Effects of Voltage Sags

5/20/2018 Effects of Voltage Sags

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May 2002

WWW.powerquality.org All rights reserved 1

The effects of voltage sags

by

Terry Chandler

Power Quality Inc/Power Quality Thailand LTD

For IEEE Hong Kong Section

May 31, 2002


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Sags or Dips?

A decrease in the nominal voltage for ashort duration.


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Standards regarding Sags

IEC 1000-4-1/11 Measurement of sags

IEEE 1159 Monitoring of Sags

IEEE P1346

ANSI C84.1

IEEE 1100


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IEEE SCC 22

Short duration variations

2.1 Instantaneous

2.1.2 Sag(Dip) 0.5 to 30 cycles 0.1 to 0.9 pu

sags (dips) have a magnitude and

duration SCC is the standard coordination committee

of IEEE


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Accepted description

Sag is a IEEE term DIP is IEC term

Sag refers to % of decrease in Voltage

IE a 20% sag is a voltage decrease to 0.8 PU

DIP refers to % of voltage remaining

IE a dip to 80% is a decrease to 0.8 PU

Is the glass half full or half empty?


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Classifying Sags (Dips)

CBEMA

100%

1 day


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Classifying sags (dips) II

ITIC (New CBEMA)

unacceptableacceptable


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Cause of Voltage sags

Faults on the distribution system

User distribution system failure

User loads

Equipment malfunction


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Faults on the distribution

system


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User equipment that can

cause sags

Copiers and laser printers

Arc welders

Motor starting

Power saws


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Welder causes voltage sag


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Voltage sag from the utility


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Semi 47 Voltage sag standard

A new standard developed by the SEMI

organization members to define thedesired minimum equipment sensitivityto voltage sags

Similar to ITIC curve in the voltage sagdomain


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ITIC Semi 47


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ITIC Semi

47

50 ms 0.2 0.5 second

20 ms

| 0.5 sec | 10 sec


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Load sensitivity to voltage

sags

Motors

Contactors that

Small 50% sag shuts down 600 hp load


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Sag indications without a PQ

meter Lights blink

Motors slow down and return to normalspeed

Computers reboot unexpectedly

Automated equipment stopsunexpectedly


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Root cause of sensitivity

Automated

Equipment

Equipment

disconnect

Ac relay

Electrical contactor on the input power


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Process sensor

Automated Equipment

Equipment

disconnect

DC relay process

sensor

With voltage sags sends shut down signal


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Emergency shutdown circuitWith voltage sag sends shutdown signal

Automated

Equipment

Equipment

disconnect

Ac relay


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DC buss sag

DC relay

AC to DC

convertor

DC to AC

invertor

AC motor

DC buss

monitor

Electroniccontrol


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Voltage imbalance sensor

voltage

unbalance

relay

AC to DC

convertor

DC to AC

invertor

AC motor

Electronic

controlDC relay


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Improving voltage sag

immunity Relay settings

DC relays Switchmode power supply configuration

oversize power supply or capacitor

Dynamic sag corrector

Connect loads phase to phase


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Voltage sense relays

Upper and lower trip points


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Ride thru device


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Sag mitigation technologies

UPS

Standby

line interactive On-Line

Dynamic voltage restorer (DVR)

Voltage Regulator

Static transfer switch


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UPS Uninterruptible Power Supplies

Battery

On-line

Standby

Flywheel

Super conductor

Super Capacitor

Fuel Cell


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On-line UPS

Battery

system

input

harmonic

filter

LoadInverter

Bypass

Rectifier

Charger

System

bypass


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Rotary UPS


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Example of rotary


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DVR

Bypass

DVR Electronics

SS Shorting Switch Inverters,

Filters, Controls

Cap Energy Storage

Isolation Isolation

To Source To Plant


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Flywheel ups


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Example of flywheel UPS

Photo compliments of Beacon.com


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Standby UPS

Battery or Flywheel

More efficient than on -line

Output meets ITIC or Semi-47 standard


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Standby UPS

Main System Container

Isolation

Transformer

Static Switch

Critical

Load

Utility

Input

up to (8) Power M odules

CB2

Output

CB1

Input

CB3

Bypass

Battery

String Battery

Charger

Inverter

Bridge

System

Control


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Example of Standby UPS


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3 phase sag


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UPS output during sag


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Conclusions

Graph compliments of WWW.powerstandards.com

Voltage sags are the #1 Power Qualityproblem

The source can be from the utility orfrom internal loads, wiring, problems etc

Solutions can be very inexpensive or veryexpensive


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WWW lit All i ht d 40

The bottom line

Voltage sags are an economic or $$ problem

It requires detailed PQ data to determine ifthe solution costs $100 or $10,000,000.

Effects of Voltage Sags

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