K2CM
6
Output Circuits
■
Internal Circuit and Operation Description
1) Overcurrent Circuit
Overcurrent Detecting Circuit
This circuit detects when the current reaches the overcurrent operat-
ing level (115% of the set current value).
Time Setting Circuit (Inverse Type)
This circuit performs time setting using the VR (variable resistor) for
the operating time setting and obtains inverse-type characteristics
using an RC time-limiting circuit. The operating time can be set within
a range from 2 to 10 s or 8 to 40 s by operating the setting switch
using a VR. The VR covers a time range 5 times the standard range.
Start-up Detecting Circuit (Instantaneous Type)
Instantaneous-type models output a trip signal instantaneously when
the motor current exceeds the overcurrent operating value (115% of
the set current value). At the start of motor operation, a starting cur-
rent several times the rated current flows and so to prevent the motor
circuit being tripped by the starting current, instantaneous operation
is not enabled until a fixed time tc has elapsed, as shown in the fig-
ure. Instantaneous operation starts after tc has elapsed. Motor start-
ing time “to” varies, depending on motor type, within a range from
several seconds to several tens of seconds. There are even slight dif-
ferences in starting time between the same type of motors and so be
sure to set tc so that to to<tc is satisfied. If to>tc, the motor circuit will
be tripped after tc has elapsed. The fixed time limit tc at the start of
motor operation is called “lock time”. The start-up detecting circuit
detects the starting operation level (30% max. of the set current
time).
Starting Time Setting Circuit (Instantaneous Type)
This circuit performs time setting using the VR for setting the start-up
lock time and obtains fixed time-limit characteristics using an RC
time-limiting circuit.
Operation at start-up is shown in the figure below. After the motor
turns ON at point A, the motor’s starting current exceeds the start-up
operating value and so the RC time-limiting circuit starts charging. If,
for example, the motor current descends below the start-up operat-
ing value (30% max. of the set current value) at point B before the
start-up lock time, tc, has elapsed, the RC time-limiting circuit is reset
immediately and when the motor current rises above the start-up
operating value again at point C, the RC time-limiting circuit starts
charging again. After the start-up lock time has elapsed (at point D),
instantaneous operation is enabled. At the start of operation, the
motor current is at its peak immediately after operation starts. It then
lowers and settles at the rated current. The peak current is about 5 to
6 times the rated current and takes from several seconds to several
tens of seconds to settle to the rated current. This time varies largely
depending on type of motor and the nature of motor load (wt). There-
fore, it is necessary to obtain the motor’s starting time for operation
with the load and to set a start-up lock time that allows for a margin of
error. Do not set an unnecessarily long start-up lock time. If the start-
up lock time is too long and an accident due to overcurrent occurs at
the start of operation, the trip signal will not be output until the start-
up lock time has elapsed, possibly resulting in motor burnout.
W
ith instantaneo
u
s-type
models, the circ
u
it section
enclosed
b
y is
config
u
red as sho
w
n
b
elo
w
.
S
1
S
2
A
R S T
Test
bu
tton
Reset
bu
tton
To each
circ
u
it
X
O
v
erc
u
rrent
indicator
Open-phase
indicator
Re
v
erse-
phase
indicator
LED
LED
LED
X/
b
2
X/
a
1
C
2
C
1
1
b
2
a
1
To OR circ
u
it
To each circ
u
it
To each circ
u
it
U
V
W
Instantaneous Type
B
C
Volta
g
e Reverse-phase
Detection Models
2
3
M
Rectifier/smooth-
ing circ
u
it
V
oltage
circ
u
it
for test
T
o each circ
u
it
Reset circ
u
it
Rectifier/smooth-
ing circ
u
it
Rectifier/smooth-
ing circ
u
it
Rectifier/smooth-
ing circ
u
it
Re
v
erse-phase
detecting circ
u
it
Re
v
erse-phase
le
v
el detecting
circ
u
it
OR circ
u
it
Rela
y dr
i
v
e
circ
u
it
Maxim
u
m
v
al
u
e
detecting circ
u
it
C
u
rrent-setting
circ
u
it
O
v
erc
u
rrent
detecting circ
u
it
Time-setting
circ
u
it
Open-phase le
v
el
detecting circ
u
it
Open-phase
detecting circ
u
it
W
ith the
v
oltage re
v
erse-phase
detection models, the circ
u
it
section enclosed
b
y in the
diagram on the left is config
u
red as
sho
w
n
b
elo
w
. The circ
u
it section
enclosed
b
y is not
u
sed.
A
C
Re
v
erse-phase
detecting circ
u
it
Rectifier/smooth-
ing circ
u
it
B
Reset circ
u
it
O
v
erc
u
rrent
detecting circ
u
it
A
N
D circ
u
it
Star
t time
setting circ
u
it
Star
t-
u
p
detecting circ
u
it
Inverse and Instantaneous
Types
As shown on the right, the K2CM
detects abnormalities in motor M
by checking its line current. The
motor’s current signal is detected
by the current transformer and is
processed separately for each
phase and input to the respec-
tive circuits. In each circuit, par-
allel judgement of failure such as
overcurrent, open-phase, or
reverse-phase (see note) is
made based on the input signals.
If a failure is detected in a circuit,
the circuit’s output is input to the
indication circuit to illuminate the
corresponding LED indicator and
also input to the relay drive cir-
cuit to drive relay X, resulting in a
trip signal to be externally output
from it. The three major circuits
are described below.
Note:
Applies to current reverse-
phase detection models
only.
to
tc
Start
Motor c
u
rrent
Operating mode
Instantaneo
u
s operation ena
b
led
Fixed time-limit
operation
O
v
erc
u
rrent operating
v
al
u
e
to: Motor's starting time
tc: Lock time at start of operation
Start
Start
tc
tc
tc
Start
Trip
O
u
tp
u
t
Operation
mode
Motor
c
u
rrent
tc: Start-
u
p lock time
*: Fixed time-limit operation
A
B
C
D
E
F
H
G
O
v
erc
u
rrent
operating
v
al
u
e
Start-
u
p
operating
v
al
u
e
**: Instantaneo
u
s operation ena
b
led
*
*
*
**
**
