Question 1

What is IEC 61850-90-4?

Accepted Answer

IEC 61850-90-4:2020 is the substation automation network engineering guideline. It covers station bus and process bus sizing, GOOSE storm analysis, sampled values bandwidth, and VLAN segregation for protection and control systems.

Question 2

What is PRP in substation automation?

Accepted Answer

PRP (Parallel Redundancy Protocol, IEC 62439-3 §4) uses dual LANs (LAN A and LAN B) carrying identical frames simultaneously. On any single network failure, the backup LAN continues without any recovery delay — achieving 0 ms recovery time. It is the recommended topology for protection-critical GOOSE functions.

Question 3

What is HSR in substation automation?

Accepted Answer

HSR (High-availability Seamless Redundancy, IEC 62439-3 §5) forms a ring topology where each node forwards frames in both directions. Recovery time is 0 ms. Worst-case latency is (N-1) × per-node delay; for 20 nodes at 7 µs/hop this is 133 µs, which is safely below the 4 ms protection threshold.

Question 4

How much bandwidth does IEC 61850-9-2LE use?

Accepted Answer

One merge unit running IEC 61850-9-2LE at 80 samples/cycle on a 50 Hz system produces 4000 sample frames per second. At 130 bytes per frame this gives approximately 4.2 Mbit/s per merge unit. At 256 samples/cycle (protection class), the rate rises to about 13.4 Mbit/s per MU.

Question 5

What is a GOOSE storm?

Accepted Answer

At fault inception each GOOSE publisher retransmits 8 frames within the first 4 ms per the IEC 61850-8-1 §8.1.3.2 retransmission sequence. A substation with 40 GOOSE publishers produces a burst of 320 frames in 50 ms — roughly 12 Mbit/s — that must not overflow switch queues or violate the Type 1A ≤3 ms latency budget.

Question 6

What are P1, P2, P3 performance classes?

Accepted Answer

IEC 61850-5:2013 Table 1 defines three protection message performance classes: P1 (≤4 ms trip initiation), P2 (≤8 ms), and P3 (≤20 ms). The class achieved depends on peak burst headroom — if GOOSE storm load leaves ≥40% link headroom, P1 is achievable without additional QoS measures.

IEC 61850 Bandwidth & PRP/HSR Sizing

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