INSTALLATION
Westinghouse
I . L . 4 1 -337 .38
•
OPERATION
•
MAIN TENANCE
INSTRUCT I O N S
TYP ES CA -16
and
CA -26 PERCE N TAGE DIFFERE N TIAL
R ELAYS F O R B U S A N D T R A N S F O R M E R P R OTECTI O N
C A U T I O N
Before putting relays into service, remove
all blocking which may have been inserted for the
purpose of securing the p arts during shipment, make
sure that all moving p arts operate freely, inspect the
contacts to see that they are clean and c lose properly,
and op erate the relay to chec k the settings and elec
trical connections.
A P P L I C A T I O N
The current transformers should not saturate
when carrying the maximum external 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 ex ceed Np V cL/ 133,
where:
Np = proportion of total CT turns in use
V CL = current transformer 10L accuracy-class
voltage
The burden voltage is described as:
Case 1 : Fault current maximum of 100A rms in CT
secondary - drop across 2-way lead burden
and relays (CA- 1 6 and CA- 2 6 restraint-coil
burden is negligible).
Case 2: Fault current greater than lOOA rms in CT
secondary - drop acro ss 2-way lead burden
and relays plus:
(!EXT - 100) ReT
where !EXT = max. external symmetrical
fault current in sec ondary
rms amp eres.
ReT
=
CT resistance, ohms
For example, if the 400/5 tap of 600/5
10L 200
wye-connected CT' s are used
Np
=
400/ 600
=
0 . 67; if !EXT
=
100A, the
burden (excluding CT resistance) should
not exceed:
Np VcL/ 133
=
(0. 67 x 200)/ 1 3 3
=
1 . 0 ohms.
C O N T E N T S
This instruction leaflet !.pplies to the following
typ es of relays:
CA- 16 Bus Differential Relay
CA- 26 Transformer Differential Rel ay
SUPERSEDES I . L . 4 l -337.3A
*Denotes change from superseded i ssue.
The CA- l� relay should not be utilized for transformer
differential applications. Likewise the O.A-26 relay
should not be used for bus p rotection with the "four
circuit bus" connections of Fig.
8 .
The CA-26 relay
is suitabl e for combination bus-transform er applica
tions. See "Connections" .
C O N S T R U C T I O N
The type CA- 16 relay consists of an indicating
contactor
switch , autotransformer, three re straint
el ements , and an operating el ement. For applic ations
where the CA- 16 rel ay is subjected 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 components of
the CA- 16 relay) also contains an indic ating instan
taneous trip unit. The principal component p arts of
the relay and their location are shown in Figures 1
to 5 .
R e s tra i n t E l e m e n t s
E ach restraint element consists o f a n
•
'E " lami
nated electromagnet with t wo primary c oils and a
secondary c oil on its center leg. Two identical c oil s
on the outer legs of the l am in ated structure are con
nected to the secondary winding in a m anner 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 c ause a contact open
ing torque.
O p e ra t i ng C i r c u i t
The op erating circuit consists of 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 unbalanced cur
rent from the various transformers connected to the
bus. The s econdary winding of the auto-transformer,
which is a tapped section of the w inding, is con -
nected to the operating e lement of the relay.
The operating element consists of an "E " type
E F FECT I VE FE BR UAR Y 1 969
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