Westinghouse KAB Installation, Operation & Maintenance Instructions Manual

CAU T I ON:
Before putting relays into servic e , remove
all block ing which may have been inserted for the
purpose of securing the parts durin g shipment, make
sure that all moving parts operate freely , inspect
the contacts to see that they are clean and clo s e
properly, and operate the relay t o check the settings
and el ectrical connections .
A P P L I C AT I O N
The type KAB re lay i s a n instantaneous r e lay o f
the high impedance type u s e d for b u s diffe rential
protection.
*
AP P L I CAT I O N
The type KAB re lay can b e applied for bus
p r otection in most cas e s wh ere bushing typ e ct's
are in use, and in metal-clad equipment where ct's
with toroidally wound cores have their windings
completely distributed are emplo y ed. Dwg.
shows the external connection .
The following points should be considered or
should be kno wn on any proposed type KAB rela y
application :
A l l ct's i n the b u s differential circuit should
1 .
have the same ratio, and should be op erated on
their full tap . I f tap conne ction cannot be avoid­
ed, the winding section between the tap s being
used must be fully distributed and the high
voltage which may appeaT at the full tap terminal
due to the auto-trans former action should b e
check ed.
The leakage impedance of the ct 's which are to
2.
be used should be low.
3. The use of the auxiliary ct's is not recommend­
ed. I f this cannot be avoided the additional
impedance from the auxiliary ct's and the high
voltage which transformed by the auxiliary ct
should be check ed.
SUP E R S E D E S I . L. 41-337.4
*Denotes change f rom s upe rseded 1ssue.
INSTALLATION
INSTRUCTIONS
TYPE KAB HIGH IMPEDANCE
BUS DIFFERENTIAL RELAY
C ON S I D E R AT I ON S
265C 196
Westinghou se
OPERATION
•
4.
The b est location for the j unction points i s
equidistant from all ct's.
The lead re sistance from the j unction points to
5 .
the relay terminals is not critical .
A lockout rela y cont act is recommended to short
6.
circuit the varistor following the relay operation
in order to prevent the varistor from o ve rheating.
7 .
T o insure a substantial margin of o peration the
voltage-unit should not be set higher than V K •
where V K =the k nee voltage value of the p oorest
ct which b e conne c ted to the r elay. The k ne e
voltage i s defined a s the inters ec tion of the
extension of the two straight line portions of the
saturation c ur v e , ordinate and abscissa must
be same s cale for each d ecad e .
8 . T h e maximum number o f circuit s which can b e
connected t o the relay or the minimum internal
fault current r e quired to ope rate the r elay c an
be estimated from the following e quation
+
l min. = ( X Je
where I min. =minimum internal fault current , RMS.
= ct secondary excitation current at
I e
a voltage
=
v alue of V-unit .
C urrent in V-unit at setting voltage
I
R
V R (i . e. l R =
I y = Cur rent
voltage equal to th e setting value
of V-unit.
=
N
ct turn's ratio.
X
= Number of circuits connected to
the bus .
CON S T R U C T I O N
The re lay consists of a high speed overvoltage
cylinder unit (V) a high speed ov ercurrent unit ( I T) ,
EFFE C T I V E DECEMBER 1 973
I . L. 41-337.4A
MAINTENANCE
•
ly)
+
l R N
equal to the setting
VR,/2600)
in varistor circuit at a