CO5 VIRTUAL LAB — METHODOLOGY AUDIT AND CORRECTION REPORT
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AUDIT VERDICT ON THE FIRST VERSION
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The first CO5 virtual lab was suitable as a visual concept demonstrator, but it
was not methodologically strong enough to be presented as a technically audited
protection study.

Critical issues found:
1. L-G, L-L and L-L-G fault currents were represented using fixed multipliers.
   Those factors are not generally valid; unbalanced faults require sequence
   impedances and an inverter sequence-current model.
2. The grid Thevenin impedance derived from short-circuit MVA was treated as
   purely resistive, despite feeder protection normally depending on complex R+jX.
3. PV fault current was multiplied directly by PV operating percentage. An
   inverter's fault response depends mainly on current limiting, ride-through,
   momentary cessation and controller logic; it is not a simple linear multiplier
   of solar output.
4. The upstream bus-fault calculation incorrectly included feeder impedance in
   the grid fault-current path.
5. Adaptive settings were changed using hidden percentage multipliers rather
   than explicit setting groups.
6. The IEC inverse-time calculation was arbitrarily clipped at 30 seconds.
7. There was no load-current security check or minimum fault-sensitivity check.

CORRECTIONS IN AUDITED VERSION 2
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1. Core study restricted to a balanced three-phase RMS fault. This is deliberate
   and technically defensible for a positive-sequence educational model.
2. Grid impedance is decomposed into R and X using short-circuit level and X/R.
3. Feeder R+jX is included only for a downstream feeder fault.
4. PV is represented as:
   a) current-limited ride-through: Ipv = k x Irated, or
   b) momentary cessation: Ipv = 0.
5. Relay currents are assigned according to source location and fault zone.
6. IEC Standard, Very and Extremely Inverse curves are available without hidden
   time clipping.
7. SG-A and SG-B are explicit user-entered setting groups.
8. Directional supervision blocks R2 only for reverse PV current.
9. Pickup security, fault sensitivity and grading margin are checked.

SCOPE AND LIMITATIONS
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This is a diploma-level phasor-domain educational laboratory. It is not:
- an electromagnetic-transient inverter model,
- an unbalanced-fault sequence-network package,
- a CT saturation or relay filtering model,
- a utility protection-setting or commissioning tool,
- an arc-flash or equipment-duty study.

Within these limits, the corrected version is methodologically proper for
demonstrating CO5 concepts: current-limited IBR fault response, location and
direction of fault-current contribution, adaptive setting groups and directional
supervision.