Advances in Grid Equipment Transmission Shunt Compensation

© ABBSlide 114-Nov-16

Advances in Grid EquipmentTransmission Shunt Compensation

Joe Warner, Electric Power Industry Conference (EPIC), November 15, 2016

© ABBSlide 214-Nov-16

Advances in Transmission Shunt Compensation

BoA: Book of Acronyms

MSC/MSR: Mechanically Switched Capacitor/Reactor

SVC: Static Var Compensator

TCR: Thyristor Controlled Reactor

TSR/TSC: Thyristor Switched Reactor/Capacitor

STATCOM: Static Synchronous Condenser

NPC: Neutral-Point Clamped

MMC: Multi-level Modular Converter

IGBT: Insulated-Gate Bipolar Transistor

Excerpt from the BoA

© ABBSlide 314-Nov-16

Shifting transmission system

Synchronous generation retirement

Penetration of distributed renewables and dynamic load

Resulting in

Weak networks with a resonance approaching fundamental frequency

Increased vulnerability to disturbance

Increased requirements for mitigation solutions

Advances in Transmission Shunt CompensationNetwork Challenges

© ABBSlide 414-Nov-16

Advances in Transmission Shunt CompensationNetwork Challenges

National Grid Electric, Ten Year Statement

© ABBSlide 514-Nov-16

Advances in Transmission Shunt Compensation

Network resonances are shifting due to system changes

Resonance frequencies and system damping affected by:

Number of un-tuned shunt capacitor banks (over-compensation)

Cable and T-line charging

Parallel FACTS and HVDC installations (filters)

System loading (active and reactive)

Network Challenges

© ABBSlide 614-Nov-16

Solutions:

Cheap and low-loss for steady-state compensation

Challenges:

Slow switch-in/out and discharge

Network dependent voltage step Δ𝑈𝑈𝑈𝑈 ≈

𝑄𝑄𝑆𝑆

Overcompensation leads to low network resonance and has resulted in inadvertent network collapse

𝑟𝑟 =𝑆𝑆𝑄𝑄

Advances in Transmission Shunt CompensationMechanically Switched Capacitors

52

© ABBSlide 714-Nov-16

Solutions:

Inertia increases system strength and provides fault current

Reactive power compensation without generating harmonics

Natural thermal overload capacity

Challenges:

Smaller output range ( < 100 MW)

Var support provided by automatic excitation control, medium speed

Maintenance

Losses

Advances in Transmission Shunt CompensationSynchronous Condensers

© ABBSlide 814-Nov-16

Solutions:

Fast, continuously variable output

Large sizes available ( > 400 Mvar)

Robust overvoltage capability

Configurable to maximize value

Challenges:

TCR generates harmonics

Filter design dependent on network harmonic impedances

Difficulty operating in a weak network

Output varies with 𝑉𝑉2

Advances in Transmission Shunt CompensationStatic Var Compensator (SVC)

´TCR TSR TSC Harmonic Filters

Static Var Compensator (SVC)

© ABBSlide 914-Nov-16

Three-level NPC concept Pulse Width Modulation

High Switching frequency (>1.5 kHz)

Maximum rating of 100 MVA

IGBT units in series

With IGBTS no voltage grading circuits (snubber circuits)

Common dc-link

Well suited for energy storage

High harmonic generation

Substantial power losses

Advances in Transmission Shunt CompensationSTATCOM Converter Topologies

-

0

+

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-2

-1

0

1

2

t [s]

u1-u

2

© ABBSlide 1014-Nov-16

Chainlink MMC concept Cascaded H-bridges.

Modular in # of cells

1 cell = 4 semiconductors (V1 – V4)

Number depends on required output.

Distributed dc-link

Low switching frequency ( ~300 Hz)

Lower power losses

Advances in Transmission Shunt CompensationSTATCOM Converter Topologies

+−

Udc

+−

Udc

+−

Udc

+−

Udc

+ −U

dc+ −

Udc

+ −U

dc+ −

Udc

+− Udc

+− Udc

+− Udc

+− Udc

+−

Udc

+ −

V1

V2

V3

V4

© ABBSlide 1114-Nov-16

−+

+

−

Udc

+

−

Udc

Advances in Transmission Shunt CompensationSTATCOM – How MMC works

20 cells vs. 2 cells above

© ABBSlide 1214-Nov-16

Solutions:

Fast, continuously variable output

MMC configuration typically filterless

Operates in a weak network

Output varies directly with voltage

Small footprint

Challenges:

Limited overvoltage capability

Advances in Transmission Shunt Compensation

VSC

V’’syst

Vconv

+ VDC -

IindIcap

Vsyst

System Voltage

Converte Voltage

Capacitive Current

Inductive Current

XT

Static Synchronous Compensator (STATCOM)

© ABBSlide 1314-Nov-16

Advances in Transmission Shunt CompensationSVC vs. STATCOM Performance

I

V

Inductive OutputCapacitive Output 0

1.0

1.0 1.0

© ABBSlide 1414-Nov-16

Advances in Transmission Shunt CompensationSVC vs. STATCOM Performance

I

V

Inductive OutputCapacitive Output 0

STATCOM (±100 MVAr)

SVC (±100 MVAr)

1.0

1.0 1.0

0.8

1.25

Vmin

SVC (+125/-100 MVAr)

A

B Performance driven by vars, not speed

© ABBSlide 1514-Nov-16

Advances in Transmission Shunt CompensationSVC TCR Harmonic Generation

HV bus

TCR

Y/d

MV SVC bus

In

Filter banks90 100 110 120 130 140 150 160 170 180

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Firing angle [degrees]

In/I1

n=5

n=5

n=7

n=7

n=11

n=11n=13

n=19 n=17

n=25

n=23

© ABBSlide 1614-Nov-16

Advances in Transmission Shunt CompensationSTATCOM Harmonic Generation

© ABBSlide 1714-Nov-16

Advances in Transmission Shunt CompensationVI Characteristics