Type CKO Overcurrent Relay
41-101.3A
3
Time
Characteristic
Designation
Short Time
2
Long Time
5
Definite Time
6
Moderately Inverse Time
7
Inverse Time
8
Very Inverse Time
9
Extremely Inverse Time
11
The relays are available in the following current
ranges:
INSTANTANEOUS OVERCURRENT UNIT (1)
Range
Taps
0.5 - 2 Amps
0.5
0.75
1.0
1.25
1.5
2
1 - 4
1.0
1.5
2.0
2.5
3.0
4.0
2 - 8
2
3
4
5
6
8
4 - 16
4
6
8
9
12
16
10 - 40
10
15
20
24
30
40
20 - 80
20
30
40
48
60
80
The indicating contactor switch has two taps that
provide a pickup 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.
3.2
Contacts
The moving contact assembly has been factory ad-
justed for low contact bounce performance and
should not be changed.
The set screw in each stationary contact has been
shop adjusted for optimum follow and this adjust-
ment should not be disturbed.
The tap value is the minimum current required to just
close the overcurrent relay contacts. For pickup set-
tings in between taps refer to the section under ad-
justments. The pickup and dropout time curves for
the instantaneous overcurrent units is shown in Fig-
ure 9.
TIME OVERCURRENT UNIT
Range
Taps
.5 - 2.5
0.5
0.6
0.8
1.0
1.5
2.0
2.5
2 - 6
2
2.5
3
3.5
4
5
6
4
- 12
4
5
6
7
8
10
12
The tap value is the minimum current required to just
close the relay contacts.
This time vs. current characteristics for the time-
overcurrent unit are shown in Figures 2 to 8. These
characteristics give the contact closing time for the
various time dial settings when the indicated multi-
ples of tap value current are applied to the relay.
3.1
Trip Circuit
The relay contacts will safely close 30 amperes at
250 Vdc and the seal-in contacts of the indicating
contactor switches will safely carry this current long
enough to trip a circuit breaker.
Figure 1. Internal Schematic of the Type CKO
Relay in the Type FT31 Case.
880A450
Sub 4
3.2.1
Trip Circuit Constants
Indicating Contactor Switch
0.2 ampere tap - 6.5 ohms dc resistance
2.0 ampere tap - 0.15 ohms dc resistance
4.0 SETTINGS
4.1
Time Overcurrent Unit (CO)
The time overcurrent unit settings can be defined ei-
ther by tap setting and time dial position or by tap
setting and a specific time of operation at some cur-
rent multiple of the tap setting (e.g., 4 tap setting, 2
Summary of Contents for CKO-5
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