S&C PureWave AVC User guide

S&C ELECTRIC COMPANY
Specialists in Electric Power Switching and Protection
Instruction Sheet 656-500
September 20, 2004 ©2004
Supersedes Instruction Sheet 656-500 dated 2-24-03
S&C PureWave AVC™Adaptive VAR Compensator
600 V
Instructions for Installation and Operation
TABLE OF CONTENTS
Section Page Section Page
INTRODUCTION
Qualified Persons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Read this Instruction Sheet . . . . . . . . . . . . . . . . . . . . . . 2
Retain this Instruction Sheet . . . . . . . . . . . . . . . . . . . . . 2
Proper Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
SAFETY INFORMATION
Understanding Safety-Alert Messages . . . . . . . . . . . . . 3
Following Safety Instructions . . . . . . . . . . . . . . . . . . . . 3
Replacement Instructions and Labels . . . . . . . . . . . . . 3
Location of Safety Labels . . . . . . . . . . . . . . . . . . . . . . . 4
SECURITY PROVISIONS
Enclosure Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Access Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
INSPECTION AND HANDLING
Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
DIMENSIONS AND WEIGHTS
Section Dimensions and Weights . . . . . . . . . . . . . . . . . 8
INSTALLATION
Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Placement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Access to Interior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
CABLE CONNECTIONS
Conduit Requirements . . . . . . . . . . . . . . . . . . . . . . . . . .15
Output Connections . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Completing the Installation . . . . . . . . . . . . . . . . . . . . . 18
SYSTEM OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
MAIN COMPONENTS
Capacitor Stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Power-Electronic Switches . . . . . . . . . . . . . . . . . . . . .20
Microprocessor Controller . . . . . . . . . . . . . . . . . . . . . .20
OPERATING PROCEDURE
Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Off-Line Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Shut Down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
PROTECTIVE DEVICES
Capacitor Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Inrush-Limiting Reactors . . . . . . . . . . . . . . . . . . . . . . .23
Cooling of SCR/Diode Valves . . . . . . . . . . . . . . . . . . . .23
Heat-Sink Temperature Sensors . . . . . . . . . . . . . . . . . 23
Surge Arresters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Frequency Scan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

656-500 2
INTRODUCTION
ÇWARNING
The equipment covered by this publication must be installed, oper-
ated, and maintained by qualified persons who are knowledgeable
in the installation, operation, and maintenance of underground
electric power distribution equipment along with the associated
hazards. A qualified person is one who is trained and competent in:
•The skills and techniques necessary to distinguish exposed live
parts from non-live parts of electrical equipment.
•The skills and techniques necessary to determine the proper
approach distances corresponding to the voltages to which the
qualified person will be exposed.
•The proper use of the special precautionary techniques, per-
sonal protective equipment, insulating and shielding materials,
and insulated tools for working on or near exposed energized
parts of electrical equipment.
These instructions are intended only for such qualified persons.
They are not intended to be a substitute for adequate training and
experience in safety procedures for this type of equipment.
Qualified Persons
Read this Instruction Sheet Thoroughly and carefully read this instruction sheet before installing
or operating your S&C PureWave AVC. Familiarize yourself with
“SAFETY INFORMATION” on pages 3 and 4.
Retain this Instruction Sheet This instruction sheet is a permanent part of your S&C PureWave
AVC. Designate a location where you can easily retrieve and refer to
this publication.
Warranty The standard warranty contained in S&C’s standard conditions of
sale, as set forth in Price Sheet 150, is applicable to the S&C Pure-
Wave AVC covered in this instruction sheet.
ÇCAUTION
The equipment in this publication must be selected for a specific
application. The application must be within the ratings furnished
for the equipment. Ratings for this device are listed on a ratings
label at the front of the unit.
Proper Application

3 656-500
SAFETY INFORMATION
Understanding Safety-Alert
Messages
There are several types of safety-alert messages which may appear
throughout this instruction sheet as well as on labels attached to the
PureWave AVC. Familiarize yourself with these types of messages
and the importance of the various signal words, as explained below.
Following Safety Instructions If you do not understand any portion of this instruction sheet and
need assistance, contact your nearest S&C Sales Office or S&C Autho-
rized Distributor. Their telephone numbers are listed on S&C’s web-
site www.sandc.com. Or call S&C Headquarters at [phone]; in
Canada, call S&C Electric Canada Ltd. at [phone].
Replacement Instructions and
Labels
If you need additional copies of this instruction sheet, contact your
nearest S&C Sales Office, S&C Authorized Distributor, S&C Head-
quarters, or S&C Electric Canada Ltd.
It is important that any missing, damaged, or faded labels on the
equipment be replaced immediately. Replacement labels are available
by contacting your nearest S&C Sales Office, S&C Authorized Distrib-
utor, S&C Headquarters, or S&C Electric Canada Ltd.
ÇDANGER
“DANGER” identifies the most serious and immediate hazards
which will likely result in serious personal injury or death if
instructions, including recommended precautions, are not
followed.
ÇWARNING
“WARNING” identifies hazards or unsafe practices which can result
in serious personal injury or death if instructions, including recom-
mended precautions, are not followed.
ÇCAUTION
“CAUTION” identifies hazards or unsafe practices which can result
in minor personal injury or product or property damage if instruc-
tions, including recommended precautions, are not followed.
NOTICE
“NOTICE” identifies important procedures or requirements that
can result in product or property damage if instructions are not fol-
lowed.
NOTICE
Thoroughly and carefully read this in-
struction sheet before installing your
S&C PureWave AVC.

656-500 4
SAFETY INFORMATION
Location of Safety Labels
Reorder Information for Safety Labels
Location Safety-Alert Message Description Part Number
AÇDANGER High Voltage! Keep Out DD260020B001
BÇCAUTION This Equipment is Powered By Three Separate Sources DD260021B001
CÇCAUTION Capacitors Inside Enclosure DD260022B001
B
B
A
A
B
B
C

5 656-500
SECURITY PROVISIONS
Enclosure Security The PureWave AVC enclosure incorporates a number of features to
minimize hazards to qualified persons and to the general public.
Enclosures are fabricated from 11-gauge steel sheet and are free-
standing and self-supporting. There are no externally removable side
sheets, rear sheets, or roofs to invite removal. Access is through wide
bulkhead-type doors having concealed cam-type, high-strength
latches that seal the doors shut. Each door has a minimum of three
concealed, extra-heavy-duty hinges with stainless-steel pins. All doors
are padlockable and have top and side flanges with double 90-degree
bends which overlap the door openings, adding rigidity and discour-
aging tampering.
Access Control Access to internal components, controls, and meters is controlled by
padlockable doors. Baffles and screens cover all vents, discouraging
wire poking. Since this unit may be located in areas accessible to the
general public as well as authorized but unqualified persons, care
must be taken to alert such persons to the presence of high voltage
within the enclosure. Therefore, do not remove any of the “Danger!
High Voltage! Keep Out” signs that have been attached to the unit. Any
organization altering or removing these hazard-alerting signs must
assume full responsibility for such actions. Take particular care to be
sure that all doors and handles are securely padlocked before leaving
the unit unattended, even momentarily.

656-500 6
INSPECTION AND HANDLING
Packing Each section of the PureWave AVC is shipped fastened to a wood
skid. A plastic liner has been inserted underneath the section to pre-
vent water or debris from entering the bottom during shipping or han-
dling. The sections should be left on their skids with the liners intact
until just prior to installation on the pad.
Inspection Examine the shipment for external evidence of damage as soon after
receipt as possible, preferably before removal from the carrier's con-
veyance. Check the bill of lading to insure that all shipping skids,
crates, and containers listed thereon are present.
If there is visible loss and/or damage:
1. Notify the delivering carrier immediately.
2. Ask for a carrier inspection.
3. Note condition of shipment on all copies of the delivery receipt.
4. File a claim with the carrier.
If concealed damaged is discovered:
1. Notify the delivering carrier within 15 days of receipt of shipment.
2. Ask for a carrier inspection.
3. File a claim with the carrier.
Also notify S&C Electric Company in all instances of loss and/or
damage.

7 656-500
Handling
The dimensions and weight of each section of the PureWave AVC are
listed in Table 1. Each section can be lifted using an overhead crane
or a forklift.
If an overhead crane is to be used:
1. Use 8-foot or longer hoist slings of equal length to prevent dam-
aging the enclosure during lifting.
2. Arrange the hoist slings so as to distribute the lifting forces
equally between the eyebolts.
3. If hoist slings or chains have been provided—match the letter
tag on each sling hook to the corresponding letter tag on each
eye-bolt on the roof of the section. See Figures 1 and 2.
4. Make sure that the lifting hooks are completely engaged in the
eyebolts before lifting the enclosure. Do not cross the slings or
chains.
5. Avoid sudden starts or stops.
If a forklift is to be used, engage the forks fully across the span of
the wooden pallet mounted to the base of the section.
If the PureWave AVC is to be transported through a building, place
roller dollies under each corner of the section
ÇWARNING
When handling a PureWave AVC with an overhead hoist, observe
standard lifting practices as well as the general instructions below.
Failure to follow these precautions can result in serious per-
sonal injury or equipment damage.
INSPECTION AND HANDLING
Figure 1. Sling hooks with letter tags. Figure 2. Section ready to lift.

656-500 8
DIMENSIONS AND WEIGHTS
Section Dimensions and Weights
System Dimensions
L D  H (in.)11
11
Number of
Sections
Approximate System Weight (lbs.) Total System
Weight (lbs.)
KVAR Voltage Stages Control
Section
Capacitor
Section 1
Capacitor
Section 2
500 480 3 87 37 121 1 6,000 — — 6,000
600 3 87 37 121 1 5,500 — — 5,500
625 480 3 87 37 121 1 6,500 — — 6,500
600 3 87 37 121 1 6,000 — — 6,000
750 480 3 87 37 121 1 7,500 — — 7,500
600 3 87 37 121 1 7,000 — — 7,000
1000 480 3 87 37 121 1 8,500 — — 8,500
600 3 87 37 121 1 8,000 — — 8,000
1250
480 3 174 37 121 2 7,000 2,500 — 9,500
4 174 37 121 2 7,000 2,500 — 9,500
600 3 87 37 121 1 9,000 — — 9,000
4 87 37 121 1 9,000 — — 9,000
1500
480 3 174 37 121 2 7,500 3,000 — 10,500
4 174 37 121 2 7,500 3,000 — 10,500
600 3 87 37 121 1 9,500 — — 9,500
4 174 37 121 2 7,000 2,500 — 9,500
2000
480 3 174 37 121 2 8,000 3,500 — 11,500
4 174 37 121 2 8,000 3,500 — 11,500
600 3 174 37 121 2 7,500 3,000 — 10,500
4 174 37 121 2 7,500 3,000 — 10,500
2500
480 3 261 37 121 3 8,500 4,000 3,500 16,000
4 261 37 121 3 8,500 4,000 3,500 16,000
600 3 174 37 121 2 8,000 3,500 — 11,500
4 174 37 121 2 8,000 3,500 — 11,500
3000
480 3 261 37 121 3 9,000 4,000 3,500 16,500
4 261 37 121 3 9,000 4,000 3,500 16,500
600 3 174 37 121 2 8,500 3,500 — 12,000
4 174 37 121 2 8,500 3,500 — 12,000
4000
480 3 261 37 121 3 9,500 4,000 3,500 17,000
4 261 37 121 3 9,500 4,000 3,500 17,000
600 3 261 37 121 3 9,000 4,000 3,000 16,000
4 261 37 121 3 9,000 4,000 3,000 16,000
5000
480 3 261 37 121 3 10,000 4,000 4,000 18,000
4 261 37 121 3 10,000 4,000 4,000 18,000
600 3 261 37 121 3 9,500 4,000 3,500 17,000
4 261 37 121 3 9,500 4,000 3,500 17,000
6000 600 3 261 37 121 3 10,000 4,000 4,000 18,000
4 261 37 121 3 10,000 4,000 4,000 18,000
1Height dimension includes outdoor fan. Height dimension with indoor fan is 108 inches. Height dimension with fan housing removed is 102 inches.

9 656-500
Storage If possible, the PureWave AVC should be immediately installed in its
permanent location. In outdoor applications, the space heaters should
be energized at once, even if the device itself is not to be energized
until later. If the PureWave AVC cannot be installed immediately, stor-
age in a clean, dry room is recommended, especially for a unit designed
for indoor installation. The PureWave AVC should be protected against
condensation, harmful gases, cement dust, and physical damage. If nec-
essary, the device can be temporarily stored outdoors prior to being
installed and put into service. Shelter it with a tent-like covering which
will allow adequate ventilation but prevent entry of rain, snow, and
contaminants through openings in the device. If the PureWave AVC is
to be stored outdoors for more than two weeks, connect and energize
the space heaters to minimize condensation.
INSTALLATION
Indoor fan
housing shown
Capacitor section 2
(if required)
Capacitor section 1
(if required)
Control
section
Figure 3. Section placement.

656-500 10
INSTALLATION
Figure 4. Outdoor fan housing (upper left). Fan power connection (upper right). Fans removed for shipping (lower left). Indoor
fan housing (lower right).
Placement 1. Note the positions of the control section and each of the capacitor sections. See
Figure 3. Determine the section having working clearances most affected by adjacent
walls or structures . . . this section should be placed first.
2. Unbolt each section from its skid and lift it into position on the pad or floor, observing
the precautions discussed under “Handling” on page 7.
3. Fan housings may have been removed for shipping. Reinstall the fan housings using the
hardware provided. See Figure 4.

11 656-500
Figure 5. Individual section with wood panel at end. Sections are joined as shown.
INSTALLATION
Assembly If the sections have shipped unassembled, assemble them as follows:
1. Remove the wood panels attached to the ends of the sections. Con-
nect adjacent sections using supplied hardware (eighteen ³⁄₈-16 
1¹⁄₂ hex-head bolts, square flat washers, lock washers, and nuts). See
Figure 5. Tighten each bolt to 240 inch-pounds. For outdoor installa-
tions, use supplied gasket material between sections.
2. Install the rear bus splices. See Figure 5 and Figure 6. Thoroughly
abraid the Aluminum buses and splices to remove any dirt or oxida-
tion prior to making the connections. Coat the contact surfaces to
¹⁄₂ inch beyond the joint with a uniform layer of Penetrox® A com-
pound. Attach the splice plates using four ¹⁄₂hex-head bolts, Belle-
ville washers, and nuts supplied. Tighten each bolt to 480 inch-
pounds.
Rear bus splices

656-500 12
Rear bus
splices
INSTALLATION
Figure 7. Ground bus splice cutaway view. In some cases, the lower tray(s) must be temporarily removed to access the ground
bus splice and anchor brackets.
Figure 6. Cutaway view between sections showing rear bus splices (left) and close-up of splice hardware (right). In some
cases, multiple washers may be required to maintain a minimum ³⁄₄-inch air gap between hardware and adjacent buses or
structure; see the drawings furnished.
Ground bus splice

13 656-500
Figure 8. Anchor bracket installation.
INSTALLATION
3. Install anchor brackets to secure the PureWave AVC to the pad or
floor. At a minimum, there should be two brackets on the left side
and two on the right side of the AVC, located approximately 6 inches
from each corner. See Figure 8. Depending on the configuration, the
bottom flange may point inward or outward. An inward flange will
require anchor brackets inside the unit – capacitor trays may have to
be temporarily removed to access the inside corners to mount the
anchor bolts. See Figure 7. Anchor brackets on outward-facing
flanges should be placed to minimize the chance to tripping on the
anchor.
Access to Interior To open a door: Remove the padlock and pull the door handle out-
wards. See Figure 9. If key interlocks have been provided, insert the
key. When the door is opened slightly past 90 degrees, the door holder
at the bottom will engage and prevent the door from closing acciden-
tally.
Figure 9. Access to interior.
6

656-500 14
INSTALLATION
To close a door: Depress the door holder with your foot while pushing
the door in the closing direction. See Figure 10. Remove your foot and
close the door completely. Push the door handle up and install the pad-
lock.
Grounding 1. Connect the cable ground wires to the grounding system as appro-
priate.
2. Connect the ground pad of the PureWave AVC to the facility system
ground in accordance with the user’s standard grounding practice
and local codes. See Figure 11. Use the equivalent of 4/0 copper (or
cable sized in accordance with the user’s standard practice) in either
a single or multiple connection to attain the momentary rating of the
unit. For a multiple connection, cables smaller than 1/0 copper or
equivalent should not be used.
Figure 10. Door holder release with foot. Figure 11. Attach grounding pad to facility system ground.

15 656-500
CABLE CONNECTIONS
Conduit Requirements The size and quantity of conduits required is dependent upon the
options ordered with the PureWave AVC. The PureWave AVC may be
designed for connection using underground conduit or overhead race-
way.
Figure 12. Control section shown with output connections for underground conduit (left). Close-up of cable entry area behind
control panel (right).

656-500 16
CABLE CONNECTIONS
Output Connections 1. Open the door of the control section to access the output connec-
tions. See Figures 12 and 13 and the drawings furnished.
Note: The bus construction in the PureWave AVC is typically alu-
minum. Terminal pads on components may be aluminum, copper, or
copper alloy. Hence, bus and terminal connections are typically alu-
minum-to-aluminum or aluminum-to-copper. Such connections
employ Belleville washers. Do not tighten factory-made connections
employing Belleville washers unless they are visibly loose; they have
been correctly torqued to 50 foot-pounds at the factory. Other con-
nections employ flat washers; if they have loosened, they should be
torqued to 35 foot-pounds. Check bus connections and, where nec-
essary, correctly tighten the connecting hardware.
a. For aluminum terminal pads to aluminum connectors: Use alumi-
num or galvanized-steel hardware with two Belleville washers
(not furnished). Torque each aluminum bolt to the manufacturer’s
specifications. Torque each steel bolt to 50 foot-pounds or, in the
Figure 13. Control section cutaway shown with output connections for overhead raceway, with internal circuit breaker option
(left). Close-up of cable entry area after output connections have been made (right).
Phase C buses
front (2)
Phase B buses
middle (2)
Phase A buses
rear (2) Neutral bus
Phase
cables
Neutral
cables

17 656-500
absence of a torque wrench, tighten each bolt until the Belleville
washers are flat, then back off one-half turn. Do not use lock
washers with Belleville washers.
b. For aluminum terminal pads to tinned-copper or tinned-bronze
connectors: Use galvanized-steel hardware, with one Belleville
washer (not furnished) against the aluminum terminal pad and
one galvanized-steel flat washer against the tinned connector.
Torque each bolt to 50 foot-pounds or, in the absence of a torque
wrench, tighten each bolt until the Belleville washer is flat, then
back off one-half turn. Do not use lock washers with Belleville
washers.
c. For copper terminal pads to tinned-copper or tinned-bronze con-
nectors use Everdur or stainless-steel hardware, with one galva-
nized-steel or brass flat washer against each terminal pad and one
split lock washer under the nut. Torque each bolt to 35 foot-
pounds or, in the absence of a torque wrench, tighten each bolt
until the split lock washer is flat.
d. For copper terminal pads to aluminum connectors, use galva-
nized-steel hardware with one Belleville washer against the con-
nector and one galvanized-steel or brass flat washer against the
terminal pad. Torque each bolt to 50 foot-pounds or, in the
absence of a torque wrench, tighten each bolt until the Belleville
washer is flat, then back off one-half turn. Do not use lock wash-
ers with Belleville washers.
2. Complete the phase connections to the PureWave AVC terminals.
Thoroughly wire-brush aluminum contact surfaces to remove dirt or
foreign materials as well as natural surface oxides. Immediately
coat the surfaces to ¹⁄₂ inch beyond the joint with a uniform layer of
Penetrox A compound.
3. For outdoor installations, seal all external conduits with RTV, and
seal all conduit openings inside the enclosure with expansive foam
to prevent water from entering the enclosure through the conduit.
CABLE CONNECTIONS

656-500 18
Completing the Installation 1. Depending on the configuration, provide 110-Vac or 208-Vac control
voltage inside the control section to power the fans and controls.
See Figure 14.
2. Close and lock all doors on the PureWave AVC.
3. Wipe down the exterior of the enclosure with a clean, damp cloth.
Refinish any scratches or abrasions with S&C red-oxide primer and
touch-up finish, which are available in aerosol spray cans. See Fig-
ure 15. Order Catalog Number 9999-061 red-oxide primer and Cata-
log Number 9999-080 light gray finish. No other primer or finish is
approved. The area to be touched up should be cleaned to remove
all oil and grease. Sand the area, removing any traces of rust that
may be present. make sure that all edges are feathured before apply-
ing primer.
Figure 15. S&C red-oxide primer and touch-
up finish.
CABLE CONNECTIONS
Figure 14. 110-Vac, 30-A safety switch configuration (left), 208-Vac panel
board for larger, outdoor applications (right).
ÇCAUTION
Before walking away. . .
1. Check the interior of the unit for foreign materials, tools, etc.,
which may have been mislaid on bus work or supporting mem-
bers.
2. Make certain that controls are in the desired positions.
3. Make certain that fuses are installed and breakers are in the
proper position.
4. Close and securely latch all doors.
5. Make certain that all temporary grounds have been removed.
6. Padlock all door handles.

19 656-500
The PureWave AVC provides transient-free cycle-per-cycle reactive
power compensation. The concept for this device was developed by
the University of Washington in conjunction with the Bonneville Power
Administration and Southern California Edison.
The PureWave Adaptive VAR Compensator is a solid-state switched
capacitor bank which is connected in parallel with the variable reactive
load. Depending on its kVAR rating, the PureWave AVC provides the
total reactive power required by a variable reactive load within one
cycle of the power frequency. The dynamic response of the PureWave
AVC offers quality enhanced electric power to the user by providing
adaptive reactive power control, which leads to the following benefits
in commercial, industrial, or utility installations:
•Voltage stabilization.
•Electric loss reduction.
•Improved usage of installed capacity.
•Reduction of peak demand charges.
•Reduction of energy consumption.
•Reduction of power factor penalty.
SYSTEM OVERVIEW

656-500 20
The PureWave AVC consists of power elements including capacitor
stages and power-electronic switches, a microprocessor-based control-
ler, and auxiliary equipment such as potential and current transform-
ers.
Capacitor Stages The per-phase reactive power supplied by the PureWave AVC is divided
into binary increments. If Q1 is the reactive power (in kVARs) gener-
ated by the first capacitor stage, then—for a four-stage PureWave
AVC—the second stage has a reactive power of 2 Q1 (twice the
kVARs of the first stage). The third stage has a value of 4 Q1 (four
times the kVARs of the first stage). And the fourth stage has a value of 8
Q1 (eight times the kVARs of the first stage). The total reactive
power of the PureWave AVC is calculated as 3 Q1 (20+ 21+ 22+
23). The number of stages and the value of Q1 are determined by the
requirements of the application.
Each capacitor stage has a discharge resistor that dissipates the
stored energy, reducing the voltage across the capacitor terminals to 50
volts within 5 minutes after disconnection.
Power-Electronic Switches Each capacitor stage is controlled by a set of power-electronic
switches composed of an SCR and a diode connected in anti-parallel.
The diode performs two basic functions: It charges the capacitors in
each stage to the negative peak value of the supply voltage and it pro-
vides a path for the flow of the negative half cycle of capacitor current.
When the supply voltage crosses zero becoming negative, the diodes
conduct, charging the capacitors to the negative peak value of the
supply voltage. At this instant, the PureWave AVC current reverses
direction and the diodes stop conducting. All capacitors are thus pre-
charged and remain in that condition until a control signal is sent to the
SCRs to set them in the conducting mode. While the thyristors are not
conducting, the discharge resistors tend to dissipate the energy stored
in the capacitors. However, during this short time (one cycle), the
change in the stored energy and the voltage across the capacitors are
negligible.
Microprocessor Controller The microprocessor controller continuously monitors the phase volt-
ages and the load current. Based on the magnitude of the imaginary
component of the load current, the controller calculates the appropri-
ate triggering sequence of the SCRs needed to compensate for the reac-
tive power requirement at that moment. Maximum compensation
capability is determined by the total rated kVAR of the PureWave AVC.
System voltage and current waveforms are used as references by the
controller. They are filtered of all harmonics and transient distortions
so that compensation is based on the 60-Hz or fundamental compo-
nents. The required reactive power is supplied by the PureWave AVC
and injected into the system during the following cycle, giving a maxi-
mum response time of one cycle, or 16.6 milliseconds for a 60-Hz
power system. Complete compensation is achieved when the line cur-
rent is in phase with its respective phase voltage.
MAIN COMPONENTS