October 16, 2012 MWG Meeting Topics for Discussion.

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

013SMOGRR-02 Impact Analysis 0...

013SMOGRR-01 Synchronization w...

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.


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.


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.


Consider the example below: Single CT configuration.

Is Xs Rs

Xb

Rb

VbZ

The effective burden (Z) is equal to the external connected burden, Z = Rb + jXb


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.


Is

Xb

Rb

VA B

Is

2Is

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 / IZe = 2Z


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.


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.


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).


• 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 re-certification 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 non-PCB 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

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


• 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


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%


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%


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


Average Interrogation Time: PSTN vs. TCP/IP

PSTN Meters = 2 minutes 29 seconds

TCP/IP Meters = 8 seconds


• Reasons Notices are Issued

– BUSY SIGNAL: 145– I/O TIMEOUT: 101– WRONG MTR: 4– NO ANSWER: 101– NO CARRIER: 557– OTHER: 3– OUT OF SRVC: 7– TCP/IP ERROR: 73

– TOTAL: 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

http://www.ercot.com/calendar/2012/09/20120924-ETWG

Questions?

October 16, 2012 MWG Meeting Topics for Discussion.

Documents

Transcript of October 16, 2012 MWG Meeting Topics for Discussion.