Superconducting Power Grid – Cryogenic IssuesBy Prof. V. V. Rao, IIT KHARAGPUR

DAE BRNS Theme meeting on LiquidDAE‐BRNS Theme meeting on Liquid Helium Plants, Cryogenics Systems and

their Applications, 25‐26th February 2013, Kolkata

Activities at Applied Superconductivity LaboratoryActivities at Applied Superconductivity LaboratoryCryogenic Engg Centre IIT KharagpurCryogenic Engg Centre IIT KharagpurCryogenic Engg. Centre, IIT Kharagpur Cryogenic Engg. Centre, IIT Kharagpur

SMES

Power Grid

HTSC Generator

HTSC Transmission

cables

HTSC Fault Current Limiter

HTSC Transformers HTSC Motors

Power Grid

BHELCPRI

&P CG, Power BHEL BHELBHEL &Power Grid

CG, Power Grid BHEL BHEL

Future Smart Power Grid (Superconducting)

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1SMES storing Li2energy in S.C. inductor Retrieving the energy to utility loadwhen required.

Using cable‐in‐conduit type S.C. wires, thousands of amperes of current can be made to flowthrough the S C coils for storing large amounts of energy which can be fed back to the load

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through the S.C. coils for storing large amounts of energy, which can be fed‐back to the loadwhen the main‐supply fails. More efficient than pumped hydro and battery storagemethods

Superconducting Magnet along with LHe Storage and power electronics housed in Trailer

SMES System Manufactured by AmericanSMES System Manufactured by AmericanSuperconductor Crop., is used by militarybases to extend battery life.

Trailers house SMES units at Tinker Air Force Base in Okalahoma city to enhance

data protectionp

Portable SMES

Very Large Scale SMES for Blackout Solutions

Parameter / Unit JAPAN USAStored energy (MWh) 5,000 5,500

Output power (MW) 1,000 1,000

Coil Current (kA) 707 765Inductance (H) 71.8 67.6Peak field (T) 8 4 7 0Peak field (T) 8.4 7.0

Conv. Efficiency 0.95 0.94

Cryogenic loss (MW) 6.0 5.3He temperature (K) 4.2 1.8p ( )Coil diameter (m) 400 376 400 1568Coil height (m) 10.8 18.0 10.8 15

No. of turns 330 112

Conductor Length (km) 403 574Conductor Size (cm) 21 x 10 13.5

Material Nb3Sn NbTi

Overall Weight (Ton) 25 000 24 000Overall Weight (Ton) 25,000 24,000

Underground structure 3‐tunnel trench

Depth (m) 150 15

SMES development at IIT Kharagpur

0 5 MJ S d i i

SMES coil

(42 cm O.D. and 44 cm height

0.5 MJ Superconducting magnetic energy storage (SMES)

(4 cm O. . and 44 cm heightNbTi Conductor)

Quench and magnetic field gsimulations of HTS‐SMES coils

by Opear‐3D

The Superconducting fault current limiter (SFCL)

Electric power network without FCL

The Superconducting fault current limiter (SFCL)

Electric power network with FCL in transmission line

The Superconducting fault current limiter (SFCL)

Key characteristics of Fault Current Limiters based on superconducting materials

Under normal operation a fault current limiter inserts negligible impedance into thet knetwork

When a fault occurs the limiter‘s impedance rises rapidly, reducing the current flowingthrough it

CURL10, 10 MVA SFCL

Indian power system is expanding at exponential rate with power demandd h 400GW b 2022expected to reach 400GW by 2022.The Corresponding addition of these generation capacity is planned in theresource rich areas of North‐Eastern and Eastern part of the country. However, theload centers are mostly at Northern, Western and Southern parts. Hence totransmit this generated energy to the distant load centers, very large powertransmission cables are required.Establishing such a large transmission network by conventional overhead linesinvolves socio-economic and technical challenges that includes Right‐of‐Way(ROW) availability environmental protection reduction of transmission losses and(ROW) availability, environmental protection, reduction of transmission losses andConductor Volume, control of fault levels, cost optimization etc.

HTS cables (2G-YBCO) cooled to cryogenic temperatures (65-77K) candd th i W k i i i d i i h i taddress these issues. Work is in progress in designing such cryogenic systemskeeping in mind AC Losses, Heat‐in‐leak, reliability and safety aspects

Cold Vs Warm Dielectrics

Cold dielectric (Within Vacuum Vessel)Dielectric at LN2 Temperature

Warm dielectric (Beyond Vacuum Vessel)Dielectric at Room TemperatureDielectric at LN2 Temperature Dielectric at Room Temperature

Has low losses Generates higher lossesPower capacities – 3-5 times theconventional cables

Power capacities- double of conventionalcables

Technical challenges due to temperaturedependent properties of cold dielectricinsulation

Less technical challenges due to use ofconventional dielectric insulation

HTS t b d hi ldi l L k f HTS hi ldi lt i ddHTS tapes can be used as shielding layers to contain magnetic fields, decreasing the amount of eddy current loss. Neighbouring cables can be closer

Lack of HTS shielding can result in eddy currents in the cryostat and other components at higher currents. Neighbouring cables cannot be closer to avoid Jc degradation

Design Issues for Cooling of HTS Cables

Electrical ThermalLosses

A.C. Losses Dielectric Losses

Thermal

Conduction and Convective losses Heat Leaks

Fluid Mechanics

Pressure Drop Friction factor

Material Science

Pressure Drop Friction factor

Mechanical

Former Materials Insulation Materials

Mechanical

Bending Radius Fracture Toughness Twist Pitch of HTS Tape

Different Cooling Schemes for High Tc Superconducting Cables

CLOSED LOOP COOLING SYSTEM (COURTESY: NEXANS)

Cryorefrigerator (Brayton,Stirling Cycles)

OPEN LOOP COOLING SYSTEM (COURTESY: NEXANS)

TERMINATION with CRYOGENIC COOLING

FIGURE ‐ Front‐view of the 25‐m HTS‐FCL cableand its corresponding 3‐phase terminationslocated at the HTS cable test facility at the OakRidge National Laboratory, USA. The HTS‐FCLcable exits the building after the firsttermination and re‐enters the building in frontof the second termination.

HTS Motors: Advantages• High Power Density: The HTS field winding produces magnetic fields higher than those with g y g p g g

conventional machines, resulting in smaller size and weight.

• High Partial Load Efficiency: HTS motors have higher efficiency at part load (down to 5% of )full speed) that results in savings in fuel use and operating cost. The advantage in efficiency

can be over 10% at low speed.

• Low Noise: Lower sound emissions than conventional machines.

• Low Synchronous Reactance: HTS air‐core motors are characterized by a low synchronous reactance which results in operation at very small load angles. Operating at a small load angle provides greater stiffness during the transient and hunting oscillationsangle provides greater stiffness during the transient and hunting oscillations.

• Harmonics: Tolerate power grids with high harmonic content.

C li l d i i i i Fi ld i di l lik• Cyclic load insensitivity: Field windings operate at nearly constant temperature unlike conventional motors and, therefore, are not subject to thermal fatigue.

• Maintenance: HTS motors compared to conventional motors will not require the common• Maintenance: HTS motors compared to conventional motors will not require the common overhaul, rewinding or re‐insulation.

Cryogenic Cooling of Rotating HTS Machines

•A Helium Transfer Coupling (HTC) is a device that puts the cryogen in and out from theA Helium Transfer Coupling (HTC) is a device that puts the cryogen in and out from thestationary cooling system to the rotating part of the HTS motor.•We have to maintain field‐pole HTS coils at the cryogenic temperatures during rotation.

HTS Transformers for the power grid – half the size and weight‐ Double the efficiencyg y

Benefits:• Greater efficiency• Greater efficiency• Compact, lighter and quieter• Can run indefinitely above rated

power without affectingtransformer lifeD t i li il lik• Do not require cooling oil like

conventional transformers, thuseliminating the possibility of oilg p yfires and environmental hazards

• Do not Require IronHence, Compact and Lighter

S d iS d i

Superconducting Power Cables

Superconducting Power Cables

S d ti F ltS d ti F ltSuperconducting Magnetic Energy Storage

Superconducting Magnetic Energy Storage

Superconducting Fault Current Limiters

Superconducting Fault Current Limiters

Role of HTS materials for power application –

growing rapidly

Role of HTS materials for power application –

growing rapidlySuperconducting Superconducting Superconducting Superconducting Cryogenic Refrigerators

with High Cooling Capacity are being

developed

Cryogenic Refrigerators with High Cooling Capacity are being

developed

Generator/MotorGenerator/Motor TransformersTransformers

Interaction with R&D Institutes and Industries

Central Power Research Institute, Bengaluru Power Grid Corporation of India Limited, DelhiBharat Heavy Electrical Limited, HyderabadCrompton Greaves MumbaiCrompton Greaves, MumbaiSchneider Electric, Bengaluru

Looking for collaboration with Academic Institutes

Future Hope: Future Hope:

Prof. V. V. Rao, Cryo. Engg. Centre, IIT Kharagpur