Date post: | 04-Jun-2018 |
Category: |
Documents |
Upload: | m-kumar-marimuthu |
View: | 220 times |
Download: | 0 times |
of 22
8/13/2019 Voltage Influence on Typical Protection and Controls For
1/22
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
8/13/2019 Voltage Influence on Typical Protection and Controls For
2/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
3/22
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
8/13/2019 Voltage Influence on Typical Protection and Controls For
4/22
Adjustable Speed Drive Tolerance
and Protection
0 200 400 600 800
Duration of Sag (milliseconds)
Upper Range Average Lower Range
%
V
80
60
40
ASD Voltage Sag Tolerance (Djokic Paper)
20
100
Overcurrent Protection
Undervoltage
Protection
8/13/2019 Voltage Influence on Typical Protection and Controls For
5/22
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
8/13/2019 Voltage Influence on Typical Protection and Controls For
6/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
7/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
8/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
9/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
10/22
8/13/2019 Voltage Influence on Typical Protection and Controls For
11/22
8/13/2019 Voltage Influence on Typical Protection and Controls For
12/22
8/13/2019 Voltage Influence on Typical Protection and Controls For
13/22
0 200 400 600 800
Duration of Sag (milliseconds)
Upper Range Lower Range
%
V
80
60
40
Ice Cube Relay Voltage Sag Tolerance (EPRI)
20
100
8/13/2019 Voltage Influence on Typical Protection and Controls For
14/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
15/22
0 200 400 600 800
Duration of Sag (milliseconds)
Upper Range DC Lower Range
%
V
80
60
40
Contactors Voltage Sag Tolerance (CIGRE 412)
20
100
AC Upper Range
AC Lower Range
DC
8/13/2019 Voltage Influence on Typical Protection and Controls For
16/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
17/22
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
Voltage drop allowance
for distribution
transformer
3 4
Minimum secondaryservice voltage
114 110
Voltage drop allowance
for plant wiring
6 (See Concern Below) 6
Minimum Utilization
Voltage
108 104
8/13/2019 Voltage Influence on Typical Protection and Controls For
18/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
19/22
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% ..."
8/13/2019 Voltage Influence on Typical Protection and Controls For
20/22
8/13/2019 Voltage Influence on Typical Protection and Controls For
21/22
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.
8/13/2019 Voltage Influence on Typical Protection and Controls For
22/22
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.