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From Symptoms to Solutions:
Managing Power Quality Issues
September 10
Meet Your Panelists
•
Mike Carter
•
Mark Shaw
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2
Why Improve Power Factor and Power Quality?
•
Power Factor
 Pros
•
•
Cost savings
Less wear and tear
 Cons
•
• Voltage rise (delta V)
• Capacitor switching transients
• Harmonic resonance
• Leading power factor
Power Quality
 Pros
•
•
Decreased downtime
Avoid equipment damage
 Cons
•
Expense
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Topics
•
•
•
•
•
•
•
•
What is Power Factor?
Correcting Power Factor
Power Quality Symptoms
What Is Normal?
What Is Acceptable?
Ride-through Solutions
Compensation Schemes
Other Power Quality Solutions
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4
Topics
5
Power Factor
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What is Power Factor?
•
Power Factor
 Real/active power (kW) does real work.
 Reactive power (kVAR) bound up in magnetic fields.
 Apparent power (kVA) must be supplied by the utility to
accommodate the reactive component.
Source: DOE Motor Challenge
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What is Power Factor?
•
Power Factor
Method #1
PF = Real/Apparent Power
= kW/kVA
= 75 kW/106 KVA
= 0.70 or 70%
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What causes power factor?
•
8
Electric motors, transformers and inductors/chokes
 Current flow in coil creates magnetic fields.
• Reactive power (kVAR)
Source: Baldor Electric Company
Source: CA Air Resources Board
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Calculating Power Factor
•
9
What is power factor for a circuit
with 150 kVA and 120 kW?
PF = Real (kW)/Apparent (kVA)
= 120 kW / 150 kVA
= 0.80
•
What is kVAR?
kVA2 = kW2 + kVAR2
kVAR = sqrt (kVA2 - kW2)
= sqrt (1502 – 1202)
= 90 kVAR
120 kW
?? kVAR
150 kVA
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Correcting Power Factor
•
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Power factor (PF)
 PF correction capacitors are generally the
most economical solution.
Source: Alibaba
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Correcting Power Factor
•
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Fixed capacitor bank
 Single value of capacitance (KVAR)
 Motors mainly operate at rated speed
•
Automatic/switched capacitor bank
 Varying value of capacitance
 Best for large swings in load
 Time delay between switching can vary
from 5 seconds to 20 minutes
 More expensive
 Can lead to more transient and harmonic
concerns for the system
Source: LANL
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Correcting Power Factor
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Power Factor Correction
 Add capacitance to correct power factor.
 Does not change demand (kW) or save much energy (kWh).
Reactive Power
Active/Real
Power
Source: Van Rijn Electric
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Correcting Power Factor
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Power Factor Correction
 PF = Real (kW)/Apparent (kVA)
Present Power Factor = 75 kW / 106 kVA = 70%
 What kVAR is needed to correct
to 90% PF given PF and kW?
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Correcting Power Factor
•
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Power Factor Correction
 PF = Real (kW)/Apparent (kVA)
?
Present Power Factor = 75 kW / 106 kVA = 70%
 What kVAR is needed to correct
to 90% PF given PF and kW?
? kVAR
40
New Power Factor = 90% = 75 kW / ?? kVA
New KVA = 75 kW/0.90
= 83 KVA
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Correcting Power Factor
•
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Power Factor Correction
 PF = Real (kW)/Apparent (kVA)
Present Power Factor = 75 kW / 106 kVA = 70%
 What kVAR is needed to correct
to 90% PF given PF and kW?
? kVAR
40
New Power Factor = 90% = 75 kW / ?? kVA
New KVA = 75 kW/0.90
= 83 KVA
kVA2 = kW2 + kVAR2
New kVAR = sqrt (kVA2 - kW2)
= sqrt [(832) - (752) ]
= 35 kVAR
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Correcting Power Factor
•
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Power Factor Correction
 PF = Real (kW)/Apparent (kVA)
Present Power Factor = 75 kW / 106 kVA = 70%
 What kVAR is needed to correct
to 90% PF given PF and kW?
40 kVAR
New Power Factor = 90% = 75 kW / ?? kVA
New KVA = 75 kW/0.90
= 83 KVA
kVA2 = kW2 + kVAR2
New kVAR = sqrt (kVA2 - kW2)
= sqrt [(832) - (752) ] = 35 kVAR
kVAR correction = Old - New
= 75 – 35 kVAR
= 40 kVAR
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16
The Cost of Power Factor Correction
•
Power factor penalty
 Power factor adjustment to the demand charge
 Power factor below 80% is an additional charge
 Power Factor Adjustment = {(minimum utility PF requirement)/
(actual PF) – 1} x Demand Charge
•
Examples with assumptions
 Bill Demand of 1190kW (present month)
 Max Demand of 1233kW (previous months)
 Demand Charge = ($13 x 1190kW) + ($1 x Max Demand)
= $16,700
 For 76% PF, Penalty = (0.80/0.76 – 1) x $16,700 = $880
 For 90%+ PF, Credit = $16,700 x 0.02 = $334
•
•
Credit only applies to General Service Primary Demand (GPD) Rate
Must be PF 0.90+ to receive credit
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The Cost of Power Factor Correction
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Cost per kVAR factors (typically $30to $90/kVAR)





•
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Voltage level of bank
Number of switched stages
Control requirements
Filter bank rating requirements and tuning point
Individual Capacitor kVAR rating
Payback for preceding example (76% → 80% PF)
kVAR cost = $30/kVAR x 125 kVAR
= $3,750
PF Penalty = $880
Payback = $3,750/$880
= 4.3 years
125
kVAR
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Disadvantages of PF Correction
•
Concerns to be addressed
 Voltage rise (delta V)
•
Never exceed 2% voltage rise from PF correction
 Capacitor switching transients
 Harmonic resonance
 Leading power factor
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Disadvantages of PF Correction
•
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Harmonic Resonance
 Large amounts of capacitance in parallel with inductance.
• Harmonic producing loads are operating on the power system.
• Capacitor(s) and the source impedance have the same reactance
(impedance) at one of the load characteristic frequencies.
XL = XC and, therefore
X = XL – XC = 0
 Two possible solutions
•
Apply another method of KVAR compensation
♦ Harmonic filter, active filter, condenser, etc)
•
OR
Change the size of the capacitor bank
♦ Over-compensate or under-compensate
for the required KVAR and live with
the ramifications.
Source: Eaton Performance Power Solutions
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Disadvantages of PF Correction
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Leading Power Factor
 Impedance is total resistance to current flow
Z = R + XL – XC
• Too much capacitance cancels inductance
♦ Excessive current draw
♦ Voltage rise


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Topics
22
Power Quality
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What Is Power Quality?
•
Any power problem manifested in voltage, current, or
frequency deviations that results in failure or misoperation
of customer equipment
 Generally, quality of the voltage
 Surveys show that 65% to 85% of
power quality problems are the
result of something happening
within the facility
•
On the customer side of the point of
common coupling (PCC)
 PCC—the point between the end user or customer where another
customer can be served
 Perfect power quality is not attainable
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Power Quality Symptoms
•
Electromagnetic Phenomena (IEEE 1159)
 Transients
• Impulsive
• Oscillatory
 Short-duration variations (0.5 cycles – 1 minute)
 Long-duration variations (> 1 minute)
 Voltage imbalance/unbalance
 Inductance and capacitance effects
• Power Factor
 Waveform distortion
• Harmonics
• Noise
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Power Quality Symptoms
•
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Electromagnetic Phenomena
 Short-duration variations (0.5 cycles – 1 minute)
 Long-duration variations (> 1 minute)
Category
Instantaneous
Typical Duration
0.5-30 cycles
Category
Voltage Magnitude
Interruption
<0.1 pu*
Momentary
30 cycles – 3 seconds
Sag (dip)
0.1 – 0.9 pu
Temporary
3 seconds – 1 minute
Swell
1.1 – 1.8 pu
Sag
Category
Interruption, sustained
Swell
Voltage Magnitude
0.0 pu*
Overvoltages
1.1 – 1.2 pu
Undervoltages
0.8 – 0.9 pu
*pu = per unit
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Power Quality Symptoms
•
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Electromagnetic Phenomena
 Voltage imbalance/unbalance (phase-to-phase)
•
•
Causes overheating that deteriorates motor winding insulation
Decreases efficiency
216 V
208 volt service
(average)
3.8% 
201 V
207 V
Goal
Do Not
Operate
Unbalance
Derating
1%
None
2%
95%
3%
88%
4%
82%
5%
75%
100 HP
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88 HP
Power Quality Symptoms
•
Electromagnetic Phenomena
 Waveform distortion—Harmonics
•
IEEE 519 Harmonic Control in Electrical Power Systems
♦ Specifies a maximum of 0.01% to 3.0% Total Demand Distortion (TDD)
♦ Depends on the short-circuit ratio at the PCC (measures stiffness of circuit)
•
•
Odd harmonic multiples of 3rd harmonic (3rd, 9th, 15th) are additive
Sources—variable speed drives, uninterruptible power supplies,
electronic ballasts, and inverter welding power supplies
•
Symptoms—overheating, audible humming noise, capacitor failure,
and circuit breaker nuisance trips
source: Micro-Poise
Measurement
Systems
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What Is Normal?
•
Sags are mostly instantaneous (<30 cycles)
 Duration of 166ms (10 cycles) or less
 Depth of 20% to 30%
• Usually caused by weather, trees, and public interference
♦ Average of 28 distribution sags per year
<1 minute (70% are single-phase)
•
Interruptions
 In the EPRI study, 37% < 0.5 seconds
and 66% < 1.5 seconds
• Average of 1 to 3 per year at distribution level
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What Is Normal?
•
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The national standard in the U.S. is ANSI C84.1
 Range A is for normal conditions
• +/- 5% on a 120-volt base at the service entrance
• -2.5% to +5% for services above 600 volts
 Range B is for short durations or unusual conditions
ANSI C84.1 Requirements for Voltage Regulation
Range A
Base
Range B
+5%
-5%
+5.8%
-8.3%
120V
126
114
127
110
480V
504
456
508
440
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Acceptable Power Quality
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•
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Voltage variation
tolerance curves
The ITIC* (CBEMA)
curve
*ITIC– Information Technology Industry Council
No
Interruption
Region
+/- 5%
No
Interruption
Region
Source: ITIC
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Solutions
•
Systematic approach
1. Fix it first!
2. Make it survive or ride-through.
3. Compensate when it does occur.
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Solutions
•
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Add a power quality relay to identify
power quality problems
 PQube three-phase and single-phase
monitoring up to 690V, 50/60Hz.
• Voltage dips, swells, and interruptions
Source: Power Standards Lab
– waveforms and RMS graphs
•
Frequency events, impulse detection,
time-triggered snapshots
•
Daily, weekly, monthly trends. Cumulative
probability, histograms, and more.
•
Built-in Li-Ion UPS.
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Ride-Through Solutions
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•
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A two to three second ride-through will
handle 90% of short-duration interruptions
Use DC instead of AC
AC Relay Drop-Out
 Control circuits, controllers,
input/output devices (I/O),
and sensors
Source: EPRI Solutions
•
Change the unbalance, undervoltage,
or reset trip settings to achieve ride-through
 IEEE P1668 contains draft ride-through recommendations
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Ride-Through Solutions
•
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Increase voltage headroom (brownout, <50% sag)
 Choose a different power supply setting range
•
•
270V
Where your nominal operating voltage is
nearer the top of the range
For a 240 voltage, choose 95 V to 250 V
versus 110 V to 270 V (bad for swells)
 Connect your single-phase power supply
phase-to-phase
•
208 V versus 120 V for a 90 V to 250 V device
because 90 V is 45% of 208 V but 70% of 120 V
250V
240V
110V
95V
250V
208V
 Reduce the load on your power supply
 Use a bigger power supply
•
120V
90V
Would be more lightly loaded
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Ride-Through Solutions
•
•
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Select appropriate circuit breakers (trip curves)
Slow the Emergency Off (EMO)
relay down
 Increase mechanical mass
(such as a contactor)
 Use a relay hold-in accessory
Source: Power Quality Solutions Inc.
•
Compensate for the upstream
voltage sag itself (last resort)
Source: Siemens AG
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Compensation Schemes
36
Redundancy
Generator
UPS
Power Conditioning
Cost
Surge Protection Devices
Good System Design
Wiring and Grounding
Source: Liebert Corporation
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Compensation Schemes
•
Facility
•
Equipment
Cost
•
Component
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Facility Level Compensation
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Solid-State Voltage Compensation
 Static transfer switch (STS)
•
•
Utility level protection
When a dual distribution feeder service is available
 Low-voltage static series compensator (LV-SSC)
•
•
•
Facility level protection
Dynamic Voltage Restorer/Compensator (DVR/DVC)
Dynamic Sag Corrector (MegaDySC)
♦ From 263 kVA to 1330 kVA
♦ For ride-through
» Down to 50% of nominal voltage
» Up to 12 cycles with no energy storage
Source: Leonardo ENERGY
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Facility Level Protection
•
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Solid-State Voltage Compensation
 Dynamic Sag Corrector (MegaDySC)—from 263-1330 kVA
•
For ride-through to 50% of nominal voltage for up to 12 cycles
with no battery storage.
12 cycles
50
0.2
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Facility Level Protection
•
Backup Generators
 Capital costs
Capital Costs, $/kW
Diesel
Natural
Gas
Microturbine
Fuel
Cell
$150$250
$200$300
$1,000
$3,000$4,000
 Installation costs
•
•
Roughly 50% of the purchase cost, and can approach
$10,000 for a 100 kW unit
Does not change drastically with size, so there is
no penalty for oversizing
 Maintenance costs
•
•
•
$500 to $1,000 per year
Includes an oil change and tune up every 1,500 hours
Diesels considered most mechanically reliable
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Facility Level Protection
•
Top Nine Reasons Generators Fail to Start
1. Battery failure
2. Low coolant levels
3. Low coolant temperature alarms
4. Oil, fuel, or coolant leaks
5. Controls not in auto
6. Air in the fuel system
7. Ran out of fuel
8. High fuel level alarm
9. Breaker trip
Source: Darren Dembski of Peterson Power Systems
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Equipment Level Protection
•
42
Voltage Dip-Proofing Inverter (DPI)
 Square-wave output to the load
 An off-line device
•
•
•
Transfer time less than 700 s
Up to 3 kVA and 25A for 120V
Up to 4.5 kVA and 20A for 208/230V
 Good for interruptions and sags
•
Source: Measurlogic, Inc.
Voltage Dip Compensator (VDC)
 Good for sags down to 36%
for two seconds
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Equipment Level Protection
•
Dynamic Sag Corrector (ProDySC)
 From 9 to 167 kVA
•
Constant Voltage Transformers/
Ferroresonant Transformers
 Maintains two separate magnetic paths
with limited coupling between them
 Provides 90% output at input voltage
range of ±40%
 Inefficient at low loads
 Current limited
•
Not good for high inrush current applications such as motors
 Size at least 2.5 times the nominal VA requirement of the load
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Equipment Level Protection
•
44
Uninterruptible Power Supply (UPS)
 Three types
• Online or true UPS (double conversion)
• Offline UPS (standby battery and inverter)
• Hybrid or line-interactive or direct ferroresonant transformer UPS
 Energy Storage (≈50% of system cost)
• Lead Acid Batteries
• Flywheels
• Ultra-capacitors
 UPS cost
• $300-2,000 per KVA
•
♦ 5 KVA for doctor’s office is $1,500 to $2,000
♦ 10-20 kW for retail chain is $15,000 to $20,000
♦ 1 MW for data center is $400,000 plus $200,000 installation
Source: LBNL
Flywheel is 50% more
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Equipment Level Protection
•
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Uninterruptible Power Supply (UPS)
 Online UPS (double conversion or true online)
•
•
•
•
•
Continuously powers the load
No switchover time
Best power conditioning
Best waveform
Delta converter more efficient than double conversion
Delta Conversion
Utility
Utility
Delta
Converter
Utility
Load
Inverter
DC
DC
AC
AC
Battery
Delta Conversion
Load
Charger
Inverter
DC
DC
AC
AC
Battery
Standard Operation
Load
Charger
Inverter
DC
DC
AC
AC
Battery
Power Interruption
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Equipment Level Protection
•
46
Uninterruptible Power Supply (UPS)
 Offline UPS (standby)
•
•
•
•
Only supplies power when power is interrupted
Switchover time can be a problem
Square nature of sine wave can cause problems
Only conditions power during interruption
Utility
Utility
Load
Load
Charger
Inverter
DC
DC
AC
AC
Battery
Standard Operation
Charger
Inverter
DC
DC
AC
AC
Battery
Power Interruption
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Equipment Level Protection
•
47
Uninterruptible Power Supply (UPS)
 Hybrid or line-interactive UPS
•
•
Supplies additional power during sags
Provides some power conditioning
 Hybrid direct ferroresonant transformer
•
•
•
UPS supports voltage regulation of ferroresonant transformer
Maintains output briefly when a total outage occurs
Can be unstable with PF-corrected power supply loads
Utility
Load
Inverter
DC
AC
Battery
Line-interactive Standard Operation
Utility
Load
Charger
Inverter
DC
DC
AC
AC
Battery
Ferroresonant Transformer
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Component Level Protection
•
Dynamic Sag Corrector (MiniDySC)—from
1.2 kVA to 12 kVA
•
UPPI PoweRide
 Uses two phases of a three-phase supply as input
and a single-phase output; up to 10 kVA
 Works when one of the two input phases is lost
AND
the remaining phase drops by 33%
OR
when both of the input phases
experience a 33% drop in voltage
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Other Power Quality Solutions
•
49
Harmonics
Solutions
Advantages
Disadvantages
Active Filters
Can handle load diversity
Highest cost
Broadband Blocking Filters
Makes 6-pulse into 18-pulse equivalent at
reasonable cost
One filter per drive
12/18-Pulse Converter
Excellent harmonic control for larger drives
(>100 HP)
High cost
Harmonic Mitigating/Phase
Shifting Transformers
Substantial (50-80%) reduction in
harmonics when used in tandem
Harmonic cancellation highly
dependent on load balance
Tuned Filters
A single filter can compensate for multiple
drives
Care is needed to ensure that the
filter will not become overloaded
K-Rated/Drive Isolation
Transformers
Offers series reactance (like line reactors)
and provides electrical isolation for some
transient protection
No advantage over reactors for
reducing harmonics unless used in
pairs for phase shifting
DC Choke
Slightly better than AC line reactors for 5th
and 7th harmonics and less voltage drop
Not always an option for drives
Line reactors
Inexpensive
May require additional
compensation
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Other Power Quality Solutions
•
Transients
 Transient Voltage Surge Protection Device (SPD)
•
A fast-acting transient device
♦ Used for lower-voltage (<1,000 V) circuit transient attenuation
(IEEE C62.72-2007)
•
•
Clamps the line voltage to a specific value
•
Energy shunting capability
Conducts any excess impulse energy
to the safety ground, regardless
of frequency
♦ Best expressed by its nominal
discharge/short circuit current
rating (UL 1449) rather than its
energy joule rating
•
Entire building or equipment level
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Other Power Quality Solutions
•
51
Voltage Imbalance/Unbalance
 Regularly monitor voltages at the motor terminals
• Verify that voltage unbalance < 3% (ANSI C84.1-2006)
 Check your electrical system single-line diagrams
• Single-phase loads should be uniformly distributed
 Install ground fault indicators as required
 Perform annual thermo-graphic inspections
 Derate the motor to ensure long life
 Install phase monitors/protectors
Source: Time Mark Corporation
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•
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