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MV/LV PREFABRICATED SUBSTATIONS : LESSONS LEARNED WITH IEC 62271-202 Conference Paper · November 2011
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MV/LV PREFABRICATED SUBSTATIONS : LESSONS LEARNED WITH IEC 62271-202 Marc BIDAUT, Schneider Electric, France,
[email protected] Thierry CORMENIER, Schneider Electric, France,
[email protected]
ABSTRACT The publication of a new edition of a product standard is often the opportunity for the customers to revise their specifications and for the manufacturers of launching new products. The type tests list and routine tests required for a HV/LV prefabricated substation will be used as discussion thread with a review of the evolutions of the user's needs and solutions which are proposed to them.
KEYWORDS IEC 62271-202, HV/LV prefabricated substation, HV/LV, type test, routine test.
INTRODUCTION In June 2006 the International Electrotechnical Commission (IEC) published the first version of new standard IEC 62271202, related to the prefabricated substations HV/LVBT, which cancelled and replaced earlier IEC 61330 standard published ten years ago. Very quickly the reference to this new standard appeared in the customer specifications and the invitations to tender. As regards manufacturers of new products were born to answer the requirements of qualification with type tests and also an increasing demand of more complex substations such as for example those intended for the photovoltaic solar farms. HV/LV prefabricated substations are segmented in two big families: substations intended for the electricity distribution companies, generally qualified like products with definite configuration and limited options dedicated to answer series markets; substations intended for various applications for industry and infrastructures, defined by project, and thus often specific. For those whose lay-outs are recurring it can be applied a conformity to IEC 62271-202 standard. The others can be regarded as HV installations complying with IEC 61936 standard, and carried out in prefabricated enclosures which follow the recommendations of IEC 62271-202 standard.
Generally the electricity distribution companies refer to the whole series of type tests of this IEC 62271-202 standard. For the specific products the temperature-rise test and the tests to assess the effects of internal arc fault remain most relevant and required. The performances of degree of protection, mechanical withstand, currents flow in the earthing circuits are generally validated by generic tests carried out during the validation of a technology (Doors / Ventilations / Material / Section and fixing of the earthing circuits). The variety of transformers with powers from 250 to 3150 kVA, with liquid dielectric or of dry type, their respective coils heating up 35 to 65K or 60 to 150K, the HV and LV switchboards versions, the various operation modes with or without operation area, the most required enclosure temperature classes (5, 10 or 20K) as well as the degrees of protection of the various compartments IP23 to IP56, would give while being minimalist, by regrouping of performance, more than 380 configurations, occulting the levels of rated currents and voltages. An organized process for the conformity evaluation of a range is necessary. The rules for the choice of the representative samples are based on healthy technical and physical principles and are justified by calculations. Figure 1 show as example the minimal quantities which could be retained for a range of HV/LV substation, and giving place to as many tests as of alternatives.
Transformer power Transformer type (oil or dry) Transformer temperature rise HV switchboard LV switchboard Enclosure class Operation mode Degrees of protection
3 2 2 2 2 2 2 2
Figure 1: Minimalist regrouping of configurations for a range of HV/LV substations The type tests list of IEC 62271-202 standard is thus the discussion thread which we will follow in the continuation of the document.
TESTS TO VERIFY THE INSULATION LEVEL OF THE PREFABRICATED SUBSTATION Since the HV switchgear, HV/LV transformer and LV switchgear contained in a prefabricated substation have been type-tested according to their relevant standards, tests to verify the insulation level applies only to the HV and LV interconnections. The majority of the manufacturers of prefabricated substations make a systematic use of HV interconnections made with HV cables equipped with by type-tested earthshielded connectors which thus do not require a type test. In the other cases it is necessary to carry them out.
The electricity distribution companies show each day through their specifications, their control, their knowledge and field-expertise of typologies of load which are more and more changing with the increasing number of microproducers on their networks. In certain areas where the seasonal average of the ambient temperature can reach 35°C, we noted that the limits of temperature rise prescribed could be reduced until 35-40K for oil and coils, corresponding to the prescriptions of the IEC 62271-202 (Appendix D) and the IEC 60076-7 (see figure 2).
With regard to the LV interconnection, to answer the customer’s specifications and/or for a greater safety and easier installation, the use of insulated cables is very widespread and makes it possible to be freed from the type tests. In the other cases such as the use of bars partially or not insulated, the design of LV interconnection must be subjected to lightning impulse-voltage tests and the shortest creepage distances must be measured and be in conformity with the requirements of Table 4 of IEC 60664-1. On the other hand, for the routine tests, a power-frequency voltage test of the HV interconnection is necessary. Thus targeting the optimal quality, these unitary tests are carried out on the manufacturing sites of these interconnections. Finally the dielectric tests of the auxiliary circuits which are not requiring expensive equipment are very easily carried out during the final control of the manufacturing of the substations aiming at checking the good performance of protection relays and other devices.
TESTS TO PROVE THE TEMPERATURE RISE OF THE MAIN COMPONENTS CONTAINED IN A PREFABRICATED SUBSTATION The introduction of the enclosure temperature class 5K was beneficial for the geographical areas having high ambient temperature thus making it possible to reduce the versions of transformers temperature rise limits. It is important to remind that the valorisation of this class is related to the choices of the of the transformer temperature rise limits and thus to the total losses. The same prefabricated substation can classifies at the same time class 10K for a transformer 1000 kVA 60-65K and class 5K for a transformer 1000 kVA 40-45K. It is also necessary to mention that if the envelope of a prefabricated substation can have different degrees of protection (for example with or without gaskets for the doors) it is preferable to carry out a test of evaluation of this thermal class with the maximum of losses and the most demanding degree of protection.
Figure 2: IEC 62271-202 and IEC 60076-7 f (class, ambient θ, load factor, O/W transformer temperature rise)
The experience from laboratories reveals that some customers specifications can be contradictory between the prescribed assigned thermal class of enclosure and temperature rise limits required by the IEC 61439-1 for low voltage equipment already qualified outside an enclosure. Let us take the case of a LV switchboard prescribed by an electricity distribution company and qualified as a freestanding product. For its use in a prefabricated substation it can require a class of enclosure 15K so that the limits of temperature rise values of the IEC 61439 are not reached whereas the specification of the prefabricated substation prescribed a class of enclosure 20K.
TESTS TO PROVE THE CAPABILITY OF THE MAIN AND EARTHING CIRCUITS TO BE SUBJECTED TO THE RATED PEAK AND THE RATED SHORT-TIME WITHSTAND CURRENTS Checking by type tests of the electrodynamics withstand of various types of LV interconnections made of insulated cables or bars makes it possible to validate design principles transposable from a type of substation to another.
TESTS TO VERIFY PROTECTION
Figure 3: Checking of the electrodynamics withstand of a LV interconnection The test of the earthing system remains important to verify the mechanical withstand under electrodynamics stresses. Sometimes the over sizing in a customer specification of its cross section on HV side appears shifted compared to the value of the fault current conditioned by the type of earthing of the neutral. In addition some devices for fault current flow to the ground through solid walls must be tested under the real conditions of use so that it is possible to guarantee the operational safety, instead of undergoing only type tests the in open air, which facilitates heat exchange. The figure 4 shows successively the product as it must be installed according to the user guide, the type test of the product alone, the type test of the product installed which result is non-conformity.
THE
DEGREE
OF
It is essential to have a degree of protection adapted to the environmental conditions of the substation. For protection against the water penetration in the case of substations for wind farms in the very hot climates according to the IEC 62271-1, the IPx3 degree appears insufficient and the IPx4 degree could appear more adapted but it is constraining to perform the natural ventilation expected with increasingly large powers of transformers installed. There is no, for now, a definition and a type test for a degree of protection against horizontal water projections, which could be more adapted to this type of use. In addition many of the electricity distribution companies would wish to specify IP23D degree privileging natural cooling but they also wish that the penetration of the wire of 1mm should not be limited in length to 100 mm in order to ensure a better safety when it is made use of connections of transformer not ensuring protection of the people against direct contacts to the active parts. Finally the verification of the degree of protection IP5X is confronted with a lack of means of tests adapted and in fact a dust room of sufficient capacity to receive a complete HV/LV substation. The alternative used for a compartmentalized metallic substation was to test only one separated compartment.
Figure 4: Tests of earth fault current flowing device
FUNCTIONAL TESTS TO PROVE SATISFACTORY OPERATION OF THE ASSEMBLY Checking of the possibility to perform all the necessary commissioning, operational and maintenance activities of the prefabricated substation is quite seldom the subject of a separate type test report. In fact for some of the electricity distribution companies, the process of validation includes, beyond the inspection of prototypes before the tests, one probationary period on the network for a limited series of substations samples. For the prefabricated substations designed for specific projects, these checks are carried out during the routine tests and the customer acceptance of the complete equipment in factory.
Figure 5: Verification of the degree of protection IP5X of a separated compartment
TESTS TO VERIFY THE WITHSTAND OF THE ENCLOSURE OF THE PREFABRICATED SUBSTATION AGAINST MECHANICAL STRESS If calculations notes are chosen for this checking, they will have to take into account the performances required by the IEC standard [1] but also by the national or local regulations. Complementary type tests can be realized to evaluate the behaviour during the phases of transport and if necessary lead to require adapted wedging. Indeed substations without good wedging can be subjected to accelerations higher than 7g. Beyond the validation test, the substations can be equipped with detectors of shocks, for deliveries towards remote sites (wind, photovoltaic) borrowing ways not very suitable for motor vehicles, and in the case of use of trucks with blade shock absorbers instead of hydro pneumatic shock absorbers (+30% of constraint).
FOR PREFABRICATED SUBSTATIONS CLASS IAC-A, IAC-B OR IAC-AB, TESTS TO ASSESS THE EFFECTS OF ARCING DUE TO AN INTERNAL FAULT Internal arc withstand initiated by a three-phase fault in the main compartment of the HV switchgear intended to check the conformity to class IAC B helped to improve the mechanical resistance of the enclosures against overpressures and the control of hot gases in the case of a possible internal fault. Usually it is preferable to carry out this test on enclosures having the minimal degree of protection IP23D when the substation comprises a transformer, or having a maximum degree of protection when the substation does not comprise a transformer. Figure 6 shows an example of internal arc test of a 36kV equipment associated with its compartment.
EMC COMPATIBILITY TESTS As HV and LV switchboards having been checked by type tests for their level of emission and immunity it is not necessary according to IEC 62271-202 standard to carry out tests on the complete substations. Indeed this test is difficult to carry out of due to the number of possible configurations in HV/LV substation as said in the introduction, and in addition with the multiplication of communication technologies for measurements and remote control. When measurements are carried out on complete prefabricated substations they relate to the intensity of the magnetic field generated in the vicinity of the enclosure of the substation. A technical report IEC TR 62271-208 dealing with solutions to measure or calculate the electromagnetic fields in the vicinity of HV and HV/LV equipment was published at the end of 2009. In practice, the normative configuration of the temperature rise test of HV/LV substations, requiring a short-circuit on transformer LV side and a second upstream of LV equipment does not reflect the real conditions of electromagnetic fields emission , however it is not rare to see proposals for combined tests. Figure 7 shows cartography of measurement where the central part corresponds to measurements on the roof, the single non accessible side, and around measurements on the various faces of the substation enclosure.
Figure 7: Examples of electromagnetic field measurement (in µT) on a HV/LV substation. Figure 6: IAC-AFL-16kA 1s + IAC-AB-16kA-1s
TESTS TO VERIFY THE SOUND LEVEL OF A PREFABRICATED SUBSTATION This test, optional, has for principal interest to provide the data of what is obvious with knowing that in front of the ventilation openings there is little attenuation of the noise transmitted by air. The enclosure of a prefabricated substation generally reduces the sound power of the transformer only of a few dB(A). The results of the noise level measurement of a HV/LV substation must be compared with the values of the local regulations and if necessary provisions of minimum distance from public places to the substation or use of transformer with reduced noise must be considered.
TESTS NOT BEING MENTIONED IN THE IEC 62271-202 STANDARD These tests are specific because not listed in the standard of reference [1], they depend on the market segments and the national regulations. They are relative to concerns such as the performance of fire resistance, the impact of a flood, the effect of the solar radiation …etc. Figure 8 shows temperature measurements during a test of resistance to fire REI 90/RE 180 of a concrete wall of 10cm alone which could reach performance REI 120 (INTO 13501-2) with an additional plaster screen. In the absence of type test, the thickness of this wall should be increased to 160 mm for a load-bearing wall according to IN 1992-1-2 Eurocode 2: Design of concrete structures — Part 1-2: General rules — Structural fire design.
Figure 9: Tests and additional provisions to face the possible floods.
SIMULATIONS Many simulations can be carried out to evaluate many specific configurations but it is essential to check the validity by comparing with type test results. These simulations become essential as soon as it is understood that a single configuration cannot correspond to the most constraining configuration for the whole of the type tests series. Example: the most constraining configuration for a temperature-rise test will not be that most constraining for an internal arc test, the same for the evaluation of the noise level.
CONCLUSION Since 2006 IEC 62271-202 standard became a reference as product standard for HV/LV prefabricated substations. The type tests are applied in their entirety, even partially according to the market segments, to these requirements are added those of the national regulations which can require complementary tests. Thus the topics developed in this article will help to support later evolutions of IEC 62271202 standard.
REFERENCES [1]
IEC; 2006; IEC 62271-202 HV/LV Prefabricated Substations, IEC, Geneva, Switzerland.
[2]
C.Sujatha, P.Tejesu HEAVY VEHICLE DYNAMICSCOMPARISON BETWEEN LEAF SPRING AND HYDROPNEUMATIC SUSPENSIONS. Machine Dynamics Laboratory, Applied Mechanics Department, Indian Institute of Technology Madras Chennai; India
[3]
T.Cormenier, L.Vieu-Viennet, P.Brun; 2011 CIRED N°477; NEW UNDERGROUND HV/LV PREFABRICATED SUBSTATIONS FOR BETTER INTEGRATION IN THE ENVIRONMENT, Frankfurt, Germany
Figure 8: Temperature measurements during a test of fire resistance of a concrete wall. Figure 9 shows a test comparable to IPx7 on an underground substation where a metallic device was added in periphery in order to fill with water all the volume from the half height of the walls until 30cm above the top of the openings (hatches). The purpose was to check the tightness of these openings. Solutions are implemented by manufacturers to face the possible floods, until 30cm for the 1000kVA or 2*630kVA underground substation intended for the urban areas mentioned above, and until 45cm for a 160kVA substation dedicated to the rural areas.
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