Medium Voltage Motor Control

Variable Frequency Drive

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Variable Frequency Drive: motors

VFD for use with:• Asynchronous motor (squirrel cage induction

motor)• Synchronous motor

– Additional: control of excitation current

• Slip ring induction motor• Slip ring synchronous motor

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VFD: Technology / control method

• Standard VFD– Open loop control (VVVF)– Closed loop control– Fans, pumps, compressors

• Vector control VFD– Open loop vector control (sensor-less vector control)– Closed loop vector control– High starting torque; conveyors, kilns, mills, lifts etc.

• Active front end– Open loop vector control– Closed loop vector control– Regenerative applications; bidirectional flow of energy between mains

and motor; e.g. rolling mills

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VFD: Range – voltage and power

• Voltage (kV)– 2.3, 3.3, 4.16, 6, 6.6, 10, 11, 13.8; 50 / 60 Hz– Mains and motor voltage need not be the same!

e.g. 13.8 kV mains, 4.16 kV motor, or6.6 kV mains, 11 kV motor

• Power range

VFDs can be applied to a motor of lower kW rating

• Rated ambient temperature: 45 degree C

Voltage 3.3 kV 4.16 kV 6.6 kV 11 kV 13.8 kVMax kW

(HP)3,600

(4800HP)4,600

(6000HP)7,320

(9800HP)12,200

(16000HP)>15,000(20000HP)

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VFD: configuration

V I/P pulses O/P level/steps3.3 18 13 (6-0-6)4.2 24 17 (8-0-8)6.6 36 25 (12-0-12)11 54 37 (18-0-18)

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VFD: Output waveform

Each power cell has PWM output (L1-L2)L1-L2 output of each cell is connected in series to get MVSeries arrangement of cells provides Multi-level PWM > good for output waveform and input harmonics

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VFD: Performance specifications

Input power factor 0.96 or better– No need for PFC capacitors– Happy electricity provider company– No penalty for poor PF, cash saving, happy accountants!

Harmonics reflected on mains very low (< 5% current)– Comply with IEEE 519– Happy electricity provider company and neighbours– Achieved with 18-24-36-54 pulse configuration

High efficiency: 96% or better, including input transformer– Full energy saving potential realized– Low heat loss in cabinets & electric room > reduced heat load for

air-conditioning equipment (e.g. <40 kW for 1 MW drive)– Low net installation cost

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VFD: 18+pulse VFD

Extract from a technical paper by WEG

AuCom VFDs offer a minimum of 18-pulse front-end rectification.24 pulse for 4.2 kV36 pulse for 6.6 kV

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VFD: Performance specifications

Harmonics reflected on motor very low, <2.5%– Clean output waveform to motor– No de-rating of motor > motor can be used up to its full capacity– Suitable for standard motors and retrofits– No stress on insulation of motor or cables– No output filter necessary– No vibration or stress on bearings– No resonance of the motor– DC component less than 1% > all torque produced is for useful work– Very long motor cable length possible > good for Oil & Gas applications,

where VFD is in safe area but motor & pump is in hazardous area with long cable run.

– PULSE NUMBER DOES NOT IMPACT MOTOR WAVEFORM

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VFD: Output waveform to motor

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AuCom VFD offers 17 level (8-0-8) for 4.2 kV and 25 level (12-0-12) for 6.6 kV, together with PWM control.This makes the output waveform to motor very sinusoidal.Extract from a technical article by WEG:

VFD: Performance specifications

Voltage-source inverter technology with multi-level PWM control

– Stable, mature and proven technology– VFD design is independent of motor design parameters (as against

with Current source inverters)– Use IGBT as devices for inverter section

• Fine control to achieve near sine-wave• Output short-circuit proof design

– Reliable VFD operationBuilt-in soft startMTBF > 27500 hoursMTTR < 15 minutes

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VFD: Dry-type transformer

– Built in with VFD, saves cabling > lower installation cost

– No oil or other fluids > safe environment– Insulation class H (rugged design)– Fan-cooled design– Protection with embedded RTDs– Multi-pulse operation achieved by phase shifted

secondary windings– Secondary windings electrically isolated from

one another– Only power cabling required is from upstream

breaker to VFD, and from VFD to motor– Designed to suit mains and motor voltage

specifications

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VFD: Transformer

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VFD: Control configuration

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VFD: Product construction features

• Conformal coating on PCBs• Surge arrestors• Space heaters in power cell and

transformer cabinets• Viewing windows for mains and motor

cable termination chambers• Lamps for each viewing window to

facilitate viewing• Start and stop push buttons on panel

door• Indication lamps: MV mains ON, VFD

running, VFD fault• RAL 7032

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VFD: Control

• Set via HMI, choice of languages – English, Spanish, Portuguese• External analog signal, 4~20 mA

• Output frequency or• Process variable

• Communications bus• Modbus (built-in)• Profibus DP• DeviceNet• TCP / IP

• Start/stop commands can also be from local or remote, independent of location of frequency setting

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VFD: Application features

• Open or closed loop control• Open: frequency as per set point• Closed: frequency determined by process variable, such as pressure,

level, temperature etc.• Ride-through, 35% dip without tripping• Auto restart, on recovery of mains supply. VFD checks motor

speed automatically and catches up.• Motor protections built in: Overvoltage, overcurrent, under-

voltage, phase loss, overload, overheat, earth fault, short circuit.• Minor and serious faults. VFD continues to operate with minor

faults

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VFD: Application features, optional

• Mains voltage different from motor voltage• External 3-phase 380 V AC control supply

• With “standard” 1-phase 110/220/240 V AC control supply, when the mains supply is OFF, the fans of VFD are also OFF

• With 3-phase 380 V AC control supply, the fans remain operational even when mains supply is off.

• Rotating start, for fan application• Power cell bypass (for 4.16 kV models and above)• VFD bypass (to run the motor at fixed speed if VFD fails)• Input / mains side switchgear• Multi-motor start, with sync transfer function• Master / slave operation, for 2 or more VFDs in tandem

• Soft coupling or hard coupling• PLC for high-end functionality

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Panels with VFD bypass system

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VFD: Performance features

• Mains voltage tolerance: +15, -20%• Mains frequency tolerance: +/- 10% (output frequency held steady)• Overload (standard): 120%for 120 s (150% for 3 s)• Acceleration / deceleration time: 0~1600 s, programmable• Output frequency range: 0 ~ 120 Hz• Frequency resolution: 0.01 Hz / 0.002 Hz

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VFD: Inspecting filters

• Removing filters for inspection is very easy. Just lift and remove. No tools are needed.

• While the filter is removed, safety of personnel is maintained by the mesh in the panel.

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VFD: Cell bypass feature (option)

• Allows the application to continue operation with 1 or 2 failed cells

• Failed cells are bypassed automatically, the user process does not see any interruption

• Corresponding cells in other 2 phases are bypassed, to maintain neutral point.

• Failed cells can be replaced with a spare one within minutes, due to draw-out construction of power cell

• Available for VFDs for 4.16 kV and above

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VFD: After sales support structure

• Multi-level• Appropriate level comes in to play• Right level of training

1. User’s electrical staff• Trouble shooting, first-aid, essential spares, accurate problem report

2. Service organization in the country• Main responsibility for installation & service, spares

3. Regional service headquarters• Expert advice, spares for the region

4. AuCom, New Zealand• Train the trainers, product & application expertize, spares for business

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VFD: Spares and tools

• No special tools needed for installation and maintenance. Tool list:• Screw driver, cross head, large and small• Screw driver, slotted, large and small• Sharp nose pliers• Diagonal cutting snipers• Wrench, size 8~24 (8 pieces)• Ratchet wrench

• Spares:• Power cells• Electronic PCBs• Fans

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VFD: Power cells

Power cell L (mm) W (mm) H (mm) Wt (kg) Use690 V/ 048A 425 200 400 20 for 48 A VFD690 V/ 061A 425 200 400 20 for 61 A VFD690 V/ 096A 478 246 400 30 for 77-96 A VFD690 V/ 130A 478 246 400 30 for 130 A VFD690 V/ 192A 508 285 455 36 for 154-173-192 A VFD690 V/ 250A 508 285 455 40 for 220-243 A VFD690 V/ 320A 600 325 530 77 for 304 A VFD690 V/ 400A 600 325 530 80 for 400 A VFD690 V/ 500A 711 503 581 130 for 500 A VFD690 V/ 600A 711 503 581 130 for 600 A VFD690 V/ 800A 711 550 578 154 for 800 A VFD

• VFDs of different voltages use the same power cells – only the quantity of cells used in series per phase changes from one voltage to another.

• For power cells > 250 A, a lifting trolley, as shown, is provided with the VFD.

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VFD: Power cells

• We use 690 V rated IGBTs in power cells• On the other hand, many other manufacturers use high-

voltage IGBTs or IGCTs• 690 V IGBTs are used by many LV VFD manufacturers,

hence are available widely and economically.• Therefore, using 690 V rated IGBTs gives the advantage of

reasonably priced spare-parts, while giving the technical advantages discussed earlier.

• When you use an AuCom VFD, you will not have to stretch your maintenance and spares budget!

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VFD: conclusion

• AuCom VFD provides a very balanced solution.• AuCom VFD comes with some unique and exciting features,

aimed at providing:• Good technical design• Good return on your investment• Ease of use and maintenance

• Your local supplier will take care of local pre-sales and after-sales service needs.

• Thank you.

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