Voltage / Reactive Power Support Application

The voltage reactive power support application was designed to provide reactive power support to the grid in case of voltage variation. In this application, BESS system absorbs or releases reactive power from or to the grid based upon the system’s instantaneous measured voltage. The voltage is measured at the point of common coupling. The BESS responds to changes in voltage conditions and provides automatic reactive power support with respect to measured voltage in accordance with pre-set band limits.

The application functions based upon the criteria as below:

If U>U_limh ,Q_{BESS_OUT}= -Q_{BESS_max} If U< U_liml ,Q_{BESS_OUT}= Q_{BESS_max}

If U ≤U≤U ,Q = Q × U-U / U -U

Where:

Q_{BESS_OUT}: Reactive power Value of BESS

U_dbh: Upper limit of the dead zone of voltage / voltage deadband Limit High U_dbl: Lower limit of the deadzone of voltage / Voltage deadband Limit Low U_limh: Upper limit of the adjustment range of voltage / Voltage Trigger Limit High U_liml: Lower limit of the adjustment range of voltage / Voltage Trigger Limit Low

Figure 21: BESS Response for Voltage / Reactive power support - Illustration

The application operates in 5 voltage zones and BESS response is based upon instantaneous voltage sensed at a particular moment. The BESS imports or exports reactive power based on instantaneous voltage measurement at the point of common coupling following voltage triggers and corresponding droop setting. Reactive power is injected or absorbed to bring the measured grid voltage to a target voltage.

1 Data Analysis

Historical data from the SCADA system was extracted and analysed to understand the variation in system parameters Voltage deadband Limit Low (U_dbl), Voltage deadband Limit High (U_dbh), Voltage trigger limit High (U_limh), Voltage trigger limit Low (U_liml), along with BESS parameters (minimum and maximum state of charge ) before the test was run in real time.

The band limit for Voltage/Reactive Power Support application for Voltage deadband Limit Low (U ), Voltage

2 BESS Operation and Response During Voltage Reactive Power

The Voltage/Reactive Power Support application was been run continuously for a sustained period within reasonable parameters. Parameters such as the Voltage deadband Limit Low (U_dbl), the Voltage deadband Limit High (Udbh), the Voltage trigger limit High (U_limh), the Voltage trigger limit Low (U_liml) , System Voltage (V) and BESS reactive power were recorded during the test run.

Prior to the test run, pre-defined voltage bandlimits such as Voltage deadband Limit Low (Udbl), Voltage deadband Limit High (U_dbh), Voltage trigger limit High (U_limh), Voltage trigger limit Low (U_liml) were configured into the SCADA settings.

Table 12: Voltage Limits for Voltage/Reactive Power Support Application Time Voltage trigger limit

High (U_limh) kV Voltage deadband Limit

High (Udbh) kV Voltage deadband Limit Low (Udbl) kV

Voltage trigger limit Low (U_liml) kV

17:00:00-21:00:00 22.22 22 21.78 21.56

After the test run was completed, data was extracted from the SCADA system to assess the BESS performance. The actual BESS response was in line with the expected BESS output based upon logics deployed for application

Figure 22: BESS Response for Voltage/ Reactive power support – Real time

Figure 22 above shows that the BESS response varies in accordance with changes in the system’s instantaneous measured voltage. The BESS remains idle while voltage measures between the Voltage deadband Limit High (U_dbh) and the Voltage deadband Limit Low (U_dbl). The BESS discharges whenever voltage measured at the Point of Common Coupling (PCC) is below Voltage deadband Limit Low (U_dbl), and it charges whenever voltage measured at the Point of Common Coupling (PCC) is above Voltage deadband Limit High (U_dbh). BESS output (discharge or charge) beyond either side of the deadband limit {Voltage deadband Limit High (U_dbh)-Voltage deadband Limit Low (U_dbl)} is governed by the actual instantaneous voltage value.

3 Sample Case A: BESS Response-During Voltage/Reactive Power Support Application (Discharging to Idle and Idle to Discharging)

The real time data set provides an example of BESS response to the voltage/reactive power support application.

• At time instant 18:06:40 the measured value of voltage at PCC is 21.76 kV between Voltage deadband Limit Low (U_dbl) i.e. 21.78 kV and Voltage trigger limit Low (U_liml) i.e. 21.56 kV, therefore BESS output, Q_BESS is 39 kVar in line with Equation No (VII)

• At time instant 18:11:40 the measured value of voltage at PCC is 21.83 kV between Voltage deadband Limit Low (U_dbl) i.e. 21.78 kV and Voltage deadband Limit High (U_dbh) i.e. 22 kV, therefore BESS output, Q_BESS is 0 var

• At time instant 18:11:50 the measured value of voltage at PCC is 21.76 kV Voltage deadband Limit Low (U_dbl) i.e.

21.78 kV and Voltage trigger limit Low (U_liml) i.e. 21.56 kV, therefore BESS output, Q_BESS is 40 kVar as per Equation No (VII)

If U_liml≤U≤U_dbl,Q_{BESS_OUT} = Q_{BESS_max} × U-U_dbl / U_liml-U_dbl (VII)

Table 13: BESS Response Mode in Real Time During Voltage/Reactive Power Support (Discharging-Idle-Discharging)

Time Voltage (kV) Q_BESS (kVar) BESS Response Mode Remark

18:06:40 21.76 39 Discharging The measured voltage is between the Voltage deadband Limit Low (Udbl) and the Voltage trigger limit Low (Uliml), so the BESS response is 39 kVar.

18:11:40 21.78 0 Idle The measured voltage is between the Voltage

deadband Limit Low (Udbl) and the Voltage deadband Limit High, so the BESS is in idle mode.

18:11:50 21.76 40 Discharging The measured voltage is between the Voltage deadband Limit Low (Udbl) and the Voltage trigger limit Low (Uliml), so the BESS response is 40 kVar.

Figure 23 shows the BESS response during the transition phase from discharging to idle and idle to discharging, along with the change in instantaneous measured voltage at the Point of Common Coupling (PCC).

Figure 23: BESS Response for Voltage/ Reactive power support – Transition phase (Discharging to Idle and Idle to Discharging)

4 Sample Case B: BESS Response-During Voltage/Reactive Power Support Application (Idle to Charging)

The real time data set provides an example of BESS response to the voltage/reactive power support application.

• At time instant 19:41:40 the measured value of voltage at PCC is 22 kV and between Voltage deadband Limit Low (U_dbl) i.e. 21.78 kV and Voltage deadband Limit High (U_dbh) i.e. 22 kV, therefore Q_BESS is approximately 0 kVar

• At time instant 19:41:50 the measured value of voltage at PCC is 22.06 kV between Voltage deadband Limit High (U_dbh) i.e. 22 kV and Voltage trigger limit High (U_limh) i.e. 22.22 kV, therefore BESS output, Q_BESS is -137 kVar in line with Equation No (VIII)

If U_dbh≤U≤U_limh ,Q_{BESS_OUT} = Q_{BESS_max} × U-U_dbh/ U_dbh-U_limh (VIII)

Table 14: BESS Response Mode in Real Time During Voltage/Reactive Power Support (Idle-Discharging) Time Voltage (kV) Q_BESS (kVar) BESS Response Mode Remark

19:41:40 22 -4 Idle The measured voltage is between the Voltage

deadband Limit Low and the Voltage deadband Limit High, so the BESS response is -4 (approx.

0) kVar.

19:41:50 22.06 -137 Charging The measured voltage is between the Voltage deadband Limit High (Udbh) and the Voltage trigger limit High (Ulimh), so the therefore BESS response is -137 kVar.

Figure 24: BESS response for Voltage/ Reactive power – Transition phase (Idle to Charging)