I want to test distance protection on a transmission line. I have set up a 110 kV network equivalent (source) at both ends, but I suspect there is an issue with the parameters of that 110 kV source. Does anyone know how to configure the R, L, and C values (and what exactly they represent when modeling a 110 kV network equivalent)?
Also, how do I “activate” the fault? The simulator is connected to an OMICRON amplifier, which feeds into the relay. However, when I start the simulation, the fault triggers immediately, and I get unrealistic current values—approximately 25 kA.
Thanks in advance for your help!
Hi there,
Testing distance relays (ANSI 21) using Hardware-in-the-Loop (HIL) with an OMICRON amplifier is a classic and robust application in HYPERSIM.
Based on your schematic and parameter window, here is a detailed guide on how to properly configure the 110 kV source equivalent (R, L, C), how to time/control fault activation, and why you are seeing a 25 kA fault current.
- What R, L, C Represent and How to Calculate Them
When modeling a 110 kV grid equivalent at the boundary of your line, the voltage source acts as a Thevenin equivalent: an ideal AC voltage source in series with the grid’s internal short-circuit impedance (Z_s = R_s + j\omega L_s).
A. What the parameters represent:
L (Internal Grid Inductance): Represents the magnetic/inductive reactance (X_s = \omega L_s) of upstream generators, transformers, and transmission lines back to the bulk system.
R (Internal Grid Resistance): Represents upstream ohmic and resistive losses, defined via the network’s X/R ratio.
C (Capacitance): Set to 0.000. For a standard series Thevenin grid equivalent, there is no series capacitance (C=0 bypasses/omits series capacitance in HYPERSIM).
B. How to calculate R and L from Short-Circuit Level (S_{sc}):
To match a specific substation short-circuit capacity (e.g., S_{sc} = 2500\text{ MVA} and X/R = 10 at f = 50\text{ Hz}):
Calculate Base Short-Circuit Impedance (Z_s):
Z_s = \frac{V_{LL}^2}{S_{sc}} = \frac{(110\text{ kV})^2}{2500\text{ MVA}} = 4.84\ \Omega
Calculate Reactance (X_s) and Inductance (L_s):
X_s = Z_s \cdot \frac{X/R}{\sqrt{1 + (X/R)^2}} \approx 4.816\ \Omega
L_s = \frac{X_s}{2\pi f} = \frac{4.816}{2\pi \times 50} \approx 15.33\text{ mH}
Calculate Resistance (R_s):
R_s = \frac{X_s}{X/R} = \frac{4.816}{10} \approx 0.482\ \Omega
(Note: In your current screenshot, you have R = 5.0\ \Omega and L = 28.98\text{ mH}, which corresponds to X_s \approx 9.1\ \Omega, yielding a relatively strong short-circuit impedance).
- Also Check: Source Voltage Unit & Phase Sequence
Looking closely at your source parameter dialog:
Amplitude (rmsLL): Notice the unit next to the amplitude field is labeled V (Volts). Ensure whether your HYPERSIM version expects the value in V (i.e. 110000) or in kV (i.e. 110). Check that your nominal base voltage matches your expected secondary scaling to the OMICRON.
Phase Sequence: Your dialog shows Phase sequence: Inverse. Unless your specific network is A-C-B, switch this to Direct (A-B-C) so the distance relay (21) polarization and directional elements see the correct sequence voltages.
- Why the Fault Triggers Immediately & How to Control It
If the simulation starts with the fault active at t = 0\text{ s}, the model cannot reach steady-state before the event, leading to severe transient DC offsets.
How to control fault timing:
Timed Fault (Internal control):
Double-click your Fault Block (the block with the yellow lightning bolt on line CP2).
Set Transition times / Fault application time (T_{on}) to a later time (e.g., 0.5 or 1.0 s) and Clearing time (T_{off}) (e.g., 1.1 s for a 100 ms fault).
This allows the system to reach steady-state load flow before the fault strikes.
Manual / Real-Time Triggering (External control):
In the Fault block settings, switch the control type from Internal to External.
Connect an interactive Manual Switch or a pulse generator block in your HYPERSIM schematic. While the real-time simulation is running, you can toggle the switch from the HYPERSIM Scope / Dashboard to inject the fault on demand.
- Why You Are Seeing ~25 kA (Is It Normal?)
A short-circuit current of 25 kA at 110 kV corresponds to:
S_{sc} = \sqrt{3} \times 110\text{ kV} \times 25\text{ kA} \approx 4760\text{ MVA}
Grid Physics: 25 kA to 31.5 kA is actually a typical standard breaking rating for 110 kV / 132 kV transmission substations.
Transient Asymmetry (DC Offset): If the fault is applied at t=0, the instantaneous peak current (I_p) can be 2.5\times higher than the RMS steady-state symmetrical fault current.
Secondary Scaling to OMICRON: Remember that the OMICRON amplifier expects CT secondary currents (typically 1\text{ A} or 5\text{ A} nominal). Ensure your model includes a CT / Scaling block (e.g., 1000\text{ A} : 1\text{ A} or 2000\text{ A} : 5\text{ A}) before routing signals to the physical analog output DACs connected to the OMICRON amplifier inputs.
@Parija Thank you very much for the answers.
I have just one question regarding secondary scaling for the OMICRON unit.
How do I insert the scaling block into the model (and which block is it)? (For 110 kV systems, we typically use 1 A scaling—i.e., the CT ratio is usually 600/1 A in the actual 110 kV grid in Croatia.)
Hi @IB_1309,
Great question! Scaling simulated primary currents down to secondary levels for an external test set/amplifier like an OMICRON unit (e.g., CMC / CMS series) is a standard step in Hardware-in-the-Loop (HIL) secondary injection setups.
Here is how to set up the scaling block and configure the ratios in HYPERSIM:
- Which Block to Use?
In HYPERSIM, you have two common ways to implement CT scaling:
Method A: Standard Gain Block (Recommended for clarity)
In the HYPERSIM component library / Schematic Editor, open the Control / Math library.
Drag and drop a Gain (Multiplication) block into your schematic.
Connect the output of your Current Measurement (Ammeter) block into the input of the Gain block.
Route the output of the Gain block to your Analog Output (AO / DAC) channel mapped to the simulator’s physical I/O card (e.g., OP5330 DAC).
Method B: Built-in Gain in the Analog Output / Measurement Deep Panel
If you map measurements directly to physical I/O without extra schematic blocks:
Select your Current Measurement block and open the Parameters / Deep Panel.
Under the Analog Output connection settings, you will find the linear transfer formula:
\text{Output } (V) = \text{Gain} \times \text{Measurement} + \text{Offset}
You can enter your combined scaling factor directly in the Gain field.
- Calculating the Scaling for a 600 / 1 A CT Ratio
There are two conversion stages to account for:
Stage 1: Primary to Secondary CT Ratio (K_{CT})
For a 600\text{ A} : 1\text{ A} CT:
K_{CT} = \frac{1\text{ A}}{600\text{ A}} = \frac{1}{600} \approx 0.001667
Stage 2: Secondary Current to DAC Voltage (K_{DAC})
The OPAL-RT simulator outputs an analog voltage (typically \pm 10\text{ V} peak or \pm 16\text{ V} peak) from its DAC channels to the OMICRON low-level voltage inputs:
Check your OMICRON amplifier sensitivity configuration (e.g., in OMICRON Test Universe or CMControl).
A standard low-level configuration is often 1\text{ V}{peak} = 1\text{ A}{peak} (or 1\text{ V}{rms} = 1\text{ A}{rms}).
In this case, K_{DAC} = 1\text{ V/A}.
Total Gain = K_{CT} \times K_{DAC} = \frac{1}{600} \approx 0.001667.
- Checking Fault Current Headroom (DAC Clipping)
For a 110 kV line with a 25 kA maximum fault current:
Primary Peak Current: I_{peak} \approx 25\text{ kA} \times \sqrt{2} \approx 35.35\text{ kA} (higher if there is a severe DC offset).
Secondary Current at 600/1 A:
I_{sec_peak} = \frac{35355\text{ A}}{600} \approx 58.9\text{ A secondary peak}
Tip: If your physical OMICRON amplifier or OPAL-RT DAC saturates at \pm 10\text{ V}, ensure that the maximum expected secondary fault current combined with your amplifier sensitivity does not exceed the \pm 10\text{ V} DAC voltage limit. If needed, configure the OMICRON low-level input range (e.g., 10\text{ V} = 100\text{ A}) and match the gain in HYPERSIM accordingly.
Summary Checklist:
Insert: Math \rightarrow Gain block after the current sensor.
Gain Value: Set to 1/600 (or 1/600 * K_DAC).
Route: Gain output \rightarrow Analog Out channel \rightarrow OMICRON low-level input.
Relay Setup: Set your physical protection relay nominal CT parameter to I_n = 1\text{ A} with a ratio of 600\text{ A} / 1\text{ A}