SERIES OVERVIEW
Page 9
710-02887-00A
TMC7 Series
3.7
Frequently Asked Questions (and their answers):
•
What is the minimum allowable motor current when using a TMC7 closed loop soft starter?
The minimum “Motor FLC” setting is 50% of the TMC7 nameplate rating. All the motor protections are based on this setting.
It is possible to operate a TMC7 with a small kW motor, for testing purposes. In this case, the motor will effectively start DOL, and
the TMC7 will not protect the motor. The starter will not trip, because there is no under-current protection on TMC7.
•
What type of motor protection does the TMC7 have?
The TMC7 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. A Motor Overload 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 a TMC7 soft starter. TMC7 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 a TMC7 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.
•
What are the TMC7 operational ratings before maintenance may be required?
The operational ratings for TMC7 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 2-phase controlled soft starter or a 3-phase controlled soft starter (refer Product
Note for more detail).
•
How do I size the fuses of the motor branch circuit when using a TMC7 soft starter?
For “Current Limit” settings < 350% and start times < 15 seconds, the nominal rating of standard line supply fuses should be
1.75 x Motor FLC. If motor rated fuses 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 should be
2 x Motor FLC. If motor rated fuses 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 TMC7 is internally bypassed, so the SCRs are in use only during starting and soft stopping.
•
What is the current consumption of the TMC7 control supply?
The steady state consumption the control supply is 100 mA maximum, for both C1 & C2 models.
However, the short time inrush current at control supply "switch-on" can be as high as 10 A for C1 models, and 2 A for C2 models
(due to the SMPS power supply).
•
How can the TMC7 programmable output relay be used?
The programmable output relay provides an N/O contact, which can be used for a “Trip” or “Run” output.
Trip output:
The relay operates when the TMC7 trips on any fault. This can be used to operate a shunt-trip mechanism of an upstream circuit
breaker to isolate the motor branch circuit. It could also be used to signal TMC7 “Trip” status to an automation system.
Run output:
The relay operates on completion of start ramp. This can be used to operate a contactor for power-factor correction capacitors. It
could also be used to signal TMC7 “Run” status to an automation system.
•
Is the TMC7 suitable for flying start application?
Yes. There is a built-in 2 second delay between the end of one stop and the beginning of the next start. This delay allows the motor
flux to decay, eliminating any chance of the TMC7 tripping on Power Circuit fault (x 1 Ready LED flash) due to detection of motor
back EMF when the start signal is applied. The major effect of a flying start is on the actual time the TMC7 “current limits”. The
ramp-up time will be reduced and is determined by the motor speed on re-application of the start signal.
