2.5.19 Current Measurement on All Three
Motor Phases
Output current to the motor is continuously measured on
all 3 phases to protect the frequency converter and motor
against short circuits, ground faults, and phase loss. Output
ground faults are instantly detected. If a motor phase is
lost, the frequency converter stops immediately and
reports which phase is missing.
2.5.20 Galvanic Isolation of Control
Terminals
All control terminals and output relay terminals are galvan-
ically isolated from mains power. This means the controller
circuitry is completely protected from the input current.
The output relay terminals require their own grounding.
This isolation meets the stringent protective extra-low
voltage (PELV) requirements for isolation.
The components that make up the galvanic isolation are:
•
Power supply, including signal isolation.
•
Gate drive for the IGBTs, trigger transformers, and
optocouplers.
•
The output current Hall effect transducers.
2.6 Custom Application Functions
Custom application functions are the most common
features programmed in the frequency converter for
enhanced system performance. They require minimum
programming or set-up. Understanding that these
functions are available can optimise the system design and
possibly avoid introducing redundant components or
functionality. See the
programming guide
for instructions
on activating these functions.
2.6.1 Automatic Motor Adaptation
Automatic motor adaptation (AMA) is an automated test
procedure used to measure the electrical characteristics of
the motor. AMA provides an accurate electronic model of
the motor. It allows the frequency converter to calculate
optimal performance and efficiency with the motor.
Running the AMA procedure also maximises the automatic
energy optimisation feature of the frequency converter.
AMA is performed without the motor rotating and without
uncoupling the load from the motor.
2.6.2 Motor Thermal Protection
Motor thermal protection can be provided in 3 ways:
•
Via direct temperature sensing via the PTC sensor
in the motor windings and connected on a
standard AI or DI.
•
Mechanical thermal switch (Klixon type) on a DI.
•
Via the built-in electronic thermal relay (ETR) for
asynchronous motors.
ETR calculates motor temperature by measuring current,
frequency, and operating time. The frequency converter
shows the thermal load on the motor in percentage and
can issue a warning at a programmable overload setpoint.
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 2.15 ETR Characteristics
The X-axis in
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
calculates the motor temperature based on actual current
and speed. The calculated temperature is visible as a
readout parameter in
parameter 16-18 Motor Thermal
.
2.6.3 Mains Drop-out
During a mains drop-out, the frequency converter keeps
running until the DC-link voltage drops below the
minimum stop level. The minimum stop level is typically
15% below the lowest rated supply voltage. The mains
Product Overview
Design Guide
MG16G202
Danfoss A/S © 08/2015 All rights reserved.
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