E-29 — Electricity Meter Calibration Console Burden Effects

E-29—Electricity Meter Calibration Console Burden Effects (PDF, 34 KB, 5 pages)

Category: ELECTRICITY
Bulletin: E-29 (rev. 2)
Document(s): S-E-01, S-E-02 (section 5.2.4)
Issue Date: 2010-11-03
Effective Date: 2011-01-01
Supersedes: E-29 (rev.1)

Table of Contents

1.0 Purpose

The purpose of this bulletin is to clarify requirements of section 7.1.5 and 7.2 of S-E-01 as relates to the impact of burden direction, (capacitive or inductive), as well as magnitude, on a calibration console.

2.0 Scope

This Bulletin applies to all electricity meter calibration consoles which are certified in accordance with S-E-01 (Specifications for the Calibration, Certification and Use of Electricity Calibration Consoles).

3.0 Background

3.1 Issue

Measurement Canada (MC) has been made aware of a technical situation which can have serious implications on the level of confidence in the accuracy of test results for verified electricity meters. In 2005 MC was informed that some electricity calibration consoles were not able to comply with certain requirements of S-E-01 pertaining to the effects of meter burden when the consoles were burdened with a certain type of meter. At the time this was thought to be an isolated incident and corrective action was implemented to address the situation. Since that time, MC has performed a study and evaluation of additional technical data and information provided by electricity stakeholders. The situation has been determined to be broader in scope than originally thought.

3.2 Effects of Burden

The amount of burden placed on a test console can vary drastically depending on the type and number of meters being tested. The error which a console indicates for any given meter under test will depend on the burden placed on the console by the meter(s), (ie: the effect of burden impacts on the ability of a test console to directly compare the accuracy of a meter under test with that of the certified reference standard). This results in a level of uncertainty in the indicated error of the meter under test.

Specification S-E-01 contains requirements pertaining to the effects of various burden conditions which are placed on the console during meter testing. The purpose of those requirements is to ascertain if a console is capable of testing meters under a range of burden conditions while minimizing the level of uncertainty in the indicated error of the meter(s).

3.3 Description of Problem

3.3.1 Section 7.1.5.1 of S-E-01 identifies the test burdens to be used during console certification testing. In general it establishes that the console be tested under conditions of high burden and again under conditions of low burden. This criteria is sufficient under the assumption that meter burden varies in magnitude only. However meter burden does have direction as well as magnitude, and can be either inductive or capacitive, this is evidenced by a growing number of meter types exhibiting capacitive burden characteristics. The result is such that a high inductive burden meter may impact on the console indicated error in a negative direction while a high capacitive burden may impact on the console indicated error in a positive direction. The limits for maximum permissible spread of error due to burden effects may be exceeded between the high inductive and high capacitive burden even if they are complied with between one of the high burdens and low burden. Therefore confidence in the test results which a console indicates for a meter under test is compromised by this significant increase in the level of uncertainty.

3.3.2 Concern regarding the level of confidence in the certainty of established meter errors has been raised to MC by electricity stakeholders. The criterion outlined in this Bulletin are established in order to mitigate the potential for increased measurement uncertainty and ensure confidence in the level of uncertainty pertaining to meter errors indicated by certified calibration consoles. As concern has been raised directly from electricity stakeholders concerning confidence in the level of uncertainty and accuracy of verified meter errors, the expeditious implementation of this Bulletin is of high importance.

4.0 Metrological Considerations

4.1 Section 7.1.5.1 of S-E-01

4.1.1 The intention of section 7.1.5.1 of S-E-01 is to identify the maximum range of burden conditions that a certified calibration console may be subjected to in order to assure that the full expected range of meter burdens is in fact assessed. This section establishes the voltage burdens to be used when performing subsequent metrological tests pursuant to section 7 of S-E-01.

4.1.2 Sections 7.1.5.1 (a)(I), (b)(I), (c)(I) are intended to include the highest inductive voltage burden and the highest capacitive voltage burden. Therefore when assessing a console pursuant to section 7.1.5.1, three tests must be performed: 1) The highest inductive burden, 2) The highest capacitive burden, 3) The lowest burden (which could be zero burden for polyphase meters). See the note under section 4.2.3 (a) below for further information.

4.1.3 The burden which causes the medium error of the three shall be used as the general test burden as applicable for tests pursuant to sections 7.8 and 7.9 of S-E-01. The burden which causes the greatest error of the three shall be used as the general test burden as applicable for tests pursuant to sections 7.3, 7.4, 7.6 and 7.7 of S-E-01.

4.2 Section 7.2 of S-E-01

4.2.1 The intention of section 7.2 of S-E-01 is to assess the console to determine if it complies with criteria which aims to minimize the level of uncertainty in the indicated errors of meters under test, under the full range of burden conditions that can be imparted by meters which are intended to be verified on the calibration console.

4.2.2 The criteria of section 7.2.1 must be complied with in order for the calibration console to be certified to verify all the meter types which are included within the statement of intended use for the calibration console as required by section 5.2.6 of S-E-01.

4.2.3 The following conditions shall be met in order for the calibration console to be certified to verify all the meter types which are intended to be verified on the calibration console:

  1. All burdens applicable to each meter type which is intended to be verified on the calibration console shall be identified. The burdens shall be assessed in accordance with section 7.1.5.1.

    Note: MC strongly recommends that calibration console owners perform the assessment of burdens (as outlined in section 7.1.5.1 of S-EF–01) for each electronic meter type, plus each electro-mechanical type fitted with an RF transmitter that is expected to be verified on each console. Such assessment would result in a complete evaluation of the meter types which may potentially impart burden effects that cause the console to not comply with specified requirements. The test procedures pursuant to section 7.1.5.1 are relatively short and will secure the needed information with minimal resources required. The added benefit of this approach is that console owners will not have to research meter burden data as the effect of all the assessed burdens will be known. This information may be useful in evaluation of corrective action considerations as identified in section 7.0 below, and determination of necessary console upgrades or modifications. Subsequently, meter owners will be able to group meter types having similar burden effects.

  2. All burdens (meter types) which impart errors of no more than 0.1% difference (spread of error) among them, have met the criteria of section 7.2.1 and can therefore be included within the statement of intended use of the calibration console subsequent to tests required pursuant to section 7.8.2.6 of S-E-01.

  3. A list of every burden (meter type) for which the calibration console is certified to verify shall be established by the console owner.

4.2.4 Calibration console errors, at any test point and under any burden condition, shall not exceed the applicable tolerance set out in section 7.8.

4.2.5 All parameters, restrictions or limitations pertaining to the use of meter burdens for the purposes of calibration console certification shall be documented in the "Remarks" section of the calibration console certificate.

Ex:This console is not certified for the verification, reverification or compliance sampling of any electronic meter type, or any meter which is equipped with a RF transmitting devices, except as listed below:

  1. ABC meter
  2. DEF meter type fitted with the XYZ Automatic Meter Reading Module.

4.3 Example

Meter W error (due to burden effect) = - 0.01%
Meter X error (due to burden effect) = - 0.08%
Meter Y error (due to burden effect) = - 0.10 %
Meter Z error (due to burden effect) = + 0.09 %

In this example meters W, X and Y comply with the requirements of 7.2 of S-E-01, and pursuant to section 7.1.5.1, the meter burden among the three which imparted the greatest error on the console must be used as the test burden for all applicable tests pursuant to sections 7.3, 7.4, 7.6 and 7.7 of S-E-01. In addition, meter Z is not eligible to be verified on this console as the error imparted by its burden (in relation to that of the meters W, X and Y) exceeds the tolerance of section 7.2.1 of S-E-01. Pursuant to sections 7.8.2 (and 7.9 if applicable) of S-E-01, all console calibration errors must be determined with the burden imparted by meter W, X or Y, (whichever one imparted the medium error on the console), as the test burden.

A listing identifying meter types W, X, and Y as complying with one range of burden shall be created which will facilitate selection of the pertinent test points, (for the meters of that burden range), which are required pursuant to section 7.8 during certification of the console. This will provide meter verifiers with the appropriate error corrections to be applied when verifying various meter types.

5.0 Implementation

5.1 The criterion of this Bulletin have been in effect since 2007-12-13 for all electricity calibration consoles which require certification pursuant to S-E-01.

5.2 The criterion of section 4.0 of this Bulletin has been in effect since April 1, 2008 for all electricity calibration consoles which require recertification (including annual certificate extensions) pursuant to S-E-01.

5.3 All expansions of calibration console scope or intended use, (additional meter types which may be verified on the console) shall be evaluated to ascertain if they include meter types which may have burden characteristics that could cause the console to be non-compliant with section 7.2 of S-E-01. Where expansion of intended use includes such meter types the calibration console shall be assessed in accordance with the metrological requirements outlined in this Bulletin.

6.0 Factors Impacting on Effects of Burden

MC has undertaken a study to determine if capacitive burden effects are limited as to the number of meter types and calibration console types which when used together may result in non-compliance with section 7.2 of S-E-01. The study demonstrated that there are a range of meter types and calibration consoles which when used in conjunction may result in non-compliance with the specified requirements for burden effect.

The following factors may result in burden effect errors which exceed the specified limits of error.

  1. Meter design - some meter types (particularly electronic meters) exhibit capacitive burden characteristics which may burden a calibration console significantly in direction and magnitude such that the error spread between it, and that of a meter type which has inductive burden characteristics, exceeds the specified limits of error.
  2. Automatic Meter Reading devices, (particularly Radio-Frequency transmitters) - some meter types which include integrated or ancillary RF transmitters have been discovered to exhibit significant capacitive burden characteristics.
  3. Calibration console design and use - some calibration consoles have been constructed with components specifically designed to compensate for the burden effects of either capacitive meter types or of inductive meter types, but not both. This increases the likelihood that the error spread between the two meter types will exceed the specified limits of error. Other possible calibration console contributing factors include the design and use of components such as: power supply, current transformers and potential transformers.

7.0 Corrective Action Considerations - Compliance with Section 7.2.1 of S-E-01

  1. Console manufacturers and service companies have identified various upgrades which allow certain calibration consoles to comply with specified requirements under a wider range of burden conditions. MC recommends that calibration console owners contact these companies in order to bring non-compliant consoles into compliance with specified requirements.
  2. Console owners may wish to designate specific consoles to be used with specific meters types as opposed to designating every console to be used with every meter type. For example console # 1111 may comply with limits of error for burden effects with meters W, X and Y, while console # 2222 may comply with limits of error for burden effects with meters Z and ZZ.

8.0 Revisions

The purpose of revision 1 was to:

  1. make modifications to the referenced sections of S-E-01 as that document underwent structural changes;
  2. require use of the medium error producing burden (as opposed to the highest) for calibration of the consoles now that there are three tests (sections 4.1.3 and 4.3);
  3. modify section 5.0 to remove implementation requirements that have already occurred.

The purpose of this revision is to:

  1. modify section 4.1.3 such that the medium error burden applies only to sections 7.8 and 7.9 of S-E-01, while the greatest error burden applies to sections 7.3, 7.4, 7.6 and 7.7 of S-E-01;
  2. delete sections of 4.2.2 which are no longer relevant;
  3. modify the example in 4.3 to be in accordance with section 4.1.3.

9.0 Additional Information

The provisions and interpretations established in this bulletin will be incorporated into S-E-01 at such time as that specification is reviewed and amended. This bulletin will concurrently be revoked at that time.

For additional information regarding this bulletin, please contact the Senior Program Officer responsible for electricity measurement.

Alan Johnston
President