Soft Starting With Voltage Ramp And Current Limiting - Siemens SIRIUS 3RW55 Equipment Manual

Functions
8.1 Start-up
Ramp up time
Maximum starting time
Breakaway time
Breakaway voltage
8.1.5

Soft starting with voltage ramp and current limiting

Operating principle
Select the starting mode "Voltage ramp + Current limiting" if, at the same time as protecting the
system during startup, you want to ensure that a specific current value is not exceeded during
motor starting. The motor is always started up with the voltage ramp. If the current exceeds the
parameterized current limit, the voltage ramp is aborted and the current limitation function
starts. The current limitation function remains active until the 3RW55 or 3RW55 Failsafe soft
starter detects that the motor has ramped up and the motor is in a normal operating state.
Application
• Avoiding current surges
• Reducing energy costs
Setting via 3RW5 HMI High Feature
• Menu: "Parameters > Soft Starter > Parameter set 1 / 2 / 3 > Start settings > Starting mode >
Voltage ramp + Current limiting"
• Menu (Parameters): "Parameters > Soft Starter > Parameter set 1 / 2 / 3 > Start settings"
• Access protection to the 3RW5 HMI High Feature is not active or has been reset.
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The ramp-up time determines the time in which the starting torque is increased to the limiting
torque. This has an influence on the motor's acceleration torque which drives the load during
start-up. A longer ramp-up time results in a shorter acceleration torque across the motor ramp-
up time. The motor runs up longer and more softly.
The actual motor starting time is load-dependent and can differ from the parameterized ramp-
up time. If the starting time ends before the motor has completely ramped up, the torque is
limited to the set limiting torque until the 3RW55 or 3RW55 Failsafe soft starter detects that the
motor has ramped up and closes the internal bypass contacts.
With the setting "0 s", the motor is switched on with a ramp-up time of approx. 100 ms.
• Factory setting: 10 s
• Setting range: 0 ... 360 s
• In steps of: 0.1 s
This time determines the period after which the drive must have completed its start-up. If the
drive is not yet operating under rated conditions after the specified interval has expired, the
generalized phase control of the thyristors is interrupted and the line voltage is raised to 100%.
The setting "0 s" deactivates the maximum starting time.
Maximum starting time ≥ ramp-up time.
• Factory setting: 0 s
• Setting range: 0 ... 1 000 s
• In steps of: 0.1 s
See Breakaway pulse for startup functions (Page 144)
SIRIUS 3RW55 and 3RW55 Failsafe Soft Starters
Equipment Manual, 02/2022, A5E35630887002A/RS-AF/006