This projects build on Part I - Site Assessment and Part II - Grid Integration & Power System Modelling where we identified candidate locations for a micro-hydropower plant in rural Southwest British Columbia and conducted load flow analysis for a 100kW plant. We will now conduct a simiplified grid security and protection analysis using PowSyBl for contingency and outage analysis. We will then apply foundational protection and reliability concepts relevant to distribution interconnection using the IEEE 1547 standards as a guide.
As defined in Part II, we are working with the following topology where VL_main (12.47kV) is the external grid, and VL_Hydro (0.48kV) is the micro-hydro generator (100kW):
The pypowsybl library in python is used for simulating the base case load flow analysis, as well as the fault and contingency cases (N-1 analysis). The following cases will be studied:
- Base case load flow
- Line1 outage (between Bus_slack and Bus1)
- Line2 outage (between Bus1 and Bus2)
- Line3 outage (between Bus2 and Bus3)
- Transformer outage
- Generator outage
Following the simulations, protection schemes will be proposed to mitigate weaknesses in the system.
This simulation models the behaviour when the main feeder (or primary transmission line) is disconnected from the Slack (external grid)
The simulation does not converge (SOLVER_FAILED). Due to the radial topology, when line 1 fails, all components downstream loses connection to the slack bus. Without the reference bus (slack) and a secondary path to the external grid, the simulation fails because the power can no longer be balanced in the subsequently formed island.
This simulation models the behaviour when the internal trunk line between local load centers fails
The results for this case can be interpreted in the same way as for case 1.1.
This simulation models the behaviour when the dedicated feeder connecting the micro-hydro generator is disconnected
This simulation converges. L3 is the link to the micro-hydro substation which fails but the rest of the grid (bus 1 and 2) stay online.
| Contingency | Result | System Impact |
|---|---|---|
| L1 Outage | Critical Failure | Blackout (main feeder lost) |
| L2 Outage | Critical Failure | Partial supply interruption (disconnect from grid) |
| L3 Outage | OK | Localized outage (only micro-hydro substation impacted) |
| T1 Outage | OK | Localized outage (LV bus impacted) |
| Micro-hydro Gen Outage | OK | Operational change (slack compensates for lost generation) |
| Zone | Equipment | Protection |
|---|---|---|
| Feeder | Lines and loads | OC relay, breaker |
| Transformer | Step-up transformer | Differential and OC |
| Generator | Micro-hydro generator | V/F/reverse power |
| PCC | Interconnection point to ex.t grid | Anti-islanding |
This zone covers the 12.47kV radial feeder:
- Slack Bus - Bus1
- Bus1 - Bus2
- Bus2 - Bus3
- Connected loads
The proposed protection mechanisms for this zone include:
- Overcurrent Relay (OC) - If current exceeds threshold, trip breaker
- Breaker - Installed between Slack Bus and Bus1
This mechanism will isolate the faulted segments, providing protection from line-to-ground faults, line-to-line faults, overloads, short circuits, and downstream faults.
This zone covers the 12.4k kV / 0.48kV step-up transformer. Differential protection is proposed for this zone, where the current entering the transformer is compared with the current leaving it. If they are not equal (after ratio adjustment), this indicates an internal fault which will trip the OC relay. This ensures that if the transformer faults, the micro-hydro plant is isolated immediately and the feeder is not exposed.
This zone covers the 100kW micro-hydro generator and its associated terminals. The proposed protection mechanisms for this zone include:
- Voltage protection (ex. 0.88 pu < V < 1.10 pu)
- Frequency protection
- Reverse power
If any abnormal conditions are detected (beyond given thresholds), the protective relay opens a breaker to disconnect and isolate the generator.
This zone covers Bus3 / transformer HV side at the Point of Common Coupling (PCC) - interface between utility grid and DER (micro-hydro). Proposed protection functions include:
- Anti-islanding - Disconnect micro-hydro generator if utility grid lost. Without anti-islanding, the generator might continue to power a "dead" section of the grid. This is dangerous for utility workers and can lead to unsynchronized re-closing
When the grid is lost, the micro-hydro turbine will either speed up or slow down instantly because the load no longer matches the generation. To implement anti-islanding, the following is required:
- Rate of Change of Frequency (ROCOF) - Detects sudden grid separation. If frequency change is greater than threshold, relay should trip.
- Synchronosim Check - Checks and matches voltage magnitude, phase angle, and frequency with the utility grid
These mechanisms ensure rapid disconnection of the micro-hydropower generator under abnormal grid conditions.
Grid -- Bus1 -- Bus2 -- Bus3 -- PCC Breaker + Protection Relay -- Transformer -- Micro-hydro Generator
Implementing a ring topology instead of a radial topology, where either Bus2 or Bus3 is also connected back to the Slack bus via a separate path ensures N-1 compliance. Even if a line in the loop fails, the micro-hydro plant will still be able to export power to the grid. The advantage with radial feeders is that fault current flows in one direction so coordination when something wrong happens is straightforward.
With Parts I, II, and III, this project demonstrated a full conceptual workflow for micro-hydropower distribution interconnection, progressing from site selection, to power flow modeling, to contingency analysis and protection planning. Simulation results showed that the 100 kW micro-hydropower unit can operate effectively under normal feeder conditions, but secure interconnection with the utility grid requires coordinated feeder, transformer, generator, and anti-islanding protection to manage abnormal voltage, frequency, outage, and reverse power events. Overall, the project illustrates the technical considerations required for integrating small renewable generation into utility distribution systems while maintaining grid reliability and operational safety.