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Research of Total Solution to

Voltage Sag and Short Interruption

Wenbo Chen

Golden Cooperate Co., Ltd

CICED 2014

2014.9.24 Shenzhen

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CONTENTS

• Research Status of Voltage Sag and Short Interruption

1

• Research Status of Voltage Sensitive Loads

2

• Impacts on power system of voltage sag and short interruption

3

• Countermeasures to voltage sag and short interruption

4

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1.1 Voltage Sag and Short Interruption

1 Research Status of Voltage Sag and

Short Interruption

Short interruption can be regarded as a kind of special voltage sag whose amplitude decreases most severely.

IEEE IEC EN

Sag 0.1-0.9 pu 0.01-0.9 pu 0.01-0.9pu

10 ms – 1min

Short

interruption

< 0.1 pu < 0.01 pu < 0.01 pu

10ms - 1 min 10ms -3 min

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1.2 Model analysis

Vector diagram (thin line: before failure; thick line: failure)


Short Interruption

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Model of sag and swell exist at the same time

3

ACKBKAKK0

150

AACCK

150

AABBK

AK

E-)UUU(3

1U

K of voltagesequence Zero

eE3E-EU

eE3E-EU

0U

j

j

AE

CEBE

CKUBKU

K0U

phase-to-ground fault

• Voltage of fault phase reduces to zero.

• Voltages of two non fault phases increase to pu.

• sag and swell happen at the same time.

• important motor stop, threat to insulation.


Short Interruption

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1.3 Generation mechanism

arbitrary point of short circuit in power supply system

• lower residual voltage, longtransmission distance

• G & T：Affecting wide area, high risk, low probability

• Distribution：The effect is small, high risk, high probability

Switch of large load or capacitor banks, transformer energization,

large motor starting

• high residual voltage

• longer duration

• Small damage, not bring big accident

Protection action：

Lower residual voltage , may be short interruption

Protection not action:

Higher residual voltage


Short Interruption

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1.4 standards of voltage sag

Sag , known as dip.

The amplitude and duration of voltage

sag are the two most important

characteristics.

单击添加IEEE

standard

IEC

standard

EN

standard

GB

standard

two dimension electric phenomenon

not able to be eliminate

But can use protection in advance


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Low voltage tolerance standards


Short Interruption

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2.1 The common voltage sensitive loads

2 Research Status of Voltage Sensitive Loads

75% Inverter & servo drive 70% AC relay

65% PLC

60% Contactor

55% Switching power supply

Percent of Nominal Voltage（

%）

100

88% sensor

78% safety relay

10

20

30

40

50

60

70

80

90

duration（ms）

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switch power supply type loads

PLC, DCS, PC etc.

Electromagnetic coil type loads

contactor, relay etc.

Power electronics type loads

Servo driver, inverter etc.

2.2 classification of Voltage sensitive loads

2 Research Status of Voltage Sensitive Loads

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3 Impacts on power system of voltage sag

and short interruption

Voltage sag has effects on every link of power system.

单击添加Generation Transmission Distribution Utilization

On generation side, equipment compatibility during voltage sag is also called

low voltage ride through(LVRT)

• LVRT of thermal power unit auxiliaries of Class one

• LVRT of wind generation

• LVRT of PV

• above three also need to satisfy HVRT (high voltage ride through)

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3.1 generation

LVRT and HVRT of thermal power unit auxiliaries of Class one

• Transient, dynamic or long time power line voltage reducing to specified zone of low voltage ride through caused by external fault, inverter and power equipment can guarantee the reliable power supply to ensure safe operation of loads.

• Sag —auxiliaries VFD trip by low voltage protection—MFT act—furnace and unit stop running —generation break off —local grid unstable

LVRT of wind generation and PV

• one of the core conditions to ensure wind generation, PV access to grid safely



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LVRT provisional standard for thermal power unit auxiliaries

• In recent years, Thermal Power Unit Outages

occurred sometimes caused by voltage sag.

• In 2011, State Grid started test projects

• In 2012, dispatching center organized the setting of

“LVRT provisional standard for thermal power unit

auxiliaries”

• State Grid clears that thermal power plants must

complete the work of LVRT for power auxiliary

• 80% plants have completed the work



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actual demand of

power plant

Transient zone

Steady-state zone



Dynamic zone

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3.2 transmission

HVDC cooling plant



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3.2 transmission

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3.3 distribution and utilization

Continuous production

enterprise

• Petroleum and

chemical industry

• Coal chemical industry

• Semiconductor

• Chemical fiber

• Glass

• Papermaking

• ......

production process shutdown

time-consuming restart

a large number of scrap products

damage expensive equipment

personal safety accident

environment pollution



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4.1 monitor, solution, test

4 Countermeasures to voltage sag and

short interruption

Monitor

• Real time monitor

• Fault wave recorder

• Event records

Solution

• AC technology

• DC technology

Test

AC technology

• UPS

• DySC

• AVC

• AVSP

• LSP

DC technology

• VSP

• HVSP

• RTM

• DC-UPS

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4.1.1 AVSP（AC voltage sag protection）

AC

DC

charger

batteries

A

B

C

C1

L

Q

D1 C2

A

B

C

load

Static switch

AVSP LOADCB


short interruption

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4.1.2 LSP（ Electromagnetic coil load voltage sag protection）

AC LSPContactor

coil

AC220V

Residual voltage time

≥0.25pu Long time

interruption 3s


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4.1.3 DC solutions

VSP（voltage sag protection）

• VSP-HZ——batteries as energy storage

• VSP-SJ——grid residual voltage（≥0.2pu）

• VSP-MF——capacitors as energy storage

HVSP（high voltage sag protection）

• AC 690V, DC 750-1150V, drawer-style structure

RTM（isolated voltage sag protection）

• DC security power supply as storage unit


short interruption

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add HVSP system in the DC bus of high voltage VFD

4.1.4 HVSP system applied in 6kV/10kV system


short interruption

AC 6kV/10kV

High

voltage

bypass

cabinet

High

voltage

switch

cabinet

VFD M

Input

transformer

Step-up

transformer

AC 690V

AC 380V

HVSP

DC 800V

| | ---| | Storage unitHVSP system

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4.1.5 DC-UPS

Groups of

batteries,

battery

redundant

Each control bus

and closing bus

has independent

loop

AC/DC

redundant

power

supply

Bus and load

isolation,

active

protection

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4.2 total solutions to sag and short interruption


short interruption

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4.3 cost - benefit analysis


short interruption

Unit: 10 thousands RMB

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4.4 Best solution: DC micro-grid/DC distribution network

• To ease the pressure on energy and environment

• Directly supply for DC loads, improve efficiency

• Friendly to distributed generations and distributed storage

• To promote the development of electric vehicle

• Effective response to voltage sag and short interruption

• To improve the power quality and reliability


short interruption

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4.5 DC micro-grid


short interruption

DC MG

DG DSload mange control

DS DGassist

Demand side needs

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M-grid:satisfy power quantity

common PQR

m-grid： community, utility

Microgrid, area EPS

u-grid:customer MG, one or few PCC

fits into current regulatory structure

n-grid： local specialized power system

possibly DC power system

Sensitive load

CRITICAL

LOADS

Power quantity needed

And common PQR

insensitive load

4.6 potential of MG?

Through integrating topological structure of DER,

MG serves sensitive load and provide different PQR.“9”s

PQR

requi

reme

nt

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Quantity

（reduce electric cost）

STS

10kV-bus

<1.5MW 2-10MW

35kV-bus

Pow

er e

lectro

nic

s sensitiv

e lo

ad

STS

380V-bus

Quality

（reduce possible loss）n-grid

M-grid

u-grid

m-grid9

6

5

4

4.7 multiple target against multiple

technical means and pay back

0.2-2MWspecial

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4.8 DC distribution network


short interruption

Solar Cell DC/DC

Battery tank

DC BUS

DC/DCDC

Load(MPPT)

AC/DC

Power GridBidirectional

AC/DCDC/AC

AC

Load

Fuel Cell

Wind

Generation

DC/DCBidirectional

DC/DC

(MPPT)

Communication and Monitoring

Protection system

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4.9 Protection of DC distribution network

Common load, disconnected

from the distribution network

and stops running

——protect power system

fuse、contactor、breaker、digital protection etc.

Prevent sensitive to go down

when voltage fluctuates and

Save costly economic loss

——protect load

Power electronics device

+

When the power system is unstable, DC distribution system

will protect load firstly, and provide non-stop operation.

Traditional

protectionActive

protection

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Principle

viewable

controllable

PE

• reduce the fault influence area

• avoid small fault turn to big accident

• monitor each feeder bus, the traditional protection

• optimal protection strategy according to the

influence of interruption on different loads

• fault occurs, don’t blind tripping

• according to the optimal protection strategy to

implement execution of protection action, such as

uninterruptible power supply load can continue to

operate in case of fault

• take advantages of power electronic devices

• integrate protection and control

Active protection

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4.10 DC distribution network in-loop


short interruption

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Pictures of DC distribution cabinet

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4.11 prospect of DC micro grid / DC distribution network

• DC micro grid and DC distribution

network are the best solutions to voltage

sags and short interruption

• DC distribution network is a part of the

future power grid

• DC distribution network is not far away......


short interruption

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[email protected]

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WWW.GC-BANK.COM

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