CWRF 2012 SHORT CIRCUIT ENERGY CONSIDERATIONS USING THE EXAMPLE OF A PULSE STEP MODULATOR BASED HVPS CWRF 8. – 11. May 2012 André Spichiger, Michael Bader, Marcel Frei
SHORT CIRCUIT ENERGY Content Motivation: Why this topic? Tube Specifications How can the arc energy be measured or calculated HVPS Stored Energy Energy dissipation / arc energy Reduction of arc energy Inverse Voltage- System Summary 2 5/11/2012
MOTIVATION Why this topic? Questions during bids and acceptance tests Increasing filter / ripple requirements what are the limitations? Frequently discussed issue: Cable length between the supply and the tube Important for a safe tube operation To give an idea / feeling about the figures 3 5/11/2012
SPECIFICATIONS What is the energy dissipated in a load (tube) arc? Arc energy specifications Usually in the region of 10..20 Joule 15 Joule corresponds to 15 bars of chocolate lifted 1m. 4 5/11/2012
VERIFICATION 5 5/11/2012
VERIFICATION Measuring the arc energy Simple test with a wire as proposed in tube Datasheets Using a real fuse I2t value Accurate Current measurement is possible (e.g. pearson coil, coaxial shunt) Accurate Arc Voltage measurement is not easy to do We proposal: Measuring the current and post-calculating the energy dissipation with a defined arc Model Calculating the arc energy Arc Model Proposal for vacuum tubes: Series connection of DC Voltage source 100V and Resistor 200mOhm. Simulations provide good basis for later verification System optimization can be easily done in simulations 6 5/11/2012
BASIC MODEL 7 5/11/2012
STORED ENERGY Basic model with a 2 – pole RLC filter network System parameter 35kV / 3.5A, a rather small system. ARC energy specifications 15 Joule Stored energy is much higher Parameter Value Stored Energy Filter Inductor 16 mH 0.1 Joule / 6 Joule 5 mH 0.03 Joule / 15 Joule Filter Capacitor 200nF 123 Joule High Voltage Power 60 modules 3420 Joule Supply 57 Joule / module Cable 100 pF / meter 0.06 Joule / meter 8 5/11/2012
ENERGY DISSIPATION Where is the energy dissipated in case of a short? What happens with the stored energy in the filter QL QC? Simulation model parameters: Turn off delay 10 us Voltage drop in the diodes: 2V / Diode Short circuit model: 100V / 0.2 Ohm 9 5/11/2012
SIMULATION MODEL FILTER LFilter 1 2 out 5m HV-Supply LOAD RFilter 2 200 ARC U5 D2 TOPEN = 100u Dbreak R10 R_ARC 1 10k 0.2 V6 V8 35000Vdc V_ARC 120Vdc 100Vdc R6 1 200n 0.72 IC = -35k ARC TCLOSE = 90u TTRAN = 0.1u 2 RCLOSED = 0.001 ROPEN = 1Meg 0 10 5/11/2012
SIMULATION: 5 MH FILTER INDUCTANCE Discharge of filter cap 200A Inductance current 100A SEL>> 2A I(RFilter) I(ARC:1) I(LFilter) 4.0 2.0 0 51us 100us 150us 200us 250us 300us 350us 400us S(W(R_ARC)+W(V_ARC)) Time 11 5/11/2012
SIMULATION: 5 MH FILTER INDUCTANCE 200A 100A SEL>> 0A I(RFilter) I(ARC:1) I(LFilter) 8.0 about 7 Joule 4.0 0 0.05ms 0.20ms 0.40ms 0.60ms 0.80ms 1.00ms 1.20ms 1.40ms 1.60ms 1.80ms S(W(R_ARC)+W(V_ARC)) Time 12 5/11/2012
SIMULATION: 16 MH FILTER INDUCTANCE 150A 100A 50A SEL>> 0A I(RFilter) I(ARC:1) I(LFilter) 2.0 1.0 0 55.3us 80.0us 120.0us 160.0us 200.0us 240.0us 280.0us 320.0us 353.2us S(W(R_ARC)+W(V_ARC)) Time 13 5/11/2012
SIMULATION: 16 MH FILTER INDUCTANCE 150A 100A 50A SEL>> 0A I(RFilter) I(ARC:1) I(LFilter) 4.0 about 3.3 Joule 2.0 0 0.053ms 0.200ms 0.400ms 0.600ms 0.800ms 1.000ms 1.200ms 1.400ms 1.600ms 1.800ms 1.996ms S(W(R_ARC)+W(V_ARC)) Time 14 5/11/2012
SIMULATION: WITH CABLE 100 METER CABLE ADDED TO THE SIMULATION 705A big oscillation 400A 0A SEL>> -225A I(RFilter) I(ARC_Cab:1) I(LFilt_Cab) 2.0 1.0 0 80us 100us 120us 140us 160us 180us 200us 220us 240us 260us 280us 300us S(W(R_ARC_Cab)+W(V_ARC_cab)) Time 15 5/11/2012
SIMULATION: WITH CABLE AND SNUBBER FILTER SNUBBER RSnubber LFilt_Cab T3 50 1 2 out_cab LOSSY LSnubber 16m 1 2 LEN = 100 100uH L = 250n 0 0 HV-Supply C = 100p G = 10p R = 0.1m 2 RFilt_Cab 200 LOAD ARC U4 D1 TOPEN = 100u Dbreak R_ARC_Cab 1 R8 0.2 10k V5 V4 35000Vdc V_ARC_Cab 120Vdc 100Vdc R4 1 200n 0.72 IC = -35k ARC_Cab TCLOSE = 90u TTRAN = 0.1u 2 RCLOSED = 0.001 ROPEN = 1Meg 0 16 5/11/2012
SIMULATION: WITH CABLE AND SNUBBER 375A smaller peak, no oscillation 250A 125A SEL>> 0A I(RFilter) I(ARC_Cab:1) I(LFilt_Cab) 1.5 1.0 0.5 0 80.0us 100.0us 120.0us 140.0us 160.0us 180.0us 200.0us 220.0us 240.0us 260.0us S(W(R_ARC_Cab)+W(V_ARC_cab)) Time 17 5/11/2012
ENERGY DISSIPATION SUMMARY Where is the energy dissipated in case of a short? Filter Capacitor: Almost everything is dissipated in the filter resistor Filter Inductance: Before shutdown of the PSM the L is charged Energy After PSM shutdown the energy is dissipated in the short and the diodes of the PSM Cable snubber are reducing oscillations and Arc Energy 18 5/11/2012
OPTIMIZATION How can the energy be reduced, measures? Filter can be optimized according operating point. More complex filters instead a simple RLC network. Tradeoff: Filter vs. Energy Using Cable Snubbers for long cables Thomson patented Inverse voltage Operation Mode 19 5/11/2012
KGP5: INVERSE VOLTAGE OPERATION Application example: KGP5 Test stand for Tubes 160 kV / 3.2 MW CW Higher power in pulsed mode 5 us Rise time Arc energy can be set between 2 Joule and 20 Joule This specifications required new solution: Inverse Voltage Operation Mode 20 5/11/2012
KGP5: INVERSE VOLTAGE OPERATION Principle 21 5/11/2012
KGP5: INVERSE VOLTAGE OPERATION Short Circuit Current Simulations Green: output current without inverse voltage operation Red: output current with inverse voltage operation 1.0KA 1.0KA 0.8KA 0.6KA 0.5KA 0.4KA 0.2KA 0A 0A -0.2KA -0.5KA 0s 0.5ms 1.0ms 1.5ms 2.0ms 2.5ms 0s 10us 20us 30us 40us 50us 60us 70us 80us 90us 100us i(v2) i(v2) Time Time 22 5/11/2012
KGP5: INVERSE VOLTAGE OPERATION Short circuit Test on Tube teststand Adjustable arc energy 2 – 20J Main Issue with IVO was the 20J not the 2J 2Point Regulation implemented Top Trace: Vout = 102kV; Energy Setting = 2.5J Charge Measured 29mAs (2.9J @100V) Bottom Trace: Two point regulation until energy is reached 23 5/11/2012
KGP5: INVERSE VOLTAGE OPERATION Two point regulation for a defined Q 24 5/11/2012
SUMMARY Summary Bigger capacitors or inductors des not necessarily mean more energy in the arc. Considering the whole system is important! Degrees of freedom allow optimization therefore it is important to know the real requirements. May be an iterative process together with the customer. Thomson’s Inverse Voltage Supplies can reduce the energy to a minimum. 25 5/11/2012
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