GB/T 19964-2024Technical requirements for connecting photovoltaic power station to power system (English PDF)

1 Scope

The document sets technical requirements for the connection of photovoltaic power stations to the power system covering active power, reactive power and voltage, fault ride-through, operational adaptability, power forecasting, power quality, simulation models and parameters and the secondary system, together with the content of testing and evaluation.

It applies to the construction, production and operation of new, rebuilt and extended photovoltaic power stations connected at voltage levels above 10 kV. Photovoltaic power stations fitted with storage follow it by reference.

3 Terms and definitions

3.3 The point of connection is, for a station with a step-up substation, the high voltage busbar or node of that substation, and for a station without one, the output collection point of the station.

3.5 to 3.7 Medium-term photovoltaic power forecasting is the forecast of active power from midnight of the following day to 240 h ahead at a time resolution of 15 min; short-term forecasting runs from midnight of the following day to 72 h ahead at the same resolution; ultra-short-term forecasting runs from 15 min to 4 h ahead, again at 15 min resolution.

3.8 to 3.10 Low voltage ride-through is the ability of the station to stay connected and running when a system fault or disturbance makes the voltage at the point of connection drop, within a given range of drop and a given time interval. High voltage ride-through is the same ability when the voltage rises, and low-high voltage ride-through when the voltage first drops and then rises.

3.11 and 3.12 The dynamic reactive current increment is the change in the reactive current injected into or absorbed from the system during low or high voltage ride-through relative to the value before the drop or rise, reactive current meaning capacitive reactive current. Its rise time runs from the moment the voltage at the point of connection reaches the trigger setting to the moment the increment reaches 90 % of its target value.

3.13 and 3.14 An island is a part of the grid containing load and source that stays running in isolation after separating from the main grid, planned or unplanned; anti-islanding is the prevention of unplanned islanding.

4 Active power

4.1 The station takes part in system frequency and peak regulation in accordance with GB 38755, GB/T 31464, GB/T 40594 and GB/T 40595, and is fitted with an active power control system able to adjust continuously and smoothly. The control modes include at least active power limit control, active power set point control, active power difference control and frequency regulation control, put into or out of service on the automation signals and dispatch instructions of the dispatching authority, with response time and control accuracy per GB/T 40289.

4.1.4 During connection, normal shutdown and rising irradiance the rate of change of active power meets the needs of safe and stable operation, its limit being fixed by the dispatching authority from the frequency regulation characteristics of the system and recommended at 10 % of rated capacity per minute. Where irradiance falls rapidly the rate of change is allowed to exceed the limit.

4.2 Under system fault or emergency the station reduces active power or disconnects on the instruction of the dispatching authority, and reconnects on its instruction once normal operation is restored.

4.3 Primary frequency regulation follows GB/T 40594 and GB/T 40595 and can be started and stopped on dispatch instruction. Where the frequency deviation leaves the dead band, the station adjusts its active power output according to formula (1). The formula as printed is broken and is not reproduced here; its symbols are the change in active power of the station in megawatts, the active frequency regulation coefficient, the system frequency and the rated system frequency in hertz, and the rated active power of the station in megawatts.

4.3.3 to 4.3.7 The frequency regulation coefficient and the dead band are fixed by the dispatching authority from the frequency regulation characteristics of the system; the coefficient is recommended to lie between 10 and 50 and the dead band at +/- 0.02 Hz to 0.06 Hz. Above 50 Hz the limit on the amplitude of the active power reduction is recommended to be not less than 10 % of rated active power, and below 50 Hz the limit on the increase not less than 6 %. The lag time of the active power response is not more than 1 s, the rise time not more than 5 s and the settling time not more than 15 s, and the steady-state regulation deviation not more than +/- 1 % of rated active power. Enabled and operated status signals are set and sent to the dispatching monitoring system, and the function can be enabled or disabled locally or remotely.

5 Reactive power and voltage

5.1 Inverters installed in the station are continuously adjustable at rated active output over a power factor range from 0.95 leading to 0.95 lagging and within the rectangle shown in Figure 1, whose axes are the per unit active power and per unit reactive power of the inverter. The reactive capacity and regulating ability of the inverters are used first; where they are not enough for the voltage regulation needs of the system, reactive compensation equipment is added, which may be shunt capacitors, shunt reactors, static var compensators, static var generators or synchronous condensers.

5.2 Reactive capacity is sized to meet the layered and zoned balance requirements of the system and to leave a maintenance margin. For a station connected to the public grid, the capacitive reactive capacity compensates the inductive reactive power of the internal collector lines and main transformer at full output plus half the inductive reactive power of the outgoing line, and the inductive reactive capacity compensates the station's own capacitive charging reactive power plus half the charging reactive power of the outgoing line. For a station collected at 220 kV or 330 kV and stepped up to 500 kV or 750 kV, the whole of the outgoing line is compensated instead of half. The type and rating of the compensation equipment may be settled by study of the reactive and voltage regulation characteristics of the system.

5.3 The station has reactive power regulation and voltage control capability per GB/T 31464 and GB/T 40594 and is fitted with a reactive and voltage control system offering constant voltage, constant power factor and constant reactive power modes with online switching between them. The main transformer is recommended to be an on-load tap changing transformer. The control system receives the voltage, power factor or reactive power value sent by the dispatching authority and controls the voltage at the point of connection by coordinating the inverters, the compensation equipment and the transformer tap position, with response time and accuracy per GB/T 29321.

5.3.5 and 5.3.6 With the grid voltage inside its normal range, a station connected at 35 kV to 110 kV can regulate the voltage at the point of connection to within 97 % to 107 % of nominal, and a station connected at 220 kV or above to within 100 % to 110 % of nominal.

6 Fault ride-through

6.1.1 Low voltage ride-through follows Figure 2. Where the voltage at the point of connection drops to zero, the inverters and compensation equipment stay connected and running for 150 ms; where it drops to 20 % of nominal, for 625 ms; and where it drops to between 20 % and 90 % of nominal, they stay connected inside the shaded area of the figure.

6.1.2 Table 1 fixes the assessed voltage by fault type: for a three-phase short circuit and for a two-phase short circuit it is the line voltage at the point of connection, and for a single-phase earth fault it is the phase voltage at the point of connection.

6.1.3 During a symmetrical fault, where the voltage falls below 90 % of nominal the reactive current injected is the sum of the pre-fault value and a dynamic increment that responds to the voltage and satisfies formula (2), valid for a per unit voltage from 0 to 0.9. The formula as printed is broken and is not reproduced here; its symbols are the dynamic reactive current increment injected by the station in amperes, the dynamic reactive current proportional coefficient, the per unit voltage at the point of connection, and the rated current of the station in amperes. The coefficient may be fixed from the actual system conditions and is recommended to lie between 1.5 and 3. The rise time of the dynamic reactive current is not more than 30 ms, the maximum reactive current output during the drop is not less than 1.05 times the rated current, and the increment is withdrawn within 30 ms of the voltage recovering above 90 % of nominal.

6.1.4 During an unsymmetrical fault the station supports both positive and negative sequence dynamic reactive current. Where the positive sequence component of the voltage lies between 60 % and 90 % of nominal, the positive sequence reactive current injected is the sum of the pre-fault positive sequence value and a positive sequence increment, and the negative sequence reactive current absorbed is the pre-fault negative sequence value less a negative sequence increment, both increments responding to the voltage and satisfying formula (3), valid for a per unit positive sequence voltage from 0.6 to 0.9. The formula as printed is broken and is not reproduced here; its symbols are the positive sequence increment injected and the negative sequence increment absorbed in amperes, the positive and negative sequence proportional coefficients, the per unit positive and negative sequence voltages at the point of connection, and the rated current of the station in amperes. Both coefficients may be fixed from actual system conditions and are recommended to be not less than 1.0, the rise time is not more than 30 ms and the maximum reactive current output not less than 1.05 times rated current. Below 60 % positive sequence voltage the station is recommended to inject positive sequence and absorb negative sequence dynamic reactive current according to the real control capability of its inverters and compensation equipment and the grid conditions, without aggravating the voltage unbalance at the point of connection.

6.1.5 For a station that has not disconnected during the fault, active power recovers quickly after clearance, the rate of recovery being recommended at not less than 30 % of installed capacity per second.

6.2.1 High voltage ride-through follows Figure 3. Where the voltage rises above 125 % up to 130 % of nominal, the inverters and compensation equipment stay connected and running for 500 ms; above 120 % up to 125 %, for 1 s; and above 110 % up to 120 %, for 10 s.

6.2.2 Where the voltage at the point of connection lies between 110 % and 130 % of nominal, the reactive current injected is the pre-rise value less a dynamic increment that responds to the voltage and satisfies formula (4), valid for a per unit voltage from 1.1 to 1.3. The formula as printed is broken and is not reproduced here; its symbols are the dynamic reactive current increment in amperes, the proportional coefficient, the per unit voltage at the point of connection and the rated current of the station in amperes. The coefficient may be fixed from actual system conditions and is recommended to be not less than 1.5, the rise time is not more than 30 ms, the maximum reactive current output is not less than 1.05 times rated current, and the increment is withdrawn within 30 ms of the voltage falling back below 110 % of nominal.

6.2.3 During the voltage rise, and once the reactive support is met, the station controls its active power, using the inverters and the storage system together to keep the whole station as close as possible to its pre-fault active power; the active power control of the inverters during high voltage ride-through and its verification meet GB/T 37408 and GB/T 37409.

6.3 Consecutive fault ride-through. The station rides through at least two consecutive low voltage events; the interval between two of them may be fixed from the reclosing time of the outgoing line and the connected system and may be chosen between 0.2 s and 2 s, and each event meets 6.1. A station connected near the sending end of an ultra high voltage direct current link also rides through a high voltage event immediately after a low voltage event and does so at least three times consecutively.

7 Operational adaptability

7.1 With the voltage at the point of connection between 90 % and 110 % of nominal, the inverters and compensation equipment run normally. Outside that band, clauses 6.1 and 6.2 apply.

7.2 Where the flicker at the point of connection meets GB/T 12326, the harmonics meet GB/T 14549 and the three-phase voltage unbalance meets GB/T 15543, the inverters and compensation equipment stay connected and running.

7.3.1 Table 2 fixes the operating requirement by system frequency band. Below 46.5 Hz the requirement is set by the lowest frequency at which the inverters and compensation equipment are allowed to run. From 46.5 Hz up to 47 Hz the station runs at least 5 s each time; from 47 Hz up to 47.5 Hz, at least 20 s; from 47.5 Hz up to 48 Hz, at least 60 s; from 48 Hz up to 48.5 Hz, at least 5 min. From 48.5 Hz to 50.5 Hz inclusive the station runs continuously. Above 50.5 Hz up to 51 Hz it runs at least 3 min and carries out the power reduction or high frequency tripping strategy issued by the dispatching authority, a station that is shut down not being allowed to connect; above 51 Hz up to 51.5 Hz it runs at least 30 s under the same conditions. Above 51.5 Hz the requirement is set by the highest frequency at which the inverters and compensation equipment are allowed to run.

7.3.2 The inverters and compensation equipment stay connected and running within the following rates of change of frequency, illustrated in Figure 4: over a 0.5 s sliding window the absolute value is not more than 2 Hz/s, over a 1 s window not more than 1.5 Hz/s, and over a 2 s window not more than 1.25 Hz/s.

7.4 The inverters and compensation equipment run continuously and stably under low short-circuit ratio conditions. A station connected to a weak or very weak alternating current system strengthens its synchronous support, which may be done with synchronous condensers, inverters with synchronous support capability or storage devices and other power electronic equipment; the assessment of the system and the strengthening measures are recommended to be settled by dedicated study. On recovery from low voltage ride-through after fault clearance such a station controls the dynamic current quickly to reduce the overvoltage at the point of connection, and study of the overvoltage and of measures to suppress it is recommended.

7.5 Where the station is connected to a weak or very weak alternating current system, or where series compensation equipment or a converter station is present nearby, dedicated study of the risk of sub-synchronous and super-synchronous oscillation and of the measures against it is carried out, the recommended approach being impedance characteristic analysis combined with time domain simulation.

8 Power forecasting

8.1 The station is fitted with a photovoltaic power forecasting system meeting GB/T 40607, providing at least medium-term, short-term and ultra-short-term forecasting at a time resolution of no worse than 15 min, and able to forecast where the station output is limited or where the plant is stopped abnormally for fault or maintenance.

8.1.3 to 8.1.5 The station reports medium-term and short-term forecasts to the dispatching authority twice a day at the required times and an ultra-short-term forecast every 15 min. With each forecast it reports the expected available capacity for the same period. Every 15 min it reports automatically the total capacity in service at that moment, and every 5 min the measured meteorological data of the station.

8.2 Accuracy floors. The monthly average accuracy of the medium-term forecast for the tenth day, that is hours 217 to 240, is not less than 75 %. The monthly average accuracy of the day-ahead short-term forecast is not less than 85 % and its monthly average pass rate not less than 85 %. The monthly average accuracy of the fourth hour of the ultra-short-term forecast is not less than 90 % and its monthly average pass rate not less than 90 %. Where the accuracy is computed for a moment when the station output was limited, available power is used in place of actual power.

9 Power quality

9.1 to 9.4 The voltage deviation caused at the point of common coupling by the connection of the station meets GB/T 12325, the voltage fluctuation and flicker meet GB/T 12326, the harmonic current injected meets GB/T 14549, the interharmonics caused meet GB/T 24337 and the voltage unbalance caused meets GB/T 15543.

9.5 The station is fitted with real-time power quality monitoring equipment meeting GB/T 19862, and where a power quality index is not met, power quality mitigation equipment is installed.

10 Simulation models and parameters

10.1 The station builds electromechanical transient and electromagnetic transient simulation models and parameters for the inverters, the reactive compensation equipment, the collector system and the station control system, and passes model validation and accuracy assessment. It also builds a short-circuit current calculation model and parameters and passes the same validation and assessment.

10.2 The station carries out performance and parameter optimisation as required by the dispatching authority. After equipment modification, software upgrade, change of control logic or change of control parameters or protection settings, it tracks the changes in the models and parameters of each component and repeats or supplements the model validation and accuracy assessment.

11 Secondary system

11.1 Protection and safety automatic devices are configured per GB/T 14285, GB/T 32900 and GB/T 33982, and meet the requirements of reliability, selectivity, sensitivity and speed. Collector system faults are cleared quickly, the fast stage setting of the collector line protection being sensitive to a fault at the far end of the line; a station connected to the public grid by a dedicated line is recommended to have fibre optic current differential protection, and the collector busbar is fitted with busbar differential protection. An independent anti-islanding device is recommended, with an operating time of not more than 2 s, coordinated with the line protection and safety automatic devices on the grid side. The step-up substation is fitted with fault recording equipment whose analogue and binary inputs meet the requirements of the dispatching authority, able to record from 10 s before to 60 s after the fault, with online monitoring and analysis of protection and safety automatic devices, collecting the protection and fault recording information of the station and communicating with the dispatching authority over the power dispatching data network. Secondary equipment meets GB/T 50866 and the technical and security protection requirements for secondary systems, and is supplied from an uninterruptible power supply or the station direct current system, the uninterruptible supply carrying the load for more than 2 h after loss of the external alternating supply. Safety automatic devices are configured as needed from the stability calculation results of the connection scheme.

11.2 Dispatch automation. The station is fitted with a computer monitoring system, an active power control system, a reactive and voltage control system, an electric energy metering system, secondary system security protection equipment and dispatching data network access equipment, meeting DL/T 5003 and the dispatching management rules for secondary systems. The scope of telemetered information meets the requirements for connection to the energy management system of the dispatching automation system. Communication with the dispatching authority meets GB/T 40604 and covers telemetry, telesignalling, teleregulation and the signals of the safety automatic devices, and the way and the real-time requirements for providing them. The metering point at the interface is at the property boundary between the station and the grid or between different station owners, the metering equipment meeting DL/T 448. A station connected at 220 kV or above is fitted with a synchronised phasor measurement device, and one connected at 110 kV or 66 kV may be so fitted as needed. A station assessed as at risk of oscillation is fitted with wide-band measurement equipment. The station has a single station-wide clock synchronisation system, and its network security protection meets GB/T 22239, GB/T 36572 and the security protection rules for power monitoring systems, the protection scheme passing security level evaluation and assessment.

11.3 Communication. A station connected at 220 kV or above has two independent optical fibre communication channels and one connected at 110 kV or 66 kV at least one. Communication equipment connected directly to the power system has the same interfaces and protocols as the equipment at the system access end; a note lists optical transmission equipment, pulse code modulation terminals, integrated access equipment, dispatching program-controlled exchanges, data communication networks and communication monitoring among that equipment. The configuration of communication equipment inside the station follows the relevant design codes.

12 Testing and evaluation

12.1 Testing and evaluation are completed before the station is connected to the power system, and repeated after rebuilding or extension.

12.2 Thirty days before the connection test, model validation and accuracy assessment of the inverters, the reactive compensation equipment and the station are completed and the test plan is filed with the dispatching authority.

12.3 Within six months of all generating units having been commissioned on the grid, the station submits its operating characteristic test and evaluation report to the dispatching authority.

12.4 The content of testing and evaluation includes but is not limited to power quality testing; active power control and frequency response capability testing; reactive and voltage control capability testing and evaluation; grid connection performance testing of the reactive compensation equipment; validation and evaluation of the electrical simulation model and its parameters; evaluation of the fault ride-through capability; and evaluation of operational adaptability.

12.5 After equipment modification, software upgrade, change of control logic or change of control parameters or protection settings, testing and evaluation are repeated or supplemented as the power system requires.