IEC 60871 1 Edition 4 0 2014 05 INTERNATIONAL STANDARD NORME INTERNATIONALE Shunt capacitors for a c power systems having a rated voltage above 1 000 V – Part 1 General Condensateurs shunt pour réseau[.]
Normal service conditions
This standard gives requirements for capacitors intended for use in the following conditions: a) Residual voltage at energization
This shall not exceed 10 % of the rated voltage (see Clause 21, Subclause 19.2 and
If the altitude exceeds 1 000 m above sea level a correction factor shall be applied to all external insulation requirements as stipulated in Clause 18 c) Ambient air temperature categories
Capacitors are categorized by temperature classifications, indicated by a number and a letter The number denotes the minimum ambient air temperature for operation, while the letters indicate the maximum temperature variation limits, as detailed in Table 1 These classifications encompass a temperature range from –50 °C to +55 °C.
The lowest ambient air temperature at which the capacitor may be operated should be chosen from the five preferred values +5 °C, –5 °C, –25 °C, –40 °C, –50 °C
With the manufacturer's consent, the capacitor may operate at temperatures below the specified limits, as long as it is energized at a temperature that meets or exceeds these limits (refer to section 27.3.1).
Table 1 is based on service conditions in which the capacitor does not influence the ambient air temperature (for example outdoor installations)
Table 1 – Letter symbols for upper limit of temperature range
Symbol Maximum Highest mean over any period of
NOTE These temperature values can be found in the meteorological temperature tables covering the installation site
To ensure compliance with Table 1 limits, the ventilation and selection of the capacitor must be managed to prevent the cooling air temperature from exceeding these limits by more than 5 °C.
Any combination of minimum and maximum values can be chosen for the standard temperature category of a capacitor, for example –40/A or –5/C Preferred standard temperature categories are: –40/A, –25/A, –5/A and –5/C.
Unusual service conditions
This standard is not applicable to capacitors unless there is a specific agreement between the manufacturer and the purchaser, as the service conditions of these capacitors typically do not meet the requirements outlined in the standard.
General
Clauses 5 to 17 give the test requirements for capacitor units
Supporting insulators, switches, instrument transformers, external fuses, etc shall be in accordance with relevant IEC standards
NOTE The year of issue (version number) of referred standards is given in test reports.
Test conditions
Unless otherwise specified for a particular test or measurement, the temperature of the capacitor dielectric shall be in the range +5 °C to +35 °C
When a correction has to be applied, the reference temperature to be used is +20 °C, unless otherwise agreed between the manufacturer and the purchaser
The dielectric temperature of a capacitor unit can be considered equivalent to the ambient temperature if the capacitor has remained unenergized at a stable ambient temperature for a sufficient duration.
The a.c tests and measurements shall be carried out at a frequency of 50 Hz or 60 Hz independent of the rated frequency of the capacitor, if not otherwise specified
General
The tests are classified as routine tests, type tests and acceptance tests.
Routine tests
The article outlines essential testing procedures for capacitors, including capacitance measurement (Clause 7), the measurement of the tangent of the loss angle (tan δ) (Clause 8), and voltage tests between terminals (Clause 9) and between terminals and the container (Clause 10) Additionally, it covers the testing of the internal discharge device (Clause 11), the sealing test (Clause 12), and the discharge test on internal fuses as specified in IEC 60871-4:1996 (5.1.1).
Manufacturers are required to conduct routine tests on each capacitor prior to delivery Upon request, purchasers can receive a certificate that outlines the results of these tests, although the specified test sequence is not mandatory.
Type tests
The article outlines several critical tests for capacitors, including the thermal stability test (Clause 13), measurement of the tangent of the loss angle (tan δ) at elevated temperatures (Clause 14), and AC voltage tests between terminals and the container (Clause 15.1) It also details the lightning impulse voltage test (Clause 15.2), overvoltage test (Clause 16), and short-circuit discharge test (Clause 17) Additionally, it covers the disconnecting test on internal fuses (IEC 60871-4:1996, Clause 5.3) and the testing of an external fuse in conjunction with a capacitor (Annex C).
Type tests are conducted to ensure that capacitors meet the design, size, materials, and manufacturing specifications outlined in the standard These tests primarily focus on verifying the design rather than identifying quality variations in mass production.
Unless otherwise specified, every capacitor sample to which it is intended to apply the type test shall first have withstood satisfactorily the application of all the routine tests
Type tests must be conducted on capacitors that are identical in design to those being supplied, or on capacitors whose design and processing are consistent in a manner that does not affect the properties being evaluated in the type test.
It is not essential that all type tests be carried out on the same capacitor unit; they may be carried out on different units having the same characteristics
The type tests shall be carried out by the manufacturer, and, on request, the purchaser shall be supplied with a certificate detailing the results of such tests.
Acceptance tests
The routine and/or type tests, or some of them, may be repeated by the manufacturer in connection with any contract by agreement with the purchaser
The quantity of samples for testing and the acceptance criteria must be mutually agreed upon by the manufacturer and purchaser, and these details should be clearly outlined in the contract.
Endurance test (special test)
The endurance test evaluates the aging of dielectric materials by assessing their performance under high voltage stress and elevated temperatures This test ensures that the deterioration process does not lead to premature failure of the dielectric components It encompasses various capacitor designs as outlined in IEC/TS 60871-2.
Measuring procedure
The capacitance shall be measured at 0,9 to 1,1 times the rated voltage, using a method that excludes errors due to harmonics
Measurement at another voltage is permitted, provided that appropriate correction factors are agreed upon between the manufacturer and the purchaser
The final capacitance measurement shall be carried out after the voltage test (see Clauses 9 and 10)
To detect changes in capacitance, such as those caused by element punctures or internal fuse failures, a preliminary capacitance measurement must be conducted prior to other electrical routine tests This initial measurement should be carried out at a reduced voltage, not exceeding 0.15 times the nominal voltage (0.15 U N).
The measuring method must achieve the accuracy necessary to meet the tolerances specified in section 7.2 If a higher accuracy is mutually agreed upon, the manufacturer is required to specify the accuracy of the measuring method.
The repeatability of the measuring method shall be such that a punctured element or an operated internal fuse can be detected
NOTE For polyphase capacitors, the measuring voltage is adjusted to give 0,9 to 1,1 times rated voltage across each element.
Capacitance tolerances
The capacitance shall not differ from the rated capacitance by more than
The capacitance value is that measured under the conditions of 7.1
In three-phase units and banks, the ratio of maximum to minimum values of capacitance measured between any two line terminals shall not exceed 1,05
NOTE 1 For filters symmetric tolerances are normally used, see Annex B
NOTE 2 A formula for the calculation of the output of a three-phase capacitor from single-phase capacitance measurements is given in Annex D
NOTE 3 For banks above 3 Mvar total rating, closer tolerances for output and phase capacitance ratios can be agreed between manufacturer and purchaser
8 Measurement of the tangent of the loss angle (tan δ ) of the capacitor (routine test)
Measuring procedure
The capacitor losses (tan δ) shall be measured at 0,9 to 1,1 times rated voltage, using a method that excludes errors due to harmonics The accuracy of the measuring system shall be reported
NOTE 1 For polyphase capacitors, the measuring voltage is adjusted to give 0,9 to 1,1 times rated voltage across each element
The tangent of the loss angle in impregnated low-loss dielectrics decreases during the initial hours of energization, independent of temperature-related variations in tan δ Routine testing often shows significant differences in tan δ among identical units produced at the same time However, the final stabilized values typically fall within a narrow range, as evidenced by the discrepancies between routine test measurements and those obtained from thermal stability testing or other conditioning methods as per the manufacturer's guidelines.
NOTE 3 The measuring equipment is calibrated according to IEC 60996 or to another method that will give the same or an improved accuracy.
Loss requirements
The requirements regarding capacitor losses shall be agreed upon between manufacturer and purchaser
The value of capacitor losses is that measured under the conditions of 8.1.
Losses in external fuses
Losses in external fuses shall be calculated using the nominal a.c resistance (specified by the fuse manufacturer at 20 °C) times the square of rated capacitor current
9 Voltage test between terminals (routine test)
General
Every capacitor must undergo a 10-second test, either according to section 9.2 or section 9.3, with the manufacturer having the discretion to choose if no agreement is in place It is essential that neither puncture nor flashover occurs during this testing process.
If the capacitors are to be re-tested a voltage of 75 % of U t is recommended for the second test
NOTE 1 For polyphase capacitors, the test voltage is adjusted to give the appropriate voltage across each element
Units with internal element fuses can only be delivered after mutual agreement between the purchaser and manufacturer, even if one or more of the operated element fuses are within the specified capacitance tolerances.
AC test
The a.c test shall be carried out with a substantially sinusoidal voltage:
DC test
The test voltage shall be as follows:
10 AC voltage test between terminals and container (routine test)
Capacitor units having all terminals insulated from the container shall be subjected for 10 s to a test voltage applied between the terminals (joined together) and the container
In banking units with isolated neutral and grounded containers, the test voltages specified in section 18.1 must be applied Conversely, for all other bank connections, the test voltage is determined proportionally to the rated voltage, as outlined in section 18.3.
If the insulation status of a unit's terminals from the container is uncertain, test voltages as outlined in section 18.1 must be applied It is the responsibility of the purchaser to indicate whether this testing is necessary.
Units having one terminal permanently connected to the container shall not be subjected to this test
Units with separate phases shall be subjected to voltage tests between phases of the same value as for the terminals to container test
During the test, neither puncture nor flashover shall occur
11 Test of internal discharge device (routine test)
The resistance of the internal discharge device, if any, shall be checked by a resistance measurement (see Clause 21 and Annex D)
The choice of the method is left to the manufacturer
The test shall be made after the voltage test of Clause 9
The unpainted unit will undergo a leak detection test for the container and bushing(s) The manufacturer is responsible for outlining the specific test method used.
If no procedure is stated by the manufacturer, the following test procedure shall apply
Unenergized capacitor units must be heated for a minimum of 2 hours to ensure that all components achieve a temperature at least 20 °C above the maximum specified in Table 1, with no leakage permitted The use of an appropriate indicator is advised.
13 Thermal stability test (type test)
General
This test is intended to a) determine the thermal stability of the capacitor under overload conditions, b) condition the capacitor to enable a reproducible loss measurement to be made.
Measuring procedure
The capacitor unit under test must be positioned between two identical units energized at the same voltage Alternatively, two dummy capacitors with resistors can be utilized, with the resistor dissipation adjusted to ensure the case temperature of the dummy capacitors is equal to or exceeds that of the test capacitor The spacing between the units should not exceed normal specifications This assembly should be placed in a heated enclosure without forced ventilation, following the manufacturer's mounting instructions for the most unfavorable thermal position The ambient air temperature must be maintained at or above the specified levels indicated in Table 2, verified using a thermometer with a thermal time constant of approximately.
1 h This thermometer shall be shielded so that it is exposed to the minimum possible thermal radiation from the three energized samples
Table 2 – Ambient air temperature for the thermal stability test
The test capacitor must be exposed to a substantially sinusoidal a.c voltage for a minimum duration of 48 hours The voltage level during the test should be calibrated to ensure that the calculated output, based on the measured capacitance, reaches at least the specified threshold.
Over a span of six hours, the temperature at the top of the container must be recorded at least four times It is crucial that the temperature increase during this period does not exceed a specified limit.
If a significant change is detected, the test will continue until four consecutive measurements meet the specified requirement within a subsequent 6-hour period If thermal stability is not achieved within 72 hours, the test will be halted, and the capacitor will be deemed to have failed.
Capacitance measurements must be taken before and after the test, adhering to the temperature range specified in section 5.2 Both measurements should be adjusted to reflect the same dielectric temperature The difference between these two measurements should not exceed the threshold that would indicate either the breakdown of an element or the activation of an internal fuse.
When interpreting the results of the measurements, two factors shall be taken into account:
– the repeatability of the measurements;
– the fact that internal change in dielectric may cause a small change of capacitance, without puncture of any element of the capacitor or operation of an internal fuse having occurred
To ensure temperature conditions are met, it is essential to consider fluctuations in voltage, frequency, and ambient air temperature during testing Therefore, plotting these parameters alongside the temperature rise of the container over time is recommended.
Units designed for 60 Hz operation can be tested at 50 Hz, and those intended for 50 Hz can be tested at 60 Hz, as long as the specified output is maintained For units rated below 50 Hz, the testing conditions must be mutually agreed upon by the purchaser and the manufacturer.
14 Measurement of the tangent of the loss angle (tan δ ) of the capacitor at elevated temperature (type test)
Measuring procedure
The capacitor losses (tan δ) shall be measured at the end of the thermal stability test (see
Clause 13) The measuring voltage shall be that of the thermal stability test.
Requirements
The value of tan δ measured in accordance with 14.1 shall not exceed the value declared by the manufacturer, or the value agreed upon between manufacturer and purchaser
15 Voltage tests between terminals and container (type tests)
AC voltage test between terminals and container
Capacitor units having all terminals insulated from the container shall be subjected for 1 min to a test voltage applied between the terminals (joined together) and the container
In banks with isolated neutral and grounded containers, the test voltages specified in section 18.1 must be applied Conversely, for all other bank connections, the test voltage is determined proportionally to the rated voltage, as outlined in section 18.3.
If the use of a unit with terminals insulated from the container, whether connected to ground or not, is uncertain, test voltages as outlined in section 18.1 must be applied It is the responsibility of the purchaser to indicate if such testing is necessary.
Units with one terminal permanently connected to the container must undergo a test voltage assessment between terminals to evaluate the insulation's adequacy to the container This test voltage is proportional to the rated voltage and is calculated accordingly.
When the voltage during testing surpasses the dielectric test standards, adjustments to the dielectric composition of the test unit may be necessary, such as adding more elements in series to prevent dielectric failure It is important to note that the insulation to the container must remain unchanged.
Alternatively, this test may be completed using a similar unit with two isolated terminals having the same insulation to the container
Units with separated phases shall be subjected to voltage tests between phases at the same test voltage as for the voltage test between terminals and container
The tests are dry for units to be used indoors, and with artificial rain (see IEC 60060-1) for units to be used outdoors
The positions of the bushings, when subjected to a test under artificial rain, shall correspond to their position in service
During the test, neither puncture nor flashover shall occur
Outdoor installation units may undergo only a dry test, provided the manufacturer offers a separate type test report confirming that the bushings can endure the wet test voltage for one minute It is essential that the bushings' positioning in this type test reflects their actual service position.
Lightning impulse test between terminals and container
The lightning impulse test is applicable for capacitor units intended for use in banks with insulated neutral and for connection to overhead lines
Units having all terminals insulated from the container and with the containers connected to ground shall be subjected to the following test
Fifteen impulses of positive polarity followed by 15 impulses of negative polarity shall be applied between bushings joined together and the container
After the change of polarity, it is permissible to apply some impulses of lower amplitude before the application of the test impulses
The capacitor is considered to have passed the test if
– not more than two external flashovers occurred at each polarity,
– the waveshape has revealed no irregularities or significant deviation from recordings at reduced test voltage
The lightning impulse test shall be made in accordance with IEC 60060-1 but with a wave of
1,2/50 às to 5/50 às having a crest value corresponding to the insulation test requirement according to 18.1
If it is uncertain whether a unit with insulated terminals will be used with the container grounded, a lightning impulse test is necessary The purchaser must indicate if this test is required.
Units having one terminal permanently connected to the container shall not be subjected to this test
General
The overvoltage test is a test on the capacitor unit dielectric design and composition, and on the manufacturing process of this dielectric when assembled into a capacitor unit
The test sample will be produced using standard materials and processing methods It must successfully complete the routine tests outlined in section 6.2 Additionally, the test sample's ratings will be a minimum of 100 kvar.
The specified test conditions are essential for power-factor correction applications as per Clause 1, aligning with the general service voltage requirements outlined in this standard For different applications where overvoltages associated with the rated voltage are well understood and managed, alternative test voltages may be negotiated between buyers and sellers.
Incorporating additional safety margins in design calculations or utilizing dielectric overvoltage protection methods, such as arresters and synchronized switching equipment, can enhance system reliability This approach addresses the repeated overvoltage conditions outlined in the relevant subclause.
16.3 b) should not be lower than 1,9 U N
Conditioning of the sample before the test
The test sample shall be conditioned for no less than 12 h at no less than its rated voltage
After the test, the capacitance of the test sample shall be measured at its rated voltage The ambient temperature for the conditioning test shall be +15 °C to +35 °C.
Test procedure
a) Place test sample in cold chamber for no less than 12 h at a temperature equal to or lower than the lowest temperature category for which the capacitor is designed
The test temperature significantly influences the severity of the assessment The low ambient temperature is either determined by the purchaser or agreed upon with the supplier After removing the test sample from the cold chamber, it should be placed in still air at a temperature between +15 °C and +35 °C within 5 minutes, after which the test unit will be subjected to further evaluation.
After applying the nominal voltage (U N), an overvoltage of 2.25 U N must be sustained for 15 cycles without interruption Following this, the voltage should return to 1.1 times U N, again without any interruptions An interval of 1.5 minutes is then observed before further actions are taken.
The overvoltage of 2.25 U_N will be applied for 2 minutes at 1.1 U_N, and this process will be repeated until a total of 60 applications are completed in one day For further details on test voltage characteristics, refer to section 16.5.4 Additionally, steps a) and b) should be repeated for four more days, ensuring the combined application of overvoltage is thoroughly conducted.
The total amount of 2.25 U N should equal 300 After completing the previous step, apply 1.4 U N for a total duration of 96 hours within one hour The ambient temperature during the test must be maintained between +15 °C and +35 °C Additionally, capacitance measurements should be repeated at the rated voltage.
For users focused on testing the dielectric withstand capability of a sample through prolonged overvoltage switching, an agreement between the purchaser and supplier may allow for an increase in the daily applications of 2.25 U_N overvoltage Consequently, the total number of days required to achieve 300 applications can be reduced.
Acceptance criteria
The acceptance criteria stipulate that no breakdown should occur during capacitance measurement In the event of a breakdown, two additional samples must be tested, and both must also demonstrate no breakdown.
Validity of test
General
Each overvoltage test will also cover other capacitor designs, which are allowed to differ from the tested design within the following stated limits.
Element design
For an element design to be deemed comparable to the units being manufactured, it must meet specific criteria: a) the tested elements should have an equal or fewer number of solid material layers in the dielectric and be impregnated with the same fluid, with the same basic type of solid material; b) the rated element voltage and electrical stress level of the tested element must be equal to or exceed those of the manufactured units; c) the design of the aluminium foil (electrode) edges must match; d) the connections of the elements should be of the same type, such as soldering or crimping.
Test unit design
A test unit is deemed comparable to the units intended for production if it meets specific criteria: a) the test elements must be assembled similarly, possess equal or thinner inter-element insulation, and be pressed within the manufacturing tolerance of the production units; b) at least four test elements should be connected to achieve a minimum output of 100 kvar at rated voltage, with all elements placed adjacent and at least one inter-element insulation assembled (including at least two series groups); c) a container conforming to the manufacturer's standard design must be utilized, with a height no less than 20% of the production unit's height and depth and width at least 50% of the production unit's dimensions; d) the drying and impregnation processes must replicate the standard production procedures.
Waveform of overvoltage
The test voltage shall have a frequency of 50 Hz or 60 Hz and the overvoltage shall be applied without any interruption of the steady voltage of 1,05 U N to 1,15 U N
The amplitude limits for the constant voltage and overvoltage are given in Figure 1
NOTE Time durations, other than T 1 , are expressed in numbers of cycles of the test frequency
T 1 is the interval of 1,5 min to 2 min between two consecutive overvoltage periods
Figure 1 – Time and amplitude limits for an overvoltage period
17 Short-circuit discharge test (type test)
The unit will be charged using direct current (d.c.) and subsequently discharged through a gap located as near as possible to the capacitor It will undergo five discharges within a span of 10 minutes.
The test voltage shall be 2,5 U N
Capacitance measurements must be taken both before and after discharge tests, ensuring that the difference between these measurements is minimal This difference should not exceed the threshold that would indicate either the breakdown of a component or the activation of an internal fuse.
NOTE 1 The purpose of the discharge test is to reveal any weak design of the internal connections
NOTE 2 For applications where overvoltages and/or transient currents are limited, test voltages lower than 2,5 U N can be used, as agreed upon between manufacturer and purchaser
Standard insulation values
The insulation levels of the capacitor installation shall be chosen from the standard values prescribed by IEC 60071-1
The standardized values of the highest voltage for equipment are divided in two ranges:
The insulation level of equipment in the range of 1 kV to 245 kV, which encompasses both transmission and distribution systems, must be carefully selected by considering various operational aspects.
– range II: Above 245 kV (Table 4) This range covers mainly transmission systems
For various rated voltages, multiple rated insulation levels are available to accommodate different performance criteria and overvoltage patterns The selection should take into account the exposure to fast-front and slow-front overvoltages, the system's neutral earthing type, and the overvoltage limiting devices used, as outlined in IEC 60071-2.
General requirements
General
The general rules below shall apply for the capacitor, which could be either a single unit or a capacitor bank installation
When selecting bushings, isolators, and other insulating equipment, it is essential to choose components with insulation ratings that meet specific requirements In cases where insulation consists of series-connected parts, each part must contribute appropriately to the overall insulation level It is important to utilize available standards for this equipment whenever applicable Full insulation is defined as having an insulation level that is equal to or exceeds that of the system.
For installations at altitudes exceeding 1,000 meters, a correction factor must be applied to all insulation requirements that define external insulation performance, including a.c wet and lightning impulse test voltage This adjustment ensures that the insulation can withstand high-altitude conditions, even though the equipment is tested at lower altitudes.
Adjacent insulating components and equipment
All phase-to-phase and phase-to-ground insulating components or electrical equipment, in parallel to a capacitor phase or phases, shall withstand full insulation according to 18.1.
Capacitors insulated from ground
For capacitors that are insulated from the ground, whether in a delta connection or a star configuration with an isolated neutral, it is essential that all insulation paths between any energized components of the capacitor, such as terminals and electrodes, are capable of withstanding full insulation requirements as specified in section 18.1.
Full insulation applies specifically to the bushings and terminal-to-container insulation for capacitor units with the container connected to ground (all terminals insulated from container)
Bushings and terminal-to-container insulation for capacitor units with containers not connected to ground shall withstand an a.c voltage of 2,5 times the rated voltage
Inter-rack insulation between line-terminal and neutral that are electrically in parallel and in close physical proximity to the capacitor dielectric shall withstand an a.c voltage of
2,15 times the rated phase voltage.
Capacitors with neutral connected to ground
Bushings and terminal-to-container insulation shall withstand an a.c voltage of 2,5 times the rated voltage
Inter-rack insulation between line-terminal and ground that are electrically in parallel and in close physical proximity to the capacitor dielectric shall withstand an a.c voltage of
2,15 times the rated phase voltage
Test between terminals and container of capacitor units
Routine and type tests are required in Clauses 10, 15 and 16 to verify the requirements on bushings and terminal-to-container insulation according to 18.2.3 and 18.2.4
For cases where the a.c voltage test (see Clauses 10 and 15) is based on rated voltage, the test voltage shall be calculated according to the following equation:
U t is the power-frequency test voltage;
U N is the rated voltage of the capacitor; n is the number of units in series relative to the electrical potential to which the containers are connected.
Capacitors in single-phase systems
For capacitors connected between line and ground, the same insulation requirements as for a three-phase system with neutral connected to ground shall apply
For capacitors isolated from ground the same insulation requirements as for a three-phase system insulated from ground shall apply
Table 3 – Standard insulation levels for range I (1 kV < U m 245 kV)
Standard rated switching impulse withstand voltage Standard rated lightning impulse withstand voltage b
Longitudinal insulation a Phase-to-earth Phase-to-phase
(peak value) (ratio to the phase- to-earth peak value) kV
The introduction of U m values above 800 kV is currently under consideration, with 1,050 kV, 1,100 kV, and 1,200 kV specified in IEC 60038:2009 The impulse component of the relevant combined test has a peak value of the power-frequency component of opposite polarity calculated as U m × √2 / √3 These values are applicable for both phase-to-earth and phase-to-phase insulation, while for longitudinal insulation, they represent the standard rated lightning impulse component of the combined standard rated withstand voltage, with the peak value of the power-frequency component of opposite polarity being 0.7 × U m × √2 / √3 It is important to note that this U m value is considered non-preferred in IEC 60038.
Table 4 is extracted from IEC 60071-1:2006, Table 3
Long duration voltages
Capacitor units shall be suitable for operation at voltage levels according to Table 5 (see 27.2 and 27.5.1)
Table 5 – Admissible voltage levels in service
Highest average value during any period of capacitor energization For energization periods less than 24 h, exceptions apply as indicated below (see 27.2)
Power frequency 1,10 12 h in every 24 h System voltage regulation and fluctuations
Power frequency 1,15 30 min in every 24 h System voltage regulation and fluctuations
Power frequency 1,20 5 min Voltage rise at light load (see 27.2)
Power frequency plus harmonics Such that the current does not exceed the value given in Clause 20 (see also 27.6 and
The amplitudes of the overvoltages that may be tolerated without significant deterioration of the capacitor depend on their duration, their total number and the capacitor temperature (see
27.2) It is assumed that the overvoltages given in Table 5 and having a value higher than
1,15 U N do not occur more than 200 times in the capacitor's life.
Switching overvoltages
The residual voltage on a capacitor before energization must not exceed 10% of the rated voltage When a capacitor bank is energized by a restrike-free circuit-breaker, it typically results in a transient overvoltage, with the initial peak not exceeding 2.2 times the applied root mean square (r.m.s.) voltage for a maximum duration of half a cycle.
It is assumed that the capacitors may be switched 1 000 times per year under these conditions (The associated peak transient overcurrent may reach 100 times the value I N ; see
For capacitors that experience frequent switching, it is essential to limit the amplitude and duration of overvoltage, as well as transient overcurrent, to lower levels These limitations must be specified and agreed upon in the contract.
Capacitor units shall be suitable for continuous operation at an r.m.s current of 1,30 times the current that occurs at rated sinusoidal voltage and rated frequency, excluding transients
Depending on the actual capacitance value, which may be a maximum of 1,10 C N , the maximum current can reach 1,43 I N (see 27.6)
These overcurrent factors are intended to take care of the combined effects due to harmonics and overvoltages up to and including 1,10 U N according to 19.1
21 Safety requirements for discharge devices
Each capacitor unit shall be provided with means for discharging to 75 V or less from initial peak voltage of 2 times rated voltage U N The maximum discharge time is 10 min
There shall be no switch, fuse, or any other isolating device between the capacitor unit and/or bank and the discharging device as defined above
A discharging device is not a substitute for short-circuiting the capacitor terminals together and to ground before handling
Capacitors connected directly to other electrical equipment providing a discharge path should be considered properly discharged, provided that the circuit characteristics are such as to meet the discharge requirements
For banks with capacitor units connected in series, the voltage at the bank terminals may exceed 75 V after 10 minutes due to the cumulative residual voltages of each unit Manufacturers should specify the discharge time to 75 V in the instruction sheet or on the rating plate.
NOTE 1 In certain countries, smaller discharge times and voltages are required In this event, the purchaser informs the manufacturer
Discharge circuits should have adequate current-carrying capacity to discharge the capacitor from the peak of the 1,3 U N overvoltage according to Clause 19
An electrical fault in a fuse-protected unit or a flashover within the bank can lead to localized residual charges that cannot be discharged in the designated time using a discharge device connected to the bank's terminals.
NOTE 3 A formula for the calculation of the discharge resistance is given in Annex D
22 Safety requirements for container connections
To ensure the metal container of the capacitor can effectively handle fault currents during a breakdown, it must be equipped with a connection provision using a bolt with a minimum thread size of M10 or its equivalent.
In the event of a complete short circuit failure in a capacitor, the resulting short circuit current may surpass the fault current capability, posing significant risks to personnel safety It is crucial to evaluate the limitations of protective measures such as fuses, current limiters, and enclosures Additionally, the potential for fire and smoke explosions must be carefully assessed, particularly in indoor or enclosed assembly designs.
23 Safety requirements for protection of the environment
When capacitors are treated with non-dispersible materials, it is essential to implement safety measures Certain countries have legal regulations governing this practice (refer to 25.3 and Annex A).
At the time of inquiry, the purchaser must indicate any specific safety regulation requirements relevant to the country where the capacitor will be installed.
25 Markings of the capacitor unit
Rating plate
Each capacitor unit's rating plate must include essential information: a) the manufacturer's name; b) an identification number along with the manufacturing year, which may be encoded or included as part of the identification number; c) the rated output, Q N, expressed in kilovars, with the total output specified for three-phase units.
The article specifies essential technical parameters for electrical equipment, including the rated voltage (\$U_N\$) in volts or kilovolts, the rated frequency (\$f_N\$) in hertz, and the temperature category It also requires the indication of any internal discharge device through specific wording, symbols, or rated ohmic values Additionally, for units with all terminals insulated from the container, the insulation level (\$U_i\$) must be stated in kilovolts.
The insulation level must be indicated by two numbers separated by a slash, where the first number represents the r.m.s value of the power-frequency test voltage in kilovolts, and the second number indicates the peak value of the impulse test voltage in kilovolts (e.g., 28/75) For units not tested according to Clause 15.2, the insulation level marking should be omitted Additionally, all capacitors, except single-phase units with a single capacitance, must display their connection symbols as per standardized guidelines If internal fuses are present, they should be marked with appropriate wording or symbols The chemical or trade name of the impregnant must be stated on the warning plate, and there should be a reference to IEC 60871, including the year of issue.
NOTE On request of the purchaser, the measured capacitance is indicated either in absolute value, or in percentage, or by symbols.
Standardized connection symbols
The type of connection shall be indicated either by letters or by the following symbols:
YN or = star, neutral brought out
III or = three sections without internal interconnections
Warning plate
Capacitor units that contain environmentally harmful or hazardous materials, such as flammable substances, must be labeled in accordance with the applicable laws of the user's country It is the responsibility of the purchaser to notify the manufacturer about these legal requirements.
Regarding capacitors with polychlorobiphenyl impregnant, see Annex A
26 Markings of the capacitor bank
Instruction sheet or rating plate
Manufacturers must provide essential information on an instruction sheet or a rating plate upon request, including: the manufacturer's name, the rated output (Q N) in megavars, the rated voltage (U N) in kilovolts, and the insulation level (U i) indicated by two numbers separated by a stroke The first number represents the r.m.s value of the rated power-frequency short-duration voltage (for U m 245 kV)
Standard rated switching impulse withstand voltage Standard rated lightning impulse withstand voltage b
Longitudinal insulation a Phase-to-earth Phase-to-phase
(peak value) (ratio to the phase- to-earth peak value) kV
The introduction of U m values above 800 kV is currently under consideration, with 1,050 kV, 1,100 kV, and 1,200 kV specified in IEC 60038:2009 The impulse component's value for the relevant combined test, while the peak value of the power-frequency component of opposite polarity, is calculated as U m × √2 / √3 These values are applicable for both phase-to-earth and phase-to-phase insulation; for longitudinal insulation, they represent the standard rated lightning impulse component of the combined standard rated withstand voltage, with the peak value of the power-frequency component of opposite polarity being 0.7 × U m × √2 / √3 It is important to note that this U m is a non-preferred value in IEC 60038.
Table 4 is extracted from IEC 60071-1:2006, Table 3
Capacitor units shall be suitable for operation at voltage levels according to Table 5 (see 27.2 and 27.5.1)
Table 5 – Admissible voltage levels in service
Highest average value during any period of capacitor energization For energization periods less than 24 h, exceptions apply as indicated below (see 27.2)
Power frequency 1,10 12 h in every 24 h System voltage regulation and fluctuations
Power frequency 1,15 30 min in every 24 h System voltage regulation and fluctuations
Power frequency 1,20 5 min Voltage rise at light load (see 27.2)
Power frequency plus harmonics Such that the current does not exceed the value given in Clause 20 (see also 27.6 and
The amplitudes of the overvoltages that may be tolerated without significant deterioration of the capacitor depend on their duration, their total number and the capacitor temperature (see
27.2) It is assumed that the overvoltages given in Table 5 and having a value higher than
1,15 U N do not occur more than 200 times in the capacitor's life
The residual voltage on a capacitor before it is energized must not exceed 10% of the rated voltage When a capacitor bank is energized by a restrike-free circuit-breaker, it typically results in a transient overvoltage, with the initial peak not exceeding 2.2 times the applied root mean square (r.m.s.) voltage for a maximum duration of half a cycle.
It is assumed that the capacitors may be switched 1 000 times per year under these conditions (The associated peak transient overcurrent may reach 100 times the value I N ; see
For capacitors that are switched frequently, it is essential to limit the amplitude and duration of overvoltage, as well as transient overcurrent, to lower levels These limitations must be specified and agreed upon in the contract.
Capacitor units shall be suitable for continuous operation at an r.m.s current of 1,30 times the current that occurs at rated sinusoidal voltage and rated frequency, excluding transients
Depending on the actual capacitance value, which may be a maximum of 1,10 C N , the maximum current can reach 1,43 I N (see 27.6)
These overcurrent factors are intended to take care of the combined effects due to harmonics and overvoltages up to and including 1,10 U N according to 19.1
21 Safety requirements for discharge devices
Each capacitor unit shall be provided with means for discharging to 75 V or less from initial peak voltage of 2 times rated voltage U N The maximum discharge time is 10 min
There shall be no switch, fuse, or any other isolating device between the capacitor unit and/or bank and the discharging device as defined above
A discharging device is not a substitute for short-circuiting the capacitor terminals together and to ground before handling
Capacitors connected directly to other electrical equipment providing a discharge path should be considered properly discharged, provided that the circuit characteristics are such as to meet the discharge requirements
For banks with capacitor units connected in series, the voltage at the bank terminals may exceed 75 V after 10 minutes due to the cumulative residual voltages of each unit It is essential for manufacturers to specify the discharge time to 75 V in the instruction sheet or on the rating plate.
NOTE 1 In certain countries, smaller discharge times and voltages are required In this event, the purchaser informs the manufacturer
Discharge circuits should have adequate current-carrying capacity to discharge the capacitor from the peak of the 1,3 U N overvoltage according to Clause 19
NOTE 2 An electrical fault in a unit protected by a fuse, or a flashover across part of the bank, can produce local residual charges inside the bank which cannot be discharged within the specified time by means of a discharge device connected between the terminals of the bank
NOTE 3 A formula for the calculation of the discharge resistance is given in Annex D
22 Safety requirements for container connections
To ensure the metal container of the capacitor can effectively handle fault currents during a breakdown, it must be equipped with a connection provision using a bolt with a minimum thread size of M10 or its equivalent.
In the event of a complete short circuit failure in a capacitor, the resulting short circuit current may surpass the fault current capability, posing significant risks to personnel safety It is crucial to evaluate the limitations of protective measures such as fuses, current limiters, and enclosures Additionally, the potential for fire and smoke explosions must be carefully assessed, particularly in indoor or enclosed assembly designs.
23 Safety requirements for protection of the environment
When capacitors are treated with non-dispersible materials, it is essential to implement safety measures Certain countries have legal regulations governing this practice (refer to 25.3 and Annex A).
At the time of inquiry, the purchaser must indicate any specific safety regulation requirements relevant to the country where the capacitor will be installed.
25 Markings of the capacitor unit
Each capacitor unit's rating plate must include essential information: a) the manufacturer's name; b) an identification number along with the manufacturing year, which may be encoded or included as part of the identification number; c) the rated output, Q N, expressed in kilovars, with the total output specified for three-phase units.
The article specifies essential parameters for electrical equipment, including the rated voltage (\$U_N\$) in volts or kilovolts, the rated frequency (\$f_N\$) in hertz, and the temperature category It also requires the indication of any internal discharge device through appropriate wording, symbols, or rated ohmic values Additionally, for units with all terminals insulated from the container, the insulation level (\$U_i\$) must be stated in kilovolts.
The insulation level must be marked with two numbers separated by a stroke, where the first number indicates the r.m.s value of the power-frequency test voltage in kilovolts, and the second number represents the peak value of the impulse test voltage in kilovolts (e.g., 28/75) For units not tested according to Clause 15.2, the insulation level marking should be omitted Additionally, all capacitors, except single-phase units with a single capacitance, must have their connection indicated using standardized symbols Internal fuses, if present, should be marked with appropriate wording or symbols The chemical or trade name of the impregnant must be displayed on the warning plate, and there should be a reference to IEC 60871, including the year of issue.
NOTE On request of the purchaser, the measured capacitance is indicated either in absolute value, or in percentage, or by symbols
The type of connection shall be indicated either by letters or by the following symbols:
YN or = star, neutral brought out
III or = three sections without internal interconnections
Capacitor units that contain environmentally harmful or hazardous materials, such as flammable substances, must be labeled in accordance with the applicable laws of the user's country It is the responsibility of the purchaser to notify the manufacturer about these legal requirements.
Regarding capacitors with polychlorobiphenyl impregnant, see Annex A
26 Markings of the capacitor bank
26.1 Instruction sheet or rating plate
Manufacturers must provide essential information on an instruction sheet or a rating plate upon request, including: the manufacturer's name, the rated output (Q N) in megavars, the rated voltage (U N) in kilovolts, and the insulation level (U i) indicated by two numbers separated by a stroke The first number represents the r.m.s value of the rated power-frequency short-duration voltage (for U m