syntheticplatformdetailintroduction.ppt

Synthetic platform detail introduction,Contents,Why to build up synthetic platformSwitchgear making&breaking testing techniquesEnergy Sh-Lab synthetic platform structure,Why to build up synthetic platform,Process needs&limits from conventional test plant,Single phase testing accounts for 70%of the total development testing,Conventional test plant generator or networkLarge,cumbersome to operateExpensiveDifficult to make analysis if test failed,Three phase short power needs for direct testing,Above table shows the three phase short circuit power that is required from the primary source(generator or public network)to perform direct tests on MV CB for the IEC rated values.The approximate cost of a 2000MVA station powered by short circuit generator is 200 million RMB.,Principle of synthetic test,Divide short-circuit breaking into 2 phases to reduce necessary powerHigh current phase(short-circuit)High voltage phase(Transient recovery voltage)High current phase:supply the short circuit test current from a source of much lower voltage than the breaker rated voltageHigh voltage phase:provide voltage stress after interruption from a low power high voltage sorceSynthetic lab is thus composed of 2 banksA high current oneA high voltage onewith good time coordination between both,Advantage of synthetic testing,Effectiveness:Widely accepted as an equivalent method as direct testing.Efficiency:Producing large number of tests quickly.Economic:Significant cost reduction on the installation compare with the cost of power source needed for direct testing.Easy to operate and maintain.Protection of prototype under test:Significantly reduction of damage to the prototype even if the test failed.Convenience for analysisProvide possibility to stop testing when time analysis of results or prototype modification is needed.Suitable environment to attempt the sophisticated measurements required to know what is happening in the interrupter,particularly during the few vital microseconds immediately before and after current zero.,Switchgear making&breaking testing techniques,3 basic types of short circuit test for MV&HV CB,Short circuit current making&breaking testLoad current making&breaking testShort time withstand&peak withstand current test,The most demanding test for CB is the breaking of its rated short circuit current.Most of the test station are fed by specially designed short circuit generator,while others are connected directly to the public network.Certification tests on MV SWGR are always carried out by direct tests,i.e.the short circuit current supplied from a source with an open circuit voltage equal to the rated voltage of the CB.Certification test on HV SWGR are normally carried out by synthetic tests due to the capacity limits of the source.,IEC short circuit test requirements,Test duty 1,2,3&4 involve breaks with symmetrical currentsTest duty 5 is known as“break with asymmetrical currents”and the severity of the test strongly depends on the instant of contact separation.The standard requires that timing is adjusted so that the FPTC separates its contacts in a major loop of current.,Remark(*):The%of DC component is referred to the ponent for a time constant of 45ms(X/R=14),Load current making&breaking tests,Load currents making&breaking tests do not normally impose a demanding duty on the switchgear as fault currents do.However,switch failure like reignitions or current chopping can cause severe over-voltage and damage the load insulation.Testing is required in particular for the disconnection to capacitive loads(like power factor correction capacitor&unloaded cables)&inductive loads(like induction motors&unloaded transformers)for two main reason:To satisfy customer,who is mainly concerned with maximum overvoltage likely to be generated by the SWGR in service and its relation to the insulation level of the network where it is going to be installed.To allow designer to find a compromise between the divergent duties imposed on the switching devices.No standard test has been agreed yet for inductive load current as the chopping level and over-voltage are strongly dependent on the interaction between the CB and local stray capacitance and inductance in the circuitThese type of tests are normally carried out as direct tests as the power required from the source is very small compare to the short circuit tests.,Short time&peak withstand current test,This test is intended to verify the ability of the SWGR main contact system and mechanical structure to withstand the thermal&electrodynamic stress imposed by the rated short circuit current passing through the device in closed position for several seconds(1/3/4s).The absence of the arc impedance allows the possibility to supply the short circuit current from a low voltage source(100V or less).This results in a low power high current source which can be easily fed from the public network without causing disturbances to other users.,3-ph direct tests,Power source:provide both test current&voltageMaster breaker:line protectionMaking switch:special designed equipment to obtain precise making angle controlCurrent limiting loads:adjust short circuit current,including L&RShort circuit test transformerRC network:for TRV controlBreaker under test,Typical oscillogram of 3-Ph breaking test,Phase R is the first pole to clear.The peak value of the TRV for the FPTC specified by IEC standard is UR=1.71Un(for 12kV product UR=20.6kV)After the first pole has cleared,Un will be distributed between the two last clearing poles,according to IEC standard the peak value of this TRV(UST)=1.98Un,but it will be shared by 2 open contacts.In summary,during CB breaking process,the highest peak voltage between contacts appears on the first pole to clear,while the other two phase obtain the longest arcing time but the TRV is less severe.Final certification test are always three phase because it is necessary to verify that all possible interactions between phase do not have adverse effects on the performance.,Single phase direct test by generator or network,The necessary short circuit power in a conventional test station is usually obtained by connecting the breaker pole under test across two phase,Single phase test by capacitor bank,An alternative form of carrying out single phase direct tests for development purposes is using a large capacitor bank.As arcing time in modern CB(vacuum or SF6)are less than a complete cycle,it is possible to separate the arcing contacts just after the current is initiated and a full cycle of current with a reasonable amplitude decay(less than 20%)between the first two peaksOne of the main draw backs of this config.Is that the current can only be varied by varying the charging voltage,this effects the TRV.The following page Introduce a better approach to over come this draw back.,Single phase test by capacitor bank(optimization),Capacitor bank is divided into several sections.Each one tuned at power frequency.Test current can be varied by different selection of capacitor banksAvoid effecting TRV through current adjustment.Main draw back:voltage source provided by capacitor bank also,which result in very high cost for capacitor investment,Synthetic test,Test current is supplied by an oscillating circuit(C&L).The second capacitor(Cs)is discharged by means of spark gap SG1 through Ls shortly before the test current reaches zero(at t1)generating a current pulse Io of frequency fo=1/2LsCsThe aux.breaker will interrupt the main current at t2,isolating both sources.The arc in the breaker under test will be driven by the high voltage source,interrupted by aux.breaker.The TRV natural frequency is given by:fn=1/2LsC1Lac is choose to provide power frequency recovery,t1,t2,SG1,How to obtain full equivalence between direct&synthetic tests,The test current distortion to the lower driving voltage should not exceed 10%of the prospective current in a direct test,this ensure the same arc energy in the interrupt chamber.The injected current peak value(Io)and frequency(fo)should comply with the following equation:(Io/Ipf)=(fpf/fo),this produces the same di/dt at current zero for a direct and synthetic test.The value of Ls,R1&C1 should be the same as in a direct test circuit,this enables to apply the same TRV as in direct test.,Method of synthetic platform to obtain longer arcing time,Certain CB could have arcing time longer than half cycle,it then becomes necessary to artificially prolong the arcing time by forcing a thermal reignition at the first current zero.This can be obtained by discharging a precharged capacitor some 50us before current zero,Single phase synthetic test with symmetrical currents&rapid reclosure function-1,CB which intended for rapid reclosure should be able to do two breaking operations at rated short circuit current with a time interval of approximately 300ms.the methods described below is a reasonable simulation,although in theory there is no apparent reason for it not to work as predicted,its feasibility remains to be verified in practice.The IEC duty cycle O-0.3s-CO could be replaced by the cycle Od-0.3s-Os where:Od:breaking operation at full test current but no injection,i.e.the TRV is provided by the high current circuit.Os:breaking operation at full test current and injection with the TRV required by the IEC standards.The only objective of the operation Od is to pre-stress the CB chamber and create the initial conditions for the subsequent Os operation.,Single phase synthetic test with symmetrical currents&rapid reclosure function-2,The first half of the current bank is used to provide the Od operation,while the other half provides the test current for the Os operation.It might be necessary to have a aux.cb with a mechanism suitable for doing rapid reclosure,in case the prototype is not capable of successfully interrupting in the Od operation,Single phase synthetic test with asymmetrical currents,Tuning each one of the four sections of the current source to suitable frequenciesand delaying the firing instant of each section in such a way that the four current pulse go through zero at the same time.The device under test will see the instantaneous sum of the four pulse,the synthesized waveform can be made very similar to the first loop of a given rated current with almost any desired X/R ratio.,Energy Sh-Lab synthetic platform structure,Overall structure,High current banks,The high current source is consist of a 470kJ capacitor bank.It is formed by 208 unit rated at 3kV,500uF.The bank is divided into four similar sections,each one formed by two identical racks with 26 capacitors.The capacitors in each of the four sections can be arranged in three series parallel combinations,resulting on the following capacitor values:26mF at 3kV;6.5mF at 6kV;1.6mF at 12kV;,Capacitor bank series parallel connection options,3kV connection,6kV connection,12kV connection,Diagram of one bank section,Each section will constitute a tuned circuit consisting in a capacitor,air inductor and a making switch.,Tuning inductors,The tuning inductor of each section will be formed by six individual coils connected in series.The inductance value will be 0.1mH,0.2mH,0.4mH,0.8mH,1.6mH and 3.2mHThe Q factors(defined for 50Hz)of each inductor is greater than 15.This arrangement has been designed to obtain any inductance value from 0.1mH upto 6.3mH by simply shorting out the required numbers of coils.A variable tuning inductor will allow to vary the frequency of the test current from 28Hz to 70Hz.This flexibility is necessary to be able to simulate asymmetrical short circuit currents.,Making switch,The making switch consists in a mercury filled ignitron valve,capable of accurate and consistant firing,shunted by a fast mechanical switch that works on the magnetic repulsion principle.This arrangement reduces the total coloumb imput to the ignitron,greatly extending its life.,HV source,The HV source consists of a 96kJ capacitor bank formed by 16 units rated at 30uF and 20kV.The bank is divided in four identical stages with four capacitors per stage.This allows to obtain a wide range of voltages and capacitance values by series parallel connections.,HV tuning circuit,The current injection pulse frequency will be varied between 300Hz and 600Hz according to the test requirements,this is achieved by tuning the high voltage inductor,which is formed by seven series connected coils.The individual inductances of the coils are:0.2mH,0.4mH,0.8mH,1.6mH,3.2mH,6.4mH and 12.8mH,Trigger of injection pulse,The injection pulse is triggered by a plasma jet type spark gap,it has a battery powered 10kV supply fired via a fibre optic link,TRV tuning circuit,The TRV waveshape is controlled by a series RC networkThe TRV control capacitor bank is formed by nine parallel connected capacitors with the following values:3nF,6nF,12nF,24nF,50nF,100nF,200nF,400nF and 800nF,all rated at 80kV.The TRB controlling capacitor can be varied from 3nF upto 1596nF in 3nF steps by shorting out the required units.The resistor that determine the TRB damping factor is formed by eight series connected ceramic disk resistors rated for 100kV peak and 90kJ with following values:2ohm,4ohm,8ohm,16ohm,32ohm,64ohm,128ohm,256ohm.The damping resistance can be varied between 2ohm and 510ohm in 2ohm steps by shorting out the required units.,Overall arrangement,Equipment cell,Control room,Testing cell,