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9.3
General Formulas Use for Estimation
The example below calculates the braking torque and the discharging resistance of a motor for
traveling machine.
(1) Rated motor torque T
T
= 9550
M
where
: Rated capacity of the motor (kW)
P
M
: Rated revolutions per minutes of the motor (r.p.m.)
N
M
(2) Braking torque (required to decelerate) T
* While this value is negative, only the inverter can brake the motor. (The BRD is not
required.)
J (N
1
T
=
B
9.55 t
where
Moment of inertia of the motor and the load (converted to motor shaft) (kg . m
:
J
: Rotational speed (r.p.m.) before deceleration and rotational speed (r.p.m.) after
N
, N
1
2
deceleration
Load torque (converted to motor shaft) (N . m)
:
T
L
:
Deceleration time (seconds)
t
B
(3) Discharging resistance R (ohms): Resistance relative to the inverter
* If this value is under the minimum value of a BRD, two or more BRDs are required.
R =
0.105
where
:
BRD operating voltage (362.5 V for the 200V class or 725V for the 400V class)
V
on
(4) Mean discharging capacity PL (W)
* The capacity of the discharging resistor should be 2.5 to 3 times the result of the formula
below.
0.105 (T
P
=
L
where
:
Operation cycle(s)
t
C
(5) Duty cycle
‡ @ The duty cycle (
t
1
B
• ...
t
5
C
‡ A The dynamic braking unit can be used continuously for the use of the discharging
resistor II.
* See 9.3 (4) for capacities of the discharging resistors.
* See Table 7.1 for details of the discharging resistors I and II.
(6) Thermal set value
Thermal set value (A) ‡ •
* This is a reference value for enameled and ribbon resistors.
(N . m)
M
P
M
N
M
N
)
2
T
L
B
2
V
1
on
1.2
T
N1
B
0.2 T
) (N
+ N
B
M
1
2
/
t
t
B
C
/
) for the discharging resistor I is as follow:
t
t
B
C
t
1
B
• ...
EZ2-30K:
t
10
C
Rated capacity of the discharging resistor (W)
(N . m)
B
t
)
2
B
t
C
2
- 23 -
Resistance of the discharging resistor ( )
2
)
1.2
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