7
K2CM
2) Open-phase Circuit
Open-phase Level Detecting Circuit
This circuit detects when the current reaches the open-phase operat-
ing level (85% max. of the set current value). Therefore, open-phase
is not detected until the maximum phase of the current exceeds 85%
of the set current value.
Open-phase Detecting Circuit
Output of the maximum value detecting circuit is divided and used as
reference values for comparison with the output of the rectifier/
smoothing circuits for the respective phases. If a phase has a value
lower than the reference value, the K2CM judges it to be open-phase
and outputs an open-phase signal.
The following imbalance factors can be selected by setting the open-
phase switch.
“High” . . .Operating imbalance factor: 35
±
10%
“Low” . . .Operating imbalance factor: 60% min.
The imbalance factor can be easily obtained from the following
graph. In the graph, the horizontal axis indicates the maximum phase
of the current whereas the two vertical axes indicate the remaining
two phases. The maximum phase of the current is taken to be 1.0 as
a reference point. The imbalance factor is obtained as a percentage
from the curve around the center of the graph. Obtain the imbalance
factor for a motor current with I
R
= 100 A, I
S
= 70 A, and I
T
= 60 A as
follows:
1.
On the R axis, locate point A, where I
R
= 1.0.
2.
Move from point A to point B, where I
S
= 0.7 on the S axis.
3.
On the T axis, locate point C, where I
T
= 0.6.
4.
Follow the curves that pass through points B and C and locate the
intersection point D.
5.
Locating the point corresponding to point D on the imbalance fac-
tor curve gives an imbalance factor of 36%. Take the maximum
phase of current on the horizontal axis without considering axes
R, S, and T.
Generally, in open-phase detection, detecting a complete open-
phase is sufficient. In such a case, set the open-phase switch to the
“Low” position. If using the motor in an imbalanced condition causes
problems, or when detecting internal open-phases of a delta-con-
nected motor, set the switch to the “High” position. Depending on the
motor’s load condition and the imbalance of the power supply, how-
ever, special consideration may be required for the detection of inter-
nal open-phases in delta-connected motors. Consult your OMRON
representative before using this method. When a transformer is con-
nected as a load, the harmonics increase at low loads. Therefore, in
such a case, set the open-phase switch to the “Low” position.
3) Reverse-phase Circuit
1. Current Reverse-phase Detection Models
Reverse-phase Level Detecting Circuit
This circuit detects whether the current is in the operating level (50%
max. of the set current value) as a precondition to detect the reverse-
phase.
Reverse-phase Detecting Circuit
The current reverse-phase detecting method is employed for detect-
ing reverse-phase as shown below. After the motor starts operating,
the current phase becomes transiently unstable during T1 (approx.
0.4 s) and so reverse-phase detection is not performed during this
period but it is performed during T2 (approx. 0.1 s). After T2 has
elapsed, reverse-phase detection is not performed. For this reason,
this method cannot be applied to cases where instantaneous
reverse-phase is not permitted. When a reverse-phase is detected,
the relay is held in the latched state even after the motor current
stops (in both manual and automatic release types).
2. Voltage Reverse-phase Detection Models
Reverse-phase Detecting Circuit
Reverse-phase detecting is performed by using the voltage reverse-
phase detection method.
By voltage division within the above RC phase circuit, the output
becomes 0 V in the normal state or 1.5 V
uv
in the reverse-phase
state. Using the output from this circuit, the reverse-phase level
detecting circuit detects when the current reaches the reverse-phase
operating level (80% or less of the control power supply).
90.0
95.0
8
0.0
8
5.0
75.0
65.0
70.0
60.0
50.0
55.0
40.0
45.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
Point D
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
T (R, S) 0.
8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.
8
S (T, R)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.
8
0.9
1.0
Point B
Point C
Point A
R (S, T)
1.0
0.5
0.5
1.0
0
S phase
T phase
Open-phase
s
w
itch
Maxim
u
m phase of
c
u
rrent: R phase = 1.0
"Lo
w
"
"High"
A
35
%
60
%
25
%
N
on-operating
area
"High"
operating
area
"Lo
w
"
operating
area
T
1
N
on-detecting area
Detecting area
T
2
Motor
Start
U
V
W
Re
v
erse-phase o
u
tp
u
t
Re
v
erse-phase le
v
el
detecting circ
u
it
OR phase circ
u
it
