Group 3.9: Protections - Siemens BT300 Applications Manual

Siemens Application
3.5.11

Group 3.9: Protections

Parameters of Motor thermal protection (P3.9.6 to P3.9.10)
The motor thermal protection is to protect the motor from overheating. The drive is capable of supplying
higher than nominal current to the motor. If the load requires this high current, there is a risk that the
motor will thermally overload. This is the case especially at low frequencies. At low frequencies, the cool-
ing effect of the motor is reduced as well as its capacity. If the motor is equipped with an external fan,
the load reduction at low speeds is small.
The motor thermal protection is based on a calculated model and it uses the output current of the drive
to determine the load on the motor.
The motor thermal protection can be adjusted with parameters. The thermal current I
current above which the motor is overloaded. This current limit is a function of the output frequency.
The thermal stage of the motor can be monitored on the control keypad display. See Chapter 3.4.
The calculated model does not protect the motor if the airflow to the motor is reduced by
blocked air intake grill. The model starts from zero if the control board is powered off.
13006.emf
Parameters of Stall protection (P3.9.11 to P3.9.14)
The motor stall protection protects the motor from short time overload situations such as one caused by
a stalled shaft. The reaction time of the stall protection can be set shorter than that of motor thermal pro-
tection. The stall state is defined with two parameters, P3.9.12 (Stall current) and P3.9.14 (Stall frequen-
cy limit). If the current is higher than the set limit and the output frequency is lower than the set limit, the
stall state is true. There is actually no real indication of the shaft rotation. Stall protection is a type of over-
current protection.
Under-load protection parameters (P3.9.15 to P3.9.18)
The purpose of the motor under-load protection is to ensure that there is load on the motor when the
drive is running. If the motor loses its load, there might be a problem in the process, e.g. a broken belt
or a dry pump.
Motor under-load protection can be adjusted by setting the under-load curve with parameters P3.9.16
(Underload protection: Field weakening area load) and P3.9.17 (Underload protection: Zero frequency
load), see below. The under-load curve is a squared curve set between the zero frequency and the field
weakening point. The protection is not active below 5Hz (the under-load time counter is stopped).
The torque values for setting the underload curve are set in percentage which refers to the nominal
torque of the motor. The motor's name plate data, parameter motor nominal current and the drive's nom-
inal current I are used to find the scaling ratio for the internal torque value. If other than nominal motor
L
is used with the drive, the accuracy of the torque calculation decreases.
Code Parameter
Response to Analog
P3.9.1
input low fault
24-hour support +1-800-877-7545 (Dial 2)
Table 39: Protections settings.
Min Max Unit
0 4
Siemens Industry, Inc. • 49
Default ID
0 = No action
1 = Alarm
2 = Alarm, set preset fault
0 700 frequency (par. P3.3.19)
3 = Fault (Stop according to
stop mode)
4 = Fault (Stop by coasting)
specifies the load
T
Description
3