ABB Automation Inc.
Substation Automation and Protection Division
Coral Springs, FL 33065
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.
!
CAUTION
Before putting protective relays into service,
remove all blocking 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. APPLICATION
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
N
p
= proportion of total ct turns in use.
V
cL
= Current transformer accuracy class
C voltage.
I
ext.
= maximum external fault current in
secondary RMS amperes. (let I
ext
. =
100 if max. external fault current is
less than 100A)
R
s
= current transformer secondary wind-
ing resistance, ohms.
For example, if the 400:5 tap of 800:5 C400 current
transformers are used, N
p
= 400/800 = 0.50, if I
ext.
=
120A, R
s
= 1.0 ohm the burden should not exceed:
N
p
V
pL
I
ext.
100
–
(
)
R
s
–
1.33 I
ext.
(
)
------------------------------------------------------------
for CA-16 applications
N
p
V
cL
I
ext.
100
–
(
)
R
s
–
I
e xt.
--------------------------------------------------------------
for CA-26 appliations
N
p
V
cL
I
ext.
100
–
(
)
R
s
–
1.33 I
ext.
(
)
--------------------------------------------------------------
=
0.05
400
120
100
–
(
)
–
×
1.0
×
1.33
120
×
-------------------------------------------------------------------------------
1.13 ohms
=
Types CA-16 and CA-26
Percentage Differential Relays
for Bus and Transformer
Protection
Effective: September 1995
Supersedes I.L. 41-337.3K, Dated October 1985
( | ) Denotes Changes since previous issue
41-337.3L
CONTENTS
This instruction leaflet applies to the following
types of relays:
CA-16 Bus Differential Relay
CA-26 Transformer Differential Relay
The CA-16 relay should not be utilized for trans-
former differential applications since it is too sensi-
tive for overriding the inrush. Likewise the CA-26
relay should not be used for bus protection with
the “four-circuit bus” connections of Figure 8. The
CA-26 relay is suitable for combination bus-trans-
former applications. See “CONNECTIONS”.
