Frequently Asked Questions - Danfoss MCD 201 Design Manual

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Frequently Asked Questions

•
What is the minimum allowable motor current
when using an MCD 201 open loop soft starter?
There is no minimum current when using an
MCD 201 open loop soft starter.
•
What is the minimum allowable motor current
when using an MCD 202 closed loop soft
starter?
The minimum "Motor FLC" setting is 50% of the
MCD 202 nameplate rating. All the motor
protections are based on this setting.
It is possible to operate an MCD 202 with a
small kW motor, for testing purposes. In this
case, the motor will effectively start DOL, and
the MCD 202 will not protect the motor. The
starter will not trip, because there is no
undercurrent protection on MCD 202.
•
What type of motor protection does the MCD
202 have?
The MCD 202 has built-in motor overload
protection of the electronic "thermal model"
type. The motor current is continuously
monitored and the expected temperature is
calculated based on this monitored current.
The rate of rise of the calculated motor
temperature is determined by the Motor Trip
Class setting. The lower this setting, the faster
the rate of rise of calculated motor temperature.
An Overcurrent trip (x 2 Ready LED flashes) will
occur when the calculated temperature reaches
105%. The setting of the Motor Trip Class pot is
similar to a motor trip class setting on a standard
thermal overload relay.
An external motor protection device is not
required when using an MCD 202 soft starter.
MCD 202 is certified to conform to the
IEC60947-4-2 standard for electronic soft
starters. The reliability of the motor protection
feature is part of this standard.
•
How do I select an MCD 200 soft starter for duty
cycles different from those listed in the standard
ratings table?
The WinStart software package is available for
selecting soft starters for different duty cycles.
•
Which MCD 200 models carry the UL mark?
All T6 models carry the UL mark.
10
MCD 200 Design Guide
•
What are the MCD 200 operational ratings
before maintenance may be required?
The operational ratings for MCD 200 are size-
dependent, and are due to the capability of the
internal bypass relays:
Size 1 & 2 (7.5 ~ 55 kW): 1,000,000 operations
Size 3 (75 ~ 110 kW): 100,000 operations.
•
When would I use a line contactor?
A line contactor may be compulsory for a
specific installation. This requirement will be the
same whether using a two-phase controlled soft
starter or a three-phase controlled soft starter
(see Product Note for more detail).
•
How do I size the fuses of the motor branch
circuit (Type 1) when using an MCD 200 soft
starter?
For "Current Limit" settings < 350% and start
times < 15 seconds, the nominal rating of
standard line supply fuses (gG) should be 1.75 x
Motor FLC. If motor rated fuses (gM) are being
used, their nominal rating should be 1.5 x Motor
FLC.
For "Current Limit" settings > 350% and start
times > 15 seconds, the nominal rating of
standard line supply fuses (gG) should be 2 x
Motor FLC. If motor rated fuses (gM) are being
used, their nominal rating should be 1.75 x
Motor FLC.
•
When would I use semiconductor fuses?
Either when specified for an installation, or when
Type 2 coordination is required.
The MCD 200 is internally bypassed, so the
SCRs are in use only during starting and soft
stopping.
•
What is the current consumption of the MCD
200 control supply?
The steady state consumption of the control
supply is 100 mA maximum, for both CV1 and
CV3 models.
However, the short time inrush current at control
supply "switch-on" can be as high as 10 A for
CV3 models, and 2 A for CV1 models (due to
the SMPS power supply).
•
How can the MCD 202 programmable output
relay be used?
The programmable output relay provides an N/O
contact, which can be used for a "Trip" or "Run"
output.
MG.17.C3.02 – VLT is a registered Danfoss trademark