Load Follow and Part Load Operation

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2 IAEA Technical Meeting TM Erlangen, October 6 8, 2014 Load Follow and Part Load Operation Use of Variable Frequency Drives (VFD) Wolfgang Michel IBL-AD (retired) Christian Peter IBL (Senior Advisors Electrical Systems) christian.peter@areva.com RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 2

3 Content Reasons for load follow and part load operation, use of variable Frequency Drives (VFD) Potential applications and solutions Historical investigations for main feed-water pumps Different schemes Economical aspects VFD equipment, applications in BWRs and PWRs AREVA-Siemens VFDs in the USA (references) Practice in the USA Motor Generators and VFDs in the Lungmen BWR RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 3

4 Load follow- and part load operation Changing power generation infrastructure requires higher flexibility of NPPs Increasing number of NPPs in some countries leads to more part load operation German Energiewende uncontrolled energy flows into neighbor countries Use of Variable Frequency Drives (VFD) Speed control of large motor driven pumps Optimizes load follow- and part load operation House load reduction Precise control of system flows Reduce high maintenance efforts on control or throttle valves Reduce start up currents of large motors Lower winding temperatures of motors support slower ageing Increased motor health result in longer life times Replaces aging motor generators for recirculation pumps in BWRs RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 4

5 Potential Applications Potential Applications of Variable Frequency Drives (VFD) or Speed Regulation Large drives: RCP = Reactor Coolant Pumps (PWR) or Reactor Recirculation Pumps (RRP in BWR) FWP = Main Feed Water Pumps (PWR and BWR) MCP = Main Condensate Pumps (PWR and BWR) CWP = Main Cooling Water Pumps (PWR and BWR) They make up ~ 90% of auxiliary power (~80 MW for a 1300 MW PWR) They are all no safety systems Electric by pass reduces impacts of disturbances within power electronics Potential Solutions Feed water pumps Recirculation pumps Other applications See following slides RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 5

6 Historical Development Investigations for main feed water pumps (largest drive > 13 MW) Application of VFD-s regularly investigated by AREVA in the past Four options were analyzed and compared: Electric motor with constant speed Electric motor with constant speed and hydraulic regulation gear Steam driven pumps with speed regulation Speed regulated electric motors (VFD) Results: All options are technically feasible. Experience from industry proved reliable operation in comparable applications. Some solutions are standard practice in other countries. The constant speed drive can be build at the lowest possible costs (standard solution in German NPP-s) It is optimized for base load operation Short periods of part load or load follow operation do not disturb plant economics However extended periods of non base load operation favor the VFD RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 6

7 Different Schemes (1) Motors with Constant Speed Variable Frequency Drives (VFD) M M M M M M Unregulated operation Optimized for full load Simple scheme 3 x 50 % High start currents of motors Lowest space and investment No active power electronics Individual speed control Good adaptation to load follow and part load 3 x 50 % motors and VFD electronics Low start currents Large space and high investment More active components RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 7

8 Different Schemes (2) 2 Constant Speed Motors + 1 VFD Alternative Flow Regulation of FWP M M M Patent N.: DE P Simplified system Less space, lower costs One VFD + electric by pass Covers full power range Staggered operation of pumps Control of water flow via bypass turbine Energy recovered in a turbine driven generator Flow regulation with aid of a VFD Less efficient than VFD-s but much less investment and less space! Can be back fitted. RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 8

9 Economical Aspects Capitalization of saved auxiliary power and other benefits Specific costs of MWh Quantitative relation of part load vs. full load operation in hours E.g.. 50% of time full load and 50% of time half load Potential energy saving at part load Part load curves of pumps and system to quantify reduced power consumption Investment (engineering, hardware, installation) Reduction of maintenance works Lower wear and tear in throttle valves (e.g. within feed water system) Longer motor lifetimes Sum of above parameters allow calculation of ROI Realized projects show, that an ROI of 5 years can be reached RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 9

10 VFD Equipment Perfect Harmony inverter Siemens Pittsburg Redundant semiconductor cells Low distortion, sine wave output No specific motor required Transport arrangement Container can be stationed in NPP No separate building RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 10

11 VFD Application in a BWR Feed Water Pumps Primary Plant: - Reactor Recirculation Pump - Cooling water for Rx - Typically 2 RRPs per Rx - One VFD per RRP Secondary Plant: - Condenser Circulating Pump - Cooling water for turbine - Typically 3-6 pumps/plant Key Attributes: - Critical to Generation - Non-safety related Rx Recirc Pump Application Condenser Circulating Pump Cooling Water Pumps RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 11 11

12 Variable Frequency Drives (VFD) mögliche Anwendung beim DWR Feed Water Pump Reactor Coolant Pump Main Cooling Water Pump RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 12

13 AREVA-Siemens VFDs in the USA 26 Reactor Recirculation Pumps in Operation Columbia 2 VFDs 1995 BFN 1, 2, 4 6 VFDs 2003, 2004, 2007 Hatch 1, 2 4 VFDs 2009 Quad Cities 1, 2 4 VFDs 2009, 2010 Brunswick 1, 2 4 VFDs 2010, 2011 Limerick 1, 2 4 VFDs 2012, 2013 Dresden 3 2 VFDs Condensate Circulation Pumps in Operation Millstone 2, 3 10 VFDs 2009, Reactor Recirculation Pumps to be installed Dresden 2 2 VFDs planned for 2013 Peach Bottom 3, 2 4 VFDs 2015, 2016 RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 13

14 AREVA-Siemens VFDs in the USA Practices in the USA Most applications are the Recirculation Pumps in BWR-s Some older BWRs use hydraulic speed regulation gear Low regulation accuracy (~ 5%) leads to lower usage of reactor power Lower efficiency and higher losses require large HVAC systems VFDs offer: higher accuracy of speed regulation, higher usage of reactor power (up to 5%) Savings in reduced house load power Lower maintenance efforts as motor/generators become obsolete But also some applications within PWRs Some countries prefer electric driven feed water pumps (3 x 50%) This usually is the largest electrical load (up to 15 MW per motor for the EPR) VFDs are an excellent alternative to cope with part load and load follow operation gang Michel Load Follow and Part Load Operation October Eigentum AREVA NP GmbH - RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 14

15 Lungmen Motor Generators and VFDs (1) Motor Generators (MG) provide safe run down or cast down energy for reactor internal recirculation pumps within BWR-s Some pictures on next slide Typical Data for MG-sets (example Lungmen) Motor 3,8 MW, 13,8 kv (Siemens) Generator 5,2 MVA (AvK with larger rotor to provide required inertia) Inertia: 4000Kgm2 to provide Safe Run Down Energy for several seconds Reactor internal Recirculation Pumps (RRP) 10 Pumps in total, 950 kw each, low inertia, pump stops nearly instantaneously upon loss of energy Speed regulation by 10 VFD converters to adjust reactor power 2x3 RRPs supplied via 2 MG-sets to provide safe run down energy Speed regulation and cast down energy provided by separate equipment 4 RRPs directly supplied from respective grid RESTRICTED AREVA - AL: N-ECCN: N - AREVA Folie 15

16 Lungmen Motor Generators and VFDs (2) Wolfgang Michel Load Follow and Part Load Operation Ocober Eigentum AREVA NP GmbH - RESTRICTED AREVA - AL: N-ECCN: N - AREVA Folie 16

17 Lungmen Motor Generators and VFDs (3) Discussion of Pros and Cons: Motor Generator (MG) constitutes a robust technology High additional inertia required to ensure run down time of several seconds External fly wheel on the shaft or oversized rotors of both generator and/or motor In all cases this kind of equipment is not standard High permanent losses (~ 600 kw) at full load to be removed by HVAC, requires another ~200 kw (fans and cooling machine) Dual energy conversion: MG sets and inverters influence on reliability Wear and tear of rotating equipment, maintenance, overhaul, lifetime Large space required, separate room Vibration isolation and earth quake design impose high requirements RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 17

18 Lungmen Motor Generators and VFDs (4) Proposal for an alternative to provide safe run down energy Reduce number of serious connected devices (MG-sets and Inverters) Avoid use of large MG sets: Lower losses Less space Higher reliability Integrated solution combines speed regulation and storage of cast down energy within the VFD electronics Two alternatives, both connected to the DC intermediate circuit of the VFD inverters: Ultracaps allow storage of high levels of energy in limited space (passive solution) Usage of a small reversible Motor/Generator with a fly wheel (active solution) RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 18

19 [Editor and Copyright, 2014]: AREVA GmbH Paul-Gossen-Straße Erlangen, Germany. It is forbidden to reproduce the present publication in its entirety or partially in whatever form without prior written consent. Legal action may be taken against any infringer and/or any person breaching the aforementioned conditions. Subject to change and error without notice. Illustrations may differ from the original. The statements and information contained in this brochure are for advertising purpose only and do not constitute an offer of contract. They shall neither be construed as a guarantee of quality or durability, nor as warranties of merchantability or fitness for a particular purpose. These statements, even if they are future-oriented, are based on information that was available to us at the date of publication. Type, quantity and characteristics of goods and services are subject to formal individual formal contracts. RESTRICTED AREVA - AL: N-ECCN: N - AREVA Page 19

20 Load Follow and Part Load Operation Use of Variable Frequency Drives (VFD) Wolfgang Michel IBL-AD Christian Peter IBL Senior Advisors Electrical Systems and Projects IAEA Workshop in Erlangen, October 6 8, 2014 Thank you for your interest