41-337.31B
4
required to close the relay contacts, expressed in
percent of the total restraint current, varies with the
magnitude of the restraint current. The relay sensi-
tivity is high, corresponding to a low percentage
ratio, at light currents, and its sensitivity is low, cor-
responding to high percentage unbalance, at high
currents. The relay is made sensitive at low cur-
rents in order to detect light internal faults on the
bus being protected. At the same time, however, its
reduced sensitivity at the higher currents allows the
various current transformers involved to depart
from their true ratio to a large extent without caus-
ing false tripping of the relay for external faults.
The variable percentage characteristics are partic-
ularly advantageous when severe saturation of cur-
rent transformers is caused by the dc component of
asymmetrical short circuits. In the case of buses
located close to generating stations where the dc
components decay slowly, the breakdown in ratio of
the current transformers will be much greater than
would ever be expected from a consideration of the
usual ratio curves of the current transformers
involved.
The time of operation of the relay is shown in Fig-
ure 4.
The main contacts will safely close 30 amperes at
250 volts dc and the seal-in contacts of the indicat-
ing contactor switch will safely carry this current
long enough to trip a circuit breaker.
The indicating contactor switch has two taps that
provide a pick-up setting of 0.2 or 2 amperes. To
change taps requires connecting the lead located in
front of the tap block to the desired setting by
means of a screw connection.
4.2.
Trip Circuit Constants
Indicating Contactor Switch (ICS)
0.2 amp rating
8.5 ohms dc
1.0 amp rating
0.37 ohms dc
2.0 amp rating
0.10 ohms dc
ENERGY REQUIREMENTS
Burden of each restraint coil at 5 amperes
VOLT AMPERES
POWER FACTOR
.75
.7
Continuous Rating
14 amperes
1 second rating
460 amperes
Burden of operating Circuit
VOLT AMPERES
VARIABLE (See
Figure 5)
Continuous rating 8 amperes
1 second rating 280 amperes
4.3.
Connections
4.3.1. CA-16
To determine the ac connections, identify each pri-
mary circuit as either a “source” or “feeder”. As
defined here, a feeder contributes only a small por-
tion of the total fault-current contribution for a bus
fault. Otherwise, the circuit is a source. Next lump a
number of feeders into a “feeder group” by paralleling
feeder ct’s, taking the precaution that each feeder
group has less than 14 amperes load current
(restraint coil continuous rating). Also each feeder
group should not contribute more than 10% of the
total phase or ground-fault current for a bus fault if
Figure 7 is to be used.
Connect per Figure 6 with three or four bus “circuit.”
The term “circuit” refers to a source or to a feeder
group. For example, assume a bus consisting of 2
sources and 6 feeders. Further, assume that the
feeders are lumped into 2 feeder groups. The bus
now reduces to four circuits
If the bus reduces to more than four circuits, parallel
source-circuit ct’s or source-and feeder circuit ct’s
until only four circuits remain. Then connect these
four sets of ct’s to the relays per Figure 6. The excep-
tion to this rule occurs when the application consists
of three feeder groups. Then Figure 7 applies.
With 3 feeder groups and more than 3 sources, paral-
lel source ct’s until the application reduces to 6 cir-
cuits; then, connect to the relays per Figure 7.
4.4.
Setting Calculations
No calculations are required to set the CA-16.
4.5.
Setting The Relay
No settings are required on the CA-16 relay.
5.0
INSTALLATION
The relays should be mounted on switchboard panels
or their equivalent in a location free from dirt, moisture,
excessive vibration and heat. Mount the relay verti-
cally by means of the four mounting holes on the
flange for the semi-flush type FT case. The mounting
screws may be utilized for grounding the relay. Exter-
nal toothed washers are provided for use in the loca-
tions shown on the outline and drilling plan to facilitate
making a good electrical connection between the relay
case, its mounting screws and the relay panel. Ground
Wires are affixed to the mounting screws as required
for poorly grounded or insulating panels. Other electri-
cal connections may be made directly to the terminals
by means of screws for steel panel mounting.
