Automatic Derating For High Switching Frequency; Automatic Derating For Overtemperature; Auto Ramping; Current Limit Circuit - Danfoss VLT Refrigeration Drive FC 103 Design Manual

Product Overview
2.5.10 Automatic Derating for High
Switching Frequency
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The frequency converter is designed for continuous, full-
load operation at switching frequencies between 3.0 and
4.5 kHz (this frequency range depends on power size). A
switching frequency exceeding the maximum permissible
range generates increased heat in the frequency converter
and requires the output current to be derated.
An automatic feature of the frequency converter is load-
dependent switching frequency control. This feature allows
the motor to benefit from as high a switching frequency as
the load allow.
2.5.11 Automatic Derating for
Overtemperature
Automatic overtemperature derating works to prevent
tripping the frequency converter at high temperature.
Internal temperature sensors measure conditions to protect
the power components from overheating. The frequency
converter can automatically reduce the switching
frequency to maintain the operating temperature within
safe limits. After reducing the switching frequency, the
frequency converter can also reduce the output frequency
and current by as much as 30% to avoid an overtem-
perature trip.

2.5.12 Auto Ramping

A motor trying to accelerate a load too quickly for the
current available can cause the frequency converter to trip.
The same is true for too quick a deceleration. Auto
ramping protects against these situations by extending the
motor ramping rate (acceleration or deceleration) to match
the available current.

2.5.13 Current Limit Circuit

When a load exceeds the current capability of the
frequency converter normal operation (from an undersized
frequency converter or motor), current limit reduces the
output frequency to ramp down the motor and reduce the
load. An adjustable timer is available to limit operation in
this condition for 60 s or less. The factory default limit is
110% of the rated motor current to minimise overcurrent
stress.
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VLT Refrigeration Drive FC 103

2.5.14 Power Fluctuation Performance

The frequency converter withstands mains fluctuations
such as:
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The frequency converter automatically compensates for
input voltages ±10% from the nominal to provide full rated
motor voltage and torque. With auto restart selected, the
frequency converter automatically powers up after a
voltage trip. With flying start, the frequency converter
synchronises to motor rotation before start.

2.5.15 Motor Soft Start

The frequency converter supplies the right amount of
current to the motor to overcome load inertia and bring
the motor up to speed. This avoids full mains voltage
being applied to a stationary or slow-turning motor, which
generates high current and heat. This inherent soft start
feature reduces thermal load and mechanical stress,
extends motor life, and provides quieter system operation.

2.5.16 Resonance Damping

Eliminate high frequency motor resonance noise through
resonance damping. Automatic or manually selected
frequency damping is available.

2.5.17 Temperature-controlled Fans

Sensors in the frequency converter control the temperature
of the internal cooling fans. Often, the cooling fans do not
run during low load operation, or when in sleep mode or
standby. This reduces noise, increases efficiency, and
extends the operating life of the fan.

2.5.18 EMC Compliance

Electromagnetic interference (EMI) or radio frequency
interference (RFI, in case of radio frequency) is disturbance
that can affect an electrical circuit due to electromagnetic
induction or radiation from an external source. The
frequency converter is designed to comply with the EMC
product standard for frequency converters IEC 61800-3 as
well as the European standard EN 55011. To comply with
the emission levels in EN 55011, screen and terminate the
motor cable properly terminated. For more information
regarding EMC performance, see chapter 3.2.2 EMC Test
Results (Emission).
Danfoss A/S © 08/2015 All rights reserved.
Transients.
Momentary drop-outs.
Short voltage drops.
Surges.
MG16G202