SINAMICS G120 Fault F30002 — DC link overvoltage

Overview

Siemens SINAMICS G120 fault F30002 indicates a DC Link Overvoltage condition. This fault triggers when the voltage in the drive's internal direct current intermediate circuit (commonly called the DC bus or DC link) exceeds the factory-defined safety threshold of the operational Power Module. Under standard operating conditions, the DC link voltage ($V_{dc}$) hovers around $1.35 \times \text{Mains Supply Voltage}$ ($V_{line}$). If $V_{dc}$ surges over the internal trip limits (such as ~820V DC on 380-480V systems), the drive initiates a protective fault immediately to protect its sensitive Insulated-Gate Bipolar Transistors (IGBTs) and internal capacitor banks from terminal dielectric failure.

Symptoms

When a SINAMICS G120 drive experiences an F30002 fault code, you will observe several immediate behaviors in your control cabinet and automation sequence:

• Drive Tripping: The drive immediately cuts output power to the motor, triggering a coast-to-stop (OFF2 state) configuration.
• HMI and LED Indicators: The drive’s Control Unit (e.g., CU240E-2) displays a solid red "SF" or "BF" LED. Basic Operator Panels (BOP-2) or Intelligent Operator Panels (IOP-2) display the flashing code F30002.
• PLC System Interrupts: A PROFIsafe or PROFINET control byte transmits a fault status word (fault active) to the host S7-1500 or S7-1200 PLC, causing downstream sequence halts or emergency stops.
• Intermittent Dynamic Behavior: The trip occurs consistently during specific operational states—most notably during the rapid deceleration phase of a process cycle, or when handling an overhauling mechanical load.

Possible Causes

An F30002 fault can stem from both electrical supply issues and dynamic mechanical load feedback. The most common causes include:

• Excessive Regenerative Feedback: The motor acts as a generator when decelerating too quickly. The kinetic energy of the mechanical load is pumped back into the motor windings, flow-routed up into the DC bus via the freewheeling diodes of the inverter stage.
• Improperly Adjusted Deceleration Ramps: The deceleration time configured in parameter P1121 is too short for the inertia of the connected load.
• Faulty or Missing Braking Resistor: The external dynamic braking resistor is electrically open, incorrectly sized in terms of resistance (Ohms) or wattage (kW), or has experienced structural failure.
• Deactivated $V_{dc_max}$ Controller: The drive’s internal dc-link voltage controller (P1240) is deactivated or wrongly configured, leaving it unable to automatically extend ramp times in high-voltage situations.
• Grid Supply Fluctuations: Transient incoming AC mains voltage surges, brownout-to-overvoltage rebounds, or phase unbalances.
• Incorrect Mains Parameterization: The incoming mains feed parameter in P0210 (Device Supply Voltage) is misconfigured, causing the drive to compute a lower-than-appropriate overvoltage trip threshold.
• Active Mechanical Overhauling Loads: Applications such as hoists, vertical winches, downhill conveyors, and high-inertia exhaust fans where the physical load continuously drives the motor mechanically faster than its synchronous operational frequency.

Step-by-Step Troubleshooting

Follow this structured sequence to locate and resolve the structural source of the overvoltage fault:

Step 1: Perform Safe Electrical Isolation

Before physically checking any wiring or modules, turn off the mains isolator feeding the drive. Wait a minimum of 5 to 10 minutes for the internal capacitors to discharge below a safe auxiliary voltage threshold (<50V DC). Verify this safety step by checking the DC link terminals ($DCP$ / $DCN$) physically with a rated digital multimeter (DMM) set to DC voltage.

Step 2: Measure incoming Line Voltage

Measure the live AC voltage across phases L1-L2-L3 at the drive’s line input terminals. Compare these values with input parameters:

• Check parameter P0210 (Mains supply voltage). It must accurately reflect the true incoming physical voltage. If your actual line voltage is 480V AC but P0210 is set to 400V AC, the internal thresholds will be too restrictive.
• Confirm that there are no high-energy transient spikes or line harmonics caused by power factor correction capacitors switching nearby.

Step 3: Inspect the Braking Resistor Circuit

If the system relies on dynamic braking to dump excess kinetic energy, verify the entire chopper and resistor circuit:

1. Disconnect the braking resistor cables from terminal blocks $R1$ and $R2$ on the Power Module (or PM240-2).
2. Use a multimeter to measure the resistance of the braking resistor. Compare this measured reading directly to the rated values printed on the resistor chassis and the minimum allowed resistance value listed in your specific G120 frame size manual.
3. Test for ground faults: measure insulation resistance between each resistor terminal and the chassis ground. Any reading below 1 Megaohm indicates a damaged insulation packet within the resistor, requiring unit replacement.
4. Inspect the braking chopper configuration. In parameter P1240, determine if the $V_{dc_max}$ controller is altered. (Note: If using an external dynamic braking resistor, P1240 must usually be set to 0 [Inhibited] to prevent the drive controller from overriding the resistor mechanics and extending the ramp).

Step 4: Examine Parameter Configuration & Increase Ramp Times

If the overvoltage occurs purely during rapid deceleration, the mechanical energy surpasses the system’s capability to absorb it:

• Navigate to parameter P1121 (Deceleration Time) and increase it significantly (e.g., from 3.0 seconds to 10.0 seconds). If the drive runs without faulting after this adjustment, the ramp rate was too steep.
• If utilizing an application where process timing prevents you from using long ramp-down configurations, ensure the $V_{dc_max}$ controller configuration in P1240 is enabled (set to 1 or 3). This parameter enables the drive to actively stretch the deceleration ramp automatically to stay just beneath the F30002 threshold.

Step 5: Diagnose Active Regenerative Power Issues

In dynamic hoisting or high-inertia applications where the load continuously drives the motor, a standard non-regenerative Power Module (like a PM240-2) cannot feedback energy to the grid. In this scenario, you must install an appropriate braking resistor or adopt a regenerative line module (such as a G120 with a PM250 Power Module), which converts regenerative DC bus energy back into clean AC current and pumps it back to the utility grid.

Recommended Actions

Depending on what you discover during troubleshooting, implement these actions to prevent future shutdowns:

• Adjust S-Ramps: Set parameters P1130 (Ramp-up initial rounding) and P1131 (Ramp-down final rounding) to introduce an S-curve. This softens the transition into deceleration, preventing sudden voltage peaks at the start of braking.
• Verify Parameter P1254: Ensure parameter P1254 (Auto detection of $V_{dc_max}$ switch-on levels) is configured properly (usually default 1 for active detection). This ensures the drive adapts its switching threshold based on the actual grid voltage.
• Install Line Chokes: If incoming grid transients are common, install a Siemens line reactor (choke) on the input of the Power Module to buffer incoming line surges.
• Upgrade Resistor Capacity: If your braking resistor gets exceptionally hot and trips on thermal overload alongside F30002, swap the component for a high-capacity model with a higher continuous power rating (kW) but identical resistance (Ohms).

Recommended Replacement Parts

If diagnostic tests reveal physical component degradation, utilize these authentic Siemens replacement elements to restore operational integrity:

Related Articles

• Siemens G120 Power Module Selection Guide
• Selecting and Sizing Braking Resistors for Siemens PM240-2
• Step-by-Step Optimization of Vdc_max Controllers in SINAMICS Drives

FAQ

Q: What is the typical physical overvoltage trip limit for my 400V SINAMICS G120?

For a standard 400V mid-range SINAMICS G120 drive, the F30002 overvoltage trip point occurs when the internal DC link reaches approximately 820V DC. For 480V line supplies, the trip threshold is scale-adjusted by the drive to approximately 860V DC based on the auto-calculated input voltage baseline.

Q: Can I run a braking resistor with the Vdc_max controller (P1240) turned on?

It is generally recommended to disable the $V_{dc_max}$ controller by setting P1240 = 0 when an external braking resistor is connected. If P1240 remains active, the drive will deliberately delay deceleration and try to avoid dumping current to the resistor, interfering with your production cycle goals.

Q: What is the difference between Fault F30002 and Fault F30001?

F30002 indicates overvoltage in the DC intermediate circuit (voltage limit exceeded). F30001 indicates overcurrent in the output phases (excessive motor current caused by short circuit, motor overload, or extremely accelerated ramp-up profiles).

Q: Could a faulty internal fan in the G120 cabinet cause F30002?

Directly, no. However, if thermal limits inside the cabinet cause the internal dynamic braking chopper to overheat, it might shut down its switching pattern prematurely as a self-protection mechanism, leading to a runaway DC-link voltage profile that causes an auxiliary F30002 trip.