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Power network disturbances 1

Power network disturbances 1. Short duration (transients) Voltage sags/dips  momentary (few 100ms up to sec) reduction of power caused by: - abrupt increases in load currents (short circuits or faults, motor starting, electric heaters turning on, etc.)

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Power network disturbances 1

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  1. F. Formenti - TB 17/03/04 Power network disturbances 1 • Short duration (transients) • Voltage sags/dips  momentary (few 100ms up to sec) reduction of power caused by: • - abrupt increases in load currents (short circuits or faults, motor starting, electric heaters turning on, etc.) • - abrupt increases in source impedance (typically loose connections) • Note: sags are mostly generated by equipments internal to the power network, rarely they come from upstream • Voltageswells  momentary (few 100ms up to sec) increase of power caused by: • - abrupt reduction in load currents on a circuit with a poor or damaged voltage regulator • - a damaged or loose neutral connection.

  2. V.sag ~75ms V. Interruption ~2sec F. Formenti - TB 17/03/04 Power network disturbances 2 • Voltageinterruptions  temporary (typically order of secs up to min) power missing caused by: • - power system faults, equipment failures, and control malfunctions • Voltage spikes (surges)  sharp (order of msec or less) and high increase of voltage caused by: • - ON/OFF of inductive/switching equipments, storm activity

  3. F. Formenti - TB 17/03/04 Power network disturbances 3 • Long duration (failures). • Sine wave distortions (harmonics, dc offsets and notching)  distortion of sine wave created by heavy non linear loads or poorly designed converters • Generate heat in the neutral conductor and transformers, tripping of circuit breakers, malfunction of UPS systems and generator systems, malfunction of sensitive devices • Steady state over/under voltages  RMS variations of thesupply voltage for period >1 minute • Generally due to weak designed power systems in presence of variable loads

  4. F. Formenti - TB 17/03/04 Principal causes for disturbances at CERN • Lightning on 400kV/130kV • Shorts outside or inside CERN • Inrush currents or switching ON/OFF of large electrical loads (~80%) • Switching ON of large capacitor banks or Static Var Compensators • Mains faults • Emergency stops • Others (human errors) • CERN power network is generally good; • however it is an industrial environment, • therefore not totally exempt from noise (~10%)

  5. FAST SURGE ARRESTOR F. Formenti - TB 17/03/04 CERN Power distribution 400KV (or 130KV, backup for critical loads) nsec SPIKES DISTURBANCES 110MVA 66KV BACKBONE FOR ENERGY DISTRIBUTION 18KV VERY DIFFICULT TO IDENTIFY POLLUTING DEVICES 1250KVA 2000KVA 400V 400V 400V NOISY DEVICE INTERNAL NOISE “CLEAN” USERS USERS

  6. F. Formenti - TB 17/03/04 Plots of disturbances on 18kV (years 2000, 2001, 2002) Order of 100 to 150 total events per year Few disturbances at larger/smaller amplitude (unbalancing, closely located shorts): 180% to 10% @ 50 to 200ms Rare cases of larger duration and small amplitude: 10% to 110% @ 200 to 1000ms Majority of network disturbances (load changes, inrush currents, remotely located shorts): 80% to 120% @ 50 to 200ms NOTE: Spikes @ 0.1 to 1ms can be detected on 400V supply (not recorded on 18kV plots). Due to their low energy content, are normally filtered by the users.

  7. F. Formenti - TB 17/03/04 Main quality parameters of LHC 400/230V distribution system • Parameters for the normal supply (LHC-EM-ES-0001 REV. 2.0): • # Vnominal = 400/230V, +/-5% typ, +/-10% Max • # Fnominal = 50Hz, +/-0.5% Max (IEC 61000-2-4) • # THD <5%, i.e. better than IEC 61000-2-4 • # Peak mains surges = 1.2kV for 0.2ms • # Mains overvoltages = +50% of Vn for 10ms • # Voltage drops = -50% of Vn for 100ms • Quality parameters needed for: • - users to design equipments with proper margins • - assuring compatibility among users of power network

  8. F. Formenti - TB 17/03/04 Main requirements for user equipments on 400/230V • Inrush currents < 14 * I nom RMS for Ptot < 5kW • < 8.5 * I nom RMS for Ptot > 5kW • Harmonic generation • comply IEC 61000-3-2 for I < 16A/phase • comply IEC 61000-3-4 for I > 16A/phase • EMC emission and immunity • CERN equipments shall follow a number of standards as listed in document LHC-EM-ES-0001 REV. 2.0 (Remark: this is for “field specialists”) • Equipment approval • quality check of CERN TS-EL for systems with P > 30kVA

  9. 230V 1 ms 1 s 230V 1 ms 1 s 230V 1 ms 1 s F. Formenti - TB 17/03/04 PA8 (CAST) 230V Power quality measurements 30/4/04 to 22/5/04 6 months recording CONCLUSIONS All recorded events are within the “Main quality parameter of the LHC 400/230V distribution system” specifications. Note that swells are longer, but with lower amplitude than specs. 22/5/04 to 2/7/04 4/7/04 to 28/10/04

  10. NOMINAL CURRENT INRUSH CURRENT: 35A PEAK (x2.2 In) FOR 30ms F. Formenti - TB 17/03/04 WIENER VME Crate Power Supply INRUSH CURRENT IS MODERATE, BUT IF DIFFERENTIAL PROTECTION USED, SUM OF INRUSH CURRENTS MAY HAVE TO BE TAKEN IN CONSIDERATION NO POWER CONSUMPTION (MICROPROCESSOR IDLE): APFC NOT OPERATING, SOME DISTORTIONS (THD=33%) BUT AT LOW CURRENTS FULL POWER CONSUMPTION: APFC OPERATING, ALMOST NO DISTORTIONS (THD=4%). HOWEVER STILL RECOMMENDED TO PROTECT OVERLOAD ON NEUTRAL AND BALANCE SUPPLIES ON DIFFERENT PHASES (MINIMIZE FUNDAMENTAL COMPONENT ON NEUTRAL) EXAMPLE OF OLD LEP TYPE VME POWER SUPPLY (WITHOUT APFC): FULL POWER, LOT OF DISTORTIONS (THD=75%)

  11. F. Formenti - TB 17/03/04 Case of PCs (desktop or rackmount) • PROBLEMS KNOWN FROM THE PAST • Low quality power supplies switch mode (poor APFC, cheap power supplies) • For many PCs of same type non linear load creates large harmonics that sums up • 3rd harmonic important for consequences on neutral loading (protect neutral) • Generally no soft start and inrush currents are high (x20 In) • Voltage dip of ~20ms at power ON and risk of differential switch malfunctioning • RECOMMENDATIONS FOR THE FUTURE • BUY CERTIFIED “CE” LABELLED PCs (pls ask official certification for clarity) • Balance the phases as much as possible • Schedule the power ON by groups of PCs (limit inrush currents) • AC Power surge protection: costly and not strictly necessary if conforming to rules

  12. F. Formenti - TB 17/03/04 Conclusions. • Problem of supply quality not straight forward (many causes, often from users) • CERN surge protection is adequate: • - no cause of damage; no additional protection needs for ALICE • Load distribution will be planned (Alice in contact with TS-EL experts ) • Quality parameters of 400/230V CERN supply exist (based on measurements) • Local disturbances are the real problem: • -user responsibility to respect quality parameters • - users MUST conform to rules and install CERN certified devices • - Isolate noisy equipments through transformers • - Balance the loads on the phases • - Schedule power ON of large equipment farms (limit inrush currents) • In case of problems ask for power monitoring and support of TS-EL

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