CZECH
METROLOGY
INSTITUTE
Okružní 31, 638 00 Brno
legmet@cmi.cz
 +420,545,555,414
P U B L I C   D E C R E E
As the authority with substantive and territorial jurisdiction in the matter of defining metrological and
technical requirements for specified measuring instruments and stipulating test methods for type approval
and verification of specified measuring instruments pursuant to §  14(1) of Act No 505/1990 on metrology, as
amended, and in accordance with the provisions of §  172 et seq. of Act No  500/2004, the Administrative
Code, as amended (hereinafter the ‘CAP’), the Czech Metrology Institute (CMI) commenced ex officio
proceedings pursuant to §  46 of the Administrative Code and, based on supporting documents, issues the
following:
I.
MEASURE OF A GENERAL NATURE
number: 0111-OOP-C089-22 
laying down the metrological and technical requirements for specified measuring instruments,
including testing methods for verification of the following specified measuring instruments:
'voltage instrument transformers'
1  Basic definitions 
For the purposes of this Measure of a General Nature, terms and definitions according to VIM and VIML1
and the terms and definitions below apply.
1.1
voltage instrument transformer (hereinafter 'instrument transformer' or 'VIT')
a voltage transformer that helps transmit an information signal to measuring instruments, electricity meters,
etc.  
1.2
primary winding
1 TNI 01 0115 International Vocabulary of Metrology – Basic and General Concepts and Associated Terms (VIM)
and  International  Vocabulary  of  Terms  in  Legal  Metrology  (VIML)  are  part  of  the  technical  harmonisation
compendium ‘Terminology in the Area of Metrology’, which is publicly accessible at www.unmz.cz.Measure of a General Nature No 0111-OOP-C089-22
the winding to which the voltage to be transformed is applied
1.3
secondary winding
the winding to which voltage circuits of measuring instruments, electricity meters, breakers or similar
devices are connected
1.4
nominal primary voltage  
the value of the primary voltage indicated on the instrument transformer plate and on which its operation is
based. The standard values of nominal voltage of a single-phase transformer connected between the phase
conductor of the three-phase system and the ground, or between zero point and ground, are given by the
product of the nominal system voltage multiplied by a factor of 1/ 3 
1.5
nominal secondary voltage
the value of the secondary voltage indicated on the instrument transformer plate and on which its operation
is based. For single-phase instrument transformers connected between phase and ground in three-phase
systems where the nominal value of the primary voltage is divided by 3, the secondary voltage value is
divided by 3, so the resulting transformation ratio remains the same.  
1.6
voltage increase factor  
a factor whose product with the rated primary voltage gives the highest voltage at which the instrument
transformer must meet the warming requirements for the prescribed time and accuracy requirements
1.7
voltage error (ratio error) 
error caused by the instrument transformer due to the fact that the actual voltage ratio is not equal to the
nominal ratio. This voltage error, expressed as a percentage, is given by the formula:  
                                                        εU=(KnUs−Up)100
Up (1)
whereKn........... is the nominal ratio,
Up  ......... is the actual primary voltage,
Us .......... is the actual secondary voltage, corresponding to Up under measurement conditions.
1.8
phase angle error  
the phase difference between primary and secondary voltage phasors; the orientation of the primary and
secondary voltage phasors is chosen in such a way that in an ideal instrument transformer the phase angle
error is zero.  The phase angle error is considered positive if the secondary current phasor precedes the
primary current phasor.  It is usually expressed in arc minutes or centiradians. 
NOTE: This definition is correct only for the alternating sinusoidal voltage. 
1.9
two-pole insulated instrument transformer 
an instrument transformer for which all parts of the primary winding, including terminals, are insulated from
ground to an insulation level corresponding to the nominal insulation level
2Measure of a General Nature No 0111-OOP-C089-22
1.10
single-pole insulated instrument transformer  
a single-phase instrument transformer that has one end of its primary winding directly grounded or a three-
phase transformer designed to connect the primary winding to a star with a directly grounded zero point
1.11
real ratio 
the ratio of the actual primary voltage to the actual secondary voltage of the instrument transformer 
1.12
nominal ratio 
the ratio of nominal primary voltage to nominal secondary voltage
1.13
impedance 
the impedance of the secondary circuit, expressed in ohms, at a given power factor (inductive or capacitive).
The impedance is usually expressed as the apparent power in VA consumed at the stipulated power factor
and at nominal secondary current. 
1.14
nominal impedance 
value of the load from which the prescribed accuracy requirements are derived
1.15
nominal load 
the load value in volt-amperes at a given power factor that the instrument transformer transmits to the
secondary circuit at nominal secondary voltage and connected nominal impedance
1.16
rated load 
the value of the apparent power at the nominal voltage that can be taken from the secondary winding without
exceeding permitted warming. The rated load must be specified in units of ‘VA’.  
Its default values are: (25;  50;  100)   VA and their decimal multiples, these extreme load values being
determined at the rated secondary voltage and at a power factor of 1. 
NOTES: 
1. At the rated load, the limits of voltage errors and phase angle errors for all secondary windings may be exceeded. 
2. If there is more than one secondary winding, the rated load for each winding must be indicated separately.  
1.17
accuracy class 
a designation assigned to an instrument transformer whose voltage error and phase angle error do not exceed
permissible values under prescribed operating conditions 
1.18
maximum voltage for an instrument transformer
the  maximum  effective  value  of  the  combined  AC  voltage  between  phases  for  which  the  instrument
transformer is designed with regard to its insulation
3Measure of a General Nature No 0111-OOP-C089-22
1.19
nominal insulation level 
the combination of voltage values that characterises the insulation of the instrument transformer in terms of
its ability to withstand electrical stress
1.20
exposed environment 
an environment in which the instrument transformer is exposed to atmospheric overvoltage
NOTE: Such a  voltage instrument transformer  is usually connected to an external line either directly or by a short
cable.  
1.21
unexposed environment 
an environment in which the instrument transformer is not exposed to atmospheric overvoltage 
NOTE: Such a  voltage instrument transformer  is usually connected with a cable grid.   
1.22
nominal frequency  
the value of the frequency from which the requirements of this legislation are derived
1.23
auxiliary winding  
the winding of a single-phase instrument transformer that is intended, in an assembly of three single-phase
instrument transformers for connection to an open triangle, for: 
a)creation of the sum voltage in fault states; 
b)suppression of oscillations during resonance phenomena. 
2  Metrological requirements 
2.1 Normal operating conditions  
2.1.1 Ambient air temperature 
Measuring transformers are classified in three categories as shown in Table 1. 
Table 1 — Temperature category
CategoryLowest temperature
(°C)Highest temperature
(°C)
-5/+40 -5 +40
-25/+40 -25 +40
-40/+40 -40 +40
NOTE: Storage and transport conditions must also be considered when selecting the temperature category . 
2.1.2  Other operating conditions for an indoor instrument transformer 
The other operating conditions to be taken into account are: 
a) the effect of sunlight; may be neglected;  
4Measure of a General Nature No 0111-OOP-C089-22
b) the influence of ambient air, if it is heavily polluted by dust, smoke, corrosive gases, steam or salt; 
c) normal humidity conditions are as follows: 
 the mean relative humidity value measured over a period of 24 hours does not exceed 95  %; 
 the average water vapour pressure over 24 hours does not exceed 2.2 kPa; 
 the average relative humidity over the course of one month does not exceed 90%; 
 the average water vapour pressure over a month does not exceed 1.8 kPa. 
2.1.3  Other operating conditions for outdoor instrument transformers 
Other operating conditions that are considered are as follows:
a) if the average ambient air temperature measured over a period of 24 hours does not exceed 35 ° C, it
can be neglected;
b) solar radiation exceeding 1000 W/m 2 (high noon on a clear day) must be taken into account;
b) the ambient air, if it is heavily contaminated by dust, smoke, corrosive gases, vapours or salts, must be
taken into account; 
d) wind pressure not exceeding 700 Pa (this value corresponds to a wind speed of 34 m/s) is not taken
into account; 
e) the presence of condensation or precipitation must be taken into account.
2.2  Nominal parameter values for instrument transformers 
2.2.1  General requirements for nominal data 
The nominal data of the voltage instrument transformers, including their accessories, must be selected
according to: 
 a) the maximum voltage for the instrument transformer ( Um); 
 b) the prescribed insulation levels; 
 c) the nominal frequency ( fR); 
 d) the nominal load;  
 e) the nominal accuracy class;
 f) the nominal voltage. 
The nominal data shall be applied under normal reference atmospheric conditions (temperature (20  °C),
pressure (101.3 kPa) and humidity (11  g/m 3)).
2.2.2  Maximum voltage for an instrument transformer 
The maximum voltage values for the instrument transformer must be selected from Table 2.
The maximum voltage for the instrument transformer is selected as the nearest value of Um that is equal to or
greater than the maximum voltage of the system where it is installed. 
For an instrument transformer installed under normal insulation conditions, Um must be at least equal to Usys. 
For a measuring transformer installed outside the normal isolation environment range, U  m may be selected
greater than the nearest Um value equal to or greater than Usys according to special needs. 
NOTE: By way of example, the selection of a Um value greater than the nearest normalized value Um equal to or greater
than  Usys when the voltage measuring transformer is to be installed at an altitude higher than 1000  m in order to
compensate for the drop in the withstand voltage.  
2.2.3  Prescribed insulation levels 
The choice of insulation level of the primary winding terminals of inductive instrument transformers must be
derived from the highest voltage Um for the instrument transformer according to Table 2.
5Measure of a General Nature No 0111-OOP-C089-22
Table 2 - Prescribed primary terminal insulation levels for instrument transformers 
Maximum
instrument
transformer
voltage Um 
(effective value)
(kV)Nominal test
voltage at 50 Hz
(effective value)
(kV)Rated
atmospheric
pulse test voltage
(peak value)
(kV)Rated withstand
voltage at
switching pulse
(peak value)
(kV)
0.72 3---
1.2 6---
3.61020
40
7.22040
60
122860
75
17.5 3875
95
245095
125
3670145
170
5295250
72.5140 325
100185 450
123185 450
230 550
145230 550
275 650
170275 650
325 750
245395 950
4601,050
300395 950750
4601,050 850
3624601,050 850
5101,175 950
4205701,300 950
6301,4251,050
5506301,4251,050
6801,5501,175
8008801,9501,425
9752,1001,550
2.2.4  Additional requirements for primary winding insulation 
2.2.4.1  Requirements for grounded primary winding terminal insulation 
The primary winding terminal to be grounded and insulated from the casing and frame must pass a test using
a short-term test voltage at a frequency of 50  Hz with an effective value of 3  kV for 1 minute applied
between this terminal and the frame.
6Measure of a General Nature No 0111-OOP-C089-22
2.2.4.2 Partial discharges
Partial discharge requirements are applicable to instrument transformers with  Um greater than or equal to
7.2 kV. Partial discharge levels must not exceed the limits set out in Table 3.   
Table 3 - Test voltages for measuring partial discharges and permissible levels
Grid ground typePrimary winding
connectionTest voltage for
partial discharge
measurement
(effective value) 
(kV)Permissible partial discharge levels (pC)
Type of insulation:
liquid or gas solid
Grounded centre
network (ground
connection factor
 1.4)Phase-groundUm 10 50
1.2Um/35 20
Phase-phase 1.2Um 5 20
It network or
network with
inefficiently
grounded centre
(ground link factor
> 1.4)Phase-ground1.2Um10 50
1.2Um/35 20
Phase-phase 1.2Um 5 20
NOTES:
1. If the network midpoint is not defined, values apply to an IT network or network with an inefficiently 
grounded midpoint. 
2. The maximum permitted levels of partial discharges are also valid for frequencies other than the nominal 
frequency. 
2.2.5  Insulation requirements between winding sections  
For interconnected terminals from each section, the test voltage of the industrial frequency between sections
3 kV must be specified.
2.2.6  Requirements for the isolation of secondary windings 
The specified test voltage at 50  Hz for secondary insulation is 3  kV.
2.2.7  Values of nominal frequencies 
The nominal frequencies are 16  2/3 Hz, 50 Hz.
2.2.8  Nominal load values 
The nominal values of apparent load power at power factor 1 expressed in VA are:
(1; 2.5;  5;  10)  VA (Load Range I). 
The nominal apparent power values at an inductive power factor 0.8 expressed in VA are:
(10; 25;  50;  100)  VA (Load range II). 
NOTE: For a given instrument transformer that has one of the nominal load values associated with the accuracy class,
the provision of nominal non-standard loads associated with another accuracy class is not ruled out.  
7Measure of a General Nature No 0111-OOP-C089-22
2.2.9  Accuracy classes and permissible errors of instrument transformers  
2.2.9.1  Determination of the accuracy class 
For instrument transformers, the accuracy class is determined by the maximum permissible voltage error
expressed as a percentage at the rated voltage prescribed for the relevant accuracy class.
2.2.9.2  Accuracy classes 
The accuracy classes for single-phase inductive instrument transformers are:
0.1; 0.2;  0.5;  1.0. 
2.2.9.3  Permissible current errors and angle errors for instrument transformers  
The voltage error and the error of the angle at rated frequency shall not exceed the values given in Table 4   at
any voltage between 80  % and 120 % of the nominal voltage and with a load in the range of: 
a) any values between 0 VA and 100  % of the nominal load value for instrument transformers with a load
of (1; 2.5;  5;  10)  VA at Power factor 1 (Load range I); 
b)between 25 % and 100 % of the nominal load for instrument transformers with a load of (10;  25;  50;
100)  VA at power factor 0.8 (Load range II). 
Errors in instrument transformers shall be determined at the terminals of the instrument transformer and shall
include the effect of fuses, resistors and integral parts of the instrument transformer.
For instrument transformers with taps on secondary windings, the error requirements apply to the highest
transformation ratio, unless otherwise specified. 
Table 4 – Permissible voltage errors and phase angle errors of instrument transformers  
Class
of accuracyVoltage error
U (%)Phase angle error U
Minutes Centiradians
0.1 0.1 5 0.15
0.2 0.2 10 0.3
0.5 0.5 20 0.6
1.0 1.0 40 1.2
2.2.10 Nominal voltage values of instrument transformers  
2.2.10.1 Nominal primary voltage values  
The  nominal  values  of  the  primary  voltages  of  three-phase  instrument  transformers  and  single-phase
instrument transformers for use in single-phase systems or for phase-to-phase measurements in three-phase
systems must correspond to the nominal voltages set out in Tables 5 to 8. The nominal value of the primary
voltages of the single-phase voltage transformer connected between one phase of the three-phase system and
ground or between the system zero point and the country must be 1/ 3 of one of the values of rated voltages.
NOTE: The property of voltage instrument transformers is based on the nominal primary voltage, whereas the nominal
insulation level is based on the highest voltage for the instrument transformer. 
Table 5 — Three-phase systems with a rated AC voltage exceeding 1  kV and not exceeding 35  kV and
related equipment a
8Measure of a General Nature No 0111-OOP-C089-22
Highest voltage for
equipment(kV)Nominal system voltage (kV)
3.6 3.3 3
7.2 6.6 6
12 11 10
(17.5) – (15)
24 22 20
36 33 30
40.5 – 35
NOTE:  Above are two series (columns) of nominal network voltage.  
a These networks are generally three-wire unless specified otherwise. 
These values are phase-to-phase voltages. 
Values in brackets are not considered preferential.  
Table 6 — AC three-phase systems with a nominal voltage above 1  kV and not exceeding 35  kV and
related equipmenta used in the Czech Republic
Highest voltage for
equipment(kV)Nominal system voltage (kV)
3.6 3
7.2 6
12 10
25 22
38.5 35
a These networks are generally three-wire unless specified otherwise. 
These values are phase-to-phase voltages. 
9Measure of a General Nature No 0111-OOP-C089-22
Table 7 — Three-phase systems with a rated AC voltage exceeding 35  kV and not exceeding 230  kV
and related equipmenta
Highest voltage for equipment (kV) Nominal system voltage (kV)
(52) (45) –
72.5 66 69
100 90 –
123 110 115
145 132 138
(170) (150) (154)
245 220 230
aValues in brackets are not considered preferential. These values are phase-to-phase voltages. 
NOTE 1: Above are two series (columns) of nominal network voltage.  
NOTE 2: Of the following groups, only one value may be used for the highest voltage for the device: 
Group 1: 123 kV or 145 kV; 
Group 2: 245 kV (see Table 7) or 300  kV or 362 kV (see Table 8) 
Table 8 — Highest voltage for three-phase AC system equipment with a rated voltage above 245  kVa
Highest voltage for equipment (kV)
(300)
362
420
550b
800c
1,100
1,200
aValues in brackets are not considered preferential. Values are phase-to-phase voltages. b525 kV is also used.c765 kV is also used.
NOTE: Only one value from the following groups can be used as the highest voltage for 
equipment:  
Group 1 245 kV (see Table 7) or 300  kV or 362 kV (see Table 8);
Group 2 362 kV or 420 kV;
Group 3 420 kV or 550 kV;
Group 4 1100 kV or 1200 kV.
10Measure of a General Nature No 0111-OOP-C089-22
2.2.10.2  Values of rated secondary voltages  
The nominal value of the secondary voltage must be selected according to practice at the place of application
of the instrument transformer. The values of these voltages shall be considered as values for single-phase
instrument  transformers  that  are  connected  in  single-phase  systems  or  between  phases  in  three-phase
systems, and for three-phase instrument transformers.  The nominal values of the secondary voltage are  100
V and 110 V. 
For single-phase instrument transformers that are designed for phase-to-ground connection in a three-phase
system where the rated primary voltage is the selected value divided by 3, the rated secondary voltage must
be one of the above values divided by 3. This will ensure the nominal ratio of the instrument transformer.  
2.2.10.3  Nominal values of the voltage increase factor  
The voltage increase factor is determined by the highest operating voltage, which depends on the system and
the grounding conditions of the primary winding of the instrument transformer. 
The values of the voltage increase factor relevant to the different grounding conditions are given in Table 9
together with the permissible duration of the maximum operating voltage (i.e. nominal duration). 
Table 9 — Nominal values of voltage increase factors
Voltage
increase factorPermissible
durationPrimary winding connection method and grounding
conditions
1.2PermanentBetween phases in all systems.
Between the zero point of the instrument transformer and the 
ground in all systems.
1.2PermanentBetween phase and ground in a system with an effectively 
grounded centre.1.530 s
1.2PermanentBetween phase and ground in a compensated network with 
automatic disconnection of the ground connection.1.930 s
1.2PermanentBetween phase and country in an IT network without automatic
disconnect of the ground connection or in a compensated 
network without automatic disconnect. 1.98 h
3  Technical requirements 
3.1  General requirements for warming of instrument transformers  
The warming of windings, magnetic circuits or any other components of instrument transformers must not
exceed the relevant values given in Table 10 if operated under specified conditions. These values shall be
based on the operating conditions referred to in Article 2.1.1. 
The warming of the winding is limited by the lowest class of insulation, either of the winding itself or the
medium surrounding it.
If the instrument transformers are in enclosures, attention must be paid to the temperature surrounding the
coolant inside the housing.
If the specified ambient temperatures are higher than those referred to in Article 2.1.1, the permissible
temperature increase according to Table 10 must be reduced by a value equal to the higher ambient
temperature.
11Measure of a General Nature No 0111-OOP-C089-22
Table 10 — Temperature limits for different parts, materials and dielectrics of the instrument
transformer 
Instrument transformer parts Greatest permissible
warming (K)
Oil voltage instrument transformer:
— oil in upper layer 50
— oil in upper layer, hermetically sealed 55
— centre of winding 60
— centre of winding, hermetically sealed 65
— other metal parts in contact with oil as for windings
Instrument transformer with solid or gas insulation  — 
windings in contact with insulation materials according to the 
following temperature classes: 
Y 45
A 60
E 75
B 85
F 110
H 135
− other metal parts in contact with the above material classes
classesas for windings
Connections, screwed or equivalent
− Bare copper, bare copper alloy or bare aluminium alloy as for windings
in air 50
in SF6 75
in oil 60
− Silver plated or nickel plated 
in air 75
in SF6 75
in oil 60
− Tin plated 
in air 65
in SF6 65
in oil 60
3.2  Requirements for external insulation  
For inductive instrument transformers for outdoor use with a ceramic insulator sensitive to contamination,
the required isolation distances measured over the surface of the insulator are shown in Table 11. 
12Measure of a General Nature No 0111-OOP-C089-22
Table 11 — Insulation surface distances
Degree of
contaminationMinimum nominal surface distance mm/kV 1)Ratio = surface distance
divided by clearance
Ilow 16
 3.5IImedium 20
IIIhigh 25
 4.0
IVvery high 31
1)The ratio of the surface distance between phase and ground to the effective value of the phase-to-phase 
voltage of the highest voltage for the equipment. 
NOTES:
1. It is found that the quality of the surface insulation is greatly influenced by the shape of the insulator. 
2. For very lightly contaminated surfaces, a nominal surface distance of less than 16  mm/kV may be used 
based on operating experience.  The generally accepted lower limit is 12  mm/kV. 
3. In cases of exceptional contamination, the nominal surface distance of 31  mm/kV may not be sufficient.  
Depending on operating experience and/or the results of laboratory tests, a higher nominal surface 
distance value must be used. 
3.3  Short-circuit resistance 
An instrument transformer must be designed and manufactured to withstand an external short circuit
lasting 1 second without damage due to thermal and mechanical influences. 
3.4  Software 
If an instrument transformer includes software that is essential for its metrological characteristics, it must be
identifiable by the manufacturer as a separate numerical version that is in conformity with the approved
measuring instrument type. It must be possible to identify software during the operation of the measuring
instrument in a simple manner.  The installed software must be secured against accidental or unauthorised
external interference.  If the software needs to be reinstalled (as measuring instrument maintenance), new
verification of the measuring instrument’s metrological properties must be conducted. 
4  Instrument markings 
4.1  In general  
This  marking  applies  to  single-phase  instrument  transformers  as  well  as  to  single-phase  instrument
transformers assembled into one unit and connected as a three-phase instrument transformer or to a three-
phase instrument transformer having a common core for three phases. 
4.2  Terminal markings  
Priority marking of terminals of inductive instrument transformers shall be in accordance with Figures 1 to
10. The capital letters ‘A’, ‘B’, ‘C’ and ‘N’ refer to the terminals of the primary winding, the lower-case
letters ‘a’, ‘b’, and ‘n’ indicate the corresponding terminals of the secondary winding.  The letters ‘A’, ‘B’
and ‘C’ refer to fully insulated terminals, and the letter ‘N’ indicates the end of the winding to be grounded
13Measure of a General Nature No 0111-OOP-C089-22
and the insulation of which is less than that of the other terminals.  The letters 'da' and 'dn' mark the
terminals of the auxiliary secondary winding.  
4.3  Polarity indications  
Terminals marked with the same lower-case and capital letters must have the same polarity at the same time. 
NOTE:  The  plate  may  contain  information  relating  to  several  load  combinations  and  accuracy  classes  that  the
instrument transformer complies with.  
 
 
Figure 1 — Single-phase double pole 
insulated transformer with one secondary 
windingFigure 2 - Single-phase single-pole 
insulated transformer with reduced 
insulation and one secondary 
winding
Figure 3 — Three-phase transformer with one secondary winding
14
Measure of a General Nature No 0111-OOP-C089-22
Figure 4 - Single-phase transformer with two
secondary windingsFigure 5 - Three-phase transformer with two secondary
windings
Figure 6 — Single-phase transformer with one
secondary winding with a tapFigure 7 — Three-phase transformer with one
secondary winding and tap
15
ororor
ororMeasure of a General Nature No 0111-OOP-C089-22
Figure 8 — Single phase transformer with two secondary windings and taps
Figure 9 — Single phase transformer with one auxiliary winding
16
orororMeasure of a General Nature No 0111-OOP-C089-22
Figure 10 — Three-phase transformer with one auxiliary winding
4.4 Information on the nameplate
All voltage instrument transformers must have a nameplate containing at least the following information: 
a)the manufacturer’s name or brand name; 
b)year of manufacture, serial number and type designation; 
c)nominal frequency;
d)maximum operating voltage for equipment;
e)the prescribed level of insulation;
f)temperature category;
g)weight in kg (if ≥ 25);
h)class of mechanical requirements (for Um ≥ 72 kV);
i)nominal primary and secondary voltages (e.g. 66/0.11 kV);
j)nominal load plus corresponding accuracy class (e.g. 50 VA, class 1.0); 
NOTE: If the instrument transformer has two separate windings, the load of each secondary winding in VA must be
indicated for the corresponding accuracy classes and nominal voltage of each winding.  
k)the voltage increase factor and the corresponding duration of the overvoltage;
l)where applicable, the software version may also be shown on a display;
NOTE: Points (d) and (e) can be combined into a single fraction (for example,  72.5/140/325 kV).  
All information must be indelibly marked directly on the voltage instrument transformer or on a plate firmly
attached to the instrument transformer. If several thermal insulation categories are used, the temperature
category  that  limits  the  warming  of  the  winding  must  be  provided.   For  gas-insulated  instrument
transformers, the highest operating voltage of the instrument transformer must be indicated on the type plate
17
Measure of a General Nature No 0111-OOP-C089-22
as the nominal voltage for the instrument transformer.  For instrument transformers in load range I. this
information must be provided immediately before the nominal load information (e.g. 0 VA — 10 VA class
0.2).  The type plate may contain a combination of several loads and precision classes that the instrument
transformer meets. 
5  Measuring instrument type approval 
The type-approval process for a voltage instrument transformer includes the following tests and activities:
5.1  Warming test 
For this test, the instrument transformer shall be stipulated to have reached a steady-state temperature if the
temperature increase per hour does not exceed 1 K. The ambient temperature must be between +  10 °C and
+ 30 °C. If the instrument transformer has more than one secondary winding, the test must be carried out on
each secondary winding. Auxiliary or protection windings must be loaded between 0 VA and 100  % of the
nominal load value of this winding.  During this test, the instrument transformer must be configured as it
will be configured in operation.  The warming must be measured using the electrical resistance increment
method.  The warming of parts other than windings can be measured using thermometers or thermocouples. 
The voltage to be applied to the instrument transformer during this test must comply with the following
points:
a)All instrument transformers irrespective of the voltage increase factor and duration (see Table 9) shall
be tested with 1.2 times the nominal primary voltage. If the value of the full load of the secondary
winding is determined, the instrument transformer must be tested at the nominal primary voltage, at a
load corresponding to the value of the full load of this secondary winding and at a power factor of 1.
Any other secondary winding must be unloaded.  If a full load value is specified for more than one
secondary winding, the instrument transformer must be tested sequentially for each winding, each of
which shall be loaded with the corresponding full load value at a power factor of 1.  The test must
continue until the temperature of the instrument transformer reaches a steady state. 
b)Instrument transformers with a voltage increase coefficient of 1.5 for a duration of 30 s or 1.9 for 30
seconds shall be tested at their respective voltage factor with a duration of 30 seconds as soon as
temperature of the instrument transformer reaches a steady state at 1.2 times the nominal voltage. The
temperature increase must not exceed the value given in Table 10 by more than 10 K.  
NOTE: A relatively short duration of 30 seconds for overvoltage does not represent a measurable increase in
temperature after measurement at nominal voltage.  As a result, the negative effect caused by overvoltage on the
instrument transformer can be best assessed indirectly from observed deficiencies during dielectric type tests. 
c)Instrument transformers having a voltage increase factor of 1.9 for a duration of 8 hours shall be tested
at  1.9  times  the  nominal  voltage  for  8  hours  immediately  after  the  instrument  transformer's
temperature reaches a steady state at 1.2 times the nominal voltage. The temperature increase must not
exceed the values given in Table 10 by more than 10 K. 
If one of the secondary windings is auxiliary or protective, the test shall be carried out in accordance with the
above test procedure, starting with the test referred to in (a), at 1.2 times the nominal primary voltage and
then immediately followed by the test according to 5.1(c).
In the pre-test preparatory process with 1.2 times the nominal primary voltage, the auxiliary or protective
winding is unloaded. During the test with 1.9 times the rated primary voltage for 8 hours, the auxiliary or
locking windings must be loaded with a load corresponding to the standard value of the full load (see 1.18),
while the other windings are loaded with nominal load value. 
NOTE: Voltage measurement must be carried out on the primary winding, as the value of the secondary voltage may be
significantly less than the nominal value of the secondary voltage multiplied by the voltage increase factor. 
18Measure of a General Nature No 0111-OOP-C089-22
5.2  Short-circuit resistance test  
During this test, the initial temperature of the instrument transformer must be between +  10 °C and + 30 °C.
The instrument transformer must be powered from the primary side, the secondary windings shall be short-
circuited. The short-circuit duration is 1 second.  
NOTE: This requirement shall also apply where fuses are an integral part of the instrument transformer.  
During the short circuit, the effective value of the supplied voltage at the primary terminals must not be
lower than the nominal voltage. 
NOTE: For inductive instrument transformers, the test may be performed by supplying power from the secondary side,
with the terminals of the primary winding short-circuited.  
The  instrument  transformer  has  passed  this  test  if,  after  cooling  to  ambient  temperature,  it  meets  the
following requirements: 
a)is not visibly damaged; 
b)its errors do not differ from those recorded before the tests by more than half of the limit errors in its
accuracy class; 
c)complies with the dielectric tests referred to in Article 5.7 with test voltages reduced to 90  % of the
prescribed values; 
d)inspection of insulation at the surface of both primary and secondary windings shows no significant
damage (e.g. carbonisation). 
A check pursuant to (d) is not required if the current density in the winding does not exceed 160 A/mm 2  for
a copper winding whose conductivity is not less than 97  % of the prescribed value. The current density shall
be determined by measuring the symmetrical effective value of the short-circuit current at the secondary
winding (divided by the nominal transmission in the case of primary windings).  
5.3  Primary winding impulse voltage test 
The test voltage must be supplied between each primary voltage mains terminal and the ground. Grounded
primary winding terminals or untested terminals in the case of a two-pole insulated instrument transformer,
at least one terminal of each secondary winding, frame, casing (if any) and core (if it should be grounded)
must be grounded during the test.  The impulse test generally consists of the introduction of reference and
test impulses.  The reference impulse voltage must have an amplitude between 50  % and 75 % of the
nominal test voltage.  The peak value and the shape of the impulse voltage must be recorded during the test.
Proof of failure is a change in the shape of the pulse voltage waveform when comparing the reference and
test impulse waveforms.  For fault detection, a recording of current(s) in the ground circuit or voltage
transferred to the secondary winding may be used, but only as additional detection to record the voltage
waveform.  
NOTE: Grounding can be done through a suitable shunt or current recording device.  
5.3.1  Atmospheric impulses test  
The test voltage must have an appropriate value pursuant to Table 2  according to the highest voltage for the 
device and the specified insulation level.
5.3.1.1  Winding with Um < 300 kV 
The test must be performed using both positive and negative polarity. At least 15 consecutive pulses of the
same polarity must be applied, without correction for atmospheric conditions.  The instrument transformer
shall be considered to have passed impulse tests for each polarity if the following conditions are met:  
each series ('plus' and 'minus') has at least 15 impulses;
 non-renewable insulation is not breached, which is confirmed by five consecutive withstand impulses,
19Measure of a General Nature No 0111-OOP-C089-22
following each arc;
the instrument transformer has passed even if there have been no more than 2 arcs in each series (this
procedure leads to a maximum of 25 pulses in series), no evidence of insulation breach (e.g., a
deviation of the waveform of the recorded quantity during production unit tests serving as verification
tests) may be found.
If arcs have occurred and evidence cannot be provided during the test that they occurred in self-restoring
insulation, the instrument transformer must be removed and inspected after the dielectric tests have been
completed. If damage to non-renewable insulation is observed, the instrument transformer failed the test. 
5.3.1.2  Winding with Um  300 kV  
The test must be performed using both positive and negative polarity. Apply 3 consecutive impulses of each
polarity, uncorrected for atmospheric conditions.  The instrument transformer has passed the test if:  
 no arcs occurred; 
there  was  no  other  evidence  of  insulation  failure  (for  example,  there  were  no  changes  in  the
waveform shape of the recorded pulsed quantities). 
5.3.2  Switching impulse test 
The test voltage must have the appropriate value in Table 2   according to the highest voltage for equipment
and according to the specified insulation level. The test must be performed using positive polarity.  Fifteen
consecutive impulses, corrected for atmospheric conditions, are applied to the instrument transformer.  For
outdoor instrument transformers, this test must be carried out in rain (see Article 5.4).  
NOTE: In order to avoid over-saturation of the core, it is permissible to adjust the magnetic state of the core in an
appropriate manner between the individual impulses.  
The instrument transformer has passed the test if: 
non-self-restoring internal insulation was not breached; 
no arc occurred along non-self-restoring external insulation; 
 the instrument transformer has passed this test even if no more than 2 arcs occurred; this is confirmed
by 5 consecutive impulses after each arc applied after the last impulse in the series; 
no other evidence of insulation breach was found (for example no changes in shape occurred during
the course of recorded values). 
If arcs have occurred and proof cannot be provided during the test that they occurred in self-restoring
insulation, the instrument transformer must be disassembled and inspected after the dielectric tests have been
completed.  If damage  to  non-self-restoring  insulation  is  observed,  the  instrument  transformer  must  be
considered to have failed the test. 
NOTE: Impulses during which there are arcs to the walls or ceilings of the laboratory shall not be considered.  
5.4  Rain tests of outdoor transformers 
For instrument transformers with Um < 300 kV the test must be carried out with AC voltage at 50  Hz and the
test voltage value according to Table 2, depending on the highest voltage for the instrument transformer
corrected for atmospheric conditions.
For instrument transformers with Um ≥ 300 kV, the test must be performed by positive polarity switching
pulses with the test voltage value as specified in Table 2, depending on the highest voltage for the instrument
transformer and the nominal insulation level.
20Measure of a General Nature No 0111-OOP-C089-22
5.5  Electromagnetic Compatibility Test (EMC) — measurement of radio 
influence voltage (RIV) 
Radio influence voltage requirements apply to instrument transformers with Um ≥ 123 kV, designed to be
installed in air insulated substations.
Because radio influence voltage may be affected by fibres or dust on insulators, it is permitted to wipe the
insulator with a clean cloth prior to the start of measurement. 
The following procedure must be followed:
An  instrument  transformer  with  accessories  must  be  dry  and  clean  and  at  approximately  the  same
temperature as the laboratory where the test is being performed.
The test shall be carried out under the following atmospheric conditions:
Ambient temperature: (10 to 30) °C 
Atmospheric pressure: (0.870·105 to 1.070·105)  Pa 
Relative air humidity: (45 to 75) % 
The test leads and their ends must not be a source of radio influence voltage.
In order to avoid interfering discharges from the primary terminals, they must be appropriately shielded by
imitation service shielding. It is recommended to use a piece of pipe with spherical ends. 
Figure 11 - Electromagnetic compatibility test arrangement
21Legend
T test transformer
C&a tested item
Z filter
B terminal with corona formation protection
M measuring set with input resistance RmMeasure of a General Nature No 0111-OOP-C089-22
The test voltage is applied between one of the terminals of the primary winding of the tested item (C a) and
the ground. The frame, cover (if any), core (if it is intended to be grounded) and one terminal of each
secondary winding are grounded.  
The measuring circuit must be tuned in the 0.5 MHz to 2 MHz band with measurement frequency recording.
The results are expressed in microvolts.  
Impedance between test conductor and ground, (Z S + (R 1 + R2 //  RM)) in Figure 11, must be 300  Ω ± 40 Ω
with a phase angle not exceeding 20° at the measuring frequency.  
A capacitor CS can also be used instead of the filter Z S; sufficient capacity is 1  000 pF.  
The filter Z must have a large impedance at the measuring frequency in order to separate the source of the
industrial frequency from the measuring circuit. An appropriate value of this impedance at the measuring
frequency can be found between 10,000  Ω and 20,000 Ω.  
The background noise level of background radio interference (RF interference caused by an external field
and a high-voltage transformer) must be at least 6 dB (preferably 10 dB) below the given level of radio
interference. 
Prior to the measurement itself, a voltage of 1.5 ×  Um/√3 is applied and maintained for 30 seconds. The
voltage is then reduced to 1.1 × Um/√3 for approximately 10 seconds, and is maintained at this value for 30
seconds prior to the actual RF interference measurement. 
The instrument transformer shall be considered to comply with this test if the interfering RF voltage level
does not exceed 2 500 μV at 1.1 Um/√3.
5.6  Accuracy tests  
Type-approval tests to verify the requirements of 2.2.9.3 in the case of class 0.1 to 1 instrument transformers
shall be carried out for 80  %, 100 % and 120 % of nominal voltage at nominal frequency  
 for load range I at 0 % and 100 % nominal load at load factor cos β = 1;
 for load range II and at 25  % and 100 % at load factor cos β= 0.8.
5.7  Primary winding test at industrial AC frequency 
During the induced voltage test, the test voltage frequency may be higher than the nominal frequency to
prevent the magnetic core saturation. Test duration must be 60 seconds. 
If the test voltage frequency is more than twice the rated frequency, the test time may be reduced to less than
1 minute according to the relationship:
Trvánízkoušky(s)=dvojnásobekjmenovitéhokmitočtu
zkušebníkmitočet×60s
Trvání zkoušky (s) Duration of the test(s)
dvojnásobek jmenovitého kmitočtu double the nominal frequency
zkušební kmitočet test frequency
22Measure of a General Nature No 0111-OOP-C089-22
5.7.1  Winding with Um < 300 kV 
The test voltage for a winding with  Um <  300 kV must have the appropriate value given in Table 2
according to the highest voltage for equipment. If there is a large difference between the applicable highest
voltage for equipment ( Um) and the nominal primary voltage, the induced voltage must be limited to five
times the nominal primary voltage. 
5.7.1.1  Two-pole insulated instrument transformers  
Two-pole insulated instrument transformers must be subjected to the following tests:
a) Applied voltage test
The test voltage is applied between the ground and between all interconnected primary winding
terminals. The frame, case (if present), core (if it is to be grounded) and all secondary winding
terminals must be interconnected and grounded. 
b) Induced voltage test
At the manufacturer’s discretion, the test may be carried out either by supplying the secondary
winding with a voltage of such magnitude as to induce the prescribed test voltage in the primary
winding or by supplying the primary winding directly to the prescribed test voltage.
The test voltage must be measured in each case on the side of the primary winding. The frame, the
case (if present), the core (if it is to be grounded) and one terminal of each secondary winding and one
terminal of the primary winding must be interconnected and grounded. 
The test may be carried out at the test voltage applied to each terminal of the primary winding for half
the time, but not less than 15 seconds for each terminal.
5.7.1.2  Single-pole insulated instrument transformers 
Single-pole insulated instrument transformers must be subjected to the following tests:
a) Applied voltage test 
The test voltage must have the corresponding values according to 2.2.4.1 and must be applied between
the terminal of the primary winding to be grounded and the ground.
The frame, case (if present), core (if it is to be grounded) and all secondary winding terminals must be
interconnected and grounded.
b) Induced voltage test
The test must be carried out according to 5.7.1.1. The primary winding terminal that will be grounded
during operation must be grounded during the test. 
5.7.2  Winding with Um ≥ 300 kV 
The instrument transformer must be subjected to the following tests:
a) Applied voltage test 
The test  voltage  must have  the  corresponding value according to  2.2.4.1   and  the  test  must be
performed according to 5.7.1.2.
b) Induced voltage test
The test voltage must have the corresponding value according to Table 2, depending on the nominal
value of the atmospheric pulse test voltage. The test must be carried out according to 5.7.1.2. 
23Measure of a General Nature No 0111-OOP-C089-22
5.8  Measurement of partial discharges 
5.8.1  Test circuit and measuring equipment 
The measuring equipment must measure the apparent charge Q expressed in picocoulombs (pC). It must be
calibrated after being connected to the test circuit.  Broadband equipment must have a minimum bandwidth
of 100 kHz with an upper frequency not greater than 1.2 MHz.  Narrowband equipment must have its
resonant frequency within 0.15 MHz to 2 MHz.  The 0.5  MHz to 2 MHz range is recommended but, where
practicable, measurements shall be made at the frequency ensuring the highest sensitivity.  Sensitivity must
allow detection of partial discharges with an amplitude of 5 pC. 
NOTES:
1. Interference  must  be  significantly  lower  than  the  indicated  sensitivity.   Known  impulses  caused  by  external
interference are not considered. 
2. Bridge connection can be used to suppress external interference. 
3. If equipment allowing electronic interference suppression is used, it must be proven by means of changes to its
parameters that it allows the detection of repeated impulses. 
5.8.1.1  Test procedure for single-pole insulated instrument transformers  
After pre-test stress according to Methods A or B, the test is carried out at the voltage specified in Table 3
and partial discharge measurement is carried out for 30 seconds.
During this time the measured partial discharge level must not exceed the values given in Table 3.
Method A: The voltage level is obtained by reducing the voltage after the induced voltage test without
interruption. 
Method B: Measurements of partial discharges is carried out after the induced voltage test.  Voltage is
increased to 80 % of the test voltage during the induced voltage test, kept at this level for at least 60
seconds and reduced without interruption to the voltage for the measurement of partial discharges. 
Unless otherwise specified, which method is chosen is at the manufacturer's discretion. The test method
chosen must be specified in the test report. 
5.8.1.2  Test procedure for two-pole insulated instrument transformers  
The test circuit for two-pole insulated instrument transformers must be the same as for single insulated
instrument transformers, but the test must be carried out twice by applying the test voltage at each terminal,
the second terminal being connected to the low voltage terminal, frame and housing (if any).
5.9  AC voltage test of secondary winding and between winding parts 
A 3 kV test voltage must be applied for 60 seconds between the shorted terminals of each winding section or
each secondary winding and ground.
5.10  Software test 
5.10 Software test 
Software tests are carried out on the basis of submitted documentation and functional checks using Welmec
7.2.
5.10.1 Documentation 
It shall be assessed whether the documentation contains the following information, including that referred to
in subsequent paragraphs:
24Measure of a General Nature No 0111-OOP-C089-22
-a description of the software in terms of its function and instrument function;
-a description of the accuracy of the computational algorithms;
-a description of the user interface, menus and dialogs;
-unambiguous identification of the software;
-a description of the hardware components;
-operating and user manual for electricity meter software.
5.10.2 Identification 
Documentation check: an assessment is performed whether the identification creation algorithm is described
in the documentation and whether it is part of the dynamic part that is generated while running.
Functional check: a check is performed that the identification conforms to the manufacturer’s information
and whether it is possible to invoke the display of identification while the instrument is running. If the device
has multiple modes in which identification can be displayed, all are tested. 
5.10.3 Functionality 
Documentation check: the documentation is assessed to determine whether it includes a basic description of
the instrument’s function and, where applicable, a description of the computational algorithms and data flow.
Functional  check:  the  instrument  is  checked  to  determine  whether  it  works  in  accordance  with  the
documentation. A test is performed using the black box method and comparing inputs and outputs with
simulated or independently read inputs and outputs.  This test may be replaced by further type-approval
testing. 
5.10.4 Influence through the user and communication interface 
Documentation check: a check is performed to determine whether the documentation contains:
-a description of the implementation of the user and communication interface; 
-a description of the physical construction (where applicable, physical interface security);
-a complete list of all commands of the user and communication interface with sufficient description
and assignment to functions or data operations;
-a declaration that the list of all commands is complete.
Functional check: randomly selected user interface commands (e.g., menu items on the display) are tested.
The  manufacturer  must  supply  all  necessary  accessories  to  make  it  possible  to  test  the  selected
communication instructions in laboratory conditions.  Response to requirements outside the manufacturer’s
specifications is tested: other commands, other ranges of values, interruption of communication, replacement
of the instrument during communication. 
5.10.5 Protection against Changes 
Documentation check: it is assessed whether the documentation includes a description of protection against
accidental and intentional changes and how appropriate the design of this protection is.
Functional check: the device’s response to power outages and outages of communication means (if used) is
tested. A test is performed to determine whether any user interface dialogs modifying the data in the
instrument are implemented in such a way that the user is required to confirm choices. 
5.10.6 Protection of transmitted data (if required) 
Documentation check: the documentation is assessed to see whether it contains:
-information needed to reconstruct the transmitted data;
-a description of the protection against accidental and deliberate changes during transmission;
-a description of the communication interfaces and communication protocols;
-proof of authenticity of transmitted data;
-a description of the detection of erroneous data generated during the transmission;
25Measure of a General Nature No 0111-OOP-C089-22
-a  description  of  the  protection  in  the  event  of  delay  or  transmission  through  communication
interfaces. 
Functional check: data transfer is tested with regard to its possible outages — the response to communication
interruptions and the response to damaged data. A test is performed to see whether data blocks contain all the
data needed to identify them.  If a custom protocol is created for communication, its implementation is
tested.  If a standard protocol is used (a routine protocol using standard libraries), its correct use is checked
with respect to the data flow in the program. 
5.10.7 Protection of stored data (if required) 
Documentation check: the documentation is assessed to see whether it contains:
-a list of items to be stored; 
-a description of the protection against accidental and deliberate changes to stored data;
-proof of the authenticity of the stored data;
-a description of the display of the stored data;
-a description of the operation for writing stored data;
-description of the capacity and management for data storage.
Functional check: the system’s response to power failure is tested with a view to retaining relevant data. It is
tested whether memory is physically protected against substitution or reset by the user.  The display of stored
data is tested.  
5.10.8 Software separation  (if required) 
Documentation check: the documentation is assessed to see whether it contains:
-a list of items that are part of the part of software affecting measurement results (legally relevant
software — LRSW); 
-a description of how the indication of legally relevant information is protected from confusion with
information
-generated by the part of the software that does not affect the measurement results (legally not
relevant software — LNRSW);
-a description of the protective interface and its implementation.
Functional check a test is performed whether the display of data generated from LRSW is sufficiently
distinguishable from the data on the display generated from LNRSW.
6  Initial verification 
Before initial verification, the number of the type-approval certificate must be indicated on the instrument
transformer plate.
When verifying voltage instrument transformers, the following tests are carried out:
a) technical inspection and the check that terminals are marked correctly;
b) determination of voltage and angle errors of the instrument transformer.  
Furthermore,  the  conformity  of  the  software  version  with  the  version  specified  in  the  type  approval
certificate is checked.
6.1  Necessary aids 
The following test equipment is used for the verification of instrument transformers:
6.1.1  Measuring set-up 
26Measure of a General Nature No 0111-OOP-C089-22
The measuring set-up for testing in the verification of an instrument transformer consists of a reference
measuring device, a reference voltage transformer or a reference voltage divider and voltage transformer
load, auxiliary measuring instruments for measuring voltage, frequency, distortion and supply circuits with
regulation.
6.1.2  Instrument transformer loads  
Loads are used with cos β = 0.8 or cos β = 1, specified for the given frequency according to 2.2.7, allowing
with the corresponding error  the configuration  of the nominal value given by the combination of the load
itself and the impedance of the measuring device. The instrument transformer loads are given by the values
in 2.2.8. 
6.1.3  Power supplies 
Power supplies are used with harmonic waveform voltage control over the required range with appropriate
adjustment accuracy, stability and distortion of less than 5  %.
6.1.4  Distortion meter 
A distortion meter is used to monitor compliance with the condition of Article 6.2 for monitoring the shape
of the voltage curve.
6.2  Conditions during the tests 
Instrument transformers are tested at the nominal frequency with a maximum deviation of 1 %, at a current
harmonic whose distortion factor does not exceed 5 %, an ambient temperature of +15 ° C to +25 ° C, a
relative air humidity of not more than 75 % and an external magnetic field up to 1 mT.
6.3  Description of tests 
6.3.1  Physical damage 
Instrument transformers are checked for physical damage, that nameplate information is complete, correct
and legible, and that terminals are properly connected.
6.3.2  Correct marking of terminals 
When checking the correctness of the marking of the terminals of the instrument transformer, the tested and
reference transformer are connected in the measuring set-up in such a way that the primary voltage is
connected to the corresponding terminals.
This corresponds to the parallel connection of terminal 'U' of the reference with terminal 'A' and terminal 'V'
with  terminal  'B'  or  'N'  of  the  instrument  transformer  being  tested.  The  secondary  terminals  of  both
transformers are connected in parallel to the identically marked terminals of the measuring device.  If errors
can be measured by the measuring device when the primary current is set to 10  %  I1N, the terminals are
marked correctly.  Otherwise, the instrument transformer is excluded from further testing. 
6.4  Determination of voltage and phase angle errors of instrument transformers
When determining an instrument transformer's  voltage and angle errors, the measuring device and the
instrument transformer load must be connected by separate cables to the secondary terminals of the tested
transformer.
For an instrument transformer with several secondary windings, its  voltage and angle errors are determined
when the winding that is not being tested:
a) remains open (zero load);
27Measure of a General Nature No 0111-OOP-C089-22
b) is loaded with the nominal load ZN.
If the voltage instrument transformer has an auxiliary winding (see Article 1.23), the auxiliary winding must
not be loaded when measuring the accuracy of other secondary windings.
Current and angle errors are read on the set-up's measuring device, and if needed corrected for errors in the
reference and the measuring equipment. The arrangement for determining the errors of the instrument
transformer by means of a reference instrument transformer is in Figure  12, the use of a reference capacitive
divider is in Figure 13.      If the reference transformer errors are known, the transformer under measurement
is corrected according to the relationship 
UX = UN +  UM , UX  =  UN + UM , (2) 
where UX and UX are the errors of the transformer under measurement (%;  ' ),  UN a UN are the errors of the
reference being used (%;  ' ) and UM a UM are system data for error evaluation (%;  ' ). 
Figure 12 — Arrangement to determine errors using a reference instrument transformer
28vXTX
naA
NTN
vNuNUN
VN
 VOLTAGE LOAD REFERENCE
VITTESTED
VIT
vX
SYSTEM FOR VERIFICATION OF THE 
VIT, e.g. TETTEX 2767U1U2X U2N
uNvNuXvXVOLTAGE 
SOURCE
vXuXMeasure of a General Nature No 0111-OOP-C089-22
Figure 13 — Arrangement to determine errors using a capacitive divider
Voltage and phase angle errors of the instrument transformer are detected in the range between 80  % and
120 %  of  the  nominal  voltage  value  U 1N,  where  they  must  comply  with  the  values  in  Table  4.  For
verification, it is recommended to check errors at 80  %, 100 % and 120 % of the nominal voltage value U 1N.
For nominal loads (1;  2.5;  5;  10)  VA and power factor 1 (load range I) are verified at a load of 0 VA and
100 % of the nominal load.  For nominal loads (10;  25;  50;  100)  VA and with an inductive power factor of
0.8 (load range II) the verification is carried out at a load of (25 and 100) % of the nominal load.  Error
magnitudes must not be greater than those shown in Table 4. 
Maximum permissible   voltage and angle errors must not be exceeded for an instrument transformer with
attached accessories if they are an integral part of the transformer.
The setting of the primary voltage at each measured point must be guaranteed with a maximum permissible
error of ± 0.5 % of the measured value. During the verification of the instrument transformer load impedance
errors in must not be greater than ±  3 % of the required value.  Errors in the real and imaginary components
of a general type impedance must not exceed 3  % of the nominal values. 
6.5   Determining  voltage  and  phase  angle  errors  in  combined  instrument
transformers 
6.5.1 For  combined  current  and  voltage  instrument  transformers,  depending  on  design  the  current
transformer must comply with the conditions specified in the regulation for current transformers and voltage
transformers with those specified in Table 4,  or corresponding to requirements for the current part. 
6.5.2 For combined instrument transformers, the following interactions must be determined: 
29R'N uN
ELECTRONICVOLTAGE 
DIVIDER
            
 vN      A
Na
n ZC1
NXvN
ND
EVALUATION CIRCUITS
KEYBOARD DISPLAYIuN vX
SYSTEM FOR VERIFICATION OF THEVIT, e.g. 
TETTEX 2767TX
U2X
I2X
RN
TDU2N
uXI2N
NN
UrU1
C2U1N
RXMeasure of a General Nature No 0111-OOP-C089-22
a) the influence of the current instrument transformer on the voltage instrument transformer;
b) the influence of the voltage instrument transformer on the current instrument transformer.
6.5.3 The influence of the tested current instrument transformer on the tested voltage instrument transformer
is determined by detecting  voltage and phase angle  errors of the tested voltage instrument transformer: 
a) when the primary terminals of the current instrument transformer are disconnected;
b) at a primary current of 120  % of I1N (or at the extended range current) and at 25  % and 100 % of the
nominal secondary load ZN.
6.5.4 The influence of the tested voltage instrument transformer on the tested current instrument transformer
is determined by detecting the current and phase angle  errors of the tested current instrument transformer: 
a) when the primary terminals of the voltage instrument transformer are disconnected;
b) at a primary voltage of 120 % U1N and at 25 % and 100 % of the nominal secondary load.
6.5.5  Detected  current, voltage and angle  errors of the operating combined instrument transformer during
interaction must comply with the conditions given in 2.2.10.3 and Table 4 for separate error detection. 
7  Subsequent verification 
Follow-up verification is carried out in the same way as the initial verification in chapter  6. 
The verification of the measuring instruments are subject to the metrological requirements applicable at the
time they were put into circulation.
8  Measuring instrument check 
When checking measuring instruments pursuant to § 11a of the Metrology Act at the request of an entity that
could be affected by its incorrect measurement, Chapter 6 is followed. 
9  Notified standards 
For the purposes of specifying the metrological and technical requirements for measuring instruments and
specifying the testing methods for their type approval and verification arising from this General Measure, the
CMI shall notify Czech technical standards, other technical standards or technical documents of international
or foreign organisations, or other technical documents containing more detailed technical requirements
(hereinafter ‘notified standards’). The CMI shall publish a list of these notified standards attached to the
relevant measures, together with the general measure, in a manner accessible to the public (at www.cmi.cz). 
Compliance with notified standards or parts thereof is considered, to the extent and under the conditions
stipulated by a general measure, to be compliance with the requirements stipulated by this measure to which
these standards or parts thereof apply.
Compliance with a notified standard is one of the ways to demonstrate compliance.  These requirements may
also be met by using another technical solution guaranteeing an equivalent or higher level of protection of
legitimate interests. 
30Measure of a General Nature No 0111-OOP-C089-22
II.
G R O U N D S 
Pursuant to § 14(1)(j) of the Metrology Act, the CMI has issued this Measure of a General Nature toward the
implementation of §  6(2), § 9(1) and (9), and § 11a(3) of the Metrology Act, laying down metrological and
technical requirements for specified measuring instruments and tests for type approval and verification of
specified measuring instruments - 'voltage instrument transformers'. 
Decree No 4.1.4 specifying measuring instruments for mandatory verification and measuring instruments
subject to type approval, as amended, classifies the measuring instruments under Item  4.1.4 in the annex
entitled ‘List of specified measuring instruments’ as measuring instruments subject to type approval and
mandatory verification. 
This legislation (Measure of a General Nature) will be notified in accordance with Directive (EU)  2015/1535
of the European Parliament and of the Council of 9  September 2015 laying down a procedure for the
provision of information in the field of technical regulations and of rules on information society services.
III.
I N S T R U C T I O N S
In accordance with §  173(2) CAP, no remedy may be applied against a measure of a general nature.
In accordance with the provisions of §  172(5) CAP, no appeal or remonstrance may be filed against the
decision on objections.
Compliance of a general measure with legal regulations may be assessed in a review procedure pursuant to
§ 94 to § 96 CAP.  A party may instigate the conduct of a review procedure to be conducted to the
administrative authority that issued the measure of a general nature.  If the administrative authority does not
identify grounds for the commencement of the review procedure, it shall notify the submitter to this effect,
specifying the reasons therefor, within the timeline of 30 days.  Pursuant to Article  174(2) CAP  a resolution
on the commencement of a review procedure may be issued within three years of the legal effect of the
measure of a general nature. 
31Measure of a General Nature No 0111-OOP-C089-22
IV.
EFFECTIVE DATE
This measure of a general nature comes into effect on the fifteenth day following the date of its posting on
the official notice board (§  24d of the Metrology Act).
Director General of the CMI
     
Effective date:  2.9.2022 
32