SIMATIC S7 EMC Compliance for IEC 60870-2-1 Substations

Overview

Substation automation projects frequently specify SIMATIC S7 controllers and SCALANCE networking components, yet the EMC test program required by the specification is often IEC 60870-2-1 (telecontrol equipment, substation environment) rather than the generic industrial immunity/emission standards that appear in SIMATIC datasheets. This creates an interpretation problem for the integrator: the SIMATIC S7-300, S7-400, and ET 200 families are tested and CE-marked against EN 61131-2 (programmable controllers) and the EN 61000-4 / EN 61000-6 family (generic EMC), but they are not type-tested against IEC 60870-2-1 directly. The decision path is therefore one of cross-mapping, isolation-voltage analysis, and field-proven record, not direct standard equivalence.

This reference documents which SIMATIC modules ship with 1500 V or 4000 V galvanic isolation, which signals at 33 kV substations require reinforced isolation, and which architectural alternatives (SICAM I/O, RUGGEDCOM switches, intermediate relays) are typically used when the IEC 60870-2-1 immunity levels cannot be met by a stock S7-300 configuration. It also collates the relevant Siemens support entries and EMC technical documentation that an engineer should attach to a substation design dossier.

IEC 60870-2-1 Requirement Set

IEC 60870-2-1 is the environmental section of the IEC 60870-5 telecontrol protocol family. It defines the climatic, mechanical, and electromagnetic conditions that telecontrol equipment must survive when installed in HV/MV substations. The two clauses most often quoted in specifications are:

• EMC immunity - Level 3 or Level 4: Continuous and transient immunity tests on power, signal, and earth ports. Level 3 corresponds to a typically industrial environment; Level 4 corresponds to a particularly severe environment (substation near primary switchgear, exposed to HV inductive coupling).
• EMC emission - Class A: Radiated and conducted emission limits for equipment intended to be used in industrial environments (Class B is residential/light-industrial). SIMATIC equipment is consistently Class A by default.

Where IEC 60870-2-1 is ambiguous, engineers frequently fall back on the protection-equipment standard IEC 60255 (Measuring relays and protection equipment) and on the IEC 61000-4 test series. SIPROTEC 7SJ64 / 7SA / 7SD protection relays and SICAM I/O modules are tested to:

• IEC 60255-5 (insulation): 2.5 kV rms, 50/60 Hz, 1 minute between all circuits except auxiliary voltage and serial ports.
• IEC 60255-5 impulse class III: 5 kV peak, 1.2/50 µs, 0.5 J, 3 positive and 3 negative impulses at 5 s intervals.
• IEC 61000-4-5 surge class III: 2 kV line-to-line / 1 kV across contacts on auxiliary voltage; 2 kV line-to-line / 1 kV across contacts on binary I/O.
• IEC 61000-4-4 (burst), IEC 61000-4-3 (radiated RF), IEC 61000-4-2 (ESD) per the generic industrial standard EN 50082-2 (now superseded by EN 61000-6-2).

The cross-mapping the engineer has to perform is therefore: SIMATIC S7 must be shown to be at least equivalent to this immunity profile for the specific ports used in the substation, and any signals crossing from the HV field to the S7 (CT/VT secondaries, binary I/O, status contacts) must satisfy the same isolation voltages.

SIMATIC S7-300 EMC Compliance Profile

The SIMATIC S7-300 is CE-marked and shipped with a manufacturer declaration against the following harmonised standards (per the SIMATIC S7-300 System Manual, chapter 7.2 "Electromagnetic compatibility", Siemens entry ID 12996906):

• Emission: EN 61000-6-4 (industrial environment, Class A).
• Immunity: EN 61000-6-2 (industrial environment).
• Product standard: EN 61131-2 (programmable controllers - PLC EMC).

EN 61131-2 prescribes a complete set of port tests (ESD, radiated RF, burst, surge, conducted RF, power-frequency magnetic field, voltage dips/interruptions) at levels appropriate to a "normal industrial environment". The CE Technical File for the ET 200 distributed I/O family, published via the TIA Portal documentation cloud, summarises the same compliance set: CE Codes and Approvals - ET 200 distributed I/O.

The S7-300 product line does not appear on Siemens' formal list of "SIPROTEC-tested" or "IEC 60870-2-1-tested" PLCs. Siemens' official position, as recorded in support responses to the question "is the S7-300 compliant with IEC 60870-2-1?", is that the S7-300 is certified to EN 61131-2 and the EN 61000-6-x generic standards, and that the integrator is responsible for cross-mapping the application requirements. This is the same position Siemens takes in the EMC technical overview EMC - Technical overview (PDF, Siemens ID 103704610), which discusses EN 61800-3 for drives and the practical installation rules that apply to any SIMATIC installation.

SIMATIC Module Isolation Ratings

The single most important parameter when sizing SIMATIC for a substation is the galvanic isolation voltage between the process side (field wiring) and the backplane / electronics. Stock SM 321 digital input modules carry 500 V DC isolation only, which is acceptable for factory automation but insufficient for 33 kV substation I/O that may see coupled transients in the kV range. The table below summarises the modules that ship with reinforced isolation.

The 6ES7 321-1FH00-0AA0 module is the workhorse for substation binary inputs: 4000 V isolation on the process side allows direct wiring to 110/220 V DC station-battery contacts and to interposing relays fed from the substation battery, without intermediate 24 V dropper relays. For CT/VT secondaries, no S7-300 AI module is rated for direct connection - the standard practice is to use measurement transducers (7KG / 7KT series) or SICAM AI modules, and to wire the secondary at the cubicle level so that the cable run between CT and transducer stays within the screened, earthed cubicle.

The 6ES7 321-1CHx0 modules at 1500 V DC are sufficient for many utility telemetry applications where the field I/O is already isolated by an interposing relay or by a SCADA-specific I/O module (SICAM 1703, SICAM DI32). They are not sufficient if the wiring is taken directly from the HV yard.

Surge and Transient Protection

The dominant EMC stress in a 33 kV substation is not radiated RF or ESD - it is surge voltage (1.2/50 µs impulse) and damped oscillatory wave (DOW), induced into control wiring by:

1. HV/MV switching operations in adjacent bays.
2. Short-circuit currents flowing in the earth grid, producing earth potential rise (EPR) and longitudinal common-mode voltage on long field cables.
3. Lightning strikes to the substation shield wire or to the line.

The test waveforms that must be satisfied are:

• 1.2/50 µs impulse, 5 kV peak (per IEC 60255-5 / IEC 61000-4-5) between each signal terminal and earth, and between signal pairs.
• 100 kHz ring wave / DOW (per IEC 61000-4-12) at 2.5 kV on signal ports.
• Fast transient burst (per IEC 61000-4-4) at 2 kV on signal and power ports.
• Conducted RF (per IEC 61000-4-6) at 10 V rms, 150 kHz to 80 MHz.

Stock SIMATIC modules are tested to EN 61131-2 levels (typically 1 kV surge on signal, 2 kV surge on AC power) which is one IEC level lower than what IEC 60870-2-1 Level 4 / IEC 60255-5 demands. The accepted mitigation is to install surge arresters (e.g. ABB OVR, Dehn Blitzductor, Phoenix Contact FLASHTRAB) on every field conductor that enters the cubicle, in addition to the SIMATIC module's own isolation. The Siemens EMC installation guide (Siemens ID 103704610) recommends the same topology: filter at the cabinet boundary, isolate at the module, and keep field cable shields bonded to the cubicle earth bar at the point of entry.

Field-Installed SIMATIC in Substations

SIMATIC S7 systems have been installed in transmission and distribution substations since the early 1990s, across voltage classes from 415 V LV switchgear to 220 kV EHV, with documented service records in:

• Rail traction substations (Siemens Mobility, in-house installations).
• Distribution substations up to 33 kV (Siemens Energy / Smart Grid partner installations).
• Power plant auxiliary controls (Siemens Energy, in-house installations).
• Industrial substation automation under the SICAM product line, which historically used S7-400 CPUs with SICAM I/O (the so-called "S7 with SICAM I/O").

Five-to-twenty-year service records do not constitute a "certificate" against IEC 60870-2-1. They constitute the field experience that supports a written waiver or a "qualified by similarity" argument when the customer accepts it. The written position that should be in the project file is typically: "SIMATIC S7-300 is CE-marked against EN 61131-2 and EN 61000-6-2/-6-4. The integration has been performed in accordance with Siemens EMC installation guidelines and the IEC 61850 / IEC 60870-5-104 protocol stack has been validated for the substation environment." This is the position a utility's protection engineer can defend to an internal review.

Alternative Architectures: SICAM I/O and Ruggedcom

When the specification mandates IEC 60870-2-1 Level 4 in writing, the standard Siemens answer is to substitute the I/O - not the CPU. Two practical architectures exist.

SICAM I/O on an S7 CPU

The SICAM DI32 digital input module (used historically in SICAM SAS and SICAM RTU) is documented with:

• Insulation test 2.5 kV AC rms / 3.5 kV DC, 1 minute, between process inputs and electronics, per IEC 60255-5.
• Impulse test 5 kV peak, 1.2/50 µs, per IEC 60255-5 class III.
• Real-time signal acquisition at 1 ms resolution.

The SICAM DI32 was the I/O board that originally allowed Siemens to ship an S7-400 with substation-grade isolation. When this I/O is used, the CPU side is a stock S7-300 or S7-400 with its 500 V-1500 V backplane isolation, and the process side satisfies IEC 60255-5 / IEC 60870-2-1. The SICAM AK / TM / AI modules extend the same isolation profile to analog and temperature inputs. Mini-RTU and micro-RTU (S7-200-based) did not have this option and had to use external isolators when installed in substations.

RUGGEDCOM switches in place of SCALANCE

SCALANCE X switches are industrial Ethernet switches tested to EN 61131-2 / EN 61000-6-2. For substation-grade EMC, many integrators have moved to RUGGEDCOM (now Siemens Ruggedcom, formerly Ruggedcom Inc.) RS900 / RSG900 / RX1500 series, which carry IEC 61850-3 (substation communication) and IEEE 1613 (substation environmental) certifications in addition to the generic industrial EMC set. RUGGEDCOM's published IEEE 1613 certificate covers the same surge and impulse waveforms as IEC 60870-2-1 Level 4. The cost difference against SCALANCE X-200 / X-300 is small at the switch level, and the certification delta is significant.

Practical Configuration Recommendations

When the specification is IEC 60870-2-1 Level 3 or Level 4, apply the following configuration rules:

1. Use 6ES7 321-1FH00-0AA0 (4 kV AC DI) or 6ES7 321-1CHx0-0AA0 (1500 V DC DI) on every binary input that runs from the field. Do not wire 500 V-rated stock SM 321 directly to substation contacts.
2. Install surge arresters on every field conductor at the cubicle entry. Choose a clamping voltage below the isolation voltage of the downstream module (e.g. 600 V clamping for a 1500 V module, 2.5 kV clamping for a 4 kV module).
3. Bond cable shields to the cubicle earth bar at the point of entry, and to the S7 cabinet earth bar, using a short pigtail or EMC backshells. Do not carry shield conductors through to the module terminal.
4. Route field wiring and LV logic wiring in separate ducts; maintain ≥ 200 mm separation or use a grounded metal partition.
5. Use RUGGEDCOM (IEC 61850-3 / IEEE 1613) or equivalent for the substation LAN. SCALANCE is acceptable for the station-bus / process-bus segment inside the control building.
6. Power the SIMATIC from a dedicated 24 VDC supply fed from the station battery via a DC UPS, with a surge arrester on the AC input of the battery charger.
7. Where CT/VT secondaries must land on the S7, use 7KG / 7KT transducers in the cubicle, never the SIMATIC AI module directly. Keep the secondary cable within the cubicle.
8. Document the EMC compliance argument in the design dossier: cross-reference table between IEC 60870-2-1 Level 3/4 clauses and the EN 61131-2 clauses met by the selected modules, plus the surge arrester schedule and the field cable schedule.

Verification Checklist

Before energising the RTU panel in the substation, verify:

Troubleshooting Matrix

FAQ