Westinghouse
I . L.
4 1 - 337. 2C
INSTALLATION
•
OPERATION
•
MAINTENANCE
INSTRUCT IO N S
T Y P E S C A -1 6
a n d
C A - 2 6 P E R C E NT A G E D I F F E R E NTI A L
R ELAY S F O R B U S A N D T R A N S F O R M E R P R OT E CTI 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 fre ely, inspect the
contacts to see that they are clean and c lose prop erly,
and operate the relay to check the settings and elec
trical connections.
AP P L I CAT I O N
The types CA- 16 and CA-26 relays are used for
the differential protection of multi-circ uit buses and
transformers resp ectively. The two relays differ in
their sensitivity and p ercentage differential charac
teristics. The following paragraphs describ e the ap
plic ation re quirements.
1. The maximum external symmetrical fault current
through the bus should not exceed 100 amperes
rms secondary current .
2. The current transformer burden external to the
CA- 16 or CA-26 relays should not e xceed (NpVcL)
I 133 ohms. Where
Np = Proportion of total number of
CT
turns in use
V CL = Current transformer 10L accuracy class
voltage
For example , if the 40015 of a 60015 multi- ratio
C'l;' is used, Np = 400 I 600 = 0. 67. If this CT has
a 10L 200 rating, V CL
=
200 and the external bur
den should not exceed
(Np VcL)I 133 = ( 0 . 67 x 200)I 133 = 1.0 ohms
In calculating the burden, use the two way lead
burden.
CON T E N T S
This instruction leaflet !.{)plies to the following
SUPERSEDES I . L.
4 1 - 337. 26
*Denotes change from superseded i ssue.
typ es of relays:
CA- 16 Bus Differential Relay
CA-26 Transformer Differential Rel ay
The bus relay should not be utilized for transformer
differential app lic ations.
CON S T R U C T 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 rel ay is subj ected to shock such as
on swinging p anels , a se nsitive fault detector circuit
is provided.
The type CA- 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 loc ation are shown in Figures 1
to 5 .
R e stra i n t E l e m e n t s
Each restraint element consists of an "E" lami
nated electromagnet with two primary c oils and a
secondary coil on its center leg. Two identical coils
on the outer legs of the l aminated 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 cause a contact open
ing tor que.
O p e r at i n g C i r c 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
EFFECTI VE DECEMBER
1965
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