K2CM

7

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

follows:

1. On the R axis, locate point A, where I

2. Move from point A to point B, where I

3. On the T axis, locate point C, where I

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

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

80.0

85.0

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

switch

Maximum phase of

current: R phase = 1.0

"Low"

"High"

A

35%

60%

25%

Non-operating

area

"High"

operating

area

"Low"

operating

area

Non-detecting area

Detecting area

Motor

Start

U

V

W

Reverse-phase output