1 Scope
This part of GB/T 16927:
——defines the terms used;
——defines parameters and their tolerances;
——describes methods to estimate uncertainties of high-current measurements;
——states the requirements which a complete measuring system shall meet;
——describes the methods for approving a measuring system and checking its components;
——describes the procedure by which the user shall show that a measuring system meets the requirements of this part, including limits set for uncertainty of measurement.
This part is applicable to high-current testing and measurements on both high-voltage and low-voltage equipment. It deals with steady-state and short-time direct current (as e.g. encountered in high-power d.c. testing), steady-state and short-time alternating current (as e.g. encountered in high-power a.c. testing), and impulse-current.
In general, currents above 100 A are considered in this part, although currents less than this can occur in tests.
Note: This part also covers the current measurement upon fault detection during, for example, lightning impulse testing.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
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GB 1984 High-voltage alternating-current circuit-breakers (GB 1984-2003, IEC 62271-100:2001, MOD)
GB/T 7676.2-1998 Direct acting indicating analogue electrical measuring instruments and their accessories - Part 2: Special requirements for accessories (IEC 60051-2:1984, IDT)
GB/T 16927.1-2011 High-voltage test techniques - Part 1: General definitions and test requirements (IEC 60060-1:2010, MOD)
JJF 1059.1-2012 Evaluation and expression of uncertainty in measurement (ISO/IEC Guide 98-3:2008)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Measuring system
3.1.1
measuring system
complete set of devices suitable for performing measurements of a quantity to be measured (measurand). Software used to obtain or calculate measurement results also forms a part of the measuring system.
Note 1: A high-current measuring system usually comprises the following components:
——converting device with either terminals to connect this device in circuit or appropriate coupling to the circuit, and connections to earth;
——transmission system(s) connecting the output terminals of the converting device to the measuring instrument(s) with its attenuating, terminating, and adapting impedances or networks; and
——measuring instrument(s) together with any connections to the power supply;
——measuring systems which comprise only some of the above components or which are based on non-conventional principles are acceptable if they meet the uncertainty requirements specified in this part.
Note 2: The environment in which a measuring system functions, its clearances to live, current carrying, and earthed structures, and the presence of electromagnetic fields may significantly affect the measurement result and its uncertainty.
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3.1.2
record of performance
detailed record, established and maintained by the user, describing the measuring system and containing evidence that the requirements given in this standard have been met. This evidence includes the results of the initial performance test and the schedule and results of each subsequent performance test and performance check
3.1.3
approved measuring system
measuring system that is shown to comply with one or more of the sets of requirements set out in this part
3.1.4
reference measuring system
measuring system with its calibration traceable to relevant national and/or international standards, and having sufficient accuracy and stability for use in the approval of other systems by making simultaneous comparative measurements with specific types of waveform and ranges of current
Note: A reference measuring system (maintained according to the requirements of this part) can be used as an approved measuring system but the converse is not true.
3.2 Components of a measuring system
3.2.1
converting device
device for converting the quantity to be measured (measurand) into a quantity, compatible with the measuring instrument
3.2.2
current-converting shunt
resistor across which the voltage is proportional to the current to be measured
3.2.3
current transformer
converting device with converter in which the secondary current, in normal conditions of use, is substantially proportional to the primary current and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections
Note: Current transformers are usually defined for a single frequency, but special designs with a wide frequency range are possible.
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3.2.4
Rogowski coil
inductive current-converting device without iron; measuring systems based on a Rogowski coil include an integrating circuit (passive, active, or numerical)
Note: Measuring systems based on a Rogowski coil can be designed for current measurements in a wide range of frequencies.
3.2.5
transmission system
set of devices that transfers the output signal of a converting device to a measuring instrument(s)
Note 1: A transmission system usually consists of a coaxial cable with its terminating impedance, but it may include attenuators, amplifiers, or other devices connected between the converting device and the measuring instrument(s). For example, an optical link includes a transmitter, an optical cable, and a receiver as well as related amplifiers.
Note 2: A transmission system may be partially or completely included in the converting device or in the measuring instrument.
3.2.6
measuring instrument
device intended to make measurements, alone or in conjunction with supplementary devices
3.3 Scale factors
3.3.1
scale factor of a measuring system
factor by which the value of the measuring-instrument reading is to be multiplied to obtain the value of the input quantity of the complete measuring system
Note 1: A measuring system may have multiple scale factors for different current ranges, frequency ranges or waveforms.
Note 2: Some measuring systems display the value of the input quantity directly (i.e., the scale factor of the measuring system is unity).
3.3.2
scale factor of a converting device
factor by which the output of the converting device is to be multiplied to obtain its input quantity
Note: The scale factor of a converting device may be dimensionless (for example, the ratio of a current transformer) or may have dimensions (for example, related to the impedance of a current-converting shunt).
3.3.3
scale factor of a transmission system
factor by which the output of a transmission system is to be multiplied to obtain its input quantity
3.3.4
scale factor of a measuring instrument
factor by which the instrument reading is to be multiplied to obtain its input quantity
3.3.5
assigned scale factor F
scale factor of a measuring system determined at the most recent performance test
Note: A measuring system may have more than one assigned scale factor; for example, it may have several ranges, each with a different scale factor.
3.4 Rated values
3.4.1
operating conditions
conditions under which a measuring system will operate within the specified uncertainty limits
3.4.2
rated current
maximum level of current of specified frequency or waveform at which a measuring system is designed to be used
Note: The rated current may be higher than the upper limit of the assigned measurement range.
3.4.3
assigned measurement range
range of current of specified frequency or waveform in which a measuring system can be used within the uncertainty limits given in this part, characterized by a single scale factor
Note 1: The limits of the assigned measurement range are chosen by the user and verified by the performance tests specified in this part.
Note 2: A measuring system may have more than one assigned measurement range, with different scale factors established for the different ranges.
3.4.4
assigned operating time
longest time during which a d.c. or a.c. current measuring system can operate at the upper limit of the assigned measurement range within the uncertainty limits given in this part
3.4.5
assigned rate of application
highest rate of specified short-time currents or impulse currents that can be applied in a given time interval, at which the measuring system can operate at the upper limit of the assigned measurement range and stay within the uncertainty limits given in this part
Note: The assigned rate of application could for example be expressed as the number of applications per minute and the time interval in minutes or hours.
3.5 Definitions related to the dynamic behaviour
3.5.1
response of a measuring system
G
output, as a function of time or frequency, when a specified current is applied to the input terminal of the system
3.5.2
amplitude-frequency response
G (f)
ratio of the output to the input of a measuring system as a function of frequency, f, when the input is sinusoidal (see Figure 1)
3.5.3
limit frequencies
F11 and f2
lower and upper limits of the range within which the amplitude-frequency response is nearly constant
Note: These limits are where the response first deviates by a certain amount (e.g. ±15%) from the constant value. The permissible deviation should be related to acceptable uncertainties of a measuring system (see Figure 1).
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3.5.4
step response
G (t)
output of a measuring system as a function of time, t, when the input is a step function
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
3.1 Measuring system
3.2 Components of a measuring system
3.3 Scale factors
3.4 Rated values
3.5 Definitions related to the dynamic behaviour
3.6 Definitions related to uncertainty
3.7 Definitions related to tests on measuring systems
4 Procedures for use and performance check of a measuring system
4.1 General principles
4.2 Schedule of performance tests
4.3 Schedule of performance checks
4.4 Requirements for the record of performance
4.5 Operating conditions
4.6 Uncertainty
5 Tests and test requirements for an approved measuring system and its components
5.1 General requirements
5.2 Calibration - Determination of the scale factor
5.3 Linearity test
5.4 Dynamic behaviour
5.5 Short-term stability
5.6 Long-term stability
5.7 Ambient temperature effect
5.8 Effect of nearby current paths
5.9 Software effect
5.10 Uncertainty calculation
5.11 Uncertainty calculation of time-parameter measurements (impulse currents only)
5.12 Interference test
5.13 Withstand tests
6 Steady-state direct current
6.1 Application
6.2 Terms and definitions
6.3 Test current
6.4 Measurement of the test current
6.5 Measurement of ripple amplitude
6.6 Test procedures
7 Steady-state alternating current
7.1 Application
7.2 Terms and definitions
7.3 Test current
7.4 Measurement of the test current
7.5 Test procedures
8 Short-time direct current
8.1 Application
8.2 Terms and definitions
8.3 Test currents
8.4 Measurement of the test current
8.5 Test procedures
9 Short-time alternating current
9.1 Application
9.2 Terms and definitions
9.3 Test current
9.4 Measurement of the test current
9.5 Test procedures
10 Impulse current
10.1 Application
10.2 Terms and definitions
10.3 Test current
10.4 Measurement of the test current
10.5 Test procedures
11 Current measurement in high-voltage dielectric testing
11.1 Application
11.2 Measurement of the test current
11.3 Test procedures
12 Reference measuring systems
12.1 General
12.2 Interval between subsequent calibrations of reference measuring systems
Annex A (Informative) Uncertainty of measurement
Annex B (Informative) Examples of the uncertainty calculation in high-current measurements
Annex C (Informative) Step-response measurements
Annex D (Informative) Convolution method for estimation of dynamic behaviour from step-response measurements
Annex E (Informative) Specification of parameter limits for certain wave shapes
Annex F (Informative) Temperature rise of resistor components
Annex G (Informative) Determination of r.m.s. values of short-time a.c. current
Annex H (Informative) Examples of IEC standards and national standards with high-current tests
Bibliography
