Test Specification 10.03

Primary frequency and voltage response after disconnection

Test Specification Definition

ID

10.03

Reference to Test Case

TC10

Title of Test

Primary frequency and voltage response after disconnection

Test Rationale

Once the protection system intervenes to isolate the microgrid, the local DER controllers (voltage and frequency droop) react to the imbalance and try to stabilize the microgrid operation. The specific test aims at characterizing the simultaneous ability of the DER units (i.e., battery storage and CHP) to stabilize the voltage and frequency.

Specific Test System (graphical)

In this TS the selected test system is the same with TS10.02 and is based on the LV distribution network benchmark application example by CIGRE1

Target measures
  • ΔVmax=+15% to -20% of nominal voltage
  • Δfmax<±1Hz
  • ROCOFmax <2Hz/s
  • Response time (frequency/voltage stabilization) <5s
Input and output parameters

Input parameters

  • Solar irradiance
  • Wind speed
  • Ambient temperature
  • Load consumption
  • Breaker state

Output parameters

  • Frequency
  • Voltages
Test Design

The test considers one power imbalance that is caused from the disconnection of the breaker and the loss of power exchange to/from the grid. This imbalance will result in activation of the droop controllers and the possible subsequent stabilization. The same test will have to be repeated several times for five (5) different initial conditions depending on the type of disturbance.

Initial system state

There are five possible initial states for the system in terms of frequency and voltage values. All five of them, however, require that initially the microgrid is connected to the grid and that both the voltage at PCC and the frequency are within allowable limits. Once these conditions are met, each one of the five disturbances should be generated through the LV source.

Evolution of system state and test signals
  1. The microgrid is running in parallel with the LV source with which exchanges some power
  2. The LV source frequency is monitored and controlled in order to increase stepwise to the maximum allowable value of 50.5Hz. The time of this activation limit is recorded
  3. The protection relay detects the disturbance and activates a disconnection of the static switch
  4. The static switch disconnects the microgrid from the LV source
  5. The frequency at the PCC and the Voltage at multiple points of the microgrid are monitored in order to estimate the response time from the protection activation to the new steady-state
  6. The relay is reset and the static switch reconnects the load to the source
  7. Step 2 is repeated with the frequency setting at 49.5Hz
  8. Steps 3-6 are repeated
  9. Step 2 is repeated with the frequency setting at ROCOF=1Hz/s
  10. Steps 3-6 are repeated
  11. Either the LV source or some of the microgrids units should be controlled in a way that allows the voltage at the PCC to increase towards the upper limit (15%). The time that the voltage crosses the limit is recorded.
  12. The protection relay detects the disturbance and activates a disconnection of the static switch
  13. The static switch disconnects the microgrid from the LV source
  14. Frequency at the PCC and Voltage at multiple points of the microgrid are monitored in order to estimate the response time from the protection activation to the new steady-state
  15. The relay is reset and the static switch reconnects the microgrid to the source
  16. Either the LV source or some of the microgrids units should be controlled in a way that allows the voltage at the PCC to increase towards the lower limit (-20%). The time that the voltage crosses the limit is recorded.
  17. The protection relay detects the disturbance and activates a disconnection of the static switch
  18. The static switch disconnects the microgrid from the LV source
  19. Frequency at the PCC and Voltage at multiple points of the microgrid are monitored in order to estimate the response time from the protection activation to the new steady-state
Other parameters

N/A

Temporal resolution

A sampling time of <1ms is required for the accurate measurement of the total system response

Source of uncertainty

Uncertainties that may arise due to the precision of the various instruments used to measure the voltage responses. Additional uncertainties may be introduced by the communication channel delays between the protection relay and the static switch, as well as from the operation of the microgrid units that are subject to:

  • Environmental conditions
  • Consumers’ demand
  • Grid parameters variability i.e., resistance/inductance ratio
Suspension criteria / Stopping criteria

The test should be suspended and restarted if one of the quality attributes described in the TC is not met.