voltage influence on typical protection and controls for

8/13/2019 Voltage Influence on Typical Protection and Controls For

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Voltage Influence on TypicalProtection and Controls for Motors,

Power Electronics, and Other

Common Loads

Presentation to:

WECC Modeling and Validation Work Group

November 18, 2010

John Kueck


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The Study Examines a Range of Standards

for Both Equipment Protection and

Voltage Tolerance Many Well Known Standards: Buff Book IEEE Std 242-2001 Protection and Coordination of Industrial and

Commercial Power Systems

Gray Book IEEE Std 241-1990 Electric Power Systems in CommercialBuildings

Red Book IEEE Std 141-1993 Electric Power Distribution for Industrial Plants Gold Book IEEE Std 493-2007 Design of Reliable Industrial and Commercial

Power Systems

Blue Book IEEE Std 1015-2006 Applying Low Voltage Circuit Breakers Usedin Industrial and Commercial Power Systems

The National Electrical Code (NEC, 2008)

These standards provide guidance on the suggested setpoint forundervoltage trip for various equipment, there is significant latitudeallowed to the designer, and really no requirement that the designerrigorously follow the standard. Also, few equipment types for whichunder voltage protection is recommended.

Biggest problem may be the ice cube relay.


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Voltage Tolerance of Programmable

Logic Controllers, A Wide Range

0 200 400 600 800

Duration of Sag (milliseconds)

Upper Range Average Lower Range

%V

80

60

40

PLC Power Supply Voltage Sag Tolerance (CIGRE 412)

20

100


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Adjustable Speed Drive Tolerance

and Protection

0 200 400 600 800


Upper Range Average Lower Range

%

V

80

60

40

ASD Voltage Sag Tolerance (Djokic Paper)

20

100

Overcurrent Protection

Undervoltage

Protection


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Motor Torque

Induction motor torque is a function of theterminal voltage squared.

During a rapid dip, the motor goes into

regeneration and will be slowed. A stiff system slows the motor faster

Low inertia in the driven equipment means evenfaster deceleration

Tests by SCE show air conditioning compressorscan stall in 1 to 18 cycles


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The IEEE Buff Book (242, 2001) Section

10.3.2.1 Motor Protection, Undervoltage

To prevent a motor from automatically restartingwhen voltage returns.

To avoid excessive inrush to the total motor loadon the power system.

To avoid reaccelerating motors before their fieldscollapse.

Time delay undervoltage protection will often notbe satisfactory because magnetically heldcontactors may drop out before the undervoltageprotection.


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Very Few Other Standards Mention

Undervoltage Protection for Motors

For large motors, the IEEE Red Book (IEEE_Standard_141, 1993)states in Section 5.6.3.1 motor protection may include: Internal fault protection - either overcurrent relays or percentage

differential relays; sometimes ground fault protection is providedusing a zero sequence approach.

Sustained overloads and locked rotor- Conventional over current

relays may provide too much margin between the motor thermalcapability curve and the relay operating time characteristic.Overcurrent relays do, however, provide excellent locked rotor andshort circuit protection. Thermal relays will give adequate protectionfor light and medium overloads.

Under voltage - Large motors and medium voltage motors should haveseparate undervoltage protection.

For small motors, the Red Book and the NEC do not requireundervoltage protection.


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What Percentage Are Large Motors?

Industrial motor systems account forapproximately twenty three per cent of allelectricity consumed.

Large motors, i.e. those over 200 horsepower,account for only one percent of the motors in theentire manufacturing inventory, but use 45percent of the energy use.

Approximately 70% of motors which are >200

horsepower, fall into the 250-500 hp size How many of these are equipped with

undervoltage protection? A growing number.


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Emerson Secure Start and ComfortAlert for

Air Conditioning Compressors

ComfortAlert will flash an alert if the voltage is

below 71%

Secure Start

Monitors supply voltage in air conditioning

compressors and protects against low voltage or

locked rotor.

Also provides a reduced voltage soft start.

Can be used in areas with problems in voltage

variation.


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0 200 400 600 800


Upper Range Lower Range

%

V

80

60

40

Ice Cube Relay Voltage Sag Tolerance (EPRI)

20

100


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Contactors

Large Motor Starter Contactors Motor starter contactors may open at 65 to 75% voltage

in the case of 2300 or 4600 Volt motors and 55 to 65% inthe case of 460 Volts and below.

The contactor dropping out or control relays dropping out

is really the only fast undervoltage protection that motorsunder 600 volts typically have. Motors over 600 voltsrepresent a very small percentage of the population.

Large Air Conditioners

Large three phase air conditioning in industrial orcommercial applications typically have undervoltagerelays which trip in perhaps six cycles after the voltagedrops below 0.6 pu.


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0 200 400 600 800


Upper Range DC Lower Range

%

V

80

60

40

Contactors Voltage Sag Tolerance (CIGRE 412)

20

100

AC Upper Range

AC Lower Range

DC


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Lamps

Incandescent filament lamps are quite tolerant

to voltage sags, but the light output and lifetime

are dramatically impacted by sustained voltage

deviations.

Fluorescent lamps may stop working anywhere

between 80 and 40% voltage and in as little as 10

milliseconds. Some electronic ballasts may keepthe light working at 40% indefinitely.


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ANSI Voltage Tolerance Limits for Low Voltage

Regulated Power Distribution System, 120 V Base

Range A Range B

Maximum allowablevoltage

126 127

Voltage drop allowance

for primary distribution

line

9 13

Minimum primaryservice voltage

117 114


for distribution

transformer

3 4

Minimum secondaryservice voltage

114 110


for plant wiring

6 (See Concern Below) 6

Minimum Utilization

Voltage

108 104


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Possible Concern NEC FPN4 states that conductors for branch circuits

should be sized to prevent a voltage dropexceeding 3 percent at the farthest outlet of power,heating and lighting loads, and where the maximumtotal voltage drop on both feeders and branch

circuits to the farthest outlet does not exceed 5%,yielding 108 at the motor.

But, the code requirement is only for ampacity, not

for voltage. As houses get larger, is the FPN notemet?

Also, what is the voltage drop across the meter? Itis assumed by all of the above to be zero.


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Japanese Study

The load drop does not occur if the lowest

voltage is higher than 0.85 pu. The load drop

occurs if the lowest voltage becomes lower

than 0.85 pu, and rapidly increases when the

lowest voltage is around 0.6 pu. The load

drop, however, saturates after that and does

not increase over 30% ..."


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Other Parameters Are Probably More

Important than the Dip Magnitude

More recent studies have shown that there are anumber of parameters which have a major impact thecapability of a device to ride through an interruptionthan just the dip magnitude and duration. (CIGRE,

2010) These parameters include: Pre dip voltage magnitude and distortion of sine wave.

Unbalance during dip for three phase devices, dipshape, and point on the sine wave where the dip starts.

Speed of recovery of dip. Source impedance (distribution transformer).

Other equipment connected close by.


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Conclusions Point on wave may have a greater impact than

magnitude and duration.

High efficiency motors are more prone to stall.

Ice cube relays are used everywhere and will dropat 70% V in one cycle.

Voltage drop in branch circuits and other parasiticdrop in low voltage systems may be a growingproblem.

Motors at 600 volts and below usually do not have

undervoltage protection unless supplied bymanufacturer (air conditioning compressor).

Motor contactors will typically provide theundervoltage protection by dropping out.

voltage influence on typical protection and controls for

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