Emerson Powerdrive F300 - Page 60

Time for Motor Protection Accumulator to reach 100%
Assuming a single time constant model is being used (i.e. Motor Thermal Time Constant 2 Scaling (04.038), the time for
the Motor Protection Accumulator (04.019) to change from its initial value to 100% is given by the following equation:
Time to reach 100.0% = -τ1 x ln[(1 − C
1
) / (C
0
− C
1
)]
C
0
represents the conditions that have persisted for long enough for the Motor Protection Accumulator (04.019) to reach a steady state value. If the
motor current and speed are I
0
and w
0
then,
C
0
= [(1 - K
fe
) x (I
0
/ (K
1
x I
Rated
))
2
] + [K
fe
x (w
0
/ w
Rated
)
1.6
]
C
1
represents the conditions that begin at the start of the time being calculated. If the motor current and speed are by I
1
and w
1
then,
C
1
= [(1 - K
fe
) x (I
1
/ (K
1
x I
Rated
))
2
] + [K
fe
x (w
1
/ w
Rated
)
1.6
]
Example 1: The effect of iron losses are not modelled (K
fe
= 0), Motor Thermal Time Constant 1 (04.015) = 89s, the initial current is
zero, Rated Current (05.007) ≤ Maximum Heavy Duty Rating (11.032) and the new level of current is 1.5 x Rated Current (05.007).
C
0
= 0
C
1
= [1.5 / (1.05 x 1.0)]
2
= 2.041
Time to reach 100.0% = -89 x ln(1 − 1/C
1
) = -89 x ln(1 − 1/2.041) = 60s
This is the default setting for Open-loop and RFC-A modes allowing an induction motor to run at 150% rated current for 60s from cold.
Example 2: The effect of iron losses are not modelled (K
fe
= 0), Motor Thermal Time Constant 1 (04.015) = 89s, the initial current is Rated Current
(05.007), Rated Current (05.007) ≤ Maximum Heavy Duty Rating (11.032) and the new level of current is 1.5 x Rated Current (05.007).
C0 = [1.0 / (1.05 x 1.0)]
2
= 0.907
C1 = [1.5 / (1.05 x 1.0)]
2
= 2.041
Time to reach 100.0% = -89 x ln((1 − C1) / (C0 − C1)) = -89 x ln[(1 − 2.041) / (0.907 − 2.041)] = 7.6s
This is the default setting for Open-loop and RFC-A modes allowing an induction motor to run at 150% rated current for 7.6s after running under rated
conditions for a significant period of time.
Motor Protection Accumulator Reset
The initial value in the Motor Protection Accumulator (04.019) at power-up is defined by Motor Protection Accumulator Power-up Value (04.036) as
given in the table below.
60
Powerdrive F300 Parameter Reference Guide
Issue: 01.15.00