Danfoss VLT AutomationDrive FC 301, Руководство по конструкции, Страница: 41 / 200

4.2.2 Motor Thermal Protection
Motor thermal protection can be provided in 3 ways:
•
Via direct temperature sensing via one of the
following
- PTC- or KTY sensor in the motor
windings and connected on a standard
AI or DI
- PT100 or PT1000 in the motor windings
and motor bearings, connected on
Sensor Input Card MCB 114
- PTC Thermistor input on PTC Thermistor
Card MCB 112 (ATEX approved)
•
Mechanical thermal switch (Klixon type) on a DI
•
Via the built-in Electronic Thermal Relay (ETR).
ETR calculates motor temperature by measuring current,
frequency, and operating time. The frequency converter
displays the thermal load on the motor in percentage and
can issue a warning at a programmable overload set-point.
Programmable options at the overload allow the frequency
converter to stop the motor, reduce output, or ignore the
condition. Even at low speeds, the frequency converter
meets I2t Class 20 electronic motor overload standards.
1.2 1.0 1.4
30
10
20
100
60
40
50
1.8 1.6 2.0
2000
500
200
400
300
1000
600
t [s]
175ZA052.12
fOUT = 2 x f M,N
fOUT = 0.2 x f M,N
fOUT = 1 x f M,N(par. 1-23)
I
MN
(par. 1-24)
I
M
Illustration 4.1 ETR Characteristics
The X-axis shows the ratio between I
motor
and I
motor
nominal. The Y-axis shows the time in seconds before the
ETR cuts off and trips the frequency converter. The curves
show the characteristic nominal speed, at twice the
nominal speed and at 0.2 x the nominal speed.
At lower speed, the ETR cuts off at lower heat due to less
cooling of the motor. In that way, the motor is protected
from being overheated even at low speed. The ETR feature
is calculating the motor temperature based on actual
current and speed. The calculated temperature is visible as
a read-out parameter in
16-18 Motor Thermal .
A special version of the ETR is also available for EX-e
motors in ATEX areas. This function makes it possible to
enter a specific curve to protect the Ex-e motor. The
Programming Guide takes the user through the set-up.
4.2.3 Mains Drop-out
During a mains drop-out, the frequency converter keeps
running until the intermediate circuit voltage drops below
the minimum stop level, which is typically 15% below the
frequency converter's lowest rated supply voltage. The
mains voltage before the drop-out and the motor load
determines how long it takes for the frequency converter
to coast.
The frequency converter can be configured ( 14-10 Mains
Failure ) to different types of behaviour during mains drop-
out, e.g:
•
Trip Lock once the DC-link is exhausted
•
Coast with flying start whenever mains return
(
1-73 Flying Start
)
•
Kinetic back-up
•
Controlled ramp-down
Flying start
This selection makes it possible to catch a motor that is
spinning freely due to a mains drop-out. This option is
very relevant for centrifuges and fans.
Kinetic back-up
This selection ensures that the frequency converter runs as
long as there is energy in the system. For short mains
drop-out the operation is restored upon mains return,
without bringing the application to a stop or loosing
control at any time. Several variants of kinetic back-up can
be selected.
The behaviour of the frequency converter at mains drop-
out can be configured in
14-10 Mains Failure and
1-73 Flying Start .
4.2.4 Built-in PID Controller
The built-in proportional, integral, derivative (PID)
controller is available, eliminating the need for auxiliary
control devices. The PID controller maintains constant
control of closed loop systems where regulated pressure,
flow, temperature, or other system requirements must be
maintained. The frequency converter can provide self-
reliant control the motor speed in response to feedback
signals from remote sensors.
The frequency converter accommodates 2 feedback signals
from 2 different devices. This feature allows regulating a
system with different feedback requirements. The
Product Features
VLT
®
AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
MG33BF02 - Rev. 2013-12-20 39
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