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c

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Station layout

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Converter transformer

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The HVDC Converter

Transformer The converter t ransform er

is an important part of anHVDC system.

These convertertransformers are theheaviest equipment in aHVDC converterstation. Single units canoften have a total weight of200-550 tons.

High AC and DC voltagesput specific requirement onthe dielectric insulation.

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converter t ransform er

converter

t ransformersconnect the ACnetwork to the

thyristor valvebridge, and adjustthe voltage on thevalve side to asuitable level

based on the DCvoltage used fortransmission.

Largest HVDC transformerSingle phase 3 winding

Power: 621/310,5/310,5 MVA

Voltage: 230/212/212 kV

Connection: Yn/Y/D

DC voltage: 500 kV

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AC

System

Dc line

Three phase 3-winding Transformer: one unitfeeding 12-pulse bridge,

6 pulse

bridge 1

6 pulsebridge 2

12 pulse

bridge

One pole

of HVDC

terminal

one end of Monopolar HVDC system

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converter t ransform er

The conver ter t rans formerscan be ofdifferent design styles depending on thepower to be transmitted, and the transportlimitations.

What influences transformer properties?

Size, how is it affected by different properties?

Power is the main driver for size, but

Voltage, both AC-side and DC-side voltage, heavily

influences size, and

Frequency also affects size (smaller core at 60 Hz)

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Most common core types

Single phase

2 wound limbs 1 wound limb and

2 side limbs

2 wound limbs and

2 side limbs

For Lower Transport Height

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Most common core type

3-phase

3 wound limbs3 wound limbs and 2 side limbs

For lower transport height

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converter t ransform er

The most common typeis a single-phase-three-winding design. If singlephase transformers are

used then three identicaltransformers are thenneeded per converter.

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Converter Transformer Functions

1. Acon verter transfo rmer

can act as a galvanic barrierbetween the AC and DC systems preventing the DC potential toenter the AC system.

2. Reactive impedance in the AC supply to reduce short circuitcurrents and also control the rate of rise in valve current duringcommutation.

3. Converter Transformers provide voltage transformationbetween the AC supply and the HVDC system.

4 Converter Transformers often can supply AC voltages intwo separate circuits with a relative phase shift of 30 electrical

degrees for reduction of low order harmonics, especially the5th and 7th harmonics.

5 Converter Transformer models often have a fairly large taprange with small steps to give necessary adjustments in supplyvoltage.

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12-pulse converter bridge

Star -star

connection

Star- Delta

connection

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More about converter transformers

http://localhost/var/www/apps/conversion/tmp/scratch_1/09.+HVDC+converter+transformers+.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/09.+HVDC+converter+transformers+.pdf