Westinghouse
I.L. 41-337.3F
INSTALLATION
•
OPERATION
•
MAINTENANCE
INSTRUCTIONS
TYPES CA-16
and
CA-26 PERCENTAGE DIFFERENTIAL
RELAYS FOR BUS AND TRANSFORMER PROTECTION
CAU T IO N
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 elec
trical connections.
*
APPLICAT I ON
The currl�nt transformers should not saturate
when carrying the
maximum
external fault current.
This requirement is met if the burden impedance
NpVcL
-
<Iext.-100) RsCos 60°.
dol's not exceed
tor
1.
33
(I
e
x
t
.l
CA-16
.
.
60°
ap ph
c
a t10n
s
and
I
ext.
for
CA-26
applications.
\\·her e Np
proportion of total ct turns in use.
V cL =current transformer accuracy class
C
voltage.
Ir•xt.
=maximum external fault current in
secondary RMS amperes. (let
I
e
x
t
.
=
100
if
m ax.
external fault current is
less than
lOOA)
R s
=
current transformer secondary winding
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
e
x
t
.
=
120A,
Rs
=
1.0
ohm the burden should not
exceed:
NpVel- Oext. -
100)
Rs Cos
60°
1.33
(!ext.)
0.50
X
400- ( 120-100)
X
1.0
X
0.866
1.33
X
120
CO N T E N T S
=
1.14
ohms
This instruction leaflet 8.!Jplies to the following
types of relays:
CA- 16
Bus Differential Relay
CA- 26
Transformer Differential Relay
SUPERSEDES I.L. 41-337.3 E
*Denotes change from superseded 1ssue.
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 Fig.
8.
The
CA-26
relay
is suitable for combination bus-transformer applica
tions. See "Connections".
CONS T RUCT I ON
The type
CA-16
relay consists of an indicating
contactor
switch, autotransformer, three restraint
elements, and an operating element. For applications
where the
CA-16
relay is subjected to shock such as
on swinging panels, a sensitive fault detector circuit
is provided.
The type
CA-26
(in addition to the components of
the
CA-16
relay) also contains an indicating instan
taneous trip unit. The principal component parts of
the relay and their location are shown in Figures
1
to
5.
Res tra i nt E l emen t s
Each restraint element consists o f a n "E" lami
nated electromagnet with two primary coils a nd a
secondary coil on its center leg. Two identical coils
on the outer legs of the laminated structure are con
nected to the secondary winding in a manner so that
the combination of all fluxes produced by the elec
tromagnet results in out-of phase fluxes in the air gap.
The out-of-phase fluxes cause a contact open
ing torque.
O p erating C i rc u i t
The operating circuit consists of an auto-trans -
former and an operating element. The primary of the
auto- transformer, which is the whole winding, is con
nected to receive the differential or unbalanced cur
rent from the various transformers connected to the
bus. The secondary winding of
t
he auto-transformer,
which is a tapped section of the winding, is con -
nected to the operating element of the relay.
The operating element consists of an "E" type
EFFECTIVE SEPTEMBER 1974
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