balanced three-phase grid supply for traction power
DESCRIPTION
Proposed technology for balancing the single-phase traction power on the three-phase grid. Benefits include the elimination of phase-breaks and isolation of traction power harmonics from the grid supply.TRANSCRIPT
Balanced Three-Phase Grid Supply for Break-Free
Single-Phase Traction
Dinesh BansalChief Electrical Engineer (Ret.)
Indian Railways
Presented by Karl Berger, P.EDCM, Inc.
Joint Rail Conference 2012 Philadelphia
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Indian annual GDP growth at 7% for the last decade.
Transport & allied sectors growth 15% last year. IR annual revenue US$21B mainly by bulk
commodities like coal, iron ore, cement and fertilizer.
64,215km route miles, 33% electrified. 4,000 electric locomotives carry 63% freight &
51% passengers. Heavier freight & longer passenger trains are
needed to haul readily available business.
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IR’s Growing Electrified Network
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Design goals for traction power system:◦ Low cost, ◦ Energy efficient, ◦ Reliable
Minimize the unbalance imposed on the three-phase utility grid by the single-phase traction load.
Isolate load harmonics from the utility supply.
Problem Statement
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Typical Practice 25kV 50 or 60Hz
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Phase Break
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Unbalance at individual substation drawing power from two phase wires can be 100% of load (15 minutes) for multiple stations.
Power factor typically 0.7 lagging with rectifier locomotives.
Harmonics could be 20-30% mainly 3rd, 5th and 7th, causing distortion PF and higher losses.
Demand charges and low PF penalty can be 10 -20% of energy bill;
Harmonics can be reduced but not eliminated with LC filters.
Large peak loads drive up utility demand charges.
Problems
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Proposed Solution
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Improved Voltage Regulation
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Synchronous power supply at 25kV 50Hz with paralleled feed has no need for phase breaks.
Relies on proven technology used on 15kV 16.7Hz European systems and 12kV 25Hz Amtrak system.
Regenerative braking power feed back to 3-phase grid possible through dc link at traction substation.
Improved locomotive and Head End Power reliability through elimination of shut downs at Phase Breaks.
Load spread over multiple parallel substations reduces peak demand charges.
Possibility for selling reactive power to the utility. 25kV break-free parallel feed could permit 40% higher
loading of existing infrastructure. Parallel feed improves operational reliability during
substation outage.
Anticipated Benefits
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Section Break
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ABB PCS 6000 (15MW 50Hz to16.7 or 25Hz)
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Load factor improvement due to parallel load sharing (double-end feed).
Reduced filter requirements at TSS with dc buffer to grid.
Balanced unity power factor load on grid. Reactive power to and from grid to
balance grid requirement. Voltage drop and energy consumption
reduced. EHV additional cost 25% for 73% increased
power.
Impact/Analysis
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Additional Capital Investment in two 20MVA converters with magnetic devices at TSS may cost about Rs 75M($1.5m). May cost less for bulk supplies.
Power factor surcharge: Rs 15M($.3m) per year (based on 10% of annual energy charges) may be saved annually.
Contract demand charges: Rs 10M($.2m) may be saved every year by reduction in contract demand from 20MVA to 15MW, by leveling of peak demand by parallel feed from adjacent TSS and unity power factor by 4 Quadrant control of converters.
Elimination of a TSS due to half Voltage drop by feeding from both ends. Saving Rs 100M ($2m) capital investment for new construction projects.
Reduced energy charges due to improved load factor and balanced power drawn at each TSS, would need to be negotiated with the SEB. Estimated savings may be Rs 10M($.2m).
The TSS dc links located 30miles apart may be used to stabilize the grid by meeting reactive power requirement. Grid authority/ SEB could pay for this service.
Increased section capacity due to reduced locomotive failures, can not be valued now.
These are estimates and actual savings may vary based on SEB tariff and load pattern in the system. A payout period of a 3-5 years may be expected.
Cost Benefit Analysis
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132 KV 20MVA magnetics Rs. 25M ($.5m). Power Electronics Rs.40 M ($.8m). $1.5M limit should be doable for a 2X20MVA SS. India has rich experience in magnetics; there are many
national and international companies. Semiconductor manufacturers around the world would
be willing to sell ready made strings of duly protected devices to make up Power Modules.
Academic institutes & industry could develop, if funded, for materials and manpower.
Line of Action
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THANK YOU
[email protected] Dinesh Bansal, Indian Railways
[email protected] Berger, PE, DCM, Inc.