characteristics of transients voltages affecting equipment

7/30/2019 Characteristics of Transients Voltages Affecting Equipment

1/24

CHARACTERISTICS OF TRANSIENT

VOLTAGES AFFECTING CUSTOMER

EQUIPMENT

Presented at

TRANSIENT VOLTAGE SURGE SUPPRESSION

IN LOW VOLTAGE AC POWER SYSTEMS

Workshop

Santa Clara, California

May 12-13, 1992

Mark McGranaghan

ELECTROTEK Concepts, Inc


2/24

Characteristics of Transient Voltages Affecting Customer Equipment, page 2

Electrotek Concepts, Inc.

OBJECTIVES

Provide examples of transient voltage characteristics

Identify important causes of transients in low voltage

systems

Identify impacts of transient voltages on equipment

Describe solutions to transient voltage problems

Note:

The information in this presentation was developed during

case studies sponsored by the Electric Power Research

Institute and Pacific Gas & Electric Company


3/24



IMPORTANT CAUSES OF TRANSIENT VOLTAGES

Transients Initiated on the Utility System

Lightning

Capacitor Switching

Line/Cable Switching

Transformer Switching

Current Limiting Fuse Operation

Transients Initiated in the Low Voltage System

Capacitance Switching

Current Interruption (motors, etc.)

Power Electronics Operation


4/24



LIGHTNING

Lightning transients are caused by a discharge of currentfrom the struck conductor or shield wire to ground.

The lightning stroke current as a very high rate-of-rise

(e.g. 1-10 microseconds).

A voltage transient results from the lightning stroke

current flowing through the surge impedance of the

transmission line - this will generally result in a flashover

or an arrester operation.

Example lightning stroke current:

-25

-20

-15

-10

-5

0

0 20 40 60 80 100 120 140

Current

(kA)

Time (uSec)

Lightning Stroke Current


5/24



PROBLEM: LOW SIDE CURRENT SURGES CAUSED BY

LIGHTNING TRANSIENT

SOLUTION: LOW VOLTAGE MOV ARRESTERS ATTRANSFORMER SECONDARY AND AT

CUSTOMER SERVICE ENTRANCE


6/24



CAPACITOR SWITCHING

Normal capacitor energizing on a power system is

characterized by a step change in the voltage followed by

a transient oscillation in the range 300-1000 Hz.

The magnitude of the transient should be in the range of

1.3-1.8 times the normal peak voltage.

Important parameters affecting this transient include:

Capacitor Size/Location

Switching Device Characteristics (Resistors,Reactors)

Size/Status of Other Capacitors

Short Circuit Capacity at the Substation/at the

Cap Bank

System Load Characteristics


7/24



Normal capacitor energizing on the distribution system:

November 19, 1991 at 06:07:56 PQNode LocalRGE_BETAPhase A VoltageWave Fault

Trigger

0 10 20 30 40 50 60 70

-1.5

-1

-0.5

0

0.5

1

1.5

Time (mSeconds)

Max 1.094Min -1.280

Uncalibrated Data

Typical capacitor switching transient coupled to low

voltage system:

Voltage: Current:

April 26, 1992 at 06:15:56 PQNode LocalETKREALPhase C VoltageImpulse

Trigger

0 10 20 30 40 50

-150

-100

-50

0

50

100

150

Time (mSeconds)

Max78.25

Min-194.8

Volt-Seconds

912.8

BMI/Electrotek

April 26, 1992 at 06:15:56 PQNode LocalETKREALPhase C CurrentImpulse

0 10 20 30 40 50

-60

-40

-20

0

20

40

60

80

Time (mSeconds) BMI/Electrotek


8/24



PROBLEM: MAGNIFIED TRANSIENTS AT CUSTOMER-

OWNED LOW VOLTAGE CAPACITOR

BANKS


9/24



Capacitor switching transient on the distribution system:

CAPMAG> SRCA(Type 1)

0 20 40 60 80 100-60000

-40000

-20000

0

20000

40000

60000

Time (mS)

Max:Min:Avg:Abs:

RMS:

CF :FF :

48362.2-31823.418100.33182320232.8

1.572851.11781

Magnified transient at 480 Volt capacitor bank:

CAPMAG> MOVA(Type 1)

0 20 40 60 80 100-1000

-500

0

500

1000

Time (mS)

Max:Min:Avg:Abs:

RMS:CF :FF :

768.217-596.431258.266768290.9732.639421.12664


10/24



These transients will often result in capacitor failures or failures

of electronic equipment.

Arrester energies are very high.

MOV arrester current:

CAPMAG> 480A- MOVA(Type 9)

0 20 40 60 80 100-2000

0

2000

4000

6000

8000

10000

Time (mS)

Max:Min:Avg:Abs:

RMS:CF :FF :

8138.62-4.100533.50978138449.82218.091613.4237

MOV arrester energy:

CAPMAG> MOVA(Type 9)

0 20 40 60 80 1000

500

1000

1500

2000

2500

3000

Time (mS)

Max:Min:Avg:Abs:

RMS:CF :FF :

2638.9802153.1126382378.251.109221.10456


11/24



SOLUTION: LOW VOLTAGE CAPACITOR BANKS CAN

BE INSTALLED AS HARMONIC FILTERS TO

DETUNE THE CIRCUIT CAUSING

MAGNIFICATION

1.00

1.50

2.00

2.50

3.00

0 100 200 300 400 500 600

Voltage

(pu)

480 Volt Compensation Level (kVAr)

Compensation = Capacitors

Compensation = Filters

1500 kVA Transformer

3000 kVAr Switched Capacitor Bank


12/24



PROBLEM: CAPACITOR SWITCHING TRANSIENTS

CAUSE NUISANCE TRIPPING OF ASDS

Transient Voltage at the 480 Volt Bus


13/24



Drive Current:

DC Link Voltage in the ASD:


14/24



SOLUTION: INPUT CHOKES OR ISOLATION

TRANSFORMERS ARE USUALLY

SUFFICIENT TO PREVENT DC

OVERVOLTAGES WITHIN THE ASD

600

700

800

900

1000

0 1 2 3 4 5 6 7 8 9 10 11

dcVolts

Choke Size (% on 10 kVA base)

Normal Operating Voltage

Typical Trip Level

3000 kVAr Switched Capacitor Bank


15/24




CAUSE FAILURE OF TAP SWITCHING

VOLTAGE REGULATOR/POWER

CONDITIONER

Transient at 480 Volt Service Entrance


16/24



Input to Power Conditioner

Output of Power Conditioner

SOLUTION: SENSITIVE ELECTRONICS MUST BE

PROTECTED WITH APPROPRIATE SURGE

SUPPRESSION/FILTERING


17/24




MAGNIFIED AT OUTPUT OF ISOLATION

TRANSFORMER/FILTER COMBINATION

Many isolation transformer-type power conditioners

include a capacitor on the output to filter high frequency

transients. This capacitor can magnify capacitor

switching transients in the 300-1000 Hz range.


18/24



LIPC Input Voltage Waveform:

LIPC Output Voltage Waveform:

SOLUTION: DO NOT USE THE CAPACITOR-TYPE

FILTERING WITH ISOLATION

TRANSFORMERS IN CIRCUITS

SUSCEPTIBLE TO CAPACITOR SWITCHING

TRANSIENTS


19/24



TRANSIENTS CAUSED BY SWITCHING IN LOW VOLTAGE

SYSTEMS

Misoperation of Tap Switching Voltage Regulator


20/24



Two different transients at 480 Volt locations close to

switched motor:


21/24



Transient due to power electronics equipment current

interruption:

Transient caused by localized fault within customer

system and fuse blowing:


22/24



Transients in a computer room that resulted in board

failures:


23/24



Voltage Notching caused by Rectifier Switching:

Chokes or isolation transformers should be used in series

with phase controlled rectifiers (e.g. dc drives) to isolate

the notching transients from other loads.


24/24


El t t k C t I

Transients caused by switching operations within

customer facilities are characterized by high frequency

components.

These transients damp out quickly in the circuit.Significant protection can be obtained by using dedicated

circuits for sensitive loads.

Transient Voltage Surge Suppressors can be used to

protect sensitive loads being impacted by these

transients.

characteristics of transients voltages affecting equipment

Documents