41-337.3L
8
appreciable if the contribution to an internal fault is
supplied principally by only a single circuit. 100
amperes from a single circuit in the four bus circuit
arrangement produces only a small net torque, and a
corresponding long operating time, because it must
flow through two restraining coils in series.
Therefore, where one circuit supplies 70 percent or
more of the total fault current for an internal fault on
the bus, only a single restraint should be effective for
this circuit. The circuits should be grouped as for the
three circuit bus or for the six circuit bus. Where
feeder ct’s are paralleled to reduce the effective num-
ber of circuits to six, they should collectively contrib-
ute no more than 10 percent of the total phase or
ground-fault current.
4.6.2. CA-26
Figure 10 shows the CA-26 relay connections for a 3
circuit bus. Where additional circuits are present, use
the Figure 9 connections; where there are more than
three sources, the source ct’s should be paralleled to
reduce the effective number of source connections to
three. The “four-circuit bus” connections of Figure 8
are not recommended to be used for bus protection
with the CA-26 since it may have too much restraint
when energizing a bus fault. Otherwise the connection
considerations are as described above for the CA-16.
5. SETTING CALCULATIONS
No calculations are required to set the CA-16 and
CA-26 relays.
5.1.
Setting the Relay
No settings are required on either the CA-16 or the
CA-26 main units.
5.2.
Indicating Contactor Switch (ICS)
No setting is required on the ICS unit except the
selection of the 0.2 or 2.0 ampere tap setting. This
selection is made by connecting the lead located in
front of the tap block to the desired setting by means
of the connecting screw. When the relay energizes a
Sub 5
187A426
Figure 11: Diagram of Test Connections for the CA-16 and
CA-26 Relays.
Sub 1
849A450
Figure 12: Percentage Slope Curve of the CA-16 and CA-
26 Relays with One Restraint Winding.
