Siemens S120 frequency converter maintenance and configuration

Siemens SINAMICS S120 AC Drive: Engineering Practice from Hardware Selection to Troubleshooting

Introduction: The Core of Modular Driver System

In the fields of high-end machinery manufacturing, printing and packaging, textiles, lifting and transportation, as well as wind power generation, extremely high requirements are placed on the dynamic response, accuracy, and functional safety of the drive system. Siemens SINAMICS S120 AC Drive, as a modular multi axis drive system, has become the preferred solution for complex drive challenges in engineering applications due to its powerful platform design, rich peripheral components, and deep integration with industrial buses such as PROFINET/PROFIBUS.

However, a complete S120 transmission system is not simply a combination of a power module and a control unit. From the selection of reactors and filters on the incoming side, to the configuration of output reactors and sine wave filters on the motor side, to the parameter setting and daily maintenance of the control unit, every step requires engineers to have solid hardware knowledge and fault diagnosis ability. This article will be based on the SINAMICS S120 AC Drive manual, extracting key technical points from installation, wiring, debugging to maintenance and replacement, to help on-site engineers quickly locate problems and develop solutions.

System composition and hardware selection foundation

The SINAMICS S120 AC Drive system mainly consists of the following components:

Power Module: An inverter that directly supplies power to the motor. According to the power range and installation method, it is divided into two frame sizes: Blocksize (book type, power range 0.12kW~90kW) and Chassis (installed cabinet type, 210A~490A). Among them, PM240-2 and PM340 are typical Blocksize power modules.

Control Unit: Implement closed-loop control, logic processing, and communication of the driver. CU310-2 PN (PROFINET) and CU310-2 DP (PROFIBUS) are typical controllers for single axis applications. They communicate with the power module and encoder module through the DRIVE CLiQ interface.

Incoming side components: including Line Reactor, Line Filter, Incoming Contactor, Fuse/Circuit Breaker, etc. Reactors mainly limit low order harmonics and power spikes, while filters are used to meet electromagnetic compatibility (EMC) standards.

Motor side components: including output reactor, dv/dt filter, sine wave filter, and voltage spike limiter. When the motor cable is long or motor insulation protection is required, these components must be selected.

DC bus components: including braking module and braking resistor. Convert regenerative energy into heat consumption when rapid braking or potential load is required.

Selection and matching points:

The rated current of the power module must be selected according to the load type (light overload LO or heavy overload HO). For example, the overload capacity of PM340-2 is divided into 110% for 60 seconds (low overload) and 150% for 60 seconds (high overload). Specific data can be found in the technical parameter table of the manual.

The incoming reactor (such as 6SL3203-0CD21-0AA0) and incoming filter (such as 6SL3203-0BE17-7BA0) must match the frame size of the power module, otherwise they cannot be installed or affect EMC performance.

For IT power grids (ungrounded systems), power modules without integrated filters must be used and the internal interference suppression capacitor connectors must be removed (see section 4.4.5).

Installation and Wiring: Key Steps for EMC and Safety

1. Five step safety method (must be executed)

Before installing or maintaining any S120 components, the following safety steps must be followed (refer to section 1.1):

① Disconnect the main power supply and notify all affected personnel.

② Confirm that the device has been powered off and wait for the discharge time indicated on the warning label (usually 5 minutes for DC bus capacitors to discharge). Use a voltmeter to measure that the voltage between L1, L2, L3 and PE, as well as between the DC bus terminals DCP/DCN, is below the safe value.

③ Identify other hazardous energy sources (compressed air, hydraulic, etc.) and isolate them.

④ Grounding or short circuiting all hazardous energy sources.

⑤ Prevent energy reconnection (lockout and tagout).

⑥ Confirm that the machine is completely locked.

2. Installation and ventilation of power modules

The PM240-2 and PM340 modules must be installed vertically (with the power terminals facing downwards) to facilitate natural convection cooling.

Requirements for upper and lower ventilation gaps: PM240-2 FSA~FSC is 80mm above and 100mm below; PM340 FSA/FSB is 100mm above and below; FSC is 125mm above and below; FSD/FSE is 300mm above; FSF is 350mm above (see Sections 4.2.2 and 4.3.2).

If multiple modules are installed in parallel, the lateral clearance should be at least 1mm (within 40 ℃). If the ambient temperature is between 40-55 ℃, it is necessary to increase the lateral clearance (FSA 30mm, FSB 40mm, FSC 50mm).

3. Cable shielding and grounding

Motor cables must use shielded cables, and both ends of the shielding layer should be extensively grounded. On the power module side, a Shield Connection Kit (order number 6SL3262-...) is required to connect the shield layer to the mounting plate.

The cable length of 24V electronic power supply should not exceed 10 meters, and the signal cable (such as encoder, digital input) should not exceed 30 meters. Long cables can cause voltage drops and introduce interference.

4. Typical wiring errors of control unit CA310

X124 (24V power supply): Two "+" terminals are internally short circuited, and two "M" terminals are internally short circuited, used for loop power supply. But if the digital output load is large, it must be powered separately.

X120 EP Terminal (Enable Pulses): If Safety Integrated Basic Functions are enabled, terminals 7 (EP+24V) and 8 (EP M1) need to be connected to 24V, otherwise the pulse will be blocked. If the safety function is not used for simple applications, it is necessary to ensure that these two terminals have 24V (usually through short circuiting or external power supply).

Stop input: TB3-7 (Stop) and TB3-8 (Stop) must be closed (short circuited or connected in series with a normally closed button), otherwise the driver will report "Stop input missing" and cannot run.

LED diagnosis and startup troubleshooting of control unit CU310

The front panel of CU310-2 (PN or DP) has four LEDs: RDY (Ready), COM (Communication), OUT>5V (Encoder Power Supply) MOD。 Understanding their colors and flicker patterns at different stages is the core of quickly locating problems.

LED behavior during startup phase (approximately 1 second after power on):

All orange LEDs stay on for about 1 second → power on normally.

If RDY red slow flashes (2Hz), COM red slow flashes → file error (memory card not inserted or damaged, or firmware missing).

If RDY red is constantly on, COM orange is constantly on → firmware is loading.

LED fault indication during operation phase:

Measures for handling the meaning of LED status

RDY red flashing 2Hz general fault check parameter settings, read fault codes.

RDY red/green alternating 0.5Hz is missing software license installation license.

RDY orange flashing 0.5Hz DRIVE CLiQ component firmware upgrade is waiting to be completed.

COM red flashing 2Hz bus communication interrupt (PROFINET/PROFIBUS) to check cable, master station status, and address settings.

COM green flashing 0.5Hz, no cyclic communication established (main station did not send set values), check PLC program or controller configuration.

OUT>5V, orange constant light encoder power supply is 24V (note: if the encoder is 5V, it may be damaged). Confirm the encoder model and modify the power supply voltage in the parameters.

Common troubleshooting process for startup failures:

RDY does not light up after power on → Check X124 24V power supply (20.4-28.8V).

RDY green is always on but the motor does not rotate → Check if the X120 EP terminal is 24V; check if the status word bit2 (Operation enabled) is 1; Force the control word 0x0F through the STARTER software.

PROFIBUS communication failure (COM red flashing 2Hz) → Check if the address switch (next to X21 of CU310-2 DP) is set to a valid address (1-126) and does not conflict with other stations; Check if the terminal resistor is activated at both ends of the bus.

DRIVE CLiQ communication error (RDY flashing orange) → Check if the DRIVE CLiQ cable (such as 6FX2002-1DC00) is connected correctly and if the plug is securely locked; Ensure that the PM-IF plug between the power module and the control unit has no bent pins.

Selection of incoming side components and EMC category

SINAMICS S120 is configured with different input filters based on EMC categories (C1, C2, C3, C4). For most industrial environments (secondary environments), it is required to meet the C3 category; If it needs to be used in a home/commercial environment (primary environment), it must meet the C2 or C1 category.

Requirements for meeting various types of standards:

C4: No filter, limited to the second environment only.

C3: Use external or internal input filters recommended by Siemens, with motor cable length ≤ 50m (PM240-2) or ≤ 25m (PM340).

C2: Add an incoming reactor (Uk ≥ 4%) on the basis of C3, and further shorten the length of the motor cable (PM240-2 needs to be ≤ 50m and pulse frequency ≤ 4kHz).

C1: The PM240-2, in conjunction with an external filter, meets the first environmental limit.

Misconceptions in the selection of incoming reactors:

Mistakenly believing that reactors are optional. In fact, incoming reactors must be used in the following situations:

The power supply voltage distortion is significant (such as multiple frequency converters sharing the same transformer).

Need to reduce incoming current harmonics to comply with IEEE 519.

The power capacity is more than 10 times the rated capacity of the frequency converter.

When using an IT system without a filter, the incoming reactor can help limit the fault current.

The wiring terminals of the reactor cannot be interchanged (input 1L1/1L2/1L3, output 2L1/2L2/2L3), otherwise incorrect coil polarity will cause heating and performance degradation.

Selection and Overheating Protection of Braking Resistors:

The Blocksize power module integrates a brake chopper internally, requiring only an external brake resistor (such as 6SL3201-0BE12-0AA0). The resistance value must meet the requirements of "Resistance value of the external braking resistor" in the manual (such as PM340 FSA 400V resistance ≥ 390 Ω).

The surface temperature of the braking resistor can exceed 80 ℃ and must be installed outside the cabinet or protected. The built-in normally closed temperature control switch should be connected in series to the emergency stop circuit or digital input of the control unit, set to OFF2 pulse blockade.

Activation of DC bus capacitor (Forming)

After long-term storage (over two years), the internal oxide film of the DC bus electrolytic capacitor in the SINAMICS S120 power module will degrade, and direct application of rated voltage may cause damage or even explosion of the capacitor. Therefore, devices stored for more than two years must undergo capacitor activation before being powered on for the first time.

Determine whether activation is needed: Check the serial number on the nameplate and confirm the production date based on the code (for example, "S" represents 2004 and "9" represents September in T-S920067000015). If it exceeds 2 years from the production date, it must be activated.

Activation circuit construction (taking 3-phase 400V module as an example):

Disconnect all loads and DRIVE CLiQ communication from the power module.

Prepare a three-phase switch, three 230V/100W incandescent bulbs (or three 1k Ω/100W resistors), and connecting wires.

Connect three light bulbs in series between the incoming terminals (L1, L2, L3) and the power supply (i.e. connect the light bulbs in series with the power module).

Turn on the power and observe the brightness of the light bulb. The light bulb should gradually dim from bright to dark, and eventually almost go out. If the light bulb remains bright, it indicates that there is a short circuit inside the module.

Keep the power on for about 1 hour (when using a resistor) or until the light bulb is completely turned off (when using a light bulb), allowing the capacitor to gradually form.

Remove the light bulb, connect it directly to the power source, and then turn it on for 30 minutes to complete the final activation.

Attention: The single-phase 220V module uses two light bulbs connected in series between L and N.

Selection of motor side output filter

When the length of the motor cable exceeds the allowable value (usually 50m for shielded cables) or the insulation level of the motor is low, an output filter must be selected.

Filter type, cable length (shielding), pulse frequency limitation

The motor reactor reduces the voltage rise rate (dv/dt) and limits the capacitive charging current to a maximum of 300m ≤ 4kHz

Dv/dt filter+voltage limiter limits dv/dt to<500V/µ s, voltage peak<1000V, maximum 300m ≤ 4kHz

Dv/dt filter compact+voltage limiter limits dv/dt<1600V/µ s, peak<1400V, maximum 100m ≤ 4kHz

The sine wave filter outputs an approximate sine wave, allowing the use of unshielded cables up to 300m or 450m (unshielded) fixed 4kHz

Important precautions:

When using a sine wave filter, the output current must be reduced by about 15%, and the filter configuration must be activated in the parameters (otherwise the control loop will be unstable).

It is strictly prohibited to operate dv/dt filters or sine wave filters without a motor connection, otherwise the filter capacitors may be damaged due to resonance overvoltage.

When the continuous operating frequency of dv/dt filter is below 10Hz, the thermal load will increase and the operating time needs to be limited (for example, every 5 minutes of low-frequency operation must be followed by 5 minutes of high-frequency operation).

Common fault codes and troubleshooting

The following table summarizes typical faults based on manuals and on-site experience:

Fault code (hexadecimal) Fault name Possible cause Solution

0x2200 Internal current power module hardware damage or motor short circuit check motor winding to ground insulation and phase to phase resistance. If normal, replace the power module.

0x2310 Short circuit to ground (U-phase) Motor or cable U-phase short circuit to ground measured with a megohmmeter. Check if the cable is damaged.

0x3210 Internal overvoltage DC bus voltage too high (regenerative energy feedback) prolongs deceleration time or adds braking resistor/braking module.

0x4210 High temperature (power unit) fan failure, ventilation obstruction, high ambient temperature. Check if the fan is rotating (refer to section 11.2.4 for replacing the fan), clean the heat sink, and reduce the ambient temperature.

0x6100 Internal software firmware error or parameter inconsistency. Download the firmware again, restore to factory settings, and debug again.

0x7520 Serial timeout (IBS) 160-IB1 module lost communication with the inverter (for InterBus option) Check the module plug and unplug again.

0x8100 Monitoring: Communication fault DRIVE CLiQ cable disconnected or poorly connected. Check the cable, unplug and lock it again.

0x8300 encoder fault encoder signal loss or power supply error check encoder cable shielding and wiring, use oscilloscope to measure A/B signal.

Read faults through STARTER: Connect the STARTER software, open "Diagnostics" ->"Fault memory" online, and you can see the current fault (r0949) and historical faults. The corresponding fault code can be queried in the List Manual.

Replacement of vulnerable parts: fan and power module

1. Replace CU310-2 fan (order number 6SL3064-1AC00-0AA0)

Step: Power off → Remove CU310 → Press the hooks on both sides of the fan → Pull out the fan forward → Unplug the fan plug → Insert a new fan → Insert into place → Install CU310.

When the internal temperature of CU310 is too high (>65 ℃), the system will issue a "Control Unit Overheating" warning (A30031). If the fan does not turn and the causes of blockage and dust are ruled out, it can be replaced.

2. Replace the PM240-2/PM340 fan

PM240-2 FSA/FSB/FSC: Release the fan lock buckle (FSA one, FSB/FSC two), pull out the fan, unplug the plug, and insert the new fan in reverse.

PM340 FSF: First, remove the screws from the cover plate, remove the cover plate, unplug the plugs of the two fans, remove the fan, install a new fan, and tighten with a torque of 3.0Nm.

The average lifespan of the fan is about 50000 hours. It is recommended to replace it in advance near the end of its lifespan to avoid damage to the power module due to overheating.

3. Replace the Powerblock (Chassis type) of the power module

For the Frame size FX and GX, the power block weighs 70-102kg and requires the use of specialized installation tools (order number 6SL3766-1FA00-0AA0).

Replacement steps: Power off and discharge → Remove all connecting cables (motor, power supply, DRIVE CLiQ, fiber optic) → Remove control interface board → Remove fixing screws → Pull out power block with tools → Push in new power block → Reconnect. Please note that the fiber optic plug has directional markings (U11/U21/U31) and cannot be plugged in incorrectly.

DRIVE CLiQ wiring and equipotential connection

DRIVE CLiQ is Siemens' proprietary internal communication protocol for drivers, based on the 100Mbps Ethernet physical layer. Improper wiring can cause communication interruptions or data errors.

Key rules:

Only Siemens pre installed DRIVE CLiQ cables (such as 6FX2002-1DC00 series) can be used, and regular Ethernet cables cannot be used.

Maximum cable length: ordinary cabinet connection is 100m; when using MOTION-CONNECT 500 cable (drag chain), the maximum length is 100m. However, if MOTION-CONNECT 800PLUS is mixed, the total length calculation formula is: L_MC500+(4/3) * L_MC800PLUS+n * 5 ≤ 100m (n is the number of couplers ≤ 3).

At the wall penetration point of the control cabinet, DRIVE CLiQ wall penetration sleeve (6SL3066-2DA00-0AA0 or M12 type 6FX2003-0DT67) should be used to ensure IP protection level and reduce damage to the shielding layer.

Equipotential connection: For dispersed DRIVE CLiQ nodes (such as SMC30), at least 6mm ² equipotential wires must be used to connect to the central grounding point, otherwise the ground potential difference may damage the communication interface.