A.) SMOGRR-13 Impact Analysis Review
B.) Paralleling of Current Transformers per SMOG 1.3.7 (e)
C.) Loss of potential per SMOG 1.4.7 - define specific threshold
voltage
D.) CCVT 5-year re-certification discussion
E.) Nameplate photos of instrument transformers
F.) EPS metering sites that are provisionally approved status
G.) EPS meter data polling (via telephone line communication vs. IP
communication)
H.) Energy Storage Resources (ESR)
A. SMOGRR-13 Impact Analysis Review
B.) Paralleling of Current Transformers
Introduction:
Paralleling of current transformers affects the overall accuracy of the
EPS metering facility because of the increasing of the effective
connected burden on each individual current transformer.
This short article is intended to explain the possible outcome
whenever paralleling of current transformers is employed.
SMOG 1.3.7 (e) will be clarified using examples to show how the
effective burden rating on each CTs changes when connected in
parallel.
Paralleling of Current Transformers
SMOG 1.3.7 (e) Paralleling of Current Transformers – Connected
burden
Paralleling of current transformers is not recommended. However,
when it is necessary, the following requirements apply.
• (e) Each current transformer must be capable of supporting n
times the connected burden within the accuracy class of the
transformers, where n = number of current transformers in parallel.
Paralleling of Current Transformers
Per SMOG 1.3.7, paralleling of CTs for EPS revenue metering
purposes is not highly recommended. However, if current
transformers need to be connected in parallel, then all current
transformers must have the same nominal ratio and accuracy
regardless of the ratings of the circuits in which they are connected.
Connecting CTs of the same model number and type is preferred
but not mandatory.
Current transformers that have their secondary coils paralleled must
be connected to the same phase of the primary circuits. (SMOG
1.3.7(a), (b)). Thus, all phases of a 3-phase circuit will contain equal
quantity and similar type of CTs.
Paralleling of Current Transformers
When two equal currents are added by paralleling the secondary
windings of two current transformers, the connected burden (in VA)
increases by a factor of 4, and as a result each CT is then forced to
carry twice the original burden rating of what a single CT would be
able to carry.
Paralleling of Current Transformers
Consider the example below: Single CT configuration.
Is
Xs
Rs
Xb
Vb
Z
Rb
The effective burden (Z) is equal to the external connected burden,
Z = Rb + jXb
Paralleling of Current Transformers
Now, when two current transformers of equal ratio and rating are
connected in parallel to supply rated current to a common burden
(e.g., meter, secondary wiring, others), with each transformer
supplying the same amount of current (magnitude and phase), and
assuming the internal errors of the current transformers to be
negligible, the effective connected burden as seen by each CT
connected in parallel becomes twice the rated burden of what a
stand-alone single CT configuration sees.
Paralleling of Current Transformers
Is
Is
2Is
Xb
A
V
B
Rb
In the above example, the burden on transformer A is equal to the burden on
transformer B, which is equal to effective burden (Ze)
Ze = V / I = Z*2I / I
Ze = 2Z
Paralleling of Current Transformers
Similarly when three CTs of equal ratio and rating are connected in
parallel, the burden seen by each CT is three times the common
burden rating, based on the same assumptions.
It then becomes evident that the effective burden, Ze
Ze = n*Z
where: n is number of CTs connected in parallel
Z is rated burden.
Paralleling of Current Transformers
Example:
One Current Transformer that is rated to handle 1.8 ohms of
connected burden can handle up to 1.8 ohms of burden if it is not
connected in parallel with other CTs.
if n=3 units of this same CT (each individually rated at 1.8 ohms
burden) are connected in parallel, then each CT is now limited to a
maximum of 0.6 ohm connected burden (1.8 ohm divided by 3).
Exceeding the 0.6 ohm burden on each CT will affect the overall
accuracy of the EPS metering facilities.
Paralleling of Current Transformers
Conclusion:
When current transformers are connected in parallel, the effective
burden on each individual transformer is no longer the individual
CT’s nameplate burden rating. This effective burden becomes the
new maximum allowable burden on each CT and this value depends
upon the number of transformers connected in parallel.
As we have seen from previous examples, this effective burden is
the rated burden divided by the number of units being paralleled as
stated in SMOG 1.3.7 (e).
Paralleling of Current Transformers
•
References:
1. Paralleling of current transformers for metering applications – O.W.
Iwanusiw; Ontario Hydro Research Division Report
2. Relaying Current Transformer Application Guide – Western
Electricity Coordination Council
3. Instrument Transformer Application Guide – ABB
C.) Loss of Potential
SMOG 1.4.7
Loss of Potential
• The secondary circuit shall be monitored for loss of potential on
each phase.
SMOG 6.5.4
Event Logging
When interrogated by ERCOT MDAS, EPS Meters shall be capable
of logging and reporting the following events:
• (k) System phase voltage has been lost on any phase.
Loss of Potential
Introduction:
• Instances of partial loss of potential of the voltage transformer’s
secondary circuits were discovered while reviewing issues related to
events other than total loss of potential.
• An example was a defective fuse in one of the phases of the PT
secondary circuit that became intermittently opened or closed due to
loose internal connection of the link.
• The partial loss of potential on PT secondary circuits was seen by
the EPS meters as voltage that were lower than true value but did
not raise “flag” because it was not a complete loss of potential
(zero voltage).
Loss of Potential
• Since the loss of potential event of EPS meter is configured to be
triggered when secondary voltage drops to zero, no event (start
time, duration) is triggered, recorded, and sent to MV90 when
voltage drops below normal level as long as the value is above zero.
• Once the low voltage event is discovered manually, the affected
meter data had to be traced to estimate the time/duration at which
the partial loss of potential has occurred data estimation.
• Data availability is affected for the period that there is partial loss of
potential on the EPS metering facility.
Loss of Potential
Threshold low voltage – assigning a value, other than zero, as the
loss of potential threshold voltage can improve the visibility of
monitoring the voltage level. The following data and examples are
provided as reference for determining the recommended threshold
value.
ANSI C84.1
• ANSI C84.1 American national Standard for Electric Power Systems
and Equipment – Voltage Ratings (60 Hertz), provides two ranges
for service voltage and utilization voltage:
Service range: -5% ~ +5% of nominal voltage
Utilization range: -13% ~ +6% of nominal voltage
Loss of Potential
• There is no standard setting for under-voltage relays (IEEE Device
No. 27). Device 27 set at 90% and below of nominal voltage with
time delay is not uncommon. Per NERC’s Technical Reference
Document (Power Plant and Transmission System Protection
Coordination) below:
• 3.3.1.4.1. Alarm Only — Preferred Method
IEEE Standard C37.102, “IEEE Guide for AC Generator Protection,”
does not recommend use of the 27 function for tripping, but only to
alarm to alert operators to take necessary actions. Undervoltage
function (27) calculation:
V27 = 90% of Vnominal = 0.9 x 120 V = 108 V with a 10 second time
delay to prevent nuisance alarms (per IEEE standard C37.102).
Loss of Potential
• 3.3.1.4.2. Tripping Used (not recommended)
• CAUTION: If the Generator Owner uses the 27 function for tripping,
the following conditions must be met at a minimum: Time delay of
the undervoltage function trip must be longer than the greater of the
local or remote backup clearing times for all transmission elements
connected to the high-side bus, but not less than 10 seconds.
Undervoltage function (27) calculation:
V27 = 87% of Vnominal = 0.87 x 120 V = 104 V with a coordinated time
delay
Note: An 87 percent set point was chosen because the power plant
is not capable of continued operation at this voltage level, and
allows for a reasonable margin for extreme system contingencies
Loss of Potential
Conclusion:
Propose to use 75% and below of nominal voltage – when
secondary voltage falls below 75% of nominal voltage continuously,
a “loss of potential” indication should appear and be recorded at the
EPS meter and/or MV-90 system to notify TDSP and ERCOT.
D.) CCVT 5-year re-certification discussion
• The most recent information regarding the CCVT testing results for
the purpose of MWG reporting was compiled on 4/9/10 after this
topic was originally opened for discussion.
• At present, responses were received from 5 (out of the 6) TDSPs
with CCVTs installed in their EPS metering facilities.
• Of the 5 TDSPs that have responded, 2 of the TDSPs provided the
spreadsheets with “As-Found” results indicating that the accuracy
values of these re-certified CCVTs to be within tolerance.
CCVT 5-year re-certification discussion
• There have been a total of 126 CCVT re-certification accuracy test
results provided.
• Of the 126 tests, there were 96 that have “As-Found” results in a
manner that the accuracy can be documented.
• Only 1 out of the 96 tests had the “As-Found” results slightly outside
the tolerance.
• There were also 5 CCVTs that underwent second round of recertification testing. The most recent CCVT test date was 3/11/10.
CCVT 5-year re-certification discussion
Open for discussion/suggestions:
E.) Nameplate photos of newly-installed instrument
transformers
Benefits of submitting photos of nameplate of newly-installed
instrument transformers (picture taken while de-energized):
•
Nameplate shows important data including exact specifications and
windings of the instrument transformers and others (including nonPCB material statement)
•
Visual record handy. No need to dispatch personnel to the
substation when verifying exact specifications of the instrument
transformers. The information is already captured on the nameplate
•
Safety. Taking pictures of instrument transformers’ nameplate,
which sometimes put personnel in close proximity to energized high
voltage busses, can now be avoided
Nameplate photos of newly-installed instrument
transformers
•
For new sites, nameplate photos will be submitted together with the
initial site certification
•
For existing site, nameplate photos of instrument transformers that
are replaced can also be submitted with the site certification
•
For other instrument transformers, photos can be taken during a
planned outage
Nameplate photos of newly-installed instrument
transformers
Nameplate photos of newly-installed instrument
transformers
F.) EPS metering sites with provisionally approved status
Currently there are 57 Sites that are Provisionally Approved
•
43 of the 57 sites - ERCOT has not received final “as-built” drawings
•
7 of the 57 sites – covered by Temporary Exemption
•
The remaining 7 are due to phase angle and burden test information
EPS metering sites with provisionally approved status
•
SMOG Section 3.2.3 (h) – Note: If a redline version is supplied, the
final “as-built” drawings shall be submitted within 45 days of the
submittal of the Site Approval Request Package.
– 8 are dated prior to 2005
– 27 are date between 2005 -2010
– 22 are dated between 2010-2012
EPS metering sites with provisionally approved status
•
ERCOT is providing information to TDSP to resolve as many
provisionally approved sites as possible.
– First round of e-mails sent on 9-6-2012
– Presentation at MWG Meeting 10-16-2012
– Follow-up
EPS metering sites with provisionally approved status
Final “As-Built” Drawing criteria:
– Should not contain hand writing updates, markings, corrections
or comments (except signature)
– Should have revision number/letter and date greater/later than
what is on the “red-lined” drawings that are on file
– If drawing number changes or revisions numbers are listed on
Site Certification, then an updated/corrected Site Certification
form is required
G.) EPS meter data polling
Discuss PSTN vs. TCP/IP communication in meter data polling;
 Total Meters Dialed/Percentage of Meter Population
 Total Number of 12-Hour & 5-Day Notices
Issued/Percentage of failures by Technology Type
 PSTN vs. TCP/IP Failure Rates
 Average Interrogation Time: PSTN vs. TCP/IP
 Reasons Notices are Issued
EPS meter data polling
Total Meters Dialed/Percentage of Meter Population
 Total Meters Interrogated = 1,236
 By Technology Type
 Phone Lines (PSTN) = 1,049 or 84.9%
 TCP/IP = 187 or 15.1%
EPS meter data polling
Total Number of 12-Hour & 5-Day Notices Issued/Percentage of
failures by Technology Type
 TOTAL NOTICES ISSUED = 991
 12-Hour = 459
 5-Day = 532
 Issued for PSTN = 918
 Percentage of 991 notices issued = 92.6%
 Issued for TCP/IP = 73
 Percentage of 991 notices issued = 7.4%
EPS meter data polling
PSTN vs. TCP/IP Failure Rates (1,236 total meters)
 PSTN had 918 notices issued for 1,049 meters (87.5%)
 TCP/IP had 73 notices issued for 187 meters (39%)
 If the 1,049 meters on PSTN were converted to TCP/IP, making
all 1,236 meters on TCP/IP, the TOTAL number of notices
issued would drop from 991 to 482 (39% of 1,236 meters),
resulting in an approximate 49% reduction in total notices
issued.
 BENEFITS:
 Reduction/elimination in phone charges
 Reduction in TDSP field site visits
EPS meter data polling
Average Interrogation Time: PSTN vs. TCP/IP
 PSTN Meters = 2 minutes 29 seconds
 TCP/IP Meters = 8 seconds
EPS meter data polling
•
Reasons Notices are Issued
–
–
–
–
–
–
–
–
BUSY SIGNAL:
I/O TIMEOUT:
WRONG MTR:
NO ANSWER:
NO CARRIER:
OTHER:
OUT OF SRVC:
TCP/IP ERROR:
– TOTAL:
145
101
4
101
557
3
7
73
991
H.) Energy Storage Resources (ESR)
Below is the link to the ESR spreadsheet that was used at the
ETWG (Emerging Technology Working Group) meeting. Please
copy and paste to the web browser:
http://www.ercot.com/calendar/2012/09/20120924-ETWG
Questions?