Westinghouse
I . L .
4 1 -337.3D
INSTALLATION
•
OPERATION
•
MAINTENANCE
INSTRUCT I O N S
TYPES CA-16
and
CA -26 PERCENTAGE DIFFERENTI AL
RELAYS FOR BUS AND
PROTECTION
C A U T I O N
Before putting relay s into serv i c e , remove
all blocking whic h may have been inserted for the
p urpose of sec uring the p arts during shipment, make
sure that al l moving p arts operate fre ely, inspect the
contac ts to see that they are clean and c lo s e properly ,
and operate the relay to c heck the settings and elec
tric al connections.
A P P L I C A T I O N
The current tr ansformers should not saturat e
when carrying t h e maximum ext ernal symmetrical
fault current (i . e. , exciting current should not exceed
one secondary amp ere, rms). This requirement is met
if the burden voltage does not exceed Np V cL/ 1 3 3 ,
where:
Np
=
proportion of total CT turns in use
V CL
=
current transformer 1 0L accur acy-class
voltage
The burden voltage is described as:
Case 1: Fault current maximum of 100A rms in CT
se condary - drop across 2-way l ead burden
and relays ( CA- 1 6 and CA- 2 6 restraint-coil
burden is negligible).
Case 2: Fault current greater than 100A rms in CT
secondary - drop acro ss 2-way lead burden
and relays plus:
(IEXT - 100 l ReT
where IEXT
=
m ax.
external
symmetrical
fault current in secondary
rms amperes.
ReT
=
CT
resi stance,
ohms
For example, if t he 400/5 tap of 600/ 5
10L 200
wye- connected CT ' s are used
Np
=
400/ 600
=
0 . 67; if IE XT
=
1 00A, the
burden (excluding CT resistance) should
not exceed:
Np VcL / 1 3 3
=
(
0 . 67 x 200)/ 1 3 3
=
1 . 0 ohms.
C O N T E N T S
This instruction leafl et e_ppli e s to the followin g
typ es of relays:
CA- 16 Bus Differential Rel ay
CA-26 Transformer Differential Rel ay
S U P E R S E D E S I . L .
41 -337 .3C
*Denotes change from superseded i ssue.
*
T_h e C A-
�
6
be u_til
�
zed for tra�s form er
differential
since It IS too se nsitive for
overriding the i nrus-h.._; Likewise the C A-26 relay
shoul d not be us ed- rpr:bus protecti on with the " four-
\ ··_.;c,i.rcuit bus " corn�c.
tYo
ns of Fig.
8.
The CA- 26 re lay
\,, is .
suitable
bus-transformer applica
tions.
See
' .
C O N S T R U C T I O N
The type CA- 1 6 r elay consists of an indicating
contactor
switch , autotransformer, three re straint
el em ents , and an op erating el ement. For applic ations
where the CA- 1 6 rel ay is subj ected to shock such as
on s winging p anels , a sensitive fault detector c ircuit
is provided.
The type C A- 26 (in addition to the c o mponents o f
the C A- 1 6 rel ay) also contains an indic ating instan
taneous trip unit. The princip al c o mponent p arts of
the relay and their location are s ho wn in F igure s 1
to 5 .
Restr a i nt E lements
Each restr aint element consists of an " E " l ami
nated electromagnet w ith t wo primary c oils and a
secondary c oil on its center leg. Two identic al c oil s
on the outer legs of the l am inated structure are con
nected to the secondary wind ing in a m anner s o that
th
e
combination of all fl uxes produced b y the elec
tromagnet results in out-of p hase fluxes in the air gap .
The
out-of-phase fluxes c ause a contact open
ing torque.
O perating C i r cui t
The operat ing c irc uit consists o f an auto-trans -
former and an operating element. The primary of the
auto- transformer, which is the whole winding, is c on
nected to receive the differential or unbal anced c ur
rent from the v arious transformers connected to the
bus. The s econdary w inding of the auto-transformer,
which is a t apped section of the w inding, i s con
nected to the operating e le ment of the r el ay.
The operating element consists of an " E " type
E F F E C T I V E OCTO B E R
1 972
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