ABB CA-26 Manual
ABB Automation Inc.
Substation Automation and Protection Division
Coral Springs, FL
Instruction Leaflet
All possible contingencies which may arise during installation, operation or maintenance, and all details and
variations of this equipment do not purport to be covered by these instructions. If further information is desired
by purchaser regarding this particular installation, operation or maintenance of this equipment, the local ABB
Power T&D Company Inc. representative should be contacted.
41-337.31B
Printed in U.S.A.
Effective: February 1995
Supersedes I.L. 41-337.31A, Dated February 1983
( ) Denotes Change Since Previous Issue
Before putting relays into service, remove all
blocking which may have been inserted for
the purpose of securing the parts during
shipment, make sure that all moving parts
operate freely, inspect the contacts to see
that they are clean and close properly, and
operate the relay to check the settings and
electrical connections.
1.0 APPLICATION
These relays have been specially designed and
tested to establish their suitability for class 1E appli-
cations. Materials have been selected and tested to
insure that the relays will preform their intended func-
tion for their design life when operated in a normal
environment as defined by ANSI standard C37.90-
1978, when exposed to radiation levels up to 104
rads, and when subjected to seismic events produc-
ing a Shock Response Spectrum within the limits of
the relay rating.
“Class 1E” is the safety classification of the electric
equipment and systems in nuclear power generating
stations that are essential to emergency shutdown of
the reactor, containment isolation, cooling of the reac-
tor, and heat removal from the containment and reac-
tor, or otherwise are essential in preventing significant
release of radioactive material to the environment.
The current transformers should not saturate when
carrying the maximum external fault current. This
requirement is met if the burden impedance does not
exceed
where
NP= proportion of total ct turns in use
VCL = current transformer accuracy class C
voltage
Iext = maximum external fault current in secondary
RMS amperes. (let Iext. = 100 if max. external
fault current is less than 100A)
RS= current transformer secondary finding resis-
tance, ohms
For example, if the 400:5 tap of 800:5 C400 current
transformers are used, NP= 400/800 = 0.50, if Iext. =
120A, RS= 1.0 ohm the burden should not exceed:
The CA-16 relay should not be utilized for transformer
differential applications since it is too sensitive for
overriding the inrush. Likewise the CA-26 relay
should not be used for bus protection with the “four
circuit bus” connections of Figure 6.
2.0 CONSTRUCTION
The type CA-16 relay consists of an indicating con-
tactor switch, autotransformer, three restraint ele-
ments, an operating element, and a sensitive fault
detector.
The principal component parts of the relay and their
location are shown in Figures 1 to 3.
!CAUTION
NPVCL Iext
·100–()Rs
–
1.33 Iext
()
---------------------------------------------------------
NPVCL Iext.100RS
–()–
1.33 Iext.
()
----------------------------------------------------------- =
0.5x400 120 100–()x1.0–
1.33x120
----------------------------------------------------------------- 1 . 1 3 o h m s=
Type CA-16
Percentage Differential
Relay for Bus Protection
Class 1E Applications
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41-337.31B
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2.1. Restraint Elements
Each restraint element consists of an “E”laminated
electromagnet with two primary coils and a second-
ary coil on its center leg. Two identical coils on the
outer legs of the laminated structure are connected
to the secondary winding in a manner so that the
combination of all fluxes produced by the electro-
magnet results in out-of-phase fluxes in the air gap.
The out-of-phase fluxes cause a contact opening
torque.
2.2. Operating Circuit
The operating circuit consists of an autotransformer
and an operating element. The primary of the auto-
transformer, which is the whole winding, is connected
to receive the differential or unbalanced current from
the various transformers connected to the bus. The
secondary winding of the autotransformer, which is a
tapped section of the winding, is connected to the
operating element of the relay.
The operating element consists of an “E”type lami-
nated electromagnet with an autotransformer winding
on its center leg. Two identical coils on the outer legs
of the laminated structure are connected to the sec-
ondary (tapped section) of the autotransformer wind-
ing in a manner so that the combination of all fluxes
produced by the electromagnet results in out-of-
phase fluxes in the air gap. The out-of-phase air gap
fluxes cause a contact closing torque.
2.3. Sensitive Fault Detector Circuit
The sensitive fault detector circuit consists of an
autotransformer and a contactor switch. The contac-
tor switch is connected across the secondary (tapped
section) of the auto-transformer winding.
The contactor switch is a small solenoid type ele-
ment. A cylindrical plunger rides up and down on a
vertical guide rod in the center of the solenoid coil.
The guide rod is fastened to the stationary core,
which in turn screws into the unit frame. A silver disc
is fastened to the moving plunger through a helical
spring. When the coil is energized, the plunger
moves upward carrying the silver disc which bridges
three conical-shaped stationary contacts. In this
position, the helical spring is compressed and the
plunger is free to move while the contact remains sta-
tionary. Thus, ac vibrations of the plunger are pre-
vented from causing contact bouncing. A micarta
disc is fastened to the bottom of the guide rod by two
small nuts. Its position determines the pick-up current
of the element.
The auto-transformer is designed to saturate at high
values of current to limit the amount of current to the
contactor switch.
2.3.1. Indicating Contactor Switch Unit (ICS)
The dc indicating contactor switch is a small clapper
type device. A magnetic armature, to which leaf-
spring mounted contacts are attached, is attracted to
the magnetic core upon energization of the switch.
When the switch closes, the moving contacts bridge
two stationary contacts, completing the trip circuit.
Also during this operation two fingers on the arma-
ture deflect a spring located on the front of the
switch, which allows the operation indicator target to
drop. The target is reset from the outside of the case
by a push rod located at the bottom of the cover.
The front spring, in addition to holding the target pro-
vides a restraint for the armature and thus controls
the pick-up value of the switch.
3.0 OPERATION
The type CA-16 relay is an induction disc relay with
four electromagnets mounted on two discs that are
fastened on a common shaft. One of the electromag-
nets is the operating element while the other three
are restraint elements. The restraint elements are
energized from the secondaries of current transform-
ers connected to the bus, and the operating circuit is
energized in accordance with the current flowing in
the differential connection of the current transform-
ers.
A current of 5 amperes in at terminal 18 and out of
terminal 19 will produce a definite amount of restrain-
ing torque (see Figure 3.) Similarly, a current of 5
amperes flowing in at terminal 16 and out of terminal
17 will produce an equal amount of torque. If both of
these currents flow at the same time with the polarity
as indicated above, their effect will be additive and
they will produce the same torque as though 10
amperes are flowing in terminal 16 and out of termi-
nal 17. Conversely, if equal currents flow in these two
coils, but in opposite directions, their ampere turns
will cancel and no torque will be produced. The same
relationship applies for the paired coils of the other
two restraining units of the relay. The restraint effect
will always be additive if currents flow in the coils
which belong to different restraint elements.
4.0 CHARACTERISTICS
4.1. CA-16 Bus Relay
This relay has variable percentage characteristics
which means that the operating coil current
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41-337.31B
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required to close the relay contacts, expressed in
percent of the total restraint current, varies with the
magnitude of the restraint current. The relay sensi-
tivity is high, corresponding to a low percentage
ratio, at light currents, and its sensitivity is low, cor-
responding to high percentage unbalance, at high
currents. The relay is made sensitive at low cur-
rents in order to detect light internal faults on the
bus being protected. At the same time, however, its
reduced sensitivity at the higher currents allows the
various current transformers involved to depart
from their true ratio to a large extent without caus-
ing false tripping of the relay for external faults.
The variable percentage characteristics are partic-
ularly advantageous when severe saturation of cur-
rent transformers is caused by the dc component of
asymmetrical short circuits. In the case of buses
located close to generating stations where the dc
components decay slowly, the breakdown in ratio of
the current transformers will be much greater than
would ever be expected from a consideration of the
usual ratio curves of the current transformers
involved.
The time of operation of the relay is shown in Fig-
ure 4.
The main contacts will safely close 30 amperes at
250 volts dc and the seal-in contacts of the indicat-
ing contactor switch will safely carry this current
long enough to trip a circuit breaker.
The indicating contactor switch has two taps that
provide a pick-up setting of 0.2 or 2 amperes. To
change taps requires connecting the lead located in
front of the tap block to the desired setting by
means of a screw connection.
4.2. Trip Circuit Constants
Indicating Contactor Switch (ICS)
0.2 amp rating 8.5 ohms dc
1.0 amp rating 0.37 ohms dc
2.0 amp rating 0.10 ohms dc
ENERGY REQUIREMENTS
Burden of each restraint coil at 5 amperes
VOLT AMPERES POWER FACTOR
.75 .7
Continuous Rating 14 amperes
1 second rating 460 amperes
Burden of operating Circuit
VOLT AMPERES
VARIABLE (See Figure 5)
Continuous rating 8 amperes
1 second rating 280 amperes
4.3. Connections
4.3.1. CA-16
To determine the ac connections, identify each pri-
mary circuit as either a “source”or “feeder”. As
defined here, a feeder contributes only a small por-
tion of the total fault-current contribution for a bus
fault. Otherwise, the circuit is a source. Next lump a
number of feeders into a “feeder group”by paralleling
feeder ct’s, taking the precaution that each feeder
group has less than 14 amperes load current
(restraint coil continuous rating). Also each feeder
group should not contribute more than 10% of the
total phase or ground-fault current for a bus fault if
Figure 7 is to be used.
Connect per Figure 6 with three or four bus “circuit.”
The term “circuit”refers to a source or to a feeder
group. For example, assume a bus consisting of 2
sources and 6 feeders. Further, assume that the
feeders are lumped into 2 feeder groups. The bus
now reduces to four circuits
If the bus reduces to more than four circuits, parallel
source-circuit ct’s or source-and feeder circuit ct’s
until only four circuits remain. Then connect these
four sets of ct’s to the relays per Figure 6. The excep-
tion to this rule occurs when the application consists
of three feeder groups. Then Figure 7 applies.
With 3 feeder groups and more than 3 sources, paral-
lel source ct’s until the application reduces to 6 cir-
cuits; then, connect to the relays per Figure 7.
4.4. Setting Calculations
No calculations are required to set the CA-16.
4.5. Setting The Relay
No settings are required on the CA-16 relay.
5.0 INSTALLATION
The relays should be mounted on switchboard panels
or their equivalent in a location free from dirt, moisture,
excessive vibration and heat. Mount the relay verti-
cally by means of the four mounting holes on the
flange for the semi-flush type FT case. The mounting
screws may be utilized for grounding the relay. Exter-
nal toothed washers are provided for use in the loca-
tions shown on the outline and drilling plan to facilitate
making a good electrical connection between the relay
case, its mounting screws and the relay panel. Ground
Wires are affixed to the mounting screws as required
for poorly grounded or insulating panels. Other electri-
cal connections may be made directly to the terminals
by means of screws for steel panel mounting.
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41-337.31B
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For detail information on the FT case refer to IL 41-
076 for semi-flush mounting.
6.0 ADJUSTMENTS AND MAINTENANCE
The proper adjustments to insure correct operation of
this relay have been made at the factory. Upon
receipt of the relay, no customer adjustments should
be required.
6.1. Acceptance Check
The following check is recommended to insure that
the relay is in proper working order. The relay should
be connected per Figure 8.
A. Minimum Trip Current
Apply current to terminals 12 and 13 of the relay. The
relay should operate as follows:
CA-16 0.15 amperes ±5%
B. Percentage Differential Characteristic
Apply 16 amperes to terminals 9 and 19 of the CA-16
relay. The contacts should close when the following
operating current is applied to the relay with connec-
tions of Figure 8.
CA-16 17.0 amperes ±7%
Check each individual restraint winding by applying
50 amperes to each winding. Apply sufficient operat-
ing current to the operating circuit until the contacts
just close. The operating current should be:
CA-16 3.9 to 5.1 amperes
C. Time Curve
Apply 20 amperes to terminals 12 and 13 of the
relays. The contacts should close in the following
times:
CA-16 52 ±5% Milliseconds
D. Indicating Contactor Switch (ICS)
Close the main relay contacts and pass sufficient dc
current through the trip circuit to close the contacts of
the ICS. This value of current should not be greater
than the particular ICS nameplate rating. The indica-
tor target should drop freely.
Repeat above except pass 85% of ICS nameplate
rating current. Contacts should not pickup and target
should not drop.
E. Sensitive Fault Detector
Apply current to terminals 14 and 15 of the relay. The
fault detector should operate between the limits of
0.142 to 0.158 amperes.
6.2. Routine Maintenance
All contacts should be periodically cleaned. A contact
burnisher is recommended for this purpose.
(S#182A836H01). The use of abrasive material for
cleaning contacts is not recommended, because of
the danger of embedding small particles in the face
of the soft silver and thus impairing the contact.
7.0 CALIBRATION
Use the following procedure for calibrating the relay if
the relay has been taken apart for repairs or the
adjustments disturbed. This procedure should not be
used until it is apparent that the relay is not in proper
working order. (See “Acceptance Check”.)
7.1. Contacts
Adjust the adjustable stop screw on the upper disc of
the relay so that a contact separation of 0.050 inch is
obtained between the moving contact and the sta-
tionary contact. Lock the screw with the nut provided
for the purpose.
7.2. Minimum Trip
The relay should be level for this test. Minimum trip
current can best be determined with the permanent
magnet removed.
Adjust the spring tension until t he relay just closes its
contacts with the following current applied to termi-
nals 12 and 13 of the relay.
CA-16 0.15 amperes
7.3. Percentage Slope Characteristic
Connect the relay per the test circuit of Figure 8.
Pass 20 amperes for the CA-16 relay into terminals 9
and 19 of the relay. Adjust the plug (when used) in
the operating electromagnet until the contacts just
close with the following currents into the operating
circuit of the relays.
CA-16 29.4 to 34 amperes
7.4. Time Curve
Place the permanent magnet on the relay and apply 20
amperes to terminals 12 and 13 of the relay. Adjust the
keeper of the permanent magnet until the contacts just
close in the following times:
CA-16 52 ±5% Milliseconds
These times should be the average of 5 readings.
7.5. Indicating Contactor Switch (ICS)
Initially adjust unit on the pedestal so that armature fin-
gers do not touch the yoke in the reset position.
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41-337.31B
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(Viewed from top of switch between cover and frame).
This can be done by loosening the mounting screw in
the molded pedestal and moving the ICS in the down-
ward position.
a. Contact Wipe –Adjust the stationary contact so
that both stationary contacts make with the moving
contacts simultaneously and wipe 1/64”to 3/64”
when the armature is against the core.
b. Target –Manually raise the moving contacts and
check to see that the target drops at the same
time as the contacts make or 1/16”ahead. The
cover may be removed and the tab holding the
target reformed slightly if necessary. However,
care should be exercised so that the target will
not drop with a slight jar.
If the pickup is low, the front cover must be removed
and the leaf springs on each side bent outward
equally.
7.6. Sensitive Fault Detector
Loosen the lock nut at the top of the element and run
the core screw down until it is flush with the top of the
lock nut. Back off the Micarta disc by loosening the
two lock nuts. Apply 0.15 amperes to terminals 14
and 15. Operate the moving element by hand and
allow the current to hold the moving contact disc
against the stationary contacts. Now, screw up the
core screw slowly. This causes the plunger to move
up, compressing the spring until a point of maximum
deflection is reached. Further upward motion will
cause the plunger to drop part way out of the coil,
thus diminishing the spring pressure on the contacts.
By thus adjusting the core screw up or down the
maximum spring deflection for this value of current
may be found.
Then lock the core screw in place. Next, adjust the
de-energized position of the plunger by raising the
Micarta disc until the plunger just picks up electrically
at the 0.15 ampere value.
7.7. Electrical Checkpoints
Figures 9 and 10 will aid in trouble shooting the
CA-16. These curves show the operating current to
trip the relay for different restraint current for one
restraint element as well as for six restraint elements
connected in series.
8.0 RENEWAL PARTS
Repair work can be done most satisfactorily at the
factory. However, interchangeable parts can be fur-
nished to customers who are equipped for doing
repair work. When ordering parts, always give the
complete nameplate data.
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